![[BikeDiagram5.svg]](img/rawmudflap.uk/images/Diagrams/BikeDiagram5.svg)
From https://rawmudflap.uk/about-mudflaps as of 2025-10-15.
See also also bike pic for other bike-related technical discussions and more failed parts.
TL;DR:
You get a lot more protection when the fender or mudflap is close to the ground.
Here is a cartoon to show the idea. Light gray is dirty water that gets past a short/high fender. Dark gray is with a long fender or mudflap:
With a long fender, when you roll off a curb or similar, it can smash the fender, causing damage. A mudflap is a "soft fender" which gives protection but is flexible to avoid damage.
Even a small change in mudflap height can make a big difference in how much of you and bike gets wet and dirty.
Jan Heine accidentally pulled out his front mudflap, then rode in the wet without replacing it. With the mudflap, the bike stays clean. Without it, the bike got dirty (shown) — and him, too (not shown). Details at [https://www.renehersecycles.com/no-mudflap-what-a-mess as of 2025-10-15].
And he got dirty even though he uses a fender which is closer to the ground than most fenders available today. Even without the mudflap, he gets better coverage than you get from most standard fenders. With standard fenders, he and his bike would get even dirtier.
![[gbwhitetires.jpg]](img/www.renehersecycles.com/wp-content/uploads/2013/02/gbwhitetires.jpg)
![[dirty_gbu.jpg]](img/www.renehersecycles.com/wp-content/uploads/2013/02/dirty_gbu.jpg)
My experience is similar. The low edge of my front fender is about 140 mm above the ground. On wet roads, even without rain, I got dirty water on my feet and shins, and the bike got wet/dirty on the drivetrain and the bottom bracket area.
I installed a mudflap, which I have been using for about two years. It has about 30 mm gap between mudflap and ground. It gives good "stay clean" results. I have seen online a few folks say they run their mudflap about 20 mm from the ground.
![[front mudflap about 30 mm above ground]](img2/front-mudflap-about-30mm-above-ground_00_e11529_1600x1200_q30.jpg)
The coverage you get depends on both the height of the mudflap, and also how far back it is from the tire contact patch. When mudflap is further back, it can be higher yet give the same coverage — although it needs to be wider to give the same side-to-side coverage.
A low-hanging mudflap gives you better protection, but there are some disadvantages:
A mudflap can act like a "scoop" and catch things on the ground and direct them up in to the fender. They can jam the wheel and throw you from the bike, hurting you. Jams happen even without a mudflap, but a low-hanging mudflap may catch more stuff.
Many fenders use stays which come apart if overloaded.
A floppier mudflap may scoop less stuff than a stiff mudflap.
A longer mudflap catches more wind.
A stiffer mudflap can reduce motion, but may weigh more, may be less durable, and might scoop more stuff.
A longer mudflap catches more wind, so has more air drag.
Water that hits a mudflap may splatter to the sides, so may still get you wet. Some water coming off the front tire is so low, it just passes under your feet, so does not get you wet — there is no need for a mudflap to block that water. If the mudlfap is long enough to go down in to that water, it could lead to splatter which gets you wet.
A longer mudflap weighs more.
A mudflap can catch the wind and
A mudflap made of something porous catches less wind, so should reduce those problems.
How much less? I do not know. But I have been using a porous mudflap for a while and it seems to work well for me — it does not blow back or cause shimmy. It still adds air drag, but blowing on it with compressed air, it feels less force than a similar-size piece of rigid plastic.
You may worry that a porous mudflap lets the dirty water through. Some porous materials do: a mudflap made of coarse screen would let through lots of dirty water.
My tests suggest some porous materials are good at blocking water. I think several things work together:
Porous materials with many layers make water take a zig-zag path to get through. The zig-zag path gets the water moving at about the speed of the bike and mudflap. Gravity takes over, and the water just runs off the lower edge of the mudflap.
Porous materials also hold some water, at least briefly. When water hits a wet porous mudflap, in order to get out the other side, the new water has to get past the old water that is already there. Or, new water has to push out old water, to make room for new water. Either way, old water already in the mudflap tends to block new water from getting through.
A floppy mudflap tends to blow back in the wind. When the mudflap blows back, it gives worse protection against water, and it can also hit your shoes or pedals. Some mudflaps use weights to keep the mudflap from blowing back. A porous mudflap is "self-weighting": When it is dry, it is light. When it is wet, the water in the mudflap makes it less permeable, so it is more prone to blow back in the wind. Also, it has to resist the force of water hitting it. But: water trapped in the mudflap makes the mudflap heavier, so tends tends to keep it from blowing back.
When water hits a smooth surface, it bounces and can splatter. A porous mudflap tends to trap water, rather than bounce it. So a porous mudflap may also work better to protect you from splatter.
I sprayed a scouring pad using a garden hose with a spray nozzle. No water got through, it all ran off the bottom.
The scouring pad is "loose" enough that you can easily see light through it. It is not as loose as a window screen or bug net, but it is pretty permeable.
Here is a mudflap made of a 3M Scotch Brite™ 223-10 scouring pad, 152 mm × 96 mm (6” × 3.8”). It is held to the shape of the fender with a strip of aluminum flashing. It is attached using three aluminum blind (POP™) rivets and some washers. The mudflap and hardware is 12 grams.
![[front mudflap made of scouring pad]](img2/front-mudflap-scouring-pad_00_e11521_1600x1200_q30.jpg)
![[front mudflap made of scouring pad]](img2/front-mudflap-scouring-pad_01_e11519_1600x1200_q30.jpg)
![[front mudflap made of scouring pad]](img2/front-mudflap-scouring-pad_02_e11525_1600x1200_q30.jpg)
You can probably figure out what you need from the pictures. Below are more comments, with little organization (sorry):
The scouring pad is stiff when new, but softens with use. The curved shape stiffens it. In practice, it does not blow back, even when riding fast.
Or, at least, I do not notice it blowing it back, nor find the bottom bracket area gets messy, like it did before I installed the mudflap. On the other hand, I have not done a systematic study.
The scouring pad is porous and rough. It seems like a lot of debris might stick to it. In practice, it often has little flecks of things on it, but most leaves/grit/etc. which get stuck on it seem to shake off soon.
The weight as-mounted is about 12 grams.
The scouring pad weighs about 9.5 grams. I cut the top part slightly to be the same width as the fender. I did not weigh it after cutting, but I estimate about 10% less, so maybe 8.5 grams.
The aluminum strap is about 2 grams. The rivets and washers together are about 2 grams. The rivets have mandrels which are broken off during installation. I weighed everything before installing, then after installation weighed the mandrels and subtracted their weight.
There is more about rivets vs. screws vs. other mounting alternatives, below.
It is common to put the top of the mudflap inside the fender. This mudflap is mounted outside the fender. There are several considerations:
An "accidental" reason: I got the bike used, with fenders installed and stays cut to length. To fit the mudflap inside, I would need to move the fender further from the tire, which would need a new stay.
The scouring pad is fairly thick, so to maintain tire clearance, the fender would need to move a significant distance (e.g., 10 mm).
Moving the fender away from the tire would risk more toe/fender overlap.
In contrast, this mudflap is low/forward enough that making that part thicker does not risk toe overlap.
The mudflap may act as a "scoop" that guides debris in to the fender, which may cause the wheel to jam. This mudflap is floppy, so it can bend out of the way. The stiff edge of the fender may act as a scraper for some debris, similar in concept to tire wipers (aka "flint catchers"). If the mudflap is inside the fender, it rounds the fender edge and so might reduce the scraper effect.
I do not know whether the "scraper" effect is real, or is just my imagination. I think it is worth mentioning, but do not treat it as a "known" thing.
It is quiet. Some mudflaps make sounds when hit with road debris or when they drag on the ground rolling off a curb.
A new scouring pad weighs about 9.5 grams. I submerged one in water, then pulled it out and held it vertical to drain. After 15 seconds, it weighed about 40 grams. After 60 seconds, it weighed about 25 grams. After 120 seconds, it still weighed about 25 grams.
When riding, the pad is continually being shaken. A few seconds of modest shaking, not vigorous, reduced pad weight from 25 grams to 18 grams. That means there is still 18 − 9 = 9 grams = 9 mL of water in it.
Once you are out of the rain and on a dry road, the pad is being air-dried. The pad is very air permeable, so there should be good air flow over water in the pad. How fast it dries will depend, in part, on air temperature and humidity.
Small grit might get trapped in the pad. I think most is shaken out quickly. I have been using mine for several thousand kilometres, and light passing through looks similar to a new pad, which suggests not much trapped dirt. But I have not weighed it.
After a wet ride, the mudflap sometimes drips. Water is 1 gram/cm^3, so if the 18 − 9 = 9 grams = 9 mL above drips out (no evaporation), it can make a visible puddle.
"How much" will vary with mudflap material and mudflap size.
A wet bike has other water on it which can also drip off. But a porous mudflap may add to the mess. In my case, I think my fenders without a mudflap sometimes make a puddle when parked, but the puddle seems a little bigger with the porous mudflap.
This is not a problem for me, but it seems different than other mudflap materials, so seems worth noting.
When you park a wet bike after a ride, there is not air blowing over it, so it can take a while to dry. A mudflap which traps water could stay wet even longer. So it could grow mold and/or fungus.
I have not noticed that on mine, but mudflap materials and drying conditions vary.
Mold/fungus can be an irritant that causes sneezing, coughing, etc. Mold/fungus can spread to other items. Mold/fungus can eat some materials — a moldy cotton mudflap might fall apart sooner.
I have not had problems. But if you already have mold/fungus problems, you might consider if a wet mudflap sitting around can make things worse.
I regularly roll off a 160 mm step, which bends the mudflap back to almost 90 degrees, about 20 mm below the aluminum strap. Once I pass the step, the mudflap springs forward/down again without me doing anything.
Sometimes, "curved for stiffness" things go over-center and get stuck in a reverse curve. For whatever reasons, that does not happen here, but it might in some other situation.
The lowest part of my front fender is about 140 mm above the ground. The bottom edge of the fender is rounded, so the sides are about 150 mm above the ground. The fender rivet holes are about 10 mm from the edge, so the holes on the sides are about 160 mm above the ground.
With this setup, I can roll off a step that is about 160 mm tall. The "extra" clearance is because the rear wheel is still on the higher part, and lifting the rear wheel raises the rear part of the fender about 30 mm.
(Riding up a 160 mm step lifts both the front wheel and the front fender, then the low rear wheel takes away about 30 mm of clearance, leaving 140 − 30 = 110 mm — lots of clearance.)
Mounting and mounting alternatives
The aluminum strap is there both to shape the pad, and also to spread load and wear along the pad's whole width. My guess is the pad will fail along the edge of the aluminum strap. My guess is without the strap, and just holding it with washers, it would fail at the edges of the washers, and fail sooner.
I smoothed/rounded the edge of the strap, but the aluminum is thin and so the edge is still relatively sharp. Better would be to bend the lower edge to have a slight curve away from the fender — looking at it sideways, instead of looking like a straight line "|", it would resemble a "J". Then, when the mudflap bends back, it could wrap around the curve, rather than folding on the edge.
Since the strap is also bent side-to-side around the fender, it is a bit more effort to bend the lower edge. I did not know if this mudflap would work, so I skipped the extra effort. The mudflap seems to work, so next time I will also slightly bend the lower edge.
The strap is made of aluminum roof flashing material. It is about 0.25 mm thick, and weighs about 2 grams.
Thinner material — such from an aluminum soda can — is lighter, easier to get, and is probably strong enough. But being thinner, the edge is also sharper, even when smoothed. It may tend cut the mudflap faster than the flashing. Folding the aluminum would create a thicker, somewhat rounded edge. Folding it around a wire should create an even more-rounded edge. But the thicker the folded material, the harder it will be to then wrap around the "C" shape of the fender.
Plastic has lower density, so could be thicker and offer a more-rounded edge — at the same weight, or less. Plastics vary: some degrade in sun, some are damaged by frequent load cycling. These may be less durable than aluminum. Many plastic fenders are durable, a strap of similar material should be as durable as the fenders.
The mudflap is curved to the shape of the fender in order to stiffen the mudflap. Away from the fender, it flattens out and is floppier. This seems to work well: it is stiff enough it does not blow back, and floppy enough it does not seem to scoop up much debris.
A longer mudflap might be too floppy, and would blow back. It could be stiffened by:
There are larger "fender" washers both inside and outside the fender, plus smaller "rivet" washers on the outside. The rivet washers have a hole sized to the rivet to ensure a good grip. The fender washers spread loads over a larger area to avoid damage to the thin fender. Click to enlarge:
The washers are stainless steel and are over 1 gram.
There are aluminum versions of these washers which are lighter, but I did not have them handy.
Rivet washers have a hole sized to the rivet shank. When the rivet is installed, it swells the end. If the hole is too big, the rivet can pull out. The "sized" hole of the rivet washer ensures a good grip. A fender washer or aluminum strap with a suitable size hole does the same thing. Except that thinner/softer materials may be damaged by rivet installation, so even if it starts with a right-size hole, damage can leave the rivet loose enough to come out.
I left off one rivet washer and the rivet has not pulled through the fender washer, so in this case the rivet washers might not be needed.
Fender washers spread load and reduce the risk of damaging the thin fender material. Mudflap loads are small, so washers might not be needed. Vibration and wind flutter mean loads may be high-cycle, which sometimes causes failure even at low load. I had the washers and handy, and used them as "better safe than sorry".
There are blind rivets with "oversize" heads which are a rivet and fender washer in one. They are relatively common, but I have not found them in the smallest rivet diameters.
![[O1CN01B7cHhF1wkW75G8PmE_!!6000000006346-0-yinhe.jpg]](img/gw.alicdn.com/imgextra/O1CN01B7cHhF1wkW75G8PmE_!!6000000006346-0-yinhe.jpg)
To summarize: the fastener weight could probably be halved.
The aluminum strap is about 2 grams.
It probably could be narrower (not as tall) and still work well. It could be lightened slightly and made more artistic by making holes or slots in it.
Aluminum flashing is probably stronger than needed, but thinner aluminum makes a sharper edge (even if smoothed) so may tend to cut the mudflap unless shaped to avoid a sharp edge.
Plastic might be lighter than aluminum and also gentler on the scouring pad.
To summarize: the strap weight could probably be halved.
It is attached with aluminum blind (POP™) rivets.
Blind rivets have a low profile inside the fender, so do not snag much debris.
By way of explanation, here are some pictures of blind rivets. There are dimensions given in the pictures, but I used a different size: 2.4 mm (nominal 3/32”) diameter.
![[15261_0.jpg]](img/www.ronical.com/x/ron/p/15261/15261_0.jpg)
![[pop-rivet-installed.jpg]](img/www.ronical.com/x/ron/y/p/pop-rivet-installed.jpg)
![[pop-rivet-dimensions-blind.jpg]](img/www.ronical.com/x/ron/y/p/pop-rivet-dimensions-blind.jpg)
There are also "countersunk" rivets, with a head shaped to fit a small dent around the hole. Countersunk rivets are flat/flush with the surface and would not collect any debris. However, they are small and so would not spread the load like fender washers. There are "Tinnerman" washers with a countersunk relief or a dimple, so the rivet and washer stand out only by the thickenss of the washer. But they are uncommon. It may be straightforward to modify a flat fender washer using a dimpling tool.
A down-side of rivets is that removing the mudflap means drilling out and discarding/recycling the rivets. Another downside is installation takes rivets and a rivet tool. How much are these problems? It depends in part how long the mudflap lasts before it wears out.
Blind rivets and the tools are fairly common, and individual rivets are cheaper than stainless screws and locknuts. A "neighborhood" hardware store near me sells a box of 20 blind rivets for about US$4 (US$0.20 each) and a blind rivet tool for about US$20. A big-box hardware store sells a box of 50 rivets at US$7 (about US$0.15 each) and a rivet tool for under US$8.
For comparison, the big box hardware store sells Stainless M5 button-head screws and and stainless M5 locknuts for about US$0.50 each — about US$3 for three screws and three locknuts. But they are sold by the bag, so the out-the-door cost is closer to US$8.
Prices vary, but to summarize: rivets are widely available, a bit lighter than screws, and may be fairly cheap, even when you have to buy more than you need. Rivets are also more hassle and generate some (recyclable) waste when installed (mandrell) and removed (rivet).
Blind rivet alternatives include:
Solid rivets:
Solid rivets are shaped by squeezing or with hammer blows. Both swell the shaft of the rivet, as well as making the head round over and "mushroom". That works well when the rivet is in a strong hole, but not where the rivet passes through something soft (such as fabric or plastic) or weak (such as thin material like an alumium fender). Solid rivets probably do not work here.
Semi-tubular or tubular rivets:
Tubular and semi-tubular rivets have a thin wall, making them easier to bend over. That makes them suited for soft materials: they are commonly used with fabric, plastic, leather, and so on. Plastic fenders are often held together with semi-tubular rivets. Tubular and semi-tubular rivets are often cheaper than blind rivets, but the tools are less common and may be more expensive.
Semi-tubular rivets often have larger heads than common blind rivets, so a fender washer might not be needed on the "head" side.
Zip ties:
The fender is curved, so running a zip tie in the left hole and out the center leaves the zip tie "hanging in space" inside the fender, which would tend to snag debris.
Maybe use vertical pairs of holes. For example, six total.
Instead of six holes, you might be able to use three holes and loop the zip tie under the bottom of the fender. However, with a strap like shown above, the mudflap will be prone to tear around the zip ties and may leak some water. Extending the strap down to the end of the fender should reduce tearing.
Maybe use more close-spaced holes: when the holes are close, the fender is almost flat between pairs of holes, so the zip tie is close to the fender and much less likely to snag debris.
Running zip ties between every pair of holes might work similar to the flat strap on my fender, in which case the flat strap could be eliminated.
Consider 6 holes: you could run three zip ties between holes 1-2, 3-4, and 5-6. Or, eliminate the strap and run zip ties between holes 1-2, 2-3, 3-4, 4-5, 5-6, and also from 1 around the edge of the fender and from 6 around the edge of the fender.
More zip ties but no strap might be lighter.
Zip ties are harder to recycle than aluminum.
Wire:
Wire in the left hole and out the middle might "hang in space" similar to zip ties, above. If the wire is somewhat stiff, it might be shaped to follow the curve of the fender.
Wire may corrode or may cause an aluminum or steel fender to corrode.
Ordinary steel wire rusts and eventually gets weak. It may be adequate if it outlasts the mudflap material, or if it lasts long enough you do not mind the replacement interval.
Ordinary wire can corrode and damage aluminum fenders.
Galvanized wire mostly avoids rust, but if scraped or abraded significantly, it can rust. That could be a problem if, for example, repeated toe overlap rubs off the galvanized layer.
Aluminum wire should be rustproof, but may corrode if used with steel fenders. Aluminum wire may be hard to find.
Stainless steel wire may be easier to find than aluminum, but may be stiff and so may tend to "cut" the fender over time.
Wire may be used similar to zip-ties, above, to form continuous line and replace the horizontal strap.
Cord/String/Twine:
String could be used like wire or zip-ties to "sew" a mudflap on to a fender. As with zip ties, you want to avoid long horizontal spans inside the fender, which can snag debris.
It is hard to tie a string tight, so a sewn-in-place mudflap is probably not clamped as tightly as with other fasteners. Thus, it may be prone to shift in use. If so, a second line of stitching might hold it.
As with zip ties and wire, running string between every pair of holes could replace the aluminum strap. String is probably gentler on the mudflap than wire, especially thin wire, so less likely to cut it. It might be gentler than zip ties.
Metal fenders are thin, so holes in them have sharp edges. Even if the holes are smoothed, they probably cut string.
It may be possible to press the hole to a smooth rounded "trumpet" shape. That needs a special "dimpler" tool, and dimpler pliers may not fit around the "C" shape of the fender, although you may be able to reach in from the end.
Or, each hole could be fitted with a grommet (hollow tubular rivet). That needs suitable tools, and grommet pliers may not fit around the "C" shape of the fender, though maybe it can come in from the end.
Plastic string is not typically recyclable. Natural fibers can biodegrade, but some common natural fibers probably rot fairly quickly in mudflap service — I expect cotton is not durable. There may be more durable natural fibers. A string which is waxed or which is shellacked after installation may be more durable.
Screws:
Button-head screws can sit relatively flush in the fender, so should not snag debris. However, they have a taller profile than rivets.
Flat-head screws can sit completely flush. However, they are small and do not not spread the load like fender washers. There are "Tinnerman" fender washers with a countersunk relief or a dimple, so the screw and washer only stand out only by the thickenss of the washer. But they are uncommon. It may be straightforward to modify a flat fender washer using a dimpling tool.
Nuts outside the fender are a little bit thicker than rivets, string, wire, or zip ties, which may affect toe overlap.
I weighed 3x flat-head screws M5 × 8 mm thread length, plus three nylock nuts. They were 9.3 grams, which would almost double the weight of the mudflap (12 grams as shown here). Maybe two screws is enough (one on either side, but not in the middle). Thinner screws (M4, M3, ...) would be more than strong enough, but may need special tools (odd size wrenches) if you need to tighten them while riding.
Use the stay mounting hardware:
It is common that the fender, fender stays, and mudflap are connected using the same fasteners. For example, here are some Bluemels "Lightweight" fenders. A metal arch connects the stays to the fender, and the mudflap is sandwiched between the arch and the fender, with everything held together using semi-hollow rivets.
![[s-l1600.jpg]](img/i.ebayimg.com/images/g/b~gAAeSwTUBopJH~/s-l1600.jpg)
![[s-l1600.jpg]](img/i.ebayimg.com/images/g/n6UAAeSw1bZopJII/s-l1600.jpg)
![[s-l1600.jpg]](img/i.ebayimg.com/images/g/PggAAeSwwWlopJIJ/s-l1600.jpg)
When clamping a thick and soft material, such as a scouring pad, the fender support may be less rigid. That could lead to fender rub, possibly mid-way between the stay and the fork crown.
When clamping a thick and soft material, nuts and screws may be prone to unscrew. You may want to use locknuts, self-locking nuts ("Nylok™) or thread locking compound (Loctite™).
The stay needs to be "close" to the end of the fender, else the mudflap has to reach a very long way up the fender. For a long fender, putting the stay near the end may leave the mid-section of the fender unsupported, leading to flex and rub, and maybe more fender damage during a fender strike.
For a mudflap mounted outside the fender, you could use something like my strip of aluminum flashing, but instead of rivets, it is held by the stay bolts.
If the stay wraps around the outside of the fender, you could use the stay itself to hold and shape the mudflap. For example Honjo fenders use a round stay; you could replace the eye bolts with P-clips (also called "loop clamps", Honjo calls them "R-clamps") oriented so the screws are above the stay — so when the mudflap bends back, it bends along the rounded profile of the stay.
Using the stay as the clamp may require reshaping the stay to follow the fender. For some fender shapes, that may be hard.
It may be possible to hold the center of the mudflap with the stay, then sew or otherwise attach the sides of the mudflap to the stay.
String may be the lightest choice.
The mount only needs to be as strong as the mudflap. Mudflap durability may be improved by large rounded shapes, but a thick wire is heavier than thick string.
My current mudflap mounting hardware is about 4 grams. Zero grams is the goal!
It seems a wire 210 mm long could hold a mudflap on my fender. A 0.90 mm × 210 mm galvanized wire weighs about 1.0 grams. This wire is quite a bit thicker than the flashing I used, so a thinner wire might still give reasonable durability — not cut the mudflap. So a thinner/lighter wire may be possible. However, thinner wire may be more prone to cut the fender.
I have several kinds of string which are somewhat thicker than the wire. I cut pieces of similar length as the wire. The string pieces weighed 0.25 grams to 0.35 grams. String probably needs to be longer than wire, as extra length is needed to tie/knot it. The string I weighed is just what I had handy — thinner/lighter string may be durable enough.
Here are some comments about scouring pads and other porous materials:
There are many kinds of scouring pads. I used a 3M Scotch Brite™ 223-10 pad.
Details: [https://www.3m.com/3M/en_US/p/d/b00042849 as of 2025-10]. 101 mm × 65 mm. 9.5 grams. 3M ID B00042849, UPC 00051141916903.
Scouring pads are also called "scuff" pads.
Scouring pads are abrasive. 3M sells many similar pads with different abrasives. They are color-coded. If green does not match your bike, you may be able to find a different color which does. The abrasive properties do not matter when used as a mudflap, so changing abrasive is no problem.
I do not know if other brands/models use the same color codes.
![[front mudflap about 30 mm above ground]](img2/scouring-pad-grits.3m-flat-stock-hand-pads.png)
There are many other scouring pads, which vary in fiber density, fiber thickness, fiber type, fiber "weave", and pad thickness. I do not know how they compare.
Scouring pads are used widely for many commercial/industrial tasks. A given task may use only some part of the range. You may find your local hardware store has one selection, the auto parts store something different, the local restaurant supply house yet something else.
Most scouring pads are plastic. There are also scouring pads from plant fibers. I expect they work well as a mudflap, but might not be as widely available. The only color I have seen is tan. I do not know the weight.
Beware there are "walnut" scouring pads, which use walnut shells as the abrasive, embedded in plastic. These are not plastic-free.
There are many semi-porous materials which might work well.
I tested a nylon pot scrubber. It has much looser weave than the scouring pad, above, but is also thicker. It might have less air drag. I turned a garden hose nozzle on it, and it also did a good job of blocking the water, despite having a much larger "pore" size than the scouring pad.
A down-side of the pot scrubber is that it is irregular, rather than flat. But it suggests a wide range of materials could work well.
Some other things which look like they might work well include: VentiSit seat pad material; 3M Nomad™ 8100 floor pad material. Possibly various foams and fabrics, maybe in several layers.
Frank Revelo made a mudflap of Cordura™, which is a Nylon cloth. More about his mudflap is below. Cloth is very flexible. To keep the mudflap's shape, and to keep it from blowing back in a breeze, he put a weight at the bottom.
Cordura is durable, fairly "breathable", and widely available in many colors. It is often used to make jackets, knapsacks, bike panniers, and lots of other things. It is available at many fabric stores, and can be "harvested" free from worn out knapsacks, etc.
There are many other fabrics which might work well, but some fabrics may work poorly. Some thoughts:
Some Cordura is coated to make it water-repellent. My experience is it quickly gets damaged and start to leak, but enough coating is left to block some wind — which may be a disadvantage for use as a mudflap.
Similarly, some fabrics are tight weave, so relatively windproof. They may blow back in the wind, reducing their effectiveness, and making them more likely to strike your shoes or pedals.
I suspect a problem with cloth mudflaps is they are somewhat likely to twist top-to-bottom. Twisting may cause it to divert water on to your left shoe or your right, rather than directing the water down at the ground. I suspect that a stretchy fabric is more likely to to twist. I suspect an internal stiffener can reduce twiting — e.g., bend a spoke to a "U" going part-way up the sides of the mudflap, and use that as part of the weight.
Some fabrics are easily damaged by UV (ultra violet) light, so are likely to fall apart sooner.
Thin fabrics may be too water permeable. Using several layers may help. Similarly, very loose-weave fabrics may be too permeable, but several layers might help.
Fabric weights vary, a lot. Cordura 1000D is about 300 grams/m^2 (gsm), and there are certainly heavier fabrics. Some lightwight nylon fabric is under 30 gsm.
Wet fabric weighs more. Cotton and some natural fibers are likely to stay wet much longer than synthetics, so add weight for longer.
Revelo says his mudflap is about 30 grams at 200 mm tall, 75 mm wide at the top and 115 mm wide at the botttom. He does not say how much is the weight at the bottom, nor whether he includes the screw weight in the 30 gram total. It appears Cordura 1000D is about 300 grams/m^2 (gsm). He uses two layers, or 600 gsm. I compute his mudflap, without weights or mounting screws, is about 11.5 grams. I estimate his mounting screws are 5 to 10 grams, so the bottom weight would be 10-15 grams. A taller or wider mudflap catches more air, so may need heavier weights.
For comparison: I estimate my Scotch-Brite pad material is about 650 grams/m^2, so a mudflap the size of Revelo's but made of the material in my Scotch-Brite pad would be about 12.5 grams. The Scotch-Brite pad is stiffer and may be more permeable, so one the size of Revelo's might not need bottom weights, or might get away with lighter weights.
Revelo's mudflap suggests a similar design but of much lighter material than Cordura 1000D or my Scotch-Brite material. If it is light enough, then even if it needs weights it might be lighter overall.
Many light fabrics are also dense weeve and fairly windproof. But some have a loose weave, so let wind through and might be good for a mudflap. Several layers of fine bug net screen might be good. I looked online and see some at 23 gsm. I also see a fabric, "Cloud 1.4", which has a denser weave, so may make a better zig-zag path, and is listed as "outstanding breathability". It is under 50 gsm.
Several layers of these might still be much lighter than two layers of Cordura 1000D. And at the same time, might be more air permeable, so it might work okay using a lighter weight at the bottom.
I have not tried any of these, but it seems promising enough to try.
A floppy mudflap in wind may be prone to twist top-to-bottom. A twisted mudflap may direct water on to your left or right shoe, rather than down at the ground.
Revelo's mudflap uses a straight rod as a weight at the bottom.
I suspect a U-shaped wire which goes part-way up the sides would tend to reduce twisting. A bent spoke may be suitable. A spoke is about 4 grams, so two or more spokes may be needed to match Revelo's weight.
Alternatively, a piece of thin foam between the two layers may stiffen the mudflap and tend to resist twisting. Foam adds more zig-zag path for the water, which may help the mudflap do its job. Foam helps trap water, which may help with self-weighting. Whereas a weight just adds weight, but no zig-zag path or self-weighting.
It seems to me a thin layer of light foam, or similar, between the two layers might substantially increase water resistance, and so might allow use of a more air-permeable fabric. Less air drag might in turn allow use of a lighter weight at the bottom.
The mudflap still needs to resist the force of the water being thrown at it. So even if you could eliminate all air drag, a floppy material would still need some weight to resist the water force.
Fabric can be "self-weighting" in that it weighs more when wet, so how much (or how little) water gets trapped probably affects how much added weight is needed.
Kermit Green made a mudflap of inner tube rubber, with the lower part cut to a fringe of "strings", sort of like linguini; then several layers, sort of like a string mop, so water going through has to take a zig-zag path. There is more on his mudflap below.
My limited testing suggests the first part of a stream of water pushes the strings sideways, which lets the rest of the stream pass through.
That suggests to me that a good mudflap material wants some horizontal stiffness, to avoid getting pushed aside.
A wet scouring pad has some trapped water. That means a wet mudflap weighs more.
For the scouring pad I used, a new pad weighs about 9.5 grams. I submerged one in water, then pulled it out and held it vertical to drain. After 15 seconds, it weighed about 40 grams. After 60 seconds, it weighed about 25 grams.
When riding, the pad is continually being shaken. A few seconds of modest shaking reduced the pad weight from 25 grams to 18 grams.
Once you are out of the rain and on a dry road, the pad is being air-dried. Since the pad is very air permeable, there should be good air flow over the wet surfaces inside the pad.
Thin materials and materials with larger holes probably hold less water. That may reduce "self-weighting".
Some materials and some weaves may hold water a long time. That may mean the mudflap stays heavy long after you are out of the rain and on a dry road. For example, cotton and some other fibers are prone to hold water — even if the weave is loose, the individual threads are prone to trap water. It traps more water than most other materials, and traps it where it is somewhat shielded from the wind, making it slow-drying.
Fine grit may get trapped in a porous material.
The scouring pad I use does not seem to collect dirt or grit — I suspect most of it gets shaken out fairly quickly. I have been using mine for several thousand kilometres, and the light passing through looks similar to a new pad, which suggests not much trapped dirt. However, I have not weighed it.
The mudflap design and construction may also affect dirt collection. For example, it is possible Frank Revelo's two-layer mudflap lets some grit creep past one layer of cloth, and then it it is trapped between the two layers and slow to shake out.
So "collects dirt" seems like a possible problem with porous mudflaps, but at least some porous mudflaps seem fine.
A coarse material may be prone to trap twigs and other things which do not easily shake free.
I tested a nylon pot scrubber with a garden hose and nozzle, it seems to block water well. However, the pore size is big enough that probably a 3-4 mm stem, twig, wire, or other such item could easily push in to the "pores" and get trapped. Once trapped, it probably would not fall out.
People sometimes make tent rain flies from fabric which is semi waterproof rather than fully waterproof. For example, some grades of silicone-treated nylon (silnylon). Less waterproofing material means these can be very light. As long as nothing inside touches the fly, you do not mind if the inside of the fly gets wet.
However, drops of water landing on the fly can make a mist inside the fly. In other words, the drop is slowed down, but not all of the water sticks to the fly and runs off.
I do not know how much of the mist is "a drop passed through" versus how much is from water already trapped in or on the rain fly, and then when a drop hits the outside, it "kicks" other water, which comes off in a mist. Possibly some of each.
The rain fly "mist" observation suggests to me something similar could happen with a mudflap. How much mist probably depends on both the shape and the depth of the zig-zag path.
The "rain fly" observation suggests to me that a thicker material that traps more water will let through less mist.
To the extent a drop "passes through", it has to expend energy to push aside the weight of water already in the mudflap. A thicker mudflap has more water to push aside, slowing the drop trying to push through.
Conversely, if it "kicks" other water off of the mudflap, the energy of each drop landing on the mudflap is spread over more water already in the mudflap. So less energy reaches the other side to kick off that water.
the "rain fly" observation suggests to me that a floppier material that bends more water will let through less mist.
My thinking: if the material moves when it is hit by water, there is more time for the material and water to match speeds.
The "rain fly" observation also suggests to me that there may be some mist coming through the scouring pad mudflap, even though I see no drops.
In practice, I do not notice the frame or my shoes getting wet if I ride on wet pavement. If I ride in the rain things are getting wet with rain, which hides anything coming through the mudflap.
The mudflap also acts somewhat like a filter. The water on the back side is not "clean", but leaves, big grit, and so on are filtered out. So if there is mist coming off of it, it is not carrying coarse debris (sticks, leaves, large-size grit) like you see without any mudflap at all. Although the water is still "dirty" it would be harder to tell the difference between that water and clean rain water.
It seems likely people have already tried porous mudflaps. Did the idea just never catch on? Or is there a serious problem with the idea, and I just have not figured it out yet? I don't know.
History can be instructive, but I have not found much about previous porous mudflaps.
Mudflaps are commonly made of non-porous materials such as sheet rubber and plastic, or leather, which is water-permeable but nearly windproof.
Some other porous mudflaps:
Frank Revelo made a front mundflap of Cordura™ nylon fabric. He does say specifically whether it is coated (waterproofed) or uncoated, I assume uncoated.
The mudflap is sewn as a 2-layer "envelope" then hung from the front fender. The fabirc is very light, so to keep the mudflap from blowing back, he uses a small weight.
| https://www.frankrevelo.com/hiking/sewing_bikemisc.htm as of 2025-10-16 |
![[sewing_bikemisc_mudflap.jpg]](img/www.frankrevelo.com/hiking/sewing_bikemisc_mudflap.jpg)
The SKS P65 fenders/mudguards I experimented with either did not come with a mudflap, or the mudflap was missing (I bought the fenders from a discount company), so I made my own from 1000d cordura fabric. Finished size is about 3" wide at the top, 8" long and 4.75" wide at the bottom. Cut two pieces of fabric sightly larger than this, sew together on sides and bottom, trim seam allowances, turn inside out. Then insert a 4.5" piece of steel rod (use trimmings from rear fender stays) into bottom of mud flap to keep it weighted down. Fold together top seam, topstitch on all four sides. Bore two holes with soldering iron, corresponding to holes drilled into bottom of front fender. Attach mud flap to fender with bolts. About 30g. |
Cordura is relatively thick, but loose weave. It is often used for jackets and bags for abrasion resistance, but for windbreakers is often laminated with more windproof materials.
The mudflap is made of two layers. That probably reduces air permeability, but probably much less than double. Two layers increases the zig-zag path needed for water to get through, so probably reduces the amount of water getting through — my guess: quite a bit.
I estimate that the fabric part of the mudflap is about 11.5 grams, or about 1/3 of the mudflap's total weight. Going to a single layer would thus reduce weight by about 1/6.
A weight is used because Cordura by itself is too floppy to hold a shape. I wonder if curving the mudflap to a "U" like the fender would stiffen the fabric and allow use of a lighter weight? If you curve the weight, it will probably just rotate inside the mudflap, leaving the mudflap flat. But if you sew a horizontal tube at the bottom and put the weight in that, the weight might keep the desired orientation.
Revelo also made a Cordura "fender" which attaches to his rear rack.
He suggests poking holes in the Cordura with a soldering iron. Beware that the tip of a soldering iron is plated, and molten plastic damages the plating layer. Eventually, solder will no longer "wet" to the tip, which makes heat transfer poor. You may want to keep a tip specifically for melting holes. Alternatively, you can make holes by heating a nail with a lighter, stove burner, etc. Or, you can cut a square hole by folding the fabric and cut a V-shaped notch. You may want to use a flame to melt the nylon, which reduces the tendency to fray.
Kermit Green made a mudflap using two layers of inner tube rubber. The lower parts were cut to a fringe of "strings", sort of like linguini. Air passes through fairly freely, but water going through often has to take a zig-zag path.
| https://dorkythorpy.blogspot.com/2014/03/diy-bike-mudflaps.html as of 2025-10-16 |
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Update 2019: I have been trying different materials over the last few years . . .the best materials by far is old inner tube. Use two layers of inner tube and "fray" the tubes so they hang down in strips. This design is super flexible, air can pass through it (wind resistance) and make no noise when gravel is bashing in to it. ![[diy+bike+mud+flap.png]](img/blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhSl_Ki0ZJnqhboB9mVxG6t8CzruUrwh-xe8f1ObW2_6xkxXj9QaxA27e4_2E4_TWd470IaHA7A464Ek0SnblJjuW1WM586c0u1UYFJo2-520kQx7UWRBGaxI9SMX1ccN0X77VbwVaIwaAc/s1600/diy+bike+mud+flap.png)
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I did not make a "fringe" mudflap, but I did do some hose tests. My limited testing suggests the first part of a stream of water pushes the "strings" sideways, which lets the rest of the stream pass through.
That suggests a "fringe" mudflap lets through some water. That is, much better than no mudflap, but it may not be as effective as continuous material.
It suggests to me a good material for a porous mudflap wants some horizontal stiffness, to avoid getting pushed aside.
I wonder about layers of inner tube, with tall narrow slits — say, a 2 mm slit with 3 mm of rubber between slits — and then offset the layers so you cannot see light through the layers.
More layers of fringe may help, but adds weight.
Green does not list a weight. A common 559 inner tube might be 100 grams for a light model, 200 grams for a heavy model. The weight and stiffness of the rubber "strings" may affect how well it blocks water.
Green does not list a weight or dimensions. Here is an estimate of weight for a mudflap the same size as Revelo's: A 559 inner tube is roughly 1.8 metres long, and when flattened might be 125 mm wide. 1.8 m × 0.125 m = 0.225 m^2, so the lighter tube is (100 grams)/(0.225 m^2) = 444 grams/m^2 (gsm), the heavy one 888 gsm. Revelo's Cordura mudflap is a trapezoid about 75 mm wide at the top, 125 mm wide at the bottom, and 200 mm tall. The area is thus 0.020 m^2. Each layer would thus be 9 grams made from the light tube, 18 grams from the heavy.
Thus, two layers would be 18 to 36 grams, plus mounting hardware. Four-layers would be 36 to 72 grams.
For comparison, Revelo's Cordura mudflap is probably 20-25 grams plus mounting hardware. A scouring pad mudflap the size of Revelo's might be 12-13 grams, but heavier if it needs to be stiffened to keep it from blowing back.
Old inner tubes are free and easy to find — you may have some already. Scouring pads cost something. Or, at least, it may be hard to find a scouring pad worn out enough to stop using as a scouring pad, without being so worn out that it is useless for making a mudflap. Grocery stores and neighborhood hardware stores may have only sizes which are too small for your fenders, so finding a large scouring pad may be a hassle.
Paint on rubber is sometimes fairly durable. I have painted marks on tire sidewalls and had it last thousands of kms without cracking or coming off. If you want a colored mudflap, it might work well enough to paint it. I have not tried it, but it seems cheap and easy enough to try. Tubes are coated with mold release when they are made. You probably want to clean the tube vigorously before painting — "scrubbing" with sandpaper and then rinsing with industrial alcohol and/or paint thinner. Paint might also protect the rubber from UV and pollution (ozone damages some rubber), so if your inner tube mudflaps fall apart quickly, painting the replacement might help.
| https://www.bikeforums.net/19640297-post7.html as of 2025-10-17 |
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06-08-2017
You know, I love SKS Longboards but I think some of these DIY solutions might have an important advantage over the Longboards. The mud flap on the Longboards (at least the really long ones you’re talking about) is kind of rigid and ends up pointing forward. I had never really considered the implications of that until last Friday when this happened to me: ![[35018231392_0db3dcf91f_b.jpg]](img/c1.staticflickr.com/5/4267/35018231392_0db3dcf91f_b.jpg)
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| https://www.sheldonbrown.com/fenders.html as of 2025-10-17 |
There is a potential severe hazard with a front fender: debris caught between the fender and the tire, or between the moving spokes and the fender stays, can cause the fender to crumple and lock the front wheel. Also, if the front fender comes loose at the fork crown, it will rotate forward and the stays can jam it against the wheel. Do not ride a bicycle with deteriorating fender hardware; consider installing safety releases if your bicycle's fenders do not already have them.
![[bashedup.jpg]](img/www.sheldonbrown.com/images/bashedup.jpg)
A fallen tree branch jammed in the spokes, crumpled this fender and launched John Allen over the handlebars. He is glad that he was wearing a helmet. |
Riders sometimes get a stick in the spokes of the front wheel, and it hits the stays. Bending the stays pulls the fender against the tire. It can then crumple the fender, and the fender material jams between the stay, fork and front wheel. This often throws the rider head-first off the bike, sometimes causing collarbones and head/brain injuries.
You can have a similar problem where a stick or similar is caught between the tire and fender. It can jam, as above. But it is somewhat likely the object will skid — which can cause quick braking, but not so likely to lock the wheel and throw you from the bike.
You can also get a stick in the spokes without fenders. This tends to bring the stick up to the fork, and the spoke breaks the stick, without jamming the front wheel. A stout-enough stick can jam the wheel, but this is less common.
Jamming the rear wheel leads to sudden braking or skidding, and may lead to falls. But since the rider is not thrown head-first, injuries are usually less common and less severe.
It is fairly common today to use fender stays designd to pull apart when overloaded. For "stick in the spokes", this basically turns it in to the "no fender" case, which usually breaks the stick. For "between tire and fender", the stays pull apart, the fender gets out of the way, and the stick can more easily skid on the tire.
An issue of Bicycle Quarterly notes that Natsuoko Hirose's C.S. Hirose bicycle has fender stays that are slightly notched, and are held at the dropouts with sprung eyebolts. These are used so the fender can be removed easily to pack the bike more compactly (Rinko). But it probably also releases the stay on overload.
John Allen notes at [https://www.sheldonbrown.com/fenders.html as of 2025-10] that SKS Securi-Clips are designed to release the fenders when the stays are overloaded, but they are also useful for removing and re-installing the fenders. They squeak, which can be remedied with silicone caulk. Rivendell has a similar note at [https://www.rivbike.com/products/sks-secu-clips-pair-27009 as of 2025-10] and says being plastic, they break occasionally — you might want to carry a spare in your toolkit.