MOBI > P.M.P. "L" Cranks

P.M.P. "L" or "bent" cranks of the early 1980's may be one of the most famous bad ideas in cycling.

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Note the arm length is clearly stamped "175", indicating somebody at P.M.P. understood it was simply an odd way to make a 175mm crank.

Advertising copy suggested improved performance:

The Characterisitcs of the P.M.P. Pedal Crank

The unique form of the P.M.P. pedal crank means improved distribution of the energy required in pedaling and a perfectly round stroke; the result: increased equalibrium.

Its L-shaped design increases the pedal's propulsion power and lessens energy disperion on the downstroke.

Pedaling the P.M.P. way means to be perfectly in the saddle; in fact, the bicycle rider is forced to lean back slightly more than usual, putting him in the best possible aerodynamic position.

The P.M.P. pedal crank means that pedaling is no longer an "ankle game" since the bottom dead-point is lightened to allow greater ease on the upstroke.

Bicycling becomes a pleasure and not a chore because the P.M.P. pedal crank and its unique features take eaway the exertion and lighten muscle strain.

The P.M.P. pedal crank has taken its place on the market after extensive testing by professional cyclists who demand the maximum performance with the minimum strain. This pedal crank is a high quality product that you can rely on.

Wholesale price, $140.00; 5 or more, $135.00 each.

http://www.classicrendezvous.com/Italy/PMP_main.htm as of 2009/04.

A moment's thought shows a straight crank and an L crank always have the same relation between pedals, chain, and bottom bracket. Thus, there is no advantage to L cranks. And an L crank always has more material than a straight crank, so is always at a disadvantage for weight, strength, stiffness, and/or cost.

That said, enough of these sold they still appear from time to time. It is unclear how many buyers believed the hype, and how many simply wanted them for their humor or art value.

The P.M.P. cranks have a spider bolted to the right crank, with the square taper formed from both pieces. The square taper is loaded heavily, and making it in pieces, especially with a few light bolts to hold them together, is likely to increase loads greatly and thus lead to premature failures. So it may be unwise to ride these, even for art or humor value.

P.M.P. was far from the first to make bent cranks:

And, it turns out, bent cranks are still production items:

The P.M.P. crank stands out in part because it manages to take a bad idea and make it worse: the crank spider is not simply bolted to the right arm. Instead, the spider is about 1/3 of the square taper, while the arm is the other 2/3. This puts a joint in the middle of a highly-stressed joint — so highly stressed that hardened steel spindles sometimes break here, even without a jointed square taper. Probably no P.M.P. arms failed due to this two-piece square taper; but just as likely few cranks were produced, and most saw little or no hard service before being replaced with something conventional.