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PMP cranks 2.jpgL-shaped cranks — explore the crazy idea that just won't die
Image: PMP cranks by robadod from LFGSS [This feature from the road.cc archive was last republished on October 15, 2020]
We take a look at one of the more bizarre technical aberrations of recent history: the wackiest cranks ever made.
In 1981 Cycling Weekly magazine published a favourable review of an unusual new crank. The magazine gave a set to “a first-category Surrey roadman to try them out.”
The write-up said: “He fitted them in March and although our test is now over they are still on his best road bike. He has come to prefer them to orthodox cranks.”
CW’s tester “enjoyed the ‘feel’ of the cranks and reported that the slower his pedalling speed the more advantage he felt, which is perhaps why they are finding favour with big-geared time triallists.”
The tester told CW: “I didn't just get the power on the downward strokes of the pedals but all the way round the pedalling revolution as at low pedalling speeds dead centre seemed to be removed. This helped me keep a steady rhythm particularly when sitting back in the saddle climbing hills.”
He didn’t feel the same benefit when pedalling quickly in a low gear, though.
CW concluded: “So there is the verdict, whatever the theories, in practice our roadman tester felt the PMP cranks offered an advantage – and surely that is the true criterion.”
An early publicity shot of the PMP Brevettato cranks
That crank was the PMP Brevettato. Its unusual (but, as we’ll see, by no means unique) feature was a right angle bend about a third of the way between the bottom bracket axle and the pedal.
PMP made some interesting claims about the Brevettato cranks. They included:
- The unique form of the PMP pedal crank means improved distribution of the energy required in pedalling and a perfectly round stroke; the result: increased equilibrium.
- Its L-shaped design increases the pedal's propulsion power and lessens energy dispersion on the downstroke.
- Pedalling the PMP 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 PMP pedal crank means that pedalling 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 PMP pedal crank and its unique features take away the exertion and lighten muscle strain.
Bold claims, and with Cycling Weekly’s Surrey roadman finding they eliminated dead centre, you have to wonder why the design isn’t now ubiquitous.
An ad for PMP cranks.
That’s simple: it’s all bollocks.
A crank is a lever. The torque you generate when you load up the end of a lever depends on just two things: the force you exert and the distance between the point where that force is applied and the pivot.
Nothing else matters, especially not the route the lever takes between the two points. It can be a straight line, a right angle bend or any other shape; it doesn’t matter. All you achieve by making a crank any other shape than straight is to add weight and flexibility.
PMP cranks were even marked with the distance between the crank and pedal holes. As the Bicycle Museum of Bad Ideas remarks: “somebody at PMP understood it was simply an odd way to make a 175mm crank”.
Pretty much everyone who was paying attention in physics at school pointed this out at the time, but that didn’t stop a fad for PMP Brevettatos, especially among time triallists.
Even the great 80s time triallist Ian Cammish used them. Cammish, who won the Best British All-Rounder contest nine times in the 1980s, mentioned them when he tried to sell one of his 1983 bikes on eBay in 2013.
“Unfortunately the PMP cranks cracked a long time ago,” he wrote.
They had a bit of a reputation for that, though to be fair so did many other high-end cranks of the era.
Perhaps because of these reliability issues, and because not many were made in the first place, PMP Brevettato cranks are now rare and collectible. The most recent set I’ve seen on eBay went for US$400 — almost £300.
Other wonky cranks
The bike industry has a serious problem with knowledge loss, which leads to people who really should know better reinventing bad ideas over and over. The PMPs weren’t the first non-straight cranks (the earliest seem to have been in 1897), nor the last. Like the monster lurching back to life at the end of a bad horror movie, wonky cranks keep coming back.
Want to make people go “What the hell?” get yourself a set of dpardo Sickle Cranks:
It’s not at all clear what advantages dpardo claimed for this design. PMP had a slight case of ‘Campagnolo spoken here’ Italglish, but dpardo really needed to get a native speaker of English to write its marketing copy. It says — and I swear I haven’t changed a letter of this:
58T gear turns once is 1.6M faster than 50T！As same as pedaling 50T ！Same pedaling force pedal 58T, the riding performance is 16% increasing than 50T with normal cranks
The craziest recent reappearance of wonky cranks has to be Z-Torque cranks, which came and went between 2010 and 2014.
The shape was claimed to have come to inventor Glenn Coment in a dream. He bent a wire coat hanger into the same shape and “when he revolved it in his hands he found that this crank assembly was different from any other crank assembly ever made. Except for top dead center and bottom dead center, this crank had no dead spots. He was amazed. And in future testing would find that during a rider's maximum effort, power increases at a bikes rear wheel of 20-25% were possible.”
If true, that would be little short of astounding.
Z Torque further claimed “many advantages, including”:
- Smoother pedaling
- More power to climb hills
- Less perceived effort to pedal
- Faster acceleration
- Less affected by headwinds
- Ability to turn higher gearing
However, the Z Torque was really just another crank that connected the bottom bracket axle and pedal by a circuitous route, with an extra problem baked in.
As you can see, the long arm of the V shape, is really, really long. Imagine trying to pedal while banked over hard in a corner and you can probably explain why Z-Torque cranks were never even as popular as PMP Brevettatos.
John has been writing about bikes and cycling for over 30 years since discovering that people were mug enough to pay him for it rather than expecting him to do an honest day's work.
He was heavily involved in the mountain bike boom of the late 1980s as a racer, team manager and race promoter, and that led to writing for Mountain Biking UK magazine shortly after its inception. He got the gig by phoning up the editor and telling him the magazine was rubbish and he could do better. Rather than telling him to get lost, MBUK editor Tym Manley called John’s bluff and the rest is history.
Since then he has worked on MTB Pro magazine and was editor of Maximum Mountain Bike and Australian Mountain Bike magazines, before switching to the web in 2000 to work for CyclingNews.com. Along with road.cc founder Tony Farrelly, John was on the launch team for BikeRadar.com and subsequently became editor in chief of Future Publishing’s group of cycling magazines and websites, including Cycling Plus, MBUK, What Mountain Bike and Procycling.
John has also written for Cyclist magazine, edited the BikeMagic website and was founding editor of TotalWomensCycling.com before handing over to someone far more representative of the site's main audience.
He joined road.cc in 2013. He lives in Cambridge where the lack of hills is more than made up for by the headwinds.
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109 comments
This does make me wonder why no manufacturer ever tried an elastomer crankset. It looks like they would have found a few customers.
[/quote]
There is one out there that I've seen with springs connecting the crank arm to the spider. All I will say is that it doesn't seem to have caught on...
...seeking crowdfunding for centrally mounted disc brakes..should fix pulling to left or right .. just need to to get the brake mechanism to move in and out to avoid the spokes.
or wait for the mark II product: double disc brakes one each side with independent actuators - can steer left or right just by braking.
Should be able to sell loads of these in a groupset including cranks made of cheese to reduce peak loads on your knees.
You could actually get a set of marzocchi bombers with dual discs in the 90's. Aimed at DH MTB.
Almost as retro as this article!
1) Apostrophe alert: "It’s unusual (but, as we’ll see, by no means unique) feature..."
2) There's more spring in a longer lever (other things being equal) so you would store energy during the down stroke and release it as your foot pressure reduces. Some would get converted to heat but some would be returned. So it could theoretically smooth your pedalling.
is my calendar wrong ?? ...
i love them. Hope they make a handlebar stem to match
Arent mountain bike riser bars (with stems with positive reach) very similar in principle ?...
The contact points are at the same position as a flat bar bike with a stem at a more upright angle?
No, riser bars don't change the length of the lever between riders hands and the axle of the steerer tube. What they do is allow fine tuning of ergonomic fit; getting the contact point at the correct height without changing spacers (e.g. if the the steerer's been cut too short to stack)
Even the 'experts' can be fooled. I remember years ago reading a review of a disc-braked motorcycle in which it was stated that, as the brake calliper was behind the fork leg, the front of the bike would lift under braking. This from a professional magazine writer.
The only possible saving grace that might be generously attributed (while squinting very hard and giving all of this year's supply of Benefit of Doubt) to the dpardo Sickle Cranks might be this:
In order to reduce weight a curved crank with a mostly empty interior containing reinforcing struts might provide the same stiffness/strength as a solid straight crank of greater weight... but I suspect they're going after the homeopathic rat-bollox crowd which Mungecrundle's market research has identified.
Lol, this is the biggest load of rubbish ever. Forget about the shape of the crank arms, the force is applied in the same place regardless of crank shape and the torque acts in the same place. All these do is add extra weight by taking the long route between your foot and the centre of the chainrings.
Last few remaining 100grm packs of Magic Beans guarenteed to give you Froome like performance, for life! Only bids over £25,0000. per pack considered.
With modern materials (ignoring shape because that's obviously a stupid idea), could you even-out power a noticeable amount utilising a crank? It'd have to flex a touch at maximum potential and return to shape before the effort you put in was negated completely. Obviously, the natural tendency of any such 'power storage' attempt would be to turn it to heat at the storage point.
The things pictured are way too hard to have done that, but I suppose it it plausible to smooth out the power a minute amount. I'm thinking hill climb rather than track obviously where maintaining V is useful.
There's nothing new under the Sun. This sort of bollocks keeps resurfacing. Currently it's 'oval' (actually eliptical) chainrings. The way to eliminate deadspots in pedalling is to improve pedalling technique. All these gimmicks are just that, gimmicks. You can't blame the manufacturers for trying to make a few quid, but simple common sense should tell you that it's a waste of money.
Oval chain rings were all the rage for a while in the late 80s/early 90s. My old MTB had them when I got it.
"Except for top dead center and bottom dead center, this crank had no dead spots. He was amazed."
True ! LOL
Anyone ever made a double-jointed crank?
We still do
https://highpath.co.uk/pulse-swing-cranks/
I would be wary of these snapping. Did this ever happen ? We're they ever used for long enough in the first place?
It does say they cracked.
To be fair, a non-straight crank could possibly be of some use with non-round chainwheels to alter the power transfer, but with a circular chainwheel, there is zero benefit for a non-straight crank.
Still a lot easier to move the chainring rather than the crank arm
just no
the relationship between the pedal spindle and the crankshaft is unchanged regardless of the shspe of the metal connecting them.
Yes, except for the angle. Imagine that a crank can have a square hole at any orientation (i.e. 90 degrees difference) and thus the orientation of that hole can change the relationship between the pedals and the chainring. With a circular chainring that makes zero difference, but an oval chainring could show a difference in where the peak power is applied. However, a non-straight crank is the most stupid way of changing that orientation (more flex, more weight and less strong) rather than changing how the crank fits onto the crankshaft.
I'm not trying to argue for any benefit with a non-straight crank, but the only possible way that it would physically make any difference would be with a non-circular chainring.
Ultimately the forces through the pedal arm lever resolve to a straight line between the pedal axle and the chainset axle. Regardless of the shape of pedal arm the pedal axle (and foot) still traces a perfect circle around the chainset axle (think about it, the foot does not move further or closer to the centre at any point). Thus even with eliptical chainrings, the foot is making exactly the same shape around the chainset axle, and an 'L' shaped pedal arm does not position the foot relative to the curve of the chain ring any better than a straight pedal arm going from one end of the L to the other.
I thought this thread was over.
What I meant was that the orientation of the crank-hole square will change the phase between the pedals and the chain-ring which will have no effect on a circular chain-ring. A phase change on an oval chain-ring may help or hinder by changing where peak power is applied. Again, a non-straight crank would not be an effective way of manipulating the phase difference between the pedals and the chain-ring.
[/quote]
Yes, except for the angle. Imagine that a crank can have a square hole at any orientation (i.e. 90 degrees difference) and thus the orientation of that hole can change the relationship between the pedals and the chainring. With a circular chainring that makes zero difference, but an oval chainring could show a difference in where the peak power is applied. However, a non-straight crank is the most stupid way of changing that orientation (more flex, more weight and less strong) rather than changing how the crank fits onto the crankshaft.
I'm not trying to argue for any benefit with a non-straight crank, but the only possible way that it would physically make any difference would be with a non-circular chainring.
[/quote]
Still "NO",
Regardless of chainring forming, the "lever" in a pedal arm is always a straight line in terms of the forces applied. Adding a bend, be it 90 degree, 120 degree, or a corve merely increases the amount of material in use to create the same lever action from pedal to bottom bracket. If you REALLY wanted you 'could' make a pedal arm with a set of zig-zags out to the pedal and claim the increased pedal arm length (from the zig-zag) means more power. But it would still be quackery, as the raw physics looks at 2 things. power applied to pedal, and direct line of sight distance from centre of bottom bracket to centre of mount for pedal.
The only way to avoid the "deadspots" would be to not have the pedals set to 180 degrees to each other, so have the sueare hole in one pedal offset by maybe 15-20 degrees. But this would result in a very ungainly pedalling rythym, and while "technically" avoidint a total deadspot would result in a more uneven application of power with a highpoint as (for example) left foot comes over top before right passed the bottom point, and a low point as both pedals are in the act of coming back upwards (good luck without cleats)
Pop into your local school and ask a physica teacher to help with some forces diagrams to see what we mean if you don't follow.
Yes, except for the angle. Imagine that a crank can have a square hole at any orientation (i.e. 90 degrees difference) and thus the orientation of that hole can change the relationship between the pedals and the chainring. With a circular chainring that makes zero difference, but an oval chainring could show a difference in where the peak power is applied. However, a non-straight crank is the most stupid way of changing that orientation (more flex, more weight and less strong) rather than changing how the crank fits onto the crankshaft.
I'm not trying to argue for any benefit with a non-straight crank, but the only possible way that it would physically make any difference would be with a non-circular chainring.
[/quote]
Still "NO",
Regardless of chainring forming, the "lever" in a pedal arm is always a straight line in terms of the forces applied. Adding a bend, be it 90 degree, 120 degree, or a corve merely increases the amount of material in use to create the same lever action from pedal to bottom bracket. If you REALLY wanted you 'could' make a pedal arm with a set of zig-zags out to the pedal and claim the increased pedal arm length (from the zig-zag) means more power. But it would still be quackery, as the raw physics looks at 2 things. power applied to pedal, and direct line of sight distance from centre of bottom bracket to centre of mount for pedal.
The only way to avoid the "deadspots" would be to not have the pedals set to 180 degrees to each other, so have the sueare hole in one pedal offset by maybe 15-20 degrees. But this would result in a very ungainly pedalling rythym, and while "technically" avoidint a total deadspot would result in a more uneven application of power with a highpoint as (for example) left foot comes over top before right passed the bottom point, and a low point as both pedals are in the act of coming back upwards (good luck without cleats)
Pop into your local school and ask a physica teacher to help with some forces diagrams to see what we mean if you don't follow.
[/quote]
You're missing the point of the phase relationship between the position of the (oval) chainring and the position of the pedals. Yes, a force diagram shows no difference as there is no difference in how much force is applied.
Pop into your local academy and get an electrical engineer to explain phases to you if you don't follow.
Still "NO",
Regardless of chainring forming, the "lever" in a pedal arm is always a straight line in terms of the forces applied. Adding a bend, be it 90 degree, 120 degree, or a corve merely increases the amount of material in use to create the same lever action from pedal to bottom bracket. If you REALLY wanted you 'could' make a pedal arm with a set of zig-zags out to the pedal and claim the increased pedal arm length (from the zig-zag) means more power. But it would still be quackery, as the raw physics looks at 2 things. power applied to pedal, and direct line of sight distance from centre of bottom bracket to centre of mount for pedal.
The only way to avoid the "deadspots" would be to not have the pedals set to 180 degrees to each other, so have the sueare hole in one pedal offset by maybe 15-20 degrees. But this would result in a very ungainly pedalling rythym, and while "technically" avoidint a total deadspot would result in a more uneven application of power with a highpoint as (for example) left foot comes over top before right passed the bottom point, and a low point as both pedals are in the act of coming back upwards (good luck without cleats)
Pop into your local school and ask a physica teacher to help with some forces diagrams to see what we mean if you don't follow.
[/quote]
You're missing the point of the phase relationship between the position of the (oval) chainring and the position of the pedals. Yes, a force diagram shows no difference as there is no difference in how much force is applied.
Pop into your local academy and get an electrical engineer to explain phases to you if you don't follow.
[/quote]
But you can set any "phase difference" you like with a straight crank by just offsetting the angle of the crankset spider. There is no point in using a bent crank to do it!
Just to check, were you on here a few months ago saying that disc brakes caused bikes to pull to the left, or was that someone else?
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