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They were claimed to eliminate pedalling dead spots — but did they work?

Image: PMP cranks by robadod from LFGSS [This feature from the road.cc archive was last republished on April 23 2018]

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.”

PMP crank B&W.jpg

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.

PMPcranksadvert.jpg
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:

dpardo r58 cranks.jpg

It’s not at all clear what advantages dpardo claims for this design. PMP had a slight case of ‘Campagnolo spoken here’ Italglish, but dpardo really needs 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 50TAs 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.

Z Torque cranks.jpg

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.

Our official grumpy Northerner, John has been riding bikes for over 30 years since discovering as an uncoordinated teen that a sport could be fun if it didn't require you to catch a ball or get in the way of a hulking prop forward.

Road touring was followed by mountain biking and a career racing in the mud that was as brief as it was unsuccessful.

Somewhere along the line came the discovery that he could string a few words together, followed by the even more remarkable discovery that people were mug enough to pay for this rather than expecting him to do an honest day's work. He's pretty certain he's worked for even more bike publications than Mat Brett.

The inevitable 30-something MAMIL transition saw him shift to skinny tyres and these days he lives in Cambridge where the lack of hills is more than made up for by the headwinds.

105 comments

Avatar
don simon fbpe [2989 posts] 1 year ago
0 likes
flobble wrote:
Quote:

 

No matter how much bollocks is included.

No matter how many bollocks are included.

Attention to detail please  1

Depends whether you thing bollocks is countable, which in this case they clearly aren't.

Avatar
zero_trooper [338 posts] 1 year ago
5 likes

Retro: L-shaped cranks - a bad article that just won't die...

Avatar
pedalpowerDC [380 posts] 1 year ago
4 likes

Won't go away because Road.cc keeps running the story through their homepage year after year?

Avatar
Fluffed [139 posts] 5 months ago
6 likes

Happy 3rd birthday L shaped cranks story!

Avatar
TRV56 [5 posts] 5 months ago
2 likes
HawkinsPeter wrote:

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.

 

maybe read the article again.  You could connect the pedal and the crank with any shaped bobble you want and it wouldn’t make a lick of difference. It’s still just a fixed relationship between bottom bracket and pedal.  Doesn’t matter what shape chainring.  

Avatar
Crippledbiker [96 posts] 5 months ago
0 likes

I'd actually be curious about how this worked for in-phase cranks ie: handcycles; I have three dead spots in my rotation on my upright, with a huge one at forward bottom - main power is at backwards bottom and upwards mid, with a small deadspot in the middle, then a small power spot in upwards-forward before we're dead again.

... In other words, from my right side so we're clockwise; 6o'clock to about 9/10 is my main power phase, using my entire core to pull towards me;
then a small dead spot, then power through to about half-one pushing upwards and forwards with my middle back and shoulders.
Mostly dead spot through to 3, using biceps and shoulders, dead-spot through to about five, small power through to six.

I wonder if having the cranks tipped back a bit with non-standard geometry might help with the dead spots a bit - I think an oval ring would likely have more effect, though. I suspect I'd end up with my cranks jammed against my thigh more often with non-straight cranks, though.

Avatar
jasecd [554 posts] 5 months ago
0 likes

Recycling articles.

 

A bad idea that just won't die...

Avatar
hawkinspeter [3849 posts] 5 months ago
0 likes
lolol wrote:

Once more, but this time with feeling

That's getting a vinyl release:

https://grizzlybomb.com/2019/03/01/buffys-once-more-with-feeling-getting...

Avatar
brooksby [4744 posts] 5 months ago
1 like
HawkinsPeter wrote:
lolol wrote:

Once more, but this time with feeling

That's getting a vinyl release:

https://grizzlybomb.com/2019/03/01/buffys-once-more-with-feeling-getting...

Well, now I've got something to sing about 

https://youtu.be/Sv8uRVLN5Dc

Avatar
hawkinspeter [3849 posts] 5 months ago
2 likes
brooksby wrote:
HawkinsPeter wrote:
lolol wrote:

Once more, but this time with feeling

That's getting a vinyl release:

https://grizzlybomb.com/2019/03/01/buffys-once-more-with-feeling-getting...

Well, now I've got something to sing about 

https://youtu.be/Sv8uRVLN5Dc

Bunnies aren't just cute like everybody supposes!
They've got them hoppy legs and twitchy little noses!
And what's with all the carrots?
What do they need such good eyesight for anyway?

 

Avatar
fukawitribe [2837 posts] 5 months ago
0 likes
Crippledbiker wrote:

I'd actually be curious about how this worked for in-phase cranks ie: handcycles; I have three dead spots in my rotation on my upright, with a huge one at forward bottom - main power is at backwards bottom and upwards mid, with a small deadspot in the middle, then a small power spot in upwards-forward before we're dead again. ... In other words, from my right side so we're clockwise; 6o'clock to about 9/10 is my main power phase, using my entire core to pull towards me; then a small dead spot, then power through to about half-one pushing upwards and forwards with my middle back and shoulders. Mostly dead spot through to 3, using biceps and shoulders, dead-spot through to about five, small power through to six. I wonder if having the cranks tipped back a bit with non-standard geometry might help with the dead spots a bit - I think an oval ring would likely have more effect, though. I suspect I'd end up with my cranks jammed against my thigh more often with non-straight cranks, though.

These won't help at all, they do nothing, may even make things worse as the actual crank arm looks like it might stick out more - not sure on that. It's a really interesting question though.. i'd definitely have thought a non-circular chainring might be able to help, although the actual profile may need to differ from a leg-cycling one to cope with the different dead spot timing. Power data with a decent sampling rate would help.. wonder if anyone has done any work on this ? Going to have a look, good luck with your search.

Avatar
Crippledbiker [96 posts] 5 months ago
0 likes
fukawitribe wrote:
Crippledbiker wrote:

I'd actually be curious about how this worked for in-phase cranks ie: handcycles; I have three dead spots in my rotation on my upright, with a huge one at forward bottom - main power is at backwards bottom and upwards mid, with a small deadspot in the middle, then a small power spot in upwards-forward before we're dead again. ... In other words, from my right side so we're clockwise; 6o'clock to about 9/10 is my main power phase, using my entire core to pull towards me; then a small dead spot, then power through to about half-one pushing upwards and forwards with my middle back and shoulders. Mostly dead spot through to 3, using biceps and shoulders, dead-spot through to about five, small power through to six. I wonder if having the cranks tipped back a bit with non-standard geometry might help with the dead spots a bit - I think an oval ring would likely have more effect, though. I suspect I'd end up with my cranks jammed against my thigh more often with non-straight cranks, though.

These won't help at all, they do nothing, may even make things worse as the actual crank arm looks like it might stick out more - not sure on that. It's a really interesting question though.. i'd definitely have thought a non-circular chainring might be able to help, although the actual profile may need to differ from a leg-cycling one to cope with the different dead spot timing. Power data with a decent sampling rate would help.. wonder if anyone has done any work on this ? Going to have a look, good luck with your search.

There has been a small amount of research done; the shape currently believed to be most optimal is egg shaped.

Good luck shifting gears, though.

Having had a think about these, I suspect it would just move the deadspot in terms of position on the rings; the position of my power and dead zones, in relation to the position of my hands, probably would not change, and the change in position of my arms in relation to my shoulder would likely move (think knees, arms want to be in a fairly narrow envelope), probably outwards which would increase agility but reduce power.

Avatar
Rick_Rude [298 posts] 5 months ago
1 like
jasecd wrote:

Recycling articles.

 

A bad idea that just won't die...

 

Can you recycle user names, as I'd like to be Superpython?

Avatar
Mungecrundle [1526 posts] 5 months ago
2 likes
Rick_Rude wrote:
jasecd wrote:

Recycling articles.

 

A bad idea that just won't die...

 

Can you recycle user names, as I'd like to be Superpython?

You sir, are no SuperPython59 or any other number.

Avatar
triwasaki [1 post] 4 months ago
0 likes
matthewn5 wrote:

Anyone ever made a double-jointed crank?

We still do  3

https://highpath.co.uk/pulse-swing-cranks/

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