Home
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
IanEdward [306 posts] 1 year ago
2 likes
Quote:

Oh and don't even mention gravel bikes - Jesus! The old saying, 'A fool and his money is easily parted' has never been more true.

OK, I'll bite, what don't you like about gravel bikes?

If I'm in the market for a new bike (so I'll be spending £1000 regardless) where's the harm in having numerous subtly different styles of bikes, each with its own catchy marketing term.

Unless you're claiming road bikes, gravel bikes, touring bikes and CX bikes all share identical geometry, materials, clearances, gearing and braking?

Avatar
alansmurphy [2220 posts] 1 year ago
1 like

Same with discs. They have advantages, they have disadvantages; why does somebody care what someone else chooses to ride. And it is choice, again to think that someone has been duped is ridiculous. We can take the argument as far back as he likes, no carbon frames, no gears, penny farthing...

Avatar
FluffyKittenofT... [2602 posts] 1 year ago
5 likes
yupiteru wrote:

Oh and don't even mention gravel bikes - Jesus! The old saying, 'A fool and his money is easily parted' has never been more true.

 

Why has this thread risen from the grave?

 

But I do agree, it's always seemed to me that gravel is a very poor material from which to construct a bike.  Bikes should only be made from roads or mountains, or some combination of the two.

Avatar
reippuert [122 posts] 1 year ago
0 likes

Give me non round wheels....

Avatar
hawkinspeter [3729 posts] 1 year ago
1 like
reippuert wrote:

Give me non round wheels....

https://www.youtube.com/watch?v=vk7s4PfvCZg

 

Avatar
rjfrussell [521 posts] 1 year ago
0 likes

I'd like to see some analysis of the physics of ordinary crank lengths.

Is it the case, for example, that for steep climbing a longer crank would be a good idea, as less force is needed to achieve the same torque (due to the longer lever)?

Avatar
Miller [242 posts] 1 year ago
0 likes
rjfrussell wrote:

I'd like to see some analysis of the physics of ordinary crank lengths.

Is it the case, for example, that for steep climbing a longer crank would be a good idea, as less force is needed to achieve the same torque (due to the longer lever)?

In practise crank length doesn't seem to make much difference . People who experiment with widely varying crank lengths are able to adapt within a wide range without power output being materially affected.

As for leverage, that leverage is modified by the rear sprocket size, the front chainwheel size and the wheel size. What you're left with is your power output available to propel you uphill and if that doesn't vary much with crank length then neither does your uphill speed.

Kind of counter-intuitive all that but it does seem to be true.

 

Avatar
fenix [1195 posts] 1 year ago
0 likes
yupiteru wrote:

Its just clever marketing at the end of the day. The same type of people who have been conned into using disc brakes, wide rims, reinforced plastic (carbon fiber) etc on their road bikes.

All a load of bollocks and totally unnecessary except on an off road bike of course and in 10yrs time we will look back and laugh our heads off!

Oh and don't even mention gravel bikes - Jesus! The old saying, 'A fool and his money is easily parted' has never been more true.

Well carbon fibre has been around for at least 20 years now ? It's a good material for frames.

Avatar
hawkinspeter [3729 posts] 1 year ago
1 like
rjfrussell wrote:

I'd like to see some analysis of the physics of ordinary crank lengths.

Is it the case, for example, that for steep climbing a longer crank would be a good idea, as less force is needed to achieve the same torque (due to the longer lever)?

Basically, yes a longer crank provides more torque. If you change your crank length, it's like changing your gearing.

Usually, people only change their crank lengths to improve their bike fit, so someone with long legs might want longer cranks and similarly, shorter legged riders might benefit from shorter cranks. It's quite useful on a tandem to have different crank lengths to allow different sized riders to use the same gear and cadence.

Avatar
srchar [1393 posts] 1 year ago
1 like
hawkinspeter wrote:

Basically, yes a longer crank provides more torque. If you change your crank length, it's like changing your gearing.

While that's true, I think it is imperceptible. Moving from a 172.5 to a 175 will give you, what, just over 1% difference in gearing?  That's not even as big a difference as moving from a 53 to a 52 tooth chainring.

Avatar
Welsh boy [652 posts] 1 year ago
0 likes
srchar wrote:
hawkinspeter wrote:

Basically, yes a longer crank provides more torque. If you change your crank length, it's like changing your gearing.

While that's true, I think it is imperceptible. Moving from a 172.5 to a 175 will give you, what, just over 1% difference in gearing?  That's not even as big a difference as moving from a 53 to a 52 tooth chainring.

 

Complete rubbish.  Changing the length of your crank DOES NOT change your gearing.  The ONLY thing which changes the gearing for a given wheel is the ratio of the chainring to the sprocket, if your chainring is 4 times the size of your sprocket, for one revolution of your chainring your sprocket will go round 4 times regardless of the length of the lever (crank) turning it.

Avatar
hawkinspeter [3729 posts] 1 year ago
2 likes
Welsh boy wrote:
srchar wrote:
hawkinspeter wrote:

Basically, yes a longer crank provides more torque. If you change your crank length, it's like changing your gearing.

While that's true, I think it is imperceptible. Moving from a 172.5 to a 175 will give you, what, just over 1% difference in gearing?  That's not even as big a difference as moving from a 53 to a 52 tooth chainring.

 

Complete rubbish.  Changing the length of your crank DOES NOT change your gearing.  The ONLY thing which changes the gearing for a given wheel is the ratio of the chainring to the sprocket, if your chainring is 4 times the size of your sprocket, for one revolution of your chainring your sprocket will go round 4 times regardless of the length of the lever (crank) turning it.

You're technically correct (the best kind of correct), but I'd like to point out that I was referring to the effective gearing which is the relationship between the force applied at the pedal and the force at the rear wheel. This can be changed by keeping all your gears the same, but changing the size of your back wheel or changing the length of your crank (although as srchar has pointed out a small size change doesn't make much difference).

Although the ratio of revolutions of chainring/sprocket is unchanged, the distance that your foot travels will increase per revolution with a longer crank and thus the work (Nm) increases. So, a much longer crank will make it feel like an easier gear.

Here's some info from the late Sheldon Brown on the subject: http://www.sheldonbrown.com/gain.html

Avatar
mdavidford [73 posts] 1 year ago
3 likes

Apparently this idea resurfaces almost as often as old road.cc articles.

Avatar
CygnusX1 [1158 posts] 1 year ago
3 likes
mdavidford wrote:

Apparently this idea resurfaces almost as often as old road.cc articles.

I think this article is road. cc's way of trolling their readership

Avatar
philtregear [135 posts] 1 year ago
1 like

what is the purpose of this article.? or comments about it? or this comment? this is all pointless.

Avatar
Griff500 [382 posts] 1 year ago
2 likes
philtregear wrote:

what is the purpose of this article.? or comments about it? or this comment? this is all pointless.

Perhaps nostalgia, or a chance to snigger at the scientifically illiterate who thought this would work. Or maybe a light hearted diversion from the endless stories of people being knocked off their bikes, which seem to dominate roadcc these days.

Avatar
ConcordeCX [1117 posts] 1 year ago
1 like
Griff500 wrote:
philtregear wrote:

what is the purpose of this article.? or comments about it? or this comment? this is all pointless.

Perhaps nostalgia, or a chance to snigger at the scientifically illiterate who thought this would work. Or maybe a light hearted diversion from the endless stories of people being knocked off their bikes, which seem to dominate roadcc these days.

L-shaped helmets offer 853% more protection against being knocked off your bike, studies reveal.

 

Avatar
WashoutWheeler [124 posts] 1 year ago
1 like

I still have a limited amount of Snake Oil and brightly coloured Magic Beans at clearance prices.

Avatar
Canyon48 [1146 posts] 1 year ago
0 likes
CygnusX1 wrote:
mdavidford wrote:

Apparently this idea resurfaces almost as often as old road.cc articles.

I think this article is road. cc's way of trolling their readership

Haha, seems about right 

philtregear wrote:

what is the purpose of this article.? or comments about it? or this comment? this is all pointless.

I'm just going along with it now. As an aerospace engineer, I'm also trying to dream up some highly complicated cycling product to hand over to marketing to see how far a product would go.

I'm thinking of a stem that points backwards with bars that curve around to the front (where they should be) - to reduce vibration and improve handling.

Avatar
Crampy [154 posts] 1 year ago
0 likes

Gents, would any of you be interested in some Nigerian real estate I currently inexplicably have laying around? Going cheap!

 

Avatar
Canyon48 [1146 posts] 1 year ago
1 like
Crampy wrote:

Gents, would any of you be interested in some Nigerian real estate I currently inexplicably have laying around? Going cheap!

 

To whom do I email my card details? 

Avatar
ConcordeCX [1117 posts] 1 year ago
1 like
wellsprop wrote:
Crampy wrote:

Gents, would any of you be interested in some Nigerian real estate I currently inexplicably have laying around? Going cheap!

 

To whom do I email my card details? 

me

Avatar
mjs [1 post] 1 year ago
1 like

Sheldon Brown on Shimano's non-round Biopace chainwheel of the 80s and 90s: https://www.sheldonbrown.com/biopace.html

Avatar
Bigfoz [180 posts] 1 year ago
0 likes

Hmmm. Central disc brake...

Fit to axle inside the spokes, operate by bluetooth? No need for wires hydraulics as self contained unit... 

 

Comes with free Ratbollock essence 

Avatar
ktache [1695 posts] 1 year ago
4 likes

A regurgitated article that refuses to die?

Avatar
don simon fbpe [2989 posts] 1 year ago
3 likes
ktache wrote:

A regurgitated article that refuses to die?

Apparently if you repeat something enough, in these parts, it becomes true. No matter how much bollocks is included.

Avatar
ConcordeCX [1117 posts] 1 year ago
3 likes
don simon wrote:
ktache wrote:

A regurgitated article that refuses to die?

Apparently if you repeat something enough, in these parts, it becomes true. No matter how much bollocks is included.

you can say that again!

 

Avatar
lolol [232 posts] 1 year ago
2 likes

Once more, but this time with feeling

Avatar
flobble [147 posts] 1 year ago
1 like
Quote:

 

No matter how much bollocks is included.

No matter how many bollocks are included.

Attention to detail please  1

Avatar
simonmb [715 posts] 1 year ago
1 like

There's nowt more retro than an increasing amount of material on road.cc

Which is a shame - because it's always mostly been a well-informed and creative site.

Pages