Cranks

Came standard on my bike. Should I change???

 

172.5 mm Campy Centaur.

I love em cos they work, feel good, and I've never tried anything else!

 

I just upgraded my moulton apb (landrover) cranks to (splined) octolink dura-ace. I kept the standard size of 170mm.
cheers
rifraf

 

There is 170 stamped on mine together with a whole lot of other stuff. I assume that is the length.

I have never thought much about crank length.

Does this mean there is a whole new world of performance optimisation out there, maybe that is way I am getting dropped on those hills

Leon

 

http://www.myra-simon.com/bike/cranks.html

 

Fascinating link AE

Leon

 

I'm the guy using 165s...

 

172.5

that's the way it came out when I was fitted for the bike.

 

Yep, 165 on a road bike. Standard Shimano 105. They drop the big chainring to 50t, which is the equivalent of 53 with the shorter cranks.

Good for spinning, and I reckon better for your knees. Better ground clearance too, which can avert embarrassment on roundabouts.

Some HPV guys use 150mm cranks (to reduce frontal area on faired machines) and it doesn't seem to slow them down. 80mph anyone?

 

172.5 Ultegra on my Kestrel.

I have been reading in several bike mags that there is a trend toward longer crank arms for better power.

I have this legnth 'cause it's what came with my bike...but, seem to be doing okay with it.

 

If you plotted power as a function of crank length, with gearing to compensate for each crank length, it would start low (imagine using 50mm cranks), rise, and then fall off (imagine using 500mm cranks). Finding out where it peaks for you is what it's about. It probably plateaus, so there would be scope for comfort changes. Anyone know of such a plot? I've seen one for saddle height.

P=W/T. There is no free lunch.

 

I ride 180 mm Dura Ace cranks. I started 13 years ago on 172.5 mm arms. Velo News years ago did an in depth test on several riders from a short (5 ft)female to a very tall (6'3"-6'4") male. ALL the riders went faster on 180 mm crankarms. I'm 6'1" (185.4 cm).

Indurain always rode on 180's except when he set the hour record where he used 190 mm cranks. To be fair, Rominger did 55 kmh on 175mm arms, but then again, Big Mig won 5 Tours on 180's and Rominger won zero tours on his normal 172.5's.

At first, 180's may seem too long, especially if you are going from a short (172.5 mm) arm. If you want to try longer cranks, don't screw around with the next bigger size like I did, go straight to the 180's.

You will find that it's easier to turn bigger gears with the longer arms. 180's will slow your legs down a little and force your legs to turn a larger circle, forcing the knees to bend more, especially the top of the pedal stroke, so people with certain knee injuries may compound their problems with longer cranks. Some riders raise their saddle as many millimeters as the increase, others leave saddle height alone. Don't worry about it though. Just go for it and see what happens.

As far as legspeed goes, train for it and it won't be a problem. On 180 mm arms, my current max cadence is around 180 rpm, and I can hold 125+ rpm for several minutes. Longer cranks are most helpful on climbs and time trialling.

Good luck!!!

 

That just tells me your gearing was too high, unless you raised it when you went to longer cranks.

 

You don't understand what I'm saying. Whatever gear your are turning, the longer cranks will give more leverage that shorter ones, period. Shorter cranks require more pedal force regardless of the gear. Longer cranks will not make the difference of being able to ride a gear higher, so gearing up with longer cranks is not a valid scenario. You must be strong enough to turn whatever gear, the longer cranks just make it a little easier.

To go fast you have to turn bigger gears. Anything that makes that easier should be investigated. Almost all the great Tour winners have increased their cranklengths for certain conditions like climbs, and especially time trials.

 

I have 165mm on track bike and 170mm on roadie, though i wouldnt mind finding a set of good quality 167.5mm track cranks (anybody have any ideas?)

J-MAT, although i am not certain i do find 190mm cranks a little difficult to believe, out of interest where did u find this info?

Also, not bragging or anything of the like, just comparing 2 values. My max cadence with 170mm cranks is around 225 (obviously in a small gear) and i dont believe this is unusually high.

I must say that small cranks do have their advantages as well. Such as weight (only minor but it is rotating mass) and spinning ability (as above). This is obviously a matter of personal opinion and wont be resolved but i feel better knowing i have had my say

 

J-MAT. Leverage is gearing. Gearing is leverage. Although there are other effects, one effect of going to longer cranks is to lower the gearing. That's why it makes sense on climbs. But it is demonstrably equivalent to lowering the gearing by other means, and vice versa.

Power is rate of work: P=W/T, i.e. Power equals work over time. Work equals force times distance, or W=FD. Therefore P=FD/T. When you lengthen the cranks, you increase the distance *and time* your foot has to go to do the same amount of work. To go further, your feet must take longer. You are increasing both the denominator and the numerator, so you will not see an automatic gain in the overall value, which is power.

That is exactly what gearing is.

Gearing is worked off diameter. An increase from 170mm to 180mm in the crank is an increase in swept diameter, or the distance your feet must go for each revolution, of roughly 62mm. That is about 6% of the swept diameter of a 170mm crank, or about the same as shifting from a 16 tooth sprocket to a 17. No wonder it's easier, you're riding along one gear lower than before.

Of course, because pedalling is a rotary-lever thing, there are other effects. Because levers are less inefficient at the ends of the stroke and our co-ordination is imperfect, you will get small efficiency gains by having a pair of cranks that are well-matched to your lever length, just like in any reciprocating engine. For short bastards like me, that might mean a 165. For you, it might mean 180.

 

1) Drewjc: The info on the 190 mm cranks Indurain used on his hour record came from Velo News and Cycle Sport magazine, 2 of the most credible bicycle racing publications out there. Cadences of over 200 rpm are not uncommon, I just don't work at it too often, being more concerned at what I do for real on the road, and that is time trialling at 95-105 rpm and field sprinting at 120-130 rpm. That's about all you will ever need for road racing. I think the current record holder for the hour record on rollers rode over 200 rpm for an hour!!!

2) Ant Evans: Gearing is gearing and leverage is leverage. The two are unrelated. If you have ever jacked up a car to change a flat tire, you should be thankful the jack handle was fairly long instead of a few centimeters long. That is leverage. Longer levers (cranks, jack handles) move a static force or resistance with less force. The downside, if you want to call it that, is it takes a longer lever more time to complete the cycle.

Let's say we had two hypothetical cranks 1 cm & 100 cm long. At 40 kmh it would require a gear-cadence product in the neighborhood of a 53x15 at 90 rpm. That gear-cadence combination would produce 40kmh uphill, downhill, with a short rider, a tall rider, 1 cm cranks or 100 cm cranks!!! Turn a 53x15 at 90 rpm and you will always go 40kmh!!!

The crank length would only effect the diameter of the circle the legs would have to turn, and how much pedal force the legs would have to exert. Short cranks are like short jack handles. The stroke or cycle is completed faster but at the expense of leverage, requiring more force. Longer cranks move slower but have more leverage and require less force. Since most folks find big gears hard to turn, longer cranks will always make it easier to turn the same big gear than with shorter cranks.

If you read my earlier post, I already said longer cranks slow your legs down a little and force your legs to turn a bigger circle. As far as gearing goes it makes it easier to turn a higher gear, not a lower one. The difference between cranklengths is not enough to be one cog.

Moving up to longer cranks (or down) is a small, but noticeable difference. A good rider is good not because of ONE way he trains or ONE piece of equipment, but rather the sum of the parts; longer cranks are only a "spoke in the wheel."

Ant, your height is not really a factor. I might be taller than you, but if we both had to jack up a car to change a flat tire, we would BOTH find it easier to get the car off the ground with a longer jack handle. Even if you are a "short bastard," I think you will find longer cranks make overall road riding better, especially climbing and TT'ing. The track is one case where short cranks are better, due the high leg speed needed. What the hell man, give them a shot. If you don't like them, someone will buy them from you, minimizing the finacial impact of this experiment. Life is short - go for it and see what happens!!!

Finally, whether you think longer cranks are good or bad, don't you think the coaches, team managers, and sponsers who backed Indurain and other greats in the TDF and the hour record cared about the outcome? Don't you think these guys had a lot on the line if their star rider failed??? To get a rider to that level, don't you think they know what they are doing???

The trend for these cycling greats is to ALWAYS go to longer cranks for important races, never shorter ones.

 

Say the jack handle wasn't a handle. Say it was a disc, which is what a handle makes when you turn it. Put teeth around the edge of the disc. Say you had a chain around this disc connected to your cranks, and you pedalled to jack up your car. Which would be easier? A small disc, or a big one? Is that gearing, or leverage?