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Originally Posted by mihlbach
(Post 11414246)
http://www.cptips.com/crnklth.htm
For FGs I like somewhat shorter cranks than is normally recommended for a geared bike. For example, I'm barely over 6' and I normally ride 172.5-175 mm cranks on road bikes and on FG bikes I ride 167.5-170 mm cranks. Track riders, in general, use shorter cranks that road cyclists. The shorter cranks avoid pedal strike and allows one to sustain a higher than normal cadence. This normally isn't a concern on geared bikes, since you can always shift into a higher gear when the cadence gets too fast, but on a FG, you are often stuck pedaling at very high cadences, especially if you ride hills. At your height, I would probably choose 165s, but a few mm variation in either direction isn't going to make that much of a difference. awesome thank you!! |
extra torque with longer cranks.. and yes, you will be able to tell the difference with 10mm.
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so i broke my FSA 39t chainring and it gave me an excuse to try something new.
i picked up a used set of truvativ omniums 165mm arms, 46t soma hellyer chainring, izumi gold chain, and now running 16t soma cog. installed it tonight, cant say i feel anything different with these crankset yet except that its a tad bit more difficult to pedal since i gained 2 gear inches. i do noticed the shorter strokes from 170mm to 165mm arms. although expecting to feel like my brothers bike, it is not even close. now its even harder to skid stop/slow down. i think i came to the conclusions that his platform pedals and leader blaq straps holds your feet better and gives better torque to reverse the revolution. |
On my rides i run 180mm crank
with 39/17 gears |
5 mm difference is .2 inches and on the 180 degree crank arms that's nearly 1/2 inch, which makes even more of a difference on the circumference of the crank for duration of any given power stroke. The other aspect of it, when leaning into turns, your pedals will be closer to the ground. Would 5 mm difference result in striking the pedal on the asphalt ? 5 mm on a crank arm for ground clearance might mean more on a bike that has a lower bottom bracket height clearance to the ground. A difference in crank arm length might mess up (mismatch) your cadence a tad. It may not seem like much on a single rotation, but accumulated over rpm's and hour(s) of riding, that's a lot of pedal travel +/-. Think of the crank arm as the radius of a circle. C=pi x D or C=pi x 2r
165 mm = 6.49inches, 12.98 diameter and a circumference of 40.77667 inches 170 mm = 6.69 inches, 13.38 diameter and a circumference of 42.03327 inches 1.2566 inches difference in circumference, about 1/2 of that on each down stroke. But on a minute of riding at 80 rpm's, pedals travel 100.528 more inches w/ longer cranks or 8.3773 feet more and over an hour that's 502 feet more pedal travel. I'll let other's figure out the difference in leverage, it's not much in terms of what more/less you put into it on each down stroke, but again, the accumulation over a minute at 80 rpms and even an hour of riding is going to make a difference and it may mean being ahead or behind after a duration of a ride, whether or not a cyclist can find enough power to make a move and go by another over the span of a few seconds ? Sorry for the equations and math, but it has to be done for perspective. |
Originally Posted by mihlbach
(Post 11410006)
The difference between 165s and 170s is so tiny, only a very experienced rider might notice the difference. All else being equal, long cranks are easier to pedal, but limit your cadence because you are pedaling larger circles. However, in your case. all is not equal. You were comparing two different bikes of different sizes, gear ratios, and geometries.
For experienced riders, there is a reason cranks come in 2.5mm incriments (165, 167.5, 170, 172.5, 175mm). Generally speaking, relatively smaller crank arms are better for high RPM work. Longer work for low RPMs and climbing. Then, if you really want to get technical, if you are a time trialer or ride really low in the drops, 165mm cranks won't bring your knees up to bang your chest like 175mm cranks will. Most casual riders won't notice a difference or have a preference. Many trained athletes don't have a preference either. But on the other hand, there are athletes that are very sensitive to such. For example, some racers prefer a 47/14 to a 50/15 which are virtually the same ratio (3.36 vs 3.33). Some can also notice a 1cm difference in handlebar height. To settle on the best for you, you will simply have to try different lengths and see which one feels best. I like to spin, even on my road bike. Last season I switched from 175mm to 170mm cranks and it was worlds different. But, I would often choose to spin a low gear up hills from the saddle instead of standing and mashing a moderate gear the traditional way. |
Originally Posted by mihlbach
(Post 11414246)
http://www.cptips.com/crnklth.htm
For FGs I like somewhat shorter cranks than is normally recommended for a geared bike. For example, I'm barely over 6' and I normally ride 172.5-175 mm cranks on road bikes and on FG bikes I ride 167.5-170 mm cranks. Track riders, in general, use shorter cranks that road cyclists. The shorter cranks avoid pedal strike and allows one to sustain a higher than normal cadence. This normally isn't a concern on geared bikes, since you can always shift into a higher gear when the cadence gets too fast, but on a FG, you are often stuck pedaling at very high cadences, especially if you ride hills. At your height, I would probably choose 165s, but a few mm variation in either direction isn't going to make that much of a difference. Long cranks are a longer lever so they give you a bit more power, but they somewhat inhibit your ability to spin fast. Short cranks allow you to spin faster/longer but decrease the amount of leverage you at the chainring. For fixies, pedal strike is also an issue with longer cranks. |
its all in your head.
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Your brother sure has a high gear ratio for a tarck bike....
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Originally Posted by happypills
(Post 11447375)
Your brother sure has a high gear ratio for a tarck bike....
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depending on the fit, 5mm can make a decent difference in hip angle, especially on the short end of the spectrum.
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I've noticed almost this exact same thing from my 52 lager to my friends 50 kilo. I think its geometry, though I have little but speculation to back that up. He's running about 80gi and I'm running about 75. His is easier to skid. I say geometry cause of the headtube angle. With a steeper headtube angle you also get less rake. This "pulls" the front wheel closer to you making it easier to put more weight on it than on your back wheel making it easier to brake your back wheel loose.
But again, this is just me guessing... |
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