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Old 05-09-06, 05:21 PM   #1
fixiemack
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Crank arm length

Just bought a Bianchi Pista Concept 2006 with crankarm length of 170mm. .......did not realize what the crank arms were when I made the purchase....I presently ride a Bianchi Pista with 165mm crank arms ..Will there be a noticeable diffrence??? What will the changes be if any?? I'm 6'4"----240lbs..

Thanks,
Mack
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Old 05-09-06, 05:43 PM   #2
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do you ride at ADT? I imagine the half centimeter would make a big difference clearance wise there. Otherwise you will spin out at a lower rpm but be able to push a larger gear.
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Old 05-09-06, 08:22 PM   #3
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You should notice a difference if you ride at least several times a week. After a short time you will get used to the change. Its all in what you're used to riding. As dutret said, you will be able to push a larger gear. In other words you will have more leverage with the longer crankarms.

Personally, I think you need to be fitted. Perhaps you can have a someone help you make the measurements.

The general concept is that when you are sitting in your normal position on the saddle, you should be able to drop a plumb bob on a string from a particular point on your knee through the center of the pedal axle. In order to locate that particular point on your knee you should find articles on on how to set up bike position.

There are other factors involved such as type of riding or racing, and frame geometry. This question requires more than a simple answer.

I did a google search for "bike position." Here are a couple of links to start with.

http://www.peterwhitecycles.com/fitting.htm
http://www.bikesportmichigan.com/bikes/karma.shtml

Its takes a bit of time to get setup properly on any bike but after you do it once and record the measurements, you can carry those measurements from bike to bike. Its good if you can get good fit on cheaper bikes and find out what works for you. Then you'll be able to get greater value from a more expensive frame because you'll know approximately what dimensions fit you best.

TJ

Last edited by tjsager; 05-09-06 at 09:22 PM.
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Old 05-09-06, 10:12 PM   #4
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I sort of agree, ideally you would choose a crank length to fit your femur. However, I think with a track bike that doesn't really apply unless you only do pursuits/TTs or you only ride on shallow tracks clearance issues trump efficiency issues when choosing a crank length.
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Old 05-10-06, 01:05 AM   #5
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You may notice some difference at first, but will probably get used to it pretty quickly. I ride 165's on the track (also ADT) and 172.5 on the road, and until recently never even noticed much change going from one to the other (or even to 175 on my mtb), even if I ride both (or all three) bikes in one day. Lately I think I've been putting in more hard miles at the track and the road cranks are feeling long, but I get used to them pretty quickly on longer rides.

I think a fair number of people ride 170 at ADT, and usually the speeds are high enough that it's not an issue, but I wouldn't go any longer for mass start racing there. If you're going to do sprints and stuff where there's a lot of slow bits (sometimes even the 4/5 races) you might bang a pedal on the wood. I've even hit a pedal with 165s at Blaine (similar banking) without sliding down, but ADT is more slippery (the wood's less grainy). I haven't hit a pedal yet at ADT and have ridden there once a week or more (with some exceptions) since a few months after it opened.
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Old 05-10-06, 03:07 AM   #6
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Track racing is all about leg speed. The main reason you want a shorter crank (regardless of leg length) is that it gives you a slight advantage. With a shorter crank, for the same crank rpm, although your feet are travelling at the same angular velocity as a longer crank, they are actually travelling at a slower linear velocity, and they are not travelling as far. (The closer you are to the center of the circle, the slower the linear velocity for a given angular velocity.) If you increase the linear velocity of your pedals, you will be cranking at a higher angular velocity; ie, more rpms, thus the bike goes faster. In other words, you can crank higher rpms with a shorter crank, a definite advantage if you've only got one gear to work with.

The fact that you can ride slower on a steep track without hitting the pedal is just gravy, and isn't really a concern for most North American riders unless they live near Burnaby, Portland, LA, Blaine, etc. or they like to travel.

One of the tallest 6-day pros was Peter Post. He won the second highest number of 6-days in his career (second only to Patrick Sercu). He's a big guy, around 6'4", as I recall, and he used a long crank by pro 6-day standards: 167.5. Unless you're riding pursuits, I figure 165 will do for most riders. I'm 6'1" (186 cm) and I use 165s.

- L.
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