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Help re. Crank Arm Length
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by Clint_Simmons on December 11, 2002
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Hi Everyone. I am 6'4", long legs, and have been riding 175mm crank arms. During short course races, I push a pretty big gear. I am considering buying 177.5mm arms on my new Tri bike....here is my concern:
Will having 177.5mm arms on my tri bike and 175mm arms on my road racing bike be problematic in any way? Will the two different crank arms lengths troublesome when I switch back and fourth?
If not, should I consider buying 180mm cranks for my tri bike? (While still using 175mm cranks on my road bike?)
Thanks guys.
C
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RE: Help re. Crank Arm Length
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by DRDUATHLON on December 11, 2002
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There are many schools of thought about this. Some say have the same length on every bike, including mountain bikes. I've used longer cranks on TT bikes before and found it to be fine. You're pretty tall, I'd consider 180s. I'm 6' tall and TTed with 177 for years.
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RE: Help re. Crank Arm Length
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by 3Athlete on December 11, 2002
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The thing to remember with crankarm length is that it takes more force to push a longer lever. Some of this is accomplished by your naturally longer legs so 180's should go well for your 6'4" frame. Some people TT with longer arms and train with slightly shorter arms to save on the wear and tear on the body. I'm 5'11" and ride 175's but I may switch back to 172.5's to adapt to my higher cadence spin.
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RE: Help re. Crank Arm Length
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by ent_geek on December 11, 2002
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good topic. i have wondered about this myself. i am not sure that is right 3athlete, about taking more force to push a longer lever. is that right? at the risk of sounding like i know what i am talking about:
i was thinking that given a constant speed on the bike, cadence and wattage are constant while torque (on your legs) decreases and the speed that your legs travel increases (hence more muscle soreness from longer cranks). for your legs to travel the same vertical distance in a half pedal stroke (180 * 2 vs. 175 * 2) they will have to move faster for the 180's. so practically speaking, a longer crank => lower cadence unless you change leg speed.
sheldonbrown.net has something called "gain" which gets into all of this but, i am somewhoat lost.
anecdotally:
at 6'1" i notice the difference between 172.5 and 175 but feel comfortable 10 minutes after switching. i think i apply more force (or is it torque?) throughout the pedal stroke with shorter cranks and get a better down-push with longer cranks. and i definitely get more sore if i ride 175's after riding 172.5's for months.
does anyone know the reason why people generally use longer cranks for TT events? maybe it goes with the forward seat position???
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RE: Help re. Crank Arm Length
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by MIKEPLUMB on December 12, 2002
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For what it is worth, at 5'9" and a 34" inseam, I use 175's on my tri bike, and 172.5's on my road bike. I do a majority of my riding on my road bike, and to be honest, I can't tell the difference between the two when I switch back and forth. I have ridden everything from 165's to 177.5's. I raced a whole year on 177.5's and I could see the difference with those, I was a bit slower so I went back down to the 175's.
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RE: Help re. Crank Arm Length
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by welshwizard on December 12, 2002
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I am lucky enough to work with one of the top pro teams in the world ;ONCE - Eroski and know the riders well and Manolo Saiz and I have many interesting chats on this subject.All the riders increase their crank length when tt. in the team Beloki (who is 5'7")uses 172.5 normally but 177.5mm when he tt's!
We made a special crank of 190mm (yes 190mm!!)for Igor at Zolder, he was fine with it,tho' I doubt he could run 1km in 15mins afterwards!!ONCE advocates longer cranks for tt and most riders improve their tt when they are at ONCE (ofcourse better aerodynamics due to special geometry on the frame helps too )I am also 6'4" and since 3 years train on 177.5 and race on 180mm and I go well.
However,you need the right kind of style to 'push' a longer crank and also you need to run again.Stating the obvious,no good improving your ride by 2 mins with long cranks and then walking the first km of the 2nd run etc etc.
However,in your case I would defintely try it this winter for a month or so then do a fast 10 mile with 180mm and see, if you can keep a 80 rpm for 1 hour you'll improve.
Hope this helps...
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RE: Help re. Crank Arm Length
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by MSC on December 12, 2002
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Hi,
Just read the article on cyclingnews.com about the TCR Composite Gold. Nice story...You wouldn't happen to have an extra one...just collecting dust, maybe that nobody would miss ;>)
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RE: Help re. Crank Arm Length
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by welshwizard on December 13, 2002
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TCR Gold waiting list is long, coming out out with something even cooler next TdF.not as scarce.
Sorry all TCR Golds sold I'm left with some Nokon gold cables as a momento...
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RE: Help re. Crank Arm Length
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by Cycliator on January 7, 2010
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Hello everybody. Excuse my ignorance, but I was completely convinced that having longer crank arms would make it easier for me to push my bike on a flat or up a hill compare with shorter cranks. I currently use 180mm and that feels easier than pushing the 170mm my KHS came with, with less of an effort to get to 28-30 mph on flat road.
I am going for 190mm in a few days. I am 6ft tall, 200 lbs. Any recommendations? Comments?
I know I have to adjust my seat. Have a sufficiently long seat post. BB height should be OK.
And I also know the pressure and flex in leg joints will be different, but I guess I can tolerate and take some experimentation alright.
Thanks.
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RE: Help re. Crank Arm Length
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by Cycliator on January 7, 2010
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Hello. I am just thinking of leverage, and in that line of thought, having longer cranks lets you control the last/ heaviest gear in your bike, allowing you to increase your speed with the same effort you would be doing on a shorter crank. I hope this makes sense; but if you are a 200 lbs rider pushing on a 180mm,this will get you going faster than a 200 lbs rider pushing on a 170mm [considering all other factors the same: bike weight, road conditions, etc]. If I am wrong I wish somebody could explain it to me.
Now because of the geometry of a human body, there are ranges to accomodate but there are also limits in how far you can stretch to get some juice of a particular set of cranks. Hope this picks someone's brain and keep the conversation going. Thanks.
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