190mm cranks??
 

According to this website I need 192mm cranks(35 inch inseam), which sounds absurd.... http://www.nettally.com/palmk/crankset.html

Anybody have any other guidelines for cranklength... I think I ride 172.5s now...

I've become a bit obsessed with crank length in recent months, but my lack of formal training in biomechanics and physiology is preventing me from fully understanding the WHOLE issue.

Before you go changing your cranks, read this article, which, although kinda dated, is a bit more balanced than some of websites which advocate proportional crank length

http://www.bsn.com/Cycling/cranks.html

then, if you have time, read this one

http://www.cranklength.info/

Lennard Zinn knows bazillions more that I will ever know about cycling, but he is a very tall guy who, in my crappy opinion, has generalized from his own positive experiences with long cranks, and REALLY wants to prove that long cranks are good for everyone.

http://www.zinncycles.com/cranks.aspx

You would destroy your knees in no time trying to pedal this thing unless you could adopt the same riding position the short legged people use that this formula is based on.

When are guys gonna figure this out?

Yeah, go put on 192mm cranks. I'll go get some 205mm ones and we seen how long our knees last with the closed hip angles created by our set-back frames.

According to this reference, http://www.cranklength.info/crankCalc.htm 182.5 would be right for you. 180 is pretty close and you can pick these up factory made.


Edit, Now of course if you like to spin you should take 5 mm of the suggestion giving you 175 mm.
Regards, AnthonyG

I have an 89.5cm inseam, I'm 6ft tall, I've recently bought some 180s, and it seems to me that 180mm is about as long as we'd wanna go on a normal bike frame before problems such as heels hitting the chain stays, toes hitting the front tyre, and pedals hitting the ground start happening (I can hit the chain stays with my heels if I try).

My latest query is this: assuming you're in the correct position on the bike at the moment, a 5mm increase in crank length requires a 5mm drop in saddle height to compensate for the extra stretch at the bottom of the pedal stroke, so, does the drop in seat height offset the leverage advantage provided by the longer cranks?

Zinn seems to have the same formula.. The reason I want longer cranks is because I feel that I have very less leverage going uphill and I have to move way forward in the saddle to get some decent momentum.. In mybike I have a no setback post with some room on either side of the rails in the seat... It is pretty high too...My knee angle is not the straightest in the dwonstroke and my thighs are still kinda open on the up stroke... I have long shins.. quite presumably I should be able to fit myself in the regular parameters with a longer crank albeit not 190mm and be able to get more power??.. I will ask terry, he has the same body type as me..

http://www.bikeforums.net/showthread.php?t=115879

That's true 531, but all dropping your seat is going to accomplish is to make your hip angle a lot smaller as well as increase your knee bend at the top of the pedal stroke. Both these things hurt power, why would you want to do this?

If you went from 172.5 to 180mm (180mm is the longest "normal" crank that's readily availble from Shimano and Campgnolo), and you drop your saddle 7.5mm (which you might not necessarily have to do, but I did), you knees will be coming up 15mm higher at the top of the pedal stroke, obviously increasing knee flexion. If you pedal efficiently, pushing down right from the 12 o'clock position, that puts more stress on the knee.

I like to be high on the bike, and I was pretty much as high as I could go on my 175s, so, even though I slid my saddle forward a bit (it was already kinda on the forward side), I had to drop my saddle about 5mm when I got the 180s, otherwize I was stretching down too far and hurting my hamstrings (I was stewing over this through my whole ride tonight :p).

If you have long shins then you need to make alowances for this in the formula's. What's realy important is your thigh length but since this is so hard to measure the formula's are based on your inside leg measurement and they are assuming normal leg proportions. Long shins means you realy need a shorter crank than the formula suggests.

Regards, AnthonyG

Yeah unless you can go even more forward basically you will have to drop your saddle then. Going forward is kind of like dropping your saddle because it decreases reach to the pedals which you need since bottom pedal is now lower.

Being off the saddle changes EVERYTHING (!!!), so position goes out the window, and I have no doubt that pedalling off the saddle up a hill with longer cranks gives me the pure leverage advantage of the longer crank arm.

Being seated is another story.

As I said, if you have to drop your saddle for the longer cranks, in my opinion, power is lost, so, this may affset the advantages of the long cranks.

The big probablem is, of course, that experimenting with different lengths can be very expensive.


Man, I'm obsessed with this topic -- I think about it heaps when I ride.

Thanks Anthony, Aussie, 53-11...Interesting reads.. so I might actually pretty close to my ideal crank length now anyways... I will ask my LBS today after work and see what they have to say...

That's true also.

What it all boils down to is keeping your knee and hip joints open enough so you aren't hurting power. If you can't do that might as well be using a shorter crank.

I was talking about being in the saddle.. I find that I have to slide my weight a bit forward(use more hammie?), contrary to popular technique to be able to go up hills..

Seriously skinnyone,

The proper crank length in my opinion is not only a function of how long your legs are but also what frame geometry you ride.

Aside from the usual clearance problems (toe overlap, BB height, chainstay clearance) you need to think about how your frame positions the seat. The final seat position is critical as it affects hip and knee bending angles.

Seat set-back results in a low saddle. Low saddle plus long crank results in a very narrow hip angle which is bad for pedaling efficicency/power.

Thanks 53... I should add that this was something I never planned to do it on my own.. I will visit my LBS one of these days and use their mirror setup/guidance to do changes, if any. If you remember, I got a second fit a month back. The guy who fit me a month back is really good at his job and he also mentioned that I should get back to him in a little bit o time to reasses how the fit is working.. ...

I have been thinking about seat position... Maybe the offset from my hip to the knee(with the cranks horizontal) is a bit too much its and hence I actually need to compensate by sliding forward a little bit.. I will try to get a few pics of my riding around and see if I can infer anything..
-AJ

Aside from the usual clearance problems (toe overlap, BB height, chainstay clearance) you need to think about how your frame positions the seat. The final seat position is critical as it affects hip and knee bending angles.

These days, seat-tube angle does not critically affect saddle position. The layback of the saddle clamp can be varied by choice of seatpost. You can replicate the effect of a steeper seat-tube by simply using an inline post (that's what I do).

Set your saddle position relative to the pedals at the 3:00 and 6:00 position. If you switch cranks and the 6:00 goes down by 1cm, then so should your saddle. If the 3:00 goes forward by 1cm, so should your saddle. In this case, your top and rear pedal positon will alter by 2cm. If your legs can handle that you will be OK.
If you want to see the effects of using a crank that is too long, observe any child riding a modern bike. With the saddle set correctly (as above), the high and rear positions are beyond the capacity of the leg length and the rider just cannot pedal effectively, esp uphill. At the top position, the knee is ~ 5cm above the hip joint. You could put that same crank onto your bike and it would probably fit you well enough to use.

Lemme sound off here…

Standard frames will have issues with cranks over 180 MM, mostly notably with the BB being to low and pedals hitting the ground. Especially since more and more frames are made with very little geometry changes through the size range to save costs.

However, to address the validity of proportional crank lengths, I think this theory has a lot of merit.

Miguel Indurain used 190’s for his hour record attempt. He maintained a cadence of 100 RPM. I suspect (but have never confirmed) that he also used them on the road.

The fact is that the human body will adapt to a wide range of bio-mechanical possibilities. And, the use of proportional crankarms is not just for increased ‘leverage’ but for better and more efficiently utilization of the rider’s musculature throughout the entire pedaling motion.

I don’t think long cranks are a magic bullet for tall folks, but would bet that over the long term, a tall rider would reap an improvement in efficiency and sustainable power by using proportional cranks.

You are partly right, I use a stright clamp on steel Bianchi because it has a slack seat tube angle. On my c-dale I get away with a set-back seatpost becasue the seat tube angle is steeper.

Only problem with straight clamp seatposts is that they effectively don't add top tube length where as a 1.5cm set-back post adds 1.5 cm top tube to the frame. (this affects stem length)

I only brought up seat tube angles to make a point about how fore/aft lets shorter riders use "long" cranks. The steep seat tube angles on small frames (76 degrees) in some cases effectively gives them much more forward seat position relative to taller riders. The forward rotation caused by the steep seat tube angle is offset by the incredibly long top tubes you will also find on these smaller frames.

I ordered some 210 cranks for my bike from zinn. I feel good about it.
on my undersized bike right now I rarely get a burn in my quads b/c my leg never extends totally. it is like a permanent hamstring curl.
When I walk my stride is way longer. when I pedal why should it be different?
You might never know what it is like to use things that are built for people who are the same size you were in 7th grade.