On my old QR private reserve - 650 wheels - I have 170 crank length. been dealing with some lower back issues - I have a 30" inseam and a friend told me I should have a 165 crank - said I would feel more comfortable - any input
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Re: crank length [superempi]
[ In reply to ]
I don't think it's that cut and dried. I think any correlation between inseam and preferred crank length is dubious. However, I switched from 172.5mm cranks to 160mm cranks on my tri bike last year and I'm very happy with the change.
I think the main thing to consider is whether your hip feels pinched or your knees strained at the top of the stroke, or your pelvis feels inclined to tilt back, or your knee is hitting your stomach. The vast majority of people on ST who try shorter cranks seem to report back that they prefer them. Changes of 2.5 or 5mm aren't dramatic and in my experience are only slightly perceptible providing you adjust your seat to suit. Larger changes may well be warranted. Without having had a chance to try out shorter cranks before buying, I was torn between 165mm and 160mm when I changed. While I was, and still am, happy with 172.5mm cranks on my road bike, and was performing well with the same length on the tri bike, I had a niggling suspicion my knees would be happier with a reduced range of motion, and that I would be more comfortable in the aero position. I had on previous bikes used 170mm and 175mm for road cycling and 170mm for tri, and had never noticed a significant difference.
I nervously decided to go all the way to 160mm (a 25mm reduction in the pedal stroke diameter) and after the first ride I though maybe I'd gone too far. I forgot all about the crank change during my second ride and only realised after I'd finished that it had gone completely unnoticed for most of the ride, but my knees felt fresher than usual!
I don't think there's much, if any, downside to a smaller crank. I think it makes sense to err on the small side of average. Too large seems to be much worse than too small, and yet most bikes seem to err on the high side (at least by ST standards).
I think the main thing to consider is whether your hip feels pinched or your knees strained at the top of the stroke, or your pelvis feels inclined to tilt back, or your knee is hitting your stomach. The vast majority of people on ST who try shorter cranks seem to report back that they prefer them. Changes of 2.5 or 5mm aren't dramatic and in my experience are only slightly perceptible providing you adjust your seat to suit. Larger changes may well be warranted. Without having had a chance to try out shorter cranks before buying, I was torn between 165mm and 160mm when I changed. While I was, and still am, happy with 172.5mm cranks on my road bike, and was performing well with the same length on the tri bike, I had a niggling suspicion my knees would be happier with a reduced range of motion, and that I would be more comfortable in the aero position. I had on previous bikes used 170mm and 175mm for road cycling and 170mm for tri, and had never noticed a significant difference.
I nervously decided to go all the way to 160mm (a 25mm reduction in the pedal stroke diameter) and after the first ride I though maybe I'd gone too far. I forgot all about the crank change during my second ride and only realised after I'd finished that it had gone completely unnoticed for most of the ride, but my knees felt fresher than usual!
I don't think there's much, if any, downside to a smaller crank. I think it makes sense to err on the small side of average. Too large seems to be much worse than too small, and yet most bikes seem to err on the high side (at least by ST standards).
Re: crank length [Ai_1]
[ In reply to ]
Ai-1, what is your inseam/height if you don’t mind me asking?
Re: crank length [Spurn]
[ In reply to ]
Spurn wrote:
Ai-1, what is your inseam/height if you don’t mind me asking?
Re: crank length [Ai_1]
[ In reply to ]
Totally understand. Interesting, me and you are basically the same measurements. Have you ever had any knee troubles in the past?
Re: crank length [Spurn]
[ In reply to ]
Yep. I have occasional pain in my right knee. This has definitely improved following the change in crank length.
Re: crank length [Ai_1]
[ In reply to ]
Ai_1 wrote:
I don't think it's that cut and dried. I think any correlation between inseam and preferred crank length is dubious. However, I switched from 172.5mm cranks to 160mm cranks on my tri bike last year and I'm very happy with the change.I think it would be a lot more cut and dried, if there were a easy to find source of cranks in a range of lengths like shoes and bike frames. Saying that there no preferential relationship when the only thing widely available is 172.5 - 175 mm is a bit dubious. Its simple trigonometry to determine what the middle ground should be for a particular inseam length.
Most of the time if you buy a bike at a shop, you won't even get asked THAT question. You get what's on the bike, and few people even know there's something else to choose from. Even those of us who DO know, have to work a little bit too hard to find a shorter crank. I have square taper BMX cranks on my TT bike in order to get down to 150mm (with a 810mm inseam). Interestingly you and I have settled on crank length to inseam ratios that are within 2.5% of each other (18.5% to 19%). Coincidence?
Just because the ROAD bike industry doesn't want to stock cranks from 150mm - 180mm, and has refused to do so for the last 30 years that I KNOW OF...doesn't mean that it wouldn't be better for the rider. One of the first (road) bike fit articles I ever read in Bicycling Magazine way back in the day talked about ideal crank length selection...but, concluded that it doesn't really matter because the smallest thing anyone made was 172.5mm..and even those were hard to find. Very litle has actually changed.
What a seasoned rider prefers is largely a function of what the seasoned rider has been riding already. There's always a high resistance to change...you are a perfect example. Heck, so am I. I was nervous, too---I think we discussed it last September. After my first week of riding, I was ready to switch back. But, I stuck with it, and got a complete professional fit (mostly we got the seat height were it should be for the shorter cranks)....and, all my worries went away.
Tom_hampton wrote:
Ai_1 wrote:
I don't think it's that cut and dried. I think any correlation between inseam and preferred crank length is dubious. However, I switched from 172.5mm cranks to 160mm cranks on my tri bike last year and I'm very happy with the change.I think it would be a lot more cut and dried, if there were a easy to find source of cranks in a range of lengths like shoes and bike frames. Saying that there no preferential relationship when the only thing widely available is 172.5 - 175 mm is a bit dubious. Its simple trigonometry to determine what the middle ground should be for a particular inseam length.
Most of the time if you buy a bike at a shop, you won't even get asked THAT question. You get what's on the bike, and few people even know there's something else to choose from. Even those of us who DO know, have to work a little bit too hard to find a shorter crank. I have square taper BMX cranks on my TT bike in order to get down to 150mm (with a 810mm inseam). Interestingly you and I have settled on crank length to inseam ratios that are within 2.5% of each other (18.5% to 19%). Coincidence?
Just because the ROAD bike industry doesn't want to stock cranks from 150mm - 180mm, and has refused to do so for the last 30 years that I KNOW OF...doesn't mean that it wouldn't be better for the rider. One of the first (road) bike fit articles I ever read in Bicycling Magazine way back in the day talked about ideal crank length selection...but, concluded that it doesn't really matter because the smallest thing anyone made was 172.5mm..and even those were hard to find. Very litle has actually changed.
What a seasoned rider prefers is largely a function of what the seasoned rider has been riding already. There's always a high resistance to change...you are a perfect example. Heck, so am I. I was nervous, too---I think we discussed it last September. After my first week of riding, I was ready to switch back. But, I stuck with it, and got a complete professional fit (mostly we got the seat height were it should be for the shorter cranks)....and, all my worries went away.
When I say "any correlation between inseam and preferred crank length is dubious", I should explain that I believe that's mostly due to a lack of data rather than because there is no link. To determine a solid correlation would require a substantial set of data from an unbiased blind tested population, or at least something heading that direction. I don't think it exists for many reasons, including those you've outlined.
As for whether our similar inseam to crank length ratios are coincidence, I'd say it's most likely the result of working off similar info to make our choices, rather than that we've both done rigorous optimisation our fits and ended up with similar results. I can't claim 160mm is the best choice for me. I haven't tried anything smaller or anything within 10mm larger either. I picked a number and I'm confident it's better than the 170-175mm range I'd used before, but I that's all I can legitimately say. I haven't switched back again since and I've tried no other options in that riding position.
To be able to speak with any authority, and even then only for my own preferences, I think I'd have to have performed back to back testing using different crank lengths from those I found uncomfortably small up to those I found uncomfortably long. Doing this sort of testing, blindly and multiple times, including taking relative seat position into account, would perhaps provide useful data. I don't know if this has ever been done. I certainly haven't done it.