Changing from 172.5mm to 175mm crankset...

RICHARDIIII

I've just bought a new bike, I was advised to get a 175mm crank set, but my old one was 172.5mm. I didnt think it would have made such a difference. It does feel better, but once I get up to 20-22mph, my legs just give up after about 3 mins. Has anyone else felt like this after changing crank lengths? How long did it take for your legs to adjust?

liversedge

I went in the other direction. I always thought that at 6'1 175mm was right for me and I should even think about 177.5. But went to 172.5 after a fitting - it gives me more space to extend and my sustainable power went up almost immediately, I will never go back to 175.

Are you sure 175 is right for you?

RICHARDIIII

... Its a bit late now as just bought a Super Record crank! It was advised at a bike fitting, I'm 6'1 too, but have slightly longer legs than average. The 175 feels alot smoother, and feels much better when sprinting out of the saddle, it also feels like I can get more power out of the bigger stroke, it's just mainingin the power! I've only been on 1 ride of 25 miles so far, so hopefully after a few hundred miles it will be ok.

liversedge

this might help to check ....

i'm 85 inseam with a freakishly even 58/58 1.0 ratio.

Alex_Simmons/RST

If your position has changed (it's a new bike), it might be that you need to adjust a few things, as the new position may not suit you or you need to adapt to it.

I'd be very surprised if 2.5mm would make any difference to power production. I ride 165, 170 and 175mm cranks on my bikes and it makes no difference to my ability to generate power. But my saddle height is appropriate for each crank length.

liversedge

Alex_Simmons/RST wrote:

If your position has changed (it's a new bike), it might be that you need to adjust a few things, as the new position may not suit you or you need to adapt to it.

I'd be very surprised if 2.5mm would make any difference to power production. I ride 165, 170 and 175mm cranks on my bikes and it makes no difference to my ability to generate power. But my saddle height is appropriate for each crank length.

Begging the question - why do the manufacturers offer lots of different crank lengths if they make no difference ?

freehub

I changed from 175 to 170, I thought I best do as at the same time as getting this bike with a 175mm cranks on my knees had BIG problems.

chrisw12

liversedge wrote:

Alex_Simmons/RST wrote:

If your position has changed (it's a new bike), it might be that you need to adjust a few things, as the new position may not suit you or you need to adapt to it.

I'd be very surprised if 2.5mm would make any difference to power production. I ride 165, 170 and 175mm cranks on my bikes and it makes no difference to my ability to generate power. But my saddle height is appropriate for each crank length.

Begging the question - why do the manufacturers offer lots of different crank lengths if they make no difference ?

Great question, marketing bull shit perhaps?

Alex_Simmons/RST

liversedge wrote:

Alex_Simmons/RST wrote:

If your position has changed (it's a new bike), it might be that you need to adjust a few things, as the new position may not suit you or you need to adapt to it.

I'd be very surprised if 2.5mm would make any difference to power production. I ride 165, 170 and 175mm cranks on my bikes and it makes no difference to my ability to generate power. But my saddle height is appropriate for each crank length.

Begging the question - why do the manufacturers offer lots of different crank lengths if they make no difference ?

While our ability to generate power doesn't vary much (at least with the commonly available range of cranks lengths) we all have different preferences and hence many of us prefer a particular length crank - it feels right (or we became accustomed to whatever we started with). Bit like cadence - we tend to have our our preferred range.

there are other considerations, like the type of bike and riding we do (e.g. common on a fixed gear to go for shorter cranks), range of hip-torso flexibility, knee flexion issues, aerodynamic considerations (a change is saddle height is required when changing crank length), front wheel-toe overlap, riding on tight circuits where pedal clearance might be an issue or on the track etc etc

funckchicken

i had a similar situation to you just last year.

i always used 172.5 cranks. i got a good deal on a new groupset but it came with 175 cranks. no big deal i figured. 2.5mm could hardly make any real difference and i was reassured by comments that the body is so adaptable that it would eventually get used to the new length after a breaking in period.

anyways, long story short i got pains in both of my knees when using the longer cranks. tried everying i could to alter the bike position and experiment, extra stretching etc. did about 800 miles. but still the pain remained.

ended up just biting the bullet, flogging them and buying a new chainset with 172.5. hey presto, knee pain gone.

owenlars

I bet you don't notice any difference.

RICHARDIIII

GOOD NEWS!...last night, after only 3 rides, I'm getting used to the 175's, I could tell straight away that my pedle action was alot smoother, and after just 3 rides, I'm riding as fast, and feel strongly that after another few tempo rides, i'll be faster with them! I'll have to get some 175's for my old bike now to train on - anyone got any for sale?