Chainset recommendations?

colm_gti

Just home from a bike fitting, during which I was recommended to shorten my cranks from 175mm to 172.5mm, and instead of replacing like with like, I was wondering if there are any in my price range that might be better?

I currently have a shimano 105 compact chainset, which can be bought for ~€150, would like to get something about that price.

Morrisseeee

Looks like they really convinced you that you needed that change ? what did they say ? and did they make any other recommendations ?

colm_gti

Morrisseeee wrote: »

Looks like they really convinced you that you needed that change ? what did they say ? and did they make any other recommendations ?

He moved the saddle forward, inverted the stem and dropped it a few mm by removing 2 spacers, said that my positioning was good but could be improved by shortening my cranks, moving my seat a little further forward and dropping the bars even more.

dermur

I would have thought the main difference between different crank lengths would be on the amount of flex in the knees and not much else.

http://sheldonbrown.com/cranks.html

Beasty

For some people 2.5mm seems to make a difference. I ride 175mm on the road and 165mm on the track, and tbh don't notice the difference. It's a bit of an expense to go to for the sake of 2.5mm, and I would ask if there are any specific issues that the persson doing the fitting mentioned as requiring such an adjustment?

Morrisseeee

Beasty wrote: »

It's a bit of an expense to go to for the sake of 2.5mm, and I would ask if there are any specific issues that the persson doing the fitting mentioned as requiring such an adjustment?

Yeah, that's what I was thinking.

Holyboy

Utter nonsense!!

colm_gti

He said:

The main problem was the drop and reach were not balanced to allow a high seat position and a lower race position. The high seat left you too much of a reach while the low aero position was too bunched. The cranks were also a little too long which exacerbated the bunched aero position.

...and suggested going for 172.5 or even 170mm cranks, I was trusting his recommendation as he is the one that does this thing on a daily/weekly basis...

pprendeville

Who fitted you? Unless your racing at a high level I don't think it's worth the upgrade. Changing your pedals might be cheaper as I'm sure heights vary slightly.

Idleater

pprendeville wrote: »

Who fitted you? Unless your racing at a high level I don't think it's worth the upgrade. Changing your pedals might be cheaper as I'm sure heights vary slightly.

Agreed, as I said in the other thread even shoes could make a difference.
Though, as someone who has been through the bikefit process albeit before buying the bike, I _have_ noticed the difference between 175 and 172.5. To be fair, it's 2.5mm less knee bend at the top and 2.5mm less stretch at the bottom. That's something that pedals or shoes won't overcome.

mp31

Idleater wrote: »

Agreed, as I said in the other thread even shoes could make a difference.
Though, as someone who has been through the bikefit process albeit before buying the bike, I _have_ noticed the difference between 175 and 172.5. To be fair, it's 2.5mm less knee bend at the top and 2.5mm less stretch at the bottom. That's something that pedals or shoes won't overcome.

I'm interested by the fact that you noticed a 2.5mm difference in crank length. Can you tell me what was the improvement - more speed/smoother pedal stroke/less pain (if there was any in the first place)?

Idleater

mp31 wrote: »

I'm interested by the fact that you noticed a 2.5mm difference in crank length. Can you tell me what was the improvement - more speed/smoother pedal stroke/less pain (if there was any in the first place)?

For me it was just removing the final stretch at the bottom and bend at the top that I mentioned. I have minimal flexibility and it was immediately apparent in my knees that it was the pedal rotation. I was basically set up exactly correct saddle height, so there was no change there, and I have the same saddle to pedal distance corrected for shoes on my two road bikes.

gman2k

If you were looking for 170mm, Tiagra compact on Rosebikes £46 +PP
http://www.rosebikes.co.uk/article/shimano-tiagra-crankset-fc-4650/aid:519976

mp31

colm_gti wrote: »

Just home from a bike fitting, during which I was recommended to shorten my cranks from 175mm to 172.5mm, and instead of replacing like with like, I was wondering if there are any in my price range that might be better?

I currently have a shimano 105 compact chainset, which can be bought for ~€150, would like to get something about that price.

colm_gti wrote: »

He moved the saddle forward, inverted the stem and dropped it a few mm by removing 2 spacers, said that my positioning was good but could be improved by shortening my cranks, moving my seat a little further forward and dropping the bars even more.

Did he say what would be the benefits of a shorter crank?

colm_gti

mp31 wrote: »

colm_gti wrote: »

Just home from a bike fitting, during which I was recommended to shorten my cranks from 175mm to 172.5mm, and instead of replacing like with like, I was wondering if there are any in my price range that might be better?

I currently have a shimano 105 compact chainset, which can be bought for ~€150, would like to get something about that price.

colm_gti wrote: »

He moved the saddle forward, inverted the stem and dropped it a few mm by removing 2 spacers, said that my positioning was good but could be improved by shortening my cranks, moving my seat a little further forward and dropping the bars even more.

Did he say what would be the benefits of a shorter crank?

He said it would allow me to move the saddle forward a bit more, and drop the handle bars more as my knees wouldn't be flexing so much...

Lumen

colm_gti wrote: »

He said it would allow me to move the saddle forward a bit more, and drop the handle bars more as my knees wouldn't be flexing so much...

Think about it from the bottom up...

For a given saddle height (relative to the bottom of your stroke, i.e. the distance to the "down" pedal at BDC), a 2.5mm increase in crank length moves your "up" pedal up by 5mm at TDC.

Assuming your ankling doesn't change, that will push your "up" knee closer to your chest by 5mm.

If you wanted to correct this (in order to keep a certain open-ness of hip, which is good for power production), you would need to raise your chest by 5mm. You can't raise your hips because that would require an increase in saddle height, so you have to make an even greater adjustment at the handlebars, because your bars are about twice as far away from your saddle as your chest.

Therefore, a 2.5mm increase in crank length becomes a 10mm increase in handlebar height. Which is still fairly small but significant.

However...

If hip angle is so critical, then

(a) why do pros ride along with their knees practically banging off their chest. What aspects of flexibility and training are important here?

(b) why not just move your saddle position forward and up to effectively rotate yourself over the bottom bracket?

I went for solution (b) in the last couple of years in an attempt to find a more aero but powerful position, and it's worked a treat. My arms take more load, and the neck has to adjust, but over time that's not a problem. Consequence: more power, more aero efficiency, but I've still needed to work on conditioning to be comfortable in the position.

With respect to (a), it is always the case with bike fit that there is a balance to be struck between fitting the bike to yourself and fitting yourself to the bike.

The innate problem with a paid-for bike fitting service is that "customers" expect all the work to be done for them and don't like being told that they need to work on their core and flexibility (myself included, I've been there). So best case is that you'll end up with a comfortable but slow position and not instead focus on the hard work you may need to do to become a stronger, faster, more efficient cycling machine.

colm_gti

Good post lumen, he did give me some core exercises too though, and traced my knee pain back to a weaker left glute that as it gets tired causes my knee to buckle inwards putting strain on the tendon. Gave me glute strengthening exercises too.