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Help with crankset

by troyc
Fri, May 08, 2015 17:48
9

After having a pro bike fit last week i was advised to change my cranks from the 172.5 to 170 - from further research i think this is worth doing, especially as i do alot of training on the wattbike with 170 cranks and i find it alot easier to get a higher cadence on it than i do on my road bike.
My existing crankset is not regarded as one of the best - a FSA Gossamer Compact 50/34t PF30. My three questions i need help with are: 1) is it worth getting a better quality crankset if i am going to replace it anyway? 2) if i do get another FSA Gossamer Compact, i have seen a BB30 model and a BB386 - will either of these fit? 3) are special tools needed for the job, or just a torque wrench?
Many thanks for any advice/help

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9 comments

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Colin Peyresourde | 9 years ago
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Listen guys, he had the bike fit. He's had advice and is acting on it. No need to second guess it.

I would go for Dura Ace because it is the bong as far as I'm concerned. But as others point out it the improvements from getting a better crank is not significant weight wise. The other thing is getting compatible components to the rest of your chain set. I wouldn't think that there is too many issues, but Dura Ace is a smooth setup

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2 Wheeled Idiot | 9 years ago
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Tbf I recently moved up to 172.5's from 170's and could tell the difference, my knee hurt like anything until I dropped the saddle by ~1.5mm....

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bechdan replied to 2 Wheeled Idiot | 9 years ago
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But that's different to getting any performance benefit from it, of course if the crank arms changes length its going to affect your knee hip angle and will need to be compensated for.

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fukawitribe replied to bechdan | 9 years ago
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bechdan wrote:

But that's different to getting any performance benefit from it, of course if the crank arms changes length its going to affect your knee hip angle and will need to be compensated for.

Comfort is performance, or rather discomfort is performance loss - and as far as the compensation is concerned, why don't you read the quote in the OPs recent reply.

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Simon E | 9 years ago
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Sounds like you've convinced yourself the Gossamer is not good enough for you. But what do you mean by "quality"? More expensive cranks are usually a tiny bit lighter but not necessarily stiffer or better.

I'd set a budget and ask your LBS to recommend and fit a compatible chainset (and bearings) within that budget.

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bechdan | 9 years ago
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Surely though, 2.5mm!? Not worth it imo, I did change mine from 170 to 165 when my chainset needed changing but I cant say I noticed all that much. I've spent a fair bit of time on my setup and geometry but 2.5mm is tiny.

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crikey | 9 years ago
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Your 'pro'* bikefitter should have taken you through the reasons he/she used to suggest the change in crank length, and given you enough information so that you could make your own mind up.

How much did you pay?

http://www.cervelo.com/en/engineering/ask-the-engineers/crank-length.html

*( I suspect that a pro bike fit is about 20% more expensive than a bike fit...)

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troyc replied to crikey | 9 years ago
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I paid £145 - with Bike Dynamics in Leamington Spa. Mike Veal is very well respected in the cycling community, and offers a holisitc approach to fitting. So along with using laser mapping with spinscan/dartfish, he also analyses flexibility/posture/foot anatomy etc http://bikedynamics.co.uk/options.htm
The whole session lasted 3 hours, and with the changes he made i have lost all pain/discomfort from my knees and my stroke is so much more efficient, it was worth every penny.
As regarding the crank length Mike has written extensively on this subject http://bikedynamics.co.uk/FitGuidecranks.htm and his comments on myself were "The 172.5mm cranks are a size too long for your leg lengths, with 170mm a better option. You are probably flexible enough to cope with the longer cranks, but given the history of knee discomfort and the fact that the knee minimum angles are still below my preferred 70degree threshold, 170mm are a sensible choice.The shorter cranks will help to make your quads more efficient in extending the knee joint. If changing to shorter cranks, I do not believe you need to make any other changes to the bike.

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CXR94Di2 | 9 years ago
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2.5mm in crank length, will you really notice? No special tools Allen keys will do

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