srm crank length

Discuss light weight issues concerning road bikes & parts.
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simoncx
Posts: 100
Joined: Sun Nov 15, 2009 12:27 am

by simoncx

I was wondering if anyone changed crank lengths on the newer srms and did you have to recalibrate? I have a sram 177.5 srm and I'd like to change it to 175 since I stopped doing tt's and put it on my road bike. I know the cranks are the same 3 bolt spider mount like the 900, cx1 or force22 which I have a extra set so that isn't a problem. I tried emailing srm but never got a reply hopefully someone can help?

by Weenie


sungod
Posts: 1638
Joined: Fri Dec 24, 2010 9:37 pm
Location: it's raining, it must be uk

by sungod

changing the crank arm on the spider does require recalibration

if you have an accurately known weight you can diy calibrate, i've done this, it's easy enough

or if you have a stable but unknown weight you could 'measure' it on the 177.5mm crank, then swap cranks and use the measurement to recalibrate with the 175mm crank

fwiw when i needed new cranks fitted (the sram three bolt fitting) i sent mine in as i was busy, it was only a week for crank swap, new battery, and recal (this was in the uk, done by scientific coaching who are srm authorised)

topflightpro
Posts: 828
Joined: Tue Jan 13, 2009 2:35 am

by topflightpro

When I contacted SRM recently about crank length on track SRMs, I was told that they no longer need to be recalibrated when changing arms. I just had to make sure that the arms were torqued to spec to the spider.

I also did not have to recalibrate my SRM when I swapped arms on my Hollowgrams.

Lastly, if you can't get an email response from SRM, give them a call. US customer service is pretty good.

simoncx
Posts: 100
Joined: Sun Nov 15, 2009 12:27 am

by simoncx

I was hoping it would be ok if I torqued it to spec and the cranks are the same model. I did the same on my quarq for the cross bike and it was the same after I changed arms, I just had to make sure I used the Loctite and torque they specified.

sungod
Posts: 1638
Joined: Fri Dec 24, 2010 9:37 pm
Location: it's raining, it must be uk

by sungod

for mine srm said it needed recal, on return the slope was different, but whether that was due to the crank arm change or simply drift since previous calibration i've no idea!

for diy calibration you can use a spreadsheet or an online calculator such as https://www.cyclingpowerlab.com/PowerMe ... ation.aspx

topflightpro
Posts: 828
Joined: Tue Jan 13, 2009 2:35 am

by topflightpro

Sungod, IIRC, it used to be that you had to send them back in for recalibration after changing arms, but my understanding is that some of the newer versions do not need it.

sungod
Posts: 1638
Joined: Fri Dec 24, 2010 9:37 pm
Location: it's raining, it must be uk

by sungod

yes that could be it

mine is c. 2010 vintage

simoncx
Posts: 100
Joined: Sun Nov 15, 2009 12:27 am

by simoncx

I think mine is 2014 but I will try to give them a call and see what they say.

by Weenie


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