TT bike build - component questions

[TheGriffter]

Hi All,
I've been building up a TT bike and have hit a little problem that I probably should have considered at the beginning of the project....

The frame (a Dolan Scala) has a GXP PF bottom bracket and has been built with a 10s SRAM Force groupset, running 53-39 chainrings and 170mm cranks (GXP), with SRAM R2C shifters.

It all works nicely, but I want to change the cranks to 165mm, which has opened up a can of worms....

Simplest would be to get a used SRAM GXP chainset with 165mm cranks as a straight swap - these are like hen's teeth - there is one on eBay but the axle / spindle has a lot of surface rust on it so not sure this would be an issue

There are more used Shimano 165mm cranksets available but these are BB30, not GXP.

Thoughts as to whether I should:
1. Try and get the eBay straight swap ( https://www.ebay.co.uk/itm/266074578187) and not worry about the surface rust?
2. Swap the BB to a Shimano BB30 and look for a more readily available 165mm crankset?
3. Move to a 1x setup (as there seem to be more 165mm 1x cranksets available)
4. Something else that I haven't thought of?

Cheers, Griff

[Benmac]

Shimano isn't BB30. All modern shimano chainsets use a straight 24mm bb axle (unlike the stepped 24mm axle used in (I think) GXP. If buying a new BB anyway someone like "Wheels Manufacturing" will make one that fits in the frame but provides the correct 24mm dimension for the axle needed for Shimano Hollowtech cranks. Failing that you should be able to get some adapters to make the existing BB fit the Shimano cranks. I've just done this with a Ceramicspeed BBright bottom bracket on a Cervelo, couple of wheels manufacturing adapters and the Shimano cranks fit fine.

[anonymous-user]

I’d seriously consider 1x, when do you really use the small chainring on a TT?

[Benmac]

Bit more on this. Check what BB it is. I had a quick look online and it suggests the Scala has a standard British threaded BB. If that's the case, you just need a bog standard Hollowtech standard British thread BB.

Edited by Benmac on Wednesday 18th January 11:28

[AyBee]

pablo said:

I’d seriously consider 1x, when do you really use the small chainring on a TT?

All the time on the turbo trainer (58/44). In answer to the OP, the surface rust wouldn't bother me. I'd probably clean it up and protect the surfaces that aren't going in the bearing though.

[TheGriffter]

Think my initial reply has been deleted, or broken rules!

Thanks everyone for all the info - very helpful.

Benmac - I bought the bike second hand so not sure if it is the original BB. I have attached a photo and it is stamped GXP >PA+GF
|https://thumbsnap.com/tojba3Mk[/url]

Pablo - my 1x consideration was mainly driven by availability of 165mm cranks; preference for turbo and hilly triathlons (Ironman Wales) would be 2x I think at the moment - won't rule it out though
Aybee - cleaning the rust (hopefully surface only) might be a good shout and lowest effort path

I'm quite new to all this component compatibility and maintenance, so appreciate all the help!

[TCX]

Can of worms? Why 165mm?I'd just stock with 170,172.5,175 or whatever already on?

[gazza285]

A quick google would suggest the the bottom bracket is a BB86…

[HelenT]

Not over fussed on electronic on my road bike but would hate to have a TT bike without it now, had a spell when in 2020 when I went back to it briefly and really missed the ability to change on both the base bars and extensions especially on hilly courses or coming out of roundabouts.Prices have gone silly, I think my first groupset was about £300 secondhand , my latest 12 speed was somewhat more.
Shorter cranks help on getting aero and can give a better hip angle.

[TheGriffter]

TCX said:

Can of worms? Why 165mm?I'd just stock with 170,172.5,175 or whatever already on?

Yep got some developing OA in my hips so 165mm keeps the hip angle more open when trying, usually unsuccessfully, to get aero - hoping it will prolong me!

Thanks for confirmation on the BB type.

[AyBee]

TCX said:

Can of worms? Why 165mm?I'd just stock with 170,172.5,175 or whatever already on?

Says somebody who hasn't tried shorter cranks I assume Shorter cranks allow you to put your saddle up a bit but have you foot lower at the top of the pedal stroke and therefore have your hip angle more open. I wouldn't go back to longer cranks now.

[TheGriffter]

It might just be me, but I like it when a thread reaches "closure", so a quick update.

I managed to pickup a virtually brand new SRAM Rival GXP chainset with 165mm cranks within local collection distance, for very reasonable price. They are immaculate having only been ridden in a research lab and are a straight swap! Looking forward to seeing how they feel and tweaking position accordingly before the season kicks in.

Cheers