[Closed] Ultegra drivetrain replacement

Replace the whole crankset, it will be more economical. Was for me anyway and people will pay for the old crankarms on ebay.

Bike Discount are fine. Currenly awaiting some drivetrain stuff and a new tyre from them myself.

I didn't replace the 34T or the 36T on either of my 6800 chainsets as they get used so rarely (it's pretty flat round here). Although for £9 I'd be tempted to change it anyway for peace of mind.

Replace the whole crankset, it will be more economical. Was for me anyway and people will pay for the old crankarms on ebay.

Pricey things just now - struggle to get one for less than £200, where they are normally available for sub-£150. Annoying, as I need to replace a creaking one and have just realised that prices are through the roof. Oh well, will have to put up with a noisy gravel bike for a few more weeks until things settle back down.

Worth noting that chainrings last miles longer than cassettes, and will often work fine with a new chain (unlike worn cassettes, which often won't). So, just cos the chain's over 1mm stretch doesn't mean the chainrings need replacing.

Worth noting that chainrings last miles longer than cassettes, and will often work fine with a new chain

This is true, although I've always had a sneaking suspicion that a chain fitted to worn chainrings stretches more quickly than with new chainrings. No science behind this, just a hunch. Think of it in the same way as a Facebook Covid-19 "fact" 🙂

I'm in a similar position, 6800 with chain at 1mm.
Just gonna chuck a £10 SRAM chain on and see if it meshes with the cassette (this will only be second chain on this cassette). If not, a 105 cassette is £35

Just a heads-up that Merlin still have compact FC-RS510 chainsets for ~£48, before you use any reward points discount for a £50+ basket and go there via Topcashback/Quidco. Something like ~908g, so a bit heavier than newer 105 R7000 (716g) or Ultegra R8000 (674g)... But better than half the price.

Nuts how a replacement Shimano 34T chainring costs ~£13+, while a 50T is ~£50+.

I keep the rings for 2-3 cassettes. We did the same on the hire fleet (though never letting the chain go past 1) and found that worked fine.

So, 2 chains to a cassette, 2 cassettes to a chainring.

FWIW I recently went from Ultegra to 105 cranks on a drivetrain replacement (because silver). I'm not sure what the difference is supposed to be but I can't notice it.

Nuts how a replacement Shimano 34T chainring costs ~£13+, while a 50T is ~£50+.

Not really. The inner ring is just a stamped piece of steel or ally and the outer ring is a hollow aluminium piece with shift ramps and profiles, I’d imagine a lot more expensive to produce.

Check out the price of Dura Ace outer rings if you think 105 is pricey!

Done a bit more digging.
Thanks to scotroutes I looked at the R7000 (105) chainset.
Can get a R7000 52/36 with 175mm arms for £95. Will I notice the arms being 2.5mm longer than current Ultegras? Same place also does R8000 52/36 172.5mm for £160.
Alternatively, can I put R7000 rings on my current Ultegra 6800 cranks?

I've got an r7000 50/34 175mm I replaced with a 165mm sitting in the shed. Didn't go for r8000 as few reports of them and Dura ace going kaboom. Hard to fault the current 105.

It's worth inspecting your chainring for wear rather than assuming they are goosed just because the chain is. IME you can really see when a chainring is worn - this vid shows some examples:

Will I notice the arms being 2.5mm longer than current Ultegras?

I personally think it's noticeable on a road bike*, which is not to say it will be better or worse, just that it might feel a bit different. I would expect that it's something that you'd quickly get used to.

*I borrowed some 172.5s for my roadbike while I was waiting for my new chainset to arrive. I thought they felt weird cos they were a different model, only realised it was a different crank length when I took them off.

The roadie’s Ultegra 6800 drivetrain still shifts ok but chain gone beyond 1mm stretch. It’ll all need replacing soon

How many miles has it done? If its still shifting OK and the chain is in good condition, no cracks etc just keep running it. Ride it through winter and change it on spring when hopefully things have settled down and stocks have been refilled?

Probikekit are selling the R7000 chainsets in most/all sizes for about £100.

Damascus - it's not perfect but still ok. I can keep it going until it causes issues but it's on borrowed time - just a case of when I change it. I can't remember the exact mileage but something like 3500 miles or so.

1mm stretch over what?

My chain is at 1mm stretch and the gears get caught up when backpedaling - mech arm pulls forward. You can see the chain isn't meshing with jockey wheels well.

Still confused...1/8" over 12" is ~1% which used to be a threshold I think (or 0.75cm?)... what is 1mm over?

And aren't backpedaling issues about chainline?

I've just replaced an Ultegra 6800 with a 105 R7000 chainset and noticed no difference, well apart from the dark grey to black.

Will I notice the arms being 2.5mm longer

Maybe, maybe not.

I certainly notice than one of my MTBs has 170mm cranks and the others 175, although I don't notice the roadie has 172.5.

I wouldn't change it unless you have fit issues, not worth the risk.

Try a new chain first though, cassette might not be that worn.