Have a bit of a hilly time coming up, so swapping my 12-25T 10spd cassette on the road bike out for an 11-28T (and retaining the 34/50T compact chainset).

It's a short cage Dura Ace rear mech on the back… so can I be lazy, and measure the new chain against the length of the old one, or should I do it properly – with the old big ring & big cog + a couple of links thing?

that combo wont work need a longer rear mech as jockey wheels will rub on sprocket

how hilly is this time trial that your gonna be using 34:28 ?

that combo wont work need a longer rear mech as jockey wheels will rub on sprocket

Depends on what rear mech he has. 7900 Dura Ace are rated to 28T. The length of the arm is not what dictates the largest cassette sprocket anyway. It is the arc the rear mech moves through. The longer arm is there to cope with the extra chain needed to cope with a wide spread gear set up, usually a triple.

Just some "time" in the hills (no mention of "trials" trail_rat! 🙂 ) – a bit of long distance riding with panniers and so on, and I need every bit of help I can!

I've just checked Shimano's site, dn-chevy, and you're right – they reckon a 27T max with the rear mech. Hmmm… back to drawing board, I think?

Why not fit a 12/27 then?

Thanks Mister P – I think it's a 7800… what do you reckon?

Mister P – Member

Why not fit a 12/27 then?

'cos they're like hen's teeth…?! 🙂 I can't justify Dura Ace cassettes, and I've struggled to find a 105 or Ultegra 12-27T – but there are Ultegra 11-28T around…

haha time trial on the brain – coulda sworn that said hilly time trial haha

11-28/32 and an mtb rear mech for the cheap option ?

lol, trail_rat – it's that time of year!

Yeah – maybe that's a way of doing it, if the one on there isn't going to work. Would an XT 9spd rear mech work with 10spd STIs? I'm guessing it will…

Yep absolutely fine.

thanks for that Mister P – I'll give it a try. Cheers.