Ultegra Di2 indexing

pedalbasher

Hi

I just bought some new wheels and fixed an Ultegra 12-25 cassette.

My bike has Ultegra Di2.

Previous cassette was an 11-28.

When I shift through the gears on the new cassette, the chain moves happily up to the penultimate sprocket but won't move into the 25. Conversely at the other end of the spectrum, it will shift down to 12 and then off the end of the cassette (worrying). I.e. the 10 shifts are out of sync with the cassette by one sprocket.

Please could someone help me set the rear derailleur up correctly. Is there a simple way? I am wondering whether I need to put another spacer in behind the 25 cassette.

Thanks v much.

Semantik

you didn't inadvertently remove the thin 0.75mm spacer from the freehub when you removed the old cassette?

pedalbasher

Nah - I've put new wheels on, so new free hub. There's def a small metal spacer behind the cassette now (i.e. I put it on the free hub on the new wheels before installing the cassette).

pedalbasher

Should have clarified - by "I've just bought new wheels", I mean I have literally bought a new wheel set, not a new bike! I.e. I have replaced the wheels, and with them obviously the free hub!

Semantik

Sounds like the rear mech is still selecting 10 ratios but starting and ending in the wrong position.

Did you select top gear (smallest sprocket position) using the shifter before putting wheel in?
If you did this, and the chain still runs badly in that gear -and was ok before- you know it's nothing YOU have altered and must be the chainline has changed and/or limit screws need re-setting.

Also,if it's a Mavic WHEEL (??) no spacer needed on those.

pedalbasher

Cheers. You're exactly right. It's selecting 10 ratios (and moving smoothly between each sprocket) but starting and ending one sprocket out.

They're Reynolds wheels. I just put one spacer behind the cassette.

Not sure I selected smallest sprocket before putting the wheel in (I think I did, but can't be sure now...) I'll try that later.

me-109

Wheels designed for 11s and in need of an extra spacer behind the cassette?

pedalbasher

Me-109 - thanks, that's the other possibility. Should be as simple as that, one spacer to compensate for the extra sprocket?

Semantik

OP- the following is useful info on all things 11 speed and which spacers you will need.

http://www.slowtwitch.com/Tech/Cassette ... _3257.html

pedalbasher

Thanks a lot for that - geeky but the table is pretty useful. I can only assume the new Reynolds freehub is actually 11sp-only and therefore I need both 1mm and 1.85mm spacers behind the cassette. This might explain why there were 2 spacers in the little plastic bags supplied with the rim tape and skewer for each wheel... obviously I was in too much of a rush to bother with those

pedalbasher

Ended up putting 3 x standard narrow (0.5mm?) spacers behind the cassette, played around with the hi / lo limit screws a bit and also tinkered with the di2 set-up (i.e. the micro-adjust function). Seems to be working nicely now, so cheers for the advice.