When I use my trainer, I take my road bike with DI2 and put it on the kickr, the two cassettes are not identical but they are both 11 speed Shimano cassettes
Recently, however, the shifting on the trainer is really poor, the chain will grind a bit, sometimes jump two spaces or not shift, and often will be a bit noisy on some cogs.
(Everything’s fine on road.)
I can find a good cog and leave it there and then it works fine, but I can’t figure out why this would be since the spacing should be the same. I also don’t know if I should care very much, if possibly him doing damage to my road bike…
I’ve had the same issue since day 1. It’s not gonna be your solution but for me I just straight-line the chain and leave in erg mode. Depending on how my trainer is feeling. One day it may run smoother in one gear. The next day (after taking it off then back on) it may be a gear up or down.
The indexing is slightly out. On a mechanical bike this normally just means moving the barrel adjuster by a half or quarter turn but is a touch more involved on Di2.
How often are you switching the bike between trainer and the road?
You’ll need to index every time you move it over, even with identical cassettes I need to index mine when I move it.
As others have said, the indexing may have to have the slightest adjustment. That said, I find it easier to leave in ERG mode on one cog, in the straightest and quietest line.
Have you tried the micro adjustment of Di2?
Press and hold the button on the Junction A box until light stays on continuously.
On my Garmin I can then see the setting it is at, which is between -15 and +15. Using the right shifter you can then change this setting which will move the rear derailleur slightly left or right. This is the equivalent of turning the barrel adjustment on the mechanical systems.
Great advice… I will try
Although then I suppose when I put my rear wheel back on , I will have to readjust
I had a similar issue with different sized SRAM cassettes (10-36 road, 10-33 trainer). I ended up getting an identical cassette for the trainer as my road wheels and have no problems. When I had Ultegra mechanical on my old bike I also matched cassettes on the wheel and trainer and needed no adjustments. Also, I assume you verified both cassettes are installed identically (e.g. no spacers).
i think the cassette on the trainer does have a spacer BUT i’m only using the largest 4 cogs so i dont think that should make a difference.
It just takes a few hundreths difference for the shifting to be off. I have the same problem not with my kicker and my main wheels, but between three different sets of wheels from three different hub manufactures. (gravel/cross/road wheel sets) Each one is just a bit different, so when I swap wheels, I have to readjust the shifting.
Yes, you need to adjust back. If you are able to see what offset is dialed in on the screen of your bike computer, it is easy to go back and forth to the setting that you need. So you don’t have to search for the right setting every time.
I had the same problem recently. I have two bikes, one totally dedicated for the Kickr, and the other just road.
What I noticed after making Di2 adjustments on the dedicated that it still wouldn’t shift nicely, especially when I rode a Zwift race and the gears were all over the place when going from flat to climb section.
I figured that it may have been that the hanger was slightly bent, so I purchased the Park tool hanger alignment tool. That helped and the shifting went back to normal.
Nevertheless, I went through and did the whole alignment and gear tweaking, which I found these two videos worth the time:
When I got my Kickr the indexing was off by 1 cog. I took a spacer from the cassette that came with the Kickr and placed it at the backside of the cassette. Fixed… It worked so well that my bike shifts perfectly on both the trainer and with the rear wheel with no adjustments.