hhk25

To explain, I have a Tacx Neo trainer. I'm trying to mount an old 7 speed Trek on it. Kind of a long story as to why. It's a freewheel not cassette. Also, I'm a bit of a newb so excuse the poor use of terminology.

I thought it would be a simple matter to install a 7 speed cassette on the trainer and mount the old bike but I am having trouble.

I measured the difference in width of the 7 vs 11 speed cassettes and I came up with 5mm. With an 11 speed Shimano cassette, I have to place a 2mm spacer behind the cassette so I added another 5mm of spacers and installed the 7 speed cassette.

I mounted the bike and the cassette is clearly in the wrong place. When I shift down, the chain jumps off the largest cog. When I shift up, I can only shift to the second smallest cog. I realize I can fix this with the derailleur screws but if I do that then I'll have to re-adjust when I take it off the trainer and install the wheel.

Clearly, the position of the cassette is more outboard than on the wheel. So, I removed 2mm worth of spacer so that I can shift the position inboard. But when I do that, I can't tighten the locknut enough. It runs out of thread before it can tighten against the cassette.

I'm scratching my head on how to fix this. One option I thought of is to go with a 9 speed cassette instead of a 7. That way, the cassette is wider (thicker?) and I won't need as many spacers. Obviously with a 7 speed derailleur, I won't be able to shift to the lowest and highest cogs. But I'm not worried about that. Also, the shifters are friction so I don't have to worry about indexing.

I'm kind of thinking out loud here. Any suggestions are appreciated.

Maybe what I'm trying to accomplish is impossible. That is, I won't ever be able to just swap from trainer to wheel without adjusting the derailleurs.

Ghrumpy

You can totally do this. You just need to measure more carefully where the spacing difference is and shuffle spacers accordingly.

Generally speaking, as you add cogs to the stack, a cassette will get wider to both sides of its centerline (which is where chainline is calculated.) You can't just add 5mm of spacers on one side or the other of the cassette and expect it to line up. You need to split the difference between both sides of the cassette. And even then you will probably need to do some fine tuning.

Leisesturm

This sounds like the easier problem to fix. Without knowing anything more about it, I wonder how accurately you are measuring things. Not judging. Just wondering. 2mm in skewer length should not mean the difference between properly securing the frame and not being able to tighten the q/r sufficiently at all. There is a 5mm difference in OLD between Road rear hubs and MTB rear hubs. Which kind is your Trek and which kind is your trainer ... if I were making a trainer I'd probably bias the thing towards the Road market. But knowing me I'd allow both options ... why not? I like you as much as I like any total stranger on the Internet but I cannot go and find the owners manual for your trainer and figure out how to set it up for a Road vs MTB rear end. That is your assignment. You may have to buy another hub .. I mean cassette. You can probably pick one up for nothing, or next to nothing at a local bike co-op. Have fun.

SkyDog75

...which you'd probably have to do no matter what. Even if two wheels -- or a trainer and a wheel -- have the exact same cogset, you commonly need to adjust the derailleur's limit screws and indexing when swapping. Tolerances for cassette/freewheel spacing relative to the axle locknut generally aren't consistent or precise enough to avoid it. (And since the potential consequences of dropping a chain inboard of the cassette are pretty bad, it pays to check to be on the safe side.)

To minimize having to do so, you can adjust spacers. But when trying to get two wheels similar, I'd suggest playing with spacers on the axle instead of the freehub/cassette. Not sure if that approach would work as well when trying to match a wheel to a trainer.

Kontact 

In a perfect world move the spacers to the right side of the cassette, but the high cog doesn't allow you to do that.

A 9 speed won't be spaced correctly for 7 speed indexing and your 7 or 8 speed chain will be too wide.

Adjusting your derailleur is pretty simple and doesn't cost anything. I would do that.

hhk25

I figured that but when I move the centerline inboard by removing a spacer, there is a gap between the lockring and the cassette. I can't tighten the lockring enough.

Are there washers or spacers available for between the cassette and lockring?

Kontact 

How do you add a spacer to the right of the high cog? Those don't have spline cuts going all the way through.


The OP could put spacers between the high cog and the next 6 and not use high.

Ghrumpy

Exactly. Put a dummy high cog there to take up the space. You could grind off the teeth if you want a pure spacer. But you won't be reaching it if the limit screws aren't moved.

hhk25

To offer more gory details, the trainer is a Tacx Neo. I bought it in the fall thinking I'll mount my newish road bike and just pull it off when I want to ride on the road. BUT...the disc brake caliper on my road bike hits the plastic housing of the trainer and prevents the bike from sitting on the trainer properly. So, if I want to use the bike on and off the trainer, I have to remove and re-install the brake caliper everytime. Not ideal.

So, I thought I would take my old Trek 520 and use it as a dedicated trainer. Simple as putting a 7 speed cassette on the trainer. Or so I thought.

The Trek has friction shifters so indexing is not a problem as someone suggested.

The dummy high cog or spacer between the high cog and the rest of the cassette are darned good ideas. I'll try that next.

Thanks for all the input.

hhk25

Another option I just thought of.

Since indexing is not an issue, why not just leave the 11 speed cassette on the trainer and put an 11 speed chain on the bike. Properly sized, of course. Any reason why this wouldn't work?

Leisesturm

Indexing may not be an issue but there may be issues with expecting a 7sp RD to shift an 11sp cassette. The shifter also might prove inadequate. But it MAY work. Try it.

Just how much switching back and forth do you do between trainer and road? Most people use the trainer as a winter training device and once the riding season begins, the trainer (happily) goes into the closet until late Fall comes around again. I sure wouldn't want, nor am I able anymore to work with small parts like limit screws, I just can't imagine frequently having to adjust limit screws to make a not quite right mismatch between a trainer and the road work. So... again, how much switching are you doing. That will decide your approach.

The dedicated trainer bike looks like a good idea. Because of the insanity that exists in the world of things bicycle, you could probably buy a complete trainer ready old school road bike on Craigslist for the cost of a premium 11sp cassette from one of the big names.

Kontact 

You must have quite the budget for parts.

An 11 speed chain will work on your 7 speed bike.

hhk25

The 7 speed cassette cost me $15.00. A KMC 11 speed chain is $30.00. And I actually don't mind wrenching a bit. Now, which way does that chain whip go again?

TallRider

I don't think anyone's mentioned this yet. Easiest for hwat you want to do is to buy a 7-speed cassette (they're like $15) an a spacer to take up the extra width on the freehub.

hhk25

I want to use the trainer during the summer too. Watch Netflix or a baseball game while I spin. Garbage miles, I know but at least I can't eat chips while I ride.

I might have to keep my eye out for a cheap bike. Yet another option is to convert the Trek to 11 speed. Likely there's some complication there I haven't thought about.

Kontact 

This is exactly what most of the thread has been discussing.

trainman999

leave the 11 speed cassett on the trainer, use an 11 speed chain, leave the derailleur limit screws alone, mount the bike you may have to spread the chain stays slightly. You said it is friction shifting, simply use the cogs that the derailleur shifts to, forget about the ones you can't get to. You will need to ckeck that you can't shift beond either side of the cassett. I am guessing you will only be able to access 9 of the 11 cogs.