Sorry if this isn’t the best place to ask this but I am hoping someone might answer.
I have a Elite Direto smart trainer but haven’t had the smoothest experience with it because my mountain bike is not 100% compatible.
Direto should be used with a bike that has 9/10/11 speeds cassette.
I’m just looking for a road bike for indoor trainer use exclusively so weight etc is not important. Can someone recommend a cheap bike that is compatible with this trainer??
Brand and age doesnt really matter as long as the fit is good and the components are in good shape. Look for a used road bike in your size that has been taken good care of. If your local bike shops are open, talk to them and see if they have any options.
Oh, and make sure it will be compatible with the Direto.
An older road bike or hybrid bike with a 7/8/9/10/11 speed cassette will work. A cassette with eight to ten cogs requires a spacer on the eleven speed hub used on modern wheel-off trainers (probably included with the trainer). A seven speed cassette requires a slightly thicker spacer ($1 to $2) and a few minutes’ work with a file in order to fit on an eleven speed hub.
So you want a frame that fits and a drivetrain that shifts. You’ve got a huge range of bikes dating back into the last millennium to shop from.
Zwift has some steep inclines (17% +). You might want to look for a triple crankset up front or at least a compact double crankset so that you have a ~30 or ~34 tooth chainring to get lower gears comparable to what you’re used to on your mountain bike. Triples were more common on older bikes. They may give you more gears that you’ll use. On the other hand, you might not want the bother of shifting more often.
Thanks. I appreciate ths info. You’ve given me a good starting point. I will research more. This whole pandemic is making me impatient and I just want to be able to bike outside too…
My mountain bike is an 8 cog cassette with triple crankset up front and even with spacers and shifter adjustments I can’t access all the gears. My shifters on this bike have an issue too but I’d like to get a perfectly compatible bike I can leave on the trainer and not have to disconnect and reconnect it and take so much time fine tuning the shifters to get decent shifter use.
Even the manufacture told me that although it may work they don’t advise using it with anything less than a 9 speed cassette. Btw I took it to two different local bike shops and they couldn’t figure out what was wrong with it either. I’m fine with using the bike as is outdoors but I want a compatible bike I can just leave on the trainer and get full use out of Zwift. 
Hubs that accept a Shimano 11 speed cassette will also accept Shimano 7, 8, 9, or 10 speed cassettes and shifting should work fine with the proper spacer in place on the hub. The 8 speed should, if I recall correctly, need a 1.85 mm spacer. And otherwise the trainer has nothing to do with the rear shifting. As long as the 8 speed derailleur and the 8 speed cassette are lined up properly, the shifting should be just as good on the trainer as outside. An lining them up is just a matter of the spacer.
With that said, it is nice to have a dedicated trainer bike. It’s easier to maintain the habit of riding if you have minimal extra work to do to get on the Zwift roads. I’d just suggest that when you’re looking for a cheap bike to keep on the trainer, don’t rule out used road or hybrid bikes going back at least to the 8 speed era.
Our trainer bike is now a compact double 11 speed drivetrain mounted on a cheap frame. With the dropped bars and brifters it is more like riding outside. But the old triple 7 and 8 speed MTB and hybrid we’ve had on the KICKR as dedicated trainer bikes over the last five years provided better gear choices than this compact double does.
I’m in this same situation now. I want to get an Elite Direto XR but I have an old 3x7 free wheel Raleigh M30 MTB. Looks like it may cost $500? to convert it to 11 speed cassette. I’ll be looking next into cost of converting it to 3x7 cassette.
What bike did you end up getting?