I've been riding road for almost a year now. I do 100-150 miles per week. I love doing 100+ mile rides on the weekends when I can.

I want to get stronger and better on climbs (like everybody) and have been using an indoor trainer frequently with Zwift on my road bike, but the tire is getting really screwed up. I don't have a spare wheel, and don't want to change my tires all the time, but I do have a spare MTB with smooth street tires on it.

What impacts if any would training on a MTB bike (position) on a trainer have on my road riding? I hate to loose any of my saddle "callus." Yeah I know find a spare wheel . . .

-And bummer, Zwift does not let you change the wheel/tire size yet.

They make tires specifically for trainer use.

Yep - check out performance bike and others.

thanks, but I don't want to change the tires all the time.

I still ride if I have enough light when I get home.

I see. What kind of tires do you normally use? Maybe get some really hard and durable tires? My current tires are ****ty Bontrager T1s and they seem to be lasting forever, both on the trainer and on the road. I wouldn't be taking corners at full lean going 30mph on them but for general riding they work fine.

I've used two old MTB's on my Kurt Kinetic trainer with great results. Rather than use a MTB wheel, I put an inexpensive (Performance Forte Titan) rear wheel on it with a Vittoria trainer tire. Since you don't need to use the brakes, it isn't important that the brake track doesn't line up with the pads.

From my spare parts bin I put drop bars, brake levers, and bar-end shifters (it was just a random mix of parts). Saddle was a random one I never got used to riding 100mi+ on, but works great for 60-75min at a time. Depending on your MTB gearing (44T big ring?), you are likely to spin out before the trainer provides enough resistance ... I bought the least expensive road double (52/39) square taper crankset I could find.

A cheap adjustable stem and tilting the front end of the bike up/down allowed me to get the exact same fit as on my roadbike. The bike as setup looks goofy, but it has worked great over the winters and I've gotten much more value out of the MTB frame than I could have by selling it.

I know you said you don't have a spare wheel, but you should just try to find an old one on Craigslist or something. It doesn't have to be anything special, just something to put a trainer tire on. I use an old stock wheel off a bike I had 5 years ago as a trainer wheel. If I were selling that wheel I probably wouldn't ask for more than 20 bucks.

I've got a whole plastic bin full of old tires that I wouldn't trust on the road, but are fine for the trainer. When you've had as much practice as I have, swapping a tire is less than a five minute job.

Get a spare wheel. Heck, if you lived in Portland, I'd just give you one.

I have a couple that that rims are too worn to be safe on the road. But since there's no wear or safety issue on a trainer, these would be great for your purposes.

Go to your LBS, see if they have a wheel with trashed hub bearings and spoke pulling out of the rim a flat spot or something. Most wouldn't ride these wheels, but they're perfect for trainer use as long as they're true enough to not hit the frame, get a cassette and just swap the wheel. You're probably only in for the cost of the cassette. Ive got a wheel like this for my rain bike, cost me $15 for the 8 speed cassette.

I pondered that a couple of years back - didn't want to swap tires or wheels or frankly take my bike on and off, since I was riding virtually every day at least once, often morning and evening, doing a triathlon training program and some one-on-one computrainer coaching sessions with a cycling coach. So I decided to use my old Cannondale mt bike. It worked but it's not exactly the same.

I bought my own computer based trainer recently to use over the winter, not Computrainer brand, but the one they sell at Performance because I ended up getting it for about $800 out of pocket for an $1700 or $1800 regular price trainer. I am NOT putting my good Roubaix on there, I don't want to risk damaging an expensive carbon wheel. Just gonna get myself a cheap road bike to throw on there.

maybe even something used of CL or from a thrift shop -

If your position is at least close, it should have no impact.

Only problem I had with the MTB on the trainer was spinning out the tallest gear as anotherbrian mentioned above. With the Kurt Kinetic I just put it in the largest combo and spun 95RPM, still a great workout.
As far as riding position, I never thought too much about it. I can't get as low obviously on the MTB but I mounted bar ends (remember those? :-p), mounted parallel to the ground, to vary my hand positions and get out front.