Does it matter what kind of bike I put on the trainer?
 

I have a hybrid "comfort bike" (Trek Navigator 100) that just sits in my garage. I've been thinking about setting it up as my trainer bike. I have a kurt kinetic fluid trainer. The position on the bike is fairly upright and I'm planning on switching the tires to a 1.5 inch slick or city tire (currently has 2 inch hybrid tire with nobby on the edges.) The bike itself is in good shape, but I only like putzing around the neighborhood on it. I'm just wondering if it makes any difference in "training" as to the position I am sitting in while I am on the trainer. I think the main purpose is to get a cardio work out on the trainer... any drawbacks to riding on the trainer in this position with this bike?

I don't think it makes any difference, as long as your position on the bike when it's on the trainer is the same as your position when you're riding on the road. Be sure to block under the front wheel so the bike is level, or tilted up a bit if you want to simulate hills. Wear real bike shorts with a pad, and buy a 24" box fan to put on a table in front of you.

Be sure your saddle height is adjusted correctly. With your heel on the pedal, your knee should lock at the bottom of the pedal stroke with your heel just touching the pedal. Start with that, anyway. That type of bike usually has a fairly "plush" saddle. If your butt gets numb, just stand up for a bit, or even pedal standing for a bit.

The only danger I see is that you might get in shape and want to do more than putz around the neighborhood. That could lead to a new bike and other seriously expensive stuff. Be careful.

If you want the full benefit from the trainer, you should put your heaviest bike on it. :D

Yes, I am switching out the saddle also. I already have a nice touring bike and the position I ride that bike in is significantly different than the position on the comfort bike. Is the position critical? I was just thinking... I might want to swap out the pedals too.. so i can use my cycling shoes with cleats.

chipcom... the bike is heavy... I would say 35+ lbs.

I want to use the trainer when the weather is just crappy or it's dark outside. I figured I should put this idle bike to use... but not if it's not going to be rather beneficial. I guess I thought the main purpose of the trainer was to provide a cardio workout... but how important is the position? I'm not really interested in putting a drop bar, new stem, shifters etc. on this bike just to use it on the trainer. If position is that important, I would be better off buying a used road frame with some cheap components.

Why not put your nice bike on the trainer? The deal is that it's a good idea to work your muscles and joints the same way on the trainer that you do on the road. It's never just a cardio workout. I always ride my fast bike on the trainer.

Dude, I was attempting a lame funny. ;) Putting the idle bike on is a fine idea. Just because it doesn't match your other bikes from a geometry or position standpoint does not mean that you won't get any benefit. Any exercise is better than no exercise. ;)