Originally Posted by
rat fink
A 19" mountain bike is significantly larger than a 17" mountain bike. In practice, it feels like a 3-4 size difference when compared to equivalent road bikes.
+1 Measure the difference in top tube length. I usually ride a 22 inch road bike, and an 18 inch mountain bike. I picked up a really, really, sweet Trek MTB recently in a 19 1/2 inch size. I thought, surely this is going to be OK. It wasn't.
No problem with standover, but top tube was way too long.
So I would play around with shorter stems, and see if you can get distance from saddle to bars close to your road bike set up. If you can, you should be fine.