Hey guys, my rear tire been worn off but I only got one spare one left for now. Was planning get new tire few more months. My question is, is there any difference when I use better tire on rear or front?

Conventional wisdom is to put the new tire on the front and rotate the other to the back. That’s because a front flat is potentially much worse at speed.

Thanks man. I'll get the new tire on my front wheel. By the way which one is better for commute ride, continental grand sport race or ultra sport II?

Sorry, I'm not that familiar with Continentals (I'm more of a Michelin guy), but the Grand Sport Race get good reviews on the websites as solid all around training/commuting tires. I wonder if a Conti fan might chime in.

Over time, if you ride with a better tire in the rear, the wheelbase of your bike will shorten due to the rear going a bit faster and putting pressure toward the front. Riding with the better tire in the front will do the opposite of course. ymmv

Both tires are older tech, I think the Ultra Sports are the older of the two techs. Might be wrong though as Continental's aren't my tire of choice right now. The two models share the same TPI of 180 in the tire casing which can be an indicator of whether one is faster than the other when all other things are the same. However these aren't the same in all other respects and the Grand Sport Race would be my choice of the two.