Haven't commuted much since november thanks to global warming taking a hiatus this year. The few days I have commuted, I've ended up with rear flats about half the time. I attribute this to a combination of being a lardazz and hitting more bumpes thanks to lots of night riding. My commute is still 100% dark both ways for atleast a few more weeks.

Anyway, I was thinking that bumping up the rear of my trek 1200 from a 25 to a 28 or possibly even a bit bigger, might lower the number of flats I get. KNocking off 40+ pounds would probably help as well, but, that's a separate matter.

Will having a 25 up front and a 28 in back cause issues? I think a 28 will fit fine, although it might require pumping the tire up after it is mounted.

It won't cause any issues, and will let you run slightly less pressure in back for a cushier ride without risking pinch flats. I run a 35 in back of my commuter, and a 32 in front, and like it fine... just set it up that way because those were the only tires i could get at the time.

However, it won't make you less likely to get a flat. If you're getting pinch flats, you should pump your rear tire up harder. If you're getting regular flats, you should get gatorskins/ marathons/ paselas/ etc.

No Problem.
I run 28 front 35 rear.

I run a 1.75x26 in front and 1.9x26 in the back. Its pretty comfortable.
Just make sure that your
- tubes aren't pinched between the rim and tire bead
- your tires are pumped up enough
- there isn't any debris on the inside of tire or the rim when you replace the tube

No issue with larger in the rear other than your saddle will need leveled out and your bars will feel lower.
Should help pinch flats, since you'll not need to run as high a PSI due to the larger tire volume.


If you grab an in-line barrel adjuster for your brake line you'll avoid having to inflate the tire after it's mounted. Just let some slack out via the adjuster and it should clear the brakes.

No issues with this unless the 28 does not fit... ran a 28/25 combo on my main commuter for a lot of miles and liked the little ride improvement I got from the 28 and have never worried much about flats.

The tyres on my folder are a 1.85 rear and a 1.35 front... it makes for a wonderful combination of handling and ride quality.

25 rear and 23 front here. i like the combo. my commute is mostly on (fairly) well maintained roads and i like a fast commute on a road single speed. there is no problem with mixing tire sizes.

If you use a rear wheel sensor for your computer you will need to recalibrate for the bigger wheel. Otherwise, no problem.

Check your rim as well. If you're getting a flat on the same rim frequently, there might be some slight damage (a small dent is all it takes) to the rim that is encouraging pinch flats.

A friend of mine rode with a 29X2.1 in the front, and a 700X28 in the back (I don't want to have to do the conversion, sorry about the mixed sizes)

It required completely re-fitting the bike, the seat angle was way off, the handlebars were abnormally high, and the trail was changed dramatically, but it rode amazingly.

Proper inflation and tire quality will do more than going up one tire size. I run 700x28 Forte GT2/ks on my commuter with thorn-resistant tubes and keep them inflated to max pressure (105 psi). I hit a ton of potholes, railroad tracks, glass and other debris. Well over a year without a flat.

On a side note - Pro Bike Kit is running folding UltraGatorSkins in 700x23 and 700x25 for under $30 each with free shipping. Ordered a pair of 700x23s for my wife's bike laste week and the price is way less than anything else out there.