Is there any significance to running a 23c tire in the rear with a 25c in the front (or vice versa)? Are there pros and/or cons to setting up a fixie this way? thanx!

I would think the 25c in the back would be the best option out of those two. Most of your weight is on your back tire.

I've run smaller in the front and big in the rear before, kinda feels like the front wheel turns faster than the rear. Probably not noticeable with those sized tires though.

Mr Brown was a fan of big-in-front, small-in-back:

https://sheldonbrown.com/tires.html#mixing

I doubt you will feel much difference between a 23 and a 25. A good argument can be made for putting the bigger tire on the front, though. More air should give a little more shock absorption and a slightly wider contact patch for steering.

i do have wrist pain sometimes, so i'm leaning towards putting the 25 up front and the 23 in the rear. if i start getting a lot of pinch flats in the rear, i'll consider swapping the tires. thanks for the info everyone, especially that sheldon brown link!

while in the past I always used 23's, I've gained way too much weight for them (by my understanding anyway, back in the day I was sub-135; now I'm... "a bit more").

one question I have that never really occurred to me in the past: what's the advantage of 23s over 25s? my understanding is that 25s generate less rolling resistance, are 23s preferable for the light cyclist because they weigh less (and therefore have less rolling weight)???

I kind of like that setup. I don't know if there's any huge advantage to it, but if you usually ride 23's, your bike might feel a little more stable. Or something.

Mountain bikes are often set up with a skinnier rear tire and a wider front tire to maximize speed and traction...I've run a wider rear and skinnier front tire on my fixed gear which improves the ride and does not really detract from it's performance.

I'm running a 23 in the front with a 25 in the back right now and have around 1200 miles on them or so. I can't notice it at all and wasn't able to from the get go either, seems to be working great. I commute on them almost every day.

Thats an old BMX racing trick that works well on dirt so has been adopted by MTBers. I don't see how having a larger tire in front would be as beneficial on the road, since traction is less of an issue. It would let you run lower pressure in front, making the front end a little cushier, and make it easier to navigate road irregularities without increasing much rolling resistance. However, if you want bigger tires for those reasons, I'd probably go with larger tires front and back. The speed difference between 23mm and 25mm tires is probably not noticeable to your average amateur, but the overal handling differences are potentially significant. I use 23s and 28s on different bikes, and the 28s are way more comfortable on rough surfaces and handle bumps, gravel and other irregularities a lot better. They are a tad slower on smooth pavement, but are actually a bit more efficient on rougher roads. The nastier the road, the better a larger tire will perform relative to a skinny one.

On my commuter I have extra weight on the back due to my backpack. Once I switched to a 25 on the back pinch flats have been a thing of the past. I still use a 23 up front.

skinny tire = higher pressure. Higher pressure = less rolling resistance.

The rolling resistance of a 23 and a 25 would not be much different at the same psi. However, to do that there's a good chance that, one tire would either be underinflated or the other one overinflated, at least according to the manufacturers legal department.

My understanding is that, at the same tire pressure, the 25 makes less contact with the ground, hence the lower rolling resistance... but of course you are correct that a 23 will handle higher pressure (although not by a lot). I wonder, though, how many people pump their tires to full pressure before every ride?

25 in front and 23 in back usualy cuz i do lots of climbing and put lots of weight on my front....hills are ftl

i ride a 28 randonneur in the back and a 23 rubino pro up front

This is true up to a point and depending on how wide the tires are.

Basically, worse of both worlds.

slighty OT, but can someone explain a little more about rider weight vs. 23's. ive never ridden on anything but 23's and im about 190 lbs. is a wider tire a comfort or safety issue?

You can run a wider tire at lower pressure without risking a pinch flat. At 190lbs., you need to run pretty high pressure to lower the risk of a snake bite.

how can 25's have less contact area with the ground than 23's?

i think sheldon brown had pictures on his site with the oval's showing the contact sizes, and it seemed to be all in order with the 23's being smallest...right?

Going to pick up a Miche Pro Race 2 for my rear tomorrow. That will have me running 23 rear, 25 front. I seriously doubt I'll be able to tell any difference though. I'm running super sub-par PSI due to a ****ty pump situation ATM, and that should negate any rolling resistance advantage. It will, howver, still be blue.

+*****points