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My used bike came with a 700x28 tire in front and a 700x23 tire in back. Should I leave the wider tire in front, or should I switch the tires? What benefits or drawbacks are there one way or the other? Is there any particular reason why the previous owner might have chosen non-matching tires? Is there any reason I should go out of my way to buy a new tire to make them match?

The found a little bit of information about tire sizing, but I still don't feel like I know what to do.

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up vote 15 down vote accepted

Generally on a road bike it is considered better to run tires of equal size.

There are a few newer tires which are designed to run different sizes front and rear, but they are usually within 2 mm of each other. (Like the Continental Attack/Force combination)

I would consider a jump from 28c to 23c somewhat large.

That said, run the larger on the rear. The higher air volume will make for a more comfortable ride, and the narrower front tire will steer quicker, which makes for more reactive handling, and has a better aero profile, (which may or may not matter to you).

The comfort part will matter though, and I'd say that's a trump card.

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I just switched the tires, and I'll see if it makes a difference tomorrow. – amcnabb May 8 '12 at 1:22
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I'd be lying if I said I noticed a huge improvement, but it's definitely not any worse. Thanks for the answer. – amcnabb May 8 '12 at 16:11
    
In this case, the only noticeable improvement I would expect to see would be a benefit in handling on the front end, especially in quick reaction situations (i.e. emergencies), so I hope you haven't noticed anything yet. – zenbike May 8 '12 at 17:52
    
You can run the 28 at a lower pressure than you had in the 23 when it was on the back wheel -- that will improve comfort. – tgdavies Jan 13 at 10:32

If you have to make a choice, put the wider tire on the back. Generally there's more weight on the back, plus having the wider tire in front will make make steering more difficult.

(Most likely the previous owner had to replace one of the tires and just used what was available.)

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+1 for the rationale. That'd be my guess as well. LBS available stock makes for some strange bedfellows. – RoboKaren Jan 13 at 16:23

A wider wheel = more traction

Traction is important for torque and braking. Torque is driven through back-wheel and braking on both, and braking too much in the front relative to the back can result in the rider flipping over the handle-bar.

Therefore, put the wheel where it matters most, i.e. the back.

Edited in agreement with comment.

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1  
Most of your braking should be with your front wheel: bicycles.stackexchange.com/questions/6616/… – amcnabb May 14 '12 at 17:11
    
Not sure if that is correct, but essentially, there is a ratio / tipping point at which any more front braking will result in a flip over. Having more traction in the front than the back will result in the rider being closer to that tipping point. – Yusufk May 15 '12 at 9:37
    
Reading this ( stoptech.com/technical-support/technical-white-papers/… ), does support your point, because a riders weight is mostly on the back wheel. However, there is a tipping point, and having more traction in the front will result in a rider being closer to that tipping point. – Yusufk May 15 '12 at 9:42
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There's no way to avoid having the front wheel being apt to lock up and flip you. The width of the tire will make only a miniscule difference, since a front wheel basically never skids (except on very slippery surfaces) -- it either rolls or locks up. (The only logical "fix" for this is my "power brake" invention that no one has ever seen fit to build. ;)) – Daniel R Hicks May 15 '12 at 11:27
    
Yusufk, as you slow down, you automatically lose traction on your front wheel as your weight shifts forward. Most braking power comes from the front wheel. Until @DanielRHicks' invention takes off, the best way to brake is to primarily use the front brake but to be careful not to make it lock up. – amcnabb May 15 '12 at 15:25

Larger front tire for the win, its a trick messengers use. Increase braking power w/ out increasing as much weight as running both tires large.

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Well if it works for them all good. I'd say the grippiest tyre should be on the front because its harder to recover from a front wheel slide, and the larger should be on the rear for weight support. Bike messengers won't be as heavy on the rear as the average rider. – Criggie Nov 18 '15 at 22:25
    
@Criggie For a road bike, the kind of friction (grip) we want from bike tires is static friction, which is independent of the contact area. Wider tires give more grip when we're on a loose surface, or sliding, and so are more use for MTBs. On a road bike, 99% of the time sliding the front tire is road rash time. – andy256 Nov 19 '15 at 3:25

I am running a 32c up front and a 23c in the rear in my single speed road bike. I commute a lot on rough roads and it rides a lot smoother.

So far it works great for me. I also remember in the old days we would run a fat tire up front and a skinny tire in the rear on our BMX bikes.

All I can say is the best thing to do is borrow a different sized tire or find an old one and experiment and if it feels right for you and go out and buy what works

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Welcome to bicycles.stackexchange. It's great to hear about your experience,. but we really prefer to have reasons rather than only anecdotes. If you can edit your answer to say why that arrangement works and ideally what the pro's and con's of that rather than same-size of fat-rear setups are that would be great. – Móż Jan 13 at 10:11

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