Commuting:Does Size Matter?
 

I am relatively new to commuting and am currently riding a '05 Cannondale 50/50 (17 miles one way) to work. The bike has 26x2.25 tires and a number of other commuters have commented on the tire size being to big. They are semi slick and my commute includes city streets, hills ,bike path gravel path w/ lost of pot holes etc. would changoing to a smaller tire size really make difference in speed? Currenlty I am average about 14mph and am carrying 20+ lbs in weight as I have to carry a full suit to work. Thanks!

Thinner tyres can accept higher pressure which makes them roll faster. Fat tyres are less aerodynamic which comes into play at higher speeds.
You can ride rough tracks with a 1.5". Pot holes can cause problems with any wheel. The best policy is to memorise your route and avoid them.
Consider leaving as much luggage as possible at work.

It certainly does. This weekend I changed my 7-year-old son bike 20" tires from 2" 40psi knobby to 1.3" 90psi slick, and his max on his way to school rose from ~12mph to ~15mph with lesser effort.

Fat tires work much better for commuting in snow.
Besides that.... what everyone else said.

Yes and no.
A thinner higher pressure slick will improve your speed somewhat but not as much as most would believe. Usually when you go thinner you talk about going from a low pressure knobbie to a high pressure slick. That is where most of the difference comes from. If pressure, tread and casing construction is the same a fatter tire will actually have a lower rolling resistance. However this is seldom the case in real tires. If your running a 40 psi tire then going to something like a Marathon Slick 26x1.75 at 70 psi would still give you good stability and durability but would roll considerably better. A narrower slick at 100+psi maybe faster but will be more fragile. If your tire is already a 65 psi tire then just ride what you got.
If one of my bikes would fit it I would go with a 26x2.35 or a 700cx60 Big Apple. This would give a nice stable contact patch but still roll pretty good.
Craig

Most agree with this dude.

Note that high pressure skinny(er) are much less forgiving in terms of comfort. Currently I am running 28 @ 100 psi, unexpected wide cracks can feel like a kick to the groin :eek:

Try that with a 23mm @ 120psi. Thats what I was running this summer as 23mm was the biggest that would fit under the fender and my 220lbs doesn't give much room to lower the pressure without pinch flats. Note that I have since sold that bike and now run nothing less than 28mm.
But luckily were still talking > 1.3" (35 mm) for the original poster. All of the 1" (28 mm) tires I know of in 26" sizes are fragile high performance models that I don't recommend for commuting.
Craig

PS: I know my metric to inch conversions are not the 25.4 mm to inch that is expected but that is how most tires are sized when both measurements are given. I assume it is due the tires being measured differently for American and European sizing standards.

I've ridden singletrack trails on a CX bike that are far rougher than any road in any city with 700x32c knobbies (sometimes 37c in front for sand) and never had a problem. I'd go smaller, perhaps to 1.5" also you don't need tread for potholes or dry light gravel on flats (although it is needed for wet dirt/snow conditions, steep hills and especially cornering on gravel). When you say semi-slick, if this is the type with slick in the middle and tread on the sides, I found those to be bad for city as you loose traction when cornering, when you need it most.

Al

Thanks for all of the info! I am already running 60 psi IRC Lover's Soul so I guess I will use what I got!

Another big gain that is often overlooked is tire weight. My 26x1.25's are much faster than the slick 26x2.125's. They're both slick, they both roll nicely. But the big ones are very heavy, so they're not as easy to get up to speed. But oh, the ride. They ride so very very nice! I'm thinking about switching back to them simply because the roads around here have gotten so bad, the 1.25's are jarring. I might even get some 1.75 or 1.9's in the future, to try to strike a balance between the two.

I saw a 50/50 hanging up in a LBS. Took one look at the tires and said whoa! There's alot of tread on there to squirm around and slow you down,plus many little creavases to hold bits of glass and whatnot.

Personally,unless most of your ride is on dirt/gravel,I'd swap them for something smoother. I'd recommend Michelin Transworld City's in either 1.95 or 1.5" width. I run them on my Sedona(bad weather bike) and they rock. Smooth rolling,puncture protection,and reflective sidewalls. Save the IRC's to swap on for when it snows.

Yea those IRC's are not exactly slicks. You'll probably gain 1-3 mph by going with a slick in the 1.5-1.75" range. If speed is more important than comfort then a 1.25-1.35" maybe what you want.
Still the IRCs are not knobbies either so you won't see a dramatic improvement.
There are some much lighter tires that will be even faster but light weight comes at the expense of kevlar belts and durable rubber so I avoid them for commuting.
Craig