hackybiker

Hi all,

I have a 99 Schwinn Frontier, a low-end mtb (it's a tank!). It suits me fine for getting around the city. When I get some cash, I may get something lighter and with better components.

A few years ago I decided I wanted a bit more speed, so I switched out the stock 1.95" knobbies for 1.75" Michelin semi-slicks. The difference was significant!!

Now I'm thinking about going to 1.25" or 1.5" semi-slicks. The rims are 20mm, I think. I wanted to get some feedback on whether this would be worth it. Would the width difference of 0.25-0.5 be negligible for rolling resistance? I am just doing street riding--some hills (I'm in Seattle), maybe some rough park roads now and then, but nothing more intense than that.

Thanks for any advice!

Bikewer

There is a constant debate about this very subject, with some feeling that (at least with road tires) the slightly wider contact patch of a wider tire is offset by the small size of the contact patch fore-and-aft.

We run Continental Town-Country tires on the police bikes at a nominal 1.90 width; but we expect to have to negotiate a bit of off-road as well. (not much....mostly grass)

I would say you would not experience any great jump in performance going from a 1.75 down to a 1.5 or 1.25, as long as they are kept properly inflated. No doubt someone has a table of excruciatingly-exact figures to study.....

DannoXYZ 

Here's a good article: Tire Rolling Resistance

Terry Morse also has a good website on rolling-resistance with tables of data from actual in-the-field testing by Jobst Brandt. Here's a chart that explains it all:



Compare two tyre models of different widths, like Specialized Touring in 25 vs 28c. Or Avocet20 in 25 vs. 28c or Avocet30 in 25 vs. 28c. You'll noticed that in ALL the cases, the wider tyre rolls faster with less resistance at the same pressure. You'll also see that pressure makes a much bigger difference in rolling-resistant than tyre-width. In all cases, the difference is in GRAMS of rolling-resistance.

A bigger factor in your observed results is probably weight and wind-drag. Larger wider tyres block a lot more wind and the faster you ride, the larger wind-resistance contributes to total drag.... which is measured in KILOGRAMS.

well biked

It's true, even though it's counter-intuitive: all other things being equal, wider tires have less rolling resistance than narrower tires. BUT, because the amount of air pressure you can safely put into a tire is largely determined by the amount of air volume the tire holds, the narrower tires can be run at higher pressures, which usually more than negates the narrower vs. wider factor, not to mention the amount of wind drag as mentioned above. Bottom line: skinny tires are usually faster when all factors are considered-

DannoXYZ 

I would say that the majority of your initial improvement was in going from knobbies to semi-slick tread on the tyres. Going the next step to even narrower tyres will give you a much, much smaller improvement. As previously mentioned, it's the pressure that makes a difference, not really because of width. Just that narrower tyres allow you to pump up a tyre to higher maximum pressures... assuming you're using maximum rated pressure. In most real-world applications, people adjust pressure to balance ride-quality and flat-resistance, so a 28c tyre @ 100psi will probably be close to a 23c @ 120psi in rolling-resistance; of course, brand/model along with tyre-construction makes a big deal here too.

I say go for a 1.5" semi-slick, will still give you enough contact-patch at a lower pressure to be able to handle the occasional off-road trip.

Old Dog

I just replaced my 1.95" tires with 1.25". They have some tread, but are not knobby. Neither were the 1.95". I moved from 55 psi to 90 psi. The difference is dramatic. I feel that I am going 40-50% faster. I was cruising at 10-12 mph. Now, I am cruising at 15-18 mph. It is much easier climbing hills. I love them.

Now for the other issue - the first time I rode with the new tires, I hit something small in the bike lane and almost lost it. I over corrected and swerved across three lanes of traffic, finally getting control of my bike in the fast lane. Thankfully, I lost it in a momentary gap in traffic and wasn't killed.

I love my new tires, but I am learning to be a lot more alert about road hazards.

hackybiker

Thanks everyone for all the great info and advice! Sounds like the improvement, if any, won't be that huge, so I'm leaning towards just keeping my existing tires for now. And checking the pressure more frequently... I didn't realize pressure was so crucial, though it totally makes sense.