Real world diff in speed due to tire size
 

I have heard and heard that the wider the tire the slower the tire. I get the concept, but... What is the REAL difference in speed? I am currently 290lb riding 700c x 28 and am going to start commuting both ways to work. I like the idea of going to 32's and am wondering the real difference in speed. I seem to average around 15 mph, would moving to 32's reduce me to 14 mph or is it more like 14.9mph?

Has anyone ever done a real world comparison between two different tire sizes that are one size off, like 23 vs 25, 25 vs 28, 28 vs 32, etc? If so, what did you discover?

I just started a thread on this recently:

http://www.bikeforums.net/commuting/...h-trouble.html

I have only begun to research this subject myself, but my tentative learning is that "all things being equal" including tire pressure, the wider tire has less rolling resistance but more wind resistance, thus is likely to be faster at typical "commuter" speeds, because it deflects less under load. The hitch is that there's a point where wider tires are rated at a lower max pressure, negating the "all things being equal" thing.

I found this article to be coherent:

Rolling Resistance | Schwalbe North America

Probably negligible next to the gains in speed you'll make by improving your fitness through commuting regularly. 700x32s should be a little more comfortable and have a little more safety margin against pinch flats. :thumb:

You've heard wrong.


Tires: How Wide is too Wide? | Off The Beaten Path

In the real world, speed is all about the legs (and the cardiovascular system). Moving up to 32 mm from a 28 mm tire isn't going to slow you down.

Select tires that won't leave you with a flat at the side of the road, in a sufficient width to be comfortable and able to handle the unavoidable bumps.

And those tests were conducted at 16 mph. The only time I ride at such a slow speed is when I'm on a group/social ride.

True. But in the real world, most commuters aren't worried about the tiny increases in air resistance that would result from a wider tire. It gets lost in the noise of our clothing selection for the day and how our panniers are packed and compressed.

yep...for the typical commuter drag from cycling position, clothing, and baggage is typically huge.

We might as well just get this out here now:

http://upload.wikimedia.org/math/9/9...7b238e5de9.png

I commute on 42mm and then went to 40mm for my new tires. There a tiny tiny difference in speed but because, but what I noticed the most was that because the new tires turned out to be more supple so the ride is actually plusher even though tire is smaller and the pressure is slightly higher.

At 15 MPH, my bet is that what you'll notice is that the larger tire will be slower to accelerate because higher moment of inertia due to increased weight. But this won't affect your top end speed. If you get to 20 MPH and keep it there you might notice it, or you might not. You might be a few seconds or a dozen seconds slower over an hour with larger tires, but unless that is the difference that get you on the podium, I say it doesn't matter.

There's much more to rolling resistance than width alone... so it's never going to be a good discussion if we talk about 28mm vs 32mm in generalities. I was using 28mm tires for a while, but I was unhappy with their performance on some gravel roads... when they wore out, I went back to a 32mm on said bike. Honestly, I don't notice a speed difference between the 28mm tires I had and the 32mm tires I currently have.

I have commuted on 23, 25, 28, 32 and 35s. FWIW my fastest commute times are consistently set on 28s. For my setup and weight, 28s seem to be a happy balance.

Ridden 40,32,28, and 23 on various bikes. Have to say I had a set of 23s that were AWFUL and a set of 40s that were great. Its more about the engine and the tire itself not the width. If you want to hold over 30kph all day and you have the fitness then your position on the bike will make more difference. Personally I gave up on Aero as riding 12 hours plus a day is torture on a road bike. Its faster yes, but comfort trumps outright speed for me.

I moved from low TPI 32mm hybrid tires to high TPI 28mm slicks. It definitely starts up faster, but once I'm at speed there's not much difference. Wind, baggage, and my leg strength has a lot more to do with average speed.

For me, 28 mm is a minimum. The worse the roads, the better wider tyres get - both more comfortable and faster.

Speed increases with circumference.

Well, from all I understand, that isn't actually true. Larger circumference gives you a higher 'gearing', but if you have smaller circumference wheels with higher gears on it (I am thinking recumbent), you can go really fast! I have heard that 26" are better at climbing because, given the same drive train gearing, they are lowered geared. (of course I am assuming the same width/weight tires)

The other thread hasn't died, so it's a little painful to see this thread start up. But you asked in earnest, so you deserve an earnest answer.

I've learned a fair bit from the other thread, chiefly that it's a very complicated question (and therefore answer). Maybe the best answer is for you to try various tires and see what YOU think the differences are. All things being equal, the wider tire has less rolling resistance, which is counter-intuitive and is counter to conventional bike wisdom. But there are counter arguments. First of all, rolling resistance is not the only concern. Second of all, all things never are equal.

A lot depends on your bike, your riding style, your physical condition, and the conditions you travel under.

And to any extent that your bike makes you faster, you lose most of the time advantages at lights and other stops and slow-downs. Coming back up to speed from a slow-down or stop is more costly than you think. So if you take a fast, light bike and no luggage and pedal like a bat out of hell one day, you'll get a high rate of speed. Next day, take a practical, heavy commuting bike, ride at a leisurely pace and carry luggage. Looking down at your speedometer, you might see a significantly lower speed. But you may not arrive at the office much later. That's because traffic and such make you slow down and stop more than you might think.

Then there is the consideration of enjoyment. Some people like light, fast tires and are willing to tolerate harsher rides. Some people like plush rides and are willing to let their bikes be heavier from them. Also, some people don't buy well. They buy wide heavy tires in pursuit of puncture resistance, but they get a super heavy tire which is hard to pedal. It might give them the impression that wide tires suck universally.

In one sense, quality matters more than width or weight. I've ridden some narrow racing tires that are surprisingly supple and not harsh. They cost money, though. I've also ridden some wide tires that don't feel heavy. They are not particularly puncture resistant, though. There are some technological breakthroughs, but they cost money, too. I've been skeptical of the reports about the Schwalbe Marathon Plus tire because it lasts so long and resists punctures so well. It's heavy, too. So I couldn't believe it would truly ride well. I figured people had made compromises, leaning towards puncture resistance at the cost of ride quality. I haven't tried it, but a friend I trust tells me he is astonished at how it rides more nicely than another well reputed tire that weighs half as much. And I can believe it. Breakthroughs do happen.

Your next question might be, what is your favorite 25mm tire and why? And same with 28mm, 32mm, and so on. These questions might get you somewhere.

For years, my favorite width was 28mm. Now I'm leaning towards preferring 32mm. Tastes change. I still ride narrow (25mm) tires when I'm in the mood.

I was considering the same aerodynamic position (upright) and 406 vs 559 vs 622. Other changes don't allow for an accurate comparison.

to the OP, if you're just debating the small difference between a 28 and a 32 for yourself, then simply follow these easy guidelines:

1. a high quality 28 is generally preferable to a low quality 32.

2. a high quality 32 is generally preferable to a low quality 28.

3. the differences between a high quality 32 and a high quality 28 will be mostly negligible for most bike commuters.

call me crazy but how about just buying the 32c tires, putting them on your bike, and riding to work with them? Let us know if you notice a difference.

@ the same RPM , a really big wheel will be moving faster than a smaller one.. BUT you still have air-resistance pushing back. :rolleyes:

fast is about lowering the air resistance , think: riding in something shaped like a Fish.

I am the OP, I think you just summed it up well!

(though I don't have fenders yet, my Surly Pacer will allow them on 28's not 32's, so I am going to stick with 28's)

Next question, which others have suggested I ask: what high quality 28's would you put on your bike for commuting in cold weather?

i have 700x28 Conti Grand Prix 4-Seasons on my foul weather bike. it's a good wet weather tire.

i have 700x35 Schwalbe Marathon Winter studded tires on my dedicated winter bike. i like the safety and security of studs during ice season.

i have 700x23 Vittoria Rubino Pro's on my road bike, but i only commute on her when i'm more or less guaranteed to have a dry ride (no fenders).

I can say from experience that I move almost the same speed on a mountain bike with street tires as I do on a road bike. I'm sure there's a difference, but it's hardly noticeable.