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Living Car Free Do you live car free or car light? Do you prefer to use alternative transportation (bicycles, walking, other human-powered or public transportation) for everyday activities whenever possible? Discuss your lifestyle here.

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Old 12-29-10, 10:06 PM   #1
bragi
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Does tire size make any difference?

I'm going to try something novel, and just talk about bikes:

I've been riding a touring bike with 622 x 37 tires for about 2 1/2 years, and I've been very happy with these tires. They deal with broken pavement well, they're comfy, and they pretty much never get flats. This Christmas, though, my girlfriend, noticing the wear of my tires, gave me new ones, which I greatly appreciated. The only thing that gave me pause was that the new, very expensive tires she gave me (Schwalbe Marathon) are 622 x 28. Being curious about the benefits of skinnier tires, I put them on my bike, and went for a ride. At first, I was unimpressed; my speed was about the same with the new tires. Then, as I continued to ride, I gathered these impressions:

1. On hills, there is no difference; weight is much more of a factor than anything else going uphill, and downhill, well, then it's just a matter of gravity...
2. On flat ground, though, there seemed to be a noticeable difference; I seemed to be able to go about 2.5 mph faster on the new tires with the same amount of effort, all other things being equal.

My question is this: Am I fooling myself? Does tire size even make any difference at all when you're riding a heavy steel touring bike on a beer run? I'm having a little trouble believing that such a small difference in surface area can mean much in terms of performance.
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Old 12-29-10, 10:28 PM   #2
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What were the old tires, and what pressures did you run and what are you running at now? Marathon what? There are many different kinds.
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Old 12-29-10, 10:38 PM   #3
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I have two tire sizes on my bikes: 32 Schwalbe Marathon Plus and a 28mm Schwalbe. The difference in speed is not that great, but the 32mm are a bit more comfortable (although you might be able to achieve something similar by reducing air pressure in the thinner tire... say 5 pounds.)

I also have a pair of 40mm studded Nokians on my winter bike. Now that thing is slow.

However to answer you question, I would say the tire width is just one factor in comfort and speed... along with tire material, degree of tread, air pressure and road surface.
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Old 12-29-10, 10:40 PM   #4
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My old tires were 90 psi (6 BAR) Continental, 622 x 37. The new ones are Schwalbe Marathon, 100 psi (7 BAR) 622 x 28.
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Old 12-29-10, 10:50 PM   #5
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My question is how did an old fart like you get such a nice girlfriend?
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Old 12-29-10, 11:11 PM   #6
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My question is how did an old fart like you get such a nice girlfriend?
I'm very blessed, I know...
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Old 12-29-10, 11:46 PM   #7
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The riders who are after performance and speed will go for the thinnest tires they can find and they insist the tires make a huge difference. They'll try for 25 mm or smaller.

My riding is primarily commuting, utility riding in town and touring, so my needs are not the same as those of the performance riders. Right now I've got 32 mm tires on my road bike and I won't go smaller than 28 mm. The reason is the riding surfaces. Some of the roads in town are nothing more than collections of patches — the result of years of cost-cutting measures by the municipality. Narrow tires on those roads will be uncomfortable at best. Also, some of my favourite roads in town and nearby are gravel and dirt. Such surfaces are not good friends with narrow tires.

I'm now planning a tour for 2011 which will include several hundred kilometres of gravel and dirt. For that tour, I'm planning on 40 mm tires.
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Old 12-29-10, 11:58 PM   #8
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Tires can make a difference, but it's not just a matter of the width. I went from some 28mm tires with very stiff sidewalls (Armadillos) to 37mm tires that were more flexible and found there to be significantly less rolling resistance with the new tires even though they were a little heavier. An aggressive tread also leads to energy losses and slower speed - and frequently wider tires have a more pronounced tread pattern

An increase of 2.5 mph seems like a lot, but it's hard to say if the tires could make that big a difference without knowing which specific tire you had before and which model of Marathon you're using now.
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Old 12-30-10, 01:22 AM   #9
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Well, you're going from wider to narrower tires, but you're also going from old to new, lower pressure to higher, and probably from cheaper to premium. So there may be several factors at work. Congratulations on your Christmas gift and enjoy the extra 2.5 mph!
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Old 12-30-10, 11:03 AM   #10
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The riders who are after performance and speed will go for the thinnest tires they can find and they insist the tires make a huge difference. They'll try for 25 mm or smaller.

My riding is primarily commuting, utility riding in town and touring, so my needs are not the same as those of the performance riders. Right now I've got 32 mm tires on my road bike and I won't go smaller than 28 mm. The reason is the riding surfaces. Some of the roads in town are nothing more than collections of patches the result of years of cost-cutting measures by the municipality. Narrow tires on those roads will be uncomfortable at best. Also, some of my favourite roads in town and nearby are gravel and dirt. Such surfaces are not good friends with narrow tires.

I'm now planning a tour for 2011 which will include several hundred kilometres of gravel and dirt. For that tour, I'm planning on 40 mm tires.
You make some good points here. I'm holding on to the fatter tires just in case.
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Old 12-30-10, 11:51 AM   #11
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I've always been told it is the motion in the ocean that really makes a difference.
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Old 12-30-10, 12:15 PM   #12
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Just to make sure...you did change the tire size in your computer to account for the different circumferences of the tires, right? That change could account for the 2.5mph. Simple thing, but I'll admit to forgetting it once.
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Old 12-30-10, 08:11 PM   #13
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Just to make sure...you did change the tire size in your computer to account for the different circumferences of the tires, right? That change could account for the 2.5mph. Simple thing, but I'll admit to forgetting it once.
Yes, that's the last thing I did before taking the new tires for the inaugural ride. I can understand why you asked about this, though; that sort of thing is not that unusual with me...
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