# How does a bicycle tyre and wheel affect its performace and speed?

I have 700 x 38c wheels on my bike. While reading online I found that wider tyres have lower rolling resistance at the same inflation pressure than narrower tyres but they will be a little heavier and will offer more aerodynamic drag. I am not bothered about the weight because it won't make much difference if I am riding mostly on flat ground -- aerodynamic drag and rolling resistance drag are far greater sources of drag than that caused by the direct increase in weight of the tyre.

Considering that, I am not sure which will perform better on the road. My online research shows that wider is better.

What are the other factors of a wheel (like untrue wheel) that contribute to performance of a bike.

• Please site where online research that wider is better for either aerodynamic drag or rolling resistance. Dec 31, 2014 at 20:20
• As far as I have seen, thinner tires have lower rolling resistance. They offer less surface contact with the ground and use higher pressures which gives less flexing of the tire walls. Dec 31, 2014 at 21:25
• To paraphrase Sheldon Brown: At the same pressure, similar constructed tires of different widths will have lower rolling resistance for the wider tire (but the wider tire should be running at a lower pressure in the first place, making this point moot). But, increasing tire pressure reduces rolling resistance. Dec 31, 2014 at 21:49
• Ignore the aerodynamic issue -- the effect is negligible unless you're racing. Up to a point, increasing pressure lowers rolling resistance, but again, if you're above about 80psi on a 38mm tire increasing pressure will have negligible effect. Whether increasing tire width beyond 30mm or so will reduce rolling resistance is hard to say -- there are competing factors involved. What does have an effect is the tread of the tire -- for low rolling resistance you want a nearly treadless tire. Jan 1, 2015 at 0:06
• @daniel i have been experimenting with 38C tyre pressure by increasing it to 90,100,110 PSI.recently i put 110 PSI in 38C tyres.way beyond the recommended value of 50-75 PSI.I rode on pretty smooth rode except for some distance of pebbles and rough road.Do you think its safe to do that on my 38C tyres? Jan 3, 2015 at 4:07

## 2 Answers

The general answer is "it depends". Certainly, weight reductions help increasing speed, but improving the rider's strength and good bike fitting will go much further for improving performance than tire faffery. (Obviously, for professional racers, this advice doesn't apply - cutting grams and everything is part of what they need to do to win).

Wider tires should be run at lower pressures than narrower tires. It is true that rolling resistance drops with pressure increases and for similar tires of different widths at the same pressure the wider will have lower rolling resistance (but this is moot by the prior sentence). Note the word "similar" - a knobby tire of the same width will have higher rolling resistance than a slick.

Wider tires can better absorb bumps and what not, so they can increase control giving net better performance in the real world. However, as you see on many road race bikes designed for purely nice pavement, thin tires are normally spec'd.

As for aerodynamic drag, the paper "Aerodynamic Characteristics of Low-Drag Bicycle Wheels", Aeronautical J., Vol. 99, No. 983, Mar. 1995, pp.109-120 (summarized here) says ~10-15% of the drag is due to wheels, and by switching wheels you can get net 2-3% improvement. This is tiny, especially when you look at how much fancy aerodynamic wheels cost (and their low durability). For someone who is not racing, its almost surely better to put the money you might spend on a fancy aero wheel into having a durable wheel.

Now, to the reality of the situation: A wider tire is going to give you better ride quality and you can get very good rolling resistance by picking a smooth tire for road use. You have to balance durability of the tire and the wheel if you choose to do improvements here. For most people who are not in race situations, pick a decently wide tire, play with the tire pressures so you get a good ride and low rolling resistance and move on with your life. In theory, depending on the terrain, you might be able to go faster with a narrower higher pressure tire, but the possible ride and control effects may hurt you in net.

• That article is almost 20 years old snd Specialized Tri Spokes aren't really state of the art wheels anymore, I'm sure you could do better now but it would be mucho dinero,
– Eric
Dec 31, 2014 at 22:40
• hi Batman, i understand the fact that improving strength is of utmost importance but if i am travelling long distance say 100 miles then smaller improvments on bicycle tyres might save me some time say an hour or so. Dec 31, 2014 at 23:56
• I seriously doubt any tires will make an hour difference on a 100 mile ride, bar grossly inappropriate tires (e.g. slicks for the Dirty Kanza). Jan 1, 2015 at 0:18
• @Eric - I doubt the numbers have changed that much, despite what all the marketers would have you think for a standard bicycle. Jan 1, 2015 at 5:18

When I raced back in the eighties /'nineties 21 and 22 mm tires were common, some folks (me) experimented with 18 mm tires. Since then they've figured out that wider tires are faster, but not that wide. In a flat smooth time trial they're commonly using 23 and 25 mm tires now. They wouldn't use a tire as wide as 38 mm in Paris Roubaix and parts of that are practically off road. I think the pros would be running really wide tires in flat time trials if it were faster.

• Even though I went from a moderate tread pattern to a more knobby/aggressive pattern, I noticeably picked up speed switching from 2.25" wide to 1.875" wide tires on my mountain bike. Feb 20, 2021 at 18:55
• For our metric friends that's going from 57mm to 48mm
– Eric
Feb 24, 2021 at 19:38