Finding The Correct Tire Size & Pressure

The best formula to go fast and fight flats

When we received a letter from Don Scheese asking about tire pressures we decided to steer him in the direction of Jake Pantone from Enve as the carbon wheel maker has been on the leading end of the tire pressure debate for the last few seasons.

 

TIRE TECH: Too much pressure?

I read with great interest the article in your November 2018 issue “Too Much Pressure.” I ride a 2018 Scott Addict 20 disc bike as an all-arounder with two sets of wheels and tires—one for pavement (with 28mm tires) and the other for gravel (with 35mm tires). At the end of the article Enve’s Jake Pantone says, “Just because a tire is larger, it doesn’t mean it’s slower.” My question is, at what point does a wider tire slow you down, all else being equal? Surely a 2-inch-wide tire would be slower than a 23mm tire, but what about a 28mm tire versus a 35mm tire? My own experience suggests there is some difference but not a lot. I’d like to see a future article in your magazine address this question with some empirical data. Enjoy your magazine very much with its nice variety of articles and personal perspectives. Never stop exploring—by bike.

Don Scheese
Placitas, NM 

Jake Pantone from Enve responds: I’ll try to provide more insight for Don here, but delivering a collection of empirical data is going to be hard, as it can’t really be pieced together in an easily digestible manner or without a major effort from engineering and product, which would take months to compile given we’re in busy season. But, here are the factors to consider: 

—Tire/rim volume

—Tire construction

—Tire pressure

—Road surface 

So to start, I’ll answer the reader’s question: “At what width does a tire make you slower?” What we’ve seen in our wind-tunnel testing is that there are minor losses in the steps up in volume from 23 to 25 and 25 to 28. However, when you step up from a 28mm tire to a 32mm, you see a much larger loss in aerodynamic terms strictly speaking, and this depends on the speed. At lower-speed tests of 32 kph/20 mph, we see less losses between the 28 and 32mm tires, but as the speed increases to 48 kph/30 mph, the losses multiply quickly.

“Enve’s Jake Pantone says, ‘Just because a tire is larger, it doesn’t mean it’s slower.’ My question is, at what point does a wider tire slow you down, all else
being equal?” 

But there is much more to the story. First, not all tires are created equal. Some constructions deliver lower rolling resistance than others. So, there exists the possibility that if you were going to ride a very rough road and one rider opts for a heavily reinforced 28mm tire to prevent flats and another rider selects a 35mm tire with a very fast-rolling construction, it is possible that the 28mm tire may be 3–6 watts faster in terms of aerodynamics, but the 35mm tire could be 6-12 watts more efficient in terms of rolling resistance. So net, the 35mm tire could be the more efficient choice. 

Again, every tire is different, and we don’t have rolling resistance data paired with aero data for all the tires out there, but this is something to think about when considering what it really means to have a fast wheel and tire set up. In this explanation, I am of course over simplifying things. Rider weight, tire pressure, rim width/type and road surface are all going to dictate what equals ultimate efficiency. In general, lower volume tires/wheels, should be run on smoother terrain at higher pressures, than a set up with higher volume tires/wheels on rougher terrain.

Photo: Linda Guerrette

 

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