High performance and low profile logically fit together when it comes to tire design. Or more accurately, high performance and aspect ratio.
The lower the aspect ratio, the wider the tire. That is because the aspect ratio is the height of the tire’s cross-section — its profile — divided by its width, sometimes called the section width. Size 225/65R17 has an aspect ratio of 65, which means the tire’s profile is 65% the length of the width. A size 225/50R17 has a profile 50% of the length of the width. So the lower the aspect ratio, the shorter the profile (at least the shorter it looks comparatively) and the longer the width.
That begs the question: How low can a profile go?
“As section width is the ratio of section height to section width, 25 or lower must have a very wide tread to make the sidewall height adequate,” says Rick Brennan, executive director of marketing for Falken Tire Corp. “With any specific aspect ratio, like 25, the wider the section width, the taller the sidewall becomes in actual measurement.
“Ultra-low aspect ratios could be feasible sidewall heights, but the section widths would not only have to be much wider than we see today, but also need a certain amount of flex area to do all the things that are requested of it. And, of course, wider, taller tires need a big wheel well in the vehicle to fit. So the minimum section height is the real limiting factor.”
Rudy Consolacion, executive vice president of the Tire & Rim Association (TRA), says the lowest profile TRA has standardized is a 25 aspect ratio. Six sizes have that aspect ratio:
TRA’s counterpart in Europe, the European Tyre and Rim Technical Organisation, has standardized a 20 aspect ratio size: 375/20R21, he adds.
Brennan says the lowest aspect ratio on a pneumatic tire he can remember is a 385/15R22, developed by Kumho Tire Co. Inc. in 2008.
At the Specialty Equipment Market Association (SEMA) Show in 2009, I remember Nexen Tire America Inc. displayed its N3000 in size 365/15R24 on the trade show floor. But it was showcased behind glass and not in production. The tire is available in size 275/25ZR24, however. “With the sidewall height a hair above 3 inches, the lowest profile tire Bridgestone currently offers is a 255/30R19,” says Robert Saul, director of consumer tire product strategy in the U.S. and Canada for Bridgestone Americas Tire Operations LLC. “This is not due to an inherent technical limitation; it’s just based on what we perceive there to be a market for — this size can be found on a handful of cars from BMW, Audi and Mercedes-Benz.
“The lowest profile size on any vehicle currently offered in the U.S. from the factory appears to be 245/30R20. That size has a sidewall height a little below 3 inches and is found on, most notably, the Honda Civic Type R.
“With pneumatic tires, ultimately the air is what carries the load of the vehicle. So all other attributes being equal, when you decrease the height of a sidewall, you are limiting the amount of air the tire can hold, thus limiting the load a tire can carry.”
In addition to load carrying limitations, Saul says low profile tires offer less dampening. “On the flip side, some drivers may prefer that more direct, responsive feel.”
So there is a realistic limit, at least with a pneumatic tire.
“As non-pneumatic, integrated tire/wheel and other emerging technologies evolve, it’s possible that the terms ‘profile’ and ‘aspect ratio’ could eventually become terms referencing only tires from the past,” says Bob Toth, director of industry relations for the Goodyear Tire & Rubber Co.
When that happens, the profile could go even lower.