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We hear it on a regular basis: What’s the widest tire I can match beneath my automobile? Greater is at all times higher, proper?
Not essentially. From a efficiency standpoint, what issues greater than tire width is perfect wheel width to help the chosen tire measurement. However don’t take our phrase for it. Let’s have a look at some knowledge from our a few years of tire testing.
What made our CRX quicker: wider tires or wider wheels?
One in every of our tire testing mules, the One Lap CRX, can use a staggered wheel fitment: 15×9-inch wheels up entrance and 15×8-inch wheels within the rear.
However we even have a number of units of every of these wheels, so it’s simple to run a wide range of entrance wheel and tire sizes for comparability. And since our front-drive machine achieves most of its grip work with the entrance wheels, it’s simple to quantify the results of those completely different setups merely by swapping out the fronts.
Let’s have a look at some knowledge from a check we did at Harris Hill Raceway utilizing the BFGoodrich g-Pressure Rival in two sizes mounted on two completely different entrance wheel widths. Each tire sizes have the identical general diameter, so gearing is unchanged. And the wheels share the identical ET36 offset, so monitor width additionally stays fixed.
We will see that going from a 205mm to a 225mm tire on the same-width wheels delivered no higher lap occasions. However mount that 225mm tire on a wider wheel, and all of the sudden the automobile has extra grip all over the place, circulating a strong half-second faster.
Nonetheless not a believer in correctly matched wheels? Right here’s some knowledge collected when testing the Maxxis VR-1 200tw road tire, once more at Harris Hill.
Earlier than hitting the One Lap of America, first a significant funding: the proper wheels. Pictures Credit score: Tom Suddard
We’ve additionally examined this idea on our more moderen One Lap of America experience, a McLaren 720S. As a mid-engine, rear-drive machine, this automobile comes from the manufacturing unit with taller, wider rear wheels.
However there’s nonetheless room for enchancment with wider wheels on each ends. Customized cast wheelmaker Finspeed made us a set that’s 1 inch wider entrance and rear. Right here’s some Harris Hill knowledge evaluating Michelin Pilot Sport 4S tires on the OE wheels versus the identical tires on the Finspeeds.
Discover a development? For optimum on-track efficiency, we have now seen quicker laps with the broader wheels.
This additionally often equates to about half an inch wider than the measured tread width, however it could possibly fluctuate a bit as a result of number of tread crown profiles and the dearth of requirements for this dimension. On condition that wheels don’t at all times are available in half-inch width increments, going as much as the following full inch commencement is usually required.
One exception to our rule of thumb comes within the type of Hoosier. Its A7 and R7 DOT R-comps are quasi-street-legal however have the development and dimensions of a race tire. The super-stiff sidewalls don’t want as a lot help from a large wheel as most actual road tires. Regardless of that, there are positive factors available–simply not as massive.
Right here’s some knowledge from a latest DOT R-comp check. Observe that Hoosiers additionally run very extensive for his or her marked measurement. These 205s have extra tread width than the 225 road tires within the check referenced earlier. Consequently, the listed rim width vary is a crimson herring on this case. These 205 marked tires match simply tremendous on a 9-inch-wide wheel and outpace the 8-inch-wide wheels by 0.3 second.
In fact, motorsports guidelines can get in the way in which of optimizing efficiency. Wheel widths are sometimes restricted, both immediately by dimension or not directly by a most mounted tire width template. Generally the alternative is true, the place the tire measurement is restricted however not the wheel width.
On our Triple Risk Miata undertaking automobile, we as soon as ran right into a scenario the place a narrower tire was quicker resulting from a wheel width rule. We initially saved our ND-chassis Miata rules-compliant for SCCA C Avenue autocross, which additionally translated to legality for the SCCA Time Trials Sport class.
That meant 7-inch-wide wheels, however the guidelines allowed us to go up or down by an inch in diameter if desired. For autocross use, we would have liked a tall tire to cut back shifting, so we selected a 225/45R17. With a 7.9-inch tread width, that tire actually wished a a lot wider rim, and a tall 205 would probably have been simply as quick. Sadly, appropriate tires aren’t made in that measurement.
For the monitor, nonetheless, a shorter tire is often a bonus because it delivers higher acceleration in all gears. We selected a 205/45R16 and located a full second over the taller, wider 225s. Along with the gearing benefit, the wheel-and-tire mixture was a full 24 kilos lighter in rotating mass and lowered the automobile’s heart of gravity by nearly an inch.
Might going smaller in wheel diameter additionally assist? The info reveals the reply.
One ultimate knowledge level utilizing the Triple Risk ND: What about larger wheels and larger tires?
After we lastly gave up on C Avenue autocross and targeted on a direct Sport 5 construct for Time Trial competitors, we mounted the widest wheels and tires that will match on the automobile–245/40R17 tires on 17×9-inch wheel–and located much more time. We did surrender some acceleration resulting from gearing and weight, however we carried far more velocity by every nook, netting a strong 0.7-second enchancment.
The subsequent time you end up wanting to higher fill out these fenders, first have a look at your wheels. Are you maximizing the tires you’ve?
If not, first attempt a wider wheel fitment. If that’s the case, do you’ve room so as to add each extra tire and extra wheel? That’s the last word improve.
And if guidelines get in your approach, get artistic and optimize what you possibly can whereas nonetheless staying compliant. Width is essential, however so is gearing and weight.
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