Is Bigger Always Better When It Comes to Wheel and Tire Packages?

Photography by J.G. Pasterjak and Per Schroeder

[Editor's Note: This article originally ran in the May 2012 issue of Grassroots Motorsports.]

 

Why order fun-sized portions when supersizing costs only 9 cents more and contains 3100 more life-sustaining calories—plus a bonus pig haunch? You’d be crazy not to upgrade, right? It’s the American dream.

Maybe bigger isn’t always better. Can upsizing your wheel-and-tire package actually downgrade your car’s performance? We hit the test track to find out. 

Past Present

Back in a simpler time we called the 1980s and 1990s, wheels were smaller. We all sat around in silent wonder when they put 16-inch wheels on Corvettes and Camaros, thinking, “Certainly man has reached the physical limits of the wheel-and-tire universe.” 

At the time, most of us were running around in our linen sport coats and sockless loafers with 13- or 14-inch wheels on our Civics or MR2s. We thought we were pretty cool, but every time we opened one of our favorite magazines, we’d see an easy way to become even cooler: Switch to plus-sized wheels and tires.

This upgrade capitalized on the burgeoning supply of low-profile tires available at the time, and the recipe was simple: Maintain the overall rolling diameter of the wheel-and-tire assembly, but increase the wheel diameter while decreasing tire sidewall. A shorter diameter would theoretically improve performance, while maintaining the tire’s outside diameter would preserve the stock gearing.

The simplest upgrade was the Plus 0. Wheel diameter stayed the same, but the tire width increased while the aspect ratio decreased. When Goodyear launched the 205/55R14 Eagle VRS autocross tire, Civic, GTI and MR2 drivers shed their 185/60R14 rubber in droves.

From there, you could take the additional plunge and do a Plus 1 upgrade. A Plus 1 would increase wheel diameter by an inch and necessitate a further reduction in the sidewall aspect ratio to maintain the stock rolling diameter. Plus 2 was the next step, increasing wheel diameter by 2 inches, and was made even easier with the introduction of super-low-profile 40- and 35-series tires.

So that’s your little history lesson. You can take the Duran Duran cassette out of the player now.

Neuworld

But something happened on the way to the forum—the forum in this case being the 2000s. Car manufacturers, enticed by the prospect of higher performance and higher sales numbers, jumped on the plus-sizing bandwagon. 

Today you can walk onto a car lot and buy an econobox with 17-inch wheels and 40-series tires, and that may not even be the upgraded wheel-and-tire option. As a result, 15-inch wheels have become as rare as 18-inchers were in 1995. 

But has all this upsizing made the world a better place? Did we, at some point, blow past the ideal configuration and let our desire for larger and larger rolling stock take us too close to the sun?

Let’s find out, shall we?

Testure

We laid out a rather simple plan for a test: Compare two wheel-and-tire packages that were as identical as we could make them except for the wheel diameter. We’d use a car with a “modern-sized” set of aluminum and rubber and give it a “Minus 1” upgrade. Or downgrade. Or, um, sidegrade. We’ll see. 

Our test subject would be our 2008 Mazdaspeed3, a car that rolls out of the factory on 18-inch alloys. Wheels of this magnitude were associated with the cars of pro athletes and rock stars until about eight years ago.

Our car had already received a small upgrade in the form of a set of 18x7.5-inch OZ Alleggeritas, and we’d use these as our modern-sized wheel baseline. For our Minus 1 setup, we picked up a set of 17x7.5 Enkei Fujin wheels. They weigh 16.8 pounds (vs. 17 for the OZs) and have a nearly identical offset (50mm for the Enkeis vs. 48mm for the OZs). In other words, they were as close as we could find to an identical yet smaller-diameter wheel.

Next, we needed rubber to stretch over our wheels. We were quite happy with the 235/40R18 tires that we’d been running on our 18-inch wheel package, so we chose them as our modern-sized tire baseline. 

The rubber for this exercise would be the new Maxxis MA-Z1 ultra-performance tire, which comes in the perfect sizes for this back-to-back comparison. The 235/40R18 MA-Z1 tires we slapped onto our OZs were 25.5 inches tall and 9.7 inches wide, while the 235/45R17 tires fitted on the Enkeis were 25.3 inches tall and 9.4 inches wide—well, that’s according to the spec sheet. 

Our own measurements revealed the installed width to be closer than that: The 17s were barely 2mm narrower than the 18s. In fact, it was hard to see any difference with the naked eye. Also fabulous: Each wheel-and-tire combo checked in at 43.6 pounds. 

Time to test.

Process

Next came the grunt work of our experiment: Mount each set of wheels and tires, run some laps on our test track, switch sets, and repeat, repeat, repeat until we came to our epic conclusion. 

We’ll spare you the play-by-play about bolting on each wheel and just get to the part you were probably going to skip to anyway. Yes, one set was conclusively faster. It was close, but after a few rounds of blind and non-blind testing, the 18-inch setup was slightly faster than the 17-inchers in both average times and fastest times. 

Why was bigger better? Let’s look a little deeper into the numbers for some clues. The 18-inch setup, with its shorter and stiffer sidewalls, took about one lap to “come on” and produce the fastest lap on our multi-lap runs. After that, heat gradually prevented the tires from producing proper traction, and by lap five performance fell off noticeably. With the 17-inch setup, the times peaked around the same point—after a single warmup lap—but fell off much more quickly after that.

Subjectively, the 18s and 17s were nearly identical in most regards. If you pressed us, we might say the steering response seemed sharper with the 17s, but we’d never testify to it in court. 

One thing we would say under oath is that the setups differed in steady-state traction. On the large, constant-radius, 180-degree corner that anchors our kart-based test track, the 18s and the 17s were like night and day, with the 18s clearly having more ultimate and more manageable steady-state grip. The times were close, so we imagine the 17s fell short due to slower speeds in this long sweeper.

Okay, so why go with the larger tires?

Well, mostly for the same reasons tire-marketing folks list when they try to sell you the bigger wheel-and-tire package. Less sidewall means less sidewall deflection. Less sidewall deflection means more of the contact patch is being managed by the suspension and not by the de facto spring created by the squirming tire. More squirm means more contact patch deflection, heat buildup and hot spots, which we clearly observed in the way the performance of the 17-inch package fell off so much faster.

ProTest

So we answered the speed question, but that doesn’t mean we’re ready to crown a winner just yet. There’s another factor that must be considered, and that’s the cost-benefit ratio.

After the times shook out, we saw that the 18s were basically a tenth of a second faster than the 17s in both average and fast times. Now, a tenth of a second is an eternity at the Solo Nationals, but not so much in the cosmic scheme of things. So the question becomes, “How much is that tenth of a second worth to you?”

The tires are very close in cost. Street prices for the MA-Z1 in 235/45R17 run about $99, while the 235/40-18s cost about $106 each. That’s less than a $25 difference for the entire set.

The wheels, however, have a bigger price gap. A 17-inch set of Enkei Fujins like the ones we used will run you $180 each from Tire Rack. The 18-inch versions of the same wheel are $225 each. If you want to pick up the same OZ Alleggeritas we used, be prepared to pay about $388 each for each one. Just scan the various listings of wheel prices, and you’ll see that the 18-inchers carry a premium of at least $20 per wheel—and in most cases more like $40 to $50—over the 17-inchers.

In the final analysis, you’re looking at a minimum of about $150—and probably more like $250 or more—to take the 18s over the 17s. Worth it? That’s for you to decide.

Dig It

Progress marches on, bigger is better, and marketing is based on truth. We may not have proved these statements across the board, but we provided some evidence that—in this case at least—there’s more to the trend of larger, lower-profile rubber than just hype.

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Comments
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Tom1200
Tom1200 Dork
9/29/20 9:42 a.m.

Difference in ride quality between the two? I'm sure it's not the night and day of stock & plus two but I am curious.

TheTallOne17
TheTallOne17 New Reader
9/29/20 10:23 a.m.

The difference in time fall off is actually much more interesting to me than the .1 second gained from the larger wheel. Is there a graph or data for that?

The article mentions a .2in difference in height in favor of the 18in wheel, which I know is nitpicky, but it does result in ~7 more revolutions required per mile for the stock 17s.  790rev/mi vs 797rev/mi, which isnt significant enough to give the smaller wheel a torque advantage out the corner, but is significant enough to lose out on top speed into a braking zone by a few tenths of a mph, which could cover the time difference depending on the track layout and driver consistency.

Tldr, the important part of the article is the consistency in laptimes before falling off performance for the larger wheel

ShinnyGroove (Forum Supporter)
ShinnyGroove (Forum Supporter) Reader
9/29/20 10:41 a.m.

Bigger is sometimes better.  Maybe even often better.  But bigger is always heavier.

wspohn
wspohn Dork
9/29/20 11:23 a.m.

I have some sympathy for the old view that 15" was the ideal rim size, given that with larger wheels you get more weight combined with less comfort on the street. The drive to larger wheels wasn't driven by performances but by sales figures - the ad guys  told people they should want this and they simply went baaa, baaa and did.

I am surprised that the difference was that small, but thanks for the interesting test.  Many people just can't seem to understand the fact that rubber weighs less than metal and handling will generally be better with the lighter wheel/tire combo. Your comments on how these combos performed differently as they warmed up was instructive.

trigun7469
trigun7469 SuperDork
9/29/20 11:30 a.m.

Do you think you would have similar results with your endurance car? 

LanEvo
LanEvo Dork
9/29/20 12:40 p.m.

On my racecar, we've seen significant improvements in lap times after switching from 225/45/16 tires on 16x8" wheels to 225/45/15 tires (or 215/580R15 slicks) on 15x7" wheels. Going from 24" to 23" overall diameter helped with acceleration out of corners and keeps the engine at the top of it's powerband.

I don't know how much this contributes to lap times, but there's also a significant decrease in the unsprung mass, especially when running those featherweight 215/580R15 slicks. Costs are a bit less as well.

Tom1200
Tom1200 Dork
9/29/20 1:53 p.m.

Weight & gearing is why I've stuck with the Hoosier TD-R vintage tire vs the R7 radial. The short gearing obviously helps and also the fact that the bias ply is 4 pounds lighter per tire. The wheel tire combo on my car is 24lbs  In a car with 80whp it's a big difference.

The article did mention the diameters and weights being nearly identical between the two sets of wheels.

Most of us don't run national level autocross and I'd give up two to three tenths all day long for the extra compliance. I typically don't like anything lower than a 50 series tire.

My son's Miata was faster with the 15" diameter wheels and wider tyres but it was way more fun with the 185/60-14s on it.

DirtyBird222
DirtyBird222 UberDork
9/29/20 2:41 p.m.

I've actually been looking into going with a 16inch wheel on my Champcar Accord for both weight savings and heat dissapation. 16in RPF1s weigh considerably less than the 15x8 wheels we are running now and given all the things going on in the front wheels of a FWD race car having a bigger opening for heat to escape might help with the durability of parts. I'm not an expert on that; but, 10 people in an elevator can get quite warm and stinky. 10 people in a classroom at least allows for some breathability. 

dean1484
dean1484 MegaDork
9/29/20 2:45 p.m.
LanEvo said:

On my racecar, we've seen significant improvements in lap times after switching from 225/45/16 tires on 16x8" wheels to 225/45/15 tires (or 215/580R15 slicks) on 15x7" wheels. Going from 24" to 23" overall diameter helped with acceleration out of corners and keeps the engine at the top of it's powerband.

I don't know how much this contributes to lap times, but there's also a significant decrease in the unsprung mass, especially when running those featherweight 215/580R15 slicks. Costs are a bit less as well.

I concur.  I ran the smaller tires on my RX7 and would consistently be faster for all the reasons noted above.

LanEvo
LanEvo Dork
9/29/20 3:04 p.m.
dean1484 said:

I concur.  I ran the smaller tires on my RX7 and would consistently be faster for all the reasons noted above.

I should have mentioned that my car is geared a little too tall to start with. Decreasing the tire diameter was a cheap way to shorten the final drive ratio. It also lowered the car by a half-inch (I know that's not much...but still) without altering suspension geometry.

15f80
15f80 New Reader
9/30/20 12:01 a.m.

There was another test where they found that lighter tire/wheel was better. Why does this test show that a heavier tire/wheel is better?

Cedricn
Cedricn New Reader
9/30/20 4:48 a.m.

A bit unfortunate that the diameter difference where so small, its one of the big reasons to go with a smaller wheel. My car is definitely quicker accelerating and more agile on 15x7 compared to 16x8. That doesnt mean that i wont maybe put in faster lap times on a larger wheel due to the increased grip, imo a fun car and a faster car doesnt necessarily use the same solution, it oculd be sometimes, but not always. But it depends alot on engine power, what final drive you ahve std etc. I wished there also were more choices for low profile and small diameter, i dont want balloon tyres just because I use smaller dimaters, at least not for track tyres, road is different, reality is more challenging than theory though, I can for example not find any 15x8 wheels for my car so I have to upsize to get 8 inch wide tyres etc.

350z247
350z247 New Reader
10/9/20 11:44 a.m.

For me, I like to live between 35 and 45 section sidewalls. Anything less is basically useless, and anything more looks and feels slow.

RX8driver
RX8driver Reader
10/10/20 9:29 a.m.

I think for most grassroots applications, a smaller tire diameter will be faster, so long as it doesn't mess up your gearing or sacrifices width. It lowers the car and gives you shorter gearing for better acceleration, which is why I used to run 225/45/15's on my FC for the track.

 

It's interesting to note though that high end factory builds (LeMans GT cars, etc) tend to run fairly large diameter tires. With a larger diameter the contact patch shape changes to be longer, which is good for more grip in braking and acceleration, allowing them to get on the throttle sooner out of the corner and brake later.

buzzboy
buzzboy Dork
10/10/20 11:53 a.m.

All else being equal wouldn't a larger diameter tire wear longer?

mxandcx5
mxandcx5 New Reader
10/28/20 7:23 p.m.

I was lucky enough to just pick up a set of these exact 17x7.5 Enkei Fujin wheels for my 2007 Mazda3. I'm trying to figure out the best size tire for them and so far it seems like most prefer a 215 or 225/45R17 tire for the wheel size. Am I missing something as to why they went with a 235/45R17 in this test?

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