[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 …
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.
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
Bigger is sometimes better. Maybe even often better. But bigger is always heavier.
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.
Do you think you would have similar results with your endurance car?
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.
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.
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.
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.
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.
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?
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.
For me, I like to live between 35 and 45 section sidewalls. Anything less is basically useless, and anything more looks and feels slow.
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.
All else being equal wouldn't a larger diameter tire wear longer?
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?
The thing is you kept the weight the same. Most people who drop down a size partially do it for the unsprung weight savings. If you bought the same OZ wheels in 17x7.5" you would have lost about 1.5 lbs. per corner.
when i bought my wheels ( rims ) for my 84 alfa spider.. i just took a bathroom scale to a couple wheel shops and weighed some rims..( 16x7 ) bought the lightest ones......on the tires.. a mix of light weight and build quality, grip.etc
DW's S60 has the optional 19" wheels. Although it is nobody's sports car, after a couple bent wheels and a pothole-induced blowout, I'm probably going to drop down to 18s.
wspohn said: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.
The drive to larger wheels was driven by larger, heavier cars needing larger brakes. A 15" isn't going to cover brakes large enough for a 3400 lb car with 250 or more HP.
I suspect most understand smaller is lighter. But if you aren't chasing wins in TT or AutoX, most people don't care. Including myself.
z31maniac said:The drive to larger wheels was driven by larger, heavier cars needing larger brakes. A 15" isn't going to cover brakes large enough for a 3400 lb car with 250 or more HP.
I don't know that this is correct. You can buy Wilwood 12"+ brakes that fit inside 15" wheels and do a fine job of braking full size American cars.
https://www.hotrod.com/articles/step-huge-12-inch-brakes-keep-15-inch-wheels/
wspohn said:z31maniac said:The drive to larger wheels was driven by larger, heavier cars needing larger brakes. A 15" isn't going to cover brakes large enough for a 3400 lb car with 250 or more HP.
I don't know that this is correct. You can buy Wilwood 12"+ brakes that fit inside 15" wheels and do a fine job of braking full size American cars.
https://www.hotrod.com/articles/step-huge-12-inch-brakes-keep-15-inch-wheels/
Agreed. And BMW has packaged 13+ inch rotors inside 16s with enough room for sliding calipers, so I'd expect that's not the limit with lower profile calipers.
In reply to Tom1200 :
Depends on how heavy the car is. The heavier the car, the less sensitive it is to unsprung weight. For example, anything larger than a 15" wheel is despised on Miata forums. Check the online forums for your car. They can give you a good answer.
In reply to buzzboy :
They should, but the aspect ratios were chosen to keep the outside diameter nearly the same.
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