Story By Per Schroeder
Dunkin’ Donuts Munchkins aren’t really made from the dough cut out of the center of each doughnut. If they were, you’d end up with a really funny-looking doughnut, one reduced to a thin ribbon of dough. That wouldn’t do a good job of filling you up (and out) in the morning. A…
Pressures on the 18's 4 lbs above the other tires. Hm-m-m-m-m. I expect they would be harsh and not grippy.
So apparently my 18" wheels are considered super radical? Aren't new cars coming with 20+ inch wheels nowadays? My buddy has a Challenger with 20" wheels and it rides more comfortably than my car with 18" wheels.
HapDL said:Pressures on the 18's 4 lbs above the other tires. Hm-m-m-m-m. I expect they would be harsh and not grippy.
And the 18s were significantly heavier too. Trying to find setups closer in weight would have been a better test, IMO. Same with testing width vs diameter separately (so test a 7" wheel with 205 in each size and then the 8" with 225).
You also have to watch out for the inevitable butterfly that farts on the tires too. All that uplifting gas will momentarily throw off the results depending on whether you are in corner or on a straight.
Good test overall there are just not enough of these tests that are even remotely controlled like this one
One of the other mainstream auto magazines (C&D ??) did a comparison using a VW Golf a couple years ago that was similar to this. If my (failing) memory served, they started with the 16" steel wheels shod with the selected comparison tire make / model to set a baseline, went +1, +2, maybe +3 (can't recall for sure) using alloy wheels beyond the 16's. Surprise, surprise ... the 16" setup was the fastest on their test course, probably due to the lowest unsprung weight.
Again, this is from memory so maybe not 100% accurate, but it stuck out in my mind at that time as pretty interesting.
Moment of inertia will have an effect not only on acceleration but also deceleration. It will effectively sap torque and subsequently horsepower from the whole operating range.
dannyzabolotny said:So apparently my 18" wheels are considered super radical? Aren't new cars coming with 20+ inch wheels nowadays? My buddy has a Challenger with 20" wheels and it rides more comfortably than my car with 18" wheels.
18" are considered radical to many who post on this site used to buying 13" autoX slicks, or 15" tires for an E30/Miata/etc.
The new GT350 and PP2 GT Mustang come with 19s, the 1LE Camaro's come with 20's, etc.
In reply to z31maniac : No! Corvettes and Camero’s come with 15 inch wheels.
Errr, in my era, but then I still own a car I can start with a hand crank.
dannyzabolotny said:So apparently my 18" wheels are considered super radical? Aren't new cars coming with 20+ inch wheels nowadays? My buddy has a Challenger with 20" wheels and it rides more comfortably than my car with 18" wheels.
It's a fairly old article. Per has not been a writer at GRM for a few years, now. So don't let the editorial part of the article bother you.
Plus sizing I always thought was a larger rim but the same overall diameter, width should stay constant. Shouldn't the test have been done with rims & tires that are the same width? The 16's were 0.5" narrower than the 17/18's, adding 2" more total width would equalize the grip levels and times.
In reply to dannyzabolotny :
Right below the headline in the full article, it reads:
From the Feb. 2008 issue
Yes, a lot can change in 10 years.
If you think about it wheel and tire combinations that weight more give you a double whammy.
You have to accelerate/decelerate the mass both linearly and rotationally. I guess if you have a need for bigger brakes it makes sense.
Then the practicality of narrow sidewall ultra low profile tires - its much easier to pinch them against a pothole and ruin them not to mention the expensive wheels you dent.
In reply to jharry3 :
Yes the wheel would be heavier but then the same diameter tire would be lighter. Assuming the same tread width isn’t it pretty close to a wash?
I suppose I can go to Tire Rack and find out.
In reply to frenchyd :
It depends on the tires and the exact sizes in question. Sometimes a step-up in wheel size doesn't change total weight significantly. Other times it does.
Lately it seems like the fastest setup is the company/size that lets you fit the most tire (unless you are in a width restricted class)
For instance the typical STU/STX/STS classes all restrict tire width and wheel width, nearly all competitors max those out and then it's simply a matter of who offers the fastest compound and what size nets you the least rotational mass.
In unlimited type classes it's a bit muddier. take CAM-S/Optima Do you run the 335/30r18 Rival S or do you run the 285/30r18 RE-71R? they're closer in time than you might expect, but then.........Bridgestone also offers the RE-71R in a 305 width....but you have to step up to a 19" wheel. Which is faster then?
Even if the total weight doesn't change much, the MOI can change enough to have an effect because the weight is farther out.
In reply to einy :
I thought they did a gas mileage test? I remember the test, just not a track comparison.
I remember this test but thought the 16's were the fastest. At least, that's what I've been telling my son. His MINI has 17's on it and I was recommending 16's, instead, for better ride, lighter rotational mass and better cornering.
-Rob
Tire choice is also a concern. My Accord runs a fairly tall tire from the factory, but came with 15 inch wheels. I can run a performance 15, but size goes down enough to screw with my gearing. In order to get back to stock-ish gearing and be on a reasonable compound I need to be up to a 17 inch wheel.
You are forgetting that the cars suspension was designed for the 16" wheels. A minor change in wheel dia will make a gain. Porsche normally offers a plus 1 wheel. Lighter wheels do help.
In reply to rob_lewis :
An R83 16" MINI "5 star" alloy wheel and Yoko NON-run-flat radial weighs a whopping TEN POUNDS LESS than a 17" MINI 8-spoke Minilite replica with MINI's OE run-flat tire.
That's a huge diff in rotating mass and unsprung weight.
In reply to The Staff of Motorsport Marketing :
Wait a minute. Shouldn’t horsepower enter into this discussion?
Assume an excess of power bigger tires would then reduce lap times.
frenchyd said:In reply to The Staff of Motorsport Marketing :
Wait a minute. Shouldn’t horsepower enter into this discussion?
Assume an excess of power bigger tires would then reduce lap times.
It all factors in, to be honest. I have been part of several of these tests over the years/decades. I hate to give a cop-out answer, but how do you find the best solution for your particular car? Test. It's what the fast people are doing. Watch what David Whitner does. We're presenting these tests in the magazine, but in the end there are lots of variables out there.
I'll give you a real-world example. Did you catch our Live show with Dynasty Racing? I'll post it here:
So, check this out: They determined that a 15-inch tire/wheel would be best for their FR-S. You'd assume that the lower-profile, 17-inch tire would help them in the turns, but they decided that the gearing advantage provided by the shorter tires would be even more valuable. End result: First and second at the Runoffs. And then the SCCA changed the rule for this year. 
Another variable that we haven't discussed too much: Tire construction for just one make and model of tire can vary depending on size. So, for example, the 17-inch version might feature different internal construction than the 18-inch version. I know, it's maddening.
Then there's reality. Like someone noted earlier regarding the Rival S and RE-71R, availability also matters. An 18-inch tire might be best for you, but what if your favored model doesn't come in that size?
Many years ago we did a heavy vs. light wheel test with a professional test driver. Same tires, same wheel sizes, etc. We used my personal Miata. I want to say that we tested the Kosei K-1 vs. a really heavy chrome wheel. In the end, the results were really, really close. So what happened? We're thinking that the smooth test surface negated some of the advantage of the lighter wheels. On a bumpier surface, the heavy wheels would have forced the suspension to work harder. Grip probably would have been less, so times would have been slower. On the smooth surface, though, that all went away.
A while back we did an article on tire testing--how to attack it so you can get the best results for you. Let me see if it's online. If it isn't, we'll get it into the queue. Andy Hollis wrote it and did a killer job on it.
Here's another thing to add to the tire discussion. I'm about to pull the trigger on new tires for my wife's Civic Si. The car came with the summer tire option, so I was going to stick with them. I discussed it with a friend at Tire Rack. He recommends an all-season tire from the same brand since it's a daily driver that sees rain. Won't the all-season tire be slower? I asked. Not really, he said. The all-season tire is newer, and advances in technology have made it just as fast as the summer tire from a few years back. So, yeah, so many variables.
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