UrS4

Now that my suspion is complete. I want to focus of upgrading my wheels and tires.

This thread isn't going to be about which style of wheel to get as personal preference is well, "personal". I want to focus on the science of increasing grip vs compromising performance by increasing unsprung mass.

Obviously putting the stickiest tire on the widest, most lightweight wheel is the best senario but will likely be the most expensive. So as with most purchases there must be a cost benefit analysis. I'm hoping there is some evidence based information out there regarding this. Parameters are as follows: Ultra summer performance, Max summer, and Extreme summer performance tires. 17 to 19 wheel, and wheel and tire package that is daily driven.

A quick review of tire rack, a well known sponsor on this site, I found the following:

Tires
235/55/17 - 295/35/19
Weight range - 27-33lbs

Wheels
17x8 - 19x10
Weight range - 16-36 lbs

Cost of these tires ranges from $89-400+ per tire
Cost of these wheels ranges from $100-600+ per wheel

Questions:
Which is more important for increasing grip, tire width vs UTQG rating vs wheel/tire weight?
At what wheel/tire weight is grip compromised given the same tire width and UTQG rating?

For example is a UTQG of 220 in a 255/45/18 tire on a typical 18x9 (26 lbs) wheel equivalent to a UTQG of 300 in a 285/40/18 tire on a typical 18x10 (29 lbs) wheel?

For the following 3 types of drivers (Novice, Intermediate, and Professional) on a road course with only variables of tire width, UTQG rating, and wheel weight: Which characteristic is most important for optimal grip?

09blkgtcal

For increasing grip tire width and compound are more important than wheel weight. Lighter wheels will give the car a better feel.

Novice- street tires (summer)
Int., Adv. - r-comps, slicks

Since your daily driving and looking at cost I would go with 18s. Theres lots of selection with the 18s. The problem with 17s is that your not going to want a 55 sidewall your going to want something lower to get better steering response and tire roll. With 17s you'll definitely run out of gear on the straights at most tracks.

eolson

You can get 9.5x18 Enkei race wheels rated for 3700 lb BMW's that only weigh 21 lbs each and clear the Stop-Tech Big brake kit. Those and some light weight Michelin Pilot Sport tires that are 275/40/18 and only weigh about 27lbs each.

You are not going to get less unsprung mass than that for the money in my opinion. I almost pulled the trigger on that combo 2 or 3 years back, but I love the phatt look of my bullitt wheels too much, and didn't want to let go of my staggered arrangement

I talked to "KIng" at Enkei, and he cleared the Stop-Tech big brake template on their 9.5x18's, so that wheel and the Pilot Sport 275/40/18's would only be a total of 48lbs per wheel. What a huge rotating mass savings on cornering and acceleration. Erik

Norm Peterson

Compound > tire width. The effect of tire width on grip is not as strong as the appearance may suggest. A 285/40 vs 255/45 is about a 12% increase in width that might be worth a 2% improvement in grip. A 5% improvement in grip due to compound, you get all 5% directly.

UTQG ratings are almost useless for what you're asking. You might be able to separate out some good tires from some not so good tires, but it'll only be a little better than sorting by general tire type (max performance, UHP all-season, etc.). Tire Rack's in-house test reports are more useful, as long as you keep in mind that the same tire make/model included in two or more different tests will very likely post different numbers. Read for the subjective evaluations, too, which will be better than the reviews of most individuals.

On a smooth track, or as long as you have sufficient damping, small differences in the amount of sprung mass won't matter at all to a novice, but probably would to an very experienced driver engaged in timed laps such as for serious autocross competition or the various Optima Challenge events.


Norm

UrS4

Hey Norm,

I went through some of my recent car mags and found a C/D article comparing 5 max summer tires and 4 extreme summer tires and the results were a little surprising. They seemed to have adequate controls, same tire size 225/45/17 mounted on same rim and placed on two supposed identical BMW 328i coupes. No mention of wheel and dimensions but from the pics looked aftermarket. They had a "pro" driver who was blinded from the tires and basically ran a dry autocross, wet autocross, dry skidpad, wet skidpad, dry braking, and wet braking. Then they muddled up the rankings with subjective stuff like price, noise, comfort, and placed more weight on dry results than wet and threw in a subjective feel category. Needless to say when I looked at the objective results, my rank was different. They also ran a reference tire, a Pirelli PZero UHP tire but didn't say how that tire did but mentioned that when they drove with that tire multiple times throughout the day, they had consistency in results implying their testing had validity.

The tires in the Max category: Michelin, Bridgestone, Goodyear, Continental, and Pirelli.

The tires in the Extreme category: Toyo, Yokohama, Dunlop, and Hankook.

Price ranged from 133 to 199. UTQG ranged from 140 to 340.

Some generalizations I came away with:
All the extreme tires did worse than the Max tires in the wet autocross but were not worse than every Max tire in all wet testing.
The Harder the tire the better it did in the wet and worse it did in the dry except for the Michelin Pilot Sport which won or was in the top three in every category except price, and had specs of 300 AA A, Max summer, $177 per tire.

What was interesting were the following:
In the dry, the Extreme tires were not better than the Max tires, there was no consistency with a softer tire being better in the dry than a harder tire, and price did not correlate with objective performance.

Now, all the tires performed within less than 3 seconds of each other on the 0.33 mile dry course, dry braking was separated by 11 feet, etc.

Problems with the article was there was no mention of tire pressures and if varying them had an impact. There was no mention of how the tires wore, their consistency, or tire temperatures, or the order in which they were tested by the same driver, etc.

Additionally, 9 tires is not all encompassing.

So Norm, or anyone for that matter, if the UTQG are at best rough guidelines, and even tires billed as focusing on ultimate dry performance objectively losing to a less dry performance focused tire, is there something else I should look at to tell if the tire will have more grip than another?

For example, due to the mustang being RWD, and heavy in general, and not a 50/50 weight balance, should I stay away from a "softer" tire as it may heat up faster and become greasy?

Thanks for your help and discussion.

Norm Peterson

What month was that C/D article in?

I would throw out all of the subjectives except the "feel" one, re-weight that and the various dry and wet results to suit youor priorities, and see what that spits out. I'm including "feel" because that tends to affect how comfortable you'll be when driving it hard, which then tends to either encourage you to go there or discourage you from doing so.


Norm

UrS4

August, 2012 issue.

Their ranking
Michelin pilot super sport
Bridgestone potenza S-04 pole position
Yokohama advan neova AD08
Hankook ventus R-S3
Continental extremecontact DW
Goodyear eagle F1 asymmetric 2
Toyo proxes R1R
Dunlop direzza sport Z1 star spec
Pirelli P zero

The tire with the best result in each test got a full score and the others got a weighted fraction of the best score which wasn't always logical. There was a subjective feel score for the dry and wey categories.

My ranking was
Continental
Michelin
Bridgestone
Goodyear
Hankook
Yokohama
Toyo
Dunlop
Pirelli

I didn't give a weighted score for 2nd and below, just a 3, 4, 5...
Subjective feel was thrown out as well as sound level and ride
Now I did value longevity and price which is why my ranking had harder cheaper tires higher on the list. Maybe creating a ratio of longevity vs price would be more accurate, or dividing objective performance by price.

But you think the subjective feel ranking has merit?
It just seems to me that car magazines throw that scoring in so they can always have their "favorites" win every comparison.

Norm Peterson

I'll have to find that issue (I'm way behind on my reading).

The only estimate I can suggest for tire longevity is 10,000 miles per 100 treadwear - if your alignment suits your driving and you keep the pressures where they need to be (note that this may not exactly agree with the mfr sticker numbers). That's for up to some fairly hard street driving, maybe a bit harder from time to time. There are a few tires down around 200 TW that are perhaps a little optimistically rated (Falken RT615's and probably the other top choices for "Street Touring" category autocross). But that may give you something to work from.

Subjective feel is kind of hard to describe, but one aspect is steering response. Is the response "crisp" or is it soft (or worse, sluggish)? A tire that deviates less from "linearity" is a little easier to drive harder because it remains more "precise". When it does lose grip, it may do so more suddenly, but you shouldn't be hammering any tire all the way up to 10/10ths until you have some idea how they're going to behave as you approach that level.


Norm

BlackBetty

You're going to get a lot more bang for your buck spending on high quality rubber than light wheels. Tires that I would recommend for maximum grip are Bridgestone RE-11, Dunlop Star Spec, and Hankook RS-3. I currently have a nearly worn out set of RE-11s and a new set of RS-3s. The RE-11's have been a great tire; great grip in the dry, really good in the wet, got 20,000 miles and over two seasons of autocross out of them, etc. I haven't done enough driving on the Hankooks yet to get a good impression. Any of these three tires will be great for dry grip... they are sort of "the" tires to have for autocross street tires.

I would recommend choosing a size of a good tire and buying a wheel to match that and your budget. If you're not looking to spend a lot then good rubber on your stock wheels is the way to go.

eolson

For sure the wider, better rubber is the first priority, but as long as you were asking, if you're not supercharged, the lighter wheels, a 1 pc alum. driveshaft and some weight loss do make a handling and acceleration difference with the 05-10's.

I find any weight you can take off the front, wheels, headers, alum flywheel, k-member, battery re-location, will make for a much more limber turning car. Erik