Matt H

Tire width has very little to do with braking performance on a stock car. Tread compound has about 75% of the determining factor. Beyond that sidewall height and tire construction make up the rest.

Let me run down the rest.

Miscalibrated butt dyno. The width of a tire (given the changes we are talking about) and making the assumption that sluggish means accelaration should make no difference in this case. Fuel economy could be slightly down (ever so slightly) due to more of a contact patch, thus greater friction. The loss in fuel economy would be so negligible that you would not notice, in most if not all cases.

Yes, it would. In fact the 225/50/15 has a smaller overall diameter, in essense changing the final drive ratio. Very common for spec racers to use this size tire for that reason.

Very possible. Not all tires are the same width even with the same nomenclature. In fact, not all tires of the same brand, type and name are the same width as there are variations from one mold to the next. I have actually had a set of 225/50/16s that were well wider than the 245/45/16 rears of the same tire. Further as the aspect ratio comes down the section width gets wider. For example, a 225/50/16 has much more section are than a 225/70/15, which helps explain the difference in width you are describing.

This is not possible. The tire that has more lateral grip will brake better in almost every instance with repeatable results.

That is only 10mm or .39 inches not even close to 2". My last comment is that GY tires generally rank about dead *** last in braking performance, the Eagle GS-DS2/3 being the lone exception, so my feeling is that there is some other issue. Not all tires perform the same at the same air pressures. It is likely that your Pirelli's are underinflated. Further, if you hope the SP8000s are going to be better than your P7000 you are going to be in for quite a shock. The SP8000 is a pile with awful wet weather characteristics.


There is a lot of plus side to a larger diameter rim, tire sizing maybe the biggest, but at the end of the day looks is the answer.
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Luis de Prat

So, is wider any better than narrower?

UDPride

One other thing you need to keep to keep in mind is the wider and larger you go, the heavier your rims will likely be, unless you are like 930Rocket running those bigass magnesium BBS wheels I get a woody for every time I see.

I think keeping weight down on the rims should be as much a concern as any. For most of us, 3-4 pounds extra on each wheel probably wont mean much. If you are on the track or something Im sure it will.

Im pretty much speaking out of my bunghole though. I dont know for sure.

I love Fuchs.

Matt H

Luis, it depends on the application. In general, yes. As Dave correctly points out there are time the answer is no, snow, ice and heavy rain are some of them. Wider tires also have much more tendancy to follow the road surface or tram.

UD - to be honest even a professional driver will not likely notice 3-4 pounds per wheel. I had held that view for a long time and recently saw an interview with Michael Andretti confirming that. On a street car you are unlikely to notice 20 pounds per wheel if all things were equal (yeah, here comes someone to disagree). What people do notice when they go bigger is that the car is harder to turn (more contact patch) and that is "feels" a little sluggish. Geo has correctly pointed out why people think it feels sluggish.
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chris924S

He put on the wrong size tires. 195-65-15 were sized for 6 inch wide tires. 215-60-15 were sized for 7 inch tires. He could have gone to 205-60-15, but not 215-16-15 on 6's. The tires are much too big and the problems he experienced are what happens with a wider than normal tire on a narrow rim. Who every told him to go to that size tire was doing him a disservice. Any competent tire installer could have told you this information.

Chris F.
924S 190K

iloveporsches

If you had a highly-calibrated butt dyno you might notice it in straight-line performance. An extra 80 pounds of rotating mass is a big amount.

Manning

Actually, for every tire I have looked at in 215/60 15, recommended rim widths typically range from 6 to 7.5 inches.

Dave

I'll join the disagreement on weight, I'm far from an expert driver but I could feel the 2 lb difference between my Fuchs and my PDs. I doubt the difference is enough to be measurable but the car feels much more nimble with the lighter wheels.
FWIW, there's actually a difference in "weight" between a 15 pound 15" wheel and a 15 pound 18" wheel (yes, you read it right), both wheels have a little weight at the center and most of their mass toward the outside (near the tire). The 15" wheel has most of its mass 7" from it's axis while most of the 18" wheel's mass is an inch and a half further out, the same weight has more leverage and thus more inertia.
Think of it this way, there are some among us with lightened flywheels and cranks and it takes quite a bit of work to do these mods (at least the flywheel is easy to get to in a 944 ) for a pretty small gain, wheel weight the same effect on the on the drivetrain that the weight of the crank or flywheel have but wheels are much easier to swap.

iloveporsches

Dave, were the tires the same model, size, and age? That would make your car feel much more nimble. Could also be a placebo effect.

My car is running without a front sway bar right now, and it "feels" better, but I know it's really driving worse.

Waterguy

I just ran some numbers on the amount of angular inertia that wheels and tires add to a car, and it probably isn't enough to feel with a butt dyno. The inertia involved in accelerating a 1400 kg car and driver consists of about 99.5% linear inertia and 0.5% angular interia from the wheels/tires (not including drivetrain.) Changing to a larger diameter wheel of the same weight may reduce your acceleration rate by 0.1% to 0.2%. If the wheel is heavier, the biggest change is in the additional linear interia, not the additional angular interia.

Dave, the flywheel is a different case. If you accelerate your car from 0 to 100 mph, the wheels accelerate from 0 to 1300 rpm. In the same period the flywheel is accelerated from about 3000 rpm to 6500 rpm three times, and back down twice. The inertial changes of the flywheel are much greater than those of the relatively slowly rotating wheels.

Elephant Chuck

I'll throw one more factor into the mix. Heat. And it's the most important.

Tires achieve best grip within a temperature range, that optimal range varies for different tire types. A typical DOT R tire needs to be in the 180-200F range. Slicks hotter, streets colder. Check with manufacturer for specifics.

Here is a simple rule of thumb (words to live by):

a) Tires are too big when you can't get into the temp range. In that scenario a narrower tire will be faster.

b) Tires are too narrow when you are running too hot. In that scenario a wider tire will be faster.

There are also other factors that affect tire temp such as tire pressure, alignment, driver technique, ambient temps, etc. Those factors must be understood and adjusted appropriately.

944S2NUT

According the pontiac grand prix wider is better! LOL

Graufuchs

totally agree, whats your driving style like, do you autoX what do you do with the car? If its a daily driver prolly stick with factory specs. If not figure out whether you want to be able to flick the rear out, of have it stick, same thing with the front. I have 17 993s, they look great but its harder to flick the rear out in an autox which can hurt and can help its all on your driving style and what you need the car to do, larger contact with the road=better grip. but then again if it snows alot near you or rains alot larger contact will hurt you=less grip...The 17's I have hav hurt me autoX wise a large deal and the 951 sus doesnt help either.