SleeperGSR

i was wondering what people thought about my setup. I have a mostly stock integra that get to alot of HPDE's and auto-x. I started on stock wheels with all season tires. I got a set of 16x7 in rims and ran a 205/45 kumo spt, then i got a set of 215/45 rt-615's. This summer i'm on a 215/45 Kumo XS. Every step of the way has felt like an improvment, but i was wondering if im going to wide with the tires. Just looking for thoughts and opinions

alterdcreations

go as wide as you can fit.
225/50 16 here

SleeperGSR

Ok but why...im just trying to understand. More contact patch but isn't it also added weight?

alterdcreations

mechanical grip is good. weight can be compensated with tire height....imo if your worried about it, but also you will need wider wheels if you were to go really wide and i have seen wheels 17" wthat were a few pounds lighter that oem so i wouldn't worry to much about it.
so in your case i would find 225/40 or 235/35 for weight purposes but i like alittle sidewall

SleeperGSR

i really don't know what i should be worried about..ha that's why i'm asking you guys???

nsxtasy

Actually, it isn't more contact patch at all. When you get wider tires, it doesn't change the size of the contact patch at all, only its shape. The size of the contact patches is only a function of the car's weight and the inflation in the tires, assuming the tires have a normal amount of inflation holding up the car. If you inflate the tires on a 2640-pound Integra to 33 pounds per square inch, the contact patch area will total 80 square inches, and that's true regardless of whether your car has 185-treadwidth skinnies or 245-treadwidth steamrollers. Whatever benefit is in the different shape of the contact patch, in terms of cornering capability as well as in heat management.

However, the treadwidth is a relatively minor factor in performance. Much more important is the make/model of the tire, which determines the stickiness of both the compound and the tread pattern. That's the main reason you felt an improvement in the XS over the RT-615, and the RT-615 over the SPT, not the treadwidth.

That's a rather long answer. Someone recently posted all of this here wisely, in a much more concise statement:

Compound > Treadwidth

Stick with the Kumho XS, in 215/45-16. It's an excellent tire, and 215/45-16 (as well as 205/45-16) is the perfect size for your Integra. Don't go any bigger, or you'll have problems with rubbing. If and when you're ready for even more grip, like if you're competing for every last hundredth of a second and you don't care about how much your tires cost or how long they last, then go for the Hoosier A6 (R compound autocross tire) in 205/45-16. Yup, slightly narrower, but they'll give you even more grip and faster lap times than the XS in 215/45 (a size for which the A6 isn't available). Because

Compound > Treadwidth

xxblazexx

well on that note... nitto nt-01's ftw
also the xtra weight will be like 4-10 lbs
which im sure you can find to take out somewhere.

solo-x

If a tire supported a car ONLY with tire pressure, nsxtasy's post would be spot on. Because the carcass of the tire does support some amount of the cars weight, the size of the contact patch does change as well. However, the main factor is as stated, the shape of the contact patch changes. A wider and shorter contact patch operates at a cooler temperature and a lower slip angle which equals more grip potential.

You've only gone too wide if the added aero/pneumatic drag results in slower lap times or if you can't fit the tire on the car.

nsxtasy

The NT-01 is an R compound tire designed for road course use. Like most such tires, it needs a good lap or two on the track before it reaches its peak performance. For that reason, it's not the best choice for autocross. If you want to go to R compounds, for autocross you're better off with a tire designed for that purpose, like the Hoosier A6, made with a softer compound that doesn't require such extensive warmup.

The carcass of the tire does NOT support the car's weight when the tire is inflated to normal street or racetrack pressures - not enough to change the size of the contact patch*. The size of the contact patch does NOT change with the tread width. In fact, the Tire Rack has actually proved this; they measured the area of tire contact patches, using the same car and tire pressure and model of tires with different tread widths. They had the exact same size contact patch, within their margin of measurement error (which they calculated as less than 2 percent).

Incidentally, if you want to read a more detailed analysis about the size of the contact patch and the effects of wider tires, click here.

bsclywilly

No one's wrong here but in reality, when you change tire width other factors do not remain the same. To maintain an equal distribution of pressure on the contact patch (to maximize grip), a wider tire will want to run at a lower pressure due to the reduced effects that the sidewall stiffness has on the entire contact patch area. Lower pressures will result in the increase in area.

nsxtasy

Wow, I've never heard anyone make that claim before. Usually there is a "sweet spot" for hot R compound pressures, depending on the tire, that has nothing to do with the width of the tread.

bsclywilly

Yes, it's very tire dependent. But it is a true generalization if comparing same tires of different widths.

xxblazexx

Hmm, for some reason I read the part where the OP competed in HPDE's but not the auto-x

mugen88crx

so dont yell, maybe i over read... but isn't it if you go too wide on a narrow factory wheel your sidewalls wouln't have enough support? say on my stock 15" blades that are 6.5" wide what is too wide?

ohsnapzafingcu

iTrader: (2)

any pics? fenders are rolled, eh

98SpecR

It is best to go with the tire manufacturer's suggested wheel widths. For example, Hankook's suggested wheel width for 225/50/15 R-S2's is 6"-8".

TunerN00b

Ask that question to the ITR autocrossers who shoehorn 275s on the factory wheels...

But, in general:

solo-x

From the link you posted "(the exceptions being so-called run-flat tyres, or tyres with extremely stiff sidewalls)". A 285/30/18 Hoosier will support the weight of an E36 BMW with zero air pressure. We've done it many times. The sidewall does not deflect in that scenario one bit.

Think of a tire as two springs in parallel. One spring is the tire's construction, the other is the air contained within the tire. The spring rate of both components combine to give the tires overall spring rate. On a soft passenger car tire, the carcass spring rate is quite small, so as a percentage of the total spring rate, it is not even worth mentioning. Once you get into racing tires, this changes. The sidewall of the tire has a rather large spring rate, and as a percentage of the overall spring rate of the tire, it is a much larger number. The higher the tire carcass spring rate, the more we diverge from pressure and weight being the direct determiners of contact patch size. The higher the tire carcass spring rate, the less the tire deflects for a given inflation pressure.

If you go too far outside the manufacturers recommended spec for wheel width (wider or narrower), you increase the chances of debeading a tire on sharp impacts. Get far enough out of the range and the tire may not bead at all, or exert so much force on the seat area that the wheel fails. 275's on a 6" wheel is indeed pushing the envelope, but for a Solo only car it's doable, and worth a couple of tenths on courses that aren't slalom intensive. I would not recommend that tire on that narrow of a wheel for a DE car or street driving.

mugen88crx

good to know! so on my 6.5" prelude blades i should be safe with 225's. thanks guys

beanbag

So what does the pressure over the contact patch look like for a stiff tire, and how is it beneficial over a street tire?

98SpecR

Also, does the width of the wheel have any affect on the contact patch?

nsxtasy

Another problem with going too far outside the approved rim widths is that excessive stress and heat can build up in the sidewalls, which can lead to actual tire failure as well as exacerbating the susceptibility to bead failure.

solo-x

Within the tire manufacturer's wheel width recommendations at similar inflation pressures, no. Outside of that, strange things can start to happen which are hard to predict and would be specific to the tire and it's construction.

The width of the wheel affects the operating slip angle of the tire. For example, a 205 RE-11 on a 15x6" wheel is going to operate at a notably higher slip angle then the same tire on a 15x8" wheel. The higher the slip angle, the more heat goes into the tire, the less peak grip it can make. Another side affect is that it takes time for a tire to build slip angle. If that amount of time is large enough, the tire will be vague with poor response. Generally speaking, this type of tire/wheel combination is easier to drive as it is more forgiving of hamfisted driving.

The width of the wheel will also affect your inflation pressures. In our previous example, the 15x6 combo would necessitate a higher inflation pressure for the tire to be "happy". The air pressure is supporting the sidewall more in this situation. With a wider wheel, the sidewall of the tire can do it's thing a bit more, allowing a lower inflation pressure.

gotocrx

This tidbit probably is less applicable to Auto-x, but at least when it comes to road courses, you CAN go too wide, a fact we discovered when engineering one of our old time attack cars. Bigger tires kept yeilding us faster laps times, right up to the point where they didn't anymore . Turns out the tires got so wide, we couldn't get heat into the tires, and fell out of the premium temperature range for our rubber.

This probably doesn't apply to your car, though. "Too big" was a 295. We settled on a 275, which consistently produced faster laps and higher G loads for this car.

BarrierIslandBum

Couldn't you fit a 215/45 tire on a 15x7 rim and would that be better or worse for an integra (or DA in my case) for autox, than the 16 inch rim?