Wheel width effect on tire performance

[bruce.weiland]

Hello you wheel and tire experts.

I have a question that a couple of quick searches with the search engine did not answer.

When a tire (lets pick a 255x50x16) spec lists wheel widths from 7" to 9",obviously a wheel wider than 9" would be difficult to mount and might cause bowing up away from the ground in at the center of the tread. A wheel less than 7" might roll the edges of the tire up off the ground.

But, all other things being equal (I know they never are);

What would be the differences in handling, steering response, etc. for this same tire, on a 7" wide wheel and a 9" wide wheel???????

Thank you in advance for any reponses.

Bruce

[szh]

When a tire (lets pick a 255x50x16) spec lists wheel widths from 7" to 9", obviously a wheel wider than 9" would be difficult to mount and might cause bowing up away from the ground in at the center of the tread. A wheel less than 7" might roll the edges of the tire up off the ground.

Yes, yes, YES!!!! Thanks for understanding the above issue!

People always assume that the wider the tire they put on their car, the larger the contact patch area, the better the lateral acceleration, the better the handling, etc., they think they will get. In most cases, they are wrong if the tire does not match the wheel properly!

Usually, the tread width, section width and section profile changes, that result by using the wrong width tire for the wheel width, can have very unexpected results. The VIP "look" of stretched tires is a fad that, I hope, passes sometime soon.

Sometimes, people try to compensate for mismatched widths, by increasing or lowering tire inflation pressure. These have the side effect of changing the load index of the tire, and, in some heavier cars (like much of the larger Infiniti line), lowering the pressure too much can be dangerous - tire failure under speed or stress (hit a bad road bump and blow out the tire!).

What would be the differences in handling, steering response, etc. for this same tire, on a 7" wide wheel and a 9" wide wheel???????

The answer, I think, is that "it depends" on the situation. (You might get away with some minor degree of mismatch beyond the limits - the worst I would consider is having a wheel that is 1/2" too narrow below the tire limit. Ideally, I would never do even that.)

Your question, is, of course, a bit different: "Stay within the limits, but what is the difference between the two extremes".

What little I know: in certain cases, with hard cornering, and incorrect tire inflation pressure, you could have tire separation from the wheel when the profile changes under stress. In some cases, with very soft sidewall tires (think Z rated), you may end up folding the tire over or not having the tread sit flat on the ground as much as the suspension allows. You may actually end up with less lateral acceleration maximums that you think you have.

FWIW, I have not done any reading on the specific answers that may apply to the above scenario (i.e., wrong width wheel for a specific tire) since I do not plan to ever be there. Maybe one of the engineering types (Q45tech?) can answer the questions a whole lot better!

Z

[bruce.weiland]

Z,

Thank you for the reply. You understood my question completely, I believe.

My intent is not to go outside the recommended wheel range. I am trying to find out whether paying the premium for a wider wheel, 8, 8.5 or 9, will gain me an atvantage over a very modestly priced 7.5" wheel. Bruce

[Darius]

It is funny you should mention Q45tech because I remember reading a post of his about two years ago explaining the change in the suspension geometry by changing where the center of the wheel was relative to the center of the stock wheel and how it affected handling etc. I really want to find that thing now...lemme get back to you because I'm curious as hell now.

[nismofly]

depends what car youre looking for this for, if you want to improve the feel of a street tire on a performance car your best bet is to run the widest or near the widest wheel the tire is recommended for, this stretches the sidewall a little which artificially stiffens it to give you good feel...race tires dont need this because their sidewalls are already stiff enough

for anything besides that application though, anything in the range works, its personal preference, i like to go no lower than halfway though on a street tire, so in your example the 225 would go on an 8-9" for me

[bruce.weiland]

Darius,

Thank you for your input.

As I understand it, if the OEM wheel/tire combination has a zero scrub radius, then any additional width added to the wheel/tire combination that is not equally balancee on each side of center will increase the scrub radius.

I don't recall the OEM offset for my 94 active Q, but I believe the OEM wheels are 15x6.5 with a +35 offset. I that is correct than an 8" width wheel would need the same offset to stay centered under the turning radius. I believe this might put too much wheel/tire outside the fender. So, I think, with wider wheels the offset is often increased putting more of the width gain under the car. And therefore increasing the scrub radius.

If I have this wrong, someone please correct me.

I would be very interested in the Q45tech post you mentioned, if you can locate it.

Bruce

[bruce.weiland]

Nismofly,

Thank you too, for the reply.

That tire size was 255.

This wheel tire combination is for a 1994 active Q.

On my two previous actives I had OEM, then 255x50x16 (8x16), and then staggered 255x45x17 (8x17) with 285x40x17 (9x17) rear.

For me it was no contest. The 255x50x16 on 16x8 gave me the best handling without making the ride go to crap.

My current car has the very light OEM BBS. I drive about 4,000 miles a year with this car. One or two 600 mile round trip freeway runs and all the rest around town and the outskirts. Lots of curves and speeds seldom above 60. Generally 35 to 55 with some 30 mph quick curves, lumpy, So. Cal. roads, dry most of the time.

I have two concerns. How much "feel" might I give up going to 7.5" wheel compared to 8" or even 8.5"?

And how much impact would 6 lbs per wheel of unsprung weight (14 lbs vs 20 lbs) have, given my "street" driving. Also, don't forget my active gets to deal with moving that extra 6 lbs. at each corner.

Thanks for any input you have.

Bruce

PS If you are wondering about the tires I am considering, it is the g-Force T/A Drag Radial-2 (dot for the street). Given the small amount of mile I drive in the Q each year I am not concerned about wear life. This seems to be as close as I can come in this size to the Yokohama AVS intermediates that were the best tires I ever had on the Q's, went through several sets before they were discontinued.