[Rap]

Tama is your clock off since the time changed? It tells me you posted at 601 and I'm looking at 502.

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[flash]

the farther the weight from the center, the more resistance to acceleration change, both increasing and decreasing



pretty sure i posted a calculator for this here. of course you need to know how much weight is where in order to use it.

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[Cloud9...68]

Yes, I've used it before. I was just thinking that all things equal, an 18" tire should weigh slightly less than a 17" or 16" tire due to the shorter sidewall, and therefore should result in slightly less weight near the outer periphery of the wheel/tire package. I'm sure the difference is very small, though, since the tread area is probably the heaviest part of the tire, and the part farthest away from the center, and the weight of this part of the tire is not a function of the diameter.

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[BeBe]

Still trying to decide what to do about the heavy handling and tramlining with current rim/tire setup.



The tires on the car are Kuhmo ECSTA. Fronts are Supra 225/40/ZR18 and rears are ASX 255/35R18. I would guess they have less than 10K miles on them. Not sure why they would not be all the same. I assume that's not helping matters any.



From exchanging emails with a guy at WheelEnhancement.com, I think my current rims weigh 30lb front and 32lb rear. With the current tires, total weight is 53lb front, 59lb rear.



If I stayed with 18" rims (Porsche 987 Boxster S), I could lower wheel/tire totals to 45lb front, 50lb rear.



If I went with SportEdition Cup4 17" (much cheaper), I would end up at 44.4lb front, 47.4lb rear.



The weights between the 17" option and 18" option are similar. The stagger, front to rear, is 1.5" for the 17s, 1" for the 18s.



Any opinions on which option should provide the best compromise between ride and handling?



Is the Porsche caution against 18" rims based on presumed added weight, or something else?

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[flash]

there are a few things involved, weight is included, as the physics there come into play and add a LOT of wear and tear on the components. tire adhesion does too. the stickier the tire, the more load. things have only gotten worse as tires have gotten better

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[bombfactory]

A few years ago on my M3 I went from the stock 17's to multi-piece 19's with no ill handling effects other than a slight, but noticeable, decrease in acceleration. The 19's each weighed about five pounds more than the stock wheel/tire combo.



While I love the look of the 18's on my 968, I too wonder if it'll handle better on 17's and may try out a set if I get a chance. I'm much too vain to go to 16's tho!

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[Ryan]

The 16's really look dated on the car in my opinion. I switched to 18's and have not noticed a huge difference, but tram-lining is a problem on bad roads. My wheels weigh 22lbs front / 25 rear, but I don't know the tire weights. I got to say it makes the car look sooo much better though.

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[flash]

that is the lure. they do look better with 18s, which is exactly why i still have them on my car. i have pretty much zeroed out the weight issue, but still have to deal with the rest. i have already had to replace a caster block, and am looking at other components soon. keep in mind that i started with all new everything 7 years ago, and have only put 25k miles on the stuff, with only a few track sessions. the added wear and tear is definitely there.



17s pushed out look good too, but in pushing them out, you pick up some of the same issues the 18s have.



definitely not a perfect world

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[BeBe]

Are the wider rims in the rear just for traction off the line or does it also affect handling? Is more better?

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[flash]

yes, and no



while it provides more traction, that is a double edged sword as maximum launch is actually best if you can just break traction, and at an rpm that allows for a brief climb up the torque band. too much tire, weight, or traction, and either the rpms drop and the engine lugs, or you have to launch at such a high rpm that you run out of torque band too quickly.



cornering can improve, depending on camber angle. it can also be negatively affected. too much rear camber and you actually end up with less net contact patch area and thereby lose traction in the corners. this happens a lot when people go to wider rims, particularly when they move the outside edge of the rim outward.



handling, which is different than cornering, can go either way, depending on sidewall flex and such. more tire means more rebound potential. depending on your tire choice, it may get better or worse.



the staggered size thing is a carryover from the 911. they needed it. we don't. in a perfect world, a 50/50 car would have the same size rim all around.



not sure that helped. lol

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[tamathumper]

So, same size rims front and back is ok and even desirable?

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[flash]

had i to do it over again, i would put 9" wide rims all around, with the same offset. this would additionally buy me tire life, as i would be able to rotate the tires.



i know that will go against the grain, and even i have a hard time giving up tire width anywhere, but yes, that is what i would do.

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[BeBe]

Very helpful. Thanks. The guy at wheelenhancement.com said that on a well-balanced car like the 968, you don't really need much stagger (or whatever the correct term is for width difference front-to-back). It didn't occur to me to go with the same width all around.



You would gain tire width up front (I think typical width would be 7.5 or 8"). Any downside to that, other than a small amount of unsprung weight?

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[flash]

sure - any time you go wider you add load to the suspension components, and increase the chance of tramlining. leverage is leverage. increase that and increase the strains. you won't be able to run a cheap tire on a 9" up front either. tread pattern will be very important there too.



it really comes down to where you want to spend your money.



if you went 8 all around, you could probably escape the load issues, but the car might not track as well in the rear.



no free lunch - sorry

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[tamathumper]

What do you mean by "not track as well"?

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[flash]

an 8" rim means less tire than a 9" rim could give you. at 8" you'll break traction in the corners, as everybody with 16s already knows

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[tamathumper]

Ah, gotcha. This thing with stock 16's already corners better than necessary on public roads, if you know what I mean.



I would truly like an "updated" wheel/tire look, but once I get into sizes, weights, offsets, etc. it's just too easy to set it aside.

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[Scott Collins]

The stock 16's made my car very quick and nimble around town, with Toyo Proxes mounted. Faster off the line, not that that mattered much, but the entire car felt lighter and quicker. But through twisties and more aggressive cornering, the grip was suspect, compared to 17's, with Sumitomo HTZ III's. The rear end really wanted to step out. I know, different tires, but I don't think the result would have been much different with Sumitomo's on the 16's.



I have never mounted 18's because with the 17's and tires I have, the tramlining is at the limit of what I can take. On the highway, though, at speed, the 17's are more stable compared to the 16's. It's just physics I suppose.

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[flash]

tramlining is an odd phenomenon with this car. a number of things contribute to it. things that immediately come to mind are:



worn caster blocks

old tires (more than 6 years and they are shot)

longitudinal grooves in tires

square block tread pattern

wrong toe setting

not enough caster setting

too much tire pressure

too much camber

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[BeBe]

Well, this surely is a complicated topic. I've learned a lot -- mostly that there isn't one "correct" answer or combination. It's all tradeoffs. It's pretty hard to reach a decision point where you have enough confidence that after you spend the money that you'll be happy with the result.

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