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[QUOTE=jguerdat,Dec 4 2004, 02:10 PM]Don't forget that the larger diameter tires put the mass at a further distance from the center of the wheel, increasing rotational mass.
Originally Posted by SM00TH976,Dec 4 2004, 07:14 PM
in an autox environment the ability to run better tires is more important than a slight loss in acceleration and braking. lighter than stock 17" wheels with azeni's would be more advantageous than stock wheels with S-02's on an autox course. that is of course just my opinion. even when you go with a more aggressive tire often times you end up with more rotating mass. it just depends on what's more important, lateral grip, acceleration/braking, or bling. on an autox course that it typically very tight, lateral grip is the most important.
I'd certainly agree with this. What's important is 1) what class you're running in (can you change wheels and remain in the class) and 2) does the change in size give you access to a combination that hurts as little as possible for (de)acceleration while increasing lateral grip. Bigger is not always better but most of us have limited funds to figure out what the optimal setup setup is so you pays yer money and you takes yer choice...
Jeff can I just clarify this point.
Do you mean that because the inside edge of the tyre is closer to the outside that the rotational mass is increased? Not something I've considered before.
Of course, the overall diameter of the wheel + tyre shouldn't change at all if you put the correct tyres on.
Also I would expect an R18 tyre to weigh less than an R16 tyre.
Overall my volk TE37s with rubber weigh considerably less than the stock, and the total radius has only increased by 1mm IIRC (due to using 255. 245 would reduce the rolling radius). That 1mm of rubber can be quickly removed with a few donuts.
However, if I'm honest, I wouldn't care oneway or another. I don't use it as a race car.
( note British spelling of tyre ... Sorry )
Your supposition that the inside (bead) being further out increases the mass at the outer radius of the whole wheel assembly would be correct. I suspect, however, that the bead area adds that much to the weight of the tire - it would be the tread area that has the most weight/mass. So, using a larger diameter wheel while maintaining the same overall diameter as stock only is important if the mass of the wheel and/or tire is increased at the outer areas. You don't have much control over the tire since they all have similar construction but you should at least verify that 1) the wheel doesn't have increased mass at the outer radius compared to stock (i.e. very light center, very heavy lip area) and 2) the tire doesn't increase the weight compared to stock.
Of course, there are diminishing returns - as pointed out in a message just above, the tradeoff if rotational mass at the outer radius may be traded off with improved later grip. Just choose wisely, not because "bigger is better"...
I am certain that nobody here has the info to actually draw an accurate scientific conclusion to the question at hand. But, if the wheel is light enough(How much lighter does it need to be and where is the weight savings in the wheel? Is it lighter in the center, the spokes or in the outer rim?) and the tire weight is similar and the diameter of the wheel and tire is the same or less, then I would have to assume that there are no ill effects on performance. I seriously doubt that my choice of the 17in CE28N and a nice grippy tyre(for you Brits )is going to have ANY negative affect on performance since the wheel is so light and the actual diameter of the wheel/tire combination that I have chosen is actually slightly smaller than stock.
[QUOTE=ProV1,Nov 29 2004, 02:48 PM]i was going to upgrade my rims from stock 16" to some 17" or 18", but decided NOT to. I got some 18" rims for my other ride, the new rim/tire weighed 13lbs more per corner.
the extra 13lb makes the car drive like a different car now, totally killed the acceleration and handling. it's like i'm driving with 900 lbs in the trunk????? WTF?
no plussized heavier rims/tires for me!! if the S drove like this i'd go crazy
Interesting.
And on top of that there's the potential for quite a different feel in cornering due to the reduced tyre roll.
I found this VERY noticeable when I went back to 16"s for a week while I was having some refurb done to the 18"s. The first thing I noticed was a softer, more comfortable ride (obviously) but I was put off by the more pronounced tyre roll in the corners... Depends what you get used to I suppose.
Not something I've considered before.
