Alternate Universes

[srivendel]

From the SCCA boards:

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Well then it is just a a weight issue. Remember adding weight to the car is additive, adding weight to the suspension is multiplicative and adding rotating mass is to the 4th power!!!! That includes adding mass at a larger diameter, ie. it has a larger lever arm and therefore its effects have a larger moment. Bad Bad Bad.
However, if those larger diameter wheels were Magnesium, then we're talking. Or if using the larger diameter allows you to use a wider and or lower aspect tire then the dissadvantages may be offset to even an advantage.

Rule of thumb is to use the widest tire, with the lowest aspect ratio on the lightest rim that the rules allow or you can afford.

BTW I just happen to have a set of Dymag Special Magnesium 9.5x17 and 11x17, 8.5 #s and 9 #s each, respectively! I saw recently where a vendor could still get them for a mere $3,000 and $3,200 each, respectively!!!!

You will have to pry them from my dead cold fingers!

Jongbloed makes a nice wheel as a cheaper alternative; Aluminum heat treated and hard anodized rims with Magnesium Centers ($750-$800) or you can get BBK Magnesium for about $2,500 each.

How fast do you want to go and how much can you afford? What price speed? I am thinking of replacing my caliper bolts, wheel studs and lug nuts with titanium; just to reduce weight at the wheels.
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$3,000 EACH!?!?!? Ti wheel studs!?!?!?

How awesome a driver would you need to be for this to make a difference?

Why not buy a Caterham, Radical, or Ariel Atom instead and be REALLY fast?

S.

[altiain]

Link? Is that from the forum on the scca.com site, or from sccaforums.com?

The former tends to attract a right share of idiots, while the latter existed long before the current SCCA website "upgrade", and is where you'll find some of the brightest minds in the sport.

I'm going to guess the former - I doubt even the Alien could tell the difference between Ti and steel lugstuds.

Of course, you'll also find Cole on the latter, but he's good for entertainment purposes at least.

[srivendel]

Linkie.

BTW: I certainly wasn't meaning to insult the users of the forums. I'm only saying that in Srivendel World, $3,000 for a wheel will always be Too Much. And ti wheel studs will always be silly.

S.

[altiain]

Yeah, we get the occasional idiot poster over there as well. Thankfully, this poster's half-assed assertions didn't last long, as you can see form the rest of the thread.

Edit: Geez, srivendel! Diggin' back in the archives? I just noticed that thread was dated 2001!

[ccage]

As I've said before, one of my friends in college used to race bicycles. His roomate walked in and said, "Check it out, I just bought a titanium bolt set that saves me 5 ounces!"

My friend says, "Why don't you just take a dump before you ride?"

Chuck

[ccage]

A cool article on plus-sizing of wheels and their impact on actual auto-x performance:

http://www.grmotorsports.com/plustest.html

Chuck

[Jiggerachi]

^good article...but they make no mention of the advantage stiffer race tires have on small wheels, while having better sprung weight & gearing.

[ccage]

^good article...but they make no mention of the advantage stiffer race tires have on small wheels, while having better sprung weight & gearing.

True, the focus of the article is on the actual performance effects of plus-sizing -- a popular visual effect. The article does, however, say:

As someone who has always felt that the added weight and increased rotational mass offered by 16- and 17-inch rims were too much for a small car like our test Civic, David came away very impressed by the larger tires and wheels. Sure the 14s rode down the highway the best, but they did nothing to inspire any confidence on both the streets and autocross course. Since all of the plus-size tires were detrimental to ride quality, why not go with the ones that look the best and offer the best handling?

...thus recognizing that the additional rotating mass had less overall negative effect on performance on a real auto-x course than the positive effect of the better "feel," leading to a net improvement in course times on plus-sized wheel/tire combos.

Though they don't actually test lower profile tires on smaller wheels, I think the overall take of the article is that there is a significant "feel" difference with stiffer sidewalls which leads to more "crisp" turning performance and documentably lower lap times. This seems to me to indicate that an additional savings of a pound or two of rotational mass wouldn't lead to earth-shattering changes in course times while a significantly improved "feel' might.

They also recognize the TCB in all of us, indicating that the 15's seem to be the best price break as the bigger (wheel) diameter tires get pretty pricey -- as do wide small (wheel) diameter tires.

In my inexperienced (read: worthless!) opinion, I won't even see enough performance difference in steel over aluminum (2 lbs. or less!) to bother paying for the aluminum. I'm going to pick up cheap-ass steels for the upcoming auto-x season, put some Azenis on them, run STS2, and try to eek some time out of myself before the car.

That said, I'll probably also put my fat ass on a diet because it'd be cheaper and easier to take 3x the weight off me than off the wheels...

Chuck