it’s a common theory in the "drag racing" world. I understand that they inferior to you because you go around cones and they only go in a straight lines but it’s common knowledge that in a drag race each pound of rotating mass is equal to eight to ten pounds of “dry” weight. You can believe what you want I truly don’t care but you can’t honestly tell me a “lighter” car doesn’t accelerate faster/harder than a heavier car.

Sorry to be a dick but I was just quoting what I’ve always been told in the drag racing world. Sorry if it’s not up to par with the theory’s of the autocross world. I guess next time I have to have a physics problem backing any “facts” I ever say. I respect you as a fellow STR guy and I'm not trying to argue but 3 different people called me out on my statment. I need to remember this is the racing forum and not off topic

Update on the buddy clubs- (from group 5) The distributor (buddy club) only has one single wheel left and isn’t getting any more because they discontinued the wheel. So I sold my wheels because some guy at evasive told me they could get them and now that’s not the case anymore. I’ll hold out until Feb. and see if anything pops up but it looks like I’ll be going back to the 949’s. The question now is to go black or nickel.

 

In STX, the 17x8 Slipstreams were 20+ lbs compared to the Rota Torque and Boost at ~18.5 lbs. Other STX wheels like the 5Zigen FN01R-C were ~17 lbs and Enkei RPF-1 and Kosei T1-S at ~15-16 pounds.

The ST 15x7.5 Slipstreams are ~13.5 lbs compared to SSR and other options at ~10-11 lbs.

The Slipstreams, as well as other Rota wheels, are a good value because they're so cheap. I think they were also made with a beefier design, so they're popular for track usage (or it could be because of the large widths available).

 

So I did some actual quick calculations to disprove this, because I'm a nerd. Here's what ends up happening:

1) Acceleration. One lb of rotating mass, if you assume the worst theoretical case of a rim not having spokes so all of the mass is at the edge of the wheel, and you assume 17" wheels and 255/40/17 tires, you get that 1 lb of additional weight will be like approximately 1.5 lbs of not rotating weight. Of course a more realistic approach with spokes is slightly less, maybe 1.4 lbs equivalently.

2) Braking. We're talking street tires here, so your tires are going to give before you reach max braking force, so rotational inertia is not going to be a factor since you're already not braking at your maximum. So 1 lb of additional wheel weight will be no different than a 1 lb weight duct taped to the control arm.

3) Handling. OK, here we're into unsprung weight. Less unsprung weight will help, but there's no way to put a number on it since it depends on the road surface.

In summary, sorry josh, but you're not gonna get 100 lbs equivalent savings.

I wonder if the rule you heard was if you save 1 lb per wheel, it'll save 8 lbs total? In other words the 8 lbs is taking all 4 wheels (4 lb rotational mass) into account already, meaning that they got 2 where I got 1.5. That's still really high, but it's at least in the ballpark and might be true for some cars on 20" wheels or something.

If anyone wants me to go into more detail on what I did I can but I'm guessing nobody cares

 

[QUOTE=IntegraR0064,Dec 9 2010, 08:28 PM]

So I did some actual quick calculations to disprove this, because I'm a nerd.

 

ouch, with "answer" in quotes, them's fighting punctuation

 

It's always nice to have the correct info or at least close to it?

 

Sorry, I confused you with the OP I quoted.

I have 800/700 off the car at the moment, and I am putting in 450/375 for the winter right now.

Next year I was thinking about going to 700/550, but the chance of me moving out of the country is good, so I'm holding off until I know.

 

It is and for that we thank you IntegraR0064, I stand corrected. Now use that math skills of yours to come up with a magical spring rate set up for us thats going to beat on on the miatas! On the topic of miatas I got told today ken M is moving to a different class next season. I don't know how true this is but it sure makes me happy!

 

I think it's good to be competing against national champs, especially the class defending champ. It's fun and good for use as a benchmark for driving and setup.

 

Use 42.



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Actually, math and magic don't work so well together...