Discussion: Optimal Wheel/Tire Setup
 

I tried running a search on wheels and tires to see what the optimal set up for a Second Gen RX-7 was, but way too many posts came up to sort through in one night. So here's the question and point of discussion: what wheel/tire set-up is best for 1/4 Mile? How about for Rally? I'm interested because I'm going to purchasing some wheels and tires for my RX-7 soon, so I want to be sure I'm spending my money wisely.

Road racing, and illegal street racing, I am partial to 225/50-16 on 16x7 inch wheels. Much bigger than that (like a 17 or 18) you loose too much suspension and HP due to the extra weight at each corner. Ideally you would want a wheel less than 17 lbs.

For tight autoX type racing then 205/50-15 or 225/50-15 on a light weight 15x6.5 or 15x7 wheel (like a 10-15 lb one).

Don't know about drag. Never saw any point in it.

as a note, 5 extra lbs on a wheel robs you of about 10 HP, so a 15lb wheel is going to make your car feel like it has an extra 10 HP over a 20 lb wheel.

Wow, I didn't know that, but it does make incredible sense that more weight at the wheels would cost you HP. I'm learning something new everyday here!

Does anyone else here have any opinions on this, or know what the best drag racing wheel/tire set up would be?

When deciding which wheel/tire package to use, consider the diameter and how it will affect gearing. If you were set up with 15 inch wheels and 205 tires with a 4:10 rear gear and go to 16 inch wheels, you could cause the ratio to go higher, which would have an impact on performance.

Before you buy anything, gather as much information that is written, and talk IN PERSON to people who are racing in the series you plan to enter. Of course, you will want to consult the rule book of the series you plan to compete in as well.

Good luck!

db

the problem with 15" wheels for road racing is that you have huge sidewalls that fold over durring hard cornering. But in drag racing, you want big sidewalls so you can get as big as a foot print as possiable. And if you run a real drag tire, big sidewalls are a part of the wrinkel wall design.

You're just full of usefull facts Icemark. :) So if you took off the stock S4 TII rims at 28lbs and put on 15lbs rims...

I've been wondering what could be done to correct the speedo to allow one to run a lower profile 16" tire...

well I mention 10 HP, but honestly 90% of the people out there could not tell the difference between 180 HP and 190 HP.

I used to run 225/50-16 on my Sports Ronal 16x7 rims, the speedo was dead on. So if you were thinking maybe a 45 series the you would need a 245/45-16 to have the same 77.5-78 inch circumfrence. Which means 8" rims...

The other option for a speedo correction is changing gears for the speedo as in this link:
http://members.ij.net/mrmazda/speedo.html

More terrific info. My dad was telling me I could do that speedo gear thing, but I was unable to find any info on it and assumed it wasn't posible on RX-7s. New bookmark, thanks.

In contrast to popular belief, I think I could easily run 235/45/16s on my 7.5" 32mm offset rims.

You're right, most couldn't tell the difference between 180 and 190hp, but most of the people on this board would pay and have paid a fair bit of coin for 10hp. :) At the very least, it's substantial incentive to avoid larger diamter rims, especially for n/a guys with stock 14 & 15" rims.

Hey Icemark - are you saying 5 less pounds per wheel (so 20 pounds total weight) is equivalent to 10 hp, or are you saying that 5 pounds less in 1 wheel is equivalent to 10hp? thanks for any clarification.

If you go from a 28lbs rim on each corner down to a 15lbs wheel, (52lbs) do you think you get an 104 extra hp? ;) (obviously it's not a completely linear relationship as I pretended it is)

Moving mass, yes 5 lbs per wheel is about 10 HP overall (according to Honda North America testing- I haven't tested real world myself, maybe in the next week or two I'll get a chance to).

in addition the other things to add in (according to the Audi board) is that 5 lbs per wheel (or 20 lbs wheel total) is equivelent to about 61 lbs of non-moving mass, due to the extra weight again having to be actually turned. So you add the weight of a small child, just by adding the cheapo 17 inch rims.