what to do with wheels and tires

[slngsht]

I'm getting the car ready for the autox season. My current wheels are 10.5" wide in the rear and 9.5" in the front (18" and 17" diameter).

I just scored a 2nd set of wheels that are 1" narrower, and magnesium instead of aluminum. Each wheel is just over 2 lbs lighter.

The last autox I went to, my current tires did not even feel warm after a run. So I'm wondering if I should run the lighter/ narrower set for autox.

On the other hand, I can use all the traction I can get for acceleration.

Thoughts?

[yellowss7]

Mazda, With your torque and hp, you are going to find it hard to put the power down unless you mount a set of Funny car rear slicks. :D

Slightly narrower tires might help you get some heat into them but probably not much more.
My 10 inch wide R25 compound slicks hardly ever get more than warm to the touch, except on hot days.

Find the stickiest tires you can get and start in 3rd gear. :D

Tom

[Silk]

Mazda,

I agree with Tom - with all your HP and TQ, the bigger the contact patch, the better. Most of the year I'm spraying my tires between runs to evaporate heat.

Now, as a competitor, I'd strongly recommend the tire in the link below. It'll build heat fast, last a long time, and it looks really smart.

http://www.universaltire.com/cart.php?target=product&product_id=25222&category_id=330

Gary

[yellowss7]

Gary, those tires would be just the thing if Mazda would put Clamshell front wings on. :D

Tom

[slngsht]

and WWII leather helmet and pipe too

[Davemk1]

Getting the power down won't be the issue. Turn in will be. You'll need to be patient with the power and resist the temptation to floor it to use all that HP you have only to push too deep into the next corner. With such short runs you'll barely get the rears warm and the fronts will be cold and understeer becomes the real issue. You can't count on tire temp being a benefit ever. Figure you'll be running on cold tires.

Suspension tuning and geometry up front will trump power in autocross every time. So dial in your front numbers and do some basic checks for front tire temp (even temps across the width of the tire) to dial in air pressures and camber.

All that said running the uber-soft Hoosiers is the ticket. I use the 25B's (13x8" all round) and they hook up very well even 5 seconds into a run when they are stone cold.

Theoretically a narrower tire will heat up faster but there isn't a tire out there that will warm up in the first 10 seconds of a run so go as soft as you can and maximize the footprint and you can do very well.

FWIW I get tire temps of about 110* front and 120* rear on a warm (80* ambient) day in my 1400lbs car/driver combo. Optimum temps for the Hooiser 25b are in the 140 range so I'm never there. But transitions are crisp and clean and the grip is very predictable.

Have fun experimenting!


dave

[slngsht]

I don't think they make the R25B in my sizes :(

[jwduncan]

Mazda,

If you can't find a R25B in the right size, another option could be the Hoosier A6 DOT tire. It looks like they have 17" and 18" options

[slngsht]

Jeff, is there a significant difference between DOT slicks like the A6 and slicks that don't have to meet DOT standards?

[Davemk1]

I don't think they make the R25B in my sizes :(

Do you have room to run 15's over whatever brakes you've got in there?

Dave

[slngsht]

nope. 17s are the smallest that fit over the brakes. that's a project for next year...

[Davemk1]

Jeff, is there a significant difference between DOT slicks like the A6 and slicks that don't have to meet DOT standards?

The rubber compound is the same or very similar and the A6 generates more grip for some cars according to Hooiser. The downside is weight (the A6 is much heaver than a race slick) and the sidewalls of the A6 are made for the weight of sedans. So they can be too stiff for a Seven and cause them to skitter around.

The A6 is a DOT tire that needs to pass the DOT tests (puncture resistance) and have a certain thread depth (which is why it has the two grooves). The race slick needs to hold air and that's about it.

Dave

[Davemk1]

nope. 17s are the smallest that fit over the brakes. that's a project for next year...

If you need to run 17's then you are stuck with DOT tires as I recall. The Hoosier A6 and the Azenis 615 are the real choices. I see the Azenis are available in lots of sizes in 17's. I just looked at the Hoosiers and they also list lots of widths available in 17".

Dave

[jwduncan]

Mazda, I've not had the opportunity to run A6s and R25Bs on the same car so I'm only guessing but I suspect the R25Bs will have a slight grip advantage over the A6s on most surfaces/temps. Again only a guess and the A6 is a very competitive tire. I suspect some folks have had the opportunity to test them back-to-back and could answer with more real data.

As Dave mentioned if you can fit 15" wheels, you could probably find some slick sizes that would work.

[Davemk1]

As Dave mentioned if you can fit 15" wheels, you could probably find some slick sizes that would work.

If you have the sump clearance it also allows for a lower center of gravity without resorting to lowering the suspension and messing up the geometry.

I run 15's on the street and 13's while autocrossing. The 13's are also easier to carry with me to events.

dave

[Boxologist]

a6 are ur best bet. followed by the kumho v710 and then toyo/nitto r comps. hoosier r25/35/45 are not available beyond 16" diameter. their new r80/100 sompounds are their.

goodyear may have some slicks available, but i am not knowledgable with their line of tyres.

[slngsht]

well, i got RA-1s on my magnesium wheels. plan is to get the A6's on the Z06 wheels - BUT, IRS will take several years' worth of autox tires out of my pocket tomorrow, so that will have to wait. :leaving:

[WestTexasS2K]

I think the Hoosier A6 is going to be your best bet. If you could get slicks then you would be better off, but I dont know of anyone that makes them in 17 or 18s.

[WestTexasS2K]

saw these on ebay with wheels http://cgi.ebay.com/ebaymotors/Corvette-C6-stock-aluminum-Wheels-Hoosier-A6s_W0QQcmdZViewItemQQ_trkparmsZ72Q3a1171Q7c66Q3a2 Q7c65Q3a12Q7c39Q3a1Q7c240Q3a1318Q7c301Q3a1Q7c293Q3 a1Q7c294Q3a50QQ_trksidZp3286Q2ec0Q2em14QQhashZitem 220393581356QQitemZ220393581356QQptZMotorsQ5fCarQ5 fTruckQ5fPartsQ5fAccessories

[slngsht]

he won't ship... and C6 wheels are even bigger than C5 wheels at 18" front and 19" rear.

I'll have to run the RA-1's for a while until i can recover from my tax payment. Still not walking straight ;)