After some track time and almost 2 yrs into my 8 I have decided that it is time to get some dedicated track tires. The o40's actually do better than I thought (with the right pressures of course) but after a NASA w/e at Roebling give your tires hell raceway I have come to that conclusion. My question as I ponder on this -is---does 17" wheels/tires offer any real benefit? I want personnel experience not what i have found doing the search thing. The wheels and tires will be a little cheaper/lighter. (I plan on running a 245/40/17 R compound). If I go with 18" I would go with the same size tire---245/40/18. Lodgic tells me the 17" would be better but since this car defiles lodgic I thought it would be good to ask.
Any experience out there!
olddragger

 

The only advantage to 17"s is cost. As far as size I have seen 275-40-17s on a 17X8" wheel on an 8. Many of the Grand Am cup cars also run 245 17"s. If you stay with 18"s run the 245-35-18, it helps your gearing.

 

For a good HPDE track R-compound like the Toyo RA-1, the cost difference from a 17" to an 18" is significant.

RA-1 pricing from Edgeracing
245/40/18, $243/tire
255/40/17 $162/tire

I'll be tracking my car on street tires for a year (Azenis 615's, most likely), but at the end of the season next year, I'll likely pick up some 17x8.5 or 17x9 wheels and run the 255 RA-1, as long as the price differential is the same.

 

I suspect that switching to 17's will indeed lower the mass of the wheel tire combo and improve gearing. Since ppl that race go through tires like a bad habit, I'd say cheaper tires would be the main advantage. The weight and gearing factor is just a bonus.

 

any recomendations for a 17" wheel?

 

SSR Competion
kosei racing
volk te37
oz superleggara

 

The higher the sidewall (to a degree), the more the tire can flex and expand, which in turn means more grip. Proved this on my Miata some time back. Stock wheel size was 14", my aftermarket wheels were 17's. The 17's had no flex, and thus no "transition" when entering corners, which made it feel faster. But, the 14's, even with all-seasons, easily out-handled the 17's. Felt a bit more "mushy" at times, but there was noticeably more grip and stability in corners.

I think the Toyo Proxes are the tire of choice for many people, but I'm not sure as far as wheels go... Might check here for some ideas, though: http://www.tirerack.com/upgrade_gara...4&autoModClar=

 

You would think that but most time that is not the case. While the 17" wheel is lighter than the 18" the 17 tire weighs more. Also in most cases the 17 is taller that the 18. The 245-40-17 is the only 17 that is shorter than the 18". The 245-45, 255 and 275 17"s are taller than the 18s.

 

When you did this "test" did you use the same brand and model tire? Were they the same width and overall diameter? If the 17 was taller it hurts your gearing.

At a recent test and tune we were at some friends were running a DSP BMW and ran most of the day on 275-40-17s, they switched to 285-30-18s for a few runs and went a full second quicker. Just to double check they went back to the 17s at the end and slowed back down a second from the 18s.

The RX8 with the sport pkg was built to run on 18s, Mazda spent a lot of time and money to get a level of performance and ride quality. If you just change one part of the package you wont see a big improvement. Also keep in mind each tire size has a different spring rate built into the sidewall, the taller sidewall on the 17" will soften up the car.

 

I figure if you are racing with a 40 series on the 17" it would be lighter/shorter then the equivalent 18". I am actually buying 17" rims so I can use a 50 series tires on the street and I'll have 40 series for the track. The roads are kinda bad in toronto so I'd prefer more comfort in this area.

Also, wouldn't going to a 17x8.5 improve handling as a 245 tire would have less flex?

 

Most guys on 18 are on a 245-35.

Here is stock and various R tire sizes:

Tire Size Sidewall Diameter Circumference Rev/Mile Difference
225/45-18 4.0 in. 25.97 in. 81.59 in. 777 0.0%
245/40-17 3.9 in. 24.72 in. 77.65 in. 816 -4.8%
245/35-18 3.4 in. 24.75 in. 77.76 in. 815 -4.7%
275/40-17 4.3 in. 25.66 in. 80.62 in. 786 -1.2%
245/45-17 4.3 in. 25.68 in. 80.68 in. 785 -1.1%

The only 17 I would run would be a 275-40-17. If I was going to give up gear it would be worth it to get the extra width for grip and heat resistance. Either way I would go with a 17X9 wheel, that way you can run a 245 now or a 275 if you want. The price difference between a 17X8-8.5 or 9 will be very small.

Due to the taller sidewall of the 245-40-17 I cant see how it would be as fast as the 18 becasue of the extra tire flex. The only thing you gain is cheap tires. One plus is you might even be able to pick up Grand AM take offs from the pro teams if you run the 17.

 

Re the GAC takeoffs: a good friend picked up 12 one-session-old Hoosier GAC-spec R3S04's from a GAC race at VIR this past weekend for $50 a pop. It had started to rain that day, so everyone was sprinting for the Hoosier trucks to get rains mounted. He made out like a bandit. These were 225/45/17, but he verified that there were plenty of 245/45/17 available.

If you're around a track that runs GAC races, it's worth bringing the tow vehicle/van/station wagon with you and a couple hundred $ in cash regardless of weather.

For us HPDE hacks, a $200 set of very usable Hoosier Road Race compounds is a heck of a deal. That alone is reason enough to consider 17" wheels for track.

 

All of this is good information but one other thing i would like to add is that with 17" wheels you can go wider in the front.
On 18's the widest i'ves seen anyone do in the front wheels is 8.5". With 17" wheels you can easily go to a 9" width. This allows you for wider tires (of course), but also allows you to keep a straight set up. Meaning 17X9 in the front and rear. While on an 18 you will be going with a staggered set up if you want more than 8.5 in the rear.

I personally do not want a staggered set up on this car. I feel very comfortable with keeping it balanced.

-hS

 

BZZZZ wrong.... Goodwin racing is using 18x9.5 on all four corners of there RX8. They sell them to.

They run 275-35-18 tires on them and yes the car is lowered.

Here are the details and pics:

http://www.good-win-racing.com/mazda...topic.php?t=53

 

great info guys. I see Goodwin has my rims on their car! I also am running (on the street) the rpf-1'a but mine are 18x8 with a 35 offset. Currently stock 040's on them. Great wheels! 17 lbs!
Cheap R compound availability is a big bonus so that is a plus with the 17's. Wheels also are less inexpensive and lets face it we are torque challedged so anything that can help with the gearing may be of benefit (depending on the track). 17's are usually lighter also. I know when I switched to a lightweight wheel it did make a seat of the pants differance in the car.
Thats why I was wondering has anyone ran 17's on their car yet? If so any differance? I haven't heard from anyone or know of anyone who has ran with 17's on the RX8.
Who will be 1st?
olddragger

 

Just an fyi....Tire Rack can get goodyear eagle F1 GS-D3 Tires in a 245/35/17. I'm not sure if they are good or not but for $150 each, they are almost half the price of an 18" 35 series.

 

yep, one of the locals here in atlanta runs 275-35-18's on stock rims for autocrossing in STU. They are huge, and have a noticable bulge to the sidewalls, but it seems to work.

 

I've run a full auto-x (STU) season on Kosei K1 TS 17x8 wheels with 255/40-17 Kumho MX's on them. The car definately feels more alive. Seems to respond better. Don't know if that is due to the loss of unsprung weight per corner (>6lbs) or the slightly better gearing or both. I swap them on just before an event and you can feel the difference just driving on the street.

 

Thanks Dark
Feels lighter and more responsive? Are you running stock wheels on the street? Your 17" wheels are what I am looking at(i do track not autocross) but I will be running a R compund maybe the 710's maybe hoosier.
Thanks
OD

 

wow, I entered this party late...

I've been on 17's for some time, and even use them daily. This is my first full season at STU (I'm currently second for the year, though I've been taking a beating lately) and I run 275/40 17 on all four corners. The tires weigh around the same (if not slightly less than) the stock 225/45 18. The rims weigh in at ~16lbs (better than the 23lb stockers )and cost $200. The front is 8" wide, while the rear is 9" wide. The total height is riiiight about the same as the factory height (tire diameter) if not a little less.

The front has a greater slip angle (I like it that way) than the rear and the Kumho MXs are great (though after the GRM test, I'm considering the new 615 Azenis next season.)

The extra sidewall helps with suspension (especially since I plan on getting coilovers with some beefy spring rates).

All in all the car handles phenominally, and yes the 17 tires are cheaper to boot

BTW: you can see all the details on my cardomain page in my sig :o

 

cool alex--- nice domain by the way. This is the kind of info I was looking for.
One thing i am concerned about is turn in and transition. I really like the way the car reacts now. Am I correct in that with the little extra sidewall it make a slight differance?
I am looking at 17's because of weight (of the tire my enkei 18 rims weigh 17.5 lbs) and the cost but--i wanted a performance advantage along with the reduced cost.
PS I am running carbotech pads (panters) --man does this thing stop! (I need more rubber!)
thanks again dude-- any personnel experience you can share i welcome--concerning the 8 of course.
olddrgger

 

How are the Kosei wheels as far as durability is concerned?

 

not a problem. i have the rpf 1's 18x 8 with a 35 offset. high quality wheel, strong and wgt is 17.5 lbs. it has taken track beatings and a few thousand miles on the street. just get lug nuts with them. Oh they are easier to clean than the stock ones also.
olddragger

 

I do the same for autox. I got a great deal on them so I'm using them. They bulge, but you still get really good contact area.

 

Does anyone know the wheel offset that Godwin uses to fit the 18x9.5 with 275/35/18?