altiain

iTrader: (3)

A 17" RIM might be faster, but both of the tire combos you mentioned are an inch larger in diameter than a 245/35-18, which is a significant difference. While your 17" wheel might theoretically be lighter than my 18" wheel, the tire is not only heavier, but most of the tire's mass is located further from the center of rotation.

I'll take the shorter, lighter tire on an inch bigger wheel any day of the week. Less mass to accelerate, and a gearing advantage to boot.

mwood

^and I'd bet you would 't be able to quantify any difference whatsover in the real world of running a stock RX8 in HPDE's...or, more importantly, from the perspective of just having fun in a non-comp environment

bellwilliam

http://www.tirerack.com/tires/Spec.j...m%3D245YR8KU31

I thought stock RX8 is
225/45-18, which has 25.9" diameter. weighs 25LB
245/40-18 like many recommended here has a 25.7" diameter. weighs 27LB
245/45-17 has a 25.7" diameter weighs 27LB
275/40-17 has a 25.7" diameter. weighs 29LB

17" wheel weigh an average of 3LB less than 18"

comparing same width/diameter size tires and wheels, at 245 width. 17" wheel is 3LB less per corner. and if you think about it: 18" wheel will have more weight on the outer diameter vs. 17"

and if you are going to run 245/35-18, which is a smaller diameter tire, you can run 245/40-17, which is of same diameter and width, but lighter overall. most of tire mass is not further away from center of rotation with 17", it is with 18". Same width/diameter tire will have same amount of rubber on the outside, but 18" wheel will have most of its mass away from center of rotation.

I am not familiar with RX8 world, so I don't want to sound I know what is better for RX8. but general rule has always been smaller diameter wheel is better. especially with low torque cars.

I might not be able to quantify any difference in real world, at least 17" tires/wheels are cheaper.

ULLLOSE

iTrader: (1)

No, they recommended a 245-35-18 which is smaller. Also you can not say ____ size tire will weigh this much, every manufacturer will be different.
Kumho V710, 245-35-18= 23 lbs and 24.8".

bellwilliam

http://www.tirerack.com/tires/Spec.j...num%3D435ZR8A6

since Hoosier A6 was mentioned before:

245/35-18 Hoosier A6 tire - $274
21LB and 24.4" diameter, tread width 9.1"

245/40-17 Hoosier A6 tire - $237
21LB and 24.5" diameter, tread width 9.3"

ULLLOSE

iTrader: (1)

There you go, keep looking and you will find data to support your idea. However that is just one tire that supports what you said, there are not many 245-40-17 R tires, most are the taller 245-45.

imho the only reason to go with the 17" is to save $$$$$$, and if you are going to buy Hoosier A6s every couple of weekends so you can get that size you wont be saving anything.

bellwilliam

sorry guys, don't want to sound like a troll.

thanks for the input.

ULLLOSE

iTrader: (1)

Asking a question does not = a troll. Just decide how fast you want to go, if you want to compete (do you need to fit a set of rules) or do you want to just have fun.

If you just want to have fun, pick up some 17"X9" wheels so you can use a 245 or 275 and look for take-offs. The Hoosier Grand-am spec tire will last a long time and you can find lots of 245 take-offs. Or just buy some Toyos, last for ever and will be faster than a street tire.

If you want to compete get another set of stock wheels, or something 18X8, and to get started buy some used 18" tires.

The wider tire, even being taller, should be faster on the road course, it will also take the heat better.

CosmosMpower

I'd run 255/40/17 or 275/40/17 on a 17X10 wheel. I actually just sold off my 17X9.5 track wheels with 255/40/17 RA1's (I loved the combo) but my car still has upgraded Koni shocks and MS springs with a performance alignment. I sent you a PM.

SolarYellow510

Bellwilliam,

You're the first guy I've ever seen come here already having a good perspective on wheel and tire fits.

I like the Enkei 17x9.5 NT03+M XYZ. It also fits StopTech's 328x28mm kit, which the 18x9.5 RPF1 does not, due to its dish. You can run 255/40-17, which virtually every good tire comes in, or you could go with 245/45-17s. 245/40-17s will give a little better gearing, and are a common size (standard rear axle of BMW 3 Series, etc.), just not as common as the 245/45s.

If you could find a 17x10 in the right offset that was affordable, some of the 275/40-17s with cheated ODs should work well.

I know you're on top of it because you knew where 245/45-17s are used. Basically, you're on exactly the right track. Everything you've written here is right; figure it out for yourself, and you'll do better than most of the advice you'll get here. Except for CosmosMPower.

I copied TeamRX-8 and tracked down what may be the last set of new SSRs in the country that are 18x10.5 +43et. So I'll be looking at 265/35-18 or 275/35-18 tires with cheated ODs.

mwood

^thanks for stepping in and clearing everything up...just what the thread needed

By the way, what is a "cheated OD"? Are you referring to the fact that manufacturers' tires will have significant variance, for a given section size and aspect ratio, in their actual physical dimensions? I'm reading that you want to have a smaller outside diameter? That may be helpful on most all tracks, but could also be a negative on others, where you would want more ceiling in the lower gears...it's hard to make generalizations, without knowing all the facts. Besides, if all you are doing is running laps with your buddies, does it really matter? Might as well find a tire that fits, lasts, grips and doesn't break the bank!

Also, unless your Enkei's have an offset related rubbing issue with the 275/40 size, it would be hard to rationalize buying a new set of rims a half inch wider to run the tire, when the starting point (9.5") is already in the sweet spot for most 275 DOT R's...we ran the 275/40-17 on even a 9" rim in numerous applications where we were limited with rules, and had great success, good wear and didn't give up all that much in terms of turn in characteristics. I'm not suggesting that most 275 DOT R's are optimal on a 9" rim, it really is the about as small as I'd want to go in a road racing application...now, autocross, on the other hand...

maskedferret

iTrader: (1)

If you're interested in staying in stock class, yet want some nice lighter wheels, I would recommend the SSR Comp-H 18x8s (TireRack has them for $469; not all that cheap, but they're quite nice); 17.5 lbs. (compared to the ~22 or so lbs. of stock wheels). I got these for autocross to step up from using all-seasons on my stocks wheels. My stock Potenza tires are on them right now, and I have no complaints. I personally cannot tell a difference in moving to these wheels because this is my first season ever, and I moved from all-season to high performance tires... but eh... they're pretty wheels! :-D

http://www.tirerack.com/wheels/Wheel...6-Speed+Manual

SolarYellow510

Exactly. Like a 265/35-18 Neova is the same OD and width (extra for a 265) as a 275/35-18 Hoosier. The Hoosier is about 3-4 10ths shorter than most street tires with that nominal size. Or a Michelin Pilot Sport Cup 255/40-17 is roughly the same width and OD as a 275/40-17 Hoosier, and the 205/50-17 Cup puts more rubber on the ground than the 225/45-17.

Most street tires fall within a tenth, maybe two, of their nominal sizes. R-comps go all over the map for various reasons. Some are strategic for performance. Others are rationalizations for production.

Nahh, it's way more fun to sit around calculating ODs.

Yeah, I'm always trying to go as wide as reasonable for a tire, in order to get the most bang from the one-time purchase (wheel) as I can for the repeated consumable purchase (tire). On the other hand, the Enkeis are fairly affordable, and the 275s would indeed work okay. The only 17x10s I've found in the right offset range are Volks +50. I don't even want to know how much they cost.

I'm wondering what would happen with a 17x10 or x10.5 on the RX-8. I know suspension clearance gets to be an issue on Corvettes when you start to go wide, and 17s are worse than 18s because the suspension is inside the wheel.

Maybe if I worked at the Tire Rack, I could check a 245/40-17, 255/40-17 and 275/40-17 on a 17x9.5 against a 265/35-18, 275/35-18 and 285/30-18 on an 18x10.5.

I have a pyrometer, anyone wanna buy some wheels and tires?

CosmosMpower

I know a 275/40/17 V710 fits on the 17X9.5 +44 Enkei NT03+M for a fact. I bought a set from an Evo owner, test fit the wheels/tires with no issues. The tires were pretty dead so I went down to a 255/40/17 RA1 due to lots of supply for sale on evolutionM.net

bellwilliam

Thanks all. I thought I was crazy. I am experienced track guy. the rule has always been:

1. wider tread the better (some exception, low HP car on long straight course might be better off with narrower tire).

2. wider wheel the better (it has to fit of course)

3. smaller diameter wheel the better (same reason I gave above, lighter, less rotational mass away from center)

I realize some of the answer came from autocross guys/gals, so they look at thing a little differently. HPDE guys are not confined to rules.

SouthFL

^
Very nice vid!

Yes indeed. It's important to drive this car on street tires first, then move up to stickies to get a full understanding of the car's dynamics (as with any car on your first few outings at the track). Performance driving schools don't make you learn on a street tire for nothing.
All this super wide tire talk makes me feel that you and I are nuts for thinking that a smallish (incomparison to the discussion) 245 tire is an appropriate size to run for HPDE events.

Spin9k

Hey - welcome bellwilliam nice to see another track addict! Some of the topics here are near and dear to my on-going (4th yr) experimentation w/the 8 for (non-auto-x) track use. So...my 2c worth...

Wheels and tires: I started w/stock and they weren't bad at all. Then when they wore out changed to 235/40/18 on oem rims. They were better (RT-615s), some more grip, easier to modulate grip.

Next year got Enkei RPF-1s 9.5" (17lbs) w/275/35/18 RT-615s. Cost wheels & tires was like $2200. The weight was the same as the oem tires and wheels (good) due to the lightweight wheels. More grip again in the twisties, but less top end speed (grrrr). I think either friction or wind resistance or more of the weight further out (rim) or all of those effects caused that. That pissed me off - it was like 116 instead of 120 at then end of a straight and seemed like somewhat slower acceleration too.

This year 17x9" (20lbs) Hot Wheels and Nitto NT-01s 245/45/17. Cost wheels and tires was $1200 Weight is 2 lbs more than the Enkei combo above. Grip is far superior as it should be w/R-Comps, much more lateral grip control, plus I GOT MY TOP END BACK! plus a bit more! Yippie! The response may be a tad softer as is the ride, but that just means they hook up a fraction of a sec later, but when they do they are extememly forgiving and they hang in like glue (as any self respecting r-comp would). Details https://www.rx8club.com/showthread.p...ighlight=nitto

One thing I recorded is that with wider tires the tire temps are lower. And I don't think that's a good thing. The 8 being balanced and reasonably light means it's fairly easy on tires and they just don't get hot enough as the tires get wider IMO. Now with the NT-01s I'm seeing ~165 deg just off track. Still Nitto says the operating range is 160-200 deg I think ... so I'm barely just getting them to the good temp range. But they ARE a wonderful thing!

Brakes: Oem w/SS lines/hi-temp fluid/pads make a dif if you track hard. OEMs pads/fluid are fine for beginners, but you'd likely get numb brakes pretty quick since you're experienced.

1st upgrade was Hawk HP+. My thought - Where's the beef? Next I got Cobalt Friction pads. Now we're talking. They puppies are awesome! Sticky, sticky, wonderful and comforting. Details https://www.rx8club.com/showthread.p...ghlight=cobalt

Some may disagree but I believe in some brake cooling for the 8, even if it's simple and cheap. It still lowers temps as the duct points at the duct on the shield and has some effect. Anything is better than nothing IOW. I take brake temps every time I return to the paddock and I decided this mod was needed when I was seeing my pyrometer go off-scale regularly (>600 deg) at the caliper. Here's my DIY you were refering too: https://www.rx8club.com/showthread.ph...ght=brake+duct BTW it has kept temps well within acceptable range since. the proof is in the results, not what people speculate just "can't" work.

Oh yea, also got some nice Racing brake slotted 2-piece rotors up front a bit later that season and those lower temp some more as well as saving weight.

Perhaps some of this experience will help you go faster, have more fun, and not waste money on pretty things that don't do so much or worse, slow you down! Enjoy and keep the sunny side up

olddragger

iTrader: (3)

We track a lot--one members car has over 5K track miles on it.
Since you are experienced and probably push it a little here is what i recommend
1- brakes pads--correct--pad of choice here, dont forget the fluid--thats a given for a old pro anyway.
2- shocks---the tail gets a little squirrelly on high speed hard braking
3- the rotory engine with its 270 degree flame front likes to run hot. Get real gauges, the ones on the car are dummies.
4- change your coolant to a 70% water and 30 % coolant.
5- do not run a 5W/20- on track--- most of us run a 10W 30 or a 10W40---make sure the oil is warm before you rev her good(tight bearing clearances)
6- all of us pre mix--some all the time some for the track only 1/2 oz synthetic pre mix per gallon.
7- new plugs usually makes a nice difference for the track---plugs go bad for peak performance in as little as 15K miles.
8--get a GOOD alignment--the factory one sucks.
Track her! Then-------
now wipe that silly assed smile off your face!!
olddragger

olddragger

iTrader: (3)

oh someone asked about tires---I use 17's with 235/40 ra 1's. the short diameter really lights this car up coming out of the corners.
olddragger

olddragger

iTrader: (3)

my wheel and tire combo saves 10 lbs a corner. and with the "small" 235 size, i really cant tell a differnce. I run carbo tec xp8 on the front and bobcats on the back--only change the fronts out for the track.
OD

RX8Maine

This has been a great thread. I have been looking into a dedicated track wheel/tire combo and the pricing had me leaning toward 17" already. It sounds like that is the way to go. I am looking at the Enkei RPF1 17x9 or 17x9.5 with 245/45/17, which does have a lot of options for r-comp tires.

I worry that the stock suspension may not be able to handle much more grip than the 245 r-comps, but I may go with the wider wheel just to have more options down the road if I beef up the suspension. (can't do it all at once) Is anyone running a 275 size R-comp tire on a stock suspension?

olddragger

iTrader: (3)

my enkei rpo 2's --a 17x8 wheel and RA 1's 235/40/17 cost me $600. I can get a set of tires every year for approx $300. Yall pay all those big bucks if you want too, but you dont have too. Each to his own though.
olddragger

Spin9k

Knowing what I've experienced this season, the tire/wheels combo I'd get is Good-win-racing's 17x9 Enkei (15lbs!) and the Nitto NT-01s 245/45/17s (~27lbs). Talk about light weight total ~42lbs. I don't think (now) that in HPDE the NA RX-8 can take adavantage of more grip than the 245 R-comps give....so why add the weight, the frontal friction, and rotational mass? The Enkie 17" wheels are $269, the tires are way way cheaper than the 18" sizes (~$50) at $175.

My setup now is like that except my "Hot Wheels" wheels weigh 5lbs more (and cost 1/2 as much) and work great. The 5lb savings may or may not make a difference, but it sounds nice!

I pretty much don't get into the grip limit with the tires unless I purposefully go off line (like pinching the hill at NHIS) then using full power to walk the back end out. Even then it's nice fun, very recoverable, I just want to see what it feels like, and that's hard to do with these tires.

RX8Maine

Thanks Spin. The 245/45 tire size has by far the most choices from what I can see, but the 255/40 is tempting. They are shorter by about 5% from stock (245/45 is shorter by 2.5%), and the extra gearing effect would feel good, and would hopefully make up for the increased rolling resistance. I do like to keep a tire stretched on the wheel though, and 255 on a 9" wheel may be a bit too square.

I'll probably let tire preference and cost make the decisionin the end. There is no doubt in my mind that anything I do will be a lot more fun than the OEM Dunlops.

delhi

Great thread! There's been lots of info on brakes and tires. But no mention of alignment specs despite it being one of the key areas to improve on with track setup.