255 or 245 width tire for autox on OEM rims?
 

I have an extra set of OEM rims waiting for STU-worthy rubber and after checking all over the place I am seeing mixed emotions on whether 255 or 245 width on stock rims would be a better autox solution. I did my first run in this car yesterday with a set of 225 all-season tires and very quickly met the limits of adhesion. I was relatively fast, given the lack of grip, but will never touch a decent driver in a prepped STi until I go with a better compound tire and wider tread.

I realize in STU we have the option to go up to 275 width tires, but I don't think it would be possible (nor a good idea) to squeeze that wide a tire on stock 18x8" rims and I'm not quite ready to throw more money at the car for a set of new, wider rims. 255's would be a bit wider tire, but I'm not sure if it would be too "clumsy" a tire for the RX-8. I've seen where 245 width is more common for people on the street, but I am just wondering if anyone has any real experience with the added benefit of tread width of a 255 compared to the "tighter" feel of a 245.

Thanks in advance,
Bill

This can be confirmed in other threads but I believe the maxium size on the 8 inch OEM rim is 245. Even if you can get a 255 on the rim, I also don't think it would sit right - meaning you might not get all of it on the road.

the 275 fits, though if you are keeping the stockers as your STU tire (funny, i'm in STU so I don't have to swap out tires :rolleyes: ) then, IMHO, The Falken RT-615 in a 265-35-18 might be the way to go. You get more contact patch and better gearing, both of them you'll need against the STI.

265 is a bit much for oem wheels. I don't think you can safely put more than 245 on them.

I have an 8" rim with a 275 on it. I run them daily, and have run two seasons and a track event (this is the third season I run that tire/wheel width). I think 265 might be ok ;)



FYI: I run a 17" rim, but there are several others who have run this size.

The 245-35-18 would be the way to go (like in BS), but they don't make too many decent ST tires in that size.

lol ...

I was already looking at the RT-615 and just couldn't make up my mind regarding the width. It appears they come in a 245, 255, and 275 width. I believe the 275 just might be a bit much for those poor rims, though. :) I'd love to see a pic of how the contact patch rests on the ground on yours.

I just recieved my Azenis in the 245 size and wow, they look huge sitting on my garage floor :SHOCKED: Can't wait to get them on :aroused:

I guess that larger sizes could be put on the 8" OEM rims but how much of the tire patch actually touches the ground if you do?

Yeah, my 255s look enormous compared to the stock 225s

Well, I went ahead and ordered the 255 RT-615's. They should be in by Thursday and installed on my day off Friday. I'll also be doing an alignment as I haven't done one since installing the RB suspension a couple weeks ago. I'll most likely be going for as much negative camber as possible up front. I'm curious now as to what pressures I'll need to run the tires to get the edges on the ground and get full grip in the sweeps.

:slap:

:bootyshak

the better to stomp you with, my pretty ... :kiss:

http://www.weirdload.com/art/wwitch.jpg


the RT-615 sidewalls are so soft you won't have any problem rolling the outer edge over to the ground, unfortunately the inner edge will be lifting off in the process ...

I'm running 255/35/18 Dunlop SP SS Race on my stock rims with no problem I'm sure a 265 would be ok and could see the 275s even working. I have full contact patch to the ground with the 255s. I ran 245s on my 7" stock BMW wheels when I autocrossed my Z3. They rolled a bit at the edges, but they worked just fine ; )

FWIW -- I had to go to two tire places to find one that would install my 245\40's on the OEM rims. First place said they would only install OEM recomendations unless they had a statement from Mazda (Lawyers)... I called the local dealer and the tech said two sizes larger would be fine eg. 245s. Found another tire shop with all the right equipmet to handle the wheels and TPMS and high tech balancing etc. $80 and done. Lovin' my Azenis. Can't wait to get back to the track.

the legal system in this country is out of f'ing control ...

I got the tires mounted and the car aligned last Friday. The 255s fit great on the stock rims. So well that I almost want to make these my everyday set of tires. (...must... save... them... for... the... track...)

they fit, but great is debatable

as long as you're happy nothing else really matters ... congrats

Yeah, I understand your point. I guess I really won't know the real "benefit" until I get the thing out there and see how much tread will hit the ground and how much grip I can actually get. One thing that is for certain: These definitely aren't R-compound tires. There's nothing like the rock-solid feel and amazing grip of a race tire.

I've got experience shoving wide tires on narrow rims. 205/50/15 Azenis on a 6" rim.

I hated it. WAY too much flex and squish. For my 8, I doubt I'll go wider than 235, unless drove a car with wider rubber and found the tires weren't squishing and rolling.

Okay how does everyone feel about the autocross performance of the 255 vs 245? I'm leaning toward the 255 for the extra grip (on stock rims), but it sounds like there may be some tradeoffs here with soft sidewalls...

I had a two day autocross weekend on the 255 width RT-615's and I'll have to say I that they did very well. They definitely don't have the stiffness or grip of an R-compound, but they are the next best thing. The challenging parts of the courses were a high-speed slalom and a pretty tight carousel. The car performed very predictably wihout the DSC on with only minimal understeer when going in hot that was easily corrected with throttle control.

After trial and error on Saturday, I finally found 42psi all around to be the optimum pressure for my setup. They were being heated evenly on the contact patch with minimal roll. Just make sure to keep the pressures in that zone as they will shoot up to 45 or so after your first run and will need some air out.

One thing, though... if you're wanting to be competetive in STU with the Subies and Evos, I'd highly suggest going with a wider 17" rim that you can fit 275's on. If you're going to stay in B-Stock I'd probably go with a 245 width R compound.

I chose to go with the 255 width because I already have an extra set of OEM rims and wanted to get the most contact patch possible to handle my suspension and alignment settings. As far as being competetive... I like a challenge and haven't been disappointed yet! :)

I have a track day this Sunday so I'll report back how they are at higher speed.

I just got some 245's installed on my car and am autocrossing this weekend. I had previously used this size tire but a different non race tire and it worked pretty well.

I'll update after sunday.

I went with the 245s, basically because the Falken manual said 8.5" was minimum for the 255. I'm sure they'll be so much better than the OEMs I won't know the difference.

2 Autocrosses this weekend against a couple STiVos in STU. I'll report back next week... FWIW I really think the RX-8 can compete in this class at a local level pretty well. I plan to give it a go at the Denver National Tour and see what happens.

I had my first track day this past Sunday in the 8 and with the 255's. One word: FUN! The tires stuck very well and were very forgiving when they started to break loose (which is a good thing when going flat out around the oval part of the track leading to the main straight... hello wall!). I was running in an intermediate group and had to wave by only one car all day... a 700 hp Supra Twin-Turbo. In the sweepers and chicane the 8 held its own very well, but I had to give it up on the main straight to the Supra.

Now, enough about the track day... let's talk autocross. One thing I might have a problem with these tires at our local regional events is the fact that they will most likely not be up to temperature soon enough to make a difference until near the end of the first run. Unfortunately our first event of the season attracted 164 drivers and we only got 3 runs all day at approximately 40 seconds each. I'm hoping my first local event on these tires will have less people so I can get another run or two and get them figured out.

I personally think I like the extra rubber on the road . The rules allow for us RWD people to have up to 275 width tires and the AWD guys are allowed to have up to 245. This is for a reason. The closer I can get to that 275 without sacrificing tire roll or dramatic feel and still save a couple bucks (this season at least) by not having to buy another set of rims... I'm sold! :)

I agree that the RX-8 could be a competitive car in STU and I hope to prove that. But we are definitely at a disadvantage in the horsepower/torque department and somewhat of an underdog, so we need everything we can get out of tire grip.

Well I'm somewhat encouraged that the RX-8 is a pretty good car for STU. I ended up a couple seconds off the pace on a 60-car course. I lost to a fairly well prepared M3, which unfortunately is going to keep getting a lot faster. I need more data and more time in my car to get things sorted out. It finally started handling properly on my last of 8 runs this weekend. I think I'm gonna throw on a bigger rear bar and see if I can keep the handling balance, while reducing some body roll.

The M3 had the tires I would like--255 17s.