Arrrrex-8

I'm going to enter into a time attack series held on a go kart track in my STX setup RX8. I'm trying to decide which tires to use.

Option 1 would be to use my STX wheels and tires, 255/40 ADO8's on 17X9 wheels.

Option 2 would be to use 245/40 BFG R1's on my stock wheels.

Every session will be 4 laps, 1 to warm up the tires then 3 hot laps. Even though it's a go kart track it not overly tight and has a decent straight. Here's a video of a lapping session I had there in Feb. http://www.youtube.com/user/miatalon.../1/QDEZlQsJYps

Thanks for any suggestions.

Modified Dave

I've done three 25 Hours of Thunderhill races on R1's as well as quite a few Time Attacks in my Civic racecar so I can tell you with a fair amount of confidence that although this is an amazing racing tire, it takes longer than most to come up to temp so is not all that well suited to 4 lap sprints on a short course. You'll probably only just reach optimum temp (180-200 F) by the fourth lap unless you live in a very hot climate in which case a couple laps may be enough to get them up to temp. Running a narrow tire like a 245 will help and so will more pressure and aggressive alignment settings, but as much as I love R1's (and I do love them for any type of road racing or lapping...check out the link below), I think you'll have more fun in a 4 lap sprint session on a r-compound that comes up to temp more quickly (ie. Kumho V710, Hoosier A6, Hankook Z214 C71, etc) or a street tire (which are designed to work well at lower operating temps). Or if you're looking for a durable r-comp that works well in cooler temps and without a lot of warm-up required, Nitto NT01's are a great option too.

http://www.modified.com/tech/modp-10...ire/index.html

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iTrader: (1)

Option 2. The R1 will beat the AD08 easily. We have been running the R1 on our SSC car for the last two years, and they work great. They do take a lap to heat up, but with the format you described you will have that. We have also used them on a number of cars for autocross, and while they are cold blooded, they will still kill a street tire.

Spin9k

Interesting story on the R1s Dave, a "How'd they do that?" not found elsewhere. My 255s have hundreds of track miles, and are worn barely to the 1st level on the wear holes. I agree they take a lap or so to warm up to very good grip....but getting to "great" takes concerted effort on a hot track surface, I guess because the 8 is pretty light and balanced. I keep wondering how many heat cycles it'll take before the grip goes away, even if the tires look good?

Arrrrex-8

Thanks guy's I had two main concerns with which tire to choose, one being would the R1's come up to temp quick enough. At that lapping day in the video it was late February and cold and damp, I was on RE11's. At the end of the 15 minute session the tires felt like they were really starting to come in. Don't really remember how many laps it was before they no longer felt too cold. But hopefully it'll be dry and 30 degrees or so warmer.

The other being the R1 is a narrower tire on a narrower wheel. I was thinking about that some today and realized that while the R1 is only a 245 the fact that it is a slick aside from two groves it probably puts the same or more tread on the ground as the 255 ADO8 once you factor in the void area of the tread. So that just leaves the question of how much of a difference the 1" difference in wheel width makes.

I think I'm leaning towards the R1, another plus for it is it's taller. I was riding the rev limiter for a few seconds at the end of the long straight the previous time I was on this track so with the R1 I should get a little more speed on that straight.

Dave, I was asking about these two tires because they are what I have. I'm not looking to buy any just for this, if I was however I'd definately get 710's or A6's.

Modified Dave

Glad you enjoyed the story, Spin9k. Can't remember if I mentioned it in that story or not, but while talking with Doug Brown from BFG at one of the 25hr races he felt a lot of guys were opting for too wide a tire when buying R1's because they're accustom to cramming as much tire as they can under their cars. However, after a lot of testing BFG went with 255's as the spec tire for the Mustang Challenge series, and those are heavier and more powerful cars than the RX-8. So those 245's on Arrrrex-8's car might actually be just about right, especially if it's nice and warm out. I can see how you'd be having trouble getting your 255's up to temp. I managed to stuff some 285 R1's under a S2000 and we couldn't get nearly enough temp in them at VIR, even after 4-5 laps. Definitely a case of way too much tire for the car.

I haven't been able to degrade a set of R1's with heat cycles yet. I'm sure there must be some drop off with enough heat cycles, but so far the set of 235/40-17s I run on my Civic racecar are hanging in there extremely well after at least 15-20 heat cycles and they're also only down to the first level on the wear indicator. Seems to be a very durable compound!

Arrrrex-8, just thinking about your 245 R1's on stock rims, and given that it can be challenging to build heat quickly with this tire, having them mounted on a slightly narrower rim might actually be a good thing since it'll have the effect of narrowing the contact patch a bit. Would love to hear how they work compared to your RE-11s, should you get a chance to test them on the same day.

Spin9k

^ No that wasn't mentioned Dave, but definitely more very useful R1 info. To wit, I was at Limerock a couple days ago, it was a sunny ~90 degrees, not sure what the track surface was at, but....let's say warm With Limerock being an rather intense short tight track 1.5m, I was happily surprised to see tire temps in the pits (surface pyrometer) in the 160 range, something I've not seen often. So likely in-session, they were hotter and in the requsite 'temp-zone' spec'ed by BFG.

Your right-sizing suggestion based on BFG recommendation sounds spot-on, as your story said they worked to reduce the amount of heat R1s generate, compared to 'normal' R-comps. That should put the OP onto success on a shorter/smaller track if he uses them.

Mine (255/40/17) generally read 130s-150s degrees in the pits and seem to work fine on track, but with subtle differences when they do get hotter... e.g., I hear a more 'gravely' tread sound and they allow a very stable tail-out attitude in tight sharp corners (thinking the Esses after Big Bend if you've been there). To put that 'zone' feel into words, I'd describe it as if I have rubber tank treads under me firmly stuck to the track, but that let the car shift side-to-side on them. Fun!

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iTrader: (1)

The Mustang Challenge runs on the 245-40-18 R1.

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iTrader: (1)

I can't believe there is a bit of doubt in your mind as to which to choose. Run the two back to back, even the best street tire will come up short of the low end R compounds. As far as temp range, don't let yourself be fooled into thinking the UHP and XHP tires don't need heat to work.

Modified Dave

I stand corrected, which only goes to show that you can put too much tire on a car and this seems to be especially true with the R1's.

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iTrader: (1)

Those cars are not in danger of being over tired... 325hp, and 3200+lbs. Using the skinny tires is a great way to bring tire management into the series. You can spot the newbies, they are the ones skating around near the end of the race because they cooked the tires.

Modified Dave

Agreed. I think they also went narrow so the tires would heat up faster and they wouldn't have too many 1st lap wrecks. I almost got to be one of those maroons skating around on toasted tires at Mosport but someone higher up the media food chain stole my seat in the media car

Modified Dave

My experience on R1's is similar to yours, meaning they still work well even when a little colder than ideal, but at these temps their slip angle is peakier, so you have to be ready to react quickly if the tail steps out on you. But when they're good and hot and have that gravely feel to them, their slip angle seems more gradual so you can control some tail out shenanigans more easily.

bse50

I would give a try to the yokohama a048 and toyo r888 tires as well.
They're not the best semislicks anymore but do their job. They are ok even with a humid\clean track and this could play a role too since rain can be a bitch even if it comes a week before the event. You don't have a lot of cars hanging around at the same time rubbering the corners for you.
I would personally stick to a 225\40 tire on 17" wheels. Bigger tires can be ok for autoX but when track racing a NA rx8 smaller tires with a good compound will give you more possibilities and reduced drag for the power output you will be seeing.
There are times when it is a tad more convenient to slightly slide out of a short radius turn in such small tracks and the handling will be better with narrower rubbers