Skinnier Tires for Tighter AutoX Courses?? Read my idea
03-30-2010, 10:55 AM
#1
Skinnier Tires for Tighter AutoX Courses?? Read my idea
I've been accused of over-thinking things before, and definitely over-analyzing things, so this may all be garbage, but here goes:
This past weekend, I had my best local autocross event ever. I finished 5th fastest out of 43, my 09 RX-8 is completely stock, on new Dunlop Star Specs. Last year I ran on Azenis 615's. I'm finally convinced that the Dunlops are way better than the old Azenis 615's I ran last year. I run 245/40's, and our events are mostly 2nd gear courses, flow extremely well, and keep you up in the 40's/50's in mph no problem.
I've been contemplating an idea for when I travel out of town for a while now. Here's a little background: When I first got my MINI, which I ran back in 07, I noticed how fast and darty the steering was when it had the OEM 175 width skinny tires on it. When I autocrossed, I changed out to 205 width, and though the steering didn't seem as quick, the limit was way higher, as one would expect, which was also very needed for the layout of our autocross courses. I notice the same thing with my RX-8, in just changing from the 225 width OEM's to the 245's for autocross, the steering isn't quite as fast, but there's no way the 225's can hold up as well on the fast stuff, the sweepers, etc....
Well, there are 2 out-of-town venues that I go to each year, 1 being as much as a 4 hour drive. Both are run in small parking lots, and for the RX-8, they are first gear courses, no more than 35 mph, and then you slam on the brakes to slow the car way down for the slow, tight turns. Last September, at the Pro-Touring event, only 6 cars out of 52 were faster than me, and that was on my Azenis in 245 width. Here's what I'm thinking: A set of better tires, whether they be the same Dunlops I'm running now, Yoko's, etc, in 225 width will probably be just as sticky as the old Azenis in 245, maybe even better, and the car may be able to benefit from the quicker turning, especially on the tight courses. Also, the 225 is slightly taller in diameter, so technically, I can get a little more speed before I'm bouncing off the rev limiter. Every bit helps. Another big factor in purchasing another set of "away" tires is that I would rather drive to the event on them instead of taking the extra time to change out. 4 hours is a good bit of driving to be listening to the tires howl, and 225's should be a bit quieter than 245's. My old Azenis are dead, so I'll have a freed up 2nd set of wheels to mount tires to. The Dunlops will still be my choice for local. I'm considering calling up Discount Tire and seeing if they will do the same deal on the Yoko Advan AD07's that the Tire Rack did last week, $99 per tire. I missed out on the TR sale while I was researching the AD07's over the weekend. Dunlops in 225 aren’t out of the question, they’re just way more expensive.
It all boils down to this: On a tight, first gear course, can I be faster on 225 Star Specs, AD07's, or similar than I would be on the old compound Azenis 615 in 245?
This past weekend, I had my best local autocross event ever. I finished 5th fastest out of 43, my 09 RX-8 is completely stock, on new Dunlop Star Specs. Last year I ran on Azenis 615's. I'm finally convinced that the Dunlops are way better than the old Azenis 615's I ran last year. I run 245/40's, and our events are mostly 2nd gear courses, flow extremely well, and keep you up in the 40's/50's in mph no problem.
I've been contemplating an idea for when I travel out of town for a while now. Here's a little background: When I first got my MINI, which I ran back in 07, I noticed how fast and darty the steering was when it had the OEM 175 width skinny tires on it. When I autocrossed, I changed out to 205 width, and though the steering didn't seem as quick, the limit was way higher, as one would expect, which was also very needed for the layout of our autocross courses. I notice the same thing with my RX-8, in just changing from the 225 width OEM's to the 245's for autocross, the steering isn't quite as fast, but there's no way the 225's can hold up as well on the fast stuff, the sweepers, etc....
Well, there are 2 out-of-town venues that I go to each year, 1 being as much as a 4 hour drive. Both are run in small parking lots, and for the RX-8, they are first gear courses, no more than 35 mph, and then you slam on the brakes to slow the car way down for the slow, tight turns. Last September, at the Pro-Touring event, only 6 cars out of 52 were faster than me, and that was on my Azenis in 245 width. Here's what I'm thinking: A set of better tires, whether they be the same Dunlops I'm running now, Yoko's, etc, in 225 width will probably be just as sticky as the old Azenis in 245, maybe even better, and the car may be able to benefit from the quicker turning, especially on the tight courses. Also, the 225 is slightly taller in diameter, so technically, I can get a little more speed before I'm bouncing off the rev limiter. Every bit helps. Another big factor in purchasing another set of "away" tires is that I would rather drive to the event on them instead of taking the extra time to change out. 4 hours is a good bit of driving to be listening to the tires howl, and 225's should be a bit quieter than 245's. My old Azenis are dead, so I'll have a freed up 2nd set of wheels to mount tires to. The Dunlops will still be my choice for local. I'm considering calling up Discount Tire and seeing if they will do the same deal on the Yoko Advan AD07's that the Tire Rack did last week, $99 per tire. I missed out on the TR sale while I was researching the AD07's over the weekend. Dunlops in 225 aren’t out of the question, they’re just way more expensive.
It all boils down to this: On a tight, first gear course, can I be faster on 225 Star Specs, AD07's, or similar than I would be on the old compound Azenis 615 in 245?
03-30-2010, 11:02 AM
#2
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From what I've read, the latest generation of ST type tires are monsters compared to the old 615.
I believe the compound is the variable that's more important in your case than the width / diameter and associated sidewall stiffness.
I believe the compound is the variable that's more important in your case than the width / diameter and associated sidewall stiffness.
03-30-2010, 12:22 PM
#4
Less grip when you're turning, braking and accelerating more doesn't make a whole lot of sense to me. Your steering doesn't get any faster with different size tires either. I agree with TopGear8 that your steering feel issue can be resolved with a wider wheel that supports the tire better.
03-30-2010, 08:17 PM
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+1 on wheel width and tire compound. I went from 245/45/17 Dunlop Starspecs on 9" wheels last season (so slightly stretched) to 255/40/17's this season on the same wheels. First event out the gate, it felt like there was some squirm in the tire. At first I thought it would be sidewall flex but logically that didn't make sense to me since it was only a small width change and the sidewalls actually got smaller. So where was this feeling coming from?
I thought about it some and looked around and found this neat article on Tire Rack: http://www.tirerack.com/tires/tirete...e.jsp?techid=5 (Note: I'd previously known about the 500 mile break in period and did properly do it on the both sets of tires)
I suspect this accounts for much of what you're seeing, as I stayed on the exact same tire and suddenly felt more squirm when I had less sidewall. I REALLY like the Starspecs and a lot of people out here in the Pacific Northwest run them because of how well they do in the wet.
I thought about it some and looked around and found this neat article on Tire Rack: http://www.tirerack.com/tires/tirete...e.jsp?techid=5 (Note: I'd previously known about the 500 mile break in period and did properly do it on the both sets of tires)
Originally Posted by Tire Rack
It is also important to note that your old tires probably had very little tread depth remaining when you felt it was time to replace them. As any autocrosser or racer who has tread rubber shaved off of his tires will tell you, low tread depth tires respond quicker."Don't be surprised if your new tires are a little slower to respond (even if you use the exact same tire as before). Their new, full depth brings with it a little more tread squirm until they wear down.
03-30-2010, 11:10 PM
#6
You are overthinking it. 
The 225s will accelerate a little faster, since they are lighter, but then since you are in first gear, they will also have a harder time putting the power down corner-exit.
You mention that the Azenis & Dunlops are on different wheels. Do the two sets of wheels have the same offset?
The 225s will accelerate a little faster, since they are lighter, but then since you are in first gear, they will also have a harder time putting the power down corner-exit.
You mention that the Azenis & Dunlops are on different wheels. Do the two sets of wheels have the same offset?
03-31-2010, 07:35 AM
#8
I think most everybody is right here. I am overthinking it.
When you think about is simply, Kenneth makes a point that I overlooked by trying to over-engineer the concept. Less grip when cornering, braking, and accelerating. The cornering was the only thing I was looking at, but braking will be important, and the Pro-Touring guys usually set up a drag race before their first turn. I do have to grab second, then slam on the brakes, turn, and use 1st for the rest of the course. The bigger tires up front will help with the braking. The bigger tires in the rear will help with the acceleration out of the turns.
Both of my sets of wheels are within legal size and offset for autocross, but I don't know off hand if they are the same offset.
I think I will just stick with the 245's, and I can probably gain some benefit from giving the car a competitive alignment. My toe-in is only less than what the factory set it at, but it is still inward. I need to fix that this year.
When you think about is simply, Kenneth makes a point that I overlooked by trying to over-engineer the concept. Less grip when cornering, braking, and accelerating. The cornering was the only thing I was looking at, but braking will be important, and the Pro-Touring guys usually set up a drag race before their first turn. I do have to grab second, then slam on the brakes, turn, and use 1st for the rest of the course. The bigger tires up front will help with the braking. The bigger tires in the rear will help with the acceleration out of the turns.
Both of my sets of wheels are within legal size and offset for autocross, but I don't know off hand if they are the same offset.
I think I will just stick with the 245's, and I can probably gain some benefit from giving the car a competitive alignment. My toe-in is only less than what the factory set it at, but it is still inward. I need to fix that this year.
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