Event: S2K Autocross - Mineral Wells - 2/28/2004

[altiain]

I didn't really experience any understeer there - it was far more noticeable on the tighter turns, like the sharp right-hander right before the finish, and the pivot cone at the end of the slalom. However, I was bouncing against the revlimiter pretty much on all the sweepers (and through the offset gates on the north end of the course), so I don't think I was quite at the traction limit for my given speed through those parts.

I did have to anticipate for it a little bit, though. On the offset gates before we crossed over the grass, and the tight turns I mentioned in the first paragraph, a little throttle lift or slight brush of the brakes seemed to help the front end bite a lot more.

This setup definitely has its tradeoffs. I know I have to anticipate what the car is going to do a lot more now. In the past I would just point it where I wanted it to go and then react to it and correct for it if it got a little loose. Doing that now would probably just result in a lot of push.

On the other hand, I find I can brake a lot deeper into the corners with this setup, as I no longer worry as much about the car coming around on me during trailbraking. In fact, during one afternon run I came into the slalom way too hot, started braking as I passed the first slalom cone and continued braking through the next two slalom cones, all the while expecting the car to step out sideways at any moment. It never did. Last season, doing the exact same thing at exactly the same speed would have resulted in a spectacular spin.

The tranistional benefit is amazing, at least on my car. I've always been tentative in transitional manuvers, as my car has always been just "this close" to coming around. Now it just flies. If I find it understeering a little bit, a quick throttle lift tucks the nose back in perfectly, without enticing the back end into coming around.

To put it another way, no matter how out of shape I got in Saturday, or how hot I came into different parts of the course, my car never got loose. It never hung the tail out at all - not once. That's never happened in my car. On the flip side, it does tend to understeer occasionally, but correcting for that is a lot easier, and has a lot less potential for disaster than correcting for oversteer. In addition, I found my confidence level went up dramatically in the transitional elements, as my car never threatened to bite me at all. I think as I relearn to drive it this way, it's only going to get faster, as the handling has become a lot more "goof proof" than it used to be.

Iain

[Kestrel]

But the first sweeping right hand turn gave me fits. Every run thru there was an excersize in holding back on the throttle to let the front tires catch traction. I experienced a good amount (bad) of understeer.

This was my second event with my bigger front bar, and I did find that I got a fair amount of push depending on my settings. I have KYB AGXs with four stiffness settings. I started with 3 on front (4 is stiffest), 3 on the back and very high tire pressures. After my first run -- where I could barely keep the car under me due to ice cold, rock hard tires -- I let out a fair amount of tire pressure. Got them down to 39 front (warm) and 38 back (warm). I also took my front shocks down to 2.

My second and third runs -- on warmer (but not hot) tires were exercises in oversteer. I had dialed out the push alright! For my fourth, I took the back shocks down to 2. The car seemed to set OK (I still couldn't get much grip), but I overcooked the top and got all sideways. The rest of the day, I ran with that set-up: 2 on the shocks both front and back, and 39psi front, 38psi back. I never felt like the car was planted, but it didn't feel terrible either.

Where I experienced the most understeer problems was that first left hand sweeper leading into the right hand transition and sweeper... lots of push, particularly right after the transition from left to right. I also could barely turn the beast on the tight left-hander right after the slalom. But I liked the way the bar kept the car flat during turns, and while the slalom was not a very good test (way to short and too much offset), I think the car behaved pretty well through there. And the car was amazing through that section from the slalom to the sweeping lefthander towards the end. It just flew through those offset gates...

I think for me, there were a lot of things at play. Poor tires. Driver fiddling with too many settings. Driver not a smooth as he'd like to be. But I never could really figure things out. Particularly during the afternoon runs, I was really trying to concentrate and notice where I was loosing time -- and I really couldn't pinpoint anything particular. I felt like I was pushing the car as hard as I could, and didn't see where I was missing opportunities to be faster. Judging by my results, something was seriously out of whack with the driver.

[altiain]

Judging by my results, something was seriously out of whack with the driver.

I don't know if I'd go that far. Judging by Jon's results two weekends running comparing old Hoosiers to half-worn Azenis (he was faster on the Azenis both weekends), I'd be willing to bet that your Hoosiers played a big part in those results. Don't forget, your tires are at least a year older than Jon's, and probably had as many (if not more) runs on them.

I'd buy some decent tires before I tried to extrapolate too much from this weekend's results. I know my car feels completely different going from good street tires to race tires. I can only imagine that the difference between your Hoosiers and decent race tires would be even greater.

Don't forget, even the handling balance of the car can be altered just by adding different tires. Higher amounts of grip increase side loading, which in turn increases suspension compression on the oustside of the car in a turn. Since the camber curves for the front and rear of the car aren't the same (i.e., compressing the front end by 2" will not yield the same change in camber as compressing the rear end by 2"), increasing the amount of grip can alter the dynamic balance of the car. In addition, the bump stops on a Miata act as non-linear "helper springs", and the effective spring rate at each corner increases as the suspension is compressed. To further complicate matters, that non-linear spring rate increase is also unequal front to back, and is also affected by the amount of grip (and therefore suspension compression) a car will develop. Last but not least, toe changes both front and rear as the suspension compresses. Guess what? Those toe changes are - again - not equal front to back, and are just as equally affected by the available amount of grip.

To make a long story short, a car on crap tires at the limit may not have the same dynamic balance as the exact same car on better tires at the limit. Especially a Miata.

Iain

[POS Racing]

something was seriously out of whack with the driver.

It may have happened durring your Parade lap as you waved at all the Miata and S2K guys!

... the first sweeping right hand turn gave me fits. Every run thru there was an excersize in holding back on the throttle to let the front tires catch traction. I experienced a good amount (bad) of understeer. I'm sure its driver error...just entering the turn too hot, but it was frustrating.

How about the others of you with a front bar, did you experience the same push thru that area.

I experienced the exact same phenomenon but my car still has the OEM bar (currently)

[Kestrel]

To make a long story short, a car on crap tires at the limit may not have the same dynamic balance as the exact same car on better tires at the limit.

I'm sure that played a part, but I don't think fresh tires would have made 5.350 seconds difference (which is how far I was behind the fastest Miata Pilot ). And besides, I don't like making excuses for a poor showing. The driver and his/her skill (or lack thereof ) makes a lot more difference than tires... or swaybars... or shocks... or...

Don't get me wrong -- I'm not contemplating hari-kari or anything, but I know I need to work a lot harder.

And get new tires.

[altiain]

Oh, I wasn't using the tires as an excuse for your poor showing. You were slow on Saturday. :P

I was merely trying to point out that any data gathered from how the car responded on those old Hoosiers might not translate readily to how the car handles on decent tires. And I'm assuming that some day you're going to pony up and buy some decent tires.

Iain

[POS Racing]

And besides, I don't like making excuses for a poor showing.

You’re doing a fine job so far!

[sammm]

There are some pics posted. There's an up-close-and-personal shot of Kestrel!

[POS Racing]

When good Shiners go bad, on the next Geraldo!

[altiain]

When good Shiners go bad, on the next Geraldo!

That's me arguing with Andy Hollis (yet again ) about STS2.

[sammm]

More pics posted on the S2K board -

http://gallery.s2ki.com/imagecatalog/image/list/8459/

[Kestrel]

I know it's just user error, but when I use your links to try to get to those pictures, I just keep getting to the "Join S2K International for only $50.00" site.

[POS Racing]

Works for me!

[sammm]

I know it's just user error, but when I use your links to try to get to those pictures, I just keep getting to the "Join S2K International for only $50.00" site.

I dunno! I just tried it again and it worked fine.

[Kestrel]

Forgive me Father, for I have sinned. It has been 28 years since my last confession...

[POS Racing]

Forgive me Father, for I have sinned. It has been 28 years since my last confession...

I was praying that I could outrun Sammm

[sammm]

Forgive me Father, for I have sinned. It has been 28 years since my last confession...

I was praying that I could outrun Sammm

<evil laugh> bwahahaha </evil laugh>