Need some help from the AutoX experts as I couldn't find what I needed with the search tool...

Attending my fourth autocross Sat. and getting to the point where I could really appreciate some more rotation in the turns. I know it's been discussed before, but I'd really like to try to dial out the countersteer by swapping my tires front to rear, rear to front, but I know this will confuse a few systems. I don't have VDC and can turn off traction control, but what about ABS? Do I need to disable this as well somehow?

Also, the notion of reducing pressure in the back tires vs. front seems counterintuitive to me...wouldn't this increase drag/traction increasing understeer?

Thanks

 

I have no idea what good it would do to swap the fronts for the rear. If it's your 4th autocross then you should get another 20 or so events of seat time before changing the car. Take an Evolution Phase 1 school. Run every event you can with your present setup and change tire pressures to see what the effects are. Then make incremental changes in equipment to see what works for you. Too bad you're now in BSP with the mods you list.

I run 245/35-18 710s all around with up to 5 lbs more in the front than back depending on the conditions. Primarily to keep the fronts from wadding up and skipping and soften the back tires for traction. Yes, turn off the VDC/traction control but I don't have a problem with the occasional time the ABS comes on.

 

I agree with DriveI65. Don't swap the wheels. Considering its only your fourth event I would say that most of your problems come with lack of experience. As you go to more and more events you will learn that on most autoX courses you have to go slower to go faster. It is a VERY hard concept to learn. If you have the opportunity to run some autocross races in the rain, then do so. A few wet events will speed up the process of learning the go slow to go fast method. I run 245/18s in the front and 275/18s in the rear. I used to have rediculous understeer as well until I sharpened up my driving skills. Try braking a little earlier until you get through a turn without breaking the tires. You will feel slower, but I guarauntee that your times will be faster.

 

Thanks guys. I don't think I'll be able to get more experience before Sat. I'm not running at an SCCA sanctioned AutoX either, just a local Miata club gathering so the course is extra tight. I was really just hoping to give myself enough of an edge to beat my friends for bragging rights as we all ran really close last time. =)

I was much quicker with the TC off as you noted...and I have read that you can decrease understeer by running less air in the rear tires, but didn't notice a difference when I tried that either. Guess that's why I was thinking of the swap...increase contact patch for more traction in the front since they seem to be the only limiting factor I can change before Sat.

 

Nonsense, you can start applying new driving techniques Saturday and improve your times.

 

You'll gain more by working on the nut holding the steering wheel than you will by working on the rest of the car.

Also, unless you have the same size wheels (not tires) on all four corners, swapping the fronts and rears would be illegal in most stock classes (you must keep the same size wheels in the same locations).

 

One of my Evolution School instructors told me that no car understeers, the driver is going too fast into the corner. Listen to 350ZNV and try it.

 

Well, again, I'm not running in a class structured event...it's run-what-you-brung. Can anyone answer my original question on whether or not doing this would confuse my ABS system?

 

I just rotated my stock tires from front to rear to make them last longer. My rears are nearing the wear bars after 25K and my fronts look new. I have a base model (with no VDC) and have never had a problem with abs. Acceleration is actually better with the smaller diamater tire in the rear. Turn-in is sloppier with the larger diameter up front.
I wouldn't do this for an autox though..

 

Thats a great point...the increase in tire sidewall height would probably negate any benefit from the wider contact patch—Guess I'll save myself the trouble and concentrate on my schkills.

 

Sunriders in st pete 10/15??

i'll be there - [lemans sunset 6mt]

i've found that most of the understeer IS due to going too quick thru the corner...

have had instructor input for runing 42 psi front / 36 rear and am doing much better getting it to turn (stock 17" potenzas)

Good Luck! Happy Zooming!
(brrr brr brr take me riding in the car, car...)

for more seat time 10 22 & 23 at brookeville airport (22nd practice day - many more runs!) must pre-reg on myautoevents.com (& deland on the 30th)

 

I very successfully autocrossed a 240Z back in the early 70's, OK, I'm an old fart, but basic priniciples don't change. Understeer is what they designed into the 350Z, same as they did for the 240Z, because they were aiming them at the inept American public, who would instantly get into trouble with a car that was neutral or god forbid, oversteered, like Porches. But I digress.

We are severely limited in stock SSCA stock class. I think we can swap ends with the tires, since the wheels are the same width and diameter, front and rear, on a 350Z. It's radical, but that's what this machine needs. You'll burn up the rear tires if you're not careful. I think we'll get "error" messages from the traction control, like maybe full time, but the ABS shouldn't complain.

I ran the 350Z once at an autocross, and 3 things are painfully evident. One was the Honda S2000's had a size advantage, but they're in A class now, not an issue. The other was the 350Z understeers when pushed to the limit (not that's not entering the corner too hard, that's doing it right). The 3rd was that those damned DOT approved racing tires ruined autocrossing for the masses, since you can't be competitive without them, and they're real expensive, and can't be run on the road in daily commutes, or they'll wear out in no time. Hence, I said F**k it.

Dave King, '03 Touring Redline Coup

 

" No car understeers," that's a good one. LOL Most cars understeer. I'm not sure there's any production car that oversteers these days. The old Porches used to, and they were tricky to drive. Can you imagine the *** end coming around if you over cooked it into a corner? Well, it takes some getting used to. You have to quickly steer into the slide, to get the backend behind you, where it belongs. I removed the front sway bar, and installed a race rear sway bar in my old 240Z, lowered it almost 2 inches, and used Goodyear Eagle racing tires, which gave me oversteer over about 45 MPH. On normal innerstate clover leaves, at about 70 MPH, the rear end would come around. Talk about un-nerving. That's why almost all manufacturers design in some degree of understeer, it's "more stable," When you push it too hard, it's easier to deal with going straight when you should be turning, than spinning around.

Dave King, '03 Touring Redline Coup

 

Yeah! hey sweet...sorry I missed it, especially when I was the only Z there last time I went. I'll have to check out how you did on the website.

 

As much as I have faith in EVO instructors, that's not an opinion that should be chiseled in stone.

I think what he meant is that even if a car has bad understeer, you can "drive around it" by changing your driving style, which will net a better time.

Saying no car has understeer is kind of a shocking statement.. only goes against about 500,000 combined years of vehicle setup experience and thoery.

*Eventually* you reach a point where a car's balance can hurt you, like if it has bad understeer.

 

There's a lot of "common knowledge" that is wrong.

"Every car understeers, except Porsches" is one of those "common knowledge" statements that are wrong. Most people will never see understeer until they are (surprise!) going too fast for a corner (exactly what the instructor said). That is why a car can go from understeer to oversteer to understeer in the same corner.

You can adjust the suspension to permit a higher speed before the car will understeer, possibly getting the car to the point where you now have more grip in the front than you have in the rear, in which case you will have oversteer. The "ideal" (which. at the extreme case, is pretty much undrivable) is to have both ends lose traction at the same time in a corner.

However if you look at understeer as the Evo instructor (or any race car driver) does, all understeer means is that you've gone too fast into the corner. How you deal with that information depends upon time, driver skill, and car adjustability.

 

"No car underseers", that's a good one...

How did your event go 350Zenophile? Beat your friends?

You will have to trailbrake to get around the "natural" understeer of your car. Watch out for the ABS kicking in though, it will ruin your effots.

 

I ended up not making it, but I typically rank in the upper third of the street-tire novice class beating out my friends who have a WRX and a BMW 3 series respectively.

 

His advice has worked for me so far.

He was riding with me at the time and diagnosed correctly that I was entering the corners too fast but blaming the push on the car. This advice has helped me lower times and save on tires.

 

I have no doubt it did help you.

Instructors will give advices on what you are doing at the time it’s happening. What is true one day might not be so true months later, after you’ve progressed in your driving.

He told you what you needed to hear to change your driving at that time.