Would like some autox advice

tamadrummer1120 · May 9, 2017

Lots of great responses, thanks everyone. Let me try and reply to a lot of the common points that came up. For what its worth this was a very technical and tight course that we were told that morning the big heavy V8 cars would have a challenge with. Only 1 real straight away the v8 could actually shine and it wasn't much.

Unfortunately I just purchased these wheels in the spring and cannot swing buying new wheels for a squared setup right now. So I have to live with that.

In regards to the BMR front bar I ordered, I had a bunch of credits at American muscle to use up, so I basically got it for free. Not like I am expecting that be some cure for understeer or something.

Also, I use this car for lots of reasons. So setting alignment specifically for autox but then the next weekend wanting to go drag racing just could not happen. I bought this car to use in about every aspect I could of motor racing throughout my ownership. And I know that would really help my cause, but trying to do everything I can that wont make this a dedicated autox car.

SteveW said:
OP,

What is your alignment? Try more negative camber and a little toe-out up front.

What were the tire pressures you were running at?

Driver mods: slow in fast out. Brake hard enough before an element that you can be balancing the car with the throttle and accelerating through it, backside cones and realize you can only lose time in tight turns. Make sure you drive down right on top of the apex cone and not chew up a ton of real estate trying to carry speed. Tight turns in autocross suck for everybody ;-)

Alignment I just had done last week and was an OEM spec alignment after I replaced a lot of the IRS stuff with BMR upgrades for wheel hopping issues.

Tire pressure honestly could have been dropped some. It was around 32-35 during the day. Now I have read that when its raining, having a higher tire pressure is better, and it was raining during the morning.

This list of driver mods is great. I need to consider that. I know there was a large sweeping turn at one point in the course that I purposely swung the first cone wide so I could apex the next. Not sure if I could have entered slower and sharper on that cone and be able to slowly apply throttle as I went through that sweeper.

Grintch · May 9, 2017

Step 1 - what class are you running?
That establishes what mods you should do for autocross (modified by budget and other planned uses).

But your primary question was why do I have understeer. And the clear answer to that is because you have big axx rear tires and only medium size front tires. There is no getting around that, though setting up the rear really stiff can help a bit. As can a point and shoot driving technique.

BmacIL · May 9, 2017

tamadrummer1120 said:
Lots of great responses, thanks everyone. Let me try and reply to a lot of the common points that came up. For what its worth this was a very technical and tight course that we were told that morning the big heavy V8 cars would have a challenge with. Only 1 real straight away the v8 could actually shine and it wasn't much.

Unfortunately I just purchased these wheels in the spring and cannot swing buying new wheels for a squared setup right now. So I have to live with that.

In regards to the BMR front bar I ordered, I had a bunch of credits at American muscle to use up, so I basically got it for free. Not like I am expecting that be some cure for understeer or something.

Also, I use this car for lots of reasons. So setting alignment specifically for autox but then the next weekend wanting to go drag racing just could not happen. I bought this car to use in about every aspect I could of motor racing throughout my ownership. And I know that would really help my cause, but trying to do everything I can that wont make this a dedicated autox car.

Alignment I just had done last week and was an OEM spec alignment after I replaced a lot of the IRS stuff with BMR upgrades for wheel hopping issues.

Tire pressure honestly could have been dropped some. It was around 32-35 during the day. Now I have read that when its raining, having a higher tire pressure is better, and it was raining during the morning.

This list of driver mods is great. I need to consider that. I know there was a large sweeping turn at one point in the course that I purposely swung the first cone wide so I could apex the next. Not sure if I could have entered slower and sharper on that cone and be able to slowly apply throttle as I went through that sweeper.

You could definitely run a more auto-x/track focused front camber without really compromising the car for daily use, or even tire wear that much. Toe is what wears the inside of tires, camber just changes where it wears. Yes, truly excessive amounts (something like -5, stanced) will increase the contact pressure enough to significantly increase tire wear on the inside, from the camber alone, but running about -2 or so will be fine.

EFI · May 9, 2017

So I was seeing a pretty good amount of understeer

I found that the cure to understeer to be right under my right foot. A little trail braking (if you have the space to do it) really helps to aim the front.

tamadrummer1120 · May 10, 2017

Thanks for the additional words guys.

In regards to class, I am not really in one. I just go out and have fun and try to constantly better my times and techniques. Maybe next year I will finally enlist in a class and compete for points and such. But I also didn't want to attend every event if I wasn't at least competitive.

In regards to the trail braking when should that be applied? For example, if I had a long straight away and came to practically a 90 degree tight turn. I assume I should go full throttle and at some point apply heavy braking with enough time to have control over turning and allow weight to transition back to the rear again. Should I trail back while going through the first half and then throttle out? Or should I not have WOT as long and stay at moderate braking which leads into trail braking.

NightmareMoon · May 10, 2017

Trail braking is overlapping the braking with turn-in, and you pretty much apply it in nearly every corner.

Max-braking 100% in a straight line, then start to reduce braking as you increase steering until you're entirely off the brake and using 100% of your traction for cornering at or before the apex.

Its easier to mess up by asking too much of your tires by trying to do both, than getting your braking done entirely before turn-in, but it helps the car rotate when done right and its definitely the fastest way around a racecourse.

There are tons of articles online about Trail Braking, with pretty diagrams and such. I would suggest some light reading.

Norm Peterson · May 14, 2017

You may find that how fast you get off the brakes and where you time that to happen relative to your steering makes a difference in how sharply the car turns in.

Experiment with different tire pressures front vs rear.

In general, OE preferred alignment specs are pretty poor choices for autocross. I understand your wider range of uses, but given that you're out of Street category as it is give some thought to camber plates and learning how to DIY your own alignments.

FWIW, if your typical street cornering has much enthusiasm in it you can easily run more than -1.5° up front. Maybe even a little past -2° if you can't pass up any opportunity for living at/beyond 0.5 lat-g. Negative front camber is at least not a bad thing at the dragstrip as long as toe is close to zero (toe increases rolling drag if it's much different from zero) and may even be preferred when you're running full-size (wide) front tires rather than skinnies.

OE preferred rear camber or even a little less might actually be the hot tip for reducing understeer with that staggered tire & wheel setup, and could well be a good thing for the straight line stuff too. But again, you'd need to experiment a bit and tweaking the rear alignment is a considerably trickier process.

Norm

tamadrummer1120 · Jun 16, 2017

I want to thank everyone again in this thread for all of the tips. Had another full day of autox this past weekend. Now, due to my other range of uses for the car, I did put on a VMP blower prior to the autox day. Before someone says something, I actually was very timid with the added power, I focused solely on trying to make great lines and finding good brake points. I also continued to monitor my tire pressures and lower them as the day went on. I stuck them around low 30's all day and they seemed to stick well. Have another event coming up in a few days, so we shall see if I can master some trail braking. Need to get a dash cam so I can post videos and you all can critique.

AutoX R · Jun 16, 2017

I see you're in Maryland. Are you ever running at Fedex Field? It's a pretty fun place to run and you can get some pretty good speed going. There's also a large pool of talent to draw experience from.

Would like some autox advice

tamadrummer1120

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Grintch

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BmacIL

Enginerd

EFI

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tamadrummer1120

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NightmareMoon

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Norm Peterson

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tamadrummer1120

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AutoX R

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