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Mike8675309
02-08-2011, 11:20 AM
I participated in a few auto-cross events in 2010 and would like to attend a few more this summer/fall. In anticipation of this I was considering my cars over all performance (as well as my performance) and remembered one problem.

Something I learned early on is that I needed to slow down more entering a tight corner due to significant understeer when moving too fast. I understand that this is a function of speed, and traction, and angle of attack. But I was wondering, from the cars standpoint, what, if anything could I do to reduce understeer to allow me to enter corners a titch faster?

Currently I have stock 93 SC sway bars, Koni adjustable shocks, and stock bushings through out. (new front upper and lower control arms). The motor is coming out to change the oil pan, which could be a good time to upgrade the front and rear sway bar.

Around at :50 in the video below you can see the typical corner I would push at. In the video I was dealing with it by taking the long way around.
<iframe title="YouTube video player" width="640" height="510" src="http://www.youtube.com/embed/kIqAAcA6aww" frameborder="0" allowfullscreen></iframe>

ricardoa1
02-08-2011, 12:09 PM
Mike you could try to put a larger swaybar on the rear to induce oversteer. But maybe you are not approaching the angle right. Not sure if your car has too much power but you can use power to balance the car out more. Its tricky and scary to try to get it where you are comfortable having the rear end want to kick out on you but still manage to have control. So thats why I suggested the larger rear bar. Weight shifting with brakes and power is the hardest thing to do, fear will always try to win.

But the car will plow if you dont have front grip and wider tires will help you in that dept the more grip up front the less it will try to plow.

Mike Puckett
02-08-2011, 01:58 PM
One of the easiest methods used by road racers is to work with tire pressures. More air pressure in the front tires will make it more responsive. You can either raise front air pressures or lower rear air pressures. It works quite well and doesn't cost anything.

fturner
02-08-2011, 02:19 PM
I agree with the air pressure. I did that and actually had to drop the pressure slightly in the rear because the back end became too twitchy.

Also, as Ricardo pointed out, you need to learn how to transfer the car's weight back to front etc to corner better. I've learned that by jabbing the brakes just before I start turning the car transfers the weight to the front and the car actually gets itself into a bit of over steer, which was a bit nerve racking at first to feel the car like that, but when modulating the gas pedal as you drive through the corner the oversteer will actually help you take the corner faster.

Also, my car is a 90, so it has the better sway bars on it.

Best thing you could do is get an instructor and/or an experienced driver in the car with you so you learn things like above and how to drive the "line". I had a regular sit in my car with me and thanks to him I'm taking the corners alot faster now... and still in as much or even more control of the car.... but my brakes are not up to it like that as I cracked both front rotors badly.

Fraser

Regul8r
02-08-2011, 02:50 PM
from that video, I say DRIFT the rear out on it!

Relying way to much on the front end doing all the work. Looked like you went in a little too hot and didn't grab enough brake to set the car for the corner. Missed the entry point that would have set you up for a good center-out apex.

Practice! and like others said, it is tricky and can be un-nerving when learning the outer limits of your car when setting and getting weight transferred at the right moment.

Good luck and have fun!

Mike Puckett
02-08-2011, 04:00 PM
The tire pressure advice came straight from Carroll Shelby himself in an article he wrote many years ago and I've been using it ever since. The ride along instructor is a really good idea. I learned in the Chin Motorsports event at Road Atlanta how to do everything from my ride along instructor, such as keep my hands at 9 and 3 o'clock, wait until the absolute last possible moment to hit the brakes and to hit them hard, and approach the corner from the outside line and apex the corner late rather than early. I don't do well in autocross myself and prefer the bigger road courses but I see the course in the video is quite big and should be a bit easier for a bigger car. Several of the members are active in autocross and are quite knowledgeable about the best way to drive it. It just takes practice, practice, and more practice.

ricardoa1
02-08-2011, 04:23 PM
100% Point on Practice. I can probably outrun my SC in my MazdaSpeed 6 with alot less power. And alot of that has to do with the fact that I have learned the way the car works alot more since I drive it everyday, taking ramps as fast as I can ect. But the SC gets driven only for one season and I can never really get to know the car that well by the end of the season I become more confident but that goes away over winter and its a new learning experience next season.

Mike8675309
02-08-2011, 09:40 PM
yes, more practice is necessary. I'll have to play with tire pressures and work on braking later. Keep in mind, this is a 5 speed car with stock gearing, so keeping both hands on the wheel isn't always possible. I.e, just before that corner I was in 3rd gear heading up to it with the pedal nearly to the floor, and shifted to 2nd as I was braking just before the corner, you can actually hear the rear tires being dragged from the down shift a bit early just before :51.

For the understeer, I guess I need to work on both throttle modulation and tire pressures. One of the examples of my issue can be seen in this picture. I don't need really more oversteer. I just want to make sure there isn't something I should be doing while I'm messing around with parts.

I know the weight of the car has a lot to do with what happens if I overdrive the tires. For example, in the picture below there is a corner in the top left which is kind of a tight sweeper, but what you can't see is that the entrance is down hill and it transitions to uphill at the outlet (running left to right, or down to up). Now yes, I can brake enough to get it so it doesn't push as I enter the corner, but that tends to be really slow. I guess I could shoot for a 4 wheel drift, but since it is autocross, typically they throw some cones in those corners making them much narrower than it looks based on the amount of blacktop.

http://www.mnautox.com/resources/courses/2007_AugustTnT.jpg

ganuolfthegrey
02-08-2011, 10:24 PM
the blower is hure loud.

ricardoa1
02-09-2011, 11:59 AM
If its autocross you need to improve the mechanicals of the car, the tracks are too small usually, And gearing is the biggest issue for not being able to modulate power, The M5R2 has very wide ratios, You could improve depending how short the track is by going to a 3.27 or 3.55s so you can be in 2nd most of the time. Not sure if you also use the heel toe technique, that will help up transition weight and be less abrubt then then popping the cluth on a downshift. You should not be barking the tires on downshifts.

But gearing and much wider tires are key for a short track. You are shifting alot of weight around very fast. Tight slow turns begs grip.

fturner
02-09-2011, 12:55 PM
This is the road course I've been running on...

http://bmwclub.ca/motorsport/tracks/cayuga.htm

On the straight stretch before turn 1 I can easily get over 100mph but I have to start braking early because of my brakes (or lack of).

Fraser

Mike8675309
02-09-2011, 02:29 PM
I have the late model trans with my stock rear gears. They would work fine on a parking lot course but the one that is close to me is on the course in the image above. On a parking lot course I can put it in 2nd and ride around the lot without issue, speed is down, and understeer is less. my car pulls plenty strong at low rpm.

I've never figured out heal toe. maybe I should.

I do need to get track specific tires. My street tires are 10" in back, 9" in front, but they are still street tires and they take a beating on the track. Another purchase to be made this spring.

ricardoa1
02-09-2011, 04:59 PM
Heel toe is key in autocrossing or track. You will kill the clutch unless you learn how to do a proper downshift. All it is raising the RPMs to match what the lower gear so it will put the engine at the right rpms. do that With the toes on the gas while breaking with the heel. Usuall you just tap the gas to flair the RPMs while the heel is on the brake slowing you down.........

Def A BIG MUST>

fast Ed
02-10-2011, 12:52 AM
Mike, what are your tire sizes? As you may already have realized, if you have a staggered setup with larger rears, that will aggravate understeer. If you are serious about autocrossing it, you need a square setup on the car.

On my old car, swapping to an 89 SC rear bar helped at the track days, never tried autocrossing it.


cheers
Ed N.

Mike8675309
02-10-2011, 10:26 AM
front: 245-45-zr17, rear:275-40-zr17

one of the goals of new track tires is track specific wheels, and with the idea of as wide as possible that will fit all the way around, thus making them all the same. just got to figure out some wheels that are good enough for the track, fit a wide enough tire, and fit my t-bird bolt pattern.

Ricardo, my ankle doesn't go that way. I looked up some stuff and see folks are doing the heal toe more as a toe on the brake pedal and heal/side of the foot hitting the gas. This looks like good info for others interested http://www.drivingfast.net/car-control/heel-toe-shifting.htm

seawalkersee
02-10-2011, 10:40 AM
What is the balance of the car? Have you moved the battery to the trunk and taken out the pass seat?

SWS

ricardoa1
02-10-2011, 12:14 PM
Mike I dont think the SC allows anyone to point the foot to the left. I use the more comfortable method. Our pedals are light enough and close enough to point your toes towards the right/middle of the car.

This is where I have my foot when using the technique.

http://media.ed.edmunds-media.com/non-make/howto/howto_72_300.jpg

Mike8675309
02-10-2011, 12:31 PM
What is the balance of the car? Have you moved the battery to the trunk and taken out the pass seat?


Haven't weighed the corners yet. battery is in the trunk, plus a water tank and pump. But a heat exchanger full of water, and an intercooler full of water are hanging off the front. Thus at best it's a wash, at worst, it's still heavy up front. And no, I didn't pull the seat and I don't intend to do that until I call it a full time race car. For now, the A/c still works and there is no cage thus I don't plan to pull the seat for racing. Probably 2011 and 2012 it'll stay street/track as I continue to work out kinks. 2013 I'll probably gut the interior, cage it, race seats, and turn it into a full time race car.

fturner
02-10-2011, 01:12 PM
Its better to keep the pax seat in the car to keep the weight balanced to the center. Take all that weight off that side, and the COG will shift over to the drivers side which will unbalance the car.

Fraser

Regul8r
02-10-2011, 04:11 PM
Its better to keep the pax seat in the car to keep the weight balanced to the center. Take all that weight off that side, and the COG will shift over to the drivers side which will unbalance the car.

Fraser

On roundy round cars we move EVERYTHING to the left side.
On a road track car I would put the battery and any other moveable thing to the right side in order to offset all the weight on the left. Me, the seat, pedal assembly, steering column etc... anything that helps level off the cross weight is a GOOD THING!

Mercutio
02-13-2011, 11:35 PM
What are your rear gears? If you have a 5-speed with street tires and stock rear gears, I can't imagine you'd ever need third gear on an autocross course. I run Hoosiers and 3.27s on my SC, and I think I've needed to hit third once or twice. Ed is exactly right, too. Of course your car is going to push with smaller tires in front. ~58% of your weight is in front, so putting more tire in back and less in front may look cool, but it's exactly the wrong thing to do for handling.

Also, if you want to race, get a good alignment. That's the second best thing you can do for an autocross car (first is tires). More negative camber is your friend.

If you square up the tires and it's still pushing, you might want to try a SLIGHTLY larger rear sway bar. Don't go crazy--I've got 1-1/4 front and 1-1/8 rear bars and that setup is pretty neutral.