Heavy "oversteer" on heavy braking

Hey guys,

More great questions from Andy. So, anytime I'm harsh with the stop pedal in the civic the ass end becomes verrrrry lose. I understand that this is part of the weight transition and doubly so with a FF car, but is there anyway to mitigate it? 700/750 springs with Koni yellows. Thick front bar, skinny rear bar, pretty neutral handling EXCEPT on braking.

You can see it happening here:

http://youtu.be/BfWOElFUjC8?t=46s

Usually it's not that bad so long as I brake in straight lines, but any twitch on the steering and it goes one way or the other. I'm getting ready from my first HPDE and don't really feel like spinning the car....

Here is the less pronounced version:

http://youtu.be/tc-_xJrQM6o?t=39s

Thanks!

adjustable brake bias? also check the condition of your rear brakes, it sounds like the fronts are doing all of the braking opposed to most of it

+1 for more rear bias, but I've mentioned the unusual properties of your suspension setup before and the relationship between your spring rates and axle weights isn't helping here.

Edit: BTW are you running rear toe-out? That seems to contribute to the same effect.

captdownshift wrote: adjustable brake bias? also check the condition of your rear brakes, it sounds like the fronts are doing all of the braking opposed to most of it

Indeed, it's the stock drums, I have a disc swap, maybe I'll fast track that modification along with a brake bias adjuster.

GameboyRMH wrote: +1 for more rear bias, but I've mentioned the unusual properties of your suspension setup before and the relationship between your spring rates and axle weights isn't helping here. Edit: BTW are you running rear toe-out? That seems to contribute to the same effect.

I haven't gotten the car in for an alignment yet unfortunately. Something to consider for sure, but I think you guys are probably more on target with the braking bias/generally what end is braking. I hadn't really considered it because it has a pretty stock setup.

I think I'll probably try to fast track the rear brake disc swap and make sure my rear pads are up to snuff. Is it sad that I'd rather update the whole brake system than do ANYTHING with drums? I hate working with drums soooo badly.

Actually, too much rear bias will make the car tail-happy. Too little should make it very stable. I'd definitely check the alignment, rear toe will make it dance all over the place.

Not really sad. Discs are easier to check for pad wear, easier to maintain and can offer better performance even though in your case a simple bias adjustment is probably all thats needed. There are more choices in pads then shoes too so not the worst choice if you already have it anyways.

Keith Tanner wrote: Actually, too much rear bias will make the car tail-happy. Too little should make it very stable. I'd definitely check the alignment, rear toe will make it dance all over the place.

If you get rear lockup first then it will get too tail-happy, but too much forward bias makes it unstable too, I've noticed the effect with worn rear pads, it's like braking a tricycle when you use the brakes hard.

(As in a kid's tricycle that had "fixie" braking on the front and none in the rear on top of being easy to tip )

You're describing what good FF cars do in rallycross. It's useful. You have a braking point where you can get the car lose is you need to, and if you stay back from that, then you are stable. All cars have a point where braking too much makes things go to hell, this is just yours. I'm not saying that you shouldn't try things to improve the braking, but you need to understand that what you have now is just the result of you stopping the car harder than it can handle dynamically.

I used brake pads to help bias the brakes on my auto-x GTI. PBS metal masters in the front and mintex red box pads in the rear. Dialed it in pretty well.

Definitely check your alignment angles. Rear and front toe-out will cause oversteer.

mazdeuce wrote: You're describing what good FF cars do in rallycross. It's useful. You have a braking point where you can get the car lose is you need to, and if you stay back from that, then you are stable. All cars have a point where braking too much makes things go to hell, this is just yours. I'm not saying that you shouldn't try things to improve the braking, but you need to understand that what you have now is just the result of you stopping the car harder than it can handle dynamically.

True but the behavior seems a bit extreme here. I can turn a bit when braking near the limit in my 'rolla, or slide it with just a bit of engine braking if I toss the car properly. In the video he goes on the brakes, and as soon as he moves the wheel off-center it starts sliding. That's not right.

In reply to mazdeuce:

I can see how the rotation would be beneficial in rallyX autoX, but on a fast road course (as in my upcoming HPDE @ infineon) it seems sketchy for a novice (that's me!). I was test driving on the road on Sunday (not driving quickly, just making sure I hadn't broken anything and my newly installed 6 point felt ok) and I came to a reasonable stop at a left hander and could feel the ass squirming (this was on 6" wide street tires though...). That seems a bit too touchy to me.

Gauging the hive mind, it sounds like I should definitely check the alignment and make sure my brake bias is even. I think I'll try to get both done, I should've started on this earlier..... Hopefully not too many of the chassis bolts are seized.....

Check rear camber too. When there is more camber than necessary, the tires slip before they deflect to get full contact.

I forget when the technical term is, but I call it the pencil eraser angle.

Check rear alignment, camber, sway bar, and tread.

Bad sawy bar, tight front, and lack of tread destroyed my Escort in wet weather.

I think you'd need a LOT of rear camber before the pencil eraser angle became an issue. Toe has a much bigger effect on both tire wear and stability.

Silly question, how does one find a shop that will be able to do a decent performance alignment? My google foo only turns up the normal alignment shops. I'm in San Francisco currently if that helps.

I knew of a few from the east coast, but found out about them from word of mouth.

What about moving to a softer rear spring?

Keith Tanner wrote: I think you'd need a LOT of rear camber before the pencil eraser angle became an issue. Toe has a much bigger effect on both tire wear and stability.

accordionfolder wrote: Silly question, how does one find a shop that will be able to do a decent performance alignment? My google foo only turns up the normal alignment shops. I'm in San Francisco currently if that helps. I knew of a few from the east coast, but found out about them from word of mouth.

I'd ask some people at events, you'll likely find someone that wrenches for a living that does performance alignments after hours or if there's a local tire shop that sponsors the SCCA or NASA region i'd contact them and see who they recommend.

If you belong to the San Francisco Region of the SCCA or another club, check out their flyers for advertisements of local shops or contact the club members to see who they use.

Try speaking to your local SCCA or NASA peeps for recommendation to alignment shops. I'm sure the locals know where to go. Alternatively, check Porsche, BMW or Miata discussion forums for references to alignment shops and race, track or autox

Cool, my HPDE is with NASA, I'll see if I can find a local forum for them.

Roger Kraus Racing.

Sounds like a prime autocross setup

I am a 10+ year autocrosser in the Bay Area. The three best alignment shops I have used (in order of increasing price) are
1. Motorsports Techniques in Hayward
2. Roger Kraus Racing in Castro Valley
3. Custom Alignment in Mountain View

Hope this helps.

In reply to DaveEstey:

It does seem to indeed work well there. Now if only the nut behind the wheel were better.... ;)

In reply to Keith Tanner:

Huh, you're much better at your google foo than I. Thanks, I'll give them a ring.