I was wondering what could be factors that causes a car to be unstable under braking. My last autocross involved a rather long straight into a a hair pin then another straight. When braking for the hairpin, my tail end was not so planted. I know there are obvious things like a lot of weight transfer the front of the car. However, what other MECHANICAL factors could cause such a thing.

 

I had this problem during my race at Portland this last weekend and it was excessive TOE-OUT. Once I adjusted the toe in the rear everything stable as can be.

Also, your radius rod bushings can cause it as well for the front. If you switch to harder urethane bushings or spherical bushings then your front will be more stable under hard braking.

Perhaps brake bias is the culprit (sp?).

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by EK4civichatch &raquo;</TD></TR><TR><TD CLASS="quote">I was wondering what could be factors that causes a car to be unstable under braking</TD></TR></TABLE>

Any toe out in the rear, and operator error. FWD cars get light under braking in the rear, and if you stomp on them the car will get loose.

 

I would make sure there isn't something you can do as a driver before looking @ your car.

For example @the last track event I went to, there was a looong straight leading into a decreasing radius turn. 100mph+ down to about 35mph.

My car was getting very light and the rear was doing some scary stuff.

After riding w/a friend of mine, I realized I was braking too late. If I just braked a wee bit sooner but not quite as hard, the car would be much more stable and I would end up carrying the same amount of speed into the corner.

An instructor @an autox school reffered to it as the "squeeze".

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by DsR &raquo;</TD></TR><TR><TD CLASS="quote">I would make sure there isn't something you can do as a driver before looking @ your car.</TD></TR></TABLE>

I have to cut in here. I think this is really bad advice. If your car is doing something funny then you MUST check it first!! If not, you could be out on track with someone WRONG with your car that could cause an accident or worse.

Looking at your car (to see if you have bad Toe, for example) is much different then making adjustments. You SHOULD know how to drive your car before you start adding/removing parts, this I agree. But, when you are out on track and your car is doing something "unpredictable" then you NEED to make sure your car is ok.

As for your "braking too late" problem with the rear end being unstable. You can fix that! If you can brake later and carry the same speed you might as well because being on the gas longer and the brakes shorter decreases your lap times. Even though you can get your car to be stable under braking by braking earlier I would recommend trying to set your car up so that IS STABLE during LATE BRAKING. My street CRX was VERY unstable during late braking but once I replaced the bushings, most importantly, the radius rod bushings, the late braking stability was GREATLY increased.

 

I also found that brake bias was an issue with stability of my car into braking zones. I started an event one morning with cobalt gt-sports on all four corners. Found out later that my hard braking would lock up the rear and woooo fun ride . I switched in my street axxis ultimates in the Rear and i helped alot with that issue.

92 civic hatchcrap, weighs nothing in the rear fyi.

 

Seems to me you are banking on that the problem is toe-out..

and if it's not? Do you just sit there looking confused? I think the next thing would be to try something different, as far as your braking/line etc.

I never thought I would see trying to improve as a driver would be called really bad advice

If the car is doing some really strange stuff that you know isn't right (ie mechanical failure) of course, fix it first.

I've found the majority of the time it's something that can be adjusted as a driver first.

But if that was the case he probobly wouldn't have asked us Because we are all perfect drivers right

 

It was the way you stated it DsR. When your car is acting funny you don't just go and CHANGE things but you should ALWAYS look at the car because, like I said, if it's something mechanically wrong (like toe, bias, or loose susp. bolts), you will find it by LOOKING AT IT.

If everything looks to be in order then try to improve the driving.

I would hate it if I came back in said, "my right rear is really unstable when I am taking hard left hand turns and it seems to be bouncy," and someone told me to that I need to drive better when in reality it's a blown shock.

If something doesn't feel right ALWAYS LOOK AT YOUR CAR FIRST TO MAKE SURE EVERYTHING IS WORKING RIGHT.... this is NOT bad advice!

If it isn't then fix it. Once everything is working right, then improve your driving, once your driving is improved and you understand the car then you can start "changing" things to go faster.

 

DsR and rice_classic,

Don't you think you can do both?

rice_classic is right in that you should always look at your car to make sure **** isn't falling off or braking. Just yesterday a co-worker asked me if it was serious that his car made a grinding noise when turning right. I said it could be a wheel bearing about to give out. He took it to a shop that night and it turned out to be the fender liner came loose and was rubbing the wheel. He could have saved himself a lot of time just by taking a look!

DsR is right too. If you're on track and the car is doing something strange, what's your option before you can check the problem? You have to adapt and change your driving. If you're coming into a turn at 100mph and the car is more loose then it should be then you need to slow it down and brake earlier and more of it. Why risk it unless you're in a race fighting for 1st place.

Always check your car and always work on becoming a better driver.

 

Yeah I'm starting to think it's just my style of driving. My toe is set to 0 all around so it can't be that. After careful thought about that section of the course i remember there was a very subtle "chicane" setup. It wasn't all that severe, but enough to say that me going through it transfered some weight to the right front tire, and then me braking hard to set up for the right turn (the hairpin i mentioned) just simply upset the car.
When I lifted my right foot off the brake to apply throttle (I tried to late apex the turn but I was too busy trying to correct the oversteer) the car again kicked out in the rear. Should I have just been quicker to get back on the gas??
Oh and thank you guys for the help!

 

I agree, like I stated. If you know it's the car, the adjust it. But too often I think we blame our car when it is really the g00ber behind the wheel.

Somehow we are saying the same things, yet still forming an arguement. Funny how that happens..




Modified by DsR at 10:33 PM 6/9/2004

 

I dunno exactly what the course was like, but it sounds like you could benefit from some left foot braking...You may already do this(I can't even do this properly yet so I won't try to explain.) Hopefully one of the pros can chime in.

Basically the transition from brake&gt;gas and vice versa would be a much shoter interval, so that way you wouldn't upset the car.

We had a course identical to this once and it caused me to spin when I was getting used to my R. But after watching a GS Prelude owner tackle it, he was much cleaner.. Turns out left foot braking helped him quite a bit.

I would also make sure you aren't doing too many things @once ie turning+braking or turning+accel. (turning+braking being the worse evile) I'm sure you've heard the string attached to your wrist and foot theory.

Also if you have rebound adjustable dampers ala Koni Yellows/KYB/Tockico etc. running more rebound in the rear would aid in slowing down the sudden weight transfer, and give you some more oversteer.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by DsR &raquo;</TD></TR><TR><TD CLASS="quote">I dunno exactly what the course was like, but it sounds like you could benefit from some left foot braking...You may already do this(I can't even do this properly yet so I won't try to explain.) Hopefully one of the pros can chime in.

Basically the transition from brake&gt;gas and vice versa would be a much shoter interval, so that way you wouldn't upset the car.

We had a course identical to this once and it caused me to spin when I was getting used to my R. But after watching a GS Prelude owner tackle it, he was much cleaner.. Turns out left foot braking helped him quite a bit.

I would also make sure you aren't doing too many things @once ie turning+braking or turning+accel. (turning+braking being the worse evile) I'm sure you've heard the string attached to your wrist and foot theory.

Also if you have rebound adjustable dampers ala Koni Yellows/KYB/Tockico etc. running more rebound in the rear would aid in slowing down the sudden weight transfer, and give you some more oversteer.

</TD></TR></TABLE>

Thing is...that when I was breaking i was busy heel toeing into 1st gear, so how would I switch to left foot braking while in the process?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by EK4civichatch &raquo;</TD></TR><TR><TD CLASS="quote">

Thing is...that when I was breaking i was busy heel toeing into 1st gear, so how would I switch to left foot braking while in the process?</TD></TR></TABLE>

heel toe would=LFB in that scenario methinks.

The only thing I could think of is slow down a bit early, get the car settled, once you have done all those things, then start the apex.

Also I dunno exactly what the course was like, but you may have been better off staying in 2nd gear... sure the pull out of the turn from 1st feels better, but you spent all that time downshifting instead of following the ideal line.

Unless you are able to do both.

Sometimes slower ends up being faster.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by DsR &raquo;</TD></TR><TR><TD CLASS="quote">

heel toe would=LFB in that scenario methinks.

The only thing I could think of is slow down a bit early, get the car settled, once you have done all those things, then start the apex.

Also I dunno exactly what the course was like, but you may have been better off staying in 2nd gear... sure the pull out of the turn from 1st feels better, but you spent all that time downshifting instead of following the ideal line.

Unless you are able to do both.

Sometimes slower ends up being faster. </TD></TR></TABLE>

Lol that just came to me after thinking about what went wrong, shoulda left in it in damn 2nd gear

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by EK4civichatch &raquo;</TD></TR><TR><TD CLASS="quote">

Lol that just came to me after thinking about what went wrong, shoulda left in it in damn 2nd gear </TD></TR></TABLE>

Always seems to work out that way

Next time you will be prepared for that scenario.

You're first couple of runs try to do something different if you aren't happy w/the times. Then after you figure out what works use your last 2 runs to put down your best times.