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      03-18-2014, 09:57 AM   #1
e90pilot
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How do you get rid of turn-in and braking understeer?

I just did a track day at Laguna Seca last weekend. I've been having issues with understeer at initial turn in. It only happens after the tires warm up (about 2 laps) and is heaviest in turn 2 and 11. Mid corner when transitioning to throttle and exit are fine. When the tires are cold, I can brake later and deeper and actually get the car sideways easily. As the tires warm up the sweet spot for brake pedal pressure for trail braking get smaller and smaller. I can still get the car to slide on corner entry but only in turns like 4 and 9.

I've got Dinan suspension, M3 control and thrust arms with BBS CH 19x9.5, 265 width tires in the back and 19x8.5, 255 width tires up front. Alignment is -2.4 camber front and -1.7 rear with 0 toe. I've got about 38psi cold in the rear tires and whatever tire pressure up front required to wear out the little Michelin Man on the sidewall. I also have 135 brakes on all 4 corners with DTC70 pads and M3 ZCP rotors up front and stock 325 rotors and stock 135 pads in the back.

So what's the solution? Am I just doing it wrong? I have a feeling my brake setup might have something to do with it. I do have a larger rear rotor and DTC70 pad for the rear but it requires me to modify the parking brake to fit. I could just use that rotor and pad on the track as I don't use the parking brake at all while at the track. One thing that did work was downshifting to second without rev-matching lol.

One more thing that's slightly not related. How do I either reduce brake pedal travel or raise its resting position? It's REALLY hard to healtoe the car when the brake pedal drops well below the gas pedal. It gets worse as the brakes fade and the pedal gets softer.
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      03-18-2014, 01:03 PM   #2
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well, if your fronts grip better when cold, and start understeering after a few laps, my instinct would tell me to drop down a couple psi on the front tires. what psi do they get to when hot?

I know different street tires tend to vary in optimum psi, but 38psi does sound a bit on the high side for a cold tire.

either way, I doubt it's a brake problem, unless you are just braking too late and locking up the fronts. don't know how to adjust the pedal travel on this car. you might want to poke your head under the dash and see if there is some sort of adjusting nut.

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      03-18-2014, 02:07 PM   #3
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38 is kinda high but it doesn't get all that much higher on the track. I didn't check what the fronts were doing tire pressure wise but I do know from other experiences that the pressure goes up 3-5psi depending on tack temp. Last time I went to Thunderhill I had the fronts at around 34psi.
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      03-18-2014, 05:20 PM   #4
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Alright here's my thoughts.

I see understeer come up frequently and it's usually blamed on the car. Alignment/suspension/tires are a factor in your understeer threshold, but the lower-level truth is that every single car on the road can be made to understeer by the driver. The solution for understeer is to slow down and take the corner at a rate where the car is balanced. The car would probably not understeer if you went half the speed you usually do. Use understeer as a warning sign that you're overdriving the car; it results in unnecessary wear & tear, higher temps, slower lap times and potential off-roading. Remember you're merely piloting this car - that means you are confined to its abilities.

This is puzzling:
Quote:
Originally Posted by e90pilot
When the tires are cold, I can brake later and deeper and actually get the car sideways easily.
The only explanation I have is that you're boiling your brake fluid well before your tires get up to temp which just kills your stopping ability. Logically you have to brake earlier at the beginning of the session because the tires aren't up to temp, equating to less grip. The tires get up to temp during the session and allow you to brake more forcefully because they have more grip.

Take it from your instructor but learn to use your brakes less; brake shorter & harder. Next time you're on the track, ask your instructor first but get that brake pedal to the floor and engage ABS at least once to feel the difference.

You didn't mention what kind of brake fluid you have. Get high temp stuff in there ASAP if you don't already have it. Brake fluid is extremely important.

And this:
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Originally Posted by e90pilot
38 is kinda high but it doesn't get all that much higher on the track.
I have almost no plausible explanation for that unless you're waiting like 10 mins after the session ends to measure your tire's psi. Tire pressures are kind of a black art and I usually avoid the topic.
My suggestion, forget about tire pressure for now. Set all four corners to 4-5 psi lower than what's listed on the driver door sill and roll with it. Tire pressure has to be really out of whack with a street tire for it to be detrimental to your driving e.g. 50 psi, unless clipping tenths of a second off your lap times is your only priority.
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      03-18-2014, 07:11 PM   #5
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In using RBF600. I have 660 in my garage for the next flush. The brakes do fade but I always have enough pressure to lock the brakes even though the pedal might be long. As far as engaging ABS, I like to avoid it. I try and brake up to the point just before it engages. ABS really heats up the fluid and also throws the brake balance to the front and really exacerbates understeer.

I was really concentrating on turn 2. That's where I have the most trouble. A few weeks ago I attended a Skip Barber event and I really learned a lot. I was trying to apply what I did at the event to my car. Ever car I drove at the event (Porsche 911 base, Hyundai Genesis Coupe 3.8 R Spec, Lexus ISF) really responded well to trail braking. My car does when the tires are cold. When the tires warm up it's not like it's terminal understeer. Just that sweet spot of brake pressure and steering angle is really hard to find.

Now on throttle the understeer is still there but much less. In fact I can get the car to power slide even when the tires are hot. The understeer isn't progressing through the turn. That leads me to believe it's me or the brakes. Of course I'm no race engineer so I could very well be completely wrong.
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      03-18-2014, 08:39 PM   #6
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Quote:
Originally Posted by e90pilot
In using RBF600. I have 660 in my garage for the next flush. The brakes do fade but I always have enough pressure to lock the brakes even though the pedal might be long. As far as engaging ABS, I like to avoid it. I try and brake up to the point just before it engages. ABS really heats up the fluid and also throws the brake balance to the front and really exacerbates understeer.

I was really concentrating on turn 2. That's where I have the most trouble. A few weeks ago I attended a Skip Barber event and I really learned a lot. I was trying to apply what I did at the event to my car. Ever car I drove at the event (Porsche 911 base, Hyundai Genesis Coupe 3.8 R Spec, Lexus ISF) really responded well to trail braking. My car does when the tires are cold. When the tires warm up it's not like it's terminal understeer. Just that sweet spot of brake pressure and steering angle is really hard to find.

Now on throttle the understeer is still there but much less. In fact I can get the car to power slide even when the tires are hot. The understeer isn't progressing through the turn. That leads me to believe it's me or the brakes. Of course I'm no race engineer so I could very well be completely wrong.
what tires and how much tread is left?

start around 34 psi cold and measure as soon as you can after the session.
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      03-18-2014, 10:50 PM   #7
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Get your braking done EARLIER for those 2 turns. For turn 2, induce rotation using throttle. For turn 11, induce rotation using trail braking.

The simple explanation is, corner entry understeer happens when you're carrying too much speed into a turn, more speed than you have grip up front anyway. Same with under steering while braking, you're simply asking the front tire to do too much. Remember, tires can have 100% traction to turn (lateral), or 100% traction to accelerate, or 100% traction to decelerate. When you do a combination of two, like deceleration AND turning, you can't decelerate at 100% traction and expect enough traction for turning.

So if you are getting corner entry understeer, you are simply asking the tire to do more than 100% turning and slowing down combined. If you start your braking a little earlier then you won't need to ask your tire to do more slowing down, thus able to dedicate more grip to actual turn-in.

The reason you feel you can brake harder in the first two laps, is because your tires are not up to temp and you're not up to speed, so your terminal speed on the straights before the turns you're having trouble with are lower in the first few laps, therefore your braking was sufficient to slow the car down enough to leave enough grip for turn-in. Once you and the car are up to speed, your straight terminal top speed is higher and the same brake point leaves your car out of shape for turn-in. Turns 2 and 11 are especially hard since turn 2 is down-hill and turn 11 has no camber, and if you mis-time your braking you will have trouble with both turns.

If you have rudimentary dax, I bet your top speed at each straight is lower in the first couple of laps, making it much easier to time the brake application.

I surmise that the P-car, Hyundai, and Lexus felt easier to drive simply because it was an instructed environment.
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      03-19-2014, 11:56 PM   #8
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Quote:
Originally Posted by The HACK View Post
Get your braking done EARLIER for those 2 turns. For turn 2, induce rotation using throttle. For turn 11, induce rotation using trail braking.

The simple explanation is, corner entry understeer happens when you're carrying too much speed into a turn, more speed than you have grip up front anyway. Same with under steering while braking, you're simply asking the front tire to do too much. Remember, tires can have 100% traction to turn (lateral), or 100% traction to accelerate, or 100% traction to decelerate. When you do a combination of two, like deceleration AND turning, you can't decelerate at 100% traction and expect enough traction for turning.

So if you are getting corner entry understeer, you are simply asking the tire to do more than 100% turning and slowing down combined. If you start your braking a little earlier then you won't need to ask your tire to do more slowing down, thus able to dedicate more grip to actual turn-in.
This is the best possible way to describe it. I have done Skip Barber courses and if there is one thing to take away from any of the classes it is this rule ^^^

Turn 2, all braking should be done in a straight line
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      03-20-2014, 06:58 PM   #9
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The tires on it right now are Michelin Super Sports. My personal best of 1:50.53 was done with Bridgestone RE11s.

The 100% rule, as Skip Barber calls it, was the focal point of most of the exercises as well as looking where you wanted to go. But as far as braking in a straight line for turn 2, well that was the opposite what they taught. One of the morning excercises of the second day was dedicated to turn 2 and trail brakinging. They had us braking all the way down to about half way between the 2 apexes, assuming you're taking it as a double apex.

I took a look at the data from the various laps. A bit of a disclaimer: I was using Harry's Lap Timer for iPhone and internal GPS/accelerometers which update once per second. Accuracy isn't exactly perfect. However of the hot laps, the entry speeds were daily consistant (101-103mph) there were some outliers (98 and 105 mph). The mid corner or minimum speeds were more interesting. A faster minimum usually resulted in a slower max speed into turn 3. However, a higher max down the front straight resulted in a lower min in 2. My best lap happened on the first hot lap of the session and had front straight max of 103 mph, a turn 2 min of 32 mph, and a max of 74 just before 3. The fastest turn 2 min was 41 mph but only resulted in a subsequent max of 71 mph.

The data seems to support was Hack is saying. While maybe the front straight speeds arent varying, maybe the actual braking point is. This program isn't accurate enough to really compare that. You can travel well over 100ft in one second at 100mph.
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      04-15-2014, 12:48 AM   #10
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Hi. I'm a newb to this forum, but have been racing and instructing on bay area tracks for over 15 years, so thought I'd chip in a few cents here. Another possibility is that you may be trying too hard to get the car to rotate through the initial turn-in. It's critical to give very smooth steering input when you trail brake into the turn as the car shifts weight to the front right. As was mentioned above, there is little to gain being on edge at corner entry... unless you are going for an aggressive inside pass. Of course there's no way to tell for sure if this is the problem without being in the car with you, but it sounds like it could be. By turning in too hard the tire could be rolling over slightly and sliding (I had this problem on a street car before). Pumping the pressure up a bit can help too. You've got really good brakes, tires, everything, I doubt it's a mechanical issue.
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      04-15-2014, 01:51 PM   #11
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You're driving a street car, not a formula car. Your car will almost never be perfectly balanced and you will be forced to drive around the weaknesses in your car.

If you only have problems with balance in one or two corners, you are more likely not going to magically "fix" those problems with adjustments to the car. Every setup is a compromise in some fashion, and with that compromise comes some corners that the car doesn't work perfectly.

Some food for thought: You don't have to trail brake into every corner. In fact, it flat out doesn't work in some situations. Try something different if it doesn't work.

In the end, if you are having turn in understeer that you can't fix with setup or technique, the only solution is to slow the car more before entry. That will most likely result in better mid corner and exit speed than if you plowed through entry with understeer.
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      04-15-2014, 10:39 PM   #12
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      04-16-2014, 01:55 PM   #13
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Quote:
Originally Posted by bcms6 View Post
Hi. I'm a newb to this forum, but have been racing and instructing on bay area tracks for over 15 years, so thought I'd chip in a few cents here. Another possibility is that you may be trying too hard to get the car to rotate through the initial turn-in. It's critical to give very smooth steering input when you trail brake into the turn as the car shifts weight to the front right. As was mentioned above, there is little to gain being on edge at corner entry... unless you are going for an aggressive inside pass. Of course there's no way to tell for sure if this is the problem without being in the car with you, but it sounds like it could be. By turning in too hard the tire could be rolling over slightly and sliding (I had this problem on a street car before). Pumping the pressure up a bit can help too. You've got really good brakes, tires, everything, I doubt it's a mechanical issue.
I agree. You have to be smooth with your driving inputs. Just throwing a car into a corner will automatically induce understeer. Exit speed > entrance speed. Always.

You mentioned that you try to trail brake into corners. This is a bad idea if you don't have a wing or significant aero. If you have no downforce pushing your rear end down, you are just going to have a very squirely rear end which might induce some understeer as well.

In terms of your tire pressure you are running WAY too high. That will automatically induce understeer. Tire pressures all depend on driver preference, but you would want them in-between 33-38 HOT.

Last point I would like to make is that your suspension might be too tight. A tight suspension is not a fast suspension. You want to transfer weight effectively and at the pace your tire can do it. You only want to run a somewhat tight suspension when you are running slicks. Slicks can handle that stiffness.

Just some food for thought, hope this has helped a little.

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      04-16-2014, 03:46 PM   #14
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Alright I need to clarify something. I shouldn't trail brake unless I have aero? That pretty much goes against what all the driving instructors across multiple schools have tought me. So a squirly rear end (squirly is usually a term associated with oversteer) causes understeer? All trail braking is as I've been taught is "trailing off" the brake while adding steering. The instructor showed us the whole grip circle diagram and "100%" rule and what not. When I hear don't trail brake or brake in a straight line only, that throws up some red flags.

As for tire pressures, I'll pay closer attention to them. I usually don't really care what the exact number is. I just look at how far the scuff marks go down the sidewall. Michelin tires have a mini Michelin man on the sidewall. I was told the scuff marks should just barely wipe him off. For the rears, I keep the pressure a pound or two higher than that point. The actual number is like someone said here a bit of a black art. It depends on when you measure it and of course weather and track conditions.

Now for setup. I'm very apprehensive about changing the setup. For the sake of argument, let's assume for the moment I'm driving correctly and the car really does understeer excessively under braking. What do I change? In what order? Front rebound? Rear rebound? Anti roll bar stiffness? All of them? I don't really have the tools to do that at the track nor do I have the knowhow to mess with the setup, so I try to drive around it.

Someone mentioned I'm having issues with only two turns. That's not perfectly accurate. I'm having trouble rotating the car on the brakes. I used those turns as an example because that's where I need it the most according to what I've been taught.

From what people have been saying here, I think I'm just trying to carry too much brake into the corner. I'm releasing the pedal too slowly and running myself out of front grip. So I either need to turn the wheel more slowly or come off the brake pedal more quickly. This will probably require me to brake earlier as well. I'm not sure when I'll be on the track next but I will gladly let any of you drive my car if you happen to be there too provided the sanctioning body is ok with it.
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      04-16-2014, 06:26 PM   #15
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Quote:
Originally Posted by e90pilot View Post
Alright I need to clarify something. I shouldn't trail brake unless I have aero?
No.

Quote:
Originally Posted by e90pilot
So a squirly rear end (squirly is usually a term associated with oversteer) causes understeer?
No.

Quote:
Originally Posted by e90pilot
All trail braking is as I've been taught is "trailing off" the brake while adding steering. The instructor showed us the whole grip circle diagram and "100%" rule and what not. When I hear don't trail brake or brake in a straight line only, that throws up some red flags.
There is no hard and fast rule for trail braking. It works in some corners, it doesn't work in others. It works on some cars, it doesn't work on others. Trail braking is simply a technique. Sometimes you should use it, sometimes you shouldn't. Sometimes it's better to brake in a straight line, rotate the car, and then power through the car. Every car is different, every corner is different.

Quote:
Originally Posted by e90pilot
As for tire pressures, I'll pay closer attention to them. I usually don't really care what the exact number is. I just look at how far the scuff marks go down the sidewall. Michelin tires have a mini Michelin man on the sidewall. I was told the scuff marks should just barely wipe him off. For the rears, I keep the pressure a pound or two higher than that point. The actual number is like someone said here a bit of a black art. It depends on when you measure it and of course weather and track conditions.
Tire pressure adjustments are easy adjustments that mask the problems of your car. They are not a solution to the problem. If you try to change the attitude of your car using tire pressure, you are giving away grip. That being said, changing tire pressure is often easier than making the real set up adjustment that needs to be made. It's a good compromise for a track day car. Play around with tire pressures to see how it affects your car, it's good to learn.

Quote:
Originally Posted by e90pilot
Now for setup. I'm very apprehensive about changing the setup. For the sake of argument, let's assume for the moment I'm driving correctly and the car really does understeer excessively under braking. What do I change? In what order? Front rebound? Rear rebound? Anti roll bar stiffness? All of them? I don't really have the tools to do that at the track nor do I have the knowhow to mess with the setup, so I try to drive around it.
You have to understand what you are saying. If you are understeering during braking, you can fix the problem without any setup adjustments. Just stop trying to turn while braking. That's easier than making setup adjustments. If you desperately want to keep trail braking, your setup adjustments will be very complicated. I would begin by stiffening the rear, but you are opening an entire bag of worms.

Quote:
Originally Posted by e90pilot
Someone mentioned I'm having issues with only two turns. That's not perfectly accurate. I'm having trouble rotating the car on the brakes. I used those turns as an example because that's where I need it the most according to what I've been taught.
What type of turn is it? Is it a long, long long, gradual turn? Is it a 90 degree turn? All of these things factor into the decision as to what type of approach you should take to the turn. Try different things.

Quote:
Originally Posted by e90pilot
From what people have been saying here, I think I'm just trying to carry too much brake into the corner. I'm releasing the pedal too slowly and running myself out of front grip. So I either need to turn the wheel more slowly or come off the brake pedal more quickly. This will probably require me to brake earlier as well. I'm not sure when I'll be on the track next but I will gladly let any of you drive my car if you happen to be there too provided the sanctioning body is ok with it.
I think you are over thinking everything. Go out there, forget trail braking, and try to do all your braking in a straight line, release the brake, then turn in, then power on and power through the turn. It seems you are fairly new to racing a car on a track. Get used to different techniques. Experiment, try new things. You will learn a lot more about your car than trying to shoehorn a setup into a driving style that doesn't necessarily apply to the corners you are having trouble with.
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      04-16-2014, 07:14 PM   #16
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Again with the don't trail brake advice. Sorry, I just can't follow that advice. It goes against what EVERY SINGLE INSTRUCTOR I've had has taught me. I'm having issue with trail braking. It doesn't make sense to just ignore what I'm having trouble with. I was a flight instructor for 4 years and training captain for a year and a half at my current job. I know a thing or two about teaching people how to operate complex machines. I can put together an ok lap so I'm not new, but I'm neither an expert nor a professional.
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      04-16-2014, 09:45 PM   #17
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Every instructor has taught you to trail brake every turn? Time for new instructors I think. I'm trying to help you with your problem. You have two options: Fuck with your setup to make the car trail brake better, or try a different but equally viable technique to see if that works without monkeying around with setup you don't understand.

Do you trail brake 90 degree turns or turns less than 90 degrees? I want to try and understand exactly what problems you're having.
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      04-16-2014, 09:53 PM   #18
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I've reread your post to see the turns you are having trouble with. They are hairpins. If you want to reduce turn in understeer while.under braking you simply need less grip in the rear. That will make.the car more neutral in that turn but will upset the balance in the other turns that you are having no trouble with. The other option is to slow the car more in a straight line and use less brake while turning. Really when you trail brake for hairpins you are not turning the wheel while.doing the heaviest braking, you point the car in a straight line heading towards a point near the apex, that way you are braking in a straight line but still negotiating towards the apex. Once you reach the point where you need to rotate the car you need to get off the brake and then turn the wheel.
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      04-16-2014, 10:05 PM   #19
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Watch this video and watch how the driver approaches turn 2. Notice that he turns in before he starts braking, and then brakes in a straight line towards the apex.



He gets almost all of his braking done during that straight line. As he approaches the apex, he then has to rotate the car. This is when the brakes are released and the wheel is turned. In a perfect world, this is done simultaneously in proportion.

Turn 11 is different because you don't have room to do that type of braking, so you brake in a straight line and then release the brakes and rotate the car. Notice in the video that he locks the front left as he turns in, this is because he still had his foot on the brake (trail braking).

He has two options at this point: less brake, or less steering input.


Here's the solution to your problem. If you are having understeer in trail braking, it's because you are asking for too much grip. Don't try to fix it with setup, fix it with driving technique. It's easier, honestly. Do more of your slowing in a straight line instead of plowing through the turn trying to brake and turn at the same time.

Here's a photo I took this past weekend of a kid asking the same question you are asking in this thread....

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      04-21-2014, 07:40 PM   #20
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LI_Goalie is shockingly spot-on for being, I assume, from Long Island. I don't know how much time he's spent at Laguna Seca but if I were you OP, I'd listen carefully to everything he's saying. I find myself nodding as I read his post.
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      Yesterday, 12:48 AM   #21
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Quote:
Originally Posted by LI_Goalie View Post

... driver approaches turn 2. Notice that he turns in before he starts braking, and then brakes in a straight line towards the apex ...


... He gets almost all of his braking done during that straight line ...


... Do more of your slowing in a straight line instead of plowing through the turn trying to brake and turn at the same time ...

This is what I was saying. And what I believe most of us are trying to tell you.

Bottom line is... We are trying to help you go faster by adjusting technique first, which is going to be the easiest way to do this. Everyone in here is giving you the same solution. Perhaps go and try that first before trying to make your street car into a perfectly-balanced, easy to drive, race car that doesnt exist.


Again, just trying to help!
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      Yesterday, 10:00 AM   #22
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Aside from what everyone is saying, I'd like to revisit this part of your post:

Quote:
Originally Posted by e90pilot View Post
I just did a track day at Laguna Seca last weekend. I've been having issues with understeer at initial turn in. It only happens after the tires warm up (about 2 laps) and is heaviest in turn 2 and 11.

what you are saying is that at the beginning of the lapping session, your car turns a lot better. I think it's worth investigate what's happening after those first few laps.

are your tires overheating? are you driving more aggressively/faster, and/or changing your technique?


some combination of events is going on that changes how your car handles. it may just be your driving, but it's still worth looking into, imo.
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