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Massive Understeer At The Track, What To Do?


xr_velocity

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Was after some advice. I hit Eastern Creek a few weeks ago, while I had a great time, my front tyres did not. Massive understeer all day, even before the tyres had got so hot they almost melted.

My setup is Lovells shocks and springs SSL all round with a 27mm sway bar on the front.

The rear end stuck like glue all day, even under full power out of corners there was zero slide from the back end. My tyres are fairly new Falken FK452 2435 19 and 275 30 19. I never expected them to be a good track tyre, but the understeer was very bad. The car had a Heasmans alignment a while ago, they set it up halfway between street and track.

Is there something else I should be doing other than buying slicks? I get the feeling that with the way the car was handling, slicks would just mask the understeer a little.

Edit: I am getting front lower and upper control arm bushes and control blade bushes done next week. All up $647 including alignment and fitting new power steering boot as mine is split. $400 labour from Bankstown Pedders, bushes are cost price from my brother. I thought I'd give Pedders a plug as I think that is a very cheap price.

Edited by xr_velocity
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You need negative camber on the front end to reduce the understeer, the way it is now the tyre is probably trying to fold under itself.

To add to that, a larger rear swaybar will help promote a more neutral stance since you already have the front bar fitted.

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How much do you guys do a proper alignment for?

I have heard mixed feelings about a bigger rear sway bar on these cars. What's the reason for going larger on the rear?

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Turn two would have been fun...not

The guys @ pedders should be able to do an alighnment to erradicate some of it.

I use 2.5 neg camber on the rear with 1mm toe. Works ok. But only about 10,000 k's at best from the tires.

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Full alignment including camber adjust is $95 :beerchug:

The larger rear bar increases the oversteer nature of the vehicle, since you have fitted a larger front bar (which increases the understeer nature) this will bring the car back to a more neutral setting.

If you don't like the idea of fitting a larger rear bar, just look into the extra camber, that should give you a decent increase in turn in.

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another in agree'ance with Senna_T, you need to stiffen the rear to loose a little grip to make the front gain it, it's all a balancing act.

Also depending on whether you have understeer going in or coming out of the corner can affect what adjustments are required

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I was at Eastern Creek early August too. Did you go on Monday or Wednesday?

I was in the silver FGXR6T with the black wheels.

I've gone through a set of Falken FK452's and they aren't really a track tyre. The temperature would really increase even close to 45-50psi after a few hard laps. What hot pressure were you running? Checking and adjusting the pressure is crucial to the car's handling. 35psi hot is a good starting point.

Rather than going to slicks (2nd hand Porsche cup front 18" Michelins are sometimes on ebay and cheap)I would try either Kumho KU36 or Federal 595RSR or Toyo R1R. Falken RT615 are good too. For more traction and street legal I'd try an R rated tyre like Toyo R888. Yokohama A050 or Dunlop DZ03G are even better but more expensive. Any of these above tyres will help you reduce your understeer compared to the 452's. Also is your front rim width 8" or 8.5"? That extra 0.5" does make a difference stopping the tyre roll slightly contributing to understeer and lets me honest, who couldn't do with an extra half inch!!?? ;-)

I also agree with the rear sway bar addition. I have the adjustable rear whiteline bar and had it in the middle setting at Wakefield experiencing huge understeer on the turns at the top of the hill. When I set it to the hardest of 3 settings, the understeer disappeared with all other variables constant.

Front camber kits are available for the BF's. A track wheel alignment with 3deg of negative camber would help reduce understeer significantly.

Driving Style also has a big influence on understeer. Maybe you are going into the turns too fast and coming out too slow?

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Thanks all. I am definitely not hitting the corners too fast, I was actually going in slow and still understeering. I didn't check the hot pressure, first time on a track day so that is something I have learnt! I will get myself a pressure gauge before the next one. Front wheels are only 8 inches, they were probably so overinfalted with the heat I had a small contact patch on the road.

I will give the rear bar a shot, will cost me bugger all cost price :)

$95 is a great price for a real alignment, if Pedders don't know what they are talking about (the alignment is included with the steering boot change), I will get it down to you for sure Senna. Heasmans charged me $180 last time!

I was at EC on a Friday, not Mon or Wed. It was a private practise day with the ARDC. Not bad I thought, $95 for the day with membership.

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I would IMO:

1. Lift the car back UP to std ride height. The current lower roll center (intersection of control arm pivots) and fixed c of g that the ssl setup is, actually means that the roll center has moved to a much lower point further away from the c of g. What this means is that the fixed c of g can now get much more leverage on the front of the car during cornering. That is where the forces in cornering are acting through. These cars usually hammer the outside edges of the front tyres. I presume that is where the tyre was most worn? Tyre wear pattern is always something I watch very closely. It's a great way to see what the tyre is actually experiencing and telling you about chassis setup. You can have more grip AND longer tyre life, the geometry and spring and bar settings just have to be correct to expose the full contact patch to the road. Lower is not necessarily better.

2. Pat is right in that a bigger rear bar will restore the balance. The bigger rear bar will lessen weight transfer to the rear, and hence grip to achieve that. More camber will then be requires to get then rear to not do the same to it's tyres as the front. My preference is to remove it though and try and get some weight transfer to the rear to help "unload" the front. The weight transfer in cornering is LATERAL and DIAGONAL. Chassis stiffness is the transmitter of that. With the 27mm front, that is in the zone, but I would remove the rear and see how it feels. That sharpens up turn in and mid corner grip as the load transfer makes the actual cornering load at each end of the car much more equal. This will actually help the front tyres to not roll over onto their outer edges so much. You can re-fit it if you don't like it. A no cost option. Have a close look at any rear wheel drive race car (that is well setup), particularly as it loads up it's suspension entering a corner. The rear will always have softer rear springs (traction) and more roll (cornering load balance). This is also why the V8 's fiddle with the rear roll centre. A turn "here or there" can make a noticeable difference. Raise it for less roll, lower it for more roll.

3. Do you know what rate the springs are on the front? I have gone from the std 520's to std XR height 620's.I am now thinking that King Springs have chosen this as a good compromise for sixes AND eights. They just seem that tad stiff for the lesser weight if the six. If I build the enthusiasm in the near future, I will get some made at about the 570-580 in/lb rate that I think will actually be an improvement from where it is now.

4. Those bushes mentioned are the ones to go for that will be the most value for dollar spent AND promote tyre (and diff/cv) life.

5. You need to get some more front camber into it. About zero is std. That is completely ineffectual for cornering. Dynamically when cornering (with the std bushes), the geometry probably goes into positive camber. Add body roll and you get the picture. The fronts have no chance but to understeer as they "fall over" onto their outer edges. Outer edges in distress usually take small chunks out of the leading edges of each tread block, or have a sort of ski ramp on each tread block caused by distortion under load. If you can get at least 1 degree negative that will help. More camber is better than more caster as to increase caster loses some camber (just the way the geometry is). More caster won't be as good as more camber, as it arrives "too late" to be effective for the small amount of wheel movement to negotiate a turn. It is also steering dependent, not load dependent as we want. About 1-1.25mm toe in per side should be the go for about 1-1.5 degrees neg camber. About 2.5 degrees is the max neg camber I would run on the street. I would also set it up with equal settings on each side.

Edited by Smoke them tyres
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How much neg camber can you get out of the stock parts?

You have mentioned more neg camber in the rear...is this adjustable stock or need a kit to do so?

Not sure on spring rates, will try find out today.

Edited by xr_velocity
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