Track Setup Ba Xr8 Ute

[Erko]

Smoke them tyres, can you elaborate on pivot geometry change please mate?

[power_slide]

I Have a BF XR6t Ute with 850's in the front and a few extra leaves in the rear, all the bushes were redone and 27mm bar on the front and bar in the rear

HWY Driving is awesome with inital bite and lane changing but on the track I still have massive understeer, I have to try and work out the swaybar I think I will back it right off on the next visit

I also bought 8mm wheel spacers to my tyres wont scrub on heavy corners and keen to see how it will go on the track

Let me know what you end up doing

[Apes]

I Have a BF XR6t Ute with 850's in the front and a few extra leaves in the rear, all the bushes were redone and 27mm bar on the front and bar in the rear

HWY Driving is awesome with inital bite and lane changing but on the track I still have massive understeer, I have to try and work out the swaybar I think I will back it right off on the next visit

I also bought 8mm wheel spacers to my tyres wont scrub on heavy corners and keen to see how it will go on the track

Let me know what you end up doing

I hope that the 850's was not the wrong choice.

I agree with you that highway driving feels great the ride is not to rough and handling is great.

Do you think the bar at the rear lets the back of the car brake traction under power when you leave the corner?

Do you run semi slicks at the track?

What shockies are you running?

Why did you need the spacers??

Do you know the values or your alignment?

I think you may have answered the question which front bar to get may have to go back to standard with these heavy spring rates...

[power_slide]

To be honest the first time I went to the track in my ute was after the setup, every other time I had been was in my old mans bf xr8 and he has not done the bars yet

I am currently running Michelan slicks, think ill go back to bridgestone RE55s on the next set

I have bilstines all round

when I put the 6 pot brembos there were dramas getting wheels that clear, I ended up getting 20" rims so I could get a style I liked, every corner I took after fitting the brembos and dba 5000's had the inside of the 8.5" rim scrubbing on the upper arm and on heavy corners it was like death on the ears. on the old mans ute he popped a front right Bridgestone RE 55s at oran park a few weeks before it closed, seeing I am running a similar setup on the front I am going to leave the spacers in and hoping it helps the understeer

I think I am running -2.5 all the time, not really fussed on tyre wear. I will see if I can get some more with spacers in as I would like to try -3.5

with the slicks the traction is unreal and with bilstines it keeps the 420rwkw nicely planted

[Erko]

hey Power Slide, what are the offsets on those front wheels you have mate?

[power_slide]

+35 is what ozzy tyres is telling me

I guess it's more now that I have put 8mm spacers in

Cheers

Matt

[Smoke them tyres]

Hi,

They are diffently 850lb springs in the front..

I dont know what bump compliance is can you please explain???

Yes it does not feel good with the 30mm front bar at the springs up front. Need to get it sorted your opinion is valued. Thanks

That spring rate is a concern.....It's just waaaaaay too stiff IMO. I don't think locking the suspension (travel) out is a valid way to set up these cars.....they just don't/can't generate the G's of grip from the tyre available to make that method work. For a given weight car, grip and spring rate go together. Add to that low profile tyres (which should be considered as part of the suspension...sidewall give/flex,tyre pressures etc) and there is no give anywhere to absorb bumps and cornering loads.

IMO, the suspension compliance is effectively what is costing you lap time. The compliance is how supple the suspension is to bumps/upsets, particularly when loaded when cornering. Also, given that there is no weight transfer to the outside front tyre with fronts that stiff means that the tyre will slide rather than grip up, and hence the understeer. The lap times will also drop off faster as the tread area is effectively overheated from all the sliding.

Straight line and initial tip in will be ok, as that relies on initial camber. However when loaded with cornering, the above lack of weight transfer is what will apply. The car will generate more grip even if it uses some of the outside of the tyre more from a softer setup than having little or no weight transfer and a more even pattern. The wear pattern may be ok, but the tread blocks will show signs of distress from the understeer. Speed of breakaway is also another issue to consider in suspension setup....how controllable is it at the limit- Do the laptimes come easy/consistently, or are they bloody hard work? What is it's best operating window....narrow or wide?

The stiffer rear springs will mean more load for the front as they will absorb less weight transfer. They will also lessen corner exit grip for the inside tyre. A rear bar will make that worse, particularly the torque that motor will have. With no bar fitted there, it may be a case of doing the changes (if you want) and see how the chassis responds. The utes I have driven, don't need much more spring rate there, as there is little weight there and it's c of g is pretty low anyway.

-I would back the front spring rate back down to the King 520SP rate or "thereabout"

-refit the 27mm front bar

-remove/don't fit rear bar

-get as much front camber with a moderate amount of caster that you can get into it

I understand the Bilsteins aren't adjustable on the car, but their damping rates will need to be considered when a spring rate change is done....

-go easy on shock compression/bump settings as it's only there to stop spring overshoot on compression

-focus on shock rebound settings. A digressive curve is what we are looking for (re: a "knee" point)

Have they been revalved with the springs currently fitted?

Hi Erko.....IMO, for a proper geometry fix for these cars the pivot point that is in need of attention is the upper control arm (UCA) one. The pivot point for that arm is a long way from the LCA (too far really), and although it is short, there is still not enough camber gain from it's upward arc to fully offset the camber loss from the pivot point/chassis outward roll in cornering. I think that the pivot point would need to be lowered by "about" 3/4-1" to increase the rate of it's camber gain sufficiently. From what I can see, this would require making new UCA mounts and UCA's (with revised ball joint mount angles) as even the std geometry places the ball joint close to bind at full compression.

These of course would need to be made PROPERLY/ENGINEERINGLY SOUND, as it is a major suspension mod.

Edited 05/12/10 12:09 PM by Smoke them tyres

[Smoke them tyres]

every corner I took after fitting the brembos and dba 5000's had the inside of the 8.5" rim scrubbing on the upper arm and on heavy corners it was like death on the ears. on the old mans ute he popped a front right Bridgestone RE 55s at oran park a few weeks before it closed, seeing I am running a similar setup on the front I am going to leave the spacers in and hoping it helps the understeer

No offence, but are you serious in letting it scrub like that?

[nelsonian101]

Crap tyres like these Pirellis WILL cause understeer on the track.

This is your problem.

Before there is any point in making things too complicated, you need to try a new set of R rated semis.

My bet is that the understeer will VANISH.

850lb is very heavy but should work on smooth tracks (but only will a seriously revalved shock)

[Gee]

If you are serious about setting up your car for the track, just found out a workshop that sets up one of the ford brute utes. That will give you the base setting, sway bar size, wheel alignment, if you need a rear sway bar, spring rates etc. These people do it every day and have the faster utes around the track.