Inside Rear Wheel Lifting - R33

[Freebaggin]

Guys,

I have S1 R33 GTS-T. Suspension mods:

Front.

- Bilstein shocks (basic type, yellow colour)

- King Springs (200lb linear I think, no idea of heights)

- Offset polyurethane castor bushes

- Stock Sway Bars

- Shock tower brace in engine bay

- Tyres are 18" 235 Bridgestone S03s

Angles: -2deg camber, -12deg castor, 1mm toe in

Rear.

- Bilstein shocks (basic type, yellow colour)

- King Springs SP version (160-200lb progressive, no idea of heights, bit low though)

- Offset polyerethane camber bushes upper and lower arms

- Full R33 GTR rear bracing setup at back end of boot and across rear shock towers

- No sway bar

- Locally designed HICAS lock kit with full mechanical replacement and rose joints

- Tyres are 18" 265, very hard and 85% bald Faulkens

Angles: -1deg camber, 0mm toe in

Main problems I have:

- Very slight understeer

- Bad oversteer mid corner with or without power on

- Can really feel a change in dynamics when weight transfers to the rear

- Inside rear wheel sometimes lifts off ground, particularly slow sharp corners

Took rear sway bar off to try and fix rear wheel lift and oversteer problem but made no difference. I also need new tyres I know but it's has been like this for a long time.

Thanks in advance for any pointers.

[djr81]

A bad handling imbalance can be due to running different tyres front & rear. I would suggest that you need to sort the tyres before making more changes as to be honest even if you fix it for the current tyres what will you have when you replace them with new rubber?

to clarify

- Very slight understeer - do you mean turn in understeer?

- Can really feel a change in dynamics when weight transfers to the rear - do you mean power on?

- Inside rear wheel sometimes lifts off ground, particularly slow sharp corners - this is a worry. Mostly when this happens it is the end of the car with stiff anti roll bars (As per say an on VW Golf GT-i) Other than that it can be due to an excessively inclined roll axis front rear. Does your car sit nose down by any chance?

[Sydneykid]

Guys,

I have S1 R33 GTS-T. Suspension mods:

Front.

- Bilstein shocks (basic type, yellow colour)

- King Springs (200lb linear I think, no idea of heights)

- Offset polyurethane castor bushes

- Stock Sway Bars

- Shock tower brace in engine bay

- Tyres are 18" 235 Bridgestone S03s

Angles: -2deg camber, -12deg castor, 1mm toe in

Rear.

- Bilstein shocks (basic type, yellow colour)

- King Springs SP version (160-200lb progressive, no idea of heights, bit low though)

- Offset polyerethane camber bushes upper and lower arms

- Full R33 GTR rear bracing setup at back end of boot and across rear shock towers

- No sway bar

- Locally designed HICAS lock kit with full mechanical replacement and rose joints

- Tyres are 18" 265, very hard and 85% bald Faulkens

Angles: -1deg camber, 0mm toe in

Main problems I have:

- Very slight understeer

- Bad oversteer mid corner with or without power on

- Can really feel a change in dynamics when weight transfers to the rear

- Inside rear wheel sometimes lifts off ground, particularly slow sharp corners

Took rear sway bar off to try and fix rear wheel lift and oversteer problem but made no difference. I also need new tyres I know but it's has been like this for a long time.

Thanks in advance for any pointers.

Bascially that's a pretty good set up you have there, just a few items that need checking, changing and upgrading.

The first thing to do is to measure the heights, centre of wheel to guard on each corner. That will at least eliminate a potential problem.

The first thing I would fix would be to toe the front tyres out around 2 mm each side and toe the rear tyres in 1-2 mm per side. That will help the turn in and remove soem of the exit oversteer.

The second this I would fix;

- Stock Sway Bars

My suggestion would be a 24 mm adjustable on the front and a 22 mm adjustable on the rear. That will stop the weight transfer and make the transition more progressive. Plus increase the tyre contact patch by reducng the roll.

Third on my list, would be rear subframe alignment bushes. If it doesn't already have them, the subframe movement distrubes the tyre contact patch causing loss of traction.

Hope that was of some help

cheers

[Freebaggin]

A bad handling imbalance can be due to running different tyres front & rear. I would suggest that you need to sort the tyres before making more changes as to be honest even if you fix it for the current tyres what will you have when you replace them with new rubber?

to clarify

- Very slight understeer - do you mean turn in understeer?

- Can really feel a change in dynamics when weight transfers to the rear - do you mean power on?

- Inside rear wheel sometimes lifts off ground, particularly slow sharp corners - this is a worry. Mostly when this happens it is the end of the car with stiff anti roll bars (As per say an on VW Golf GT-i) Other than that it can be due to an excessively inclined roll axis front rear. Does your car sit nose down by any chance?

Yep time for new rubber and I have grippy stuff in garage waiting to go on the rear.

Only slight turn-in understeer at middling speeds, OK at high speeds.

I mean weight transfer to outside rear mid corner with or with out power on.

I'm thinking the -12deg castor might be inducing the inclined roll axis so I might drop it to -7 odd deg

Edited March 16, 2006 by Freebaggin

[Freebaggin]

Sydneykid.

I been advised for street use (daily drive), front toe out would be a pain due to tramlining, slight instability under braking and scuffing in inside of front tyres.

But I'll see how it goes with more toe in on rear when I put new tyres on.

I had Whiteline sway bar there but found them to make handling worse and exacerbated inside rear wheel lift, so went back to stocky on front and none on rear. I'll put the rear one back on with polyurethane bushes on both front and rear to stiffen up a bit as I sold the Whiteline sway bars.

Subframe bushes sounds good. grepin is in the process of puting them on so I'll get a idea from him.

Anyone else with +ve experiences with subframe bush replacements?

Thanks guys.

Edited March 16, 2006 by Freebaggin

[Bl4cK32]

check my sig freebaggin

[djr81]

Sydneykid.

I been advised for street use (daily drive), front toe out would be a pain due to tramlining, slight instability under braking and scuffing in inside of front tyres.

But I'll see how it goes with more toe in on rear when I put new tyres on.

I had Whiteline sway bar there but found them to make handling worse and exacerbated inside rear wheel lift, so went back to stocky on front and none on rear. I'll put the rear one back on with polyurethane bushes on both front and rear to stiffen up a bit as I sold the Whiteline sway bars.

Subframe bushes sounds good. grepin is in the process of puting them on so I'll get a idea from him.

Anyone else with +ve experiences with subframe bush replacements?

Thanks guys.

Freeballer,

The chief suspect in your handling woes (As seen from the other side of the country & without setting eyes on the car) is a mismatch between the front & rear roll centres. It can cause the exact behaviour you are describing. Hence the question about is the car sitting nose down on its suspension? Can you measure between the centre of the rim & the underside of the wheelarch and perhaps post a photo. This may well eliminate one candidate from the list...

[Freebaggin]

Freeballer,

The chief suspect in your handling woes (As seen from the other side of the country & without setting eyes on the car) is a mismatch between the front & rear roll centres. It can cause the exact behaviour you are describing. Hence the question about is the car sitting nose down on its suspension? Can you measure between the centre of the rim & the underside of the wheelarch and perhaps post a photo. This may well eliminate one candidate from the list...

Yeah, forgot to respond to that. Have measured heights before but can't remember, will do when I get home.

The rear end does sit lower than the front for sure, so it's nose up.

Edited March 17, 2006 by Freebaggin

[Sydneykid]

Sydneykid.

I been advised for street use (daily drive), front toe out would be a pain due to tramlining, slight instability under braking and scuffing in inside of front tyres.

But I'll see how it goes with more toe in on rear when I put new tyres on.

I had Whiteline sway bar there but found them to make handling worse and exacerbated inside rear wheel lift, so went back to stocky on front and none on rear. I'll put the rear one back on with polyurethane bushes on both front and rear to stiffen up a bit as I sold the Whiteline sway bars.

Subframe bushes sounds good. grepin is in the process of puting them on so I'll get a idea from him.

Anyone else with +ve experiences with subframe bush replacements?

Thanks guys.

What were the ride heights? They are very important on all Skylines but GTR's in particular. Other suggestion/comments follow;

1, The small amount of front toe out I suggested would make no difference to tyre wear, compared to the 2+ degrees of negative camber.

2. Don’t do the rear toe in without doing the front toe out. It will make the turn in understeer worse.

3. Sorry I don’t understand, a larger front stabiliser bar will reduce the roll and help keep the inside rear wheel on the track. Replacing the bushes from the standard rubber to polyurethane makes ZERO difference to the mid corner and corner exit anti roll. They only effect the initial turn in roll, once the compliance difference is taken up, the bars react according to their size.

With a 200 lbs per inch front spring rate, I can assure you that a GTR will need an upgrade in its front anti roll. To balance that, a rear anti roll upgrade will also be required. The suspension is a package, change one thing and it will affect the others.

cheers

Edited March 17, 2006 by Sydneykid

[Freebaggin]

OK so let's review current setup after I had a proper look:

Front end:

- Camber -1°45'

- Castor +7°40'

- Total Toe +0°8'

- ride height = 337mm

Rear end:

- Camber -0°42'

- Total Toe +0°6'

- ride height = 325mm

Edited March 19, 2006 by Freebaggin

[Sydneykid]

OK so let's review current setup after I had a proper look:

Front end:

- Camber -1°45'

- Castor +7°40'

- Total Toe +0°8'

- ride height = 337mm

Rear end:

- Camber -0°42'

- Total Toe +0°6'

- ride height = 325mm

Well, let's start of with its too low, far too low. The roll centre is now too close to the CoG ie; the roll couple is too small. The lower control arms are pointing upwards to the wheel, not parrallel to the ground, so the dynamic camber change angles are reversed ie; it's going posititive camber under compression. Plus there will be noticeable bump steer. Hence the oversteer/understeer balance changes due to the roll couple inbalance and tyre contact patch issues. The front height should be 350 to 355 mm and the rear should be 340 to 345 mm.

The front should be toe out a little, as discussed previously.

The rear toe is OK, but if it is still reluctant to tuirn in, then try some toe out as discussed previously.

It doesn't have enough camber, front or rear for the circuit and R type tyres. It needs another 1 degree negative both ends.

Then do the stabiliser bar upgrades as per the previous posts.

Hope that helps

Cheers

Edited March 20, 2006 by Sydneykid

[Freebaggin]

Thanks all and SK.

Can I have clarification on what some terms mean?

- Roll Centre

- Roll Couple

- Bump Steer (sounds obvious but I want to be sure)

Thanks again.

[djr81]

Thanks all and SK.

Can I have clarification on what some terms mean?

- Roll Centre

- Roll Couple

- Bump Steer (sounds obvious but I want to be sure)

Thanks again.

Broadly (ie the abridged explanation so please don't flame me for not including everything or for being a little generalised).

Roll centre - this is the geometric point about which the car rolls. It is dependent on the suspension geometry eg with wishbones the angle of inclination of both suspension members goes a long way to determining where the roll centre is located & also how it migrates (ie moves) when the car rolls. Note that the front & rear roll centres are commonly at different heights which in turn allows the balance of the car to be modified to give more or less understeer/oversteer.

Roll couple - the couple (ie torque) produced by the product of the mass of the car acting through the centre of gravity multiplied by the distance between the centre of gravity and the roll centre. The roll couple is the quantified torque that makes the car roll or lean through a corner.

Bump steer - when a suspension is compressed (or unloaded, bumps go down too!) the toe of the wheel changes. The outcome of this is known as bump steer. Most manufacturers use toe in for their front suspension because it makes the car more stable when one wheel hits a bump.

[Sydneykid]

Thanks all and SK.

Can I have clarification on what some terms mean?

- Roll Centre

- Roll Couple

- Bump Steer (sounds obvious but I want to be sure)

Thanks again.

Roll Centre = the point around which the chassis rolls. There is a front and a rear roll centre, determined by the location of the control arms in relation to each other.

Roll Couple = the distance between the roll centre and the centre of gravity (both front and rear).

Bump Steer = the amount the toe angles change when the suspension is compressed and extended fully. There is bump steer both front and rear.

cheers