How "stable" is your car on the open road???

[Plums]

I have just had my car in for a wheel alignment, and the car still feels nervous on the open road. The car feels great at around town speeds, but out on the highway it tracks (I think that's the term) quite badly. It feels as if someone just randomly gives the wheel a little tug in either direction.

Here are the Front figures:

Toe: .1 toe out total

Camber: -1.5 degrees (both)

Castor: L 3 degrees, R 2.5 degrees

When I got there, I had 3.1 toe in total and this was the only thing he adjusted. I queried him on the toe out but he assured me it was all good... He reckoned the camber was good, and the castor was also good (but I know I have the castor at the max anyway, unless I start modifying things).

The Rear figures were:

Camber: L -1.5, R -.5

Toe: L 1.4 toe in, R 2.8 toe in.

I just got the figures for the rear and I'll have to play with it myself, (I need to remove the tank to get the lower arm link out to take out some toe from the drivers side)...

The guy reckons just one shim in the right will bring the toe to about spot on, and will probably get the camber close to the left too....

Any help or comments would be welcomed....

[Aussie Mike]

Not enough castor there Bobby. Put 4 degrees in and it should be a lot more stable. The toe out won't help either, you should probably have a little toe in on the front.

A bit of toe in on the rear is good as it'll try to toe out under brakes when you want the car to be stable and run straight.

Cheers

[Gav]

I had mine set up with-
Front-
Camber -1.5
Caster 4.1
Toe in 1.0

Rear-
Camber -1.1
Toe 0

It felt great when it was first done but I have since lowered it again and needs redoing.

Gav

[bobcowan]

Bad handeling is usually caused by improper alignment.

Mine seems to be just rock solid at highway speeds (80mph). On the track I'm very comfortable with 140mph down the front stretch.

Caster 4*
Camber 0.25-0.5* (for the track I increase this to 1.5*-2.0*)
Toe in 1/16" total

Have you checked your bump steer? If it's a random tug to one side or the other, is it associated with irregularities in the road surface?

Before aligning the car, make sure you have the ride height set exactly where you want it. If you're going to adjust corner weights, do that first.

[Tenrocca]

Bobby, if you need more castor and have Series 2\3 upper arms, you can maybe go to series 1.

Cheers

[Plums]

Bingo Tenrocca, I've got HarryMac searching his shed for some early arms as I type this... Thanks Harry
EDIT: In fact he just found some, Thanks heaps Harry!!!

I've been thinking that to get more castor I'd need to change the upper arms, (either to different Jag items or custom arms like PhilM runs) as I have reached the maximum amount of adjustment already.

At the alignment place this morning, the guy was adamant about running slight toe out, which didn't sound right to me. To be honest I don't think it made much difference to my car's "nervousness"...

Thanks for the replies fella's

[Ross Smith]

Hi Bobby,

My car also has 2.5 degrees of castor, I am very interested to hear if changing to 4 degrees solves your problem.

Ross

[Harrymac]

Hello Ross,

Can you send me your email address in a PM.
I have the two photo's and weight charts and the Printed sheet for you,
I shall take them to the club tonight, if not I shall email them to you.

Cheers,

Harry.

[stephen low]

Bobby et al

Haven't had a chance to drive mine at serious speed but just too had alignment prior to my engineering visit on Friday with the following outcomes:

Before After
Castor: L +1.33 R 2.34 L +2.41 R 2.30

Camber: L -0.07 R -0.24 L -0.31 R-0.49

Toe In L 4.0 R 3.7 Tot 7.7mm L 1.5 R 1.6 Tot 3.1mm

Had requested Castor 3.0 degrees and Toe 3mm and would live with whatever camber for the moment, as front is so far up in the air for clearance with 50 series tyres it looks like a 4WD at the front.

My guy's been at this 25 years so I had some confidence. Definitely felt more sensitive on the road but still stable. Would agree toe out is for race cars, makes direction changes much faster with the loss of stability. Do you want this for a road car Bobby? Is your guy a race car tuner?

Its the same issue for castor, heaps of caster helps in turning stability but without power steering you have to be superman from 6 or so degrees onwards, at park speeds anyway - don't you Mike!!

I'd like to get to about 4 degrees castor and - 1 degree camber and lowering the front will all help after engineering. However I do have S1 uppers and have run out of adjustment.

It took my fellow some time and jiggling to tweek what I've got in terms of camber 10 minutes extra left and only 3 extra right ie bugger all.

Knowing of the G Force / RMC rear axle alignment issue he was able to indicate my car has rear toe as L -1.5mm R +2.3mm but one or two turns on the left rose joint will give about equal toe in.

He said this helps compensate camber in cornering and improve stability and grip somewhat in corner ie achieve more tyre face to road in corner (all marginal stuff of course).

I too would like to hear about the changes to handling if you hit 4 degrees castor.

Cheers

[David Hodgson]

Get rid of the toe out. Toe out can help 'turn in' on the track, but on a rear wheel drive car on the average Aussie road is not good

1 -1.5 mm Toe in with around 3 degrees caster should be a good starting point for street.

I experimented with alignment setting a bit for the track and toe out seemed to help a bit on turn in, but was very nervous under brakes. On the road it was wandering all over.

[Rebel1]

Here is my take on the RMC...and to a certain extent the G-force for a start point for a stable road car.

Front toe...total 1/16 to 1/8" in.
Front Caster...as much as your muscles will allow at parking lot speeds. 6 degree common but achievable only with series 1 uppers.
Front camber 1/4 to 3/4 positive.

Rear toe total 1/8 in.
Rear Camber 0- 1/4 to 3/4 positive.

Rear camber doesn't change much with suspension travel but try to set the rear with the drive shafts near horizontal. The lower arms will still incline slightly upwards to the diff and will cause negative camber with body roll.

Dial in both the rear toe and camber by making your own shims. Because of the shortened rear shafts the standard Jag shims may not be quite right. Purchase some Champion 316 stainless shims sheet and make your own shims. ( comes in a pack with a 100x100mm sheet of .002,003,005,012.).

The standard jag camber shims are .020 so the .12 stainless shim will give you a half thickness shim approx.

The thinner champion shims are great for dialling in the toe.

I think it is unwise to "pull" toe by loading the drag arms.

Cheers

[400TT]

My RMC was running around with these figures for years:

Front
Camber: -0.5(L) -0.5(R)
Caster: 4.0(L) 3.6(R)
Toe in: 1.0(L) 1.0(R)

I'm not sure yet what I will run with.

[Rebel1]

Yep..pretty close to my start point for the front Craig.

If I remember the previous owner told me the car was great on a smooth highway by a bit nervous on an undulating road.

One of the problems with the RMC is the variation of the placement upper arm mounting.

My car has the two bolts holding the upper arm above the bottom of the front chassis cross member. If you look at the picture in Ross Smiths gallery at his chassis pic you'll notice the same holes are below the cross member.

Whilst not an issue at rest Ross's car will invoke negative camber with less body roll which is exactly what you want.

Sadly the RMC chassis varies quite a bit.

[400TT]

As you know my car has already got some and is getting the rest of Scott(Ozvenom) RMC Enhancement package.

In his words, it will be a pleasure to drive on the road. I'll look to Scott for guidance on the wheel alignment settings.

[PCC]

All sounds good guys, but....

I went from complete nerves on undulated roads to complete confidence by simply replacing the Falkens with Toyos T1R's.

I have absolutely no wandering at all now.

Grips as good as the WRX! (Well at least 2 wheels at a time).

[stephen low]

Les

My fellow indicated that use of some rose joint movement ok for the rear, that's why they have bushes and rubbers, but there is a limit to what can be achieved.

In my case he is of the opinion that 1 - 2 turns of my LH rose joint is all that is needed to get toe in so both rear tyres are at about similar angles. This overcomes any later dabbling with the rear axle, given the out of line mounting hole issues for RMC and G Force cars.


Interesting to see you quote positive camber though.

Cheers

[Rebel1]

Originally Posted by 400TT

As you know my car has already got some and is getting the rest of Scott(Ozvenom) RMC Enhancement package.

In his words, it will be a pleasure to drive on the road. I'll look to Scott for guidance on the wheel alignment settings.

And the same fella will be doing mine Craig. He has already done a little bit.

But that's exactly my point....Scotty is a wizard because he:
1. Knows the cars
2. Attends to the detail.
3. Makes the required changes.

He was the one who drew my attention to flattening the upper arm. Since then I have noticed the variation between RMC's.

Both the RMC and G-force ( being closely related) can be made to be an absolute pleasure to drive. Dare I say, ( and I just know I'm gonna cop $hit for saying this) that the RMC, ( and G-force by implication) properly set up are close to the best street cobras you will find.

There, I said it.

[Rebel1]

Originally Posted by stephen low

Les

My fellow indicated that use of some rose joint movement ok for the rear, that's why they have bushes and rubbers, but there is a limit to what can be achieved.

In my case he is of the opinion that 1 - 2 turns of my LH rose joint is all that is needed to get toe in so both rear tyres are at about similar angles. This overcomes any later dabbling with the rear axle, given the out of line mounting hole issues for RMC and G Force cars.


Interesting to see you quote positive camber though.

Cheers

Nope, not in favor of any "pulling" to achieve your geometry. There are enough stresses both fore and aft for the rubber bush to deal with as it is. Using it to pull the toe will only cause wear of the bush and then you are back to square one.

The geometry can be perfectly set using the shims and that leaves the trailing arm to deal with it's own problems. In the case of the RMC it runs straight forward so will pull on squat and rebound anyways.

The positive camber was just a starting point and depends on your top mounting point. Static positive camber in some cases can quickly turn negative with very minor body roll.

[NASSTY]

Originally Posted by Rebel1

Nope, not in favor of any "pulling" to achieve your geometry. There are enough stresses both fore and aft for the rubber bush to deal with as it is. Using it to pull the toe will only cause wear of the bush and then you are back to square one.

The geometry can be perfectly set using the shims and that leaves the trailing arm to deal with it's own problems. In the case of the RMC it runs straight forward so will pull on squat and rebound anyways.

The positive camber was just a starting point and depends on your top mounting point. Static positive camber in some cases can quickly turn negative with very minor body roll.

The issue of trailing arms of the jag rear end in a cobra is not new ground. The original jag diff is in a sub frame that is completely rubber mounted. If there were no trailing arms then there would be very little to stop the diff sub assembly from rotating forwards and backwards on its rubber mounts. Any binding caused by the training arms not having the same geometry as the lower arms is offset by the sub assembly's rubber mounts as well as the bushes on the trailing arms.

Conversely in a cobra where the diff is solidly mounted to the chassis, there is no additional play as there are no rubber mounts. The roller bearings in the lower control arms have far less play than the rubber bushes in the trailing arms which effectively make the trailing arms redundant, in my opinion.

Perhaps you may also place too much lateral preload on the roller bearing in the lower control arms if pulled in.

[stephen low]

Hmmmm this is bringing us back to that 101 suspension thread from some time back!!

If shimming is a possibility, I'll have to read up on the rear suspension arrangements now.

Cheers