Harrison wheel alignment

[sambo]

I know there are plenty of suspension-related threads out there but I have some specific questions about the Harrison setup with R33 rear end.

After giving up on the big brand tyre places, yesterday I had a proper wheel alignment done at Traction Tyres here in Melbourne. Very knowledgeable, passionate about their trade and two of the technicians have R33 Skylines, so they're familiar with the Harrison IRS.

So now the car tracks straight and true when launching/stopping hard and the stance is finally looking good with an even 4" clearance around the floor pan. It's a pleasure to drive compared to the "Bridgestone boys" setup.

One niggle though - when cruising in a straight line, if I move the wheel slightly left or right it wants to dart off in that direction. I wonder whether I have too much toe in?

Final settings (in degrees/minutes or mm):

Front (L,R)
Camber: -1.34, -1.23
Caster: 2.24, 2.05
Toe: 0.9mm, 1.0mm

Rear (L, R)
Camber: -1.17, -1.22
Toe: 1.6mm, 1.5mm

I wanted more caster but the front left upper A-arm is wound out to the end of the bolts. Without changing the bolts, more caster will introduce excessive neg camber. Right hand side had plenty of room to move - crooked geometry?

I'm running 17" wheels at 30psi, not sure whether lowering the pressure will help with stability?

Fire away brains trust!

[Modena]

30psi it a bit low eh? What tyres do you have? I run at least 36 in passenger cars.

[sambo]

I was advised to go down to mid-high 20 psi for the street based on the light weight of a Cobra. I've fitted Kumho KU31 at the front.

[gjkrv8]

Paul, I thought toe-out caused what you are experiencing. (I was told this but I know nothing about it). Great to hear you have the rear sorted.

You coming to Nationals this time?

Cheers

Gregg

[Krait]

Originally Posted by sambo

Final settings (in degrees/minutes or mm):

Front (L,R)
Camber: -1.34, -1.23
Caster: 2.24, 2.05
Toe: 0.9mm, 1.0mm

Rear (L, R)
Camber: -1.17, -1.22
Toe: 1.6mm, 1.5mm

Paul,

For what it's worth I'm running:

Front (L,R)
Camber: -2, -1.8
Toe out: 1.0mm, 1.0mm

Rear (L, R)
Camber: -1.6, -1.4
Toe In: 1mm, 2mm

Still looking for my castor numbers...filed safely somewhere I had new top arms made to increase castor and added adjustable radius rods. Made a big improvement.

Which front end do you have?

My rear is not the Nissan IRS.

[Rog246]

Sambo, were you in the car when they did the alignment ie In the drivers seat ?
Howard Revell, a former Australian speedway champ from the ACT and an ace aligner, used to ask the driver to sit in car when doing an alignment (I will stand corrected on this) on performance cars, reckoned it made a difference.
That being said WH&S would most likely screw that up today. And running such a low tyre pressure in a KU 31 wouldn't in my opinion be a good idea either. I'd muck about with the pressures as I think you might find you will get a response from the car.
hope it helps

[Treeve]

Pressures sound high, in my clubbies I run 24 (albeit a couple hundred kg lighter still).

For my clubbies I like 5 deg castor, less and it becomes twitchy around the straight-ahead. I experienced the same when I used to drive an 81 Range Rover with 2" lift - even with a solid front axle. Some castor shim plates soon fixed it.

Treeve

[muzzza]

Sambo, You need longer bolts and more castor. 4 - 6 deg castor should work fine. Having caster the same each side is as important as having it spot on.
I have played around with various settings and found that almost zero toe works best for me. Approx 50' neg camber. I measure toe with 2.0m long straight edges. Set it dead straight, then just a pinch in - perhaps 1mm over all......just to ensure no toe out. Tyre pressure 22 psi all round. I run 245 series tyres at the front. Wll try and fit narrower more compliant tyres next time around, as tracking can be an issue on some road surfaces.

The Holden subframe used in the Harrison sits a lot lower in a Cobra than it does in a Commodore, which means the lower arms are inclined too far upwards to the uprights. Roll centre is too low and bump steer is induced.

Currently working on some ideas to improve front suspension geometry and raise roll centre ( roll centre resides underground at the moment - would like it at approx 70mm above ground) Ideally lower outboard ball joints need to be dropped down another 20mm or so.

[sambo]

Thanks for all the suggestions guys. I'll try to respond in one...

Gregg - you're right, toe out encourages the car to turn more. So toe in isn't to blame here.

Krait - standard Harrison (Holden) front end with custom top A-arms. VK Commodore power rack. It's a very "quick" rack on this car. Would an underdrive pulley slow the rack down?

Rog - no I didn't sit in the car and I wouldn't have enjoyed sitting up on the hoist for 3 hrs. I'm sure it makes a difference but I'm not chasing 10ths of seconds, just after a good, stable setup.

Treeve - I might lower the tyre pressures a little to see whether it makes the steering any heavier.

Muzza - looks like I'm off to the bolt bloke on Saturday. I did ask for +6 deg caster so maybe I'll attempt that myself. I have a Longacre camber/caster gauge which I know how to use except I have trouble getting the toe right - relative to the back. Total toe amount is one thing, relative to the centre line is another (for me). Any tips?

Also Muzza, what is the effect of the roll centre being too low?

Here's a photo of the left side. The front lock nut just covers the bolt - maybe 1 thread off. I'll fix that on Saturday.

[sambo]

Forgot to mention, I've ordered poly bushes to replace the solid upper/lower bearings on my QA1 shocks. Got sick of all the crashing and bashing.

250lb springs on the rear and 400lb on the front. Does that sound about right?

[sambo]

I'm going to try making some turn plates, found a good DIY below.

Make your own turn plates for a front end alignment

Just need to find some plexiglass or lexan and a steering wheel holder.

[byroncobra]

Sambo
Warwick recommended 2 degrees castor, 2 degrees neg camber and 2mm toe in for my car.
I needed longer bolts to achieve this. I'm at caster 3 1/4 left and 2 1/2 right also neg 1 1/16 l and r camber.
The toe-in was set at 2mm and I had the same darting left and right as you.
I grabbed a spanner and tweaked the tie rods in about 1/8 of a turn increasing the toe in a bit more. It made a big difference, turning in is much better....

[sambo]

OK, is that recommendation of 2 deg caster for a power assisted rack? Non-assisted steering seems to go with 2 deg, from my research.

Is that 2mm toe in per side or total?

I guess we have a couple of options: increase rolling resistance by a) dialling in heaps of toe, b) deflating the tyres. Or use caster to help the wheel self-centre. After a bit of toe-in I think I'll go with caster.

I've located some perspex and will make up those alignment plates tomorrow.

[byroncobra]

mine's not power assisted........that's for pussies

that was total toe in, I've no idea what mine is now with 1/8 of a turn....but it feels fine

[byroncobra]

Pressures sound high, in my clubbies I run 24 (albeit a couple hundred kg lighter still).

For my clubbies I like 5 deg castor, less and it becomes twitchy around the straight-ahead. I experienced the same when I used to drive an 81 Range Rover with 2" lift - even with a solid front axle. Some castor shim plates soon fixed it.

speaking of clubbies Treeve, what are the camber, caster and toe in recommendations for the Rush?

[400TT]

[quote=sambo;1255560]I've ordered poly bushes to replace the solid upper/lower bearings on my QA1 shocks. Got sick of all the crashing and bashing.[\QUOTE]

Sambo, from our experience you just need to poly bush just one end of each shock to give you the compliance you are looking for. Just make sure your shock mounting alignment is true or you will chop out bushes, this is also the other reason we only poly bush one end, usually there is always one end with misalignment requiring a bearing.

[Krait]

Originally Posted by sambo

Krait - standard Harrison (Holden) front end with custom top A-arms. VK Commodore power rack. It's a very "quick" rack on this car. Would an underdrive pulley slow the rack down?

My rack is unpowered. Thought a rack was only slowed by a ratio change, no idea of the effect of slowing the pump down.

My modded A arms and radius rods added castor as the issue was a reluctance to self centre.

[muzzza]

Sambo, Your question re roll centre goes something like this.

I mentioned the Holden sub frame is lower in a Harrison than a standard Commodore ( measure for yourself ) ..........this is equivalent to lowering a Commodore without addressing all the other suspension parameters.
Simply talk to anyone who has significantly lowered a Commodore or Skyline without addressing the other issues.......No1 problem ....Bump Steer !!
That is why the market is full of correction kits.
Raising the front roll-centre back to its correct height will increase front roll resistance, reduce suspension compression of the outside front wheel during cornering (less roll). Weight distribution is improved and camber angles don't change as much.......result better corner grip, usually less understeer and improved cornering stability.
Raising front roll centre would also improve the roll axis to make it more compatible with rear roll centre. ( will reduce pitching )
There are a stack of other complex issues involved as well.
The Cobra being a least 10% shorter wheel base than a Commodore, means we have Ackerman issues. Reduced Ackerman is fine when rear tyres are sliding across the race track ( front wheels will remain straighter - ask the drift guys ) but at lower speeds you would get better corner turn in with a little more Ackerman ( Outboard steering arms moved in )
Best solution is always a suspension setup, designed and engineered for the car where adjustments can be readily done........just ask Craig???

[sambo]

Thanks Muzza. Can you fix mine after yours is done?

Geoff, are those adjustable radius rods available off the shelf? I'm toying with the idea of adjustable top arms from Summit. The strut would need to be modified for a different ball joint so it's not a simple bolt in replacement.

The Harrison guys getting all the good lap times up there, how many of them have made these mods I wonder?

[Treeve]

Bump steer is physically designed into the system based on the location of the suspension pivot points and the rack. Lowering a car without physically changing these does not cause bump steer.

You will suffer other effects, but the misuse of the term bump steer is my point.

Treee