Roger440

Said customer is now no longer sure it pulls, more that is is less stable/direct in a straight line than it was before! Now he tells me This makes more sense. The total toe has been reduced from 20' to 09'. Spec is 5-10'. However, given that virtually every Monaro i see has inner tyre wear, and are not directionally stable.,when checked everything checks out to spec. I experimented with mine at 20' which relly helped. Did another one today after fitting a full coilover kit and set it to 20' total toe. Drove superbly, really stable. The more i do of these, the more convinced i am that the factory spec is wrong. I'd still like to know the likely effect of the castor difference though.

I think i agree, never really understood X,Y and Z type stuff, well at least not when you add formulas. I just visualise mechanically, if that makes sense?

One of my suppliers used to a do lot of racing and is adamant toe out was good on the track for good turn in. I've told him i don't agree, but he won't have it! Tried to make me set up his road car like that, so i agreed and gave it a touch of toe in!!!!! He thinks it drives great As for 911's, understeer is good, oversteer is uncontrollable and contact with the tyre wall inevitable! I might not be good at maths, but i do know hanging all the weight out behind the rear axle doesn't make good engineering sense. Porsche built some cars with 50/50 weight distribution (944, 928 etc) but the customers wanted the engine at the back!!

Because the rack is behind the axle line and is undamged?

What size wheels and tyres does this run?

Hi Ian, That wouldn't be the autobahnstormers by any chance? Tony, Do you not think the difference in castor left to right could be an influencing factor? A good 3/4 degree there. The front suspension is not torsion bar, just regular Macpherson strut, hence unlikely to be hight related, but worth checking anyway. Given the difference in camber at the back, there will be a greater rolling resistance on one side, but i can't imagine that this would give rise to any problem? The car DID drive OK prior to its alignment check. Thats not to say it was right though!!!!

Sadly not, thats all ive got. I did work on it recently though (not suspension!) and it wasn't visibly leaning at all.

I'll have a think about that. Never got involved in a mid engined car before. Driven a couple, both lotus elise early and late. Early one was a disater, it was always turning round!! Im guessing things will be a bit different. Ok so it says MR2 in the thread title. Sorry!

One of my customers has recently taken his car back to the main dealer as a result of uneven tyre wear at the rear. They have twiddled a bit and now the cars pulls to the left. He has sent me the results before and after. The rear camber on the left is well out by nearly a degree, should be 1-1.5 degress, but i don't think that is where his problem lies (though something is clearly not right). They seem to have corected the small toe out at the rear so have probably stopped the wear issue. More interesting is the difference in castor. Given the spec is 7.5 degrees, i amazed that they are as high as they are, but more important uneven. They have also dabbled with the front camber, which is factory adjustable on Vauxhall Monaros. Any views? Am i missing something? Sorry if its hard to read, struggling to manipulate my IT"! Rear Axle Initial Final Camber Left -0o18' -0o20' Right -1o19' -1o21' Individual Toe +0o10' +0o04' -0o05' +0o05' Total Toe +0o06' +0o09' Setback +0o10' +0o04' Geometrical Driving Axis -0o07' +0o01' Front Axle Castor 20o +9o22' +9o19' +8o44' +8o51' KPI 20o +5o28' +5o45' +6o08 +5o16' Toe Out on Turns -1o58' -2o17' -1o46' -2o09' Camber -0o50' -0o21' -0o28' -0o28' Individual Toe +0o10' +0o05' +0o10' +0o05' Total Toe +0o20' +0o09' Setback -0o15' Included Angel 20o +4o41' +5o24' +5o38' +4o47' Max Steer to Left +39o48' +39o24' +31o53' +31o32' Max Steer to Right +32o17' +31o19' +41o21' +40o40'

Roger440: How would you address this set-up if requested? Errr, what is a SW20? Im guessing at something Jap given the nature of most of the forum members? I'm big into american and aussie cars (nothing like a challenge!) so excuse my ignorance. Could you expand on what a winding response is?

All the theroy with X and Y vectors etc is a bit heavy when you no good at maths. Maths is fairly important in engineering, and its my weak area! As a result i struggle to keep up sometimes.

Eh? What does that mean?

As a late comer i didn't see this thread earlier. In my experience bigger/stiffer anti roll bars on a road car rarely improve things. Roads are generally anything but flat. If you want a car that you can make progress in on the average british B road, you need some suspension compliance. Bigger anti roll bars are not going to help this. When setting up 944's in particular, i always try to establish what the owner is going to do with the car. Many are now used as occasional track day cars, and a lot have been set up with big anti roll bars etc focused primarily at track work. Try driving one of these at speed along my journey home and you will end up in a ditch! And thats actually an A road - allegedly! Track car, yes definietly a good idea. On a road car, not so sure. As far as bracing is concerned, i'm open to suggestions. A flexible bodyshell can't be a good thing i don't think? Had an interesting conversation with an engineer at the old TWR set up who were asked to sort out a certain sweedish convertible. In order to resolve some issues, eventually the anti roll bar was binned, and the spring rates upped instead. Result was, i am told, superb, but sadly for marketing reasons it went into production with one albeit a small one. Okay a convertible, but relevant i think. Post is a bit unstructured, but hopefully it makes sense?

And i think i should have paid more attention in maths class!

How do you know the front wheel moves? Does it do it stationary?

Axle tramp, wheel hop, call it what you will, is ultimately caused by the location of the axle/hub being insufficent to keep the wheel under control whilst undergoing the forces you are transmitting through it. When you completely break traction the forces put into the suspension are not that great, as it starts to try and grip, you put a sudden shock into the driveline. That shock (force) has to go somewhere, and the thuding noise you can here is some part of the suspension (poss engine trans mounts) reaching their limit of travel. You will need either stiffer springs, dampers and or suspension bushes to eliminate it. Sadly your ride quality will go downhill quickly, hence the reason it is as the manufacturers set it. If your prepared to make the necessary compromises it, it can certainly be dialed out. An LSD might be a better idea. Much less likely to induce wheelspin in the first place.

Any progress on the photo thingy?

Defo not there!! I know where it should be, same place as some other forums i use, but not there on this one!

Im assuming you mean when i have clicked on add reply and i am in the reply section. Sadly i can't see a browse button. I was expecting to see one but i can't find it? Can add links etc, but not a picture. Help!!

Ok, i have some piccys of our camber/castor gauge. Sadly, i can't work out how to post em! They are not on a site anywhere, just on my machine.

Yes, i will take some piccys. No, at no stage do i need to input a wheel diameter.

Yes indeed. By true, i mean the angle you would obtain by placing an angle finder against the front strut/imaginary line if no strut fitted. By effective, i mean the effective angle that actually influences the characteristics of the car. Let me explain what i mean. In answer to my original post, it seems that changing the wheel size could influence the castor angle. This i didn't quite understand. To my mind if the car were placed on 4 stands connected to the hubs, and the angle of the strut measured the angle will be what it is. Nothing will change it other than adjusting the suspension components themselves. So, therefore, if changing wheel size can have an influence i can only conclude that we are talking about an effective angle. Hence my query of actual and effective. Make sense? Probably got the wrong end of this, but i hope you can bear with me.

Hmmm, i was getting carried away there. Lets forget about the actual effect, trail etc for now. Confusing enough as it is Back to the last bit of my previous post, are we measuring the true angle or an effective angle? I "think" the answer to this will steer my thoughts in the right direction.

If i read that correctly then, the castor angle as set by the design of the suspension is a figure, lets say it is 4 degrees. This will give an intersect point with the ground a certain distance ahead of the tyre contact point with a given TYRE size. If the TYRE were bigger then the "effective" castor angle would be greater, giving the same effect as a greater castor angle, ie more than 4 degrees. Assuming the above is correct, when we measure the castor angle on a car, are we measuring the true angle or an effective angle?

I dont disagree, because i don't follow it Let me theorise if i may? In order to calculate the castor angle, we use the usual technique of 20 degree swing etc. As i understand it we are effectively measuring an angle at 2 different points, each end of the swing, and as a result calculating what the castor angle actually is from these results. The figures obtained at each end of the swing would indeed be different for different size wheels and offsets, but surely however, the calculated figure would be the same? The castor angle imaginary or otherwise remains the same. I do follow that if the TYRE is a different diameter than the point at which the caster angle line, (if i can call it that) intersects with the ground will be different. Indeed, the bigger the wheel the further forward that imaginary intersect will be. But the actual angle is still what it is surely?