How much castor?

[greenamex2]

Oh yeah, and for any smart arses you try checking the formula against their actual car, the figures will NOT be exactly the same.

The formula doesn't allow for the front of the car 'tilting' as the wheel on the rise and fall due to the castor. It also doesn't allow for the wonders of the pneumatic tyre.

[dtype38]

Originally Posted by Denis Bassom

The formula doesn't allow for the front of the car 'tilting' as the wheel on the rise and fall due to the castor. It also doesn't allow for the wonders of the pneumatic tyre.

Not to mention the fact that Al says he arrives at hairpins on opposite lock

Seriously though This is the interesting bit....

Originally Posted by Denis Bassom

The main thing you notice, as well as more castor give a 'steeper' rise in gained camber, is at a certain point your start LOSING camber. The point this happens at is again dictated by the castor, the more castor the greater wheel angle it occurs at.

On really, really tight hairpins (Mallory, Croft Complex) I find that I'm struggling with front end grip on initial turn-in. Are you suggesting that less castor might help this situation? Or is this just a trade off I have to accept for having really good stability in medium and fast corners?

[greenamex2]

Depends whether your turn in problem is caused but too much or too little camber.

Does the car fail to grip initially and then get better, or just understeer throughout the corner?

[johnny yuma]

Denis are you sure a point is reached where camber improvement starts to revert back? I'm sitting here simulating with a biro and a CD and obviously thats dodgy but ...think what you see watching say a modern Mercedes parking.On full lock they seem to generate an enormous amount of neg camber on what would be the outside wheel on a turn.

[greenamex2]

johnny, modern cars have MASSIVE amounts of castor and the KPI is kept to a minimum. They can cope with this because they have power steering.

Feed a KPI of 6 degrees and a castor of 8-10 degrees into the equation and yes, camber keeps increasing until you hit the highly unlikely wheel angle of 90 degrees.

[johnny yuma]

DENIS--Once you get into it the permutations seem endless.When you move boltholes and mounting points etc the factory geometry starts to go out the window and you'll be scrubbing tyres,bump steering etc unless you're on top of it.You can even tweak the Ackerman angle to promote stability on high speed corners you may have compromised by extra neg camber/pos caster to help you on tight turns.As a racing rule I would always sacrifice the correct line on tight corners if it meant compromising the line on an previous high speed corner,similarly stability on high speed corners maybe should take priority.I dont think you will match the FWD cars by adding excessive pos caster for tight corners--there are other options.

[greenamex2]

What I seem to spend my time doing is, apart from camber, trying to get the suspension back to standard after lowering the car about 3 inches!

Unfortunately there is a limit as to what I can move around in our regulations. Basically pickup points are standard, you can just adjust things.

I'm open to suggestions on other ideas but it seems to make sense to chase camber improvements on a car that has proved hyper sensitive to camber settings.

This is also particularly important as on fresh tyres my car handles fantastically but after a couple of meetings the fronts start to drop off and the car understeers. We are going to start rotating the tyres every meeting to even things out. All the evidence on the tyres points to it being an excessive static camber problem leading to localised tyre overheating under certain corneringconditions.

I also have the problem of way too much static negative camber for the front to work properly in the wet.

[graham bahr]

Originally Posted by Denis Bassom

What I seem to spend my time doing is, apart from camber, trying to get the suspension back to standard after lowering the car about 3 inches!


I also have the problem of way too much static negative camber for the front to work properly in the wet.

the first bit sounds about right, maybe one answer is not to run such a low ride height, that will all have the effect of making your roll bars a bit stiffer and probably lessen the amount of camber you need, a half inch raise might be all it needs.

as already disgussed i would dial out a little camber and put some more caster in, i know you found it difficult to believe but my car is quite steerable without power steering and 10 degrees, although its good for developing muscles when pushing/steering round the paddock,

but if it works on circuit....

[dtype38]

Originally Posted by Denis Bassom

Depends whether your turn in problem is caused but too much or too little camber.

Does the car fail to grip initially and then get better, or just understeer throughout the corner?

In theory my car should understeer on power (the diff fully locks on power) so I've tried to make it "pointy" to compensate. I's now neutral mid corner and is a joy on full power exit. I would have thought this would make turn-in great, but I have two probelms. First, at a hairpin, I can't get the front end to come across at all until I get off the brakes and get the car settled. As soon as it's moving I can add power and all gets back to normal. The second is that in the very high speed entry at the first corner at Snett, I get initial turn-in, but then the front end tends to wash wide and its all a bit of a balancing act until a bit of speed scrubs off. Although that might be just a property of that particular corner.

Any ideas?

[greenamex2]

Unfortunately raising the car isn't an option, Corolla's REALLY don't like running too high as they are too long/thin/tall to start with and have a lot of very thick glass up top pulling it over. The engine is also fairly idiotically placed being quite high up and forward.

If I knew then what I know now.....

I think a bit filing and wider wheel arches are in order over the winter.

[greenamex2]

dtype38, IF it is geometry related then it could be negative camber/castor related. Have you tried increasing the negative camber and seeing what happens on that type of corner? If more negative helps on that but not on fast corners then more castor could be the way to go. If the opposite then do the opposite!

Could just be that the front is too stiff for hairpins. For instance my car will not do hairpins with any form of uprated front anti roll bar. Uprating the springs has a similar but reduced effect, increasing the bump damping even less.

[graham bahr]

d type, i would guess that your hugely heavy jag engine at the front, probably has a lot to do with the car being reluctant to turn in, which is probably why it doesn't like turning in on the brakes, which theretically will put more weight on the front wheels and therefore give more grip, so i guess there already is too much weight on the nose, or the front springs are too stiff

it would be a fair bit of work but could you move the engine back a bit? you have such a heavy engine and box i would expect just an inch or so rearwards would make quite a difference, and if you could manage a couple of inches well...
from memory did jaguar not cast some Alloy blocks for racing? ok you'll never get one, but it would of been a lot of work for them had they not felt the need to get the front end weight down.

failing that as dennis said try some softer springs

[Cameron Winton]

Everyone seems to be playing around with front geometry trying to get the best slow corner/fast corner wet/dry characteristics. Anyone though about looking at the other end of the car? Dtype38 mentioned the characteristics of his diff. A possibility that may be causing Denis's tyre problems is that his diff is too tight, pushing the car on turn in and he has ended up trying to compensate with Geometry at the front. This may work well on dry fast corners but on slower corners, the CF of the car on turn in will be lower, causing less roll and hence the camber change from static will be less.
You might want to think about rear ride height as well as that will have an effect on weight distribution on turn in.
I know someone who runs a Westfield in speed events and he changes camber & ride height both front & rear when the weather changes. I run a 205 & one recommendation was to disconnect the front a/roll bar in the wet. I don't know if you run an a/roll bar at the back of the Toyota or whether you can adjust it or not but that might be worth a try.
This is a great thread! Maybe the answer is lots of testing and develop 4 different set ups across the different combinations of slow & fast tracks & wet & dry weather. Whoops - that sounds like money & time - not much of that about these days.

[dtype38]

OK, some good info and some good questions. To answer some of the latter...

Denis, yes my car is very stiff. I started by upping the springs to get contol of the dive but then had to throw the ARB away to get any turn in. I then had to stiffen it a bit more, partly because I lowered it by 2" and I need it that stiff to keep the body away from the tyres without an ARB... and partly because I kinda really want a big kart

That's an excellent tip about trying camber though. I've added a bit more (negative) recently to even out tyre wear at the front, but it could do with a little more.... just need to machine away some of my upper wishbone pivot mounts to get it

Graham, I moved the engine back 2" at the last rebuild (limit of the chassis). And yes it was a LOT of work I also moved my petrol tank back and put in an aly rad, and moved my battery and extinguisher to the middle and....... well, everything I could think of! Not got an accurate measurement but I think my weight distribution is now about 54/46 F/R (I stuck each end on the weighbridge at a meeting). Dont' think I'm gonna get it any better without an aly block. Later Jag engines have aly blocks but I haven't heard of one for the original XK engine I've got. Trouble is, the later ones have the head on the other way round, so the exhaust would have to go through my legs

Cameron, excellent point about the back end. My only difficulty playing with that is its a Jaguar Independant rear end with the diff bolted straight to the chassis. Camber adjustment is by re-shimming the drive shafts Maybe I'll change it one day

[graham bahr]

in my experience a tight diff does make make for a bit of inital understeer but that quickly changes to oversteer, and if it doesn't all on its own, with a bit of right foot it soon will

[graham bahr]

Originally Posted by dtype38

Dont' think I'm gonna get it any better without an aly block.

silly suggestion time,

if you cant move the engine further back,
move the front suspension forward 2 inches!!

or fill the boot with heat wrap!

[Al Weyman]

Well from my recent experiences I would say there is definitely some merit in the raising of the rear suspension and as Cameron suggests looking at the rear end of the car.

When I parked my car up and started racing a Mk 3 Camaro what 12 years ago, the last time I used this 2nd gen car I had increased the negetive camber on the front and the car was brilliant, bit twitchy and nervous but very controllable oversteer with a bit of power. Then.... I rebuilt it for CTCRC and had to add what 80 or 90 pounds to the front end, remove 16 inch rims and fit little 15 x 8's with skinny Dunlops and worst of all raise the suspension on the front by 1.5 inches. I also raised the rear but not enough on first attempt. The net result was I turned the car into a tyre destroying understeering pig.

To attempt to recify things I have raised the rear suspension .75" shed 40 pounds off the front end (courtesy of a regulation clarification, thanks Stacy) set the toe to netural and intend to fit a thicker rear anti roll bar. Well I never really got the chance to open it out at Silverstone as the clutch went the moment I pulled out the assembly area but the car definitely felt more stable.

In eccence I too have a nose heavy understeering car and know I can do no more on the front end (I already have a lot of negetive 1.25 antiroll bar right springs etc) so as a compromise I am trying to get the rear to come unstuck to balance everything out.

Now I reckon with Dtypes more effiecient all independant rear end (mine is cart springs) I recon he may have more of a problem but I agree with Camaron that he may well be advised to look at a way of making the rear end a bit more loose.

[johnny yuma]

A heavier front sway bar usually INCREASES understeer,fitting or increasing the diameter of a rear bar will promote oversteer ie reduce understeer by lessening weight transfer to the front outside wheel at turn in especially under brakes. When you hit the power you may then get too much oversteer or traction problems [RWD] if your limited slip diff is tired as the rear bar tries to pick up the inside back wheel.
In my experience 1 degree of static neg camber and as little as 2 degrees of positive caster makes a sweet driveable RWD club car with no scrubbing or bump steer but thats another story.

[greenamex2]

1 degree of static neg camber

Is this at the front or the back?

2 degrees of positive caster

On what type of car (saloon, single seater, heavy/light)?

[johnny yuma]

sedan 1000kg 3 litre live rear axle leaf springs Australian historic hybrid 1951 Holden model, coil and wishbone kingpin front end limited caster & camber available,think torana XU1 .

[greenamex2]

And I thought I had problems!

Certainly my car would understeer badly with those settings and the trend for even modern road cars is a lot more castor than that, and perhaps a tad less camber.

Out of interest I found an article somewhere that reckoned that the current trend for high castor was due to most cars now having rack and pinion steering and, often, power steering and cope with it.

[tzei]

McPherson struts in front of my and my friends bimmers are 8-14 deg castor and 1-3 deg camber (930 - 1150 kgs) roughly. Rearend camb. in same range. Many uses electric power steering system.

[johnh875]

Originally Posted by johnny yuma

sedan 1000kg 3 litre live rear axle leaf springs Australian historic hybrid 1951 Holden model, coil and wishbone kingpin front end limited caster & camber available,think torana XU1 .

For the benefit of those outside Australia, the year should be 1971 not 1951

[dtype38]

Originally Posted by graham bahr

if you cant move the engine further back,
move the front suspension forward 2 inches!!

Nah, that would just make it go round corners like an E-type (ie badly). My short wheelbase is one of my best advantages against the big boys on a tight track

Originally Posted by graham bahr

or fill the boot with heat wrap!

Anyway, I put the petrol tank in the boot and now there's only space for a ham sandwitch and a car mag in case I break down half way along the Revitt Straight

More seriously, I've moved anything with any weight as close to the middle of the car as possible with the exception of the tank. With that I decided to sacrifice a bit of total rotational inertia in favour of balance. I find that with about 4gal of 4star hung out behind my back wheels I get just about perfect four wheel drifts

As for the back end, I've seen some easily adjustable camber/castor/toe systems on some cars so I might give that a try and have a play at that end (if it doesn't add weight).

Straw pole... what sort of toe in/out values do you all use at the front and rear? To keep it simple can you use degrees rather than inches then I don't have to ask how big your wheels are

I use 1/4 deg total toe out at the front and about the same toe in at the back.

[Tim Falce]

Originally Posted by dtype38

Straw pole... what sort of toe in/out values do you all use at the front and rear? To keep it simple can you use degrees rather than inches then I don't have to ask how big your wheels are

I use 1/4 deg total toe out at the front and about the same toe in at the back.

I have about 10 minutes of toe out on the front, and a bit of toe in on the rear. I know what the rear is in inches but not degrees so I wont bother being too accurate on here.