caster and its effects on the car

[big andy]

can somebody please explain in plain english what affect caster as on the way a saloon car handles .

[GORDON STREETER]

http://en.wikipedia.org/wiki/Caster_angle
Best to have a read first, its down to the individual driver as to how much you can cope with.
IMHO at first it's best to put a fair bit of positive on for a start (heavy steering) so that the car dosen't dive about in a straight line and slowly take it off untill it starts to get "nervous" and find a compromise, it's all about "self steering" like a shopping trolly or a sofa caster !

[tristancliffe]

Also consider that castor is "dynamic camber". At high speed, the wheels aren't steered very much, so the influence is low, but at low speeds (hairpins), lots of steering angle is used, and the castor will influence the actual camber at the wheel (in conjunction with static camber, body roll and the camber recovery rate).
Plus, the castor tends to jack up the inside wheel, so more castor will tend to decrease the overall weight transfer on the front axle and correspondingly increase it at the rear, which case also be used to adjust handling at higher steering angles.

Finally, the most important thing for most people, is to make sure both front wheels have the same castor angle. Feels a hell of a lot nicer than if they're different.

[GORDON STREETER]

Andy to see a simple demonstration of what caster actually does on a car look at a chopper motor bike with loads of rake on the front forks.
Ultimately if you could imagine the forks parallel with the road it wouldn't change direction at all as the wheel would only tip over when you turned the handlebars.
More positive caster normally gives more negative camber on the outside wheel of a corner as it turns.

[big andy]

Thanks for replys lads . I have a m3 evo and now have the means to adjust the caster . The car handles very well but would like a little more instant turn in as it seems slow to do this . It's not understeer just a little slow to actually change direction especially on slow corners ? . Am I right thinking I can adjust the caster to improve this .... Thoughts please !

[GORDON STREETER]

More neg caster will make it "sharper" but is a trade off in control on fast corners.
Depending on what it is going to be used for you can alter caster and camber for different tracks depending on whether the track has more slow or fast corners.
Dont forget that every change on caster will alter the steering track.

[MGDavid]

A tad more toe-out on the front usually sharpens up initial turn-in.

[Peter Mallett]

But then creates more understeer as you go through the corner.

[Casper]

Keep in mind also that the more caster the greater the height change at the road wheel when lock is applied. If instead you increase the scrub radius you will get the height change as well without the unwanted effects of steered camber gain. Increasing the scrub radius will on the other hand reduce the effective chassis stiffness as well but I imagine on a lot of cars that you can't move it that far to be noticed.

If the car was running a locker I imagine it would be beneficial to want height change to unload inner rear much as a kart does. When it is all said and done if given the choice I would move the scrub radius as it tends to do the same job without the side effects of nervousness and camber change. The problem with cars and I imagine why it is not used as often as it could be is that the SR is largely controlled by wheel offset and that makes it expensive to change unless you use spacers. I would use spacers as a try and learn just to see what happens if it were me. You also do not need to alter the tracking which is a big plus.

[Notso Swift]

The unwanted effects of steered camber gain?
Quite the opposite, I think it is beneficial in most circumstances and the lowering of the outside ride height isn't a bad thing either for cars

Most saloons simply don't have enough castor, I usually run around 7, (FWD with a locked diff) and and large powerful V8 supercars are the same, Most manufactures only give you about 3deg at most. Being an M3 Evo (assume that is the E30 one) means he may have a lot more because it was built as a real race car not a tarted up road car like the last 20 years.
Check where they raced, probably give you a good feeling
(oh and I am assuming you have power steering, otherwise you may want to stop at about 5deg)

[Casper]

Why would you want to sacrifice tyre on the road just when you need it?

[GORDON STREETER]

Most saloon cars used in anger on the track dont have enough room between the tyre and inner wing to play about with increased scrub radius unless major surgery is done.
Depending on what you are allowed in a controlled series plays a big part in this.

[SidewaysFeltham]

Personally, I would always consider Steering and Suspension Geometry as an holistic process: tweaking one bit without carefully considering its affects on the other bits can lead to all sorts of problems.

I well remember (As I know Gordon will too!) the vogue for applying massive Negative Camber on saloons, particularly 105Es and Escorts and even Minis! Didn't actually achieve too much, other than scrub out the inner part of the tyre tread.

From experiment (As we used to build competitive rally, and race Minis), I discovered the factory standard rear location plates for the Mini swinging arms could vary by as much as + or- 5 Deg: as did the factory body shells.

Similar with the front forged radius arms. The trick was to achieve BALANCE: same in my book with everything to do with building competitive race cars: replication, or if you like, blueprinting.

Same as over-wide wheels: neatly forgetting by extending a wheel outwards, rather than equally between the hub, such changed totally (and potentially dangerously!) the steering angles.....

May have looked good for the Boy Racers, but added in various nasty components.

Often forgotten is ride height: dropping spring heights changes the relationship between the steering arms and the rods.

Always commence with the basics: ensure the weight distribution is as equal as possible between pairs of wheels. With adjustable springs this is reasonably easy, more so today with digital scales using strain gauge technology.

Aldon Racing years ago developed a neat hydraulic Spring Height setting tool, which used an hydraulic pressure gauge to balance out distributed weight loading on single seaters.

Hello, Gordon: hope I find you well?

How's Espana: in Torrox and Sayalonga in mid-October and now, just returned from la belle France for a spell.

Vaya con Dios !

[GORDON STREETER]

Also some people don't realise that altering the rear ride hight also alters the caster angle !
Hi mate, not in Spain at the moment, another 3 weeks yet.

[zefarelly]

On the Crustina, just lowering the ride height gives me 1 1/12 - 2 degrees neg camber and the rest is standard, I don't think crossplies want any more. the cambers controlled by the anti roll bar . . . so variable at best!

[GORDON STREETER]

Originally Posted by zefarelly

the cambers controlled by the anti roll bar . . . so variable at best!

Funny that ! a lot of the "FIA Tina's" seem to have a longer wheelbase

[morninggents]

Concertina camber is limited by the track control arm - so no adjustment available there, then!

[GORDON STREETER]

Originally Posted by morninggents

Concertina camber is limited by the track control arm - so no adjustment available there, then!

You ought to go on the stage Pete

[Notso Swift]

Originally Posted by Casper

Why would you want to sacrifice tyre on the road just when you need it?

You mean when you turn and the weight transfers to that wheel? An d the body roll is reducing the camber on the outside wheel as it is, so you want to increase to compensate.

Of course, with handling, balance is king

[Paceracing]

Originally Posted by tristancliffe

Also consider that castor is "dynamic camber". At high speed, the wheels aren't steered very much, so the influence is low, but at low speeds (hairpins), lots of steering angle is used, and the castor will influence the actual camber at the wheel (in conjunction with static camber, body roll and the camber recovery rate).
Plus, the castor tends to jack up the inside wheel, so more castor will tend to decrease the overall weight transfer on the front axle and correspondingly increase it at the rear, which case also be used to adjust handling at higher steering angles.

Finally, the most important thing for most people, is to make sure both front wheels have the same castor angle. Feels a hell of a lot nicer than if they're different.

Totally agree. In very simple terms:
- More castor will add camber when you want it, (i.e when cornering).
- It also means you can run less static camber which in turn means the tyre contact patch with the tarmac is optimised for braking and accelerating in a straight line.
- It helps straight line stability
- It helps self centre the steering when comming out of a corner.
- Too much castor will give the unwanted 'jacking' issues that can adversely affect handling, (I once drove a SEAT Altea rental car which had this - it was awful).

[big andy]

thanks for the advice. heres a video of car in action

http://www.youtube.com/watch?v=3x-KemXTLPk

will more caster help turn in ? or am i better playing with anti rollbars ,tyre pressures etc . its all abit confusing

[SidewaysFeltham]

Originally Posted by big andy

thanks for the advice. heres a video of car in action

http://www.youtube.com/watch?v=3x-KemXTLPk

will more caster help turn in ? or am i better playing with anti rollbars ,tyre pressures etc . its all abit confusing

What you seem to be looking for, Andy, is a change of handling in terms of less Understeer.

Which presumes your car at present is Understeering on the entry to a corner, rather than Oversteering: which is what you seem to require?

Unless I am wrong (often these days as I am well out of touch! Poor old sod! ) the M3 Evolution is a Front Engined Wheel Wheel Drive car.

Now on power, then the rear wheels will tend to make the car Oversteer: however, on a trailing throttle, then the weight bias will probably induce understeer.

Heavy braking on the entrance to a corner will cause massive weight transfer to the front wheels: acceleration will correct this.

Yes, tyre pressures will allow some balancing between OS and US.

As will spring rates, damper adjustments and, as you suggest, roll bar torsion.

When next practising, try opening the loud pedal earlier, into the corner.

If you spin out then don't blame moi!

[wdave0]

Originally Posted by big andy

thanks for the advice. heres a video of car in action

http://www.youtube.com/watch?v=3x-KemXTLPk

will more caster help turn in ? or am i better playing with anti rollbars ,tyre pressures etc . its all abit confusing

If turn-in is really the issue then less toe-in at front and rear will help, hold the brakes a little longer to keep front tires well loaded, move the brake bias a little rearward (gently - sudden course reversals can result), turn-in is a dynamic situation.
Caster will more affect relative behavior in slow and fast corners giving more negative camber and thus more front grip in slow corners and less in fast cornrs - my setup preference was always no high speed oversteer but some low speed oversteer. Also good steering "feel".
Rollbars and tire pressures are more steady state or overall changes - always over or understeer

[davyboy]

This is a good vid that provides an introductory explanation on all of this stuff.

[Trikes]

Hmmm My Proton Satria GTi FWD Hill Climber suffers from losing the rear in high speed and low speed corners. I was thinking about increasing the rear Toe-In but now I'm not sure after browsing the info above. When I say high speed it's doing 130+ at turn in point then the Track has a sharp right right then left left. It's a 'by crikey' set of turns. Then two Tracks later I'm at 31 Bends Lake Barrington. That's 31 bends in 1.89k's and it was wet! Was I busy? You betcha. Anyway it was loosing the back going in on nearly all the corners. I was hard on throttle lift turn in big push on the throttle to straighten the car. This procedure for 29 bends. The other two corners were down to 15k's, heavy on the brakes and work the throttle thru the turn. Most of the runs were done in 2nd gear with the other two mostly done in 3rd with only 2 changes back to 2nd. Interestingly the 3rd gear runs were worse and I nearly left the Track backwards but being FWD I was able to drag my ass back on line. So I'm also thinking of adding a Wing as I have a Factory R3 Splitter with stiffening mods and it can make the steering quite heavy out on the Highway at 110kmh. The Satria GTi has sort of Wing std and I added a Wicker. This helped balance a little but not enough. So am looking for a mechanical improvement and an aero one. What are your thoughts guy's?