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Author: Subject: Car geometry info and advice
bi22le

posted on 4/10/11 at 10:56 PM Reply With Quote
Car geometry info and advice

Hi all,

I have got some bench mark settings (caster, camber, toe) to set my Striker up to over the next month before my next track day. I will see how it feels but I may want to change it a little so the car handles how I want, currently its not how I want at all so I will check and change the lot.

I understand what caster, camber, toe is but not how it affects the handling of the car. I have done some searching but not found much so thought I will ask the people in the know. So below I have some prompts. If you have the time and knowledge please could you fill in the below. Add anything else in that you feel fit including advice on wet weather (I guess a soft set up) and dry weather (I guess a harder set up) Thanks in advance.

Caster.
Positive improves . . .
negative improves . . .

Camber.
Positive Improves . . .
Negative improves . . .

Toe.
Positive improves . . .
Negative improves . . .

Bump / rebound (I have GAZ GOLDs fitted)
adding bump / rebound at front creates . . . .
adding bump / rebound at rear creates . . .

Also I would like advice on how to analyse the wear on my current track tyres (R888). They have rubber build up in different areas and colours in different areas. I think the colour is to do with heat.

Lots of questions, so please answer where you can. Thanks again, you lot are great.

PS: I will be building my own geometry alignment kit. Any reccomendations on where to get a cheap digital angle finder and digital distance reader? Any other advice regarding this? I have a pretty good idea about this so concentrate your advice on the above.





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Autosri

posted on 4/10/11 at 11:26 PM Reply With Quote
positive caster inreases the cars want to track straight normaly but when cornering you get whats called camber gain the inside wheel becomes more positive camber and the outside wheel gains more negative camber so you gain more cornering grip but the disadvantage is it requires more steering effort on your part especialy when driving slowly with lots of steering like parking ect

positive caster is the reason you could ride your push bike no handed as the wheel wants to return to straight

you want as much positive camber as you can get really


you wont run positive camber on a race track as positive camber reduces cornering grip so you will be running negative camber front and rear

more camber on the front than the rear will give the front more grip than the rear whilst cornering so will be more prone to over steer andmore neg camber on the rear than front will be prone to understeer

the more camber you run the more grip you will get during the corner to a point obviously but the bad part to that is the more camber you run the less straight line grip you have to accelerate and brake so its a pay off if its all fast corners with low braking levels you run more camber but if you have lots of hard braking you could find the wheels lock up faster as there is less rubber on the road

more road bassed the more camber you run the more the car will follow the bumps in the road like the lorrys leave in the slow lane on the motorways

toe has a lot to do with steering response and the initial corner entery balance toe in give stability toe out gives a quick response

toe in the car will feel numb like it doesnt really want to turn where you tell it and wears tyres quickly but will feel stable at high speeds
zero toe is a good starting point the car goes where you tell it with quick response and has the least tyre wear but can start to feel unstable at high speeds like faster than 100mph for example
toe out gives lightening fast response to steering input it will eat tyres the fastest and can feel dodgy at high speeds but will have the most agressive feel of the three

you must always run toe in on the rear of a rear drive car even if just a small amount as it will get very snappy and will most likely result in you facing the wrong way or in a hedge but you can run any of the three on the front

not really played with damping much but a stiffer front than rear shound make the car under steer and vica verce

on my bmw 3 series which is mostly road use and occasional track i use

caster +5 degrees
camber front -2.5 degrees
camber rear - 1.5 degrees
toe front zero static toe which will give some dynamic toe out on cornering and braking
shallow toe in rear 0.18 degrees i think

this give a very ballanced road car lots of braking grip good cornering grip with a hint of over steer with throttle and is stable at all speeds

when i go to the track i change the front cmber to 3 degrees this gives a little more toe out as the two are linked and it gives the most corner grip withought the loss of brakes too much and an even wear across the tyre




settng up the toe is purley personal feel but you can sort of gauge camber adjustments you want to be using the full contact patch of the tyre if you go on the track take some kids chalk with you go do a couple of laps come to the pits dray some marks on the tyre starting at the tread and up the side wall go give it some stick and see where your lines are left if you have rubbed it all off the side wall you need more camber if its still on the treads you have too much you want the line to finish a little past the outside tread

hope that helps

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britishtrident

posted on 5/10/11 at 06:45 AM Reply With Quote
Although it increases self-centering Too much positive caster makes the steering heavy especially in tight corners and when braking.

Negative Camber (depending on geometry) up to 2.5 degrees generally improves front end bight in the dry giving better turn in but it over loads the inside edge of the tyre causing excess wear. Low profile tyres are less tolerant of negative camber than those with deeper sidewalls.

As a general rule toe-in on the front should be just on the toe-in side of parallel ie 0 to 0.1 degrees toe-in accross the axle . Too much toe-in makes the car very reluctant to turn-in. The built in geometry of the uprights and the fore-aft position of the steering rack should give toe-out in turns but most home builds and kits don't toe-out in turns anything like enough. Some racers resort to adding static toe-out but this makes the steering feel unpleasant and more importantly makes the car highly unstable in a straight. line.

The rule is always have toe-in on the rear --- more toe-in than the front depends a lot on type and geometry and wishbone bush type but 0.1 to 0.25 degrees is a good start.


Damper settings on a light car should be soft --- if you increase the damping too much the car will feel great but suddenly dump you into the scenery in the blink of an eye as too much damping effectively stops the wheels following the road surface. General rule of thumb would stiffen the dampers to the point where the cars feels better then turn them back a couple of positions. Changing the damper settings effects transient handling, ie if you stiffen one end it alters the turn in.

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Bluemoon

posted on 5/10/11 at 08:21 AM Reply With Quote
I have a "GemRed" Bevelbox for setting up caster and camber, cheap and cheerful but quite accurate (you do need to tap it like a barometer sometimes when it gets stuck!! but good to 0.1degrees).. about 20 quid from ebay...
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mikeb

posted on 5/10/11 at 09:20 AM Reply With Quote
Don't forget ride heights front to rear (i.e. rake angle). Front lower than the rear. Jack up the back and it may turn in better with more front end grip but you'll have more oversteer. 10 -20mm rake would be a good starter for ten then fine tune once you have finished playing with springs, arbs and camber.

In the wet a soft setup is good, try anything to get the tyre temperatures up

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