smart51
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| posted on 14/10/07 at 08:47 AM |
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too much oversteer
I want to adjust my car's handling a bit as it is too oversteery. If I turn into a corner too quickly (read carrying too much speed in) the
front end turns in very quickly, the car rolls (it takes 1/2 to 3/4 of a second) then the back end comes round. Steering into it can catch it but
I'd rather the car be a bit more neutral.
What do I adjust to improve balance?
I have slightly more front camber than rear as per manufacturers instructions and I adjusted the corner weights a bit earlier in the year which did
improve things.
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Phil.J
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| posted on 14/10/07 at 08:51 AM |
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I'd start by putting stiffer front springs on. Up the rate of the springs by, say, 50lb and see how that goes.
When starting off to balance a car you should start with springs, then anti-roll bars, and then (if appropriate) aero.
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BenB
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| posted on 14/10/07 at 09:02 AM |
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You could also put more PSI into the front tyres... (obviously depends how much you've got in them already!!)
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higgsti
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| posted on 14/10/07 at 09:04 AM |
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before you start changing springs (which can cost you a lot of moneyeven at £15 each)try changing shocker settings ,tyre pressures .has your car been
corner weighted .what size tyres are you running some use narrower tyre on front has your car got anti roll bars.what make of tyres are you using the
way your driving the car ie going into a corner to fast with certain tyres you cant expect the result to be any different
[Edited on 14/10/07 by higgsti]
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mackei23b
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| posted on 14/10/07 at 09:10 AM |
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Yip I would go for adjusting the shocks.
Stiffinging the front should tend towards understeer, stiffening the back tends towards overstear normaly.
It's a case of trial and error to get the best balance fron and rear with the maximum grip.
P.S. try calling Marc to see what damper settings he uses, may save you a lot of time.
Cheers
Ian
[Edited on 14/10/07 by mackei23b]
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smart51
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| posted on 14/10/07 at 09:13 AM |
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I have Toyo T1-S 195/50/15s all round. I'm running 17 PSI all round. I found that 16 was too low on the track and that 16.5 was fine. 17 is
just as good.
The rear suspension is fully adjustable and is set with a bit of toe out as per the build manual.
Which way should I adjust toe / camber at the front / rear to improve things?
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Volvorsport
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| posted on 14/10/07 at 09:36 AM |
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toe out ?
i can only imagine thats the problem , a rear wheel pointing outwards on entry to a corner will give the reults you have explained.
www.dbsmotorsport.co.uk
getting dirty under a bus
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progers
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| posted on 14/10/07 at 09:39 AM |
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Rear Toe
I think you have hit upon the cause. Typically RWD cars have a small amount of toe in, not toe out. Toe out will promote a more unstable feel to the
back end under cornering.
Change the rear to 2mm toe in (total) and you should notice a difference.
After that you can fine tune the balance with shock settings.
- Paul
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Mark Allanson
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| posted on 14/10/07 at 09:43 AM |
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Don't be afraid of dialing in loads of toe in, before the Locost I had many years of X19 ownership. I normal driving the 5mm-9mm toe in was fine
but driven hard, upto 13mm of toe was ideal.
If you can keep you head, whilst all others around you are losing theirs, you are not fully aware of the situation
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higgsti
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| posted on 14/10/07 at 09:50 AM |
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you might find if you smooth out your driving style (im not having a go here)ie if just before the corner your heavy braking late loading the front of
car up then turning in the back of the car is light because the weight has shifted forward under braking ,causing the rear tyres to lose grip and if
your turning front in hard you will get oversteer.there arnt many adjustments you car make to the car to solve doing the above .how old are tyres and
i take it this is on track or private road.your pressures seem ok what engine you using whats car weight .when you corner weighted the car what was
the split and was you or your weight in driving seat
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britishtrident
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| posted on 14/10/07 at 10:36 AM |
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Toe-out at the rear is a very bad thing, Toe-in is needed --- 3/16" ( roughly 5mm) across the axle should be regarded as a minimum.
You might also want to check the front for roll steer, if the outside front wheel is getting toe-in when the car rolls it will cause over steering
(slightly different from oversteer).
The delay in the car rolling raises alarm bells that
the dampers might be turned up too hard
As others have said stiffening the front roll resistance or softening the rear will reduce over steer. Do this by changing the springs or fitting a
front anti-roll bar NOT by turning the dampers up.
Check your tyre temps across the tread if the outside edges of the rear tyres are hotter than the inside you could try adding more negative camber to
the rear.
Tyre pressure have an effect but less so than they did in the days of Xply tyres.
With a BEC the weight distribution is going to have a substantial rear bias so consider fitting narrower tyres to the front.
[Edited on 14/10/07 by britishtrident]
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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russbost
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| posted on 14/10/07 at 01:46 PM |
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Sorry, but I completely disagree with the above comment on dampers, just increasing the damping on the front &/or softening the rear can have a
massive effect. You want the car to understeer slightly, switching to oversteer as you prod the throttle. Obviously it's essential that toe,
camber, caster etc is all set as per the manufacturers settings & they should have advised you, or supplied, the correct spring weights. If all
the above are correct a quick tweak of damper settings is probably all that is required.
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NOTE:This user is registered as a LocostBuilders trader and may offer commercial services to other users
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britishtrident
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| posted on 14/10/07 at 02:24 PM |
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quote:
Originally posted by russbost
Sorry, but I completely disagree with the above comment on dampers, just increasing the damping on the front &/or softening the rear can have a
massive effect. You want the car to understeer slightly, switching to oversteer as you prod the throttle. Obviously it's essential that toe,
camber, caster etc is all set as per the manufacturers settings & they should have advised you, or supplied, the correct spring weights. If all
the above are correct a quick tweak of damper settings is probably all that is required.
Dampers only affect the transient handling balance not steady state cornering.
For example if a car is reluctant to turn in but neutral once turned in the dampers would be the first port of call ----- soften the front or/and
harden the rear.
In this case we have a car that is both nervous on turn in and oversteers through the corner, that points to roll couple distribution or tyre area or
geometry (rear toe-out)
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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smart51
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| posted on 14/10/07 at 05:30 PM |
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I've adjusted the rear by turning the rearmost lower wishbone to rear upright rose joint out 1 turn for both wheels. This adds toe in and a bit
of negative camber to each wheel.
It has improved things a bit. It still turns in quickly and rolls but there is less oversteer. It is still there and can be added to with the
throttle but doing so makes the front run slightly wide too. In a steady state corner under these conditions, more steering doesn't tighten
the radius much but more throttle changes the attitude of the car in the corner pushing the rear slightly wide.
The rear looks more toe in now than it did so I don't want to add any more. Would more front tyre pressure help a bit?
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higgsti
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| posted on 14/10/07 at 05:46 PM |
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If I turn into a corner too quickly (read carrying too much speed in) the front end turns in very quickly,
he hasnt a problem turning the car in he himself says when he has gone into the corner to fast and turns in he gets oversteer.if adjusting the
dampers does nothing to the suspension settings of the car then whats the reason for them they are there to fine tune .As said rear toe needs looking
at all camber settings /castor and toe being right i would then change damper settings /tyre pressures .changing springs is a mine field and an
expensive one which should be done by someone with experience of car set up not just raising rates by 50lb at a time
http://www.rogerkrausracing.com/TechSheets/overunder.shtml
[Edited on 14/10/07 by higgsti]
[Edited on 14/10/07 by higgsti]
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britishtrident
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| posted on 14/10/07 at 05:51 PM |
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Reduce the front tyre pressure increase the rear.
On road tyres within limits increasing tyre pressure increases grip lowering it reduces it. This isn't written in tablets of stone but is the
generally accepted rule.
Reducing the front tyre pressures will make the turn in slightly less sharp (eg it introduces a "sneeze factor" .
Generally the more weight a wheel carries the higher pressure should be --- you car should be a tad tail heavy so rear pressures should be a little
higher than the fronts.
Make only a small changes start at -2psi front +2 psi rear then try with -1 psi Front and + 1 psi rear.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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smart51
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| posted on 14/10/07 at 05:53 PM |
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thanks gents
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britishtrident
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| posted on 14/10/07 at 06:07 PM |
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Changing springs isn't a minefield all it takes is a test track time and stop watch. The size of step of spring rate change depends a lot on how
stiff the chassis is and what is available, 25lb/in changes always worked for me. Changing springs is not expensive because there is a health
secondhand market for 2.25 id springs.
Smart51 comments on the amount of roll -- unusual in a Sevenish car to me this indicates the car lack roll stiffness. If the car were mine rather
than change the springs I would be tempted to make up a front anti-roll bar (nb -- not too thick) as a winter project.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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smart51
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| posted on 15/10/07 at 07:10 PM |
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Tyre pressures - wow! I left the fronts at 17 PSI and upped the rears to 19. What a difference. Its still slightly understeery on fast turn in but
not nearly so sharp. Its also very neutral in a steady state corner.
There's power oversteer, lift off oversteer and with gradually increasing speed, slight oversteery change in attitude to the corner but steering
into the corner shows that the front tyres are also slipping but not in a run-wide understeer sort of way. Thanks everyone.
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