scutter
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| posted on 28/7/09 at 09:07 PM |
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Roll oversteer
I know I'm opening a huge can of worms here
But, having done my second trackday last friday, I was suffering an almost pendulum like state of oversteer, I'l try to describe it below.
1st stage of the corner, after coming off the brakes i turned the car in, all happy.
2nd stage, the car once almost settled in it's new attitude, very gently started to move toward oversteer, yes I did spin it (it was funny, the
moment of shear panic, then realising there's nothing to hit). This happened with what i believe was no further inputs to either steering brake
or throttle.
Was this roll oversteer as there were no further inputs to upset the car?
I'm the first to admit, as i did on the day, that my talent pool runs shallow most of the time, hence the track work, So did I cause it to
happen.
If not my fault what can be adjusted to prevent it happening. I'm saving for the funds to fit R888's in the future.
ATB Dan.
Thought I'd better put some car details in;
Locost book chassis
Cortina rear axle with matching width front suspension.
300lbs front and 190lbs rear springs
rear ride height 10mm lower than the front(can't remeber the exact measurements)
[Edited on 28/7/09 by scutter]
The less I worked, the more i liked it.
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Marcus
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| posted on 28/7/09 at 09:14 PM |
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Hi Dan, sounds like you may have run out of suspension travel on the outside of the car. Try it again to repeat the experience, then raise the ride
height by 10mm all round and try again. You may need an ARB on the front or stiffer springs.
Marcus
Because kits are for girls!!
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Volvorsport
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| posted on 28/7/09 at 09:32 PM |
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locost book cars should be about 120-150 lbs in .
even my heavy volvo axle type is only 175 lb/in . and i know that is too stiff .
when i first drove the car , the suspension had no markings on the springs , and i ended up with them wrong way round , oversteer at 120 mph at a
marham track day .
i did change them round and it was brill , but it bottomed out with 2 people in , so i went to heavier springs , and i do get what you are feeling ,
which is just oversteer .
basically youve gone past the transient stage , the springs and dampers are settled , and since you have a stiffer back end , more weight will get
transferred through it .
try some 150 lb/in to start with it .
check also that you arent bottoming out as above , but im sure it wouldnt be progressive as you say it is , pull your bump stops down to see if they
go all the way up .
www.dbsmotorsport.co.uk
getting dirty under a bus
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craig1410
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| posted on 28/7/09 at 11:19 PM |
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Hi,
Are your trailing arms set to run downhill from axle to chassis when the car is at normal ride height?
The above is important to ensure that the loaded side of the axle moves forward in roll which gives the effect of toe-in and reduces oversteer. If the
arms slope down from chassis to axle then the opposite happens and you get oversteer in roll.
I'd be surprised if this is your problem but it can happen if you make your trailing arms mounts on the chassis too high. The ones on the axle
tend to take care of themselves.
The other thing which sprang to my mind was tyre pressures and if it hadn't been a live axle I might have suggested a little bit of negative
camber on the back wheels.
I hope you get it sorted.
Craig.
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procomp
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| posted on 29/7/09 at 07:06 AM |
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Hi
As already mentioned check there is enough travel on the dampers in bump and you may as well check droop also whilst checking.
The angle of the arms dose have an effect but it's so small it would not be the cause in this situation.
However ride height and springs can be a big influence the usual comments banded around are run the rear 10-20mm higher than the front. In truth this
is not applicable to all cars. Assuming the dampers Do have enough travel in bump the next step would be to drop the rear ride height by say 10mm and
try. If the rear springs are any higher than the 150Lb mentioned above then thats also causing a problem. so reduce to 150Lb max and min of 140 if
using the car with two people and 110Lb if using driver only. Next on the list after finding no improvment with any of the above is to think about a
front antirollbar.
Now the big question. Is the rear setup using the plastic bushes as supplied by most of the kit manufacturers at the moment. If so these are just not
realy suitable for live axle applications. They simply do not have the compliance required to allow roll articulation of the axle. True polly bushes
are whats required for the aplication to gain the best in control and articulation.
And last but not least the dampers. Highly unlikely you have had the dampers dynoed i would imagine. But in general 99% of dampers supplied for
kitcars are valved wrong. So theres always room for improvment there.
Cheers Matt
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procomp
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| posted on 29/7/09 at 08:23 AM |
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Hi
AHH just spotted in your first post 190Lb rear springs. Get Them changed for 150 or 140Lb.
Cheers Matt
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scutter
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| posted on 29/7/09 at 02:54 PM |
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Cheers to everyone, Looks like the first order is softer springs.
The car is fully rose jointed at the rear, i'm slowly working through replacing the budget ones with better quality.
Matt once my new atlas is fitted, I may bring the car up and get you to look at the chassis settings and dampers.
ATB Dan.
The less I worked, the more i liked it.
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