rodgling
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| posted on 25/9/12 at 10:10 AM |
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springs too soft?
Having a look at some of the photos from a sprint on Saturday, there is a lot of roll at the front - it looks like the outside front may be leaning
past vertical, though it's hard to tell for sure.
Should I be thinking about stiffer springs on the front?
I've also noticed that it very very rarely understeers - feeding in power gently mid corner usually goes straight to oversteer, another hint
that stiffer springs on the front would be warranted?
Another alternative, would installing an ARB be a better bet? More expensive and more hassle so it's not obvious that this is a better
option.
[Edited on 25/9/12 by rodgling]
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craig1410
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| posted on 25/9/12 at 10:37 AM |
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Disclaimer - I'm no expert on this, just a keen amateur who has a read a few good books... 
I think the tyre rolling under at the bottom is what is giving the impression of positive camber.
In general, I understand that you want the weakest springs possible which get the job done (whatever that means to you). So, if body roll is your
concern then I'd say a front ARB is the way to go. It also depends how bumpy your typical track is because if you go too hard on the springs
then you might find it gets "interesting" on the bumps.
Another approach might be to soften up the rear. As long as it isn't bottoming out at the rear on bumps then a softer rear spring will have a
similar effect to a stiffer front and might help to correct your oversteer. A slight adjustment on tyre pressures might even be enough (increase front
by 1 or 2 psi and decrease rear by the same amount). Note, don't go below minimum safe pressures.
Hopefully "procomp" will be along to help shortly.
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rodgling
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| posted on 25/9/12 at 10:47 AM |
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My first concern is getting the grip more balanced front-to-rear (at the moment I think there is too much grip at the front relative to the back). So
softening the rear would also do the job, but given the amount of roll here, I would think that stiffening the front is maybe a better way to go?
At the moment tyre pressures are 16 psi cold all round, perhaps a touch low.
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loggyboy
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| posted on 25/9/12 at 10:51 AM |
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Have you tried stiffening the shocks (i assume they are adjustable).
Mistral Motorsport
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rodgling
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| posted on 25/9/12 at 10:59 AM |
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I have but this isn't a transient issue - it happens mid-corner in steady state. So I don't think the adjusting dampers is the right
solution.
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craig1410
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| posted on 25/9/12 at 11:10 AM |
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Yeah I wouldn't go any lower than 16psi normally. So maybe try 18psi at the front. That will reduce tyre roll-under on the outside tyre and will
also reduce tyre compression slightly which will help overall roll a little bit at least. What weight is your car and what tyre size are you using?
I don't actually think the amount of roll you are getting is excessive if I'm honest. The camera angle makes it look worse than it is I
think. Comparing number plate with the ground it doesn't look so bad. Bear in mind if you improve the front end tyre contact patch then you will
get even more front grip which will make balance worse.
What adjustment do you have on the rear? Have you checked for toe and camber? I'd suggest a small amount of overall toe in and a small amount of
negative camber would be a good start for exit stability.
Anyway, that's about the limit of my input - I'll leave you in the hands of others who might know what they are talking about... 
Good luck!
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cloudy
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| posted on 25/9/12 at 11:30 AM |
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I was running 10psi all round at Barkston this saturday, what tyres are they?
Photo looks normal to me, given the heavy engine and passenger on board, I would think you'd need ARB to eliminate that sort of roll..
James
www.warnercars.com
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rodgling
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| posted on 25/9/12 at 11:51 AM |
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quote:
Originally posted by craig1410
...
Good luck!
Thanks, this all basically echoes what I'm thinking.
Car is 700 kg with 15" wheels on AD08s (i.e. summer road tyres).
Cloudy - I'll go through some of the other photos and see how it compares to the other cars there. I think 10 psi might work on your car (350
kg?!) but perhaps less so on mine.
I suspect I'll end up trying some stiffer springs as a first effort, since it's the easy and cheap option. Interested to hear opinions on
here first though.
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britishtrident
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| posted on 25/9/12 at 11:53 AM |
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Personally I would go for a fairy soft adjustable front ARB to balance the handling.
The only really way to get the handling balanced is a bit of track testing against the stopwatch as drivers impressions can be misleading, often
an oversteering car will feel faster but in reality be slower.
[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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chillis
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| posted on 25/9/12 at 11:56 AM |
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The car should be able to cope with two people. From the picture I would say you have quite a lot of front roll. More than I would expect. Just look
at the angles between the two top wishbones. You also say the car is taily. Roll centre on 'locost' type cars is not ideal so anything to
reduce roll improves the cornering experience in my opinion.
This would point towards a Front anti roll bar, and this would be my chosen path to 'cure' the problem in this case. Not for nothing are
many Caterhams fitted with them. Reducing 'body' roll will reduce the outside pos camber which is always a problem on all but very unequal
length wishbone set ups. Its not going a lot positive but it won't help your oversteer problem. Siffening the front springs would have the same
result when cornering but may make the ride too firm at the front under normal driving. Siffening the dampers will only make the ride harsher all
round, as you said the problem isnt transient. No point rattling all your fillings if it ain't gonna help!
Could you borrow a set of stiffer springs and try them to see if it a, resolves the cornering problem, b, what its like down a bumpy country lane. If
yopu can tolerate the stiffer front springs that would be an easier solution. Has someone fitted softer springs previously to (wrongly) cure
'bump steer' ?
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craig1410
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| posted on 25/9/12 at 11:57 AM |
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Is it my imagination or does your rear outboard wheel have a touch of positive camber? It might just be the taper of the rear arch but I'd check
it. If you are getting more body roll than is ideal then maybe the rear camber is not negative enough. That might explain some of the exit
oversteer.
Also, 10 psi is way too low for a 700Kg car. I wouldn't even go that low on a 350Kg car. Of course I'm not a tyre expert either so should
probably reel my neck back in...
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cloudy
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| posted on 25/9/12 at 12:10 PM |
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Certainly wasn't suggesting using 10psi on a 700kg car! - but lowering them from your road settings on short sprints helps get some heat in
them,
What is your ground clearance? dropping that could help a little
(http://s1243.photobucket.com/albums/gg546/Rob_Fisher33/Barkston/?action=view¤t=IMG_6635_zps232b5220.jpg)
Also what are your static settings for camber front and rear?
James
www.warnercars.com
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rodgling
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| posted on 25/9/12 at 12:14 PM |
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quote:
Originally posted by craig1410
Is it my imagination or does your rear outboard wheel have a touch of positive camber? It might just be the taper of the rear arch but I'd check
it. If you are getting more body roll than is ideal then maybe the rear camber is not negative enough. That might explain some of the exit
oversteer.
No, I noticed that too on the rear. But I'd expect roll oversteer to be quite snappy and it isn't at all, the back just slowly and gently
lets go as you feed in the power. So for that reason I was ignoring that for now as it doesn't seem to be causing a problem? I could be wrong
though, perhaps that is reducing rear grip. Easy enough to add a bit more rear camber, so that's worth a try.
Interesting that there's more than one person saying an ARB is the way to go, perhaps this will be a good winter project.
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rodgling
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| posted on 25/9/12 at 12:19 PM |
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quote:
Originally posted by cloudy
Certainly wasn't suggesting using 10psi on a 700kg car! - but lowering them from your road settings on short sprints helps get some heat in
them,
What is your ground clearance? dropping that could help a little
(http://s1243.photobucket.com/albums/gg546/Rob_Fisher33/Barkston/?action=view¤t=IMG_6635_zps232b5220.jpg)
Also what are your static settings for camber front and rear?
James
Unfortunately ground clearance isn't great due to having a tall engine with a reasonably deep sump in a car which lives up a steep drive :-) So
there's not much possibility of lowering it unless I move.
IIRC camber is about 0.7 degrees rear and 1.1 front.
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craig1410
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| posted on 25/9/12 at 12:23 PM |
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It's always dangerous to take "measurements" from photographs, especially if the camera is something like a mobile phone as you can
easily get geometric distortion from the lens. Also the road contours make judgements very difficult.
On the ARB, I think if you are serious about getting the best performance then it would be a good move to have at least a front ARB as it gives you
another adjustment "tool". As you say, a good winter project. In the meantime try tweaking static geometry and tyre pressures. Maybe also
worth buying a tyre temp gauge as it may help to identify contact patch issues when testing. I've got one of those laser dot thermometers which
comes in handy at times.
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Jon Ison
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| posted on 25/9/12 at 02:32 PM |
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My car similar corner
My car same corner
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loggyboy
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| posted on 25/9/12 at 02:41 PM |
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quote:
Originally posted by Jon Ison
My car similar corner
My car same corner
Different car, passenger, (engine?), speed, condtions, tyres.....
as mentioned above, its not wise to use pictures to gauge setting up, just as bad to compare apples and pears!
Mistral Motorsport
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rodgling
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| posted on 25/9/12 at 02:53 PM |
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Yes and no Loggyboy, I certainly think they can help give you an idea of how much roll you're getting which is pretty hard to tell from inside
the car.
They are different cars etc but Jon's is clearly controlling the camber angle of the front wheels much better (esp. the inside front), obviously
his geometry and dynamic camber change will be different but it suggests I could be doing better on my car. That said it looks like Jon is also
getting some positive camber on the outside wheels?
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Bare
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| posted on 25/9/12 at 03:50 PM |
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Stiffer springs will surely eff up the ride /handling on public roads.
Soft is good for keeping tires ON the road surface .. important, that bit.
Not useful to reduce that simply to have a wee bit less roll in a corner photo
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sdh2903
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| posted on 25/9/12 at 03:52 PM |
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Fit a bike engine!
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britishtrident
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| posted on 25/9/12 at 05:11 PM |
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quote:
Originally posted by Bare
Stiffer springs will surely eff up the ride /handling on public roads.
Soft is good for keeping tires ON the road surface .. important, that bit.
Not useful to reduce that simply to have a wee bit less roll in a corner photo
The OP wants to improve the balance of the car by reducing oversteer by altering the the roll couple distribution to take download off the
inside front wheel and transfer it to the inside rear wheel, so taking some grip from the front and adding it to the rear.
Doing this by changing only the front springs should not involve a huge change in spring rate, the better option of fitting a fairly soft front
ARB will have even less impact on ride quality.
[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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procomp
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| posted on 25/9/12 at 06:41 PM |
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Hi
The roll does look a little excessive.
My advise would be to change the springs first at the front an increase of maybe 50Lb should see an improvement.
An anti roll bar is a good idea to give you adjustment in balance. However on cars of this type it is not advisable to use an anti roll bar to stop
roll. It is the job of the springs and dampers to control the cars weight transfer / roll. An anti roll bar is really only used to give an adjustable
element to the weight transfer. If you use an anti roll bar to stop the majority of weight transfer / roll you end up with a bar that is far to stiff
for the application and simply remove the independence of the suspension. So to sum that up a light poundage anti roll bar is good to give an
adjustable element to the control of weight transfer but should not be used as the main component to stop weight transfer / roll.
The front geometry like a lot of current Kitcar manufacturers has the basic geometry set wrong. It will give a gain in negative camber in equal
compression on the front but in roll the out side working rim / tyre will see a loss in camber. This gives all sorts of problems due to the fact that
you have to run extra static camber to end up with the correct amount of camber during the corner. This leads to poor grip on the initial turn in on a
corner and on the road causes the car to have a wandering effect.
Cheers Matt
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rodgling
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| posted on 25/9/12 at 08:06 PM |
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Very helpful, thanks Matt & other posters. I will try some stiffer springs as a starting point.
Would be very interested to know more about your second point though. The car has the usual unequal length wishbones with the longer bottom arm
roughly parallel (from balljoint to pickup point) at rest, upper arm point pointing up slightly. This is the conventional starting point for a decent
handling car isn't it? What should be different? I can see how in roll the upper outside suspension pickups will move out and the lower ones
will move in, reducing camber on the outside wheel, but can't see how that could possibly be avoided, that's just how roll moves the body
of the car?
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franky
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| posted on 25/9/12 at 08:12 PM |
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Dave, what poundage did you go for on the front? The same I had on mine?
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rodgling
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| posted on 25/9/12 at 08:33 PM |
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No, I tried what you thought you had (675 lb/in?) but I'm 100% sure that's not what you actually had as it made my car undrivable, nothing
like yours to drive - suspect the bloke who set the car up didn't want people copying his setup. Currently I'm at GKD's stock 350 lb
springs, but my wheels are a lot further out which makes the springs effectively 10% softer (front and back).
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