JeffHs
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| posted on 19/11/08 at 06:11 PM |
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Help wanted - evil handling
Any suggestions would be welcome. I've only managed a few drives since SVA, but so far I'm very disappointed with the ride and handling
It's a book live axle chassis, pinto, 52:48 weight distribution. 185/70 Yokos on 13 inch alloys, escort rack, 300 lb front 180 pound rears on
Gaz. Mods to achieve self-centring. 0.5 degree toe-in 18 psi tyre pressure all round
I have 2 distinct but related problems. The car is excellent on smooth roads but bounces about like a pea on a drum when bumpy. I daren't push
it hard round twisty bits because it tends to dive all over the place. The steering wheel kicks hard on potholes. I suspected bump steer but
I've been measuring with lasers and I can only measure less than 1 degree 'steer' at full travel. The front springs are angled at
about 60 degrees so they are softer than rating and feel about right.
I think the backs are too stiff, I get a nasty kidney chopping lurch on some surfaces - I can't decide if it's at the top or the bottom
of its travel.
I think my steering wheel is too small for the road (11 inch), I think I'd be better with a bigger wheel and a quicker rack. I find it hard
getting lock on or off fast enough
Jeff
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TOO BADD
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| posted on 19/11/08 at 06:19 PM |
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Front springs are way to stiff. I have 180 front 150 rear with the dampers virtually backed off. I am sure someone will give you more technical advice
than me regarding setup but it sounds very hard.
I have a small wheel as yours and they will be a bit more twitchy than a larger one.
[Edited on 19/11/08 by TOO BADD]
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MikeR
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| posted on 19/11/08 at 06:26 PM |
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i'm planning on fitting 220 lbs front and 150ish rear (currently got 175 i think, but i'll change before on the road).
I think you're far too hard for the road, track maybe at the front.
tyres generally should be around 18psi ish.
damper fully to soft then slowly wind it up as you driven it a bit.
good luck.
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MikeR
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| posted on 19/11/08 at 06:27 PM |
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forgot to add, i've got a crossflow engine.
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theconrodkid
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| posted on 19/11/08 at 06:59 PM |
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try the 180,s on the front if they will fit and 150 ish at the back,i have 14 psi at the rears and a loverly comfortable ride
who cares who wins
pass the pork pies
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Antnicuk
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| posted on 19/11/08 at 07:04 PM |
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I tend to agree with above, your springs sound very heavy. I have a spare set of 180's and a set of 150s in 2.25 8 inch springs £20 each pair
if you want to have a play.
How much ddoes your car weigh?
600 BHP per ton, Stylus Brought back from the dead! Turbo Rotary Powered!
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nitram38
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| posted on 19/11/08 at 07:24 PM |
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What are your "centering mods" ? Have you changed actual castor?
Have you also made sure that your rack has the bumpsteer "dialled" out?
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COREdevelopments
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| posted on 19/11/08 at 07:40 PM |
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funny because think i have the same problem but only with back. mine feels way to stiff! the shocks are set on the softest setting, i am trying to
think what my spring rates are. at first i put it down to being a live axle but shouldnt be this hard.
Rob
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Mal
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| posted on 19/11/08 at 07:59 PM |
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Damper Travel
If you want to find out if your dampers are hitting the bump stops on an undulating road surface try the following.
Cut a 10mm long piece of plastic tubing of a suitable diameter to fit around the piston rod of your dampers. The tube will need a longitudinal cut in
it so that it can be fitted over bottom of the rod. It will need to have enough friction grip so that when pushed upwards by the damper body it will
stay at the point of maximum lift.
Try the car on a smooth road and observe the amount the ring has been lifted. Then repeat on a bumpy road and see if the ring reaches the bump
stop.
Mal
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Mark Allanson
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| posted on 19/11/08 at 08:00 PM |
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I have GTS dampers with 275lbs at the front and 175lbs at the rear and the car drives very nicely
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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thepest
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| posted on 19/11/08 at 09:05 PM |
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Same here, I am using GTS coilovers, I could do with some softer front springs thou. A very stiff front end will give you lots of understeer!
if you're not racing go for 180-220lb/inch on a book chassis with a pinto.
I am running a xflow so I am a few kg lighter.
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David Jenkins
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| posted on 19/11/08 at 09:39 PM |
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I have 275lb/in springs on the front, and they're more upright than normal so I've probably got the equivalent of 300lb/in in a
conventional setup... and it works very well (for me). In fact my whole car is very much like yours in many respects, apart from having a x-flow
instead of the Pinto. I have 140 lb/in springs at the back, but I do sometimes hit the bump-stops with a heavy passenger (i.e. 2 heavy people in the
car!).
Mine is neutral in corners, tending to oversteer if I boot it - just the way I like it. It also gets 'in the groove' when cornering fast.
I use a 10" steering wheel on a 2.4 quick rack, simply because I can't get my legs under a larger wheel, and I like responsive
steering.
It might be worth getting back to basics:
First of all, ride height. I have the front at 5.75" from floor to the bottom of the chassis next to the front suspension. The back is 6"
from the floor to the rearmost chassis member in front of the back axle. With the same wheels as yours, this puts the suspension in exactly the right
place - front lower wishbone pivot points (not wishbones) level, rear arms horizontal. Note that these cars seem to work better if the back is
a little higher than the front - they can be very unpleasant if the front is higher than the back.
The wheels, tyres and pressures are the same as mine, so I'd guess that you're not far wrong there.
In the past I was advised to set my shocks to minimum damping to start with, and slowly increase it click by click until it starts to get too choppy,
then back them off. Even now they're only 2 or 3 clicks off minimum at the back, and fully minimum at the front.
0.5 degree toe-in should give you stable steering. 0 degrees is as far as I would go - and that's where I am at present. I wouldn't go
there until whatever the problem is has been fixed, as that's just fine tuning to get the feel you want.
By 'self-centering mods' do you mean moving the top wishbone ball joints back a little to improve the castor? If so, that's a good
move, but it won't affect handling in the way you describe - it will just hold a straight line better. The book design will help you corner
better on a track, but isn't too pleasant on the public road - you're forever adjusting the wheel a tiny bit to go in a straight line.
Finally, what camber have you set your front wheels to? Mine are at 0 degrees (i.e. vertical), but some people go to 1 or 2 degrees leaning
inwards.
HTH,
David
Oh - I knew that there was something else - corner weighing. My car felt a bit out of shape so I borrowed a corner weighing gauge and set up all 4
corners so that the 2 fronts matched and the 2 rears matched - felt much nicer afterwards.
[Edited on 20/11/08 by David Jenkins]
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procomp
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| posted on 20/11/08 at 08:13 AM |
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Hi.
Given the angle of the front spring / damper units. The front springs are in the ball park possibly drop to 250Lb but 300lbs will not give the
problems described on a CEC setup. Although as yet not sure whether it is CEC or BEC.
At the rear Spring poundage for the English live axle setup is usually around the 120Lb - 160Lb max. The usual problems at the rear is that unless you
have specific valved dampers for a live axle setup they are not going to be valved correctly. Usually on the softest setting most dampers supplied as
STD are OTT for slow speed response and way OTT for high speed response.
Then theres the balance of dampers. Most dampers supplied as STD are out of balance by 2-5 clicks depending. Could just be a damper out of balance by
some margin. Unfortunately the only way to check that accurately is on a damper dyno.
Re The size of steering wheel 11" or 280mm-285mm is what the majority of people driving these types of cars use. Again most people run with
quick racks of a 2.4 ratio ( Rally desighn ) or for a more track biased setup the 1.9 or 2.2 ratios ( Quaife ) .
Cheers Matt
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Syd Bridge
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| posted on 20/11/08 at 10:44 AM |
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Steering kickback will be due to scrub.
What uprights are you using?What offset are your wheels?
Cortinas have humongous scrub on anything but using original wheels. Sierra hubs are a little more sensible when you look at the scrub.
Cheers,
Syd.
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rb968
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| posted on 20/11/08 at 09:57 PM |
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You lot have got me worried now. The part built Mk Indy I bought is BEC and I have a receipt for Protech shocks and 350lb front and 200lb rear springs
from MK that the previous owner bought. Seeing as he got the engine cradle from them as well they must have known it was a zx9 engine so....... I
haven't driven it yet obviously so will have to see but it sounds like they might be a bit much !!
Assuming he didn't spec it as a trackday tool I suppose! Oh bugger.
Rich
[Edited on 20/11/08 by rb968]
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procomp
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| posted on 21/11/08 at 08:19 AM |
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Hi
The MK indy is not the same setup. Here we are discussing an original book chassis setup.
On the Indy at the front they have moved the location of the damper on the wish bone further away from the lower ball joint Ie more inboard and also
the damper lays at a flatter angle More towards 45 deg rather than 60-70deg. This gives the wheel more leverage on the damper so it requires a
stronger spring. It also reduces the amount the damper moves which is BAD for control of the wheel.
At the rear you have an IRS setup where the damper is again at an angle and also the whole car is generaly more heavy compared to the original book
desighn. So it requires a stronger spring than the original book setup using an axle where the damper is vertical.
It dose not sound like you are far out with what you have. Don't panic .
HTH cheers Matt
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nitram38
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| posted on 21/11/08 at 08:23 AM |
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You still have not said how much castor you have.........................
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Syd Bridge
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| posted on 21/11/08 at 10:21 AM |
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quote:
Originally posted by procomp
Hi
On the Indy at the front they have moved the location of the damper on the wish bone further away from the lower ball joint Ie more inboard and also
the damper lays at a flatter angle More towards 45 deg rather than 60-70deg. This gives the wheel more leverage on the damper so it
requires a stronger spring.
HTH cheers Matt
The damper being further inboard, puts more bending loads into an already overstressed wishbone.
Are there any properly educated and qualified engineers in the kitcar industry at all???? 
Cheers
Syd.
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David Jenkins
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| posted on 21/11/08 at 12:18 PM |
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Now now Syd - say what you REALLY mean!
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Mark Allanson
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| posted on 22/11/08 at 11:56 PM |
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quote:
Originally posted by David Jenkins
Now now Syd - say what you REALLY mean!
I know Syd can, lets say take the topic by the scruff of the neck, but he is seldom wrong
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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David Jenkins
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| posted on 23/11/08 at 09:41 AM |
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I just wish that Syd would be a bit more constructive - instead of saying "can't anyone design anything properly", or
"you're doing it all wrong", or otherwise generally rubbishing people's efforts, wouldn't it be better if he offered
solutions.
As an example, look at the work put in by cymtrix (or however he spells it). Instead of rubbishing the chassis for lacking rigidity, he offered ways
to increase it by relatively simple modifications.
Anyone can criticise - but it's nicer to offer a better alternative.
That's just my 2p's worth - I don't intend to get stuck in a flame war about it!
best regards (to ALL)
David
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RK
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| posted on 25/11/08 at 05:18 PM |
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If there is widespread lack of proper engineering (ie. built in bumpsteer issues or wishbone stresses) then why not say it?
See "Why does Caterham cost more?" thread...
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