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Quick To Understeer Then Oversteer, Normal?


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#1 al_reidy

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Posted 03 November 2009 - 05:56 PM

I have finally got my Type R zcars mini on the road! but its a massive handful!
if you drive it at a small roundabout and slow corners it feels like its on its tip toes, steer a little more then it grips and sends the back end out.

it might just be that there is bog all weight at the front and im a newbie with rear wheel drive cars but its very disconcerting.

im running 18psi front tyres and 20psi rears. 6 clicks on every shocker and zcars setup my suspension (nearly 2 years ago!). I have probably messed up the geometry though by taking the thing to bits 2 times since then for paint spraying etc.

its mentally quick in a straight line but wants to wander around the road a bit when you back off the throttle. (is that the limited slip diff?)

Can anyone help?

Cheers

AL

#2 Ade

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Posted 04 November 2009 - 10:50 PM

I have finally got my Type R zcars mini on the road! but its a massive handful!
if you drive it at a small roundabout and slow corners it feels like its on its tip toes, steer a little more then it grips and sends the back end out.

it might just be that there is bog all weight at the front and im a newbie with rear wheel drive cars but its very disconcerting.

im running 18psi front tyres and 20psi rears. 6 clicks on every shocker and zcars setup my suspension (nearly 2 years ago!). I have probably messed up the geometry though by taking the thing to bits 2 times since then for paint spraying etc.

its mentally quick in a straight line but wants to wander around the road a bit when you back off the throttle. (is that the limited slip diff?)

Can anyone help?

Cheers

AL


I'd definatley get the geometry checked as it will make a huge difference to the feel of the car if it is out.

Also the tyre pressures to me seem a little high? I've got a funny feeling from memory that mine was running something like 12 front and 14 rear but was a while back now so not too sure. Best advice would probably be to phone Chris. He usually knows whats what :thumbsup:

#3 SukiDawg

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Posted 08 November 2009 - 10:44 AM

Concur with the above.

I'm no Z cars expert, but suspension geometry is everything when it comes to handling, and there is definitely plenty that can be adjusted on these things.

Sounds like its time for a check at least.

#4 z cars chris

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Posted 09 January 2010 - 09:55 PM

this will definatly be a set up issue ive had lots of problem cars in and sorted them with very minor changes to the geometry
you have to appreciate the cars are very powerful and a small amount wrong will be magnified by just how fast the power can build once you pres the loud pedal
as many of you have experianced by having a demo with me in the white demo car they do work well if set up correctly
also theres a way of getting the best from them in the way you approach bends and apply the throttle
if you have only ever driven front wheel drive cars then you will be turning in too late and applying too much power too soon
ive raced for years rear wheel drive
i built a front wheel drive racer five years ago and was hopeless for the first few meetings till i got the lines and style of driving sorted in my head
once i did that i was winning loads of races
chris

#5 al_reidy

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Posted 10 January 2010 - 07:51 PM

this will definatly be a set up issue ive had lots of problem cars in and sorted them with very minor changes to the geometry
you have to appreciate the cars are very powerful and a small amount wrong will be magnified by just how fast the power can build once you pres the loud pedal
as many of you have experianced by having a demo with me in the white demo car they do work well if set up correctly
also theres a way of getting the best from them in the way you approach bends and apply the throttle
if you have only ever driven front wheel drive cars then you will be turning in too late and applying too much power too soon
ive raced for years rear wheel drive
i built a front wheel drive racer five years ago and was hopeless for the first few meetings till i got the lines and style of driving sorted in my head
once i did that i was winning loads of races
chris


cheers chris,
I managed to figure out with the help of a mate that the toe in on the rear was 6 mm, all on the near side rear! i have set it to 1.5mm total but equally. the front is now at 1.5mm instead of 3mm.
its only been wet or ice since then so i dont know what difference it has made, i have no doubt that the car can handle as i have seen your demo car and others do well.

is it worth fitting anti-roll bars front and rear? is so how much?

any idea what suspension settings i should be setting the car too? at the moment im just guessing from my vast experience of about 2 weeks..


i know im a crap driver and unsure how to handle rear wheel drive fast cars, just cant wait for better weather!

#6 z cars chris

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Posted 10 January 2010 - 08:57 PM

the settings we now use after tweeking for several years are as follows
front half a degree negative camber each side
toe 1 mm each side
caster 3.5 degrees
rear 1.5 degrees negative camber
1.5 mm toe in each side
the toe in you had would throw the car about depending on weather or not you were accelarating
one other thing that can give you a weird feeling is only found in cars with the limited slip diff IF THE CAR GETS A HARD KNOCK ON THE WHEEL say by kerbing it or being hit by another car it can flatten the preload washer in the diff
this manifests itself in violent twitching from left to right when you come on and off the power as the diff locks and un locks
ive only had this twice once on my race car after i got clouted on the drivers wheel in a race and recently i had it with a road car that had been hit by another car on the passenger wheel
took a bit of diagnosing at first till i remembered what my race car did then it was an easy fix
if in any doubt about handling always call me to ask
id rather spend ten mins sorting out the car than mending it after youve pranged
chris

#7 al_reidy

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Posted 11 January 2010 - 01:50 PM

the settings we now use after tweeking for several years are as follows
front half a degree negative camber each side
toe 1 mm each side
caster 3.5 degrees
rear 1.5 degrees negative camber
1.5 mm toe in each side
the toe in you had would throw the car about depending on weather or not you were accelarating
one other thing that can give you a weird feeling is only found in cars with the limited slip diff IF THE CAR GETS A HARD KNOCK ON THE WHEEL say by kerbing it or being hit by another car it can flatten the preload washer in the diff
this manifests itself in violent twitching from left to right when you come on and off the power as the diff locks and un locks
ive only had this twice once on my race car after i got clouted on the drivers wheel in a race and recently i had it with a road car that had been hit by another car on the passenger wheel
took a bit of diagnosing at first till i remembered what my race car did then it was an easy fix
if in any doubt about handling always call me to ask
id rather spend ten mins sorting out the car than mending it after youve pranged
chris



Thanks again chris, i may well be in touch when the weather improves.

Do you sell anti-roll bars? if so how much?

#8 gixer1

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Posted 12 January 2010 - 03:56 PM

I have all these problems too, i thought mine felt bouncy on the front end but describing it as 'on tip toes' is exactly how it feels! I too have dropped the air to around 20 psi front and rear and the clicks on the shocks are all the same, it was like it straight from z cars after the set up but to be honest the mini is in hibernation mode for the winter all tucked away in the garage so i cant fiddle with it untill the weather sorts itself out!!

#9 al_reidy

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Posted 31 May 2010 - 05:49 PM

So i have sorted the main problems with the handling.
laser 4 wheel alignment from http://www.tyreandtech.co.uk. The guy Steve Hoe is a legend, he knows his stuff.

both front and back wheels had toe out, rears were crabbing and 1 had no camber.
the front nearside wheel was 1 cm further out than the rest of the car and had no camber.

crazy stuff.

anyway its all great now, what a difference to the confidence when driving now. its much more predictable (in the dry at least).

ive gone for 20 psi in the rears and 18 at the front.

#10 cptkirk

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Posted 01 June 2010 - 11:27 AM

Al - do mind me asking how much it cost to get it sorted?

#11 al_reidy

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Posted 01 June 2010 - 11:37 AM

Al - do mind me asking how much it cost to get it sorted?


i managed to get mates rates because of a business relationship, but i think it was 35 an hour. it took 3 hours ish to sort. well worth the time and money though.

#12 cptkirk

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Posted 01 June 2010 - 11:40 AM

Cool - my folks live just outside Newark which is a stones throw from Lincoln so I might invest when I take the car up - even if it just confirms all is well it'll make me sleep better.

Edited by cptkirk, 01 June 2010 - 11:41 AM.


#13 al_reidy

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Posted 01 August 2010 - 05:26 PM

ok, so this problem never really was solved. it just got massively better with the alignment.
I think there is something with the steering rack.
Its a new rack, bought from zcars with the kit, there is a bit of play when driving in a straight line you can move the wheel about 2cm without it changing the direction of the car. when the car is stationary you can trace it moving all the UJ's inside the car, it just doesnt move the track rods.
ive read about the preload adjustment, but cant find out much about it other than its stiffer if you tighten it. i have not touched it yet just wanted to see if you guys have seen it before? is it a worn rack or am i missing something....?

#14 v-tec van

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Posted 01 August 2010 - 08:03 PM

ok, so this problem never really was solved. it just got massively better with the alignment.
I think there is something with the steering rack.
Its a new rack, bought from zcars with the kit, there is a bit of play when driving in a straight line you can move the wheel about 2cm without it changing the direction of the car. when the car is stationary you can trace it moving all the UJ's inside the car, it just doesnt move the track rods.
ive read about the preload adjustment, but cant find out much about it other than its stiffer if you tighten it. i have not touched it yet just wanted to see if you guys have seen it before? is it a worn rack or am i missing something....?




Ive got the exact same problem with my orange turbo. it too was a new rack when i fitted it but its never been right.
it`s on the 'to do' list ill get round to it at some point i was just going to swap it for another.

Edited by v-tec van, 01 August 2010 - 08:04 PM.


#15 pete

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Posted 01 August 2010 - 08:07 PM

First rack I fitted in the pickup had similar amounts of play and this was new from a local motor factor. Didn't feel I should take it apart to adjust it as it was new so took it back to swap it and the replacement was just as bad. Probably wouldn't notice it in a standard mini with all the standard rubber bushes and speed difference.
Ended up buying one from minispares for a lot more money but had no play what so ever. You might just be unlucky and have a duff one as well.

Pete




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