28 replies to this topic

[MRA]

Wil, can you explain the misconception over "lift off oversteer" I made a completely rose jointed 5 link beam axle for the rear of my Mini in 1989 (yes yes old git) that definately had lift off oversteer, so much in fact that if I didn't keep the load pedal firmly embedded in the ground it would exit slideways on all but the almost straight bends, but nothing could get close on the bends

Surely as tyres need heat to give good grip, in the wet there is too much surface area and they rapidly cool down losing valuable grip I run 195 45 13" and in the wet they are fun..... but in the dry i just throw it it to corners and so far exit the other side of the bend, with big grin intact...

Don't lets forget that winter rally tyres are very narrow that is to keep some heat in the tyres and to cut through the ice and snow to firmer..... well ice and snow

[Ethel]

Hopefully a silly question, they haven't put the tyres on the wrong way round have they?

To my mind lift off oversteer is something experienced on RWD cars where driving the rear tyres hard while leaning heavily in a corner causes them to skew and travel sideways to some degree when you ease off on the accelerator the tyres go more in a straight ahead direction, and since your arse was hanging out that's now towards the inside curb. FWD cars do similar but as acceleration creates less grip at the front you get understeer and easing of gives less understeer which will also direct you towards the inside curb - only, since your arse isn't hanging out at least the car's pointing more or less in the right direction.

[Wil_h]

I suspect with a 5-link beam rear you did get lift-off oversteer, but not with the standard radius arm setup. the suspension works in a completly different way. In a mini if you have reached the limit of the front end grip and you lift-off all that happens is that you get less understeer, not lift-off oversteer.

Now, it is possible to induce a mini to oversteer, but you need to do more than lift off mid corner. A rear beam is a completly different thing.

Road tyres are not so dependant on heat to generate grip, so in the rain, it's the ability to displace water that is the limiting factor.

Winter rally tyres are designed to dig down to gain grip as far as I am aware.

[GraemeC]

As we're throwing opinions in - 'lift off' over steer is produced by the suddon weight transfer experienced in lifting off the throttle mid-corner. This transfers the weight of the vehicle forwards on hence the back end goes light and breaks away, ie induces 'oversteer'.

In a front wheel drive car any application of power will immediately bring the car back into line, in a rear or 4wd car then application of power could (dependant on the angle the car achieves to direction of travel) create a drift scenario - this is what some will class as true oversteer.
In extreme cases a spin will be the result.

In all honestly 'lift off' oversteer isn't really oversteer at all, it is merely a loss of grip, or more traditionally - a skid. True oversteer/understeer is generated by the driven wheels pushing the end of the car they are located at away from the apex of the corner - yes it still involves some loss of grip but from a very different reason.
As such a Mini will not

[Cooperman]

I can assure you that my Mk. 1 Cooper 'S' Historic Rally Car has lots of 'lift-off oversteer' and, on gravel, it feels almost like a rwd car at time. I do set-up my rear suspension to achieve this and the front, with zero toe-in, also helps with this. 1.5 deg neg camber on the front, 0.5 deg neg on the back, 2 mm toe-in on the back and slightly raised ride height help achieve this together with a few other 'tweaks' I have evolved over my 48 years with Minis in rallying.
It is actually not completely accurate to say that the more tyre rubber in contact with the road the more grip you get. Tyre grip is dependant on a number of factors. The design of the tyre will impart an ideal contact pressure per sq. cm. Thus, the ideal tyre size can be calculated by dividing the weight on a specific wheel by the ideal contact pressure to give the ideal area. This is especially critical in wet or icy conditions. For example, on a winter tyre for gravel it is necessary to have a very narrow tyre. The old works rally Minis used a very narrow 'knobbly' tyre on gravel, studded on ice and snow.
The problem is knowing what the ideal applied pressure is for different tyres in different conditions. The manufacturers will know, but to get this information is probably impossible.
IMHO, the optimum tyre width for a road-going Mini is a 165 section. For racing on a smooth track in the dry it could be wider, but then the compound will probably be much softer giving a different ideal contact pressure /sq. cm.

[Kerrin]

I thought a standard 3.5x10" wheel had just under 1" (24mm) positive offset, not zero.

Front tracking - the standard is 1.5mm toe out (around 12 minutes from memory)
Rear Tracking - the standard is 3.2mm toe in - this cannot easily be altered on a Mini with std rear suspensions parts.

Is the 12 minutes toe out correct, I think I set mine to about 20 no wonder it is a bit scary overtaking.

Can anyone confirm?

[MRA]

Understeer is where you do not have enough steering to follow the intended direction of travel.

Oversteer is where you have too much steering to follow the intended direction of travel.

Lift off or more welly is simply the means to get that oversteer........ it is still oversteer or understeer if your intended path is NOT the one you are taking


Kerrin, 12 minutes or 20 minutes ??? tell us have you got standard suspension or any heavy duty parts fitted ??

Edited by mra-minis.co.uk, 29 April 2009 - 09:55 PM.

[the.grizzle]

Woah haha, this thread grew alot more than i thought it would.

Ok to answer a few questions, I thought about the tyre direction when i first tested them and luckily no they were on correctly.

Only the front tyres were replaced, and although as cooperman mentioned the tyres generally take a bit longer to wear in than regular tyres, i have now done pushing 300 miles on them, still no difference to the 100mile mark.

But im going to have to wait a few weeks now to sort it as boogers getting fibreglass doors now as the standards have got too much rust for my liking as they are the worst part of the car. So im going to have to wait until the doors are replaced before i continue in my search for handling again.

But thanks for the help so far guys, keep up the good work

[Kerrin]

Understeer is where you do not have enough steering to follow the intended direction of travel.

Oversteer is where you have too much steering to follow the intended direction of travel.

Lift off or more welly is simply the means to get that oversteer........ it is still oversteer or understeer if your intended path is NOT the one you are taking


Kerrin, 12 minutes or 20 minutes ??? tell us have you got standard suspension or any heavy duty parts fitted ??

I have fully adjustable minispares bottom arms and tie rods with the uprated bushes that come with the kit, Minisport adjustarides standard cones(brand new)
and AVO shocks.

I have my own set of Dunlop optical tracking gauges. They have a dial on them where you set the wheel width (10")and the required toe out (1/16") and the dial gives you the angle in minutes. I have just been out to the garage to check and the gauge advises me 22 minutes. Which is what the car is set to.

I have a set of the longer track rod ends arrived from Minits today so will be putting them on tommorrow night and could do with a second opinion on the tracking settings.

[MRA]

Standard suspension bushes should be set approximately to the book values....

Rose jointed bottom arms and rose jointed heavy duty tie bars setups can be set fairly near to neutral as there is no rubber to "give"

systems in between these two should be set as a rule of thumb somewhere between the two

[Kerrin]

Righto

I will tweek them in a bit and see how it feels on the road.

[icklemini]

Is the 12 minutes toe out correct, I think I set mine to about 20 no wonder it is a bit scary overtaking.

No - its about 22mins (standard) but to be honest it will not make a lot of difference!

different parts and components can equal different settings

Lift off oversteer? - Rear wheel toe is sticking out

[Kerrin]

Is the 12 minutes toe out correct, I think I set mine to about 20 no wonder it is a bit scary overtaking.

No - its about 22mins (standard) but to be honest it will not make a lot of difference!

different parts and components can equal different settings

Lift off oversteer? - Rear wheel toe is sticking out

Oh dear, that means the scary overtaking is actually down to my driving and not the tracking.

The new suspension cones are still settling so will check the settings again after the weekend.

Thanks for the help icklemini, I thought you would get fed up with me PMing you again

[MRA]

scary overtaking....... have you also checked things like bottom arm bushes tiebar bushes, wheel bearing / CV joint etc.... jack it up and see how much "free play" you have, then get someone to apply the brakes to see if you still have as much "free play"..... if its the same then wheel bearings and or CV joint need inspecting and replacing, if when the brakes are applied it "goes" away then top and bottom swivel pin (ball joints) need replacing.........

Of course it could just be the power ??