Lifting the inside rear.

[Kozy]

Is anyone here aware that their car does this under heavy cornering?

If you do, how much do you lift by and what setup does your car have?

 

[tama666]

Is anyone here aware that their car does this under heavy cornering?

If you do, how much do you lift by and what setup does your car have?

A stiff suspension will cause this to happen. It happens to stock setups on civic as well if you really turn in hard with enough speed. Normal occurrence really. Harder to see on a stock setup vs. stiff suspension.

* Eibach Pro Kit Springs
* ASR Subframe Brace and 24mm sway bar
* SI front sway bar 26mm
* Hondata S300
* Tokico Illuminias
* Potenza RE11

Curious, why do you ask about this rear wheel lift anomaly?


FWD lifting

RWD lifting

So as you can see, these are mostly images of cars with a stiff suspension...common place really.

 

[Kozy]

Just curious as to whether people suffer with it. According to my maffmatiks, I should be three wheeling around my autotests, but I don't. Maybe I'm not trying hard enough, but to me, this is a good thing, suggests I've got the front and rear roll resistance balanced.

Lifting seems to be a major thing for US Autocrossers, due to their trend of using massively rear biased suspension setups in order to get the car to rotate. The way I see it, this ends up being counter productive, as you should plough into understeer with a rear wheel in the air.

Stiff suspension alone should not cause it. Big imbalances in F/R roll resistance will.

Also, I wanted to engage in some debate about handling, other than what the best coilovers for a fiver are.

 

[tama666]

You are on the right path -- kind-of.

I have the front suspension a tad softer than the rear, which makes this happen more than having all corners of the suspension set evenly.

Having the front suspension set soft over the rear provides better traction to the outside front wheel [opposite to the lifting rear wheel]. This rear wheel lift helps combat the FWD under-steer by applying chassis torque to the outside front wheel. You add LSD to this equation [use your maffmatiks lol] and you have a cornering machine.

 

[Kozy]

Yes I can see your point, to a point.

However if you are lifting more than an inch say, then the outside rear cannot take any more load and the remaining load transfer is being taken up by the front axle, so although you're loading up that outside front, you'll also now be unloading the inside front quicker than you would be with the inside rear on the ground, and so loosing grip and going into understeer...

 

[tama666]

Yes I can see your point, to a point.

However if you are lifting more than an inch say, then the outside rear cannot take any more load and the remaining load transfer is being taken up by the front axle, so although you're loading up that outside front, you'll also now be unloading the inside front quicker than you would be with the inside rear on the ground, and so loosing grip and going into understeer...

...that's what you would think would happen, but there is more grip and less under steer when you see lifting during hard cornering. Its needed at low speed.

You don't really see this lifting often during high speed cornering, mostly happens during low speed tight corners, like one would see during an autox event--tons of tights low speed corners.

If you were to keep all 4 wheels planted on the ground, you will end up with longer track times and more under steer.

This topic is not a new one for sure; a CRX is where I first learned about this rear end lifting, back in the late 80's, nothing has changed much with these independent suspensions on a FWD car, rear end lifting is common place.

 

[Kozy]

...that's what you would think would happen, but there is more grip and less under steer when you see lifting during hard cornering. Its needed at low speed.

If you were to keep all 4 wheels planted on the ground, you will end up with longer track times and more under steer.

Ok, but how does this work? I'm not saying you're wrong, but you kind of state it in a matter of fact way, where as I have tried to work out the physics of it and have come to the conclusion that (excessive) lifting results in understeer because of the aforementioned load transfer at the front axle.

If we assume equal roll resistance front and rear, then both axles will loose overall lateral grip at an equal rate and the car will be neutral, until the point where the inside rear lifts. At this point the grip from the rear becomes fixed, as no more load can be transfered off the inside wheel. With the rear grip fixed, the front continues to transfer load off the inside wheel meaning that the front axles grip continues to drop, resulting in understeer. This effect appears to be exacerbated by the fact that the load transfer is now not shared equally between front and rear axles, the front now has to deal with what would have otherwise been dealt with by the rear.

If you are saying that lifting reduces understeer, which bit am I misunderstanding?

 

[tama666]

Ok, but how does this work? I'm not saying you're wrong, but you kind of state it in a matter of fact way, where as I have tried to work out the physics of it and have come to the conclusion that (excessive) lifting results in understeer because of the aforementioned load transfer at the front axle.

Its is the load transfer that I am pointing to..."matter of fact"

If we assume equal roll resistance front and rear, then both axles will loose overall lateral grip at an equal rate and the car will be neutral, until the point where the inside rear lifts.

First, the body roll front to back is not equal on civics, either its stiff in the front or in the rear, they are not 50/50 in weight distribution either and that plays on grip as well.

At this point the grip from the rear becomes fixed, as no more load can be transfered off the inside wheel. With the rear grip fixed, the front continues to transfer load off the inside wheel meaning that the front axles grip continues to drop, resulting in understeer.

Lateral grip is not equal due to weight distribution and body roll combined during hard cornering. Plus the one wheel left in the rear still in contact with the asphalt is gaining more grip as the lifting wheel applies more downward force to the opposite rear wheel.

This effect appears to be exacerbated by the fact that the load transfer is now not shared equally between front and rear axles, the front now has to deal with what would have otherwise been dealt with by the rear.

Downward and lateral grip will increase to the front wheels with more going to the front outside wheel. As the rear continues to lift up more weight and grip is then transferred to the front.

If you are saying that lifting reduces understeer, which bit am I misunderstanding?

I think your missing a drivers ability to transfer weight to the front left or right prior to corner entry.

 

[Kozy]

Its is the load transfer that I am pointing to..."matter of fact"

First, the body roll front to back is not equal on civics, either its stiff in the front or in the rear, they are not 50/50 in weight distribution either and that plays on grip as well.

I think this bit is crucial in where I am going wrong. I have a theoretical 'neutral' setup (in that the car does not tend towards over/understeer with increasing cornering force, weight distribution aside), and I was assuming that the equal roll resistance front and rear was providing equal roll front and rear, when what I actually had was an average across both axles.

Back to the drawing board...

 

[tama666]

Back to the drawing board...

Sorry Kozy, I wish you the best of luck in finding what your looking for.
BTW, What are you looking for?
Just curious as to whether people suffer with it.
...taking advantage of it with LSD is what people are doing with it, suffering no. Its like cheating, point and add throttle, its an advantage if you look at what is going on.

cheers.

 

[Kozy]

An understanding of vehicle dynamics really.

I am not looking to change my setup on the back of whatever I find, my car does not lift and I find this suits me fine, any more roll resistance in the rear I think would only slow me down, but then this is probably more of a driver preference.

I get how this is beneficial in an LSD equipped car in terms of traction. Mine is helical so still requires load on the inside, but for clutch pack cars I can see it working. However, I think the focus I have been working on is on pure lateral acceleration, so the diff shouldn't come into it, I am just focusing on what happens between front and rear grip in a corner at a constant speed, front / rear wheel drive isn't really a factor.

It will do, but I haven't figured that out yet. I need tyre data or pacejka's magic formula to do that, and I can't see me getting it any time soon!

 

[Kozy]

Here is my model of the grip balance F/R so far.

We can see front and rear grip drop off at an almost equal rate as the lateral acceleration increases, up until the point where the inside rear lifts at just over 1G. Here, the load transfer at the rear axle has hit its limit, the outside tyre cannot gain any more grip and so we see the rear axle grip level off. The front however, is still transferring load beyond 1G and as a result the front axle grip continues to fall, but it now also has to deal with anything more the rear tries to shift in addition, so we see the overall grip drop off faster as a result.

The net result of this is understeer, or at least a reduction in oversteer.

Again, I can appreciate the extra load on the front being beneficial for getting the power down in an LSD equipped FWD, but I haven't got that far yet...

 

[tama666]

Nice work, but what is this all for? A personal project of yours?

...taking speed into a corner is key, slowing down to keep wheels all planted to the ground is not. It does not bother me one bit that the rear inside wheel is lifting off the ground, I cant even feel it.

...buddies of mine would often comment while watching autox'ers that a racer is not going fast enough into a corner if their rear wheel did not lift off the ground.

...now the "pushing" effect or "understeer" will not go away if the rear wheel is lifting...it just lessens or combats that effect for a short period of time, until the car/suspension settles down--enough time to get through the tight corner. Some call this driving on the limit, I call it racing.

...[fwd] now if you are rear wheel "lifting" you should have an LSD, or its all for nothing as the open diff will only spin the loosest grip front wheel--lowers, lap speed and increases lap times, both significantly.

 

[Kozy]

It is not 'for' anything particularly, so yes I guess it is just a personal project that is of interest to me. One aim is to create a tool so that should I ever choose to go racing (one day I'll be rich enough to consider pissing £10k+ up the wall a 'triviality' ) , I have a good understanding of the car (any car once the inputs have all been measured) and a good idea on a baseline setup. Saves a lot of time and money testing. Something like this would tell me for instance that if a heavily rear biased setup was understeering, it is because the front roll stiffness was so low that the resulting roll angle was causing to the outside front to decamber, reducing front grip. A few minutes playing around with numbers tells me that to reduce understeer in this situation, I actually need a stiffer front spring/ARB, against intuition. No need to waste time and money fitting and testing parts which may have the wrong outcome.

I know there are programs you can buy that do this, but that is not the point. I don't learn anything using those.

 

[tama666]

you could save a ton of time and money by just asking to take a spin with someone as a passenger on a track. You can really get a feel of what the car suspension is doing. Video will not give you this perspective, this is really a "feel" in person deal. Plus its fun!
Racers would be happy to take you for a test lap, try different setups too on different car setups.

ciao...im done with this one.

 

[Kozy]

I get what you are saying, but that's not the aim.

Thanks anyway for your input!

 

[tama666]

your welcome, have fun!

 

[webartie]

Im going to jump in ha ha

see link to begin... good start

RACELINE CENTRAL: Ultimate Racing Car Chassis Setup Guide and Tutorial problems & possible causes

there are two ways it seems to start basic setup
american (heavy rear springs lighter front to create as above)
jap (heavier front and lighter rear with more focus on arb)

the american theory is quiet good but only if roll center and castor / camber are in good combo, so you can start by cocking a rear wheel but may still handle crap.

roll center here comes into way more affect

good basic guide
Suspension Tech - Sport Compact Car Magazine


the japs get the same turn in affect buy large roll bars rear. smaller on the front. take upgrades from 96 spec tef to 98 spec!!!

even 4 conor weighting comes into play.

my theory from experience, is that cocking a wheel is good for adding turn in, BUT without grip ie castor, camber and roll center taking into account then its not great. you will also lose grip on the rear so depending on conditions ie wet dry this my not help.

there in racing is always a good balance to be found. take the quickest FWD race car in Ireland currently, the ex demo J's racing CRX. amazing car... but doesnt cock a wheel and runs softer springs rear.

so i suppose its down to driver style and setup... either way you will need testing!!!!!

 

[tama666]

^^^^^


Thank you Webartie. spot on. testing and driver ability are key.
And yet another thing a computer can not aid with, camber...as well as tire compound and track condition: hot, wet, cold [snow? lol].

 

[webartie]

to defend as i do use maths to work out spring rates etc, you do need a starting point, after that the extra tenths are due to testing, aslo toe is a major part.

if anyone needs help with set up just ask even for starting pointers