Understeer in RWD
Discussion
Hi,
I drive an E36 323i, fitted with Continental Conti Sports (225's), and was hoping for a bit of explanation / education. Today I was entering a roundabout to go right, I was in 2nd gear lowish revs about 1500. As I put the lock on to turn I powered on (bit silly really I know!) & I felt the the front understeer a bit. It wasn't like being in a front drive car but the front wheels did seem a bit disconnected and not doing what they were told. After thinking about it afterwards my mind is telling me that as the rear wheels were pushing the car forward & the front wheels weren't straight the front wheels were basically being pushed the wrong way to what they were pointing hence causing the understeer feeling. Am I right, and should throttle only be applied when the front wheels are straight in a RWD?
I drive an E36 323i, fitted with Continental Conti Sports (225's), and was hoping for a bit of explanation / education. Today I was entering a roundabout to go right, I was in 2nd gear lowish revs about 1500. As I put the lock on to turn I powered on (bit silly really I know!) & I felt the the front understeer a bit. It wasn't like being in a front drive car but the front wheels did seem a bit disconnected and not doing what they were told. After thinking about it afterwards my mind is telling me that as the rear wheels were pushing the car forward & the front wheels weren't straight the front wheels were basically being pushed the wrong way to what they were pointing hence causing the understeer feeling. Am I right, and should throttle only be applied when the front wheels are straight in a RWD?
225's sound like pretty big feet for a 323i, how big are the tyres on the front? Sounds like in that situation you had (for one reason or another)more grip at rear than front. Giving it more gas to get the tail out may work, provided the car actually has enough power to do it.
ETA: rather than applying throttle as you turn the wheel, try getting it turned in first and then getting on the throttle once the nose has tucked into the turn. Should give a better result.
ETA: rather than applying throttle as you turn the wheel, try getting it turned in first and then getting on the throttle once the nose has tucked into the turn. Should give a better result.
Edited by GravelBen on Tuesday 3rd October 00:40
How quickly did you turn the wheel? How hard did you apply the gas?
In slippery conditions you need to take extra care to make sure the front end has 'hooked up' before cracking the throttle open, it sounds as though the throttle was opened a bit too quickly, which pushed the unladen front end into understeer. Oddly enough, winding off a little lock could be enough to get the front wheels hooked up and you can start to steer round the bend again.
I'd advise against using more throttle to bring the back end round because (a) the understeer will have caused the car to run wide, closer to the kerb and therefore you'll have less room to slide the rear (b) it'll be more difficult to control and recover as you'll have more lock wound on than usual and the steering feedback will be less intuitive (c) if it doesn't break rear traction you'll just exacerbate the understeer state and possibly run out of road (d) if the rozzers catch you, they'll have your licence and relieve you of a few quid too
In slippery conditions you need to take extra care to make sure the front end has 'hooked up' before cracking the throttle open, it sounds as though the throttle was opened a bit too quickly, which pushed the unladen front end into understeer. Oddly enough, winding off a little lock could be enough to get the front wheels hooked up and you can start to steer round the bend again.
I'd advise against using more throttle to bring the back end round because (a) the understeer will have caused the car to run wide, closer to the kerb and therefore you'll have less room to slide the rear (b) it'll be more difficult to control and recover as you'll have more lock wound on than usual and the steering feedback will be less intuitive (c) if it doesn't break rear traction you'll just exacerbate the understeer state and possibly run out of road (d) if the rozzers catch you, they'll have your licence and relieve you of a few quid too
i agree with trackdemon on this one, letting off lock if your getting understeer is the way to go but its definetly not one's natural reaction when the front end wont turn in.
regarding only putting the throttle down when the wheels are straight ahead, yes if you have a very powerfull car and or it is exteremely slippy you dont want a big boot of full throttle with the steering turned or you'll spin but in most instances you can apply a little throttle progressivly and proportionally to the amount of lock you are letting off as you exit the corner. The old saying slow in fast out still applies.
regarding only putting the throttle down when the wheels are straight ahead, yes if you have a very powerfull car and or it is exteremely slippy you dont want a big boot of full throttle with the steering turned or you'll spin but in most instances you can apply a little throttle progressivly and proportionally to the amount of lock you are letting off as you exit the corner. The old saying slow in fast out still applies.
xanderjones said:
Hi,
I drive an E36 323i, fitted with Continental Conti Sports (225's), and was hoping for a bit of explanation / education. Today I was entering a roundabout to go right, I was in 2nd gear lowish revs about 1500. As I put the lock on to turn I powered on (bit silly really I know!) & I felt the the front understeer a bit. It wasn't like being in a front drive car but the front wheels did seem a bit disconnected and not doing what they were told. After thinking about it afterwards my mind is telling me that as the rear wheels were pushing the car forward & the front wheels weren't straight the front wheels were basically being pushed the wrong way to what they were pointing hence causing the understeer feeling. Am I right, and should throttle only be applied when the front wheels are straight in a RWD?
I drive an E36 323i, fitted with Continental Conti Sports (225's), and was hoping for a bit of explanation / education. Today I was entering a roundabout to go right, I was in 2nd gear lowish revs about 1500. As I put the lock on to turn I powered on (bit silly really I know!) & I felt the the front understeer a bit. It wasn't like being in a front drive car but the front wheels did seem a bit disconnected and not doing what they were told. After thinking about it afterwards my mind is telling me that as the rear wheels were pushing the car forward & the front wheels weren't straight the front wheels were basically being pushed the wrong way to what they were pointing hence causing the understeer feeling. Am I right, and should throttle only be applied when the front wheels are straight in a RWD?
Front wheels have a slant on them when you start to apply lock into a turn (I can't think of how to say this better right now). Thinking about it, the rears would have had a greater contact patch, therefore, more grip. The rears will then dictate what the fronts do.
So, you turn in. As some lock is applied, you should have waited for the fronts to 'bite' before getting on the power. As you applied the power the car understeered as the rears had the most grip and 'pushed' the car away from your chosen line.
Now think about weight transfer. For argument's sake we'll say your car weighs 1000kgs. Again for argument's sake 250kg per corner. When you accelerate, the weight transfers rearwards and so the rear wheels have the equivalent of say 300kgs eachand the fornts have 200kgs each. Which are going to naturally have more traction? Then add into the equation, he fact that you were truning and so the weight was transfered more to one side, in effct, 'unloading' one of the front wheels. One front wheel, with a smaller contact patch than the rears, was essentially having to take the task of turing your car in.
Applying the throttle just destabilised it to the point where it wasn't going to grip and as such, wasn't going to get you round the corner.
ETA: Just wait for the front tyres to grip before applying throttle. And do it gently and progressively. Only do it to a point where you can feel that the front tyres can cope. Any more than hat and you'll understeer.
Edited by combover on Tuesday 3rd October 07:13
This all depends on tyres, grip (ice, rain, dry), suspension setup, bumps in the road surface.
My RWD MG understeers on roundabouts in the rain, although I can provoke the back end out if I fed it more throttle quickly. Not advisable. I just back off a LITTLE and straighten up slightly and let the front bite again.
In the dry it will oversteer first, but only after a significant squeal and therefore warning.
Some manufacturers deliberately build in understeer initially as it's safer and easier to control by those with less experience.
The converse is also true - I once had a company issue FWD Vectra that oversteered in the wet, even with power on. They'd economised with the tyres; once I put some decent tyres on it, it behaved more normally.
My RWD MG understeers on roundabouts in the rain, although I can provoke the back end out if I fed it more throttle quickly. Not advisable. I just back off a LITTLE and straighten up slightly and let the front bite again.
In the dry it will oversteer first, but only after a significant squeal and therefore warning.
Some manufacturers deliberately build in understeer initially as it's safer and easier to control by those with less experience.
The converse is also true - I once had a company issue FWD Vectra that oversteered in the wet, even with power on. They'd economised with the tyres; once I put some decent tyres on it, it behaved more normally.
E36 has a LOT of understeer (for a RWD car!) built in by BMW after many people criticised the E30 for being too easy to spin (tho they put that axle back under the compact ). Running the fronts at 2psi more than the rears was suggested to me when I put up a similar query, and it seems to do the job just fine 
). Running the fronts at 2psi more than the rears was suggested to me when I put up a similar query, and it seems to do the job just fine GravelBen said:
225's sound like pretty big feet for a 323i, how big are the tyres on the front? Sounds like in that situation you had (for one reason or another)more grip at rear than front. Giving it more gas to get the tail out may work, provided the car actually
They're the same all round. It's fitted with M-tech 16's from the factory.
pikeyboy said:
i agree with trackdemon on this one, letting off lock if your getting understeer is the way to go but its definetly not one's natural reaction when the front end wont turn in.
That's what I used to have to do in my old FWD cars, definetly not something you think of doing in a panic. Had a few moments in the past of understeer and winding on more lock only for it to then grip and send me across the other way rather sharpish!
combover said:
Front wheels have a slant on them when you start to apply lock into a turn (I can't think of how to say this better right now). Thinking about it, the rears would have had a greater contact patch, therefore, more grip. The rears will then dictate what the fronts do.
So, you turn in. As some lock is applied, you should have waited for the fronts to 'bite' before getting on the power. As you applied the power the car understeered as the rears had the most grip and 'pushed' the car away from your chosen line.
So, you turn in. As some lock is applied, you should have waited for the fronts to 'bite' before getting on the power. As you applied the power the car understeered as the rears had the most grip and 'pushed' the car away from your chosen line.
I thought that was what happened. It wasn't like the front was washing out, but more of it felt like they were being pushed to that point. I think as it was a slow and tight roundabout, and the power doesn't come in a big lump the rear stayed very grippy. I have found before that if I'm moving along at more pace and go into a tight corner carrying speed not accelerating it does turn in quite sharp and no real drama from front or back, (Sometimes in summer heat a bit of tyre squeal!) then power out once it starts to straigten up. To be honest I think I was trying to be clever and get the back out, but instead pushed on the front instead. The only time I've got the back stepping out is when its a bit icey, I do rate the Contis quite highly, even if they are a bit noisy!
I will be hoping to do a few courses soon, hopefully the Rob G one!
Also as a side note I may be moving onto a 4WD soon. As everyone says they handle really well what is difference in driving style compared to RWD, advantages, disadvantages? Thanks for all the advice.
Almost all rear wheel drive cars will understeer under gentle acceleration with tight lock on. The tight lock introduces excessive camber due to the effects of castor. The gentle acceleration produces a tendancy to understeer due to a subtle interaction between weight transfer and the grip circle of the driven wheels. This will be masked or exagerated by the car's inherent oversteer/understeer charactistics, but if it's going to understeer anywhere this is when it's most likely. How big the 'understeer' region is depends on various factors such as the amount of grip available, and the weight distribution of the car. It tends to be more prominent with more powerful cars because they tend to be set up with a general tendancy to understeer, to reduce problems with power induced oversteer.
If you have enough torque available you can usually drive through the understeer, but you need to be on the look out for a sudden transition to oversteer combined with lots of lock putting you into a spin.
If you have enough torque available you can usually drive through the understeer, but you need to be on the look out for a sudden transition to oversteer combined with lots of lock putting you into a spin.
xanderjones said:
Also as a side note I may be moving onto a 4WD soon. As everyone says they handle really well what is difference in driving style compared to RWD, advantages, disadvantages?
main advantage is traction, and lots of it - unless it has a lot of power wheelspin is something that just won't happen in anything close to straight lines. In general 4wd will understeer more on the limit than RWD (though dependent on car, setup etc), try to trailbrake a bit to transfer more weight onto the front tyres for turn-in, and once its turned in get on the gas.
The main generic rule for 4wd, especially on loose/slippy surfaces, is 'when in doubt, power out' - if you get a 4wd out of shape (which takes some doing, theres a bit of a knack to it), the best way to recover it is to point the front wheels where you want to go and keep your foot on the gas. Lifting off will tend to destabilise the car (which you can use to get the tail out), they are at their most stable under acceleration. If you get in a big slide, remember not to wind on as much opposite lock as you would with a RWD and wind it off as you feel the power start to lose the battle with grip, as its quite easy to snap them back the other way very suddenly and violently when the front wheels regain traction.
www.pistonheads.com/gassing/topic.asp?t=307606&f=18&h=0 has a video and discussion of someone doing this at a track day in an Impreza STi.
In general though 4wd cars are very easy to drive fast, they seem to do most of the work for you and the challenge is getting them out of shape in the first place rather than avoiding it. What car/s are you considering? as different 4wd systems do behave differently.
BliarsGoing said:
Think of where you were, entering a roundabout just at the point where you turn? If so it was diesel on the road. That's just a bikers perspective but I'll bet I'm right
Definetly wasn't diesel. My old man's got a Kwak 600 and round by me there are a few haulage yards that did spill diesel on the road (Not so bad know). Been on the oily stuff (car and bike) and it's not pleasent. One time it was all over the road, even on the straight up a hill I couldn't get traction. It was like trying to drive up a frozen waterfall!
GravelBen said:
In general though 4wd cars are very easy to drive fast, they seem to do most of the work for you and the challenge is getting them out of shape in the first place rather than avoiding it. What car/s are you considering? as different 4wd systems do behave differently.
Will be getting an Impreza P1. Love the sound and the UK setup suspension. But please no comments about being a chav or blown bottom ends, I've heard it all before!
the "standard" response on the road to any kind of loss of grip is to remove the cause - normally excessive braking or excessive throttle. Also steering into the skid helps to regain traction.
In the case of rwd into a roundabout understeering, then that's often an entry speed too high. In most mild cases then easing off sorts it out. You can also try de-clutching although it's not a technique I particularly like. I have used it on the skid pan and it seems to work.
Converting understeer to oversteer is not a particularly sensible road technique and can be quite hard to do. In my caterham, the application of power wont do it (not enough), so you have to de-stabilise the car more (lift off and back on the power or even lift and hit the brakes before the power). In my TVR it has the power, but the switch from under to over is very hard to catch!
Regarding 4wd, I have driven 2 generations of subaru and an evo and they were all very different on the limit, but all much more reticent (in different ways) to get to a limit in the first place!
Graham
In the case of rwd into a roundabout understeering, then that's often an entry speed too high. In most mild cases then easing off sorts it out. You can also try de-clutching although it's not a technique I particularly like. I have used it on the skid pan and it seems to work.
Converting understeer to oversteer is not a particularly sensible road technique and can be quite hard to do. In my caterham, the application of power wont do it (not enough), so you have to de-stabilise the car more (lift off and back on the power or even lift and hit the brakes before the power). In my TVR it has the power, but the switch from under to over is very hard to catch!
Regarding 4wd, I have driven 2 generations of subaru and an evo and they were all very different on the limit, but all much more reticent (in different ways) to get to a limit in the first place!
Graham
xanderjones said:
Will be getting an Impreza P1. Love the sound and the UK setup suspension. But please no comments about being a chav or blown bottom ends, I've heard it all before!
No comments like that from me, I'm on my third Subaru now - just slow practical wagons though, the upgrade to STi-RA turbonutterism has been put off at least until I finish uni. Subaru 4wd systems don't really have any nasty surprises like sudden torque transfer, theyre pretty neutral with a 50/50 split in most (STi type R and RA are 64/36, not 100% sure on P1 though - does it have the adjustable centre diff?) Best way to get used to 4wd handling tendencies is to play with it in a wet paddock, then allow for a bit more understeer on grippier surfaces where the power isn't enough to help the tail out as easily.
Oh.....and scandinavian flicks are
GravelBen said:
Subaru 4wd systems don't really have any nasty surprises like sudden torque transfer
Oh yes they do! The Subaru 4wd systems produce different results in different guises. I had 3 years in a P1 and it was pretty sublime. It's predominant characteristic is understeer (there is a classic mod from the likes of Powerstation to dial it out). When understeering unless you take drastic action to unsettle the car, your only course of action is to back off and it tucks nicely in. However it can oversteer on the entrance to faster corners if the entry speed is too much. The only course of action there is to remove the steering input with opposite lock, and get the weight backwards once it all comes together again with a bit of gas.
The MY06 wrx sti (which I ahevn't owned but driven) is entirely different. In the circs where push on understeer happens, if you push a bit harder it pretty easily snaps to oversteer. It gave me the impression of being quite oversteery which might make it fun, but takes away the sense of having a 4wd on the road certainly.
I also drove a MY05 Spec C (litcho imports) which I didnt drive in an environment that was sensible to test (my) car control but gave the impression of being razor sharp and pretty adjustable in all respects!
And last but not least (and not relevant to subarus), the 4wd drive system in my Evo 8 was completely unfathomable and astoundingly good. I couldnt really work out what was going on, but it sorted it all out. You only had to think of the direction you wanted to go and it threw you that way! However, because I couldnt really work out what was going on it was ultimately not very rewarding.
I am now back to TVR rwd power which is very simple! Never, never, ever press the rh peddle unless it is dry and you are in a straight line!
Better do some work now.
Graham
PS absolutely no road traffic laws or byelaws were harmed during the course of this research! Seriously, all my hooning actually does take place on tracks and airfields.
gridgway said:
The MY06 wrx sti (which I ahevn't owned but driven) is entirely different. In the circs where push on understeer happens, if you push a bit harder it pretty easily snaps to oversteer. It gave me the impression of being quite oversteery which might make it fun, but takes away the sense of having a 4wd on the road certainly.
I also drove a MY05 Spec C (litcho imports) which I didnt drive in an environment that was sensible to test (my) car control but gave the impression of being razor sharp and pretty adjustable in all respects!
I haven't driven any of the newer ones, but an 96 STi RA V-ltd was the best to drive that I've experienced - no hint of understeer at the point I was pushing it too, which when I looked at the speedo turned out to be comfortably at least 20kph faster through most corners on one of my 'test' roads than any other Subaru I've driven through there. It did get the tail out much more easily, still completely controllable though, and great fun. The DCCD (driver controlled cenre diff) equipped cars all understeer less than the regular 50/50 cars though
and I think the 05/06 STi's are DCCD. By nasty surprises, I was thinking more of the Nissan ATTESA systems, which shuffle torque front-to-rear where they think it's needed, and on the older cars sometimes get it wrong - in the snow a while back in a mates Stagea, the right rear wheel bit through the snow into the gravel beneath (while the car was a bit sideways under power), the ATTESA computer detected more grip there, transferred torque to the rear, and the car neatly torpedoed itself into a bank. Not so much fun, but not aproblem I've ever experienced with Subaru systems. The Evo's I believe actually shuffle torque from side to side from what I've heard, giving a quite unnatural feel (never driven one though).
GravelBen said:
The Evo's I believe actually shuffle torque from side to side from what I've heard, giving a quite unnatural feel (never driven one though).
They do indeed and make quite a noise doing it. The problem is that the feel doesnt make sense even though it is fantastically effective. I guess that as clever electronics and control systems get into more and more use, it will be hard for manufacturers to make cars where the handling makes sense to the driver.
The standard things that fwd, rwd and 4wd cars do will become less and less standard.
Graham
I've had and E36 320 and it also understeered chronically. It was obvious that the 205 tyres on it were too wide and also the front anti-roll bar was too hard. The E36 suspension set up need softening at the front, with smaller diameter anti-roll bar and softer springs & dampers. This will cure the understeer.
Re- coverting understeer to oversteer- I do it regularly in my MGB and it usually takes two lanes (ie roundabout) to pull off. Its feasible but not reccomended unless you're sure you can do it within your skill/space boundaries.
Re- coverting understeer to oversteer- I do it regularly in my MGB and it usually takes two lanes (ie roundabout) to pull off. Its feasible but not reccomended unless you're sure you can do it within your skill/space boundaries.
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