320 reducing understeer

[kipsy]

Hi guys, my 320 coupe understeers at the moment so I'm on a bit of a mission to make it handle better. The first things I've fitted are some h&r -35mm lowering springs with Bilstein b8 shocks. The ride is quite compliant and handles reasonable but still understeers. The car has Goodyear tyres with the standard 205 55 15s. It grips well but will understeer when pushed. Today I have fitted eccentric lollypop bushes (powerflex) whic was all done in around 2 hours. Quite an easy job didn't even have to take wheels off etc. The tracking was then set to 0. Took the car on a small test run to see the results. The car turns in more positive and I think is a nice improvement for the £55 paid. I don't think it's totally eliminated the understeer though but it seems to have helped.
My car isn't fitted with a rear antiroll bar so I'm in the middle of purchasing one and I'll put my results/thoughts up once I've bought it and fitted.
This is just a bit of info I thought people might be interested in if they have similar issues.

[ACJJ619]

Understeer and oversteer are about the balance of grip front/rear, not overall grip.

Understeer can be reduced by either increasing grip at the front, or reducing it at the rear. In your case it sounds like you've got a reasonable set up already so minor adjustments to the front aren't likely to suddenly give you a tonne more grip and lessen the understeer, so I would look at balancing out the rear.

First of all, what diff are you running? An open diff typically understeers whereas an LSD will allow more oversteer.

Installing the rear ARB should help lessen the understeer as stiffening up the rear will probably actually reduce grip a little there.

Tyre pressures aren't to be sniffed at. They're often under-appreciated. What are you running? Try increasing the rears.

[Motorhole]

Understeer and oversteer are about the balance of grip front/rear, not overall grip.

Understeer can be reduced by either increasing grip at the front, or reducing it at the rear. In your case it sounds like you've got a reasonable set up already so minor adjustments to the front aren't likely to suddenly give you a tonne more grip and lessen the understeer, so I would look at balancing out the rear.

First of all, what diff are you running? An open diff typically understeers whereas an LSD will allow more oversteer.

Installing the rear ARB should help lessen the understeer as stiffening up the rear will probably actually reduce grip a little there.

Tyre pressures aren't to be sniffed at. They're often under-appreciated. What are you running? Try increasing the rears.

I used to have a 320i too, completely OEM. That also had a tendency to understeer when pushing on.

With regards to an LSD - it will only aid oversteer when the limits of grip at the rear are breached and both wheels can spin (break traction) at the same time. In a RWD car, when locked up and with the wheels gripping, (at least, a 2-way), an LSD will increase the tendency for understeer. A diff that is open upon braking and turning will not induce understeer - however some lock up under hard braking helps keep the car stable, hence why a 2-way diff is desirable. In short, an LSD won't fix your issue!

Tyre pressures are worth playing with. There will be a sweet spot, somewhere, where the sidewall flex is sufficiently minimised to keep the contact patch stable under load whilst not compromising too much the pliancy of the tyre. This will vary from car to car, from tyre to tyre and across wheel sizes, so find what works for you. For road use on road tyres, I've often found about 10% above recommended pressures (on the front) to be a good starting point. Also as already suggested, playing with the camber (using adjustable camber plates) might also help.

I'd suggest it would be bad practice to change the balance of the car by reducing overall grip, so I wouldn't suggest reducing grip at the rear. However fitting a rear ARB could help control weight transfer a little more and help turn in. I don't think 320i's came fitted with one from the factory, but somebody else will be able to confirm whether they did or not.

For me though, the biggest help is, before making any changes, learn to drive around the faults first! Then you'll understand and appreciate any changes more. By staying on the brakes into the corner and on turn in, you'll keep weight over the front tyres for longer, increasing front end grip. Make your apex further round the corner and get on the power later, as getting on the power too early will make the car tend to understeer, if you don't have enough power to break traction.

As an additional note - although it won't technically affect the balance of your car - if you're still on an E30 steering rack, a 3-turn E46 '067 rack will increase feel and responsiveness no end!

[ACJJ619]

Understeer and oversteer are about the balance of grip front/rear, not overall grip.

Understeer can be reduced by either increasing grip at the front, or reducing it at the rear. In your case it sounds like you've got a reasonable set up already so minor adjustments to the front aren't likely to suddenly give you a tonne more grip and lessen the understeer, so I would look at balancing out the rear.

First of all, what diff are you running? An open diff typically understeers whereas an LSD will allow more oversteer.

Installing the rear ARB should help lessen the understeer as stiffening up the rear will probably actually reduce grip a little there.

Tyre pressures aren't to be sniffed at. They're often under-appreciated. What are you running? Try increasing the rears.

I used to have a 320i too, completely OEM. That also had a tendency to understeer when pushing on.

With regards to an LSD - it will only aid oversteer when the limits of grip at the rear are breached and both wheels can spin (break traction) at the same time. In a RWD car, when locked up and with the wheels gripping, (at least, a 2-way), an LSD will increase the tendency for understeer. A diff that is open upon braking and turning will not induce understeer - however some lock up under hard braking helps keep the car stable, hence why a 2-way diff is desirable. In short, an LSD won't fix your issue!

That's the idea - you give it enough on the loud pedal that the rear tyres get close enough to the limit to corner tighter

It all depends where the understeer is. There are many parts to a corner, but essentially it boils down to three parts - entry, apex and exit. Where are you understeering, Kipsy?

[kipsy]

Thanks for the replies. I've sourced a 1.9 z3 rack and will be fitted shortly. The car has a standard small case lsd. It actually locks quite well to my surprise for 150k miles. The b8 suspension on the h&r springs is actually quite comfortable. A few months ago I sold my e30 325 rally car which handled beautifully to be fair. That had eccentric lollipops, m3 top mounts, full polybushes, challenge bilsteins and matching eibachs, z3 rack etc. The car was a pleasure the drive and was very well balanced where understeer was never a problem. I don't want to turn my current car into a rally car with a solid ride and rattles etc etc. But I would like it to drive a little more like it where for instance if going around a corner and the front end starts to brake away then giving it a little more throttle would transfer the weight to the back to reduce the understeer rather than induce it.
Thanks for all the replies guys much appreciated.

[kipsy]

Currently running about 33 psi all round on the tyres too.

[ACJJ619]

It all depends where the understeer is. There are many parts to a corner, but essentially it boils down to three parts - entry, apex and exit. Where are you understeering?

Also, what type of LSD is it? I don't think all LSD's suffer the understeering issues, such as a Torsen for example.

Try creating a differential between the front/rear pressures. If it were me, I'd go to 35psi on the rears and see how that feels.

I've not driven a 320i but wasn't the issue with those being that they had all the weight of a 6cyl lump in the front but with none of the power benefit of a 6cyl. It may just not be gutsy enough to utilise the LSD capabilities.

[kipsy]

sorry lots of replies-lots to reply too a˜‰. The car understeer for example roundabouts. About 40mph around a quiet roundabout if the Throttle is applied the car will accelerate and gradually the front end will push out wide. There isn't a lot of immediate 'shuv' from the 2.0 to transfer the weight to the rear to induce the oversteer. I'm not really into 'clutch kicking' to upset the rear of the car to induce oversteer. My 325 used to just apply more throttle around corners and gradually the rear would let go instead of the front.
Little picture of my old car just for the hell of it

[ACJJ619]

Okay, and if you're going round a roundabout and you suddenly give it full beans, will it understeer then too?

It sounds like you just need to reduce the rear grip. It's pushing your car forwards and it's far easier to reduce rear grip than increase front grip. Pump up the rear tyres and get back to us.

Also that rear ARB should help.

[kipsy]

Cheers. Still awaiting a response on the rear antiroll bar but I will get one and write down my results. The car will push on as not loads of go to get the rear to step out. I enjoy experimenting with stuff so I'm sure I will get there eventually!
Cheers

[ACJJ619]

Let us know either way!

[kipsy]

Update-fitted standard touring rear anti roll bar today with the used bushes and mounts it came with. The car now turns in better again and when accelerating around a tight corner (eg a roundabout) the back end will eventually brake out (not a great deal of bhp in the 320) and it will even hold a small drift until it runs out of power a˜Š.
I would recommend fitting a rear anti roll bar if you don't already have one fitted guys. Plus it only cost me £30 posted so can't fault it for the money.
Next mod is to fit the z3 rack and probably going to change the tyres once worn for 195-50-15s for a little less grip and better feel through the wheels with smaller sidewalls. Won't be for a while though as got a fair bit of tread left in the good years.
Cheers