Staggered vs. Square setup BMW people here please

[Floydian]

Hi,

I think it's time I ditch the oem rft tyres. I am thinking of going for Goodyear Eagle F1 AS3 tyres.

My car current has style 383m rims (fronts 17x7,5 225/45R17 - rears 17x8 245/40/17)

I've noticed wear on the outside edge of the front tyres. I believe there are four possible setups I can go for with the same rims:

A. Factory staggered 225/45R17 fronts and 245/40R17 rears

B. 225/45R17 fronts and 225/45R17 rears

C. 235/40R17 fronts and 235/40R17 rears

D. 235/40R17 fronts and 245/40R17 rears.

What I want to achieve?

1. More controllable oversteer and less prone to snap oversteer.

2. Increase or maintain overall grip.

3. Less understeer.

I am totally confused which setup to go for. Any suggestions and comments welcome.

Thanks

 

[TinyVoices]

There are way more options than that and to achieve your desired handling characteristics you need to run a similar or taller sidewall in the back. I'd run a 40 front and 40 rear, 45 both as a well, or 40 front 45 rear. You want 1cm to 2cm more width in back than front. I'd be looking at a 225 front and 235/245 rear. Nothing else.

Source: daily drive and race toyota mr2s which are the most snap oversteer prone cars on the road.

 

[RooflessVW]

You won't decrease oversteer AND understeer at the same time. That's a bit of a tug of war.

Keep the OE sizes and buy the best tire you can afford. I would not run a square tire setup on staggered wheels - you still won't be able to cross rotate without dismounting tires.

 

[RooflessVW]

Originally Posted By: TinyVoices
There are way more options than that and to achieve your desired handling characteristics you need to run a similar or taller sidewall in the back. I'd run a 40 front and 40 rear, 45 both as a well, or 40 front 45 rear. You want 1cm to 2cm more width in back than front. I'd be looking at a 225 front and 235/245 rear. Nothing else.

Source: daily drive and race toyota mr2s which are the most snap oversteer prone cars on the road.

Gibberish. His sidewalls are more or less the same size now. 225/45R17 and 245/40R17 are within spitting distance depending on tire make and model. 225F + 255R would be identical diameter front and rear.

 

[TinyVoices]

Right which is why he needs to change to a setup that give a little more sidewall in the back. Even a couple millimeters more sidewall in the back than the front gives you much more rear stability on corner exit and entry in an FR car.

 

[Floydian]

Originally Posted By: TinyVoices
There are way more options than that and to achieve your desired handling characteristics you need to run a similar or taller sidewall in the back. I'd run a 40 front and 40 rear, 45 both as a well, or 40 front 45 rear. You want 1cm to 2cm more width in back than front. I'd be looking at a 225 front and 235/245 rear. Nothing else.

Source: daily drive and race toyota mr2s which are the most snap oversteer prone cars on the road.


Yep I've heard a lot about MR2's and snap oversteer on lift off etc still a very nice car although for experienced drivers.

The problem I have is the rear end not breaking (on gas) and mild understeer then suddenly breaking. The phase from mild understeer to oversteer is very sudden, my aim is to make it more linear without reducing overall grip.

How does increasing the sidewall can you explain further? Thanks

 

[TinyVoices]

More rear sidewall just allows small changes and even some big ones such as power application or braking to take place without upsetting the lateral grip of the tire in the corner. More sidewall in the rear vs the front allows for more fore and aft grip on the rear tires before the point of breaking loose occurs. Look at some pictures of race cars, and you will see a larger rear sidewall on rear wheel drive vehicles.

 

[TinyVoices]

More rear sidewall just allows small changes and even some big ones such as power application or braking to take place without upsetting the lateral grip of the tire in the corner. More sidewall in the rear vs the front allows for more fore and aft grip on the rear tires before the point of breaking loose occurs. Look at some pictures of road race cars, and you will see a larger rear sidewall on rear wheel drive vehicles.

 

[Floydian]

Originally Posted By: TinyVoices
More rear sidewall just allows small changes and even some big ones such as power application or braking to take place without upsetting the lateral grip of the tire in the corner. More sidewall in the rear vs the front allows for more fore and aft grip on the rear tires before the point of breaking loose occurs. Look at some pictures of road race cars, and you will see a larger rear sidewall on rear wheel drive vehicles.


I see. In this case which of the one of the above setups do you recommend?

 

[TinyVoices]

Of the setups you list there I would run option D if it was my car. The slightly wider rears and extra .2 inch sidewall will just be noticeable on turn in and exit and should balance the car a bit more.

The understeer will still present itself but that's easier to fix with swaybars than minute differences in tire sizes.

I'd also recommend better tires. Even in a less optimal size, better tires will make quite a difference.

 

[Mr Nice]

Originally Posted By: rooflessVW
You won't decrease oversteer AND understeer at the same time. That's a bit of a tug of war.

Keep the OE sizes and buy the best tire you can afford. I would not run a square tire setup on staggered wheels - you still won't be able to cross rotate without dismounting tires.


Yep. I agree.

 

[Egg_Head]

I'd start by checking the alignment and tire pressure from the tire manufacturer. Not sure if your car has a factory sports suspension but I'd make sure you and your alignment person are on the same page. My 540 has the sports suspension and staggered tires and my front tires wear on the outside edges, its the old "they all do that". I run Continental DW's and they spec 29/33 front/rear psi where BMW says 30/36 psi, running the Conti spec makes for slightly better wear primarily on the rears. Only suspension mod I have is M5 swaybars front/rear. I will let others speak to the understeer/oversteer dials to turn but by design a suspension that is set up to go through a corner with optimal traction will not give optimal tire wear when going in a straight line. If tire wear is a concern ditch the sports alignment setup.

 

[Floydian]

Originally Posted By: Egg_Head
I'd start by checking the alignment and tire pressure from the tire manufacturer. Not sure if your car has a factory sports suspension but I'd make sure you and your alignment person are on the same page. My 540 has the sports suspension and staggered tires and my front tires wear on the outside edges, its the old "they all do that". I run Continental DW's and they spec 29/33 front/rear psi where BMW says 30/36 psi, running the Conti spec makes for slightly better wear primarily on the rears. Only suspension mod I have is M5 swaybars front/rear. I will let others speak to the understeer/oversteer dials to turn but by design a suspension that is set up to go through a corner with optimal traction will not give optimal tire wear when going in a straight line. If tire wear is a concern ditch the sports alignment setup.


My car has M sport package with cancelled M sport suspension option from the factory but has Eibach springs. Alignment was checked recently and is to factory spec.

Tyre wear is of no concern. I absolutely hate the current RFT tyres anyway, they are setting concrete. Tyre pressures should be 32/33 according to bmw, but the rearrs are currently pumped up to 37.

 

[RooflessVW]

Originally Posted By: TinyVoices
Of the setups you list there I would run option D if it was my car. The slightly wider rears and extra .2 inch sidewall will just be noticeable on turn in and exit and should balance the car a bit more.

The understeer will still present itself but that's easier to fix with swaybars than minute differences in tire sizes.

I'd also recommend better tires. Even in a less optimal size, better tires will make quite a difference.

He needs to run a better tire and leave well enough alone. Right now he is over driving his tire by booting it in the middle of the corner like a teenager. Of course he has understeer transitioning into quick oversteer. He's on an AS tire and not driving the car properly.

 

[Floydian]

Originally Posted By: rooflessVW


I'd also recommend better tires. Even in a less optimal size, better tires will make quite a difference.

He needs to run a better tire and leave well enough alone. Right now he is over driving his tire by booting it in the middle of the corner like a teenager. Of course he has understeer transitioning into quick oversteer. He's on an AS tire and not driving the car properly. [/quote]

How do you reckon one can drive a car "properly"?

I have been karting since early age. I track my car on a former GP circuit occasionally. I don't stab the throttle in the middle of the corner if that's what you mean.
I am looking for a setup that will improve my track times and make the car easier (and thus more fun) at the limit. What's wrong with wanting advice on this?

 

[555]

Two separate and different handling aspects of a vehicle you may already know.
1. TTO = Trailing Throttle Oversteer. Your car is sensitive to this condition.
2. When your vehicle starts to oversteer without lifting your foot off the gas(opposite of TTO) you must apply throttle to control it. Even one millimeter more on the gas could be the difference between steady state oversteer or spin. Of course this means you have to approach corners with a different strategy.
I would buy some great tires but research their breakaway characteristics through magazine sites e.g. "Grassroots Motorsports" etc. TireRack reviews are okay but I'm focused on your track days and not
daily driving.
"TinyVoices" has some good info.
I would change one thing at a time. Better tires and a change in sizes and sidewalls could leave you wondering what made the difference. Plus we don't know if you track your car in the rain.
Last but not least, what track are you driving? Mont Tremblant? Paul Ricard? Jerez? Kyalami?

 

[Linctex]

Regardless of tire size,
I would be more concerned about the rubber compound.

Honestly, the unfortunate truth is if you want better grip,
you have to be willing to buy softer tires..... more often.

 

[jjjxlr8]

Your best option is A., sticking with the factory staggered sizing but going with non-RFT tires. The non-RFT will be more compliant and may help with the snap over steer.

 

[mightymousetech]

Step 1, get rid of run flats. God they are horrible, got rid of mine as fast as I could.

The only reason to go square is to save money, as the tires can be rotated.

Stick to the stock staggered size and put some decent rubber on there. Go from there.

What kind of car is this? 17's seem small.

Your outside wear on the front and corresponding understeer show a lack of front camber, which is true of pretty much every BMW built, even the M cars.

Just curious, how much track experience do you have? "snap oversteer" tends to require a driver mod, not a car mod, smooth is fast.

 

[MCompact]

I'd fit Michelin PSS tires in the OEM sizes.