? Reduce understear w/ wider front tires

[WOODYBROWN]

I have an 06 550 w/ sport suspension. Tires are 275/35R18 rear and 245/40R18 front RFT's. I do not have specifics for the wheels, but they were standard from BMW with that package in 06.
I feel the car has too much understeer for me. I have been told that I could reduce this somewhat with wider front tires.
Is this correct? Are there specific tires that would also help? I was tending toward Michelins.
I do not want to replace the rims. The car came with a spare(!) and I can live without the runflats.
Any thoughts?

[wingspan]

Why can't you differentiate the tire pressures to effect the same thing?

BMW Engineers go through a lot of trouble to dial in the suspension settings to be safe over a wide range of conditions. I'm not convinced that widening the contact patch, on it's own, would achieve what you are looking for, without some other serious undesirable knock-on effect elsewhere.

I'm sure the resident track experts will weigh in, but increasing the tire pressure will, within limits, generally increase grip. So if you want to increase understeer (which I define as the front tire slip angle being higher than the rear tires), you can either increase the tire pressure at the rear (increase grip, reduce slip angle) or reduce tire pressure at the front (decrease grip, increase slip angle).

Track experts - have I got this right? :dunno:

[lukeeesteve]

My course of action would be:

1) Tire pressure
Re-evaluate
2) Sway bars
re-evaluate

The stiff run-flat tires might be a little harder to fine tune with tire pressure.

[ganseg]

I agree with the idea of wider front tires and/or narrower rear. When you drive it hard and well, are your front and rear using the same amount of the side of the tread? Usually there are arrows marking how far down the side of the tread you should come. I think 255/35 Michelin PS2s or Goodyear F1 GS D3s on the front would help a lot.