Tires

[vision]

Had a question about tire pressure on sports cars. Just bought new tires for our Boxster and the side wall of the tires says 50 PSI. The tire guy said that 50 psi would cause the car to slide all over the road and fell every bump. So he put 30 PSI in it. What type of issue could this cause or is that better to put the 30 PSI?
They are 255/40 ZR17 size tires. What do you think?

[Ad Sach]

I use 33 front, 35 rear.

The 50 PSI on the tire is the MAXIMUM pressure, the manufacturer is indicating that if you go over 50 PSI the tire may explode.

The Boxster manual recommends 29 PSI in front and 36 PSI in the rear - with these pressures and stock suspension you will have fairly large understeer(front end slides in a straight line instead of turning around the curve if pushed too hard).

With 30PSI in front and rear you will have moderate oversteer (back end slides out like an old Camaro when pushed too hard in a curve).

Porsche is delivered with 205 int the front and 255 in the rear(17 inch wheels). If you have 255 in the front you are likely to scrape the front of your tires on body parts during hard bumps or hard cornering. If all 4 tires are 255 you also will have more oversteer - you probably have 205s in the front.


30 PSI is a little too low for good grip in most street tires.

My favorite pressure is 33 front and 35 rear as this seems to have very neutral handling (for S M030 suspension).

What kind of tire did you get?
Can you confirm you have 205s on the front?

[vision]

great information. yes they are 255 in the rear and 205 in the front. I have replaced the two back because someone rode on them with very very low pressure. it created a beed so they had to be replaced. I will replace the two fronts shortly.

[Alienz]

I have snw tires (Blizzaks) and haven't changed/replaced them yet. The steering wheel shutters while driving over 70 mph. Plus I think I need alignmet,the steering wheel is not straight (tilted to the right). My friend says the alignment got screwed up because of the the pot holes ( we do have so many of them around here). My steering wheel used to be straight and normal.

[Ad Sach]

vision,

I get 8-10,000 miles out of rear tires and 20-25,000 out of front tires. If I drove less aggressively thay would last longer, but it is reasonable to expect your front tires to last much longer than the rear.

Alienz,
you are going to extremes to save money there! I know Blizzaks are a lot cheaper than good summer tires for the Boxster, but you are leaving a lot of fun untouched if you don't buy your baby a set of summer shoes. A good 4 wheel alignment is about the cost of a single tire, and can save you an equal amount in wear on all 4 tires. I would definitely get an alignment ro protect my new tires - especially since you have 'symptoms'.

Your steering wheel is probably shuddering because some of those famous New England potholes knocked the balance weights off your wheels. A Hunter 9000 should be able to balance your tires flawlessly up to maximum speed. That said, I have yet to need to balance my snow tires - and I purchesed them used with one winter on them.