Tires for my 16 7+8's

[78Jason]

I have a few questions about replacing the tires on my 78 16's 7&8's: (and would like your opinion)

Facts:
- currently have Bridgestone S02's, and am up to 25k on them (reading other posts, I don't know how that is possible).
- have 205/55 and 225/55 (f&r)
- car is lowered - bump steer is going in this weekend.
- replaced my rear shocks - not the front (yet?) all are bils-std.
- strictly daily driver - 50/50 between street and freeway

1) I like the stickeness of the s02's. However, I have nothing to compare to... How 'stiff' are these compared to others, say yoko's, khumos, toyo... etc. I would prefer a softer (and cheaper) ride rather than having the high performance of s03's since i'm not too agressive - and since rain is minor here - that doesn't concern me.

2) how can I tell if my front shocks need replacing? do they last longer than rear's? I don't know when - if ever they were replaced. Rears were shot at 160k miles - would that have been 1st or 2nd (or more) set of shocks?

3) what sizes can I go with without having to adjust suspension/speedo? seems like 225/50's or 245/45's are more common than my 225/55 in the rear? how does the 50 and 45 numbers compare to my 55?

4) Porsche dealers won't change just 2 tires - only 4. However, all over this bbs I see some talking about doing just 2 at a time... is that safe? My fronts really need it because of a camber wear problem on the inside...(it wasn't aligned well for street when I got it and I drove it too long without adjusting)
Do I have to have a specific rating for insurance purposes?

5) will bump steer spacer change camber?

Thanks for revisiting this topic ad nauseum...

[masraum]

You should have 225 50 16 on the rear not 225 55 16

1 I have used the Bridgestone RE 730 and 750 on my car. I think the 750 (new replacement of 730) is softer than the 730 which I can only guess is softer than the S03 (they wouldn't want the step down to outperform the top rung)

2 If the backs were bad then the fronts are bad. I just replaced the front and rear on my car '88 with ~150K miles, they were original and in horrible shape.

3 Your best bet is 205 55 and 225 50 since those are stock sizes and will fit well on your wheels. Again, your current 225 55 are the wrong size anyway. You can fit the 245 45 which are virtually the same size as the 225 50's (just a hair shorter), but with the extra rubber you'll likely have more understeer.

The middle number is the aspect ratio, so the sidewall is equall to 55% of the width, so 55% of 225. If that first number stays the same, then the height of the tire changes, but if the first number changes then it will depend on the math. a 225 50 is about 25" and a 245 45 is about the same, but maybe a hair shorter.

4 You can change just two tires, but then you really should stick with the same make and model of tire. Changing to a different model of the same manufacturer even can make a huge difference and be quite scary.

5 Only changing the alignment or raising or lowering the car will change camber, bumpsteer kits won't.

[78Jason]

Thanks Steve.

Now if I put the correct 225/50 on the rear (why is 55 wrong?) that seems to me that my diameter will change - therefore causing a change in my speedo? Or will it be negligible?

[marcesq]

Jason:

The 225/55 is not the stock tire on your car. The 225/50 is so assuming that Porsche had the speedo set right to begin with, your speedo is off now because of the taller tire.

The 50 series tire will make your car slightly quicker because of the smaller diameter.

[masraum]

Generally the taller the sidewall the worse the handling (that's a gross generallization), so you would expect a tire with the same width to handle better with the shorter sidewall. Generally the shorter the sidewall the lower the load rating on the tire (on a tire of the same width ie 225 55 and 225 50), which is why you wouldn't necessarily go to a 225 40 (if you could find it). As Marc said, your speedo is probably already off due to your current tires being taller than stock (assuming it wasn't recalibrated) Generally the speedo is actually off a little anyway, so the difference is probably less than the amount that it is off from the factory.