rickjaffe

ok I looked over the tires

front: michelen radial x, 235/35/zr/19 91Y (don't know what 91 Y is
rear: michelen radial x 315/25/zr/19 98Y

tread: there is a noticible difference between the tread wear. of course the rears are new.
the front tread are maybe half. obviously difference in the depth of the groove and the tread wear bar is considerably closer to the tread. maybe half, maybe alittle more than half.
is there a way to check out if that's the problem or is there a rule of thumb in a four wheel drive porsche as to when all four tires have to be replaced.

also, it's not just about the psm coming on is it? the mismatched groove depth/tire wear between axels is reduces grip all around and would right, but I would think could surely cause psm to come on because the fronts are holding the same grip as the rears.

I did the canyons about 300 miles after I picked up the car and that should be enough time to break in the rears, right? also the tires were warmed up, when the psm kept coming on. had driven probably 70 miles on the highway before the canyons.

rickjaffe

checked again. they are ps2's but I didn't see an N marking on any of them

also, I think I was engaged in wishful thinking, wear bar on the fronts are pretty close to the top. have some left but more or much more than half. I guess that's the most logical cause right?

wross996tt

Sunset Parts discounted from Renntech Yes you get the blank and then program it with PST2 or PIWIS. You will need the IPAS codes to do this (from Porsche or a dealer). With the codes and the tool, anyone can program it.

The age of the tires is not the problem. If the rotating diameters are different sizes, then you will have an issue.

rickjaffe

I called tire rack to get some info.

michelin doesn't make an N 315/25/zr/19, that and the fact that I don't see an N on the tires leads me to believe that they are not N.

as to the front. michelin currently only makes (according to tire rack) an N 235/35/zr/19, they used to sell an non n but they've been discontinued.

so if I'm going to stick with ps2's, I'm going to have to get N's and will have non N's on the rear. The guy told me there's no way to know if there is any difference between the N and non N, porsche might have required some small changes, but that info is proprietary.

would rather not replace all four tires since the rears are brand new.
thoughts?

"02996ttx50

yes, it has been known to trigger the abs/psm cels but only until the ecu adapts. it's a senstive system, and once the rears are scrubbed in the cels shopuld stop. it's common, which is why i asked. no, you don't need to swap four at a time.

rickjaffe

thanks, not concerned about the age, it's the wear, the fronts are most worn
maybe 20% tread left to the wear bar. would that big of a difference create psm coming on, I guess because there's much more grip in the rears because they're new have have deeper grooves? or would that just be relevant in rain?

the ps2 are 350 each. the supersports are on 250, and ore supposedly a newer and much better performing tire. maybe I should just swtich to supersports and sell the two new rear ps2, but the superspots are not N.
how big of a deal is it not to have N tires????

wross996tt

see here for N rating Many folks use non-N rated tires. I would not be concerned with N vs. non-N. I would be concerned if the rolling diameters are >2-3% different.

rickjaffe

rolling diameters? don't know what that is.

I'm going to find some place to make some sharp low speed turns and test it out more, with and without psm. funny did just a few turns alittle while ago and it seemed better, but just 90 degree turns not the twisties like at topanga.

about to call the closest porshe dealer (niello) to see what they want for the key.

seemed like one way or the other, you have to pay 170 for the innards and pay 130 for programing and you have to pay for the actual key. so it seems hard to do it much under the 450 quoted.

rickjaffe

NEXT QUESTION:

how do I find out my key number. I have a porsche gt key and there's no number on the outside. Is in the inside? or in some manual?

John 996 TT Cab

You shouldn't be mixing PS2's and Supersports anyway. Different compounds and different side wall specifications. Tire make/model needs to be the same on a Turbo. You can check rolling diameter information on Tire Rack's site. If more than 3% difference you run the risk of destroying front differential or whatever it's called.

rickjaffe

fyi: sonnen porsche will do a key for around 250. they have a key cutting machine which alot of dealers don't have. that's a good enough deal for me.

rickjaffe

I'm not sure what rolling diameter is, but unless it has to do with the difference between the amount of tread left between the tires on the two axels, I don't think it's relevant to my issue because it's my understanding the seller did not change the tire size of the rears. he just bought new tires of the same size.

the front and rears are both over OEM recommendations at 235 instead of 225 and 315 instead of 295. Is the concern that these dimensions regardless of the tire where might be a problem?

on a cursory look, looks like rolling dimersion is just some formula based on tire to wheel parameters.

rickjaffe

ok rolling diameter seems to be the measurement for a tire on the ground under load to the top of the tire.
so suppose a bald or almost worn tire would have a significantly less rolling diameter which could cause a problem. is that it?
if so, can I just take a tape measure and measure the tire diameter and make sure it's not more than 2-3 percent?

"02996ttx50

you should really begin by reading up on the countless threads on these topics with particular attention paid to the notion of "revs per mile" vis a vis the rolling diameters and tire size choice(s).

based upon your questions, i'm sure it will help you a lot. try a search in here and even a google search will bring you pertinent results. then you'll have a more basic understanding of the issues youre facing.

new rears against worn fronts will trigger abs/psm cels until they get scrubbed in and the ecu adjusts. if that is the issue causing the cels? they'll stop soon enough. i'll try it another way. yes, a worn set of tires paired with new ones will trigger cels. however, that is not relevant to the issue of keeping your rolling diameters within a few revs per mile as per the oem fitments in an effort to accomodate the demands of the awd and front differential..

here's an example of what you'll need to grasp. though this won't help as a guide since you run 19's. but perhaps you'll get the gyst of it.


the numbers to the right of the example illustrate the difference between front and rear measured in percentages. the time honored wisdom suggests that the differences in rolling diameters front to rear should not exceed 3 %.


Spec Sidewall Radius Diameter Circum Revs/Mile Difference
225/40-18 3.5in 12.5in 25.1in 78.8in 804 0.0%
235/40-18 3.7in 12.7in 25.4in 79.8in 794 1.3%
295/30-18 3.5in 12.5in 25.0in 78.4in 808 0.0%
315/30-18 3.7in 12.7in 25.4in 79.9in 793 1.9%

the 315 has a diameter of 25.5". The 295-30 is 25.1"

the 235- has 25.4", and the 225-40 is 25.1"

Melb-Mike

That's funny. However, after I sat in the "customer lounge", sipping on Starbucks coffee while munching on the "free" danish, I realized what "shop materials" really were. The irony of it all is if you don't enjoy their hospitality, you still pay for the shop materials. You always end up paying. ALWAYS.