Tahoe Shark

I need to get the factory recommended tire pressure listed on the car for the original 16" wheels and tires. Front were 225/50/16 and rears were 245/45/16. I would look at my own but it is not here. It's probabaly on the inside of the door sill or the inside of the gas tank flap. Can someone help me out and post the original factory recommendations for the front and rear.

daveo90s4

36 front, 44 rear, from 1990 S4 owner's manul. It seems from my Rennlist reading that the general view is that 44 in rear is too high (but neceesary to keep rear tyre pressure warning lights off, if that sub-system has not been disconnected).

HTH

Tahoe Shark

Thanks, that is all I needed.

heinrich

Tim as you may know we do not recommend you actually attempt such insane pressures.

Tahoe Shark

I would never do that H, I need the stock pressure so Michelin could do a conversion for my new tires to be used in ORR this year. They require the original size, pressure, weight and distribution as well as speed. Just talked to them and I'm good to go. Thanks for the heads up though.

Bill51sdr

Why?

daveo90s4

44lbs in the rear tyres leads to premature tyre wear. They handle better with less than 44lbs. The ride comfort is better with less than 44lbs. The possibly cynical view is that Porsche just specified much the same for the back of the front engined 928 and they specified for the back of the rear engined 911, using the same sensor parts and so on.

Interesting that the rear tyre pressures for the 17" GTS rear tyres is lower than for the 16" S4 tyres, at 36lbs as I recall (?), and the pressure sensors are different for that reason. Maybe by 1993 Porsche realised that 44lbs in the rear was too high?

I've got 18" wheels on my car (ET60 in front, ET50-something rear) and I run them at 34lbs all round and that feels about right.

Cheers

Bill51sdr

They have specified 44 psi for the rear on 928's prior to the sensors you refer to, my '86 did. Yes the rears wear prematurely in the middle due to this pressure, hence I have lowered mine to 40, but anything lower than that makes the tires feel like they are squirming under high lateral loads, at least to me, an effect that does not inspire confidence. I have a feeling the pressures were lowered on the 17's due to the lower aspect ratio of the tires, and the additional pressure was not needed. As I said in another thread, most companies designate pressures for ride comfort, not performance. Porsche seems to be among the very few that do not do this.

heinrich

Tyre wear is nothing IMHO. SAFETY and HANDLING. There is no chance that 44 or even 40 in the rear or in any tyre for that matter on a 50-50 balanced 3500lb car can be acceptable. Corvettes are basically American 928's and the recommended pressures there are 30 - 32 and some will run as high as 34. I have owned many 928's and my personal preference is 31 - 33 aka 32. Higher that that in the rear and you will absolutely be in a dangerous situation.

Bill51sdr

H, Corvettes run with 18-20" wheels/tires, hence my comment about the aspect ratio. You can run lower pressures in those tires with minimal sidewall flex. The 45 & 50 series tires Porsche installed on the 16" rims are a different story.

Bill51sdr

How I have lived as long as I have at 44 psi is beyond me!!

C'mon H, do you honestly believe Porsche, or any othe manufacturer (Ford a possible exception) would recommend an unsafe specification and willingly deal with the legal ramifications? I have experienced no problems running at these pressures, other than the tire wear, and I have been driving 928's for 13 years.

Shane

I used to run 34 in mine all the way around, and this was just fine for sedate driving. But when I check tire pressures after some spirited driving, they were up around 38psi, even more when I was running at the track. So now I drop them to thirty when I know I'm going to put a lot of heat into the tires.

Bill51sdr

BTW, a E36 M3 I owned had tire pressure specs at... wait for it...




36 F, 44 R.




No mayhem on the roadways that I know of yet!

Bill51sdr

Um H, they are talking about pressures right around where you run yours. Your point?

I don't see anyone stating they are having any safety issues and in fact, some of them are dramatically increasing pressures in the interest of economy and handling.

Lexus is a manufacturer that I would definitely consider to be in the "for comfort" category.

Bill51sdr

M3's and 325/328's have different tire pressure specs, hence the confusion.

Still don't get your point H. You're proving mine very nicely!