Can someone look at their 87 or 88 S4 for me?
02-06-2007, 05:06 PM
#31
Fleet of Foot
Rennlist Member
Rennlist Member
Heinrich, I have never advocated overinflating tires. The pressure listed on the sidewall is the COLD pressure, as I am sure you are aware. As I stated before, a pressure increase due to heat/friction is built into that. Why don't you ask Good Year about that one? 
Running a tire at it's max listed pressure is STILL within specifications and there is no safety issue there.
As for the mounting psi, that has to do with the unusual stress a tire is put under when being mounted and has nothing to do with operating conditions.
Different tires have different specs, YMMV!
Running a tire at it's max listed pressure is STILL within specifications and there is no safety issue there.As for the mounting psi, that has to do with the unusual stress a tire is put under when being mounted and has nothing to do with operating conditions.
Different tires have different specs, YMMV!
02-06-2007, 05:10 PM
#33
Administrator - "Tyson"
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Originally Posted by Bill Swift
Why don't you ask Good Year about that one?
If my 79 gets anywhere near 40psi in the rear, I might as well be on marbles. This is on 17" or 18" wheels.
02-06-2007, 05:11 PM
#34
928 Collector
Rennlist Member
Rennlist Member
Answer the question Bill. WHY do you advocate higher pressure on the rear of your Porsche 928 with 50/50 weight distribution than the front? And while you're at it go ahead and read the words written by Good Year. They are the ones who emphatically capitalised the words "NEVER EXCEED THE MAXIMUM INFLATION PRESSURE LISTED ON THE SIDEWALL OF THE TIRE."
02-06-2007, 05:15 PM
#36
Fleet of Foot
Rennlist Member
Rennlist Member
Originally Posted by heinrich
VERY weak answer Bill.
Your car has 50/50 weight distribution. Other than BLINDLY reading and following the sticker on your 25yo car, please explain in logical terms WHY you think you need more pressure in the rear of your 928.
Your car has 50/50 weight distribution. Other than BLINDLY reading and following the sticker on your 25yo car, please explain in logical terms WHY you think you need more pressure in the rear of your 928.
How is it you feel you know more than Porsche about the requirements of the cars it builds? They've been doing this a few days now, I respect they're judgement and history.
H, the 928 has a static 50/50 distribution AT REST, in motion, that changes. Tell me how much your car weighs in the front under braking, for instance?? There are many dynamics affecting the way a car handles and weight distribution is just one of them. The 928 is a heavy car, I am sure Porsche took this into consideration when they began dictating what tire pressures should be, for instance.
02-06-2007, 05:18 PM
#40
928 Collector
Rennlist Member
Rennlist Member
Originally Posted by Bill Swift
Heinrich, I have already explained why, twice now. Go back and read up.
How is it you feel you know more than Porsche about the requirements of the cars it builds? They've been doing this a few days now, I respect they're judgement and history.
H, the 928 has a static 50/50 distribution AT REST, in motion, that changes. Tell me how much your car weighs in the front under braking, for instance?? There are many dynamics affecting the way a car handles and weight distribution is just one of them. The 928 is a heavy car, I am sure Porsche took this into consideration when they began dictating what tire pressures should be, for instance.
How is it you feel you know more than Porsche about the requirements of the cars it builds? They've been doing this a few days now, I respect they're judgement and history.
H, the 928 has a static 50/50 distribution AT REST, in motion, that changes. Tell me how much your car weighs in the front under braking, for instance?? There are many dynamics affecting the way a car handles and weight distribution is just one of them. The 928 is a heavy car, I am sure Porsche took this into consideration when they began dictating what tire pressures should be, for instance.
I so not FEEL anything Bill. I KNOW that the 928 actually needs MORE pressure in the front than the rear because the rear is the part that swings out like a pendulum. You are an autocrosser, you should know this. Your reply is therefore:
"Because Porsche put it onto a sticker back in 1976" ... crect?
I KNOW I know better than that sticker Bill. From experience. And from logic. And from the danger sign on the sideewall of my tyres.
02-06-2007, 05:23 PM
#42
928 Collector
Rennlist Member
Rennlist Member
Weight transfer ovccurs forward far more severely than rearward, meaning that the 928 actually needs more forward tyre pressure. This is .... wait
THIS IS WHY PORSCHE PUT THE WRONG PRESSURE ONTO THE 928's STICKER .....
Because the 911 needs that exact pressure
and the rear hosts the engine. Makes a lot of sense in a 911. No sense in a 928.
THIS IS WHY PORSCHE PUT THE WRONG PRESSURE ONTO THE 928's STICKER .....
Because the 911 needs that exact pressure
and the rear hosts the engine. Makes a lot of sense in a 911. No sense in a 928.
Bill
02-06-2007, 05:24 PM
#44
Fleet of Foot
Rennlist Member
Rennlist Member
Originally Posted by heinrich
Well apparently there IS more. Nkay ....
I so not FEEL anything Bill. I KNOW that the 928 actually needs MORE pressure in the front than the rear because the rear is the part that swings out like a pendulum. You are an autocrosser, you should know this. Your reply is therefore:
"Because Porsche put it onto a sticker back in 1976" ... crect?
I KNOW I know better than that sticker Bill. From experience. And from logic. And from the danger sign on the sideewall of my tyres.
I so not FEEL anything Bill. I KNOW that the 928 actually needs MORE pressure in the front than the rear because the rear is the part that swings out like a pendulum. You are an autocrosser, you should know this. Your reply is therefore:
"Because Porsche put it onto a sticker back in 1976" ... crect?
I KNOW I know better than that sticker Bill. From experience. And from logic. And from the danger sign on the sideewall of my tyres.
02-06-2007, 05:24 PM
#45
Addict
Rennlist Member
Rennlist Member
Thread Starter
Join Date: Aug 2003
Location: Lake Tahoe, Ca
Posts: 749
Likes: 0
Received 0 Likes
on
0 Posts
I think everyone must remember that in 1988 tires were a lot different than they are today. What started this thread is that I have changed the size of tire on my ORR car and wanted a starting place for air pressure at various speeds. I won't try to second guess why Porsche rated the pressure they did it 1988 but they did it in conjunction with the tire manufacturer.I would also venture to guess that there are no 1988 928's around that still are shod with original tires, original sizes perhaps but not the tires that were produced in 1988.
So this is the info Michelin gave me about my new tires as cross referenced from the ORIGINAL manufacturer data. Tires are PS2's in 245/45/18 (Y) 26.7" front and 275/40/18 (Y) 26.6" rear .
Speed Front Rear
0-143mph 32 30.5
143 -149 33.5 32
149-155 35 33.5
155-161 38 36.5
161-170 39.5 38
170-???? 39.5 38
Personally I would not run the tires that low at the 0-143 mph speed, but that is my decision. Michelin says it's OK. I'm quite sure that Michelin would not have given the same recommendation in 1988.
So this is the info Michelin gave me about my new tires as cross referenced from the ORIGINAL manufacturer data. Tires are PS2's in 245/45/18 (Y) 26.7" front and 275/40/18 (Y) 26.6" rear .
Speed Front Rear
0-143mph 32 30.5
143 -149 33.5 32
149-155 35 33.5
155-161 38 36.5
161-170 39.5 38
170-???? 39.5 38
Personally I would not run the tires that low at the 0-143 mph speed, but that is my decision. Michelin says it's OK. I'm quite sure that Michelin would not have given the same recommendation in 1988.