Post by: pgackerman on March 22, 2017, 12:26:46 pm
While reading the latest issue of Fiero Focus I learned Pontiac changed tire pressure and the V6's HP (140 to 135 HP) in '87s & '88s to meet noise mandates.
What was the original recommended tire pressure? FYI, 30 psi on my '88 GT.
Post by: Drewbdo on March 22, 2017, 12:54:28 pm
Was the PSI also lowered for the noise mandate, or only the HP?
Post by: pgackerman on March 22, 2017, 01:00:59 pm
PSI was also lowered for the noise mandate.
Sticker on the door panel says 30 PSI.
Post by: Fierofool on March 22, 2017, 01:19:43 pm
The 86 and 88 coupe came with 14 inch tires and the 87GT and Fastback Formula had 15 inch tires, but inflation pressures are the same across the board.
I have heard that the horsepower rating was changed due to insurance ratings for the car. The 135 HP rating is actually at a lower rpm than the years that were rated at 140.
I normally run 35 psi in my tires, front and rear, and it seems to give me good tire mileage. I also do that to stiffen the sidewalls, reducing the flexing when taking hard curves. Too much pressure will balloon the tires causing them to run on just the center of the tread. That reduces traction. Reducing pressures will allow the sidewall to flex too much causing the tread to roll sideways in hard turns.
Post by: pgackerman on March 22, 2017, 01:26:50 pm
Have you noticed any differences other than cornering at 35 PSI?
Anyone with an '85 have different recommendations on their decal?
Post by: Fierofool on March 22, 2017, 01:47:58 pm
I've owned 2 85's but I don't remember what the pressure recommendations were. I always ran 35 in them, too. One had 14's on it as long as I owned it, but the other got converted to 15's. The 86SE is the same as the 85GT, except it has a 3rd brake light, so I wouldn't expect any difference in recommended tire pressures.
Post by: Fierofool on March 22, 2017, 02:27:14 pm
I have an owner's manual for the 1985 model year and it doesn't give a tire inflation pressure. It only says to refer to the door placard. It also says that there could be from 4 to 8 kilopascals increase in pressure after driving at highway speeds. Never heard that word before.
Post by: TopNotch on March 22, 2017, 02:50:16 pm
Place sheets of paper under your tires like in the picture, so that the sheets are tight against the tires. The distance between the sheets is your contact area. Higher pressure results in a smaller area.
I run 35 PSI rear, 32 PSI front, which gives close to equal contact all around.
ps. Yes, I know I need to get new tires.
Post by: scottb on March 22, 2017, 05:59:35 pm
Post by: Fierofool on March 22, 2017, 06:47:40 pm
We could sprinkle some flour around in the parking lot at the next RFTH and let people drive through it the night before to decide if they need to adjust tire pressures before the run.
Post by: GTRS Fiero on March 22, 2017, 06:51:55 pm
Post by: pgackerman on March 22, 2017, 08:13:00 pm
To see how much of your tires contact the road, do the paper test...
Place sheets of paper under your tires like in the picture, so that the sheets are tight against the tires. The distance between the sheets is your contact area. Higher pressure results in a smaller area.
I run 35 PSI rear, 32 PSI front, which gives close to equal contact all around.
ps. Yes, I know I need to get new tires.
Thought they were racing slicks...
Post by: GTRS Fiero on March 22, 2017, 08:19:58 pm
Post by: scottb on March 24, 2017, 07:48:10 am
I love those ideas. They verify how cheap us Fiero owners are. I'm sure there's a much more expensive way to get someone else to determine the best psi.
I prefer the term "frugal"
Post by: pgackerman on March 24, 2017, 09:51:01 am
FrugalFieros. Sounds like a website.