jdana24

Originally my car, a 1968 Olds Cutlass S convertible, came with bias ply tires and the recommended tire pressure was 24 pounds. Currently I am using the BF Goodrich Radial TA P245/60SR14. The curb weight of the car is 3,364 pounds. According to BF Goodrich, they say that when installing a different size than the original equipment tire, all vehicle manufacturer specifications must be maintained. The replacement tire should be inflated to provide the same load capability of the original tire size at the manufacturer’s recommended pressure.

By looking at the car, it just seems that 24 pounds is low. Any thoughts on what tire pressure I should use would be appreciated.

oldcutlass

Yes, 24 is way low, I would run 28-30 as the max tire pressure with load is probably 32.

MDchanic

My habit has always been 28 front, 30 rear, but I never had the patience to experiment systematically.

- Eric

RetroRanger

I got a good tip a long time ago concerning tire pressures w non stock tires. take a piece of chalk and mark it across your tire treads front and rear. drive around the block look at the chalk marks only worn in the center is too much pressure let out a couple pounds and try again. I ussually start high and work my way down cuz I think that if the pressure is to low it will just wear all the chalk off

Im at 32psi all around on 245-15s

cutlass xombie

I worked in a tire shop for years back in the day and for a heavy car 30-32 is good. 24 is just going to ruin your tires.

jdana24

Thanks everyone for the input. I'll try 32 pounds and use the chalk trick and see how it turns out.

Allan R

A bias ply tire is completely different construction than a radial. If you put only 24 psi in a radial you'll overheat the sidewall badly and cause underinflation wear on the tread.

The tire sticker was based on tire production at the time the car was built. If you look closely at the tire, it will actually specify what the max tire inflation pressure is. You can go with a few psi lower for a smoother ride, but you should check the pressures periodically to make sure they are holding air properly. Most of the weight on these old cars was distributed closer to 60% front and 40% rear. So if anything, make sure your front tires are closer to the recommended pressure; you can back off the pressure a bit on the rear ones.

jadatis

Registered to this forum to give you info about how the tire-pressure-advice is calculated. Once got hold of the formula that the European tire-makers used for decades and the American since 2006.
Made spreadsheets for it, for wich I learned myself Excell first, and translated a few to English to go worldwide with it.
Because I dont have a classic car, I will not introduce myself in an opening topic.

The formula has a power in it, and this power is different for diagonal and radial tires. The lower the power the lower the pressure for a sertain load, or the other way around the more load for a given pressure.
For diagonal tires the power is 0,585 and for radial in Europe 0,8.
In America for normal radial car tires, wich you have ,before 2006 a power of 0,5 was used ( to calculate load for a sertain pressure) And the Ford/Firestone proved it to be wrong, to my opinion.
So even the advicepressures for old cars with radial tires where to low in America before 2006.

What does this mean for your car.
Calculate the needed pressure with my spreadsheet, with the power of 0,8. For this you need the GAWR ( gross axle weight ratings) wich are mostly on the same plate as de old advice-pressures, and the maximum speed.
From tires you need the maximum load and pressure at wich it is carried.
Or the kind of tire. If you see "max load xxxx lbs at yyy psi"then the yyy is the pressure you need. If only the maximum pressure is stated, the the kind of tire determines the needed pressure, reference-pressure it is called.
If you can determine the real weights on the wheels, for the situation you want to know the pressure for, then you can give "your own imput" to get a better pressure for that use.

https://skydrive.live.com/?cid=a526e...E092E6DC%21235
in this map on my public map of skydrive from hotmail, spreadsheets and examples. Click on the I in a cirlce at the end of the document you want to use , the at the rightbarr click "Download". After downloading you can check it for virusus if you want, then open it in Excell or compatible program to use ist.. From this link you can navigate my complete public map for more.... there is much more !!!! and if you cant work it out, give me the details, and I will do it for you.


Greatings from Holland
Peter