rl153 wrote on 03/19/13 at 10:55:47:

Yup,...  needed tire pressure is based on weight...  same tires on two different cars will require different pressures...

A #300 pound rider on a Savage should have a little more air in his tires, than a #100 pound rider...

Greg wrote on 03/19/13 at 12:36:17:

Yup this is the only way to correctly set the pressure that I know of.  I do this for all my 4 wheeled vehicles when they get new tires and most of the time it's different then what the tires were on before even if it was the same brand/model tire.

R.F.

I would just roll down the driveway. You don't want it to disappear, just see what is going on. Less than 100 feet.

rfw2003 wrote on 03/19/13 at 14:17:56:

You are correct. I guess my finger did a double tap. It should have read 10 feet.  

Gyrobob wrote on 03/27/13 at 05:16:52:


GYROBOB......This might just be a topic you and I aren't going to agree on.......I am not going to believe the connection of the sidewall tire pressure and a bureaucrat?  I do believe that it is necessary for some labeling of the tire with a maximum load and a maximum pressure - or else users won't have a clue what they can or can't do with that tire.  I just prefer to believe those numbers are etablished by engineers and not politicians.

Here is some supporting data from one knowledgable source....which was not written by a Bureaucrat.  And just about every tire manufacturer or distributor states that the pressure listed on the tire is the recommended pressure at the maximum load rating of the tire.  And just about everyone that monkeys around with cars or motorcycle knows that this is not the pressure to use when adjusting your tire pressure.

Every vehicle should have a manufacturer recommended tire inflation value, usually on a sticker on the driver's side door jamb. This figure is determined by the manufacturer based upon the vehicles stock weight distribution, wheel and tire size. This is probably the best value to use if it applies. However, if you have changed wheels, tires, or weight significantly, this number may not be appropriate. Also, it is sometimes unclear as to what were the assumptions used to determine those pressures. For example on a pickup or SUV, they often list a much higher rear than front tire pressure. This is likely a pressure setting at the maximum vehicle load ratingm so on a 1/2 ton pickup, for example, thise would be with approx. 1000 lbs. or cargo in the bed. With little or no bed load, this "factory" tire pressure may be too high, so take those numbers with a grain of salt.

Tires, too, come with manufacturer-specified inflation specifications. These, however, are not vehicle specific, but rather refer to the maximum inflation pressure the tire can handle in relation to its maximum load carrying capacity. For example, assume you have a light truck tire with a 2500 pound maximum load rating at 50 PSI air pressure. Lets say there are four of these tires mounted on a 5000 pound vehicle (with 50/50 weight distribution), so the per-tire load is 1250 pounds (5000/4). Clearly, the tire is nowhere near its maximum load, in fact it is at 1/2 load in this case. A case could be made for inflating the tire to 1/2 its maximum pressure (25 PSI in this case) based upon the load on the tire.

Actually, while there is a fairly linear relationship between a tire's inflation pressure and its load carrying capacity, it is simply not a straight line from 0 to the maximum load. I did a least-squares-fit analysis on some pressure vs. load data for a series of agricultural tires and found that the following factors seem to fit the data quite well:
mL = maximum tire Load (lbs)
mI = maximum tire Inflation (psi)
L = the actual load on the tire (lbs)
L = 0.21*mL + (0.79*mL/mI)*inflation
Here is the link for the source of the above....You can find more by just searching the internet.
http://www.4crawler.com/Diesel/Tires.shtml#ProperInflation

justin_o_guy2 wrote on 03/27/13 at 09:44:17:


When I was autocrossing we would use white shoe polish.  We were not adjusting for even tire wear - we were looking to see how far the tire would roll over onto the sidewall.  The idea was to adjust the tire pressure so that the tire would just barely stay within the tread and not roll too far over onto the edge or sidewall - this would give the most useable footprint area without damaging the sidewalls.  If you put too much air in the tread contact patch is reduced and the traction would suffer.

If you have some leftover white shoe polish from your Pat Boone look alike days......you might try that!    

I alway look at the sidewall pressure on a tire as a starting point, once set you go out and run the bike, car, truck as you plan to drive. If it doesn't seem right jack the pressures around and try it again. How it handles is a personal choice which can be adjusted by fine tuning tire pressure.

MAXIMUM tire pressure is the highest pressure that the engineers at the tire company have determined is safe to operate. (As per government mandate)  It is best to start with the vehicle manufacturer's recommendation, and go up as load increases.  If you find yourself going past the weight or psi on the sidewall, then you need to either reduce your load, or upgrade to a tire with a higher load rating.  In other words, it's a more precise way to measure load ratings, improve safety, and protect the tire company from people installing the wrong tires on their rigs.  Sorry no bureaucrats were implicated in this post.