Correct PSI? - PeachParts Mercedes-Benz Forum

jacobwissler · #1 09-07-2003, 07:35 PM

What is the correct PSI for a 1984 300 SD? Should I follow Mercedes instructions, or the tire manufacturers instructions?

manny · #2 09-07-2003, 08:21 PM

I have not heard of a tire manufacturer recommending a pressure, other than maximum inflation pressure ( when the tire is being mounted ).
I usually run mine at M-B spec., plus a couple of pounds.
This seems to be a good trade-off between handling, tire wear, ride & fuel economy.

conversekidz · #3 09-08-2003, 12:50 AM

Run it a few pounds shy of the max PSI the tire recommends....

If you do it off the hand book, it might say something like 34lbs, but the new tires you have want to be run at 60lbs...

This is the whole issue with firestone and ford....

Trust the tire company...since they are the ones that made the tires.

yhliem · #4 09-08-2003, 03:39 AM

Quote:

Originally posted by conversekidz
Run it a few pounds shy of the max PSI the tire recommends....

If you do it off the hand book, it might say something like 34lbs, but the new tires you have want to be run at 60lbs...

This is the whole issue with firestone and ford....

Trust the tire company...since they are the ones that made the tires.

I disagree with this advice.

No...wait...i STRONGLY disagree with this advice. if you run your tires at too high a pressure (such as "a few pounds shy of the max PSI the tire recommends") you will drastically change the handling characteristics of your car.

For example, I have a larger than stock front anti-sway bar in my 2.3-16 which has resulted in increased understeer. to offset this I run my rear tires at about 42 PSI.

Use the CAR manufacturer's recommendation as a guideline and experiment with your tire pressures from there. they are usually found on a sticker inside the fuel filler door, or in the car's manual.

Higher tire pressures will cause the tire to lose traction sooner and results in a slightly harder ride. Lower pressures soften the ride and provide more grip, but you also increase the rolling resistance of the tire and therefore your fuel economy will suffer.

The issue with ford and firestone is that firestone made an inferior tire. period. regardless of how they spin the stories I have NEVER had a tech recommend to me that the tire pressure should be anywhere near the max PSI of the tire. If Firestone says that you should run your tires at 50-60 PSI they're just trying to find a way to deflect responsibility.

and for anyone who happens to be running with tire pressures that high, no offense, but give your head a shake or two.

manny · #5 09-08-2003, 03:38 PM

Quote:

[i]
Run it a few pounds shy of the max PSI the tire recommends....

If you do it off the hand book, it might say something like 34lbs, but the new tires you have want to be run at 60lbs...

This is the whole issue with firestone and ford....

Trust the tire company...since they are the ones that made the tires.

I haven't laughed so hard for a very looooooong time.

yhliem · #6 09-08-2003, 08:31 PM

Quote:

Originally posted by manny
I haven't laughed so hard for a very looooooong time.

*lol*

conversekidz · #7 09-08-2003, 10:50 PM

What I was trying to say was, Run the PSI that the tire company tells you to run, not what the car company tells you...

yhliem · #8 09-08-2003, 10:58 PM

Quote:

Originally posted by conversekidz
What I was trying to say was, Run the PSI that the tire company tells you to run, not what the car company tells you...

yes, i am aware of what you were trying to say; however, I still disagree. The tires are an integral part of the suspension system and it's the car company that engineered the suspension system, not the tire company.

aain, tire pressures are like dino vs. synthetic oil. everyone has an opinion and everyone thinks theirs is the correct one, but i have yet to have a technician recommend the tire manufacturer's pressures to me.

Luke@tirerack · #9 09-09-2003, 10:49 AM

tire companies do not tell you what pressure to run because when the tire is built they have no idea what type or model vehicle the tire will be installed on. They only list he maximum pressure the tire can safely hold .....

the air inside of your tire is what is holding your car up ... so go with what the car manufacturer recommends because the weight of your car has not changed

there is a small caveat to this though

the car maker recommends a pressure which is a compromise between three things:

ride quality
steering response
load capacity

you can easily raise the pressure to get better steering response without any issues but, when you do that the ride of your car will be a little stiffer .... I typically am willing to trade a little of the ride quality for crisper steering so, you have about 5 - 7 psi to play with to tune the steering/ride to your personal tastes

yhliem · #10 09-09-2003, 12:34 PM

hehehe...I was wondering when His Holy Tire God would make an appearance

Luke@tirerack · #11 09-09-2003, 02:04 PM

I'm here everyday ... just letting you guys vent for awhile to see who has learned the most and who still needs some direction from the 'force'

yhliem · #12 09-09-2003, 02:56 PM

Quote:

Originally posted by Luke@tirerack
...who still needs some direction from the 'force'

i do! i do!

:p

Luke@tirerack · #13 09-09-2003, 02:59 PM

Quote:

Originally posted by yhliem
i do! i do! :p

yes you do .... the Firestone/Ford issues was more Fords problem than Firestones

yhliem · #14 09-09-2003, 04:47 PM

Really? what'sthe scoop? Last I heard it wasFirestone's issue.

autozen · #15 09-10-2003, 10:57 AM

Actually tire mfgs do have recommended pressures. You won't find it on a tire, because as someone pointed out they don't know what you will put it on.
They do however print a book with all the info about each tire line including things like loaded radius, revs per mile, acceptable rim widths, etc. They also list all the cars and suggested pressures. At least they used to do this, but I've been out of the loop for awhile. I've found these books useful in the past to help me decide on substitutes. Unfortunately as a rule you can't rely on people in the tire business for advice, because most of them haven't got a clue about tires although they think they do. It is rare to find a tire person who knows his stuff. I think this info is available on line at places like Tire Rack. I'm not sure, because I only buy 3 tire sizes for my 123 cars, my 126 cars, and my F250, and that requires no thought.

Peter