Jump to content
fxrdriller

TIRE CALCULATOR

Recommended Posts

I used the tire calculator on MoparMan's site. I tried using it and it would not give me any psi. numbers. Then I did it with the math that you showed here on the site. I must be doing something wrong! It showed my front tire psi. at 45 and rear at 30. Please help MoparMan!

Share this post


Link to post
Share on other sites

We've been betting this out in PM's...

It seems he's in the same boat as me with the tire pressures...

Load Range G's I've got are 3750# at 110 PSI

Axle weights

Front - 4420

Rear -- 3040

GAWR

Front - 5200

Rear -- 6084

So the Math...

Formula: ((Axle Weight / 2) / Tire Max Weight) x Tire Max Press = Required Air Pressure

4420 / 2 = 2210 / 3750 = .59 x 110 = 64.8 PSI

3040 / 2 = 1520 / 3750 = .40 x 110 = 44.0 PSI

So now at full axle weight...

5200 / 2 = 2600 / 3750 = .69 x 110 = 76.2 PSI

6084 / 2 = 3042 / 3750 = .81 x 110 = 89.2 PSI

So front axle is between 64-76 PSI and the rear axle is 44-89 PSI...

So lets change tires... I'll go back to my Cooper Load Range E's... 3042# @ 80 PSI

4420 / 2 = 2210 / 3042 = .72 x 80 = 58.1 PSI

3040 / 2 = 1520 / 3042 = .49 x 80 = 39.9 PSI

Ok... Full axle load...

5200 / 2 = 2600 / 3042 = .85 x 80 = 68.3 PSI

6084 / 2 = 3042 / 3042 = 1.0 x 80 = 80.0 PSI

Now you can see how Load Range E's are at MAX limit with a 3/4 ton truck and why a dually comes into play for weights above 6084# on the rear axle...

(As for my page I know the PHP script is screwed up and I'm going to convert it over to the CMS soon.)

Edited by Mopar1973Man

Share this post


Link to post
Share on other sites

I think it is best to just follow the manufactures recommendations as far as what pressure to use. I say this because I always thought that if you put too much air in then you would have pre-mature wear in the center of the tread. And the reverse is true for too little air pressure.

I have always gotten low mpg numbers out of my Mega since I drove it off the lot. I have always tried to get the best mileage out of it anyway that I can. When it was new I asked my local Costco tire shop manager what pressure to run my Michelin tires at to get the best mileage out of them and the best MPG out of the truck. He told me that believe it or not to run them at the max. 80 psi no matter what. I asked him if it wouldn't wear out the center of the tread and he assured me that it wouldn't.

I ran those tires at 80 psi all the rest of their life. I easily got over 60,k out of them and they still have a little way to go. The wear is as even on those tires as I have ever seen!! I'm also pretty sure that other brands would have had the center worn out of them way before the outside of the tire at max pressures......

I've seen these pressure formulas before and I'm not against them or anything; but, I just think that they will only get you 'close'.......

Another way I saw and would like to try is to: Use the formula to get a starting pressure. Then take the vehicle to a known smooth surface (Preferably a cement parking lot!). Make a chalk mark across the tread of each tire with something like large sidewalk chalk. Drive slowly, and smoothly in a straight line and check to see how the chalk is wearing off. You want to adjust the air pressure to get as even of wear as possible and this should get you the correct pressure.

(I'll have to do this with those Michelin tires next year!! They can certainly do summer duty for a while yet . . . . )!!

Share this post


Link to post
Share on other sites

True a hard tire (over inflated) will have the less amount of drag. But also has the worse traction at speed because as you increase in speed the tire flexs which typically wears the centers out. But also now the ride of the truck suffers to very rigid, hard, solid feeling. Try that on a washbaorded road and you'll have a very tough time controlling the vehicle.

In all my studying on my truck I can be 10% below calculated and still not change MPG numbers. But the ride is so much nicer and traction in snow, ice and sand is way improved. Like from a jeep site most of them decrease tire pressure down to 20-25 PSI for walking in deep snow or sand better traction.

So looking at both side of the coin the calculated give the middle of the road best for ride and best for MPG's.

Now if you got the owners manual with the truck you should of had a tire pressure place card in the manual and it should have the recommend pressure for the stock tires.

Tire crayon is the actual best test for getting pressure right for traction and best wear...

Share this post


Link to post
Share on other sites

It kind of amazes me how many different tires and designs there are! I think my bro runs Toyo but they might be BFG's on his 1/2 ton. They are either 35's or 37's. He runs about 10 to 15 psi in them and still doesn't have all the tire touching the ground!! He went and got firewood one time and forgot to 'air up'. Even with the extra load those tires still stayed up!

You are correct on the ride and handling with the tires maxed out for pressure!! This time I went with BFG's in the OEM style. They put them at about 60 psi rear and 65 front. These seem like really good tires so far! The truck handles and drives the same as it did with the Michelins but it has better traction!

Share this post


Link to post
Share on other sites

Sorry to follow up so late! The reason my numbers were coming up so different was from the 3750# rating on a E tire with max 80 psi. If I get some time I really want to do the chalk test. This has been some really good information and gives me a good starting psi. Now if I can get my mileage figured out on this truck I will be happy! My mileage is all over the place and can not pin point it at all!

Share this post


Link to post
Share on other sites

This is a great graph! Im guessing that there is some of the numbers that are pulling a trailer. My mileage is varying 4 mpg without pulling a trailer. I am leaning towards my transmission or my vp44!

Share this post


Link to post
Share on other sites

Some of that is loaded heavy and some is empty running.

Ok another clue...

2002 Dodge Ram 2500 (Cummins)

[ame=http://www.youtube.com/watch?v=SRQdoPs_tLo]New Meadows Valley - Cruising at 55 MPH - YouTube[/ame]

1996 Dodge Ram 1500 (Magnum V8 5.9L) 13-15 MPG

[ame=http://www.youtube.com/watch?v=eN-w9jhHyI8]96 mpg.wmv - YouTube[/ame]

I've got the them dial in fairly well... :ok:

Share this post


Link to post
Share on other sites

Mike You Suck!!!

I would post up a graph of my Mega's mileage but I can make it simple: Let's just say 14

Good job man! Take good care of that truck!! I will keep working on my 2 Cummins and maybe someday soon I can give you some competition on mileage. Not to worry, I'll let you know when I beat you!! . . . LOL

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now



  • Upcoming Events

    No upcoming events found
  • Recently Browsing

    No registered users viewing this page.

×