245/75R16 General Grabber AT 2 Tire Pressure Recommendations?

[workmeistr]

Hi, I haven't had success finding a happy setting for street driving with my 245/75R16 General Grabber AT 2 tires and the Rancho 9000s.

The max. pressure on the tire is 70 psi. I am running them at 58 psi and the Ranchos at 9.
The ride seems both bouncy (tires?), and rough (shocks?), at the same time.

Should I be running a different psi for firm, yet comfortable, street driving?
Should I max. the psi and drop the shocks to 7?

I guess I can play with the shock firmness; my question really focuses on aftermarket tire psi recommendations. If the max. psi is 70 on the tire, do you get best wear by running max. psi? Is it better to run under, maybe 10 lbs psi, to get some comfort with best wear? In this case, either psi option is still substantially higher than the intended recommended psi for the vehicle running OE rubber. Is this a problem for overall performance and ride?

Any suggestions, particularly regarding what psi for 245/75R16 General Grabber AT 2s for max. wear with best expected road comfort, given the max. psi on tire is 70 lbs psi, is appreciated. Thanks.

[tom4bren]

Typically, tires should be run at the pressure recommended by the manufacturer rather than what is recommended by the vehicle they are mounted on. That said however, you can play with the pressure for the benefit of ride comfort or tire wear (typically, trade off one for the other). It may be time to contact the tire manufacturer to get their take on min/max/recommended tire pressure.

Sorry, can't give you any insight into the Rancho settings.

[circmand]

a mixture between 3 factors

tire pressure
shock setting
how fat your but is

the ideal setting is based on your preference

[Ldub]

In theory, that tire could be inflated to slightly less than Isuzu OEM specs, due to the fact that it has more volume & a higher load range.

While this would soften the ride, it would also have a negative effect on rolling resistance & lower your gas mileage.

I'd try a "happy medium" of 45-48 psi & go from there.

[VX KAT]

Wow, didn't think tires in our size range had a max pressure that high (70). Anything near that high is going to give you a very hard tire and I believe some very hard jolts in ride. My 295/60-18s max is 44.

Driving at max psi will maximize your MPG. Over that, tires can wear unevenly down the center, way under that, you'll see more wear on the outer sides.

Ranchos:
I keep my Ranchos at 4/4, for both highway and general. I do get a little bit of "float" or "bounce" with the Ranchos at 4, but only over my rocky road. Lower than that was too bouncy for me.
For off-road Rancho suggests 6/4. This yr in Moab I forgot to up the fronts , and I felt a lot of bouncing on the trails.

PSI:
My tires are at 41 psi. I found 44-45 psi was just too hard of a ride.

I "think" you might want to first find a Rancho setting that you like, then play with psi.

And lastly, have you considered cutting your rear bump stops in half? That really was the 3rd leg of this stool and improved the ride.

[Gizmo42]

Here is the best way to determine what pressure your tires should be at for general driving.

http://www.jeepfan.com/tech/tire-pressure-chalk.php

For long highway runs outside of normal daily driving, air them up more to decrease rolling resistance. Mine are max 50 psi and I run 45 on long highway runs and 35 for daily driving.

For shocks I normally run 3 in front and 4 in back (rodeo is longer wheel base though) unless I have a lot of stuff inside such as for camping. Then I run 4 front and 5 or 6 in back. Offroad I crank them all up to 9. Its a matter of personal preference, some like stiffer ride then others.

BTW, what load range are your tires? Load range C will give the softest ride, D is acceptable. Load range E would be way too stiff for a VX.

[VX KAT]

BTW, what load range are your tires? Load range C will give the softest ride, D is acceptable. Load range E would be way too stiff for a VX.

He apparently got the E load range, at least according to RiffRaff:
http://www.vehicross.info/forums/sho...59&postcount=8

[Gizmo42]

Never going to get a good ride out of them. The sidewalls are way too stiff. I wouldnt use E's on anything smaller then a 1 ton truck.

[workmeistr]

Thanks for the info, all. I'm going with 48 psi and 7 on the front and back Ranchos this week to give it a try. If it bounces like a lunar rover, or if I find out that's way too lean on the air for these tires, then I'm going 65 lbs and maybe a little softer on the front shocks.

Gizmo, I understand about Load E and sidewall thickness affect on ride. I'm fine with a stiff ride, just not scary-handling bounce. Thanks for the link, I will do this as well to ensure I'm not too under inflated: http://www.jeepfan.com/tech/tire-pressure-chalk.php

[Riff Raff]

The max. pressure on the tire is 70 psi. I am running them at 58 psi and the Ranchos at 9.
The ride seems both bouncy (tires?), and rough (shocks?), at the same time.

Should I be running a different psi for firm, yet comfortable, street driving?
Should I max. the psi and drop the shocks to 7?

Any suggestions, particularly regarding what psi for 245/75R16 General Grabber AT 2s for max. wear with best expected road comfort, given the max. psi on tire is 70 lbs psi, is appreciated. Thanks.

Bren--- According to both the General Tire & Tire Rack websites your MAX PSI is 80, not 70. Thus, let's properly identify the exact tire in question.

You have the Grabber AT2 in LT245/75R16-120/116S (30.5" O.D./44.4 lbs), Item #568408000 which is a E-Load Range/10-Ply tire with a MAX PSI rating of 80 PSI (per tire sidewall panel).

At your current PSI setting of 58, your AT2's are way too underinflated and it is helping contribute to the bouncy feel you are experiencing. Further, your MPG and tire wear is not the best it could be with the increased drag.

You will get the absolute best MPG by running the tires at the MAX PSI of 80, and your tires will turn easier when parking and turning street corners. The Grabber AT2 is a very "meaty" tire and it will cause a lot of drag and rolling resistance if not inflated to the higher end spectrum of its MAX PSI rating.

My personal recommendation is to inflate your AT2's to the MAX PSI of 80 and to adjust your Rancho shocks to a more softer setting as you described in your initial post. If after riding at the 80 PSI setting for a while; you deem the ride too harsh for your personal tastes, then you can gradually reduce the PSI setting in incremental steps more to your liking. However, I would not go any lower than -10 PSI of the Max Rating (in your case, no lower than 70 PSI of the 80 PSI allowed). Give your AT2's a thorough test at the 80 PSI setting, as I believe you will like the firmer and more responsive ride while attaining the very best MPG.

[PK]

Well, it looks like most of the above so called tyre experts above need to take Tyres 101 again.
The tyre manufacturer marks the sidewall with the absolute maximum tyre pressure you should use, and the maximum load you should use.
If you are not running that maximum load (and our VXs don't) then you don't use the maximum pressure.
That is where the vehicle manufacturers recommendation come into play. If you use the "standard" tyre size nominated by Isuzu, you would run at the Isuzu nominated pressures. That is your starting point.
Then, if you are running a wider, or narrower tyre, you adjust that pressure (Higher for a narrow tyre, lower for a wider tyre).
There is then more room for adjustment for the loads you might carry on a regular basis, or for personal taste.
Then the final check is the chalk line across the thread width, and see if it wears off evenly. That will give you maximum tyre life.

Of course you can always deflate a bit for softer ride, and pay more for gas and tyres.
Or over inflate for a harsher ride, and pay less for gas but more for tyres.
Your choice.

But to automatically inflate to the tyre manufacturers maximum with our little VXs, is total BS.

PK

[workmeistr]

PK, I agree. When I saw the 80 psi on the side of the tire, I inflated to 70 and did the chalk test. Lots of chalk left on the outside, like it was inflated like a donut. A heavier vehicle might flatten it out on the ground, but not a VX. Chalk wear was consistent front and back, is the VX close to 50-50 weight distro?

Bottom line, I'm at 60 psi, due to reading the chalk, 7s all around on the Rancho. I'll ride that this week. Thanks for the suggestions.

[Riff Raff]

.........is the VX close to 50-50 weight distro?

The VX is damn close to a perfect 50/50 weight distro. According to www.MotorTrend.com (magazine), here are the weight specs:

Curb Weight = 3955 lbs.
Weight Distro, f/r, % = 51/49

[workmeistr]

Oh, and regarding my originally bouncy ride, maybe, just maaaybee, I had the back Ranchos on "0" insted of "9," just maybe.

Today's 30-min. ride to work was much better. I'm going to do another tire chalk test when it's cooler, as the air in the tires last night, by the time I finished testing, was very warm. I'd like to get one perfect chalk test, as in, I can't find the chalk marking after driving 1 block in a straight line. I was still showing a little chalk at 60 psi on the very outer sipes of the tire. I think 54-56 will be the best, or even slightly lower.

Thanks again.

[Ldub]

The VX is damn close to a perfect 50/50 weight distro. According to www.MotorTrend.com (magazine), here are the weight specs:

Curb Weight = 3955 lbs.
Weight Distro, f/r, % = 51/49

I don't think I'd take anything in a MT article as gospel...

If they can get something as major as suspension wrong...

(The following is excerpted from this MT article)

"Augmenting a full-coil suspension that uses MacPherson struts up front "

I'm not saying they're wrong on the weight distribution, I'm saying it's certainly a possibility...

And PK is spot on with regard to the max inflation pressure...max load = max pressure. Just because you CAN inflate to 80, doesn't mean you should.