I just bought a 99 Mitsubishi Fuso FG in North Carolina and I'm driving it home to Denver. It's a 12000lb GVWR 4wd truck with a service body on the back and some lube oil tanks (probably almost empty) so there is not much weight on the truck. Probably similar to an empty pickup truck. It was giving a pretty harsh ride and I remembered a comment on another board by someone who bought just the cab and chassis and reduced the tire pressure on the ride home to soften the ride. I checked the pressure in the rear duals and they were at 70psi. I reduced them to 60 psi and the ride improved pretty significantly. I'm wondering what the lowest safe pressure is with essentially no significant load on the back. The manual says 80psi lbs for load range E tires, which is what is on the truck. But even at 70psi it felt as if the back of the truck was bouncing up over the interstate cracks.
I've done nothing to the front tires, but I assume keeping them at spec would be appropriate, or could they even be reduced with no load on the truck? The manual calls for 65psi for load range D tires on an FE 639 with GVWR at 11,600 lbs although mine is the 12,000lb GVWR calling for Load Range E at 80psi.
Thoughts?

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Kerry, I am jealous..........later on put the 235-85x16 Yokohama rally tires on them. For now stick to 75 and look for sidewall and wear pattern by marking the outder edges with chalk, if the wipe out, you are too low.

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99 Gurkha with OM616 IDI turbo

2015 Gurkha with OM616 DI turbo

2014 Rexton W with OM612 VGT

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I agree with what he said.

Used to deal with lots of heavy equipment.

Impossible to know the weight of the equipment all the time.

Keep some chalk in the cab.
Put marks on the tires from rim to tread.
Drive a short distance, few hundred feet or so.
If the chalk has rubbed off the tire near the tread,
your pressure is too low.


RichC

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When the power of love overcomes the love of power the world will know peace.
Jimi Hendrix

My buddy had one of those a few years ago and it always rode like, well, one of these:



You can see the resemblence... Since you're sitting out over the front wheels, you'll get an accentuated effect from every bump. My F250 has a GVW of 8800# and I can run the E rated tires at 40PSI in the rear and 50 PSI up front without it feeling too mushy.

__________________
-Evan


Benz Fleet:
1968 UNIMOG 404.114
1998 E300
2008 E63


Non-Benz Fleet:
1992 Aerostar
1993 MR2
2000 F250

Thanks for the advice. I didn't have any chalk with me on the trip but I will experiment. At 60psi, the sidewalls on the duals were not deflecting at all so I don't think it's an issue on the rear.
I'll try different pressures and see what happens. The weight of the empty cab and chassis is 6000lbs.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

I think you should as Obama. He's an expert on tire pressure.

I take it down to forthsomething on my Dodge 3/4 for comfort when there is no load. I have 87K on the ones that came on the front so far and am shooting for 100K.

tom W

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

The first Goodyear store I worked at as an assistant manager handled road service for local municipalities as well as NJ Transit non-revenue vehicles - boom trucks, repair trucks,etc. I spent a lot of time with tires ranging from 235/75R15s up to 12R24.5 and 295/75R24.5s as well as "super singles". Just remember that it's the air pressure that handles your load capacity. Any Load Range E or higher tire will ride very stiff no matter what.

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Sharing my partner's 2012 Forte 5dr SX til I find my next 123 or 126..
-
Do I miss being a service advisor ???

I think I'm going to try 60psi in the front also when empty to see if it makes the same kind of difference. They're currently at 70psi.
I should have taken my non-contact thermometer with me so I could monitor tire temperature. I was checking with my hands and the 60psi duals did not seem any warmer than normal.
Some people are putting super singles on Fuso FG's when they turn them into campers. Any opinion as a tire guy on the advantages/disadvantages.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

You've got a couple working against you here.

1. There's a tremendous difference between the empty and GVW.

2. The huge unsprung weight of that heavy rear axle with the duals.

When you get the truck finished and the camper fitted, you might want to consider "de-rating" the suspension down to the new weight of the truck. Since the weight of the truck won't vary as widely as it would when it was a beast of burden you can tune the suspension for a much better ride. You might be able to swap springs from another model or another make of truck.

Compare the weight of the super singles to the duals. Any weight reduction will help out.

I've always thought these trucks were pretty cool. I've considered buying one to outfit as a tow vehicle with a sleeper cab. Kind of like a mini semi for towing 5th wheel campers.

Need some pictures!

__________________
-Evan


Benz Fleet:
1968 UNIMOG 404.114
1998 E300
2008 E63


Non-Benz Fleet:
1992 Aerostar
1993 MR2
2000 F250

Here's one picture. Some Australians have modified the suspension on these to meet their use better.

Attached Thumbnails

 

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

One thing to keep in mind is the difference between front and rear presure for the load you are carrying. You probably want to maintain close to that difference in presure. Remember, all things being equal, if you just raise the front presure only, the car will oversteer more. Raise the rear only and the car will understeer more.

Ran across this:

http://www.goodyear.com/truck/pdf/databook/loadInflation.pdf

VERY helpful in determining proper tire pressure. I could be running lower pressures.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Excellent links, thanks Kerry.

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99 Gurkha with OM616 IDI turbo

2015 Gurkha with OM616 DI turbo

2014 Rexton W with OM612 VGT