GXV Patagonia on the Kenworth K370 chassis

waveslider

Outdoorsman
Following this discussion intently as I was trying to understand the relationship of loading, pressure and speeds from the brochure GREG posted.

Recognizing that some assumptions must be made in lieu of Greg actually weighing his rig, just using some sample weights in order to have the discussion is still useful for those of us trying to wrap their head around that speed/heat/load relationship.

Charile, is it useful to perform some testing of pressures and speeds by using a infrared thermometer to get actual tire temps or is it more of a “core temp” vs surface temp kind of thing?
 

gregmchugh

Observer
I am using a cold tire pressure of 95 psi front and rear which was the pressure recommended by GXV for highway driving. The ride is very smooth on the highway at this pressure and I limit the speed to the 65 mph limit for the tires. When I get a chance to weigh the truck I will look at the options for lowering the pressure.
 

waveslider

Outdoorsman
using a cold tire pressure of 95 psi front and rear which was the pressure recommended by GXV for highway driving. The ride is very smooth on the highway at this pressure and I limit the speed to the 65 mph limit for the tires.
So, is that max speed independent of loading or is it relative to loading rates?
 

gregmchugh

Observer
So, is that max speed independent of loading or is it relative to loading rates?
Max speed on highway is 65 mph with tire pressure no lower than tire inflation load charts above but max speed would be lower if you reduce tire pressure off highway as shown in the military brochure above, tires still handle the same load at the lower max speeds.
 

Britboaters

Observer
Just to summarize:
- weigh each axle fully loaded
- Refer to the Goodyear published document I posted - note these are industry standard load / pressure tables for 65 mph.
- Use those recommended pressures for best tire performance, if you like.
There are also instructions in the document on the relationship between speed and pressure requirement.
Bob
 
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So, is that max speed independent of loading or is it relative to loading rates?
Some but not the majority of large tires have a dual rating or “singular point”.
For example 18PR Michelin 395/85R20 XZL/XZL+ have a 168G rating (5600kg at 90kph) and also 161J (4750kg at 100kph).
 

gregmchugh

Observer
Just to summarize:
- weigh each axle fully loaded
- Refer to the Goodyear published document I posted - note these are industry standard load / pressure tables for 65 mph.
- Use those recommended pressures for best tire performance, if you like.
There are also instructions in the document on the relationship between speed and pressure requirement.
Bob
Yes, this has been my plan. Thanks for the info I needed for the Goodyear tire load specs.
 

gregmchugh

Observer
Just noticed that the specified max speed for the G278 is 68 mph, not the 65 mph that I mentioned I used as the max speed.
 

beardinc

Observer
I believe our truck with the 18.5 ft body weighed in at right around 21K. Add 1100 lb of water, 1388 lb of diesel and a full stock of recovery equipment, tools and all the things you need I would expect to be around 25-26K max. I've been on some soft sand and on some somewhat rough terrain. Aired down to around 60 psi it did well in moderately loose sand. Keep in mind the tires are designed to operate at 110 psi max. As far as traction goes we had no trouble getting up a fairly loose steep grade in 4wd lo. It has a locking transfer case and I believe it locks front and rear drive axles once engaged. With the locking rear we had plenty of traction. I can see where a front locking diff would be desirable and I'm sure its available but I didn't see the need. I did opt for manual hubs and I think GXV is putting them on all the Kenworth trucks standard now. The first one didn't have them. I'll double check but I really believe the massive divorced transfer case that is going in the Kenworth isn't a "center diff" but a true locking transfer case.

Forgive me if this has already been answered. Any more info on the TC/front drive axel used in this conversion? Make/model would be appreciated.
 

waveslider

Outdoorsman
Not to speak for him - Greg mentioned he might be out of range for a bit but he is a wealth of information and served as a great resource when we were shopping. He also has more miles under his KW platform than many.

Got our kenworth in Feb and its been great.

This weekend.
 

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