26 replies to this topic

[rubberlegs]

Hey "Taco around the world", you might want to weigh each axle at a truck weigh station. We have several in Washington state, for example.

 

On ours, the front axle load is about the same as our empty truck, 2700-2800 lbs or 90-94% of Toyota's rated front axle load. 

 

But the rear axle load empty was 2000 lbs, with the camper 3100-3600 lbs depending on extra stuff, one to three people, etc. It's 95% to 110% of Toyota's rear axle specs.

 

If you look at the pressure tables here, the rear tires should be at quite a higher pressure than front, to maximize tire life at high speed, because they are loaded quite a bit more. The tires build up heat if pressurized too low. It's surprising how much more pressure they recommend for just a little more load. Read the link for how to use the table, but you can get an idea from the change in the numbers. In my case I use 45psi front, 55 rear. I probably should use 42 front, 62 rear at my highest weights, if I followed the method exactly.

 

I was really surprised how much different the pressures should be.

 

From the top of page 21 at https://www.toyotire...es_20170203.pdf

                     35   40   45   50   55   60   65   70   75   80
LT275/70R17 Single 2000 2195 2380 2600 2760 2925 3085 3120 3160 3195 

RC Pilot Jim, your pressures seem too low, especially the rear. However, if you drive slowly, then you won't damage the tires. I can't find the data on speed vs. pressure unfortunately.

[Taco around the world]

Hey "Taco around the world", you might want to weigh each axle at a truck weigh station. We have several in Washington state, for example.

On ours, the front axle load is about the same as our empty truck, 2700-2800 lbs or 90-94% of Toyota's rated front axle load.

But the rear axle load empty was 2000 lbs, with the camper 3100-3600 lbs depending on extra stuff, one to three people, etc. It's 95% to 110% of Toyota's rear axle specs.

If you look at the pressure tables here, the rear tires should be at quite a higher pressure than front, to maximize tire life at high speed, because they are loaded quite a bit more. The tires build up heat if pressurized too low. It's surprising how much more pressure they recommend for just a little more load. Read the link for how to use the table, but you can get an idea from the change in the numbers. In my case I use 45psi front, 55 rear. I probably should use 42 front, 62 rear at my highest weights, if I followed the method exactly.

I was really surprised how much different the pressures should be.

From the top of page 21 at https://www.toyotire...es_20170203.pdf

35   40   45   50   55   60   65   70   75   80LT275/70R17 Single 2000 2195 2380 2600 2760 2925 3085 3120 3160 3195

RC Pilot Jim, your pressures seem too low, especially the rear. However, if you drive slowly, then you won't damage the tires. I can't find the data on speed vs. pressure unfortunately.

Thank you for commenting. I like the reference to the Toyo PDF. I will try to more fully understand it when I am more awake. I have in fact taking it to a scale and I am going to have reweighed and this time get the weight on each tire. Going to install some custom rear springs either Alcan or Deaver, due to the newly installed extreme heavy duty Dobson rear springs not being sufficient.

Do you have a flatbed Fleet as well?

Edited by Taco around the world, 16 September 2019 - 05:07 AM.

[rubberlegs]

Nope, ours is a slide in. I understand the flatbeds are heavier.

[Taco around the world]

Yes flatbeds definitely are.  I took your advice and weighed my piggy.  The front axle is 2,860 and the rear is 3,980 lbs with a full tank of gas and recovery gear but no people, propane, water, or food, etc.  So to use the Toyo PDF do you divide these weights by two to determine the per tire load?

[Vic Harder]

i would

[rando]

Yes flatbeds definitely are.  I took your advice and weighed my piggy.  The front axle is 2,860 and the rear is 3,980 lbs with a full tank of gas and recovery gear but no people, propane, water, or food, etc.  So to use the Toyo PDF do you divide these weights by two to determine the per tire load?

 

Yes you do divide by 2. 

 

I have a Fleet Flatbed on a Tacoma and have settled on 45PSI front 55PSI rear on the highway.   If we have a significant amount of dirt or washboard road I will drop this to 30 PSI / 40PSI to increase the ride comfort and for the technical 4low stuff I will go down to 20/27.   This is on 235/85R16E BFG ATs.  

 

If you watch the pressures on the TPMS display, you can get an ides of tire heating, which is a the main issue with reduced tire pressure.   A 10% increase in pressure from cold corresponds to a ~30C rise in tire temperature.   If I see more than this, I will get out and check the tires by hand. 

[rubberlegs]

Yes flatbeds definitely are.  I took your advice and weighed my piggy.  The front axle is 2,860 and the rear is 3,980 lbs with a full tank of gas and recovery gear but no people, propane, water, or food, etc.  So to use the Toyo PDF do you divide these weights by two to determine the per tire load?

 

Yes, divide by 2 for each tire, but you don't use the chart numbers directly. According to the method I used (see post #4), I would use 44 front, 71 rear before adding payload. In our setup, most of that weight goes to the back. Those numbers seem extreme, so I might round off to about 46 front, 65 rear (easier to remember). Note that we have a slightly different tire size though. I've not used your exact tire size, but it's probably close.

 

On our Taco, the display only goes up to 55 psi. I wish it displayed higher. Our front tires go from 45 cold to 49-51 warm depending on temperature. Rear I'm not sure since we start at 55. The 10% increase sounds about right, maybe a bit more in our case.

Edited by rubberlegs, 21 September 2019 - 04:32 PM.