Help me understand suspension and tires benfits on F350 w 2000lbs truck camper

[TexasSixSeven]

Are you sure it's TPMS vs TPIS?

TPIS is information only, TPMS is monitoring and has alerts that cannot be turned off when under recommended pressures.

The TPIS doesn't care, it gives you the same information, just without the alerts and dash lights.

Yes. Ran my 37s at 50-55 when not hauling. Had alerts constantly from it anytime under 60.

 

[TexasSixSeven]

I think you mean 305/70r18... couldn't find any 75s. They are both nominally 34.8", but since 35s are typically 34.6", they are taller.

There is one 305/70r18 that is quite large though, the Nitto Dura Grappler which is 35.28" and 12.8" wide on a 9" rim.

Yes 305/70. On a calculator sure they come out to 34.8. In real life the few 305s out there measure considerably larger. I’ll dig back through and see if I can find pics I took a couple years ago when I replaced mine.

When I say considerably I guess I should clarify. Most are measuring around 35.3-35.6. The Duratracs in 285 are on the small side around 34.6. The only other 285s I looked at measured under 35 as well.

 

[Kingsize24]

Yes. Ran my 37s at 50-55 when not hauling. Had alerts constantly from it anytime under 60.

Interesting. I was always under the assumption that Ford and Ram both did TPIS in their 3500 and up platforms. Maybe a certain year cutoff Ford did it on the 4500 and up now. Hmm

 

[TexasSixSeven]

Interesting. I was always under the assumption that Ford and Ram both did TPIS in their 3500 and up platforms. Maybe a certain year cutoff Ford did it on the 4500 and up now. Hmm

This was in single wheel trucks though. I haven’t paid attention to duallies.

 

[GetOutThere!]

285/75r18... not 70. Nominally it's 34.8" diameter vs 33.2" diameter for the 275/70r18.

I think that is a fine choice if you are ready to get new tires, but I would look at the obvious free option first. Tire pressure.

You're tires are supposed to carry 3640 lbs at 80 psi. I doubt you are anywhere near that.

Lets say you are at 9,000 lbs loaded for a trip, with even for-aft balance, so 2,250 lbs per tire. Per this chart:

StackPath

... a LT 275/70r18 will support 2250 lbs with 40 psi. So on the highway, you have been running 2x the pressure you need, and you'd probably be fine dropping down to 30 psi on washboard or even less.

OP here-

Weighed truck. 1/4 tank of gas and camper (with a couple hundred pounds equipment) I am 4600 front and 4850 rear.

2300 per tire front
2425 rear

According to chart i can run 50 upfront (2470/tire front) and could run same in rear.

I am currently running 50 front and 70 rear.

50 lbs allows 2470#/tire. 70 lbs allows 3060#.

note: i think the chart provided above has single and dual reversed.

Any reason to air down or should i just leave it?

Are all lt275/70r18 e tires going to have the same load/psi chart?

 

[klahanie]

OP here-

Weighed truck. 1/4 tank of gas and camper (with a couple hundred pounds equipment) I am 4600 front and 4850 rear.

2300 per tire front
2425 rear

According to chart i can run 50 upfront (2470/tire front) and could run same in rear. I'm reading it differently, using "single" row (assuming yours is single rear wheel) @ 45 psi max load is 2470 lbs

I am currently running 50 front and 70 rear.

50 lbs allows 2470#/tire. 70 lbs allows 3060#.

note: i think the chart provided above has single and dual reversed. Per tire load rating is derated when used in a dually position

Any reason to air down or should i just leave it? If you are unhappy with the ride off highway then I would expect lowering front from 50 to ~42 and rear from 70 to 45 will make a noticeable difference. You don't have too use those numbers but it costs nothing to try. Carrying an air compressor would be useful, and a worthwhile purchase.

Are all lt275/70r18 e tires going to have the same load/psi chart? Most likely for your market. That table is based on various standards incl TRA. TRA standard would be common for LT tires sold in the USA. Best if you can obtain the mfr chart.

 

[GetOutThere!]

Dropped front to 50 and rear to 60.

I actually dont mind the ride in hwy at 60/80.

If i can stomach the ride is it better for gas mileage/truck/tires to just run 60/80 on hwy?

 

[rruff]

If i can stomach the ride is it better for gas mileage/truck/tires to just run 60/80 on hwy?

It depends. If the pavement is kinda rough, I'd favor low pressure for best mpg, down to the Toyo spec for your load. If it's very smooth, higher pressure is probably better.

I'm more familiar with this from racing road bicycles. When I started in the 80s, pretty much everyone ran 20mm tires with 120+ psi. Now the norm is 28mm with 75psi... even for pros... because it's actually faster, even considering the weight increase and poorer aerodynamics. If it's a particularly rough course they will go even bigger. The reason is that the bigger tire with lower psi absorbs the road irregularities that slow you down. Even a smooth road is not smooth enough for smaller tires and higher psi to win out. High psi is only used on the track now.

With MTBs it's even more noticeable. The limiting factor is usually how low you can go before the handling is effected and risk of destroying the rim is too great. It's not uncommon to use ~2.4" tire with a foam noodle inside to keep the rim intact when you bottom out, and run 15-20 psi.

I'm thinking an insert would be real nice for airing down a truck offroad also...

 

[klahanie]

Dropped front to 50 and rear to 60.

I actually dont mind the ride in hwy at 60/80.

If i can stomach the ride is it better for gas mileage/truck/tires to just run 60/80 on hwy?

Here's one take on inflation. This for cars.

Overinflated Tires Symptoms

What happens when you have over inflated tires? The effects can be subtle yet significant, impacting everything from the comfort of your ride to your vehicle's

tiregrades.com

I'd suggest tho that one good source is your own experimentation and experience. Buy a tire pressure gauge, a ire depth gauge - they're cheap, track your fuel consumption, note driving characteristics with different pressures etc. Can even contact the tire mfr for recommendations.

That way you're not relying on some random (no disrespect) or some non relevant application. And let's face it: your truck, you're prob going to do what you want to anyway.

One anecdote: when we go on trips I usually set pressures in the driveway in the am. We're not too far off sea level. At some point after climbing into the hot interior country on the hwy I'll often notice the steering needs more input to maintain straight travel. That can be annoying and tiring so I'll check the fronts and if they're high will bleed off a little air. Then it's back to one finger ability on the straights.

Some don't care and I'm good with that but I like to pay attention to that type of sensitivity with the rig and believe it can pay dividends.