How To Set the Tire Pressure in Your RV


If you’ve seen some of my other posts (like this one, and this one) you know that I’ve put a fair amount of time (and money) into improving the ride and handling of our Sprinter-based RV.  But the one thing I haven’t addressed yet is probably one of the easiest and cheapest to deal with, and that’s tire pressure.  And the good news is that even if you don’t have a motorhome based on the Sprinter, setting your tire pressure properly can help you too.

Now, a lot has been written – online, in magazines, in forums, and who knows where else – about tire pressure.  And there’s probably some accuracy in all of it.  So let me just say this up front – I’m not a “tire engineer”, or even a mechanic.  What I am is an RV guy who’s come up with a way to set the tire pressure in my RV that – in my opinion anyway – leads to improved ride and handling, and still addresses the safety concerns about proper inflation.  Now, other opinions may differ, but I’m going to share what I do.

But first, there are two common things that people do, and I want to explain why I don’t do them.

What I Don’t Do #1 – inflating tires to the maximum pressure on the sidewall

The first is simply inflating all the tires to the maximum pressure listed on the sidewall.  All tires will have their maximum pressure stamped on the sidewall.

SONY DSC

This is what mine look like, and on these tires (Firestone Transforce) it’s 80 psi.  Now, inflating the tires to 80 psi will certainly provide all the load carrying capacity that the tires are capable of.  But there’s a decent chance you don’t actually need all that, and riding with the tires at max will lead to a pretty harsh ride.

What I Don’t Do #2 – inflating tires to the pressure on the chassis plate

I’ll confess this is what I used to do, but the second thing I don’t do anymore is to inflate the tires to the numbers listed on the plate attached to the vehicle.  Now, on my Sprinter, that info is on the driver’s seat pedestal.

Chassis Inflation Pressures

This is certainly a better idea than just inflating things to the max on the tire, but this was put on by the manufacturer.  They certainly knew their vehicle, but they didn’t know what particular tires you were going to use.  They also didn’t know how loaded your rig was going to be – so they had to assume the maximum (in this case, 8550 pounds).  So basically, these numbers aren’t optimized for you.  Nevertheless, you can’t go wrong by using them, and that’s actually what I did for a while before I figured out what I’m about to show you now.

Step 1 – Find your RV vehicle and axle weight ratings

On my Sprinter, you’ll find them at another point on the driver’s seat pedestal, and they’re usually around the driver’s door somewhere.

SONY DSC

My RV has two axles, so there are three numbers I’m interested in.  The first is the Gross Vehicle Weight Rating, which in my case is 8550 lbs.  The others are the Gross Axle Weight Ratings for both axles.  For me, that’s 3860 lbs in the front and 5360 lbs in the rear.

We want these numbers because we’re going to head out and weigh the vehicle, and we want to be sure that we’re not over any of these weights.  And speaking of weighing the vehicle, that’s the next step.  But there are a few things we need to do before we head to the scales, and they all begin with “Fill the RV with…”

Step 2 – Load up your motorhome

Now, when I was thinking about weighing the rig, I wanted to be sure that I was weighing the vehicle as fully loaded as I could ever expect it to be.  I wanted it full of stuff – so I had to wait until we were headed out on our next RV adventure to make sure that I had it full of food, bedding, fitness equipment, bikes, and anything else we might take on a road trip.  You should do the same.

Fuel has weight, you’ll also want to fill the RV with fuel (gas, diesel, propane, whatever you use).  The weigh station I use is a Flying J that also sells diesel and propane, so that’s easy enough.

You’ll also want to fill the RV with water.  Head to the scales with a full fresh water tank and a full water heater.

And finally, you want to make sure that the grey and black tanks are full.  Now, when I did this, I didn’t wait to fill these naturally… because, you know… eew…   So I just filled them with water.  I don’t ever anticipate traveling this way intentionally because that would be bad form – but we’re looking for a theoretical maximum, so that’s what I decided to do.  Also, I want to point out that the RV is very heavy while doing this.  So drive very conservatively, and if this is the first time you’ve done this, then make sure the tires are at least inflated to the pressures listed on the vehicle plate for now.

I also want to point out that it’s best if you can locate a scale that can weigh all of your wheels independently.  The scale I use can’t do that, so I have to assume that the axles are more or less evenly weighted side to side.  I happen to know my grey and black tanks are on the mid-line of the vehicle, and the batteries and fresh water more or less balance out, so for me, that’s not a bad assumption.  But if your tanks are not located along the mid-line, weighing all the wheels becomes more important.

Step 3 – Weigh your rig

First, let me warn you – if you’re going to use a scale that’s normally used by truckers, when heading to the weigh station, you’re going to want to bring a long stick.  Just trust me on this one.  At the Flying J I use, here’s how it works:

I head inside first to tell them to expect me on the scale.  Though this probably isn’t strictly necessary, I feel better about it.  That way, if something unexpected happens, they know they’re dealing with a total amateur.

Then, it’s back into the motorhome and drive onto the scale, stopping where indicated.  This is where you need the stick – the button that says “weigh me now” is set up for truckers, and it’s like 14 feet in the air.  I can’t hit it without a stick.  When you hit the button, they will ask you for a number – but you can just say “Private”.

Once you’re weighed, drive off the scale and head back inside to get your weight.  They should give you something that looks more or less like this:

RV Weight

Now, if your waste tanks are totally full, dump them (again, easy at the Flying J) and head home to sort things out.

Step 4 – Validate your weights vs. the maximums

So the next thing we want to do is to check and make sure that we’re not over the max weights for either the vehicle as a whole, or any of the axles.  Since I rebuilt our RV myself (details here), I can’t rely on the old manufacturer ratings, so I was sweating this one the first time I did it.

RV Weight Comparison

Good news!  I’m under.  Barely, but under.  I came in at 8380 pounds of an 8550 max, so I’m good as long as Stef and I don’t gain much weight.  But remember, this was as overloaded as I can make the vehicle, so we’ve got a safety margin here.

Also, I’m under on each of the axles.  On the front, I’m at 3580 pounds of an allowable 3860, and on the rear, I’m at 4800 of an allowable 5360 pounds.  Hopefully, you get good news like this too.

Step 5 – Obtain the proper load and inflation tables for your tires

For this you’ll need to hit the internet, or contact your tire dealer.  What you are looking for is the load and inflation tables for your particular tire.  I mentioned before that I run on Firestone Transforce HTs – but I also have a set of Blizzaks that I use in the winter.  So I need two sets of tables.  Here are some links to a few of the load and inflation tables I found online.  You’ll need to find the right ones for your tires.

The interesting thing was, when I checked them, for the same size tire, they all seemed to indicate the exact same weight and inflation numbers…  So either I’m in the Twilight Zone, or these things are more or less standard for E load rated tires.  Either way, I recommend checking the ones made for your tires.

Step 6 – Determine your tire pressures from the tables

So I’ll just use the Firestones as an example here.  (But the Blizzaks have the exact same numbers.)   I need to mention that our Sprinter is a 2500, with the single rear wheels at each side.  I’ll be using that when I read the tables.  Here’s my page from the Firestone book.

Tire Tables

So for the front axle, my weight was 3580 pounds.  Since I wasn’t able to weigh each side individually, I’m just going to divide by two.  3580/2 gives me 1790 pounds per tire.

Sprinter Front Axle Tire Pressure

Now, with my size tire, in a single wheel configuration, it shows that I can get away with inflating my tires to just 45 psi (!) and they will still carry the 1790 pounds.  But 45 psi seems awfully low to me.  And remember that I wasn’t able to weigh both ends of the axle.  So unless my load is exactly evenly distributed – 45 psi isn’t going to cut it.

Therefore,   I’m going to select 50 psi for the front tires.  That’s a cold inflation pressure.  This will allow me a 300 pound difference – side to side – and the tires will still safely carry the load.  And remember too, that the rig is never likely to get this heavy again.

Now, for the back tires, just dividing by half (4800/2) yields 2400 pounds per tire.

Sprinter Rear Axle Tire Pressure

And from the tables, it shows that I should run 70 psi to handle this load.  I could elect to run them as high as 75 psi and still be in the ballpark.  But I am going to run with 70 psi.

This allows an 80 pound swing, side to side.  That might not seem like a lot.  But I know that my grey and black tanks are behind the rear axle.  And since I don’t normally drive with them both insanely full – my typical running weight is about 60 gallons of fluid less than how I weighed.  Water weighs about 8.3 pounds per (US) gallon.  So normally, I’m about 8.3 x 60 = 498 pounds lighter behind the rear axle.   That makes me pretty comfortable with 70 psi.

Step 7 – Inflate tires and go for a drive!

In my case, 50 psi front and 70 psi rear is a few pounds less than what the Mercedes Benz specified (by 5 and 9 pounds).  But when I set the tires this way a drove a bit, I liked it.  I found it to be less harsh – like when hitting seams in concrete highways – and it also provided good control when cornering.  I am very confident that I am inflating the tires enough to carry the load.  And since the Blizzaks have the same ratings, I have just one set of numbers to remember.

SONY DSC(OK.  I don’t usually inflate my motorhome tires with a bicycle pump.  But since I almost always travel with bikes and a pump, I thought I’d try it just to see.  The good news is, it does work.  The bad news is, it takes about half an hour per tire!)

Anyway, for my rig, my equipment, and my weights, 50 psi front and 70 psi rear were the answer.

How do these numbers shake out for your rig?  There’s only one way to find out – so load up and head out to get your weight!

We’ll see you on the road.

 



James is a former rocket scientist, a USA Cycling certified coach, and lifelong fitness buff. When he's not driving the RV, or modifying the RV (or - that one time - doing both at once), you can find him racing bicycles, or building furniture, or making music. In his spare time, he works for a large IT company.


    17 thoughts on “How To Set the Tire Pressure in Your RV

    1. Tom Graf

      James,
      Are there any currently available systems to monitor tire temperatures, say with permanently mounted infra red sensors when the tires are rolling? This would seem to be another way to determine if you under inflated a tire. One would have to establish a baseline as I am guessing tire companies don’t publish temp vs. load curves. Izze racing has an advanced IR tire surface temp monitoring system. but me with my dually F350 and 4 tires on my fiver would take me into data overload. How about one integrated temperature average per tire, with a system to alarm you if any one tire went over the average of all tire temperatures by some value. Maybe we need to get together and build such a system if none is out there!

      Reply
      1. James - Post author

        The one I use is called the TireTraker. (Yeah, they spelled it funny.) You can buy it on Amazon, here.
        Besides tire pressures, it also monitors temperatures through the valve stem end caps. It’s probably not as accurate as infrared monitoring, but while I’m driving, I’m only really concerned about emergency situations. I think it would handle those just fine. It also has alarms for over/under temp, over/under pressure. You can buy additional valve caps to extend to quite a few tires. Check it out!

        Reply
    2. lee Harris

      have a 08 national tropical motor home, only had it 6 mos. put new tires on sure track new tires 255/70r/22.5. dealer put in 115 lbs each. have driven 300 Miles. very harsh drive feel every dent. put on new shocks plus safe t plus stabilizer better but still feeling all the bumps. dropped the tire pressure to 95 psi, much better. I’m about 8k below max load. I agree with your plan to come up with a desired psi.

      Reply
    3. Dennis Olmstead

      Lots of RV forums discuss tire pressures, and they are all over the map. Mostly they recommend max pressure. Your method is the correct one. And well written. You should post it on the forums. I’ve also read the Bicycle Quarterly articles, same principle: inflate according to load on the tire. Re: your road bike/buffalo blog: just ride a touring bike with 35mm tires and you have no problem on dirt, and also get a slightly better workout. Not that much more, actually.

      Reply
      1. James - Post author

        I haven’t run them yet.
        I really want to, but since Dodge went with Nexen tires for the ProMaster, I can’t find load and inflation tables for them!
        I even called Nexen, and it seems they just don’t have them. They have maximum loads, but nothing else.
        When I switch to Blizzaks in the late fall, this will come to mind again, and I’ll run them then.

        Reply
      1. James - Post author

        I read that same article about bike tire pressure!! Excellent!!
        That’s why my bike tires (Conti GP 4000s) are 100 in the front and 110 in the rear. Unless it’s raining.

        Reply
    4. Rick Az

      OK, I’m late to this, I know. But I wanted to add something about side-to-side weighing. I found a CAT scale with a wide apron on each side (and no steep dropoff!), and, after a normal weighing, carefully drove my class A onto the scale a second time with one side in the middle of the scale and the other side on the apron. After getting out and double-checking my position, I signaled for a weight. I then knew what one side weighed, and subtraction gave me the other side. It worked well, and they didn’t even charge me full price for the second weighing.

      Reply
    5. Mickjonny

      Great post james!

      Nice information in this blog about tire pressure and useful information which you have shred with us. keep sharing…

      Reply
    6. David Brimhall

      Read with interest your cold inflation scheme and we are doing much the same, except for the weighing bit – yes, that needs (must) be done.
      Presently we are fixing to travel back to Advanced RV – last year they installed a screen door for us, this year we are getting upper cabinets for the cab. For the trip we thought we would get some new tires, do you have any recommendations?

      Reply
      1. James - Post author

        Das Bus originally came with Michelin LTX tires, which we liked. When it came time to replace them, the Michelins seemed a bit spendy. The staff at our local tire shop recommended Firestone Transforce HTs. They put them on local ski shuttle vans, and were having good luck with them. We have been VERY happy with them on our Sprinter. They’re less expensive than the Michelins, and the ride is just as nice.
        And very cool that Advanced RV is making some additional storage for you! Tell them we said “Hi!”

        Reply
    7. Tom Boles

      Great piece on tire inflation! We’ve towed 3 different travel trailers with our Ford E350 van and each unit was a different weight and we used three different hitches. Weighing your rig, adjusting the tire pressure to the load/inflation tables and then checking how your weight distribution hitch changes things when it’s adjusted properly is all part of the thinking person’s approach to Rv’ing. I’ve never been able to weigh each wheel independently but that would be an eye opener for sure!
      Thanks for your posts!

      Reply
      1. James - Post author

        Thanks, Tom! I’ve never been able to do the four-corner weighing either. I hear sometimes they offer this at the big national rallies, so it’s on my list to check out. I’ve spent enough time under my rig so that I think my assumptions about weight distribution are good, but I would love to confirm. Thanks for the kind words. See you on the road!

        Reply

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