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Topic: Easy way to determine correct PSI for tires (Read 413 times) previous topic - next topic
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Easy way to determine correct PSI for tires
I have, for years, talked to RVers  about tire pressure because this info is not shared often so people don’t know.

It is best if you know the load on each tire and the load table (from the tire manufacturer for your specific tire) to:
1) make sure you are not overloaded for the tire (or the axles)
2) know the proper tire pressure to use
Having properly inflated tires (and not overloading your RV) increases safety (more tire on the road, less flats), and saves tire wear

A 4 wheel weigh is best to determine if you have your load distributed well.
But 4 wheel weigh stations are hard to find (typical through Escapees, Fmca, and sometimes at a race car place or other locations).  CAT scales give you axle weighing (specific instructions are around to determine your tongue weight if you tow with a truck) which is better then no weighing but not weights for each tire.

I just saw this video about the chalk method in a Truck group that can be done on any paved even road. 
And if you do all 4 tires it can give you a rough idea if your load is heavy in one spot (eg left rear heavier than right rear).

https://youtu.be/rcLaXzw-Sds

Note:  a scale weight is still useful to confirm you are not overweight for your axles as many people do overload their RVs (typically more storage space than available cargo weight capacity which includes passengers, liquids like water, propane, gasoline, waste tank contents, all food, belongings, and accessories added to the RV on top of the typical configuration they used for their dry weight number).
Jane & Scott
Currently have a 1989 TK  LD we did a lot of upgrades on.
Bigfoot 25RQ Twin on order with early summer 2024 ETA

Our smartphone autocorrects into very poor English.
 We disclaim the illusion of ignorance this creates as we have enough ignorance we rightly claim.
Re: Easy way to determine correct PSI for tires
Reply #1 –
Great video, thanks!

I am bothered by him not mentioning doing this on cold tires, ideally first thing in the morning.  Especially problematic if the sun is cooking one side’s tires.   Otherwise the concept is sound.

I’ll run the test later this month on my new tires when I have a passenger again.
Dave

2017 TK
Re: Easy way to determine correct PSI for tires
Reply #2 –
Quote from: Dave Katleman  - 
I am bothered by him not mentioning doing this on cold tires, ideally first thing in the morning.  Especially problematic if the sun is cooking one side’s tires.   Otherwise the concept is sound.
My understanding is very different, because I think the "check pressure on cold tires" advice applies only when you get the correct pressure setting from the tire company's tire tables.

If you set your pressure based on this test (uniform contact across the tire), you should have the tires at the temperature you will using the tires, because that's when you want the uniform contact. The pressure for cold tires will be too high when the tires heat up, and you will not have uniform tread contact when you are driving and the tires are hotter.

If would be interesting to do this test on tires with the pressure set according to the tire tables; frankly, I'm skeptical about the value of this method, because the steel belt in radial tires makes the tread much less affected by tire pressure. So, you'd discover you have "uniform tread contact" over a wide range of pressures.

I've never had trouble getting my RV weighed: a nearby tire store has a scale, ditto for the local gravel/asphalt plant, the city landfill, and a couple of truck stops. Some highway weigh stations will weigh you, too.
2005 Jayco 24SS
Re: Easy way to determine correct PSI for tires
Reply #3 –
The tread contact pattern can be changed simply by charging to wheels that are wider or narrower, it’s done all the time by four-wheelers. The contract pattern has little to do with the correct air pressure for the load weight.
Four-wheelers use the tread contact method on tires with excessive capacity ratings, the tires on our Jeep can carry over twice the total weight of the vehicle. My brother’s nearly identical Jeep requires 32 psi to acheive a even tread contact pattern, my Jeep’s wheels are an inch narrower and need only 28 psi to get an even pattern...same tire size and manufacturer. If I run at 32 psi, the outer edges of the tire do not touch the ground.

IMO. the correct pressure is set the only way the tire manufacturers recommend, weighing the rig and setting the pressure cold, according to the manufacturer's pressure chart. 

Larry
Larry
2003 23.5' Front Lounge, since new.  Previously 1983 22' Front Lounge.
Tow vehicles  2020 Jeep Wrangler Rubicon, 2001 Jeep Cherokee
Photo Collection: Lazy Daze
 
Re: Easy way to determine correct PSI for tires
Reply #4 –
Quote from: Larry W  - 
IMO. the correct pressure is set the only way the tire manufacturers recommend, weighing the rig and setting the pressure cold, according to the manufacturer's pressure chart. 

Agree completely.