confusion on psi on TT

[baileyandnat]

Hello! I have a new trailer and I bought a TPMS for our upcoming long trips. I got confused when i was installing my system on what my psi warning should be? The sidewalls says 65psi cold max. Is that what i should have my tires inflated to or should i not exceed 65psi? What should i put as my warning setting on my TPMS? Thanks for helping a newbie out.

 

[Bob K4TAX]

The sidewall pressure is the MAXIMUM the tires should be inflated when cold. Otherwise having not being towed and allowed to heat. Thus ambient temperature. This also assures the tires can safely carry the maximum rated load for the tire. There is no reason to inflate to less than the MAXIMUM pressure as posted on the tire. If it says 65, then inflate to 65.

Underinflated tires will heat during rolling and may be prone to early failure due to excessive sidewall flexing. Underinflated tires are dangerous.

 

[Buly]

If you fill in all your inf about the coach type, model etc. people will know what ate you talking about. But in general, the tire inflation depends on the weight applied on the tire.
You should weigh the RV under each tire fully loaded. Than the tire manufacturer usually has tables that you can look up the inflation pressure for your tire against the weight.
The number on the tire, only means max inflation limit.

 

[sanda]

If you fill in all your inf about the coach type, model etc. people will know what ate you talking about. But in general, the tire inflation depends on the weight applied on the tire.
You should weigh the RV under each tire fully loaded. Than the tire manufacturer usually has tables that you can look up the inflation pressure for your tire against the weight.
The number on the tire, only means max inflation limit.

I agree. Max tire pressure can create poor wear/life of a tire if the load is much less than the max load on the tire. Weigh the trailer fully loaded and divide by four to get a close idea of your true per tire load. Adjust pressure to the manufacture recommendations.

 

[BGMAC]

I agree. Max tire pressure can create poor wear/life of a tire if the load is much less than the max load on the tire. Weigh the trailer fully loaded and divide by four to get a close idea of your true per tire load. Adjust pressure to the manufacture recommendations.

I tend to disagree with max psi creating poor tire wear. (Radial Tires)
with the tire at max pressure the tire has less deflection when in contact with the ground. This allows for easy rotation thus less heat thus less wear. It also decreases hydroplaning.

There was an articulate about this I believe in Road & Track magazine back in the 70’s to increase your tire pressure to 15psi over the rating of the tire on radial’s. I’m not advocating that, but I have done it. There are many studies on this with aircraft tires and there are videos of these tests online.

here is a link to a formula to show you how tire pressure effects hydroplaning. https://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=2919&context=roadschool

if I remember correctly, tires have to be tested to 2 1/2 times the rating on the sidewall. Pressures will increase when they get hot and that is accounted for.

 

[Buly]

Over inflated tires wear faster in the middle. Under inflated ones wear faster on both sides. You are right there is lest rolling resistance on over inflated tires. Trains with their steel wheels have the least rolling resistance .
But over inflated tires give you a harder ride, and under inflated wear faster an heat up more when in use.
It is all a compromise. Aircraft tires are a different ball of compromises. They are in fast motion only for under a minute at the time. Me thinks

 

[sanda]

In my case this is the manufacturers chart that I use.

https://www.goodyearrvtires.com/pdfs/rv_inflation.pdf

 

[FL-JOE]

If you inflate those trailer tires at 60psi for example, and you are running 65mph on a sunny 90 degree day they will no doubt heat up. I would set the TPMS high heat warning to come on between 140 and 160 maybe. If I recall correctly most tires will fail above the 150 degree range.

As far as setting your psi parameters. On a hot day when towing a tire you have set at 60psi for example could have an increased psi of 75 to 80. This is normal so set your parameters accordingly. You don't want a warning to come on at 55psi nor do you want a warning to come on at 78.

Hope this makes sense?

 

[BGMAC]

Over inflated tires wear faster in the middle. Under inflated ones wear faster on both sides. You are right there is lest rolling resistance on over inflated tires.

This is mainly true with the old bias ply tires. With radials not so much as long as you have the correct tire for the rim width. It’s true. It will be a little harder ride. I’ve actually run 15 psi over the rating of the tire for many years and never wore the center of the tire (since I read the article). The truck tires I have today is rated at 45psi and I have 60psi in them now and have over 20,000 miles on them. Again I don’t advocate doing so.

 

[BGMAC]

In my case this is the manufacturers chart that I use.

https://www.goodyearrvtires.com/pdfs/rv_inflation.pdf

Yes, good chart. It shows the minimum tire pressure per weight. To be on the safe side I would run a little more. Running to low a pressure causes stress on the sidewalls.

 

[Buly]

Here is the Michelin radial tire wear patterns chart. Over and under inflation pattern is still in play.

 

[BGMAC]

Well, I’m not sure about all that. Looks like they kept pics of the old bias ply’s. It could happen if excessive over pressure. I’m running 15 psi over. Been doing it for 40 years since I read the article with no uneven tire wear. I’m comfortable with that.

Id say follow the limits, you won’t go wrong. I’m just stating what I read and what I practiced and what my results were.

This has been a fun discussion. i enjoy stuff like this. @Buly Id like to meet you sometime around a fire. I think we could have a lot of fun bantering back and forth.

 

[Buly]

Well, I’m not sure about all that. Looks like they kept pics of the old bias ply’s. It could happen if excessive over pressure. I’m running 15 psi over. Been doing it for 40 years since I read the article with no uneven tire wear. I’m comfortable with that.

Id say follow the limits, you won’t go wrong. I’m just stating what I read and what I practiced and what my results were.

This has been a fun discussion. i enjoy stuff like this. @Buly Id like to meet you sometime around a fire. I think we could have a lot of fun bantering back and forth.

BGMAC, we can meet the end of Sept. We are going to the annual canards fly-in at Rough River KY ?

 

[Lunge motorsport]

Tire pressue on a TT, here’s my take…

I’ve pondered this a lot over the years and this is what I do. I inflate to max recommended pressure as stated on the sidewall. My rationale is this. For most RV’s the tires age out long before they wear out. If yours don’t then good for you, you are getting your monies worth. Mine age out so over inflation for wear considerations does not concern me. Ride quality with the stiffer sidewall is not a consideration for me either. Most TT’s have leaf spring axles which I consider to be junk suspension, softly sprung, and bumpy without quality dampening characteristics. I secure all of the stuff in my trailer and no one rides in there. I read a post on another forum where the guy was suggesting that he wants maximum contact patch with his trailer tire for best grip and performance. Really? If a trailer requires that consideration, I would suggest that it is being pulled way too fast. So, I run max and I hope to wear the center tread out at the same time they age out, doesn’t happen for me. A side benefit would be that the reduced rolling resistance may increase my fuel mileage, however little that might be on a 10k brick going down the road.

Now I’m no stranger to tire inflation pressure adjustment, in fact I encourage it in the tow vehicle and any street car. I set mine on all my vehicles using a pyrometer. I do this loaded and unloaded. This method will provide you accurate pressure settings by giving you accurate tire temps across the tread. My dually rides crazy stiff empty, unloaded and loaded the inside rears want 5 psi greater pressure than the outside rears. I would only know this by reading the temps after a long run down the highway. I have to be fast because the temps tend to average together if an immediate measurement is not taken. My rears empty run 35 psi inside and 30 psi outside, for example. I’m sure some of you out there will argue this, I’m okay with your opinion, change my mind…

Cheers

 

[Bob K4TAX]

We run LT radials on the truck tow vehicle and ST radials on the trailer. I'm informed that P-rated tires are for passenger car applications. Normally around town, I have 30 PSI in the truck tires for a bit more comfortable ride. When we tow, I bring the truck tires to 40 PSI. The Max Pressure on the side of the tire is 44 PSI for the rated load. The trailer always starts out at 55 PSI. I figure it will always be loaded to the max and likewise for the truck.

A very important point, we do not exceed the speed rating of the trailer tires. The load range D tires are rated at 60 MPG as I recall. We drive 60 MPH and let the "show outs" pass us by. I'll likely pass them as they change a tire on the side of the road. The 60 MPH and 70 MPH difference on a 300-mile run is less than 45 minutes. That speed number is there for a reason. The human stress factor is much less during a 60 MPH run as well as lessened fuel consumption.

My saying "if you intend to exceed the maximum speed rating, then you just became a very underpaid tire designer or tire test driver." We all are going to end up on the mortician's cooling slab at one time or another. I prefer to arrive later than sooner.