New Tires

[gserve]

Just replaced the tires on my RV. I went from load range C to load range D tires. My question is about the cold PSI. The C rated tires were 50 PSI max. The new are 65 PSI. What should I go by? Any comments welcome.

[YeatesB]

Part of the load rating of a tire is the PSI that it’s run at. Running at a lower than rated PSI will reduce the performance of the tire (and it’s ability to safely support the rated load). So, go with the PSI of the new tires.

[Airdale]

Originally Posted by gserve

Just replaced the tires on my RV. I went from load range C to load range D tires. My question is about the cold PSI. The C rated tires were 50 PSI max. The new are 65 PSI. What should I go by? Any comments welcome.

If the 50 PSI is on the vehicle certification label it is the minimum requirement for that trailer. New tires of the same designated size use an identical load inflation chart for all Load ranges. So, to take advantage of the extra load capacity of the LRD tires, your PSI options are between 50 to 65 PSI.

Depending on the age of the trailer you should insure the new ties provide a load capacity at least 10% above the trailer's vehicle certified GAWRs. A very high percentage of trailers manufactured before 2016 did not have much load capacity reserves and may have had none. The RVIA recommendation is 10%. Many in the industry will recommend 15% to 18% above certified GAWRs.

[NavyLCDR]

Originally Posted by gserve

Just replaced the tires on my RV. I went from load range C to load range D tires. My question is about the cold PSI. The C rated tires were 50 PSI max. The new are 65 PSI. What should I go by? Any comments welcome.

is there an inflation pressure v. weight chart available from the manufacturer of the tires? I would take the GVWR of the trailer divided by the number of tires, and add 20%. Use that as the weight to determine what pressure to inflate the tires to - unless it is less than the inflation pressure specified by the placard on the side of the trailer - then I would go with the placard pressure (in other words, whichever is higher).

If you have a dual axle trailer with a GVWR of 6,000 that is 1,500 per tire. +20% is 1,800 lbs per tire. Goodyear Endurance LRD tires call for 50 or 55 PSI depending on tire size.

[Airdale]

Originally Posted by NavyLCDR

is there an inflation pressure v. weight chart available from the manufacturer of the tires? I would take the GVWR of the trailer divided by the number of tires, and add 20%. Use that as the weight to determine what pressure to inflate the tires to - unless it is less than the inflation pressure specified by the placard on the side of the trailer - then I would go with the placard pressure (in other words, whichever is higher).

If you have a dual axle trailer with a GVWR of 6,000 that is 1,500 per tire. +20% is 1,800 lbs per tire. Goodyear Endurance LRD tires call for 50 or 55 PSI depending on tire size.

Using the proper terminology is important when writing about tires. Each standard in tire applications are designed to have the end vehicle product pass vehicle certification. The following is a FMVSS standard within a standard.

FMVSS 571.120 paragraph S5.3.1 Tires. The size designation and the recommended cold inflation pressure for those tires such that the sum of the load ratings of the tires on each axle is appropriate for the GAWR.

Additional certification information can be found in CFR 49 part 567.

[NavyLCDR]

Originally Posted by Airdale

Using the proper terminology is important when writing about tires. Each standard in tire applications are designed to have the end vehicle product pass vehicle certification. The following is a FMVSS standard within a standard.

FMVSS 571.120 paragraph S5.3.1 Tires. The size designation and the recommended cold inflation pressure for those tires such that the sum of the load ratings of the tires on each axle is appropriate for the GAWR.

Additional certification information can be found in CFR 49 part 567.

OK. Thank you for the correction. On a dual axle trailer, take the GVWR and divide it by 2. That should give you the GAWR for each axle. Take that number and divide it by 2. That should give you the maximum load on each tire. Add 20% for safety margin. Then inflate accordingly.

So, in my previous, obviously erroneous example, for a dual axle trailer with a GVWR of 6,000 lbs, divide that by 2 to get 3,000 lbs GAWR. Divide that by 2 to get a max tire loading of 1,500 lbs per tire. Add 20% to account for unbalanced side to side loading and you get 1,800 lbs for each tire.

Is that better?

[NavyLCDR]

And if you don't feel comfortable with weight calculations and reducing tire pressure - the max inflation pressure marked on the side of the tire is always safe. The only advantage to reducing tire pressure (again, never below that posted on the placard) is a softer ride for the trailer, less bouncing.

[KMP44]

Originally Posted by NavyLCDR

The only advantage to reducing tire pressure (again, never below that posted on the placard) is a softer ride for the trailer, less bouncing.

This.

We put LR D tires on our Roo years ago. Have put thousands of miles on 2 sets of LR D's at 55 psi. I was originally going to set them at 65, but the guys at the tire shop recommended staying close to the 50 psi on the manufacturer's sticker. Stared there and never changed it. I was looking for a better quality tire when I upgraded, not to carry more weight. The trailer always had a nice soft ride with the torsion axles, so keeping the ride quality was nice. And of course there is the endless theoretical debate about pressure rating of the rims. But regardless, that's what we did and it's worked well.

[Airdale]

Originally Posted by NavyLCDR

OK. Thank you for the correction. On a dual axle trailer, take the GVWR and divide it by 2. That should give you the GAWR for each axle. Take that number and divide it by 2. That should give you the maximum load on each tire. Add 20% for safety margin. Then inflate accordingly.

So, in my previous, obviously erroneous example, for a dual axle trailer with a GVWR of 6,000 lbs, divide that by 2 to get 3,000 lbs GAWR. Divide that by 2 to get a max tire loading of 1,500 lbs per tire. Add 20% to account for unbalanced side to side loading and you get 1,800 lbs for each tire.

Is that better?

Attachment 270889

The only GAWRs to be used in calculations are displayed on the vehicle certification label. Since year 2015 trailer, manufacturers have added a 10% (minimum) increase in load capacity above vehicle certified GAWRs for all OEM tires. There is nothing wrong with increasing load capacity from that point, providing the OEM tires are not already maxed-out. Adding a load range for tires of the same designated size as the ones on the certification label allows more inflation pressure to gain more load capacity.

The 10% is a recommendation and not binding for OEM tires. However, the recommendations came from the RVIA organization. About 98% of all RV trailer manufacturers are members of RVIA and abide their recommendations.

[mwdilday]

Originally Posted by NavyLCDR

And if you don't feel comfortable with weight calculations and reducing tire pressure - the max inflation pressure marked on the side of the tire is always safe. The only advantage to reducing tire pressure (again, never below that posted on the placard) is a softer ride for the trailer, less bouncing.

And a proper footprint / tire profile on the pavement.

[NavyLCDR]

It should noted that when Airdale talks about increasing the load capacity of the tires, that in no way means you can increase the cargo capacity of the trailer. The weight limits for the trailer remain the same. You don't gain cargo carrying capacity just by changing tires or inflation pressure.

[Airdale]

Originally Posted by NavyLCDR

It should noted that when Airdale talks about increasing the load capacity of the tires, that in no way means you can increase the cargo capacity of the trailer. The weight limits for the trailer remain the same. You don't gain cargo carrying capacity just by changing tires or inflation pressure.

Isn't that another subject? The vehicle certification label defines the GVWR and GAWR requirements. RV trailers are inherently unbalanced. Therefore, their tires need to have some load capacity reserves to protect from unbalanced conditions.

The trailer, as a whole, when fully loaded and weighed may be under GVWR but the weight across the axles can be very different from side to side.

So, a consumer has weighed the trailer including wheel positions and all weights are acceptable and a few hundred pounds under GVWR. After leaving the scales and departing on a trip water is added. Where's the tank that's holding that water?

[MNtraveler]

Get the load and inflation recommendations from your tire manufacturer and follow those for the weight of your unit, at each axle as mentioned. You should have GVWR and GAWR front and back on your driver’s side door frame. Weigh the unit per axle if possible at a truck scale.

Do not go by “max PSI,” but do not exceed it.

There is a proper inflation for your tires and your weight load. Figure it out and use it.

Side note: this is only needed because OP change tire load range. For original tires, follow the manufacturer’s recommendation on the panel inside the driver’s side door.

[Airdale]

Originally Posted by MNtraveler

Get the load and inflation recommendations from your tire manufacturer and follow those for the weight of your unit, at each axle as mentioned. You should have GVWR and GAWR front and back on your driver’s side door frame. Weigh the unit per axle if possible at a truck scale.

Do not go by “max PSI,” but do not exceed it.

There is a proper inflation for your tires and your weight load. Figure it out and use it.

Side note: this is only needed because OP change tire load range. For original tires, follow the manufacturer’s recommendation on the panel inside the driver’s side door.

The above method is from the trucking industry (FMCSA) and is not applicable with FMVSS standards for RV trailers.

[MNtraveler]

Originally Posted by Airdale

The above method is from the trucking industry (FMCSA) and is not applicable with FMVSS standards for RV trailers.

So what are you recommending? You posted quoting regulations about tire selection that don't really say what to do about psi, and said something about doing calculations, but you never said what you are recommending. What calculations are you recommending the OP do given that they changed tire load range?

<<If the 50 PSI is on the vehicle certification label it is the minimum requirement for that trailer. New tires of the same designated size use an identical load inflation chart for all Load ranges. So, to take advantage of the extra load capacity of the LRD tires, your PSI options are between 50 to 65 PSI.>>

The OP did not have a vehicle certification at 50 psi. The OP stated that the max PSI for the LRC was 50 and the max PSI for the LRD was 65.

Regarding the 10% or higher margin, the OP's RV had LRC tires which we can assume were appropriate for the RV. No reason to think otherwise. OP moved to LRD which would have an even higher safety margin.

None of which answers the OP's question of what psi to use.

The OP never stated what the labeled tire psi levels are on the RV's door jamb.

Someone else responded about dual axle trailers and dividing the weight by two, etc. OP never said they had a trailer, they said it was an RV. I certainly agree with what you said about the GAWR for each axle being labeled on the RV. The psi for the LRC tires would be posted there too, for the original LRC tires, but that does not answer it for LRD tires.

Thx.

[Airdale]

Originally Posted by MNtraveler

So what are you recommending? You posted quoting regulations about tire selection that don't really say what to do about psi, and said something about doing calculations, but you never said what you are recommending. What calculations are you recommending the OP do given that they changed tire load range?

<<If the 50 PSI is on the vehicle certification label it is the minimum requirement for that trailer. New tires of the same designated size use an identical load inflation chart for all Load ranges. So, to take advantage of the extra load capacity of the LRD tires, your PSI options are between 50 to 65 PSI.>>

The OP did not have a vehicle certification at 50 psi. The OP stated that the max PSI for the LRC was 50 and the max PSI for the LRD was 65.

Regarding the 10% or higher margin, the OP's RV had LRC tires which we can assume were appropriate for the RV. No reason to think otherwise. OP moved to LRD which would have an even higher safety margin.

None of which answers the OP's question of what psi to use.

The OP never stated what the labeled tire psi levels are on the RV's door jamb.

Someone else responded about dual axle trailers and dividing the weight by two, etc. OP never said they had a trailer, they said it was an RV. I certainly agree with what you said about the GAWR for each axle being labeled on the RV. The psi for the LRC tires would be posted there too, for the original LRC tires, but that does not answer it for LRD tires.

Thx.

Cone on, I do my homework. The OPs profile says his RV is a trailer.

Everyone seems to have their own opinion about tire inflation pressures. It's very simple. Follow the vehicle manufacturers recommendations. Adding a load rage to the certified OEM tires changes nothing except a gain in load capacity. That gain in load capacity is optional and acceptable providing the wheels and their valve stems are certified for the increased inflation pressures.

[MNtraveler]

Originally Posted by Airdale

Cone on, I do my homework. The OPs profile says his RV is a trailer.

Everyone seems to have their own opinion about tire inflation pressures. It's very simple. Follow the vehicle manufacturers recommendations. Adding a load rage to the certified OEM tires changes nothing except a gain in load capacity. That gain in load capacity is optional and acceptable providing the wheels and their valve stems are certified for the increased inflation pressures.

I agree with you on that. But that does not mean to go with the tire rated max of 50 or the max of 60. I agree with following the VEHICLE manufacturer's recommendation. Thank you.