Proper Tire Pressure...

[sloman2001]

I am changing all my tires on out 5ver from STs to LTs. I have looked for an answer to my question but to no avail, so I will try here, you have all been helpful in the past.

I'm going to put 80lb psi in the tire per the RV recommendation. The max tire pressure is also 80lbs. I'm putting on Michelin LT235/85R16 size tires. They are load range E tires (3042 lbs. at 80 psi), I have 5200 lb. axles.

While driving, this pressure will increase to various levels depending on the ambient temperature as well as speed (we drive 55 mph).

So 2 questions,
1) What is an acceptable level of psi above the 80lbs, and
2) If the pressure exceeds that, do I merely stop and remove some air?

I do not want another tire failure.

I have a TPMS in place so I can monitor the pressure real time.

Thanks in advance. I'm learning the hard way.

Tom

[sloman2001]

Sorry about that, Chris was correct. I had ST on the brain. I was planning on putting on LT235/85R16 LRE tires tomorrow. I think I am going to call the guy and check out the R250 or RIB tires he is suggesting to see cost difference. I'll let you know.

[Me_Again]

jadatis wrote:

To my opinion the LT here has only slighty more savety then the old ST of 235/80/16 .

You are here a lot and have not read all the threads on early failure of cheap light weight lowest bid ST tires? Maybe that is getting lost in the translation!

I ran Michelin XPS RIB on a similar trailer for 6.5 years and around 40K miles. Try that with any ST tire. I removed them because one was getting hair line cracks in the sidewall(it was actually 8.5 years old according to the date code) I sold the for tires with around 65 percent tread left for 200 bucks to a guy with an old pickup he used for garbage dump runs a couple times a month. He was tickled pink to get them.

I now have the R250 that I noted above and have two years of use going on them. I made sure they were fresh when I got them and plan of 7-8 years of used from them.

Chris

[jadatis]

Ok then thats solved .
but the difference in maximum load between the old ST and the new LT with almost same sises and that 80 psi the same wont give substantial difference in livetime and does not bring the chanche on blowouts back to zero.
In fact they are almost the same when you calculate it back to the same speed
ST Vr( velocity reference- is speed for wich the maximum load is calculated) is for the ST 65m/104km/h and for the LT probably N speedrated is 140km/83m/h.
If you calculate that back to the same speed of N speedrated the ST has 4 LI steps lower to my estimations in my topic.

Best would be to give the LT tire a bit higher pressure for absolute savety , Calculated it with my spreadsheet treating it as for 99m/h and dual load for absulute savety to need 86 psi real cold pressure ( measured with calcibrated device can stil give 5% higher reading.
To my opinion the LT here has only slighty more savety then the old ST of 235/80/16 .
Calculated with LI of 115-2679lbs and GVWR of 2*5200+10% hichweight.
Then your weighed 1820 hichweigt proves to be about 18% wich is over the 15% that is allowed.
So thats more then the 10100 you weighed , but was it weighed fully loaded.
Then weightdifference possibel right left of 1145 lbs before damage or bumping . This seems a lot but can even happen for 5th wheelers.
I have read of someone who weighed seperate wheels of 400 lbs per axle and even crossed weight difference between the axles.

[Me_Again]

jadatis wrote:
I am a bit confused now, you write

Tuesday, (1-28-14) I am putting on LTXMS2 Michelin tires all around, ST235/85R16. The load rating is a bit less than the ST tires, but well within spec. The size is slightly taller, but I should be OK. The load rating is 3042 @ 80 psi, with 5200 lbs axles on the trailer. That gives me some breathing room. But I also weighed the rig, the trailer rear axles weighed 8,240 lbs, while the hitch weight was an additional 1,860 lbs.

Are you saying that tuesday you will again put other tires on ST235/85R16 and those are others then the Michelin LTXMS2??

What you have try to determine is the maximum speed for wich the maximum load is calculated for. For that you have to read my topic I linked to in former reaction.

He is have a hard time getting ST out of his brain. I think he intended to write LT235/85R16. Chris

[jadatis]

I am a bit confused now, you write

Tuesday, (1-28-14) I am putting on LTXMS2 Michelin tires all around, ST235/85R16. The load rating is a bit less than the ST tires, but well within spec. The size is slightly taller, but I should be OK. The load rating is 3042 @ 80 psi, with 5200 lbs axles on the trailer. That gives me some breathing room. But I also weighed the rig, the trailer rear axles weighed 8,240 lbs, while the hitch weight was an additional 1,860 lbs.

Are you saying that tuesday you will again put other tires on ST235/85R16 and those are others then the Michelin LTXMS2??

What you have try to determine is the maximum speed for wich the maximum load is calculated for. For that you have to read my topic I linked to in former reaction.

[Me_Again]

sloman2001 wrote:
I bought the Cougar with an option called the "Mountain Package" at the time. It came with a larger tire and some extra suspension. So while the specs say the tire size is ST225/75R15, it actually came with an ST235/80R16, LR E. The axles have not been de-rated, they are 5200 lbs per axle.

On our way to AZ this year, we had a severe tire blowout in New Mexico, and it did about $2,000 worth of damage to the rig. So now, I am trying to be smart and maybe be overly cautious. So I am going to the LT tires, and was just trying to make sure I am going to be OK with the extra pressure after travelling. I do have metal valve stems with the TST TPMS system.

Tuesday, (1-28-14) I am putting on LTXMS2 Michelin tires all around, ST235/85R16. The load rating is a bit less than the ST tires, but well within spec. The size is slightly taller, but I should be OK. The load rating is 3042 @ 80 psi, with 5200 lbs axles on the trailer. That gives me some breathing room. But I also weighed the rig, the trailer rear axles weighed 8,240 lbs, while the hitch weight was an additional 1,860 lbs.

I really want to thank you guys for all your help. Any other thoughts welcome.

Tom

It is not to late to choose a better LT tire. The LTX M&S2 is a highly sipped traction type tire. The Michelin XPS RIB or Bridgestone Duravis R250(which is closer in cost of the LTX) are much better choices. Both are steel ply sidewall/carcass offerings and have lower rolling resistance, which is good for a trailer tire. The M&S2 also has by design a softer sidewall for ride quality of pickup trucks.

Price comparison on the tire rack site.
R250
245 =$230
235 =$232
M&S2
235 =$201
245 =$198
Note: They have really good prices on this tire. You were most likely quoted more.

Here is a picture of the R250.


In this picture of the M&S2 look at all the sipes, you do not want or need those in a trailer tire. In tight turns they will gripe the pavement to much, putting extra stress on the trailers springs, shackles, hangers, and frame. Tread can squirm going down the road when heavily loaded also, which a trailer tire is all the time!

Also compare the outer rib on each tire. The R250 and XPS RIB have close outer ribs without gaps, while the M&S2 has the gaps and sipes in the outer rib, again not good for tight cornering.



Again, take a serious look at the BS Duravis R250 for similar money!

Chris

[sloman2001]

And yes, I did run to the old tires @ 80 psi per the spec on the side of the certification label. So I can only assume the rims are rated for 80 psi.

Thanks again, Tom

[sloman2001]

I bought the Cougar with an option called the "Mountain Package" at the time. It came with a larger tire and some extra suspension. So while the specs say the tire size is ST225/75R15, it actually came with an ST235/80R16, LR E. The axles have not been de-rated, they are 5200 lbs per axle.

On our way to AZ this year, we had a severe tire blowout in New Mexico, and it did about $2,000 worth of damage to the rig. So now, I am trying to be smart and maybe be overly cautious. So I am going to the LT tires, and was just trying to make sure I am going to be OK with the extra pressure after travelling. I do have metal valve stems with the TST TPMS system.

Tuesday, (1-28-14) I am putting on LTXMS2 Michelin tires all around, ST235/85R16. The load rating is a bit less than the ST tires, but well within spec. The size is slightly taller, but I should be OK. The load rating is 3042 @ 80 psi, with 5200 lbs axles on the trailer. That gives me some breathing room. But I also weighed the rig, the trailer rear axles weighed 8,240 lbs, while the hitch weight was an additional 1,860 lbs.

I really want to thank you guys for all your help. Any other thoughts welcome.

Tom

[wandering1]

sloman2001 wrote:
I am changing all my tires on out 5ver from STs to LTs. I have looked for an answer to my question but to no avail, so I will try here, you have all been helpful in the past.

I'm going to put 80lb psi in the tire per the RV recommendation. The max tire pressure is also 80lbs. I'm putting on Michelin LT235/85R16 size tires. They are load range E tires (3042 lbs. at 80 psi), I have 5200 lb. axles.

While driving, this pressure will increase to various levels depending on the ambient temperature as well as speed (we drive 55 mph).

So 2 questions,
1) What is an acceptable level of psi above the 80lbs, and
2) If the pressure exceeds that, do I merely stop and remove some air?

I do not want another tire failure.

I have a TPMS in place so I can monitor the pressure real time.

Thanks in advance. I'm learning the hard way.

Tom

The correct PSI is what is on your sidewall. Fill while tires are cold, that means before you drive on them which will make them warm.

The tire pressure will increase as you drive on them, that is whats supposed to happen, do not adjust the pressure.

[mpierce]

Put 80# in COLD, and leave them alone! Do NOT let air out when hot. They are designed for heating up.

And, by the way, FIRE the tire guys, and NEVER go back to talk to them, or have them even TOUCH your tires! They are not only stupid, but dangerous.

[JIMNLIN]

So 2 questions,
1) What is an acceptable level of psi above the 80lbs, and
2) If the pressure exceeds that, do I merely stop and remove some air?

I've seen my LT235/85-16 E tires on my equipment trailers with max tire loads go to 92-94 psi while on a all day run. All is normal per the tire mfg.

Tire mfg also tell use to never let air out of a hot tire.
Your wise to keep them pumped to the max sidewall pressure. They will run cooler and last longer.

[jadatis]

You are even allowed to put 90 psi cold in them if that is needed.
The 80 psi is called the maxloadpressure or reference-pressure( further Pr for pressure reference) and is not the maximum cold pressure of the tire ( further Pmax).
From C-load always the Pr is written on sidewall , but for standard load /P-tire and XL/Extraload/reinforced the Pmax is written on sidewall. The Pr is SL/P-tire 35psi/2.4bar and XL// 41psi/2.8 bar for American tires, Europe a little different and some exeptions.

Once determined by and article of Semperit(continental) that the Pmax cold is 1.4 times the Pr cold.
So your tire can stand even 1.4 X 80= 112 psi cold. Also the valves are given cold maximum pressure in their standards and a normal rubber valve can stand 65 to 70 psi cold and may rise to American mildest standards to 26psi/1.8 bar higher so 91 to 96 psi warm.
This is needed because when severe braking the inside tire temperature can rise incidentially to even boiling point of water, and with that the pressure rises that 1.8 bar.

You probably have metal valves so they can stand the pressure even more ( above 10 bar / 145psi) but Highpressure rubber snapp in valves from the TR600HP series can stand a cold pressure of 6.3bar/95psi to mayby 6.8bar/100psi depending on the brand. Probably even more psi rising for warm , but I dont have the standards for them given.

So dont be afraid with the pressure and never bleed air when warm.
Best would be to give the tire a pressure that is save for it at the coldest outside temperature you ever get in , so then its still save.
Then when outside gets warmer, you have higher pressure but still within the limits so you wont get terrible bumping, and within the limits of what tire organisations allow.

Also look at my opened topic about
Comparing tires for replacement

[Old-Biscuit]

Max Load at Max PSI on sidewall states 80# then you can put 80# in the tires (cold).
Then check them again the NEXT day and adjust accordingly to 80# (cold)


Provided your rims are rated for 80# psi or 3042# weight.

And with 5200# axles....you can run those tires at 65# psi and have a load capacity of 2623# (5246# per axle).

So are your rims rated for the higher PSI/Load??
Did you run the ST's at 80#?

[Me_Again]

old guy wrote:
I asked the tire guys this just last week. they said put 75 in so when they get hot they will have a 5 psi to expand

You need to fire those tire guys, as they are not well trained. If one has a tire installation that requires the full 80 inflation it is OK for them to go over that when warmed up driving. Manufacturers factor that into the tire. Chris

[old_guy]

I asked the tire guys this just last week. they said put 75 in so when they get hot they will have a 5 psi to expand