Determining best tire pressure

[booster]

Originally Posted by Pam G

Booster,
It's interesting reading through this whole thread but I just have a simpler question. I remember reading through this topic not too long ago, but I don't think I asked it there.

I have a 1999 RT 190P. The door tag says to use 45 front and 80 rear, so that's what places like Jiffy Lube will put it. As the typical Dodge, the handling is a little loose but it seemed more so when I got it 5 years ago. When I bought it, I asked at several places what they thought would be the best tire pressure to use, but I never got a clear answer, so I was putting them at 45/80. I had to have the tires replaced while on a trip, and the man there told me to set them at 55 front and 75 in the rear. So, I have been doing that for about 3 years now, and I've thought the handling is much better. Your post explained why I would find that. I'm curious, though, about the rear tire pressure. The reason I had to have the tires replaced is that a rear tire blew out while on the highway - the tires had dry rot (previous owner didn't use it much). So, I'm assuming the man told me to air it to 75 since the air pressure increases from the heat produced while driving. Is that correct?

Is 55 okay on the front or should I go with 60? Is it better to go with 80 on the back instead of 75?

Pam

Good questions, and I am sure some Dodge experienced folks will chime in on the Dodge specific parts.


From what we have seen and I remember, 60-65 psi in front seems to be where most Dodges like to run, but again the Dodge owners will know best on that. Trying out higher pressure in the front has essentially no risk, so trying 60 first would be a way to go and if you like that better then try 65 and see what you think.


If the tire failed because of dry rot, you really can't blame the pressure or heat for the failure, IMO. I would not agree with the theory of reducing the pressure to allow for heating pressure gain. Essentially all the tire manufacturers recommend against it as they claim, rightly IMO, that can make the problem worse. The pressure may stay some lower when hot, but the softer tire may actually run quite a bit hotter, which is the biggest issue. I would only reduce rear pressure in a class b if the rear weights were approaching the front weight, so in the low 4000# range and most 190s will likely be above that with the big rear overhang they have.


It is not surprising that the handling might be feeling worse as the van is approaching 20 years old and has bunch more miles on it than it used to. There have been numerous discussions on improvements for Dodge on the forum and I hope the Dodge folks will put them here, too. Dodges, particularly around your year are known to be spotty on handling and some worse than others.

[Pam G]

Booster,
Thanks so much for your response. I'm hoping some Dodge owners do respond too, but you answered my question. I haven't been able to get a straight answer from anyone here, but then I was asking people who usually don't work on motorhomes. I'm far from being a mechanic or an engineer (my degree is in wildlife management), and I didn't know if it would be a problem to increase the pressure on the front tires. I think the handling has been better since I went to 55 on the front, so I will try 60. This is my 3rd Dodge Ram 3500 chassis, so it's the only one I have experience with. My first was a 1998 Coach House, the second a 2001 Coach House. I thought the steering on my 1999 Roadtrek has been the worse of the three, but this vehicle also sat more than the other 2. It only had 39,000 miles on it when I bought it 5 years ago, as compared to around 75,000 miles on the Coach Houses. I've never had tires with dry rot before so I wasn't experienced with that either until the tire blew out. There are 3 other issues I've had because of the RT not having been used very much, but 2 of them have been fixed. I think I have around 80,000 miles on it now.

I will be heading out on a trip on May 1, so I will try 60 psi on the front and will use 80 on the rear and see how that goes! I'm hoping that I'll have the RT for a few more years. I'm planning on retiring in 3 years and want to go full time in it for at least a year, if not more.

Thanks again!!

Pam

[Bud]

"my degree is in wildlife management"

Very good Pam as sometimes the forum needs a little of that. For example, joining 2 four letter words together in the last 2 months definitely stirred up some of the wildlife here.

Bud

[Rockwood27]

Pam G, before you run high tire pressures, make sure your tires can handle it. Your RV is 20 years old. Certainly the tires have been replaced due to age out. Were they replaced with the same or higher load rating? Or a lower rating? Look on the tire sidewall to determine what the maximum pressure is. Don't exceed it. Also, your wheels have a maximum pressure and load rating. Make sure those values aren't exceeded. Higher capacity tires may exceed the wheel rating.

[booster]

Originally Posted by Rockwood27

Pam G, before you run high tire pressures, make sure your tires can handle it. Your RV is 20 years old. Certainly the tires have been replaced due to age out. Were they replaced with the same or higher load rating? Or a lower rating? Look on the tire sidewall to determine what the maximum pressure is. Don't exceed it. Also, your wheels have a maximum pressure and load rating. Make sure those values aren't exceeded. Higher capacity tires may exceed the wheel rating.

She is currently setting at 80psi rear, so hopefully her tire guy put in the high pressure valves in all wheels, which also should be fine as I am almost certain the van came with load range E tires on it.

[Pam G]

Originally Posted by Rockwood27

Pam G, before you run high tire pressures, make sure your tires can handle it. Your RV is 20 years old. Certainly the tires have been replaced due to age out. Were they replaced with the same or higher load rating? Or a lower rating? Look on the tire sidewall to determine what the maximum pressure is. Don't exceed it. Also, your wheels have a maximum pressure and load rating. Make sure those values aren't exceeded. Higher capacity tires may exceed the wheel rating.

I've replaced all 4 tires twice since all 4 of the original ones (when I bought it) had dry rot. The new tires are the same kind as the original ones, and I think they're the same as what were on the Coach House's that I had, so they should all be the correct load rating. My mechanic/body shop replaced the tires the last time, and he's worked on my RT and bigger motorhomes, so I'm assuming he knows what is correct. I believe all 4 tires are the same brand and size, etc. I will look at them when I get home. Thank you for the information!

Pam

[Pam G]

I'm pretty sure they're load E tires. I should remember the numbers on the tires by now, but I don't want to write something incorrectly, so I'll look when I get home tonight. They're the same as what I've been using the past 12 years on all 3 Class B's.

Thanks!

Pam

[Scottnelson@srmg-link.com]

As a non- rocket scientist my solution is simple: Follow manufacturers recommendations & then simply adjust 2 conditions. the "kiss" principal.

[GallenH]

1997 PleasureWay on Dodge chassis. I've been running 55/80 and it appears to work out fine. Given booster's comments I'll probably try 60/80 on next trip and see how it handles.

I've gotten used to the quirks on the steering/handling yet I still notice the difference when I get home and drive my RAV4. The latter seems like manual steering for a while. So the Dodge is light. There have been numerous posts throughout the forum about steering stabilizers, rear wheel spacers and the like. For the most part though, the PW handling is ok. Still don't like blind curves on mountain roads. But........I possess a great fear of heights so it's partially that.

[booster]

Originally Posted by GallenH

1997 PleasureWay on Dodge chassis. I've been running 55/80 and it appears to work out fine. Given booster's comments I'll probably try 60/80 on next trip and see how it handles.

I've gotten used to the quirks on the steering/handling yet I still notice the difference when I get home and drive my RAV4. The latter seems like manual steering for a while. So the Dodge is light. There have been numerous posts throughout the forum about steering stabilizers, rear wheel spacers and the like. For the most part though, the PW handling is ok. Still don't like blind curves on mountain roads. But........I possess a great fear of heights so it's partially that.

A good idea, IMO, as it never hurts to try something as easy to do as a tire pressure change that others have found to be good. No guaranty that you will like it, as handling is so very much personal preference, but also no risk.


Be sure to let us all know what you think, as more data points is never a bad thing in stuff like this.

[Mfm]

Booster- very informative. I have a question regarding tires that you or others may be able to help me with. I have a 2014, MB, RT Agile with about 25K miles on original tires. The tread is good according to last visit to MB service. However, it was pointed out to me that in between the tread, there were cracks in the rubber. Is this something that I should be concerned. Thanks in advance. Mike

[booster]

Originally Posted by Mfm

Booster- very informative. I have a question regarding tires that you or others may be able to help me with. I have a 2014, MB, RT Agile with about 25K miles on original tires. The tread is good according to last visit to MB service. However, it was pointed out to me that in between the tread, there were cracks in the rubber. Is this something that I should be concerned. Thanks in advance. Mike

I think it is certainly something to get checked out by a reputable tire dealer for the tire brand, as I don't think any cracks are ever considered normal. Tires are probably in the 6-7 years old range for a 2014 conversion so reaching age out besides.

[Phoebe3]

Originally Posted by jadatis

Then I judged it right about the weights,.
Will give link to map on my onedrive that belongs to my hotmail.com adress with same username as in this forum ( so jadatis) https://onedrive.live.com/?id=A526E0...26E0EEE092E6DC
In that map my calculator, wich you can fill in in the claud, but then you see , when looking back later , your chanches or from others behind you.
Best is to download it to your computer, and after eventual virus-check, use Excell or similar programm on your computer.

In that calculator 3 parts
1 to give the tire and vehicle data
2 if only gawr filled in gives advice for front adding first 5% because front seldom overloaded. Rear a floting scale , 18% adding for the lighter motorhomes, and going down to 10% for the heavyer ones, because those are seldomly overloaded on rear axle.
When in part 2 given weight on axles, adding 10% for R/L unbalans, and calculates automatically for those given weights.
But you can chanche the % if you think different.

parts 3 is for when you did axle-end weighing ( fully loaded as going on tripp) . Notice the torsion, often crossed weightdifference between the axles, so for instance front Right more heavy and rear Left more heavy.

Will leave it at this, can write a book about it.

Thank you for doing this! I used your most recent file (I think, it said it was updated last Friday).

Here is a screenshot of the top portion.

I put the Ford GVWR and GAWR in the dark blue cells at the top.

I put the Ford GVWR and GAWR and the Ford recommended tire pressures in the light blue cells that are in the grey ovals. Since this is the maximum weight that would ever occur on the axles.

In the light blue cells below, I put the actual weights of the axles that we got from the scale.

Since the recommended tire pressures are far too low, I must have done something wrong. Can you explain it further?

[booster]

Originally Posted by Phoebe3

Thank you for doing this! I used your most recent file (I think, I said it was updated last Friday).

Here is a screenshot of the top portion.

I put the Ford GVWR and GAWR in the dark blue cells at the top.

I put the Ford GVWR and GAWR and the Ford recommended tire pressures in the light blue cells that are in the grey ovals. Since this is the maximum weight that would ever occur on the axles.

In the light blue cells below, I put the actual weights of the axles that we got from the scale.

Since the recommended tire pressures are far too low, I must have done something wrong. Can you explain it further?

I just did our Chevy with the larger tires and got 46/60 psi, which come fairly close to what the Michelin chart list for what appears to be min pressure for the weight, so likely that is what the calculator is also doing.







We actually have found the best balance of driveability and comfort to be at 63/76 psi.


If this is the case, the calculator would be checking to make sure you get in under the max tire load for safety, but would not have anything to do with driveability.

[Phoebe3]

Originally Posted by booster

I just did our Chevy with the larger tires and got 46/60 psi, which come fairly close to what the Michelin chart list for what appears to be min pressure for the weight, so likely that is what the calculator is also doing.

We actually have found the best balance of driveability and comfort to be at 63/76 psi.

If this is the case, the calculator would be checking to make sure you get in under the max tire load for safety, but would not have anything to do with driveability.

You must be doing something different. Or maybe I downloaded the wrong calculator. As you can see, mine claims I only need 11 psi for the rear wheels and 26 psi for the front. I just don't believe it on a 9,000 lb vehicle.

[booster]

It looks like your put the weights back in the area that is circled on your pick.


That is the tire rating, so click on it and select from the flyout what load rating number or weight rating your tires are. I did the same thing when I went through it the first time.

[Roadtrek Adventuous RS1]

Question; when you mentioned 80 pounds of tire pressure you're talking about fully warmed up tires, correct?

[Roadtrek Adventuous RS1]

Originally Posted by booster

I think it is certainly something to get checked out by a reputable tire dealer for the tire brand, as I don't think any cracks are ever considered normal. Tires are probably in the 6-7 years old range for a 2014 conversion so reaching age out besides.

I was advised that it's all about age, especially because of the kind of vehicle... almost 10 feet tall.... blowing a tire is going to be much more dangerous and expensive than replacing them....So, I was pretty much planning on every 5 to 6 years regardless of mileage or wear.....

The tire shop said... we'll see you way before you can wear them down...so far, I believe that...

You'd have to be doing 10,000 miles or more to take advantage of the mileage warranty..... not going to happen in my case.

[BillsPaseo]

Tire pressures are spec'd cold, so you should either check before driving or wait 30 minutes after driving for them to cool down before checking pressure.

[gregmchugh]

Originally Posted by Roadtrek Adventuous RS1

Question; when you mentioned 80 pounds of tire pressure you're talking about fully warmed up tires, correct?

Recommended tire pressures are always for cold tires not tires that are warmed up from driving. Usually I check in the morning.