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Old 04-14-2017, 12:53 AM   #15
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I generally agree that assuming can get you in trouble, but so can statements that begin with "never". If Tiffin is sending out new MHs that are heavier than what their components are rated for then Tiffin has some massive liability issues coming. Also, it is in fact safe to assume that Tiffin knows a thing or two about how much pressure to put in the tires when they ship their new units. Considering that at this point there isn't anything in our coach aside from a couple of chairs, cutlery, plates/cups and some spices, I think I'm okay with running their shipping pressure.

What I'm getting from the responses is that there is a huge variance in how much pressure people run and that is because of the huge differences in 1) tire types and MH type/model and 2) how heavy people are depending on how loaded up they are and 3) different theories in regard to how much pressure is correct for safety and ride quality.

I'm also surprised and a bit worried to hear that the label can be off as much as 25 psi compared to what it should be according to weight?! Wow. I figured it would be at least within 5 maybe 10 psi.

I'm going to check my pressure, see how close it is to the label from Tiffin and run that until I can get it properly weighed. I might even call or research what Michelin has to say on the topic since it seems various tire manufacturers have differing opinions on the matter. Also, if anyone has the same coach as we do and is running the same tires, I'd be curious to know what psi you are running.
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Old 04-14-2017, 05:26 AM   #16
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When it comes to assumptions, "never" pretty much covers it.

As far as any liability issues, YOU are the owner / operator; Tiffin isn't in the equation any longer.

There are no "theories" on tire pressure - only formulae. Formulae you can't use until you provide a variable.

There is no such thing as "same coach running same tires", unless that other coach has the same stuff in it as yours. After that, there are no longer comparisons.

The tire pressures listed by Tiffin are a baseline until you get your MH weighed, which is pretty much what everybody who has responded to you has suggested you do sooner than later.
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Old 04-14-2017, 08:07 AM   #17
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OK, enough theory - here's how you do it:

1. Locate a CAT scale (truck stops have them)
2. Leave your toad at home and fill the motorhome as you would for a trip
3. Pull onto the scale and get your front and rear axle weights
4. Go inside and pay your $11 weigh fee and get your printout

Now for the arithmetic:

Get out your Michelin tire chart for truck tires (either in your big blue bag or online)

1. Take your front axle weight, multiply by 1.05 and divide by two. Look that number up in the tire chart for the inflation pressure. Add 5 psi to that number for a little safety margin. You are half done.

2. Take the rear axle weight, multiply by 1.05 and divide by two. Look that number up in the dual tire section of the tire chart. The chart for dual tires will give the inflation pressure for each tire in the pair. Add 5 psi to that. You are done.

The use of 1.05 (5%) is compensate for side to side variation in lieu of getting individual wheel weights.

Individual wheel weights are fine, if you can find someone that does them. Your best bet is at rallies. Driving up the side of a CAT scale will give you inaccurate weights and are about in the same league as the 5% estimate you used above.

Individual wheel weights:

1. You still will inflate both (or all 4) tires to the pressure required for the heaviest wheel.
2. If you find a weight that is more than 5% from side to side, you need to talk to the manufacturer on how to best correct that. The stuff you can move around usually won't impact the weight that much.
3. However, if you can get them at a rally you should do so. Peace of mind if nothing else.
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Old 04-14-2017, 02:38 PM   #18
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Weighing can prove that you should better use a higher pressure then given on the official plate, so that is the use of weighing.

For that advice on official plate , often the GAWR's are used and if 2 tires on axle, pressure calculated for GAWR/2.
If then all to law , so extact GAWR, but for instance a loaddivision R/L of 55/45 on the axle, the pressure for 50% calculated needs to be at least 10% higher to cover the weight on the "heavyest" wheel with that 55% on it.

Then also some inacuracy cal be in the device to measure the pressure .
So its always best to use as much possible reserve, but to much gives discomfort and bad gripp. Trick is to find the best balance .

Last is that Pressure loadcapacity lists are different made with different formula's, and law of nature allows only one calculation , because tires are in basics the same all over the world.
American TRA calculation for LT and trucktires comes to lower pressures then the European calculation, and my deterinened calculation gives even higher pressures then the European calculation.

So once you determined , as acurate as possible , the weights on seperate tires ( like this because wheelpair in Dual load axle has 2 tires), give those weights , and the tire data , and determine the speed you drive and wont go over for even a minute, and I will put it in my made calculator, and give you a pressure range in wich the tires are save, and gripp and comfort is still acceptable.
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Old 04-14-2017, 03:04 PM   #19
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Quote:
Originally Posted by luvlabs View Post

The use of 1.05 (5%) is compensate for side to side variation in lieu of getting individual wheel weights.

Individual wheel weights are fine, if you can find someone that does them. Your best bet is at rallies. Driving up the side of a CAT scale will give you inaccurate weights and are about in the same league as the 5% estimate you used above.
I strongly disagree, I did it with three different coaches I've owned over the years. I just pulled up with one side off the scale, and the other as near center as possible.

then the other side
I also do full on for F/R so a total of three weights

Later on did individual scales at a rally, that 5% theory would have fallen on it's face on several rigs

some were almost 15%


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Old 04-14-2017, 04:21 PM   #20
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Nope, gotta disagree that "never" covers assumptions. In fact, it would be near impossible to get through life believing that for too many reasons to list here. That's not to say "never" doesn't cover it most of the time.

Tiffin is very much liable for various things after you drive off in their coaches same as any company that sales a product in today's world. This is why you see idiot stickers/warnings all over their coaches and manuals and anything you buy these days. We live in a litigious society where people actually derive their entire income from exploiting liability. Selling a coach that is overweight for the tires/chassis they use would be at the top of the list. I'm sure you can figure out why. So I'm going to go ahead and assume that when my coach left the Tiffin plant the tire pressure was correct for my make and model and tires. I feel comfortable making that assumption.

As far as what I do in the future, I'll most probably be getting her weighed and using the formula. I'm still going to research Michelin's ideas on the topic, but until I can find the time I'm going to "assume" they believe the same as the majority of manufacturers.
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Old 04-14-2017, 04:29 PM   #21
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Ajadatis, for some reason it doesn't surprise me that there are different formulas out there and everyone probably thinks they know better why the one they use is the best. It also makes sense that, depending on the method ones uses to weigh, the results are going to vary quite a bit. If you don't mind, I'll take you up on your offer to use your calculator. I like to have more information than less, that always helps!

So nobody out there running a 2016/17 Bus 40SP with Michelins the same size? I'm just curious what a ballpark figure is before I weigh. Thanks!

EDIT: for the hard of reading posters out there, here's what I said earlier:

"I'm going to check my pressure, see how close it is to the label from Tiffin and run that until I can get it properly weighed." Maybe read before giving out the same advice...
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Old 04-14-2017, 06:20 PM   #22
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Originally Posted by Rzani View Post

EDIT: for the hard of reading posters out there, here's what I said earlier:

"I'm going to check my pressure, see how close it is to the label from Tiffin and run that until I can get it properly weighed." Maybe read before giving out the same advice...
I think the problem many reading your posts are having is your apparent nonchalant attitude towards weighing your coach. Most everyone has suggested very strongly that you do not "run with it" until you get it weighed, but rather, get it weighed - now.

That's because you literally have no idea what weights are running on your tires right now. None. And while you may want to rely on someone else (Tiffin) for your security, most everyone has suggested that course of action is problematic and very trusting on your part.

Don't get me wrong; by and large we all love Tiffin, but even Tiffin makes mistakes. Ronald Reagan made the quote famous, "Trust, but verify". For $11 bucks, it's cheap insurance that Tiffin has, in fact, done their job right.

I don't know about the others, but I'm kinda wondering why you asked the initial question if you were going to ignore the almost unanimous advice given you in the responses.
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Old 04-14-2017, 08:09 PM   #23
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Really? Seriously, your the only one who thinks Tiffin ships their coaches without the required amount of PSI in their tires or too much. Everyone else seems to think it's a good idea to run with what they put in there and to get it weighed when I can and then follow the formula which is what I've stated I will be doing...twice. Rather than run out the day you get it and have it weighed because Tiffin, although building arguably the best and longest lasting coach in the industry, can't seem to figure out how much PSI to put in their tires?? Tiffin builds a great coach, but they aren't perfect, but even being not perfect I have a feeling that when they produce a 40SP (or name the model) it's going to be very, very close in weight to the next 40SP they build and they are aware of the PSI that should go into their tires for that weight. Just because you think otherwise doesn't make you correct.

I'm not worried about it because there have been numerous contradictory answers to my initial question. Yes, most go with weighing it (although, by no means all). And still, there is even disagreement about how to weigh the coach and which formula to use. Quite a few people think they know "for sure" what to do only to have someone follow up right away with, nope, that's not the way to do it. In other words, there really isn't that big a consensus here so people are running around with lots of different PSIs (I'm not just talking about because they have different weights to account for) thinking they are the only ones doing it right. Yet I haven't found a lot of posts about catastrophic tire failure, so there must be at least some wiggle room here.

If you can't tell, I took issue with the smug and condescending tone you used early on in this thread with the whole "never assume" chide and so on with other snide remarks. I don't care for people who approach internet forums in that manner, especially on topics that have more than a few views...it just really rubs me the wrong way.

I just joined this forum and I can see that you did as well. I've never been the type to give any forums trouble and I'm not going to start now, so let's just agree to go about things in different ways and move on. Have a nice evening.
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Old 04-14-2017, 11:42 PM   #24
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Claiming there is no consensus when there is strikes me as rather foolish.

Tell you what. Let us know what roads you'll be traveling on so that we can be on any other for our own safety.
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Old 04-15-2017, 05:30 AM   #25
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Claiming there is no consensus when there is strikes me as rather foolish.

Tell you what. Let us know what roads you'll be traveling on so that we can be on any other for our own safety.

I have been following this thread since the beginning and am still confused. Can you tell us what the consensus is? Is it the consensus of Toyo tire to stay at the placard pressure or the consensus of Goodyear to use the tables?

Since one of the definitions of consensus is "group solidarity in sentiment and belief", I believe we are not even close.

Now, there may be a consensus vis-à-vis, if you don't know your weight, to use the placard pressures in lieu of an arbitrary pressure as it is better to be at the placard pressure than too low of a pressure.
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Old 04-15-2017, 07:14 AM   #26
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Quote:
Originally Posted by DWRichard View Post
Claiming there is no consensus when there is strikes me as rather foolish.

Tell you what. Let us know what roads you'll be traveling on so that we can be on any other for our own safety.
Will do. Next time I hit the road I'll shoot you a pm letting you know my travel itinerary

You may want to avoid RVs in and around the Red Bay area as well as newish looking Tiffins leaving RV dealerships...just to be safe

If anyone else is uncomfortable with me running my PSIs at what Tiffin thought appropriate until I can get her weighed, let me know and I will extend the same courtesy.

Thanks for the advice everyone!
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Old 04-15-2017, 09:07 AM   #27
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I have been following this thread since the beginning and am still confused. Can you tell us what the consensus is?
The consensus is to get it weighed - sooner than later.

The road of life is littered with the carcasses of people who live by the motto, "I'll get around to this".
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Old 04-18-2017, 02:32 PM   #28
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Originally Posted by 96 Wideglide View Post
Here..... This is from Toyo tires website, in the RV tire care section.

What Air Pressure Should Be Used?
The pressure your tires require is determined by the vehicle manufacturer in conjunction
with the tire manufacturer and is based on the vehicle’s gross axle load.
Every vehicle is required by federal regulations to include a tire information placard. This
placard may also be referred to as the tire certification label or federal tire tag. Vehicle
manufacturers are required by federal motor vehicle safety standards (FMVSS) to apply
tires of a suitable size, load range and inflation pressure (as shown on the tire information
placard) that are capable of supporting no less than the gross axle weight rating (GAWR).
Consequently, the vehicle manufacturer’s specified tire inflation pressure is not arbitrary; it is
established by federal safety regulations (ref: Code of Federal Regulations 49, 571.120, and Part 567).
Toyo Tire recommends that you maintain your vehicle’s cold tire
pressure to the pressure specified on the vehicle tire information placard.
Consult the owner’s manual for the placard position. In most cases it is placed on the
bulkhead at the left of the driver’s seating position.


Now you have read it
And yet, they (Toyo) still provide full load inflation tables for all of their tires. Why?
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