Micro-minnie tire upgrade

[Marine359]

Thanks for the great post Sidpost.

[tinglett]

Originally Posted by sidpost

As someone who has sold tires in the past, I can tell you that if you have a blowout on the road at some random location, you will find a 15" tire a lot easier than a 14" tire and, the 15" tire may actually be cheaper!

This is a point I hadn't thought about and another great reason to move to 15". I find the LT vs ST tire interesting because I think (someone correct me if I'm wrong!) that the latest model Micro Minnies are actually shipped with LT tires.

I don't mean to imply they know what they are doing, though I'd hope as a huge manufacturer that they have at least one engineer specializing in this space. It's just an observation that surprised me. I've seen on forums people talking about LT tires, but didn't know manufacturers were doing it too. But again, someone should probably confirm this because I might have misinterpreted what I saw. I'm not a tire expert!

[sidpost]

Originally Posted by tinglett

This is a point I hadn't thought about and another great reason to move to 15". I find the LT vs ST tire interesting because I think (someone correct me if I'm wrong!) that the latest model Micro Minnies are actually shipped with LT tires.

I don't mean to imply they know what they are doing, though I'd hope as a huge manufacturer that they have at least one engineer specializing in this space. It's just an observation that surprised me. I've seen on forums people talking about LT tires, but didn't know manufacturers were doing it too. But again, someone should probably confirm this because I might have misinterpreted what I saw. I'm not a tire expert!

It is possible that a supply chain problem caused this. If you are running less than the tires load capacity, it should be safe for that trailer assuming you don't overload it. In my personal experience, I would also expect to pick up more flats from things on the road and for it be much more sensitive to air pressure in terms of trailer sway because of the typical sidewall differences.

I should note that I am a bit more cautious with tires than most people in general because I know what it means when my 14,000lb trailer had a blowout on a good trailer tire on I-40 doing 70MPH with an ambient air temperature of 104F (the payment actually lightly burned my bare hand).

I also know what it means to spend 3 days traveling <300 miles with 5 destroyed trailer tires, two mangled wheels, and how to replace 3 lugs at the side of the road with a 16oz ball-peen hammer and dimestore punch. This particular trailer was a dual axle model that weighed about 3,000lbs at the time.

My friend thought he was saving money by purchasing "best value car tires". 5 years later, those same trailer tires I bought at half the cost of the car tires he wanted, are still on that trailer and working well. That trailer also doesn't sway now at any legal speed!

I WOULD GLADLY PAY AN EXTRA $100 A TIRE TO AVOID LOSING MY VACATION DAYS TO BLOWOUTS, FLATS, ETC. If you get trailer sway, slow down by coasting if you can and don't apply heavy braking. If you can, lightly apply the trailer brakes only as you coast, you can often settle it down. If it is swaying because you have too much weight behind the trailer axles, absolutely do not stomp the brakes which will unweight the rear axle of the tow vehicle and will likely lead to a jackknife if you are lucky or, upside down in the median or a ditch if you aren't lucky. This is why Mini-vans should be banned from pulling a 6x12 Uhaul trailer IMHO. Seeing children's toys, strollers, clothes, etc in a scene with a Minivan and U-haul on their side or upside down still bothers me long after I drove by the carnage and I am hours down the road.

[jadatis]

Speedrating is not only for the speed you drive important.
Maximum load of a tire, is determined for reference-speed and -pressure.

Below Q speedrating reference-speed is mostly max speed .
Above Q speedcode up to V 160kmph/99mph.

So if you drive for instance 70mph with a L speedrated tire ( 75mph max- and reference-speed) the tire material comes close to its critical temperature. When driving with Q or higher speedrated tire the temperature stays cooler so always better.

This ofcource with pressure in tire determined on the pressure/loadcapacity list for the right speedcode.

[sidpost]

Originally Posted by jadatis

Speedrating is not only for the speed you drive important.
Maximum load of a tire, is determined for reference-speed and -pressure.

Below Q speedrating reference-speed is mostly max speed .
Above Q speedcode up to V 160kmph/99mph.

So if you drive for instance 70mph with a L speedrated tire ( 75mph max- and reference-speed) the tire material comes close to its critical temperature. When driving with Q or higher speedrated tire the temperature stays cooler so always better.

This ofcource with pressure in tire determined on the pressure/loadcapacity list for the right speedcode.

Yes, you want some speed rating overhead for your tires so, I would say 87mph is plenty for the vast majority of people. If you are traveling at 75, 80, or 85mph routinely I would look for a higher speed rating. Very few people pulling a travel trailer are going to be able to safely pull a travel trailer at those speeds. If you have a 1-ton dually and a reasonable trailer, you can certainly travel at those speeds but, most OWNERS are not going to have the skill and experience to do that safely IMHO.

SPEED and LOAD ratings are both important. Realistically, I don't see trailer tires that have an issue with their speed rating assuming you stick to quality tires. It is only on the lesser Chinese branded trailer tires generally that have too low a speed rating. LOAD ratings are the one that gets most people into trouble.

Again regarding speed, just because you have the powertrain power to pull at high velocity doesn't mean you are safe to do so. You need the suspension and brakes to do so safely assuming your trailer is properly balanced to avoid sway or upsets with crosswind and passing or being passed by large "box/van" semi-trucks.

[jadatis]

Originally Posted by Tireman9

If you had done some 20,000 tire autopsies as I have over my 40 years you might be able to see the signs of separation as I did in the above example. That's how I knew where to cut.

But not all the tire-specialsts that are needed to check all the tires yearly, have that 40 years experiënce. So the methods have to be learned in a weak or so, to get enaugh profesional checking capacity.

I think the hammering methode can be a welcome addition, to detect cavaties , before you can see them from the outside.

A sidewall bulb is easy to detect, but I think those are made by air of inside tire , leaking into weak enaugh cavities, so a stage further.

Can you make us wiser about those signs of seperation, when no bulbs are seen yet.

[outthere]

We purchased five Endurance tires from discount tire in Lake Mary Fl. for our 2020 2108DS. The tires we removed were 235-75-15 passenger car tires and the GYs are
st225/75r15s E load that I run @ 70psi. When They switched out the tires they also balanced them. Only 5K so far but they have been great performers. My friend bought 5 16" of the same tire for his 35' grand design 5th wheel.
He runs to Tx and Maine. No issues..very satisfied. It's good to have the higher speed
rating for those long rolling downhills where you can let the speed increase (within reason) and not have to hold it back for fear of tire failure.
I too was concerned about stiffness and excessive shock imputed to the camper with these tires. Truthfully, it's a non issue and you have a pretty good working range of
psi versus load to work with instead of airing up to max psi as your only choice.

[tinglett]

Originally Posted by outthere

We purchased five Endurance tires from discount tire in Lake Mary Fl. for our 2020 2108DS. The tires we removed were 235-75-15 passenger car tires and the GYs are st225/75r15s E load that I run @ 70psi.

I see the max for these tires is 80psi. How did you determine to set the pressure at 70psi? Sorry, I'm not a tire expert so the answer isn't obvious to me. Does GY have some book to calculate this?

[Bcborn]

Originally Posted by tinglett

I see the max for these tires is 80psi. How did you determine to set the pressure at 70psi? Sorry, I'm not a tire expert so the answer isn't obvious to me. Does GY have some book to calculate this?

I wonder the same thing the original tires were load range "C" max (50lbs max) and I have now moved up to a load range "D" (max 65lbs)


Do I inflate to decal on side of trailer (think it was 50lbs) or to the tire max 65lbs

[outthere]

Try goodyearrvtires.com and click around....or....
I googled goodyear endurace psi chart and found the endurance tire inflation to weight recommendations.

If I read it correctly I could reduce my psi lower than 70. My 2108ds is about 4000lbs dry.
I have two 3700lb axles. I didn't speak with a tire engineer but for my trailer 80psi
would seem unnecessary.
I'm sure at some point the lowest psi to support your rig may not be the wisest choice.

[Tireman9]

Tire Design Engineer here. I reviewed all the posts in this thread. My comments & observations.
Tire selection can be a challenge but there are only a few things you need to consider.
1. Load carrying capacity. If you want to decrease the potential for early life failure you need to select tires that can provide AT A MINIMUM 110% of the actual you are putting on the tires with 120% being better. Just as you do not drive with the TV engine at REDLINE why would you think it is good practice to run the tires at their "REDLINE" The calculation for load capacity of ST type tires is based on 65 mph. Note they have different rules and standards in Europe and do not have ST tires there so maybe it's best to focus on the US market.
2. The only way to know YOUR weight is to get your RV on a truck scale when the RV is loaded to its heaviest. "Dry weight" plus a guess for the weight of stuff you load into the RV will not get you the number you really need. Asking others what their RV weighs also will not work as not everyone carries the same amount of water, tools, books, clothes, tools etc.
3.CAT scales at Interstate truck stops are reliable. There are even

YouTube

videos
on how to weigh an RV. Alternately you can check with local sand & gravel supply or some large building supply HERE is a worksheet and information on how to best weigh your RV While THIS site is aimed at 5th wheel trailers they have lots of good information for any RV owner.

4. Tires. Once you know the actual load on your tires you can decide if you can upgrade to 15" or 16" to have a greater selection. The key bit of information is the tire load capacity vs your scale weight. (See item #1.) Every tire has a stated maximum load capacity. Note that if you are changing tires, different Type tires ST or LT or even P typs even of the same size can have significantly different load capacities so you need to pay attention to the details.


5. Inflation Load capacity is a function of Type, Size and inflation. All three are important.

[jadatis]

Originally Posted by outthere

We purchased five Endurance tires from discount tire in Lake Mary Fl. for our 2020 2108DS. The tires we removed were 235-75-15 passenger car tires and the GYs are
st225/75r15s E load that I run @ 70psi. When They switched out the tires they also balanced them. Only 5K so far but they have been great performers. My friend bought 5 16" of the same tire for his 35' grand design 5th wheel.
He runs to Tx and Maine. No issues..very satisfied. It's good to have the higher speed
rating for those long rolling downhills where you can let the speed increase (within reason) and not have to hold it back for fear of tire failure.
I too was concerned about stiffness and excessive shock imputed to the camper with these tires. Truthfully, it's a non issue and you have a pretty good working range of
psi versus load to work with instead of airing up to max psi as your only choice.

Together with the GAWR 2 times of 3700lbs, i trew this in my calculator, and lowered the maxload of 2830lbs by 6 Loadindex steps to give the tires a deflection an LT tire of that sise would need.
Gave 68psi, so your 70psi is with max reserve, with still no screws or rivets going loose.

Then most likely, if GVWR fully used, still no 3700lbs on the axles, but I realise this is a dangerous statement.

[Bcborn]

Originally Posted by Tireman9

Tire Design Engineer here. I reviewed all the posts in this thread. My comments & observations.
Tire selection can be a challenge but there are only a few things you need to consider.
1. Load carrying capacity. If you want to decrease the potential for early life failure you need to select tires that can provide AT A MINIMUM 110% of the actual you are putting on the tires with 120% being better. Just as you do not drive with the TV engine at REDLINE why would you think it is good practice to run the tires at their "REDLINE" The calculation for load capacity of ST type tires is based on 65 mph. Note they have different rules and standards in Europe and do not have ST tires there so maybe it's best to focus on the US market.
2. The only way to know YOUR weight is to get your RV on a truck scale when the RV is loaded to its heaviest. "Dry weight" plus a guess for the weight of stuff you load into the RV will not get you the number you really need. Asking others what their RV weighs also will not work as not everyone carries the same amount of water, tools, books, clothes, tools etc.
3.CAT scales at Interstate truck stops are reliable. There are even

videos
on how to weigh an RV. Alternately you can check with local sand & gravel supply or some large building supply HERE is a worksheet and information on how to best weigh your RV While THIS site is aimed at 5th wheel trailers they have lots of good information for any RV owner.

4. Tires. Once you know the actual load on your tires you can decide if you can upgrade to 15" or 16" to have a greater selection. The key bit of information is the tire load capacity vs your scale weight. (See item #1.) Every tire has a stated maximum load capacity. Note that if you are changing tires, different Type tires ST or LT or even P typs even of the same size can have significantly different load capacities so you need to pay attention to the details.


5. Inflation Load capacity is a function of Type, Size and inflation. All three are important.

Wasn't the question how much air to put into a tire based on scaled weight or RV's GVWR. Many upgrade tire load based on different factors; tougher sidewall (less sway), back road excursions (tread plys).

If the trailer is Manufactured with load range "C" and the load is kept to no more than manufacturers specs and you inflate to manufactures recommended psi (50psi) your in range. Is this correct.

But if your scaled weight is at 75% of GVWR then wouldn't the tires be over inflated?

Now what if the RV owner replaces the tires with a higher load range "D or E" and still loads to 80% of the trailers GVWR and inflates to the load range "D or E max, then again would they not be over inflated as well. Likely to a greater extent.

If I read this correctly your suggesting you wouldn't put a load range E tire on a trailer with a 3000lb GVWR and fill it to max psi.

[Tireman9]

Originally Posted by Bcborn

Wasn't the question how much air to put into a tire based on scaled weight or RV's GVWR. Many upgrade tire load based on different factors; tougher sidewall (less sway), back road excursions (tread plys).

If the trailer is Manufactured with load range "C" and the load is kept to no more than manufacturers specs and you inflate to manufactures recommended psi (50psi) your in range. Is this correct.

But if your scaled weight is at 75% of GVWR then wouldn't the tires be over inflated?

Now what if the RV owner replaces the tires with a higher load range "D or E" and still loads to 80% of the trailers GVWR and inflates to the load range "D or E max, then again would they not be over inflated as well. Likely to a greater extent.

If I read this correctly your suggesting you wouldn't put a load range E tire on a trailer with a 3000lb GVWR and fill it to max psi.

First the difference in base inflation between LR-C and LR-D is only 15 psi (30%) and LD-D to LR-E is also 15 psi which is only 23%. Some might think this is significant but your question started off with a LR-C at 100% load capacity i.e. 0% reserve load. You can look at the tables for your size tire and see how much Reserve Load you would have with LR-D load capacity. People seem to think that tires have an on-off switch for durability vs load capacity.
A couple years ago I checked the weight on my daily driver car and using the Load Inflation tables I confirmed that the car company specs would provide 28% reserve load capacity. This is about what you will find for most non-RV applications.


Ask yourself how long your car's engine would last if you always drove with the engine at 95 to 105% of engine redline.


RE GVWR. Please do not use that number when talking about tires. Each tire will only perform or last based on the actual load and inflation on that particular tire. Individual tire loads are almost never equal to 25% of GVWR.


Even GAWR can not be split 50/50 between each tire as almost zero percent RV have side to side load split to 50/50 with most having at least 51% on one axle end and many having as much as 55% load on one axle end.


If you can't get "4 corner weights" then the least you can do is to figure that one tire on each axle is supporting 52% and use that number when consulting the load tables. While that isn't 100% accurate it will cover many applications.


Finally to your first point I know for a fact that just going up in a Load Range is no guarantee of "stiffer" or "stronger" sidewall. The actual difference in tire construction may be just made in the belt with or even just in the bead wire.

[Bcborn]

Lets assume your RV comes with Load Range C tires.

The tire pressure decal says inflate to 50lbs.

Am I correct this would refer to a trailer loaded to capacity in manufacturers rated cargo weight.

What if the cargo is 50% of maximum capacity, would the owner need to adjust tire pressure down from the 50lbs as stated on the tire decal on trailer.

My car has two recommended tire pressures. 2 people and loaded.

Trailers don't come with a psi scale as to tire pressure at any given load (empty/full).

One member stated that they reduced the tire pressure down from maximum on a heavier rated tire as to not shake the heck out of the trailer. Another member asked, and this is where this posting started; how does one determine correct tire pressure for a given weight when the tire only provides max pressure and the trailer decal only provides one tire pressure.

This is especially the case when one upgrades the tire (size, load range) from the originally manufacturer installed units.

I'm sure I would be wrong if I said, inflate to decal on trailer not to tire max no matter what tire is installed.

[jadatis]

Originally Posted by jadatis

Together with the GAWR 2 times of 3700lbs, i trew this in my calculator, and lowered the maxload of 2830lbs by 6 Loadindex steps to give the tires a deflection an LT tire of that sise would need.
Gave 68psi, so your 70psi is with max reserve, with still no screws or rivets going loose.

Then most likely, if GVWR fully used, still no 3700lbs on the axles, but I realise this is a dangerous statement.

First a little correction. If you have less then 3700lbs on the axle, still some bumping to my determined standards.

But lets assume 3700lbs exactly 100% acurate determined.

Then the question is, what reserve do you have.

If the never existing 50/50 loaddivision my calc gives still no bumping.
I once determined, if less then 80% of loadcapacity belonging to the pressure realy on a tire, bumping begins, but is discusable, some say you can even go lower.

But lets assume my borders are right.
The 68psi is using 90% of the loadcapacity so half of 3700 lbs is 1850/ 0.9= 2055lbs is what the pressure is calculated for.
80% of that is below 1644lbs on one side of the axle screws begin to turn loose.
Then the other. Side is 3700- 1644= 2055 lbs.
So the other side using 100% of loadcapacity belonging to 68psi. Is a weiggtdivision of rounded 45/55 on the axle. If lesser fi 48/52 there is some space for higher or lower axleweight.

2nd is that I calculated for 99mph to give no overheating, wich gives extra reserve.
Lets assume your max speed 75mph, my calc gives, using 4 li steps higher, 61psi.
So real cold pressure can drop to 61psi in time, and weightdivision 45/55 and stil no overheating on one of the tires when driving constant speed of 75mph.

Why that much reserve? Yust because it can, and is needed to cover inacuracies in measurement or determining load and pressure.
So calculated for max reserve, but can end up with only yust enaugh for the real situaton, by the inacuracies.

[Tireman9]

Originally Posted by Bcborn

Lets assume your RV comes with Load Range C tires.

The tire pressure decal says inflate to 50lbs.

Am I correct this would refer to a trailer loaded to capacity in manufacturers rated cargo weight.

What if the cargo is 50% of maximum capacity, would the owner need to adjust tire pressure down from the 50lbs as stated on the tire decal on trailer. NO

My car has two recommended tire pressures. 2 people and loaded.

Trailers don't come with a psi scale as to tire pressure at any given load (empty/full).



Yes because the regulations specify the tire pressure is what is needed to support GAWR. Even with zero "stuff" loaded into your RV the tire load is probably close to 80% or more of the tire max load capacity.


One member stated that they reduced the tire pressure down from maximum on a heavier rated tire as to not shake the heck out of the trailer. Another member asked, and this is where this posting started; how does one determine correct tire pressure for a given weight when the tire only provides max pressure and the trailer decal only provides one tire pressure. See below

This is especially the case when one upgrades the tire (size, load range) from the originally manufacturer installed units.

I'm sure I would be wrong if I said, inflate to decal on trailer not to tire max no matter what tire is installed.

Read above in bold

The goal of inflating tires is to prevent cumulative damage. We want to provide at least a 10% Reserve load on newer RVS. Before 2017 they didn't even allow for any reserve. But the data from thousands of actual scale readings shows that over 50% of RV are overloaded.
We suggest you load to the heaviest you ever expect to be and then learn the load. Ideally on each tire as the load is almost never evenly split across all the tires. We have seen some larger RVs with 1,000# more load on one tire than another. While most are maybe supporting between 44 and 56% of the axle loads.

We do not want you to have to mess with inflation each trip and having more inflation than the minimum needed to support is not a problem. Most cars specify inflations that yield about 30% reserve load. I do not recall ever seeing an RV with the Reserve load based on sticker inflation being greater than 20%

The sticker is based on the OE tire and should be followed unless you change the Type ( P vs ST vs LT) tire or change the Size dimensions or change the Load Range C, D, E

If you want greater Reserve Load (i.e.margin) you will probably have to change tires. When you change tires you need to do some work so you get the extra load capacity you want and paid for. This means consulting Load/Inflation tables and learning the actual load on the heaviest loaded tire on the RV so you are selecting the correct tire and learning the appropriate inflation for the new tire.
I have a few posts on my RV Tire Safety blog on the specific question of changing tires and cover the detailed steps and information needed to do the change correctly.

[Bcborn]

Tireman9 thank you for your input.

I pulled this link from your blog.

https://www.rvtiresafety.net/2019/08...ange-what.html

From reading your blog, if that guy inflated his Load Range "D" ST tires to the 50lbs as shown on the decal, you stated he would gain nothing as the 50lbs would give him (see charts below). One might add, If he wanted to try that, would he not need to know, if the given Load Range "D" ST tire would support the manufacturers stated GAWR of 7000lbs at 50psi (as did the Load range "C" originally equipped tire). Looking at the table below, for the endurance yes. If so would he not gain a smoother ride at 50lbs inflation? Would he though loose longevity?

Increasing the label recommendation 10% (55psi) or 20% (60psi) as you suggested would give him more reserve and he would still be under the Load Range "D" ST tire max of 65psi. Again would he be sacrificing longevity.

If you over inflate a tire past its required air pressure for any given load based on tire load inflation tables (in this case he is guessing as the weight every trip could be different), does the tire not tend to wear in the center as the GAWR weight may not be their to flatten out the tire to achieve even wear. Same holds true if you under inflate a tire, would you not get greater wear on the outer edges?

Winnebago the Manufacturer achieved compliance by installing the Load Range "C" tire (1760lbs load rating). Why would they install a Load Range "D" (2040 lbs load rating) on this same trailer, except for greater reserve. I get it greater reserve means increased safety (assuming the trailer gets overloaded).

Did I and many others make the right choice in replacing the OEM tire with a tire of greater load capacity (I Carlysle Radial Trail HD and other's with the Goodyear Endurance) when we never load the trailer to the maximum GAWR (3300lbs cargo)?

Thanks again Tireman9

[jadatis]

On the Airstream-forum, I discovered that Airstream TT s have in any case for the tandem axle, 1st. Comfortable reserve in GAWR to the GVWR, and 2nd, comfortable reserve in the tires for the GAWR 's, and is an exeption to the rule in TT land.

Then even with the C-load ST tires more then the 10% reserve RVIA ( right spelled??), and even with my standards still no 50 psi calculated.
Then D-load upgrade stil does not need the full 65 psi, sometimes even rivets popping by trembling.
For centrewear the pressure must be even higher then the border of screws turning loose.


I would like to know how the reserves are for Winebago in general
So if some of you would give me next, I can calculate it.
GVWR
GAWR (s) and if single or tandem axle.
The tiresise and loadrange.
Better maxload AT?? Psi. And if ST or LT.

LT????!!!, yes airstream dellivers sometimes TT with LT tires, have extra reserve because for 99mph maxload calculated, and most likely only max 75mph used. ST is calculated in maxload for 65mph, also the Endurance with max speed 87mph.

[RocknRoll]

Very informative thread. If I may throw in my recent experience...

One thing I do not see mentioned is how outside temperatures can affect tire pressures. Last Nov-Dec, I had a R/T excursion from upstate SC to the Keys.

Outside temperatures ranged from the mid-30's to the 90's and I found myself either adding or reducing air not only prior to every trip, but on a few occasions during mid-travel. The tires on the side of the trailer facing the sun would increase by 2-3 lbs. alone. This was worrisome as I was constantly attempting to monitor and maintain a constant psi in the tires.

The point I'm trying to make and what I've discovered is that having a margin of safety, especially in temperature extremes cannot be understated.

I still have the stock china bomb tires still on my TT and consider myself extremely fortunate that I did not suffer any negative consequences. I plan on replacing them this year with a "D" or higher rating before my next trip.