Journey with Confidence RV GPS App RV Trip Planner RV LIFE Campground Reviews RV Maintenance Take a Speed Test Free 7 Day Trial ×


Reply
 
Thread Tools Display Modes
Old 03-28-2023, 09:08 PM   #1
NXR
Senior Member
 
NXR's Avatar
 
Join Date: Mar 2019
Location: Family room couch
Posts: 4,072
Dual wheels on blocks problem

Here's a pair of tires that may fail in the not-too-distant future. This pic is from a post where the owner said the newly-paved site was angled the wrong way so he had to use blocks under his rear tires.

I posted back that he massively overloaded those outer rear tires by only blocking the outer tires, thereby making those tires support 100% of the weight on each corner instead of 50%.

Look at how flattened that tire on the board is. The tire on the other side (in shadow) looks like it's flattened out over almost the entire board but it may be a shorter board, of course.

That's a 15,000 lb GAWR rear axle using Michelin 235/80R22.5 tires. The dual pair can support just over 7,500 lbs so each outer tire is now supporting close to that weight instead of about 3,700 lbs.

I know him and he has a 2019 model year on a 2018 F53 chassis so his tires likely are from 2017 or 2018. I suggested he might want to accelerate his tire replacement timeframe a bit...

Ray
Attached Thumbnails
Click image for larger version

Name:	Rear dual about to blow.jpg
Views:	141
Size:	390.4 KB
ID:	285209  
__________________
2020 Georgetown GT5 34H5
NXR is offline   Reply With Quote
Old 03-29-2023, 08:45 AM   #2
Senior Member
 
Join Date: Jul 2015
Posts: 221
Quote:
Originally Posted by NXR View Post
Here's a pair of tires that may fail in the not-too-distant future. This pic is from a post where the owner said the newly-paved site was angled the wrong way so he had to use blocks under his rear tires.

I posted back that he massively overloaded those outer rear tires by only blocking the outer tires, thereby making those tires support 100% of the weight on each corner instead of 50%.

Look at how flattened that tire on the board is. The tire on the other side (in shadow) looks like it's flattened out over almost the entire board but it may be a shorter board, of course.

That's a 15,000 lb GAWR rear axle using Michelin 235/80R22.5 tires. The dual pair can support just over 7,500 lbs so each outer tire is now supporting close to that weight instead of about 3,700 lbs.

I know him and he has a 2019 model year on a 2018 F53 chassis so his tires likely are from 2017 or 2018. I suggested he might want to accelerate his tire replacement timeframe a bit...

Ray


Since the wheel is not rolling, it isnít flexing dynamically, therefore not generating heat. Isnít it the heat that ultimately leads to an overloaded tire to fail?
Daxinarian is offline   Reply With Quote
Old 03-29-2023, 08:50 AM   #3
Senior Member
 
Join Date: Jan 2018
Location: Raleigh, NC
Posts: 7,322
Not always

Quote:
Originally Posted by Daxinarian View Post
Since the wheel is not rolling, it isnít flexing dynamically, therefore not generating heat. Isnít it the heat that ultimately leads to an overloaded tire to fail?
Not always. How much heat is generated when the driver hits a curb or deep pothole and simply applies more stress to certain portions than they are designed for. It doesn't matter whether that overload is applied quickly (curb, pothole) or slowly (driving up ramp, applying overload).
__________________
Larry

Sticks and Bricks: Raleigh, NC
2008 Cherokee 38P: at Ivor, VA permanently
Larry-NC is offline   Reply With Quote
Old 03-29-2023, 09:45 AM   #4
NXR
Senior Member
 
NXR's Avatar
 
Join Date: Mar 2019
Location: Family room couch
Posts: 4,072
Quote:
Originally Posted by Daxinarian
Since the wheel is not rolling, it isnít flexing dynamically, therefore not generating heat. Isnít it the heat that ultimately leads to an overloaded tire to fail?
Heat will contribute but we're talking about a possible 100% overload in this case.

I don't know how much the axle design and the wheel bearings factors in but now just the outer part of the axle is supporting 100% of the weight as well. And only one wheel bearing is bearing all of the weight (no pun intended).

The problem is that if the failure occurs weeks or months later then the owner likely will not correlate that failure with the time they massively overloaded the tire. They may even blame "China bombs".

Ray
__________________
2020 Georgetown GT5 34H5
NXR is offline   Reply With Quote
Old 03-29-2023, 11:08 AM   #5
Senior Member
 
Join Date: Jul 2017
Location: North of Seattle, WA
Posts: 16,145
Quote:
Originally Posted by NXR View Post
Heat will contribute but we're talking about a possible 100% overload in this case.

I don't know how much the axle design and the wheel bearings factors in but now just the outer part of the axle is supporting 100% of the weight as well. And only one wheel bearing is bearing all of the weight (no pun intended).

The problem is that if the failure occurs weeks or months later then the owner likely will not correlate that failure with the time they massively overloaded the tire. They may even blame "China bombs".

Ray
When a tire is built and tested for certification it's subjected to a test that imparts far more stress on a tire than the tires pictured is being subjected to.

The test is variously referred to as V-1 or "Tire Strength Test. The test involves mounting a tire on a wheel, inflating to rated pressure and conditioning to ambient temp for a given time, then pressing a rounded steel rod (3/4" dia) into the tire at a rate of 50 mm/min. The pressure on the rod must meet a minimum for the given tire's rating but usually the rod will push the inside of the tread "package" against the wheel without breaking the tire.

There's a HUGE difference between a static load on a tire and the dynamic loads on a tire moving down the highway under load and with heat buildup.

In reality it's not as much the load placed on a tire that causes failure but rather the heat that is generated by that load as it rolls down the highway.

The tires pictured could well outlast tires that are sitting flat on a level surface as it all depends on what happens to the tire as it's driving down the road. The load on that tire, sitting on a block with 10+ times (or more) the surface area as the "V-1 test rod" is being subjected to a fraction of the pressure it was tested for.

Now if the owner had just come in off the highway with tire temps approaching 200 degrees, and hit the leveling block at 50+ mph, then their might be an issue.

Now would I do that with my tires? Nope. But mainly because it doesn't look all that safe/stable.
__________________
"A wise man can change his mind. A fool never will." (Japanese Proverb)

"You only grow old when you run out of new things to do"

2018 Flagstaff Micro Lite 25BDS
2004 Nissan Titan
TitanMike is online now   Reply With Quote
Old 03-29-2023, 11:56 AM   #6
Junior Member
 
Join Date: Feb 2022
Location: Toronto
Posts: 225
Quote:
Originally Posted by TitanMike View Post
When a tire is built and tested for certification it's subjected to a test that imparts far more stress on a tire than the tires pictured is being subjected to.

The test is variously referred to as V-1 or "Tire Strength Test. The test involves mounting a tire on a wheel, inflating to rated pressure and conditioning to ambient temp for a given time, then pressing a rounded steel rod (3/4" dia) into the tire at a rate of 50 mm/min. The pressure on the rod must meet a minimum for the given tire's rating but usually the rod will push the inside of the tread "package" against the wheel without breaking the tire.

There's a HUGE difference between a static load on a tire and the dynamic loads on a tire moving down the highway under load and with heat buildup.

In reality it's not as much the load placed on a tire that causes failure but rather the heat that is generated by that load as it rolls down the highway.

The tires pictured could well outlast tires that are sitting flat on a level surface as it all depends on what happens to the tire as it's driving down the road. The load on that tire, sitting on a block with 10+ times (or more) the surface area as the "V-1 test rod" is being subjected to a fraction of the pressure it was tested for.

Now if the owner had just come in off the highway with tire temps approaching 200 degrees, and hit the leveling block at 50+ mph, then their might be an issue.

Now would I do that with my tires? Nope. But mainly because it doesn't look all that safe/stable.

That's quite a test!!

How big is the testing INSTRON and what type of cage is provided for those tires that don't have the 3/4" penetrator depress to the rim??

(Is the penetrator perpendicular to the tire circumference?? ASTM # ??)

Thanks
__________________
2012 Rockwood A122,
2017 Kia Sorento 3.3 V6 AWD ,
2012 Subaru Forester with MT (gone to TV heaven)

Cheers and greetings from a Toronto Canuck
Brandoni is offline   Reply With Quote
Old 03-29-2023, 03:23 PM   #7
Senior Member
 
Join Date: Jul 2017
Location: North of Seattle, WA
Posts: 16,145
Quote:
Originally Posted by Brandoni View Post
That's quite a test!!

How big is the testing INSTRON and what type of cage is provided for those tires that don't have the 3/4" penetrator depress to the rim??

(Is the penetrator perpendicular to the tire circumference?? ASTM # ??)

Thanks
The "penetrator" is, if memory serves, is 3/4" with a "rounded" tip and is positioned in the center of the tread (but not in a tread groove). "Points" directly at the axis. The rest of the machine is about twice the size of the largest tires tested. Rest assured there are safety shields in place for the test.

This test has been used in one form or another since ~1969 and is just one of a battery of tests to ensure tires are a lot safer than those that were sold up to that date. I wonder how many people here were around when tire cords were made from Cotton? (trivia----Goodyear,AZ got it's name from the cotton fields around it owned by Goodyear Tire).
__________________
"A wise man can change his mind. A fool never will." (Japanese Proverb)

"You only grow old when you run out of new things to do"

2018 Flagstaff Micro Lite 25BDS
2004 Nissan Titan
TitanMike is online now   Reply With Quote
Old 03-29-2023, 09:13 PM   #8
Senior Member
 
Join Date: Nov 2017
Posts: 1,572
I was around when cotton was being phased out and the rayon and nylon wars were starting. Although more prevalent in bias ply tires being parked like that for extended time could creat flat spotting. Not damaging but irritating.
aircommuter is offline   Reply With Quote
Old 03-29-2023, 09:27 PM   #9
Senior Member
 
Join Date: Jul 2017
Location: North of Seattle, WA
Posts: 16,145
Quote:
Originally Posted by aircommuter View Post
I was around when cotton was being phased out and the rayon and nylon wars were starting. Although more prevalent in bias ply tires being parked like that for extended time could creat flat spotting. Not damaging but irritating.
Flat spotting was primarily due to nylon. They eventually came up with a version of nylon ( which really is kind of a catch-all term for several polymers) some tire co's advertised as "NF Nylon". Supposed to mean non-flat spotting nylon. Was better and if you had a half mile or so to drive slow the ride was a lot better than the old nylon which could take 4-5 miles.
__________________
"A wise man can change his mind. A fool never will." (Japanese Proverb)

"You only grow old when you run out of new things to do"

2018 Flagstaff Micro Lite 25BDS
2004 Nissan Titan
TitanMike is online now   Reply With Quote
Old 03-29-2023, 09:36 PM   #10
Senior Member
 
Join Date: Nov 2017
Posts: 1,572
Yep, we had a bunch of cabover trucks that could give a pretty bumpy ride in those days.
aircommuter is offline   Reply With Quote
Old 04-05-2023, 11:14 AM   #11
NXR
Senior Member
 
NXR's Avatar
 
Join Date: Mar 2019
Location: Family room couch
Posts: 4,072
Michelin's bulletin on the proper use of blocks when leveling an RV: https://www.michelinb2b.com/wps/b2bc...motorhomes.pdf

Extreme caution must be taken to ensure that the tires are fully supported when using blocks to level motor homes and/or RVís. The load on the tire should be evenly distributed on the block and in the case of duals, evenly distributed on blocks for both tires. If not properly done, the steel cables in the sidewall of the tires may be damaged and could lead to premature fatigue of the sidewall.

While I found some of the observations here interesting, they may fall under that old saying of "In theory, theory and practice are the same. In practice they are not."

Ray
Attached Thumbnails
Click image for larger version

Name:	Duals.PNG
Views:	37
Size:	94.5 KB
ID:	285502  
__________________
2020 Georgetown GT5 34H5
NXR is offline   Reply With Quote
Old 04-05-2023, 11:45 AM   #12
Senior Member
 
Join Date: Feb 2018
Location: TEXAS
Posts: 7,689
Ignoring the tire problem.... Is the front tire also on blocks so that there isn't added stress to the frame of the unit?

BTW. I agree that both wheels should be supported properly.
__________________
2015 Dynamax REV 24TB class C
Reverse_snowbird is online now   Reply With Quote
Old 04-05-2023, 04:07 PM   #13
NXR
Senior Member
 
NXR's Avatar
 
Join Date: Mar 2019
Location: Family room couch
Posts: 4,072
Quote:
Originally Posted by Reverse_snowbird
Ignoring the tire problem.... Is the front tire also on blocks so that there isn't added stress to the frame of the unit?

BTW. I agree that both wheels should be supported properly.
Dunno.
__________________
2020 Georgetown GT5 34H5
NXR is offline   Reply With Quote
Old 04-06-2023, 10:39 AM   #14
Senior Member
 
Join Date: Nov 2017
Posts: 1,572
Quote:
Originally Posted by Reverse_snowbird View Post
Ignoring the tire problem.... Is the front tire also on blocks so that there isn't added stress to the frame of the unit?

BTW. I agree that both wheels should be supported properly.
Huh? You mean trucks must level at all times?
aircommuter is offline   Reply With Quote
Old 04-06-2023, 12:27 PM   #15
Senior Member
 
Join Date: Feb 2018
Location: TEXAS
Posts: 7,689
Quote:
Originally Posted by aircommuter View Post
Huh? You mean trucks must level at all times?
I mean that you don't want to just one portion of a rig. You don't want to twist the frame. The exception would probably be if one wheel was in a hole and you needed to raise it to get it level with the rest of the rig.
__________________
2015 Dynamax REV 24TB class C
Reverse_snowbird is online now   Reply With Quote
Old 04-06-2023, 12:31 PM   #16
Senior Member
 
Join Date: Nov 2017
Posts: 1,572
Doesn’t that happen when one parks their rig and not planning on sleeping or running the refrigerator? Frame twisting is a normal daily occurrence.
aircommuter is offline   Reply With Quote
Old 04-10-2023, 09:08 PM   #17
Senior Member
 
MNtraveler's Avatar
 
Join Date: Oct 2015
Posts: 2,356
Quote:
Originally Posted by aircommuter View Post
Doesn’t that happen when one parks their rig and not planning on sleeping or running the refrigerator? Frame twisting is a normal daily occurrence.
Bigfoot for example warns that if you are going to 'manually' level the RV, you should raise two front jacks, two rear, two left or two right together. Never just one of either axle nor one of either side (same difference, really).

The stated reason for this is to avoid twisting the frame.

I guess it could happen in un-level parking situations, but only if you put the right front wheel up on the curb, for example. Typically these levelers would be raising one corner 3-5" or more.
__________________
2016 FR Forester 2401R
Towing 2014 Honda CR-V
MNtraveler is offline   Reply With Quote
Old 04-11-2023, 05:54 AM   #18
Senior Member
 
ilmor's Avatar
 
Join Date: Jul 2011
Posts: 893
Both dual wheels must definitely be blocked when leveling, which is yet another reason I avoided them w/ my current RV (class B van).
__________________
former 2017 Forest River Sunseeker 2250SLE owner - replaced by a Pleasure-Way Tofino and then an Ontour 2.0

ilmor is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


» Featured Campgrounds

Reviews provided by

Disclaimer:

This website is not affiliated with or endorsed by Forest River, Inc. or any of its affiliates. This is an independent, unofficial site.



All times are GMT -5. The time now is 03:23 PM.