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mguay

Rear Tire Pressure

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When I bought the truck it had a bunch of mismatched rear tires on the tandems.  It did have 2 close to new Aeolus HN 308’s so once I singled it I bought another pair so I would have all matching drives. I put the new ones on the outside. The new set is wearing a bit funny after about 4000 miles of bobtailing with the Smart on. The outer ribs are great. It’s the inner blocks that are wearing funny. The leading edge is higher than the tailing edge. Yes it has had an alignment since singling. No this is not a debate about my Chinese drives. We have been using them on all of our FL 70’s at work for years. 

Unfortunately I haven’t weighed it with the 5er yet. I have weighed it with the smart and full of fuel. 21800#

The sidewall states 110psi and that is what I have them at. It rides fine. Is anyone running lower than sidewall pressure?

 

Thanks for the help

 

Edited by mguay

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The ideal scenario would be to put the 2 new tires next to each other, the other tires in the remaining location. Putting a new tire next to even one that has some wear on it will cause the older tire to "skid" along since the 2 tires have 2 different circumferences.  The result will be an unusual wear pattern like you describe. Now that it is done there isn't much you can do about it. There is nothing unsafe going on. You will probably age out the tires before wearing them out. 

You can run less than maximum pressure on a tire is it is carrying less than maximum load. There are tire manufacturers that publish charts, size tire, load on it and the recommended tire pressure at that load. Of the 21,800 you have, probably 12,000 is on the steer. When you put the 5th on it it will probably be at maximum load for the rear axle, so you will need to run the 110 psi. 

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We had our Volvo and trailer weighed on the way into the National HDT Rally.  I am singled short.  Rear weight with the Smart loaded and no trailer: 5,250 lbs.  With trailer: 7,425.  Therefore, the weight either way does not even get to the minimum pressure/weight ratio on the chart of 70 p.s.i. for the duals.  I found I should be running 105 in the steers and perhaps as low as 70 in the rear duals!.  I have 95 psi crossfires on the rear so I will likely try the 70 before buying new crossfires. 

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I went from 110 to 80psi in the rear (we are dual axle). It made a huge difference in ride comfort, especially over really bad bridge joints.

I do have axle weights with the trailer on, and could run as low as 70PSI according to the tire manufacturer's charts but that seems really low so I haven't tried that yet.

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5 minutes ago, NeverEasy said:

We had our Volvo and trailer weighed on the way into the National HDT Rally.  I am singled short.  Rear weight with the Smart loaded and no trailer: 5,250 lbs.  With trailer: 7,425.  Therefore, the weight either way does not even get to the minimum pressure/weight ratio on the chart of 70 p.s.i. for the duals.  I found I should be running 105 in the steers and perhaps as low as 70 in the rear duals!.  I have 95 psi crossfires on the rear so I will likely try the 70 before buying new crossfires. 

That's interesting comparing to my weights. Is your front carrying a good bit of the weight? We are singled short (184" wb) with no bed and no smart. We did have a small dual sport motorcycle on the back, but it's 330lbs at most. 

I was 6,075 on the rear with just the truck (no bed or anything, just a rail to hold the motorcycle) and 10,650 on the rear with the trailer. Our pin weight is 3,725. My front was 10,825 with just the truck and 9,975 with the trailer, so off loading about 800# on the front. It seems strange my rear has more weight on it when I don't even have a bed or a smart, but maybe it's because I'm so short the rear is picking up more of the weight compared to the front? My total truck weight was 16,900 lbs bob tail. 

I was trying to figure out the pressure chart they gave me on the rear tires. When we chatted, they said I was off it on the low side. I'm looking at the column that says Dx2 and the lowest pressure is 70psi at 8190lbs and about 105psi at 10,880. How do you read this chart for the rear? Do you split your weight in half to find the correct one? I was thinking I should be at 105psi for the 10,880 wiht the trailer, but maybe not? 

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I have 24.5 tires and run them at 80 front 70 rear.     Jeff beat me to the punch with both new tires on the same axle end.    At lower pressure the scrubbing may not be as bad, the load radius at lower pressure may be more even?     My truck weighs just under 10K on the steer axle and 3900 on the rear with no hitch, my small hitch and deck add about 800 pounds.     The pin weight on my trailer is 4400 so all up 9100 on the back.     The only down side to lower air pressure is a slight drop in MPG and increased heat from side wall flex, neither has been an issue         At least with 24.5's 85 PSI is good for 10400, I see 22.5's are a bit lower 10300.     

 

Blue, 

The DX2 is dual rating, on many charts the listing show single and dual ratings.   For example Bridgestone shows 295/75-22.5 tire at 70 PSI rated at 4500 single and 4095 in dual applications or 8190 per axle end or 16380 for a rear axle.   

 

Steve 

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The reason I didn’t put the 2 new ones on the same side was that I was worried about having a taller tire on one side of the axle and having unequal torque on the spiders. I knew the new ones would wear quickly to a similar wear of the older ones. I’m going to load the Smart and hit the scale tonight for a front and rear weight. The 5er is set up in a tight spot at the CG for a couple more weeks but I know what the pin weight is. 3800# give or take. I’m thinking I’m going to leave the older ones at 110 and drop the new ones to 90psi or so. I’m worried that dropping them too much will cause the outer ribs to wear off rather than cleaning up the inner blocks. 

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As I heard a tire rep from a major manufacturer say to one of our {automobile} customers who came in with bad front end induced wear( inside of tire wearing faster- bad camber):

"Rubber is ignorant. Even after you realigned the front end, the missing rubber is gone forever. That pattern will continue until the tire is worn out, which will occur first in the inside in this case. "

Adjusting pressures, changing positions, etc whatever will not cause the irregular wear to change. If you do manage to get the footprint perfect on the pavement, the bad pattern, once set is nearly impossible to correct. 

 

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2 hours ago, beyerjf said:

As I heard a tire rep from a major manufacturer say to one of our {automobile} customers who came in with bad front end induced wear( inside of tire wearing faster- bad camber):

"Rubber is ignorant. Even after you realigned the front end, the missing rubber is gone forever. That pattern will continue until the tire is worn out, which will occur first in the inside in this case. "

Adjusting pressures, changing positions, etc whatever will not cause the irregular wear to change. If you do manage to get the footprint perfect on the pavement, the bad pattern, once set is nearly impossible to correct. 

 

I’ve heard that before...but my fingers are still crossed!

I farmed out the tires and the tire shop installed them as outers, then gave me the story about the torque on the spiders being less with them out there. After I wrote it and heard the words come out of my mouth, I was thinking...wow what a dumb @22! The spiders are there to compensate one side spinning faster in a turn and they have no idea if the truck is turning or going straight!

Edited by mguay

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Yep, sorry, I was misleading.  I referenced the weight on each dual as it applied to the Load Table.  Total rear axle weight, singled short is 10,600 w/o trailer.  15,125 w/ trailer.  Front axle weight is 11,075 w/o trailer, 9,900 with trailer.  Pin weight is 3,350. 

And I concur with the pucker factor running 70psi in the rear but it should soften the ride.  I will run temp checks on the way home to see if there is a delta with 70 vs 95.

 

Edited by NeverEasy
added info

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You are not likely going to change the wear pattern on those tires to any significant degree at this point, no matter what you do. Jeff is spot on. I've seen it, I've experienced it myself, and I've talked to the tire manufacturer reps about it. That is the way it usually goes.  So you should do whatever makes you feel best, at this point....and hope for the best. :( 

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