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Got some weights, how to determine ideal tire pressure?


jeffw

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I finally had time to get our truck & trailer weighed. The NH DOT weigh station scales are open all the time, so I stopped in when the station was closed to get weights.

 

I was able to get weights for just the truck and then the truck and trailer:

 

Truck only: 22,740

Front axle: 10,200

Rear axles: 12,540

 

Truck and Trailer: 45,020

Front axle: 8,000

Rear axles: 21,640

Trailer axles: 15,380

 

The trailer has 3 axles with 215/75R17.5 tires from 5 different manufacturers (Bridgestone, Firestone, Geostar, Hankook & Linglong) thanks to the previous owner.

 

It surprised me how much weight came off the front axle with the trailer on.

 

The truck is has dual rear axles (i.e. not singled). Right now I'm running 110 PSI everywhere, but was wondering if I could bring the pressures down some to improve the ride quality. Thoughts? Thanks! -jeff

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There are charts out there that will tell you the min pressure to support X lbs of load based off the tire. But they are MFG. specific. but you "could" ball park it a bit.

 

here is a link to one of the Good Year documents.

 

https://www.goodyeartrucktires.com/pdf/resources/publications/2010_loadinflation.pdf

 

Your size is on the 6th page.

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Very nice set of numbers, here we go.

 

Truck and trailer weight minus truck weight only. 45,020 - 22,740 = 22,280 Therefore the trailer weight is 22, 280 lb

Trailer weight minus the trailer axles weight 22,280 - 15,540 = 6,900 Therefore the pin weight of the fifth is 6,900 lb

Front axle truck loaded minus front axle truck empty 10,200 - 8,000 = 2,200 Therefore the front axle off load is 2,200 lb

Truck rear axle loaded minus axle off loaded 21,640 - 12,540 = 9,100 Load difference on that axle

Pin weight plus front axle off load 6,900 + 2,200 = 9,100 Yippee, isn't basic math grand!

 

Snoopy.jpg

 

Trailer weight vs. pin weight 22,280 vs. 6,900 = 31.9% You definitely do not have a "floater"!

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Jeff, do you really have 9,100 pin weight on your trailer??? Rear of truck hitched = 21,640, - unhitched rear, 12,540 = 9,100???

 

The trailer's a race car hauler. It's got a generator and fuel tank for the generator right up front, so I'm not surprised it's heavy up front.

 

The trailer axles are rated at 8,000 pounds, FYI.

Also, I only had 1 car in the trailer at the time. A second car would add about 2,000 pounds over the axles. Hopefully I can get over the scales

when we have 2 cars in it.

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Very nice set of numbers, here we go.

 

Truck and trailer weight minus truck weight only. 45,020 - 22,740 = 22,280 Therefore the trailer weight is 22, 280 lb

Trailer weight minus the trailer axles weight 22,280 - 15,540 = 6,900 Therefore the pin weight of the fifth is 6,900 lb

Front axle truck loaded minus front axle truck empty 10,200 - 8,000 = 2,200 Therefore the front axle off load is 2,200 lb

Truck rear axle loaded minus axle off loaded 21,640 - 12,540 = 9,100 Load difference on that axle

Pin weight plus front axle off load 6,900 + 2,200 = 9,100 Yippee, isn't basic math grand!

 

Snoopy.jpg

 

Trailer weight vs. pin weight 22,280 vs. 6,900 = 31.9% You definitely do not have a "floater"!

 

Henry: Any concern with that pin weight on the ET Sr?

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There are charts out there that will tell you the min pressure to support X lbs of load based off the tire. But they are MFG. specific. but you "could" ball park it a bit.

 

here is a link to one of the Good Year documents.

 

https://www.goodyeartrucktires.com/pdf/resources/publications/2010_loadinflation.pdf

 

Your size is on the 6th page.

 

Thanks for that. I've got goodyears on the drive tires, which are likely the only ones I would want to reduce much. I think the steers are Bridgestone. I'll see if I can find their similar doc....

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I've got 295/75R22.5 on the drive axles. 22,000 pounds over 8 tires gives me 2750 pounds per tire.

 

The goodyear PDF starts at 4500 pounds at 70 PSI for that size.

 

I assume I don't want to go all the way down to 70 PSI to give some margin of error. What would be a reasonable tire pressure to see if it improves ride quality?

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I've got 295/75R22.5 on the drive axles. 22,000 pounds over 8 tires gives me 2750 pounds per tire.

 

The goodyear PDF starts at 4500 pounds at 70 PSI for that size.

 

I assume I don't want to go all the way down to 70 PSI to give some margin of error. What would be a reasonable tire pressure to see if it improves ride quality?

I'd say that with the difference between 2750 actual weight/tire, and the chart starting at 4500/tire, you already have a pretty good margin at 70 psi.

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"

Very nice set of numbers, here we go.

 

Truck and trailer weight minus truck weight only. 45,020 - 22,740 = 22,280 Therefore the trailer weight is 22, 280 lb

Trailer weight minus the trailer axles weight 22,280 - 15,540 = 6,900 Therefore the pin weight of the fifth is 6,900 lb

Front axle truck loaded minus front axle truck empty 10,200 - 8,000 = 2,200 Therefore the front axle off load is 2,200 lb

Truck rear axle loaded minus axle off loaded 21,640 - 12,540 = 9,100 Load difference on that axle

Pin weight plus front axle off load 6,900 + 2,200 = 9,100 Yippee, isn't basic math grand!'

 

This is so right on!!! Must not be on pain drugs yet! Or, I'm still on mine. I wonder how core math would have come out? :o

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Henry: Any concern with that pin weight on the ET Sr?

You are on the high side of the Sr. and on the bottom of the Super Sr. I wouldn't be concerned if yours is the latest Sr. model. (Sorry can't tell from jeffw who you are). Upgrade to Super Sr. is relatively "painless", should you want to do it.

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You are on the high side of the Sr. and on the bottom of the Super Sr. I wouldn't be concerned if yours is the latest Sr. model. (Sorry can't tell from jeffw who you are). Upgrade to Super Sr. is relatively "painless", should you want to do it.

 

I'll try to give a call tomorrow to talk about the Super Sr. upgrade. Is that something Stephen Winter in NH could do for us? We're outside of Boston...

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Hi jeffw I also run about the same weight with my TC and 26 ft. 3 axel trailer, All your number are real close. The thing I use is a thermo "red" eye heat gun(Harbor Freight), to find out tire temp. Cool tire just last longer. Adjust the tire pressure, according to the load. Some times with car, sometimes without, and all.... the other toys. I just put a new set of 14 ply. 16 on the trailer. Just got the trailer builder tire wore out. Also did a axel alignment. two axel were out 1/4 inch. Will see. OU812

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It surprised me how much weight came off the front axle with the trailer on.

I finally had time to get our truck & trailer weighed. The NH DOT weigh station scales are open all the time, so I stopped in when the station was closed to get weights.

2,200 pounds off the front axle vs. 6,900 pounds pin weight. That's a 3.13:1 ratio. Does that match your [wheelbase]:[centerline of tandem to hitchpin centerline] ratio? Making a guess using 230" wb, is your hitch about 73" aft of tandem centerline?

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I'll try to give a call tomorrow to talk about the Super Sr. upgrade. Is that something Stephen Winter in NH could do for us? We're outside of Boston...

Steve could do it with no problem, he was actually involved with the development and the original installation of the Super Binkley head prototype. He hasn't done any upgrades but I would provide him with all the know how how to do it quickly and efficiently.

 

You'd have to be patient with me for a while, I'm scheduled for a surgery next month so I am just finishing the work that I have in the pipeline and then will need a month or two to "recover", before I start on hitches and heads again.

 

The conversion involves replacing the four smaller air bags with one large one and the round Binkley head with square Super Binkley that I manufacture. It also includes other improvements to increase its weight carrying capacity.

DSC_0147.JPG

 

Send me couple of pictures of the hitch, particularly the front of it, so that I can determine if it needs other things, yours was built during the "transition" period from the older design to the new design so I'm not certain what improvements it actually has.

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