mywifelovesme
Member
I took my TT to the shop the other day for some warranty work. And thinking that since I have E load tires, I should inflate them to almost max for towing. It was the worst experience of my life towing the TT (I have towed it over 1K miles before with a Silverado on P metric tires at 38PSI and the truck never moved around). White-Knuckled the whole time and I one point I spun the tires taking off from a stop light with the trailer hooked up. Granted it was raining but still...
So I started researching tire pressures while towing and read tons of threads on inflation. What I found for the most part. A majority of posters said inflate the tires to the max PSI (or really close to) for towing. That is great and all until I started researching more. The Rebel has Duratrac E load tires. Each tire at max inflation can hold a weight of 3300(and something)lbs. That would mean per axle the tires can hold 6600 lbs. The problem is the GAWR on front is 3900 and on the rear 4100 lbs on the Rebel. So as you can see you don't need 6600 lbs for either axle. Also the door jam sticker says cold psi should be 55psi for the front and 45 for the rear (and yes it is specific to the tire size on my truck). So I found an interesting post about inflation, tire contact patch and weight, sorry I don't remember where. Here is what is said...
Let's say we have a 5,000lb vehicle where the owner's manual recommends 35 PSI for normal operation. Based on that alone, 5,000 (pounds) / 35 (pounds/ square inch) = a contact patch of ~143 square inches. In other words:
Weight/ PSI = ContactPatch
If we load up 1,000 pounds of tongue weight, we want a tire PSI that gives us the same contact patch we had with no load. To find this, we simply re-arrange our formula with the new weight and original contact patch:
PSI = (new)Weight/ ContactPatch
This gives us 6,000 lb/ 143 = 42 PSI to match the original contact patch.
Note that every vehicle has a different weight distribution, etc. but for a very rough estimate on how to match what the manufacturer recommends as you increase load, that should help.
I am just using the rear for my example... What I did when I put 70 PSI in the rear was reduce the contact patch of my tires from the original set by Ram. Here were my calculations for the rear PSI:
Let's say my truck weighs 5776 ( for the sake of math I took the GVWR 7100-payload 1324 (I plan on actually weighing it on CAT scales this weekend). Based on Ram's recommendation for the tire PSI (45), I took 5776 divided by 45. That gave me a contact patch of 128.35 sq inches. I added 600 lbs of tongue weight...5776 + 600=6376. Divide 6376 by 128.35 to get 49.676 (PSI)...rounded up to 50 since my tire gauge doesn't read decimals).
When I inflated my tires to 70 PSI here is how the numbers look... 5776 divided by 70 = 82.5 sq inches (new contact patch) which is significantly lower than 128.35. That explains why the truck was all over the road (yes I have a WDH and it is set up properly). It was riding on doughnut tires essentially. Needless to say my inflation was reduced to 50 that night. I pick up the TT tomorrow from the shop and will update the towing feel. I thought this might help others who tow. If I am wrong somewhere in my logic and numbers someone kindly correct me but I won't ever increase my tire PSI back to 70 to tow a 6k trailer. It really was a horrifying experience for me.
So I started researching tire pressures while towing and read tons of threads on inflation. What I found for the most part. A majority of posters said inflate the tires to the max PSI (or really close to) for towing. That is great and all until I started researching more. The Rebel has Duratrac E load tires. Each tire at max inflation can hold a weight of 3300(and something)lbs. That would mean per axle the tires can hold 6600 lbs. The problem is the GAWR on front is 3900 and on the rear 4100 lbs on the Rebel. So as you can see you don't need 6600 lbs for either axle. Also the door jam sticker says cold psi should be 55psi for the front and 45 for the rear (and yes it is specific to the tire size on my truck). So I found an interesting post about inflation, tire contact patch and weight, sorry I don't remember where. Here is what is said...
Let's say we have a 5,000lb vehicle where the owner's manual recommends 35 PSI for normal operation. Based on that alone, 5,000 (pounds) / 35 (pounds/ square inch) = a contact patch of ~143 square inches. In other words:
Weight/ PSI = ContactPatch
If we load up 1,000 pounds of tongue weight, we want a tire PSI that gives us the same contact patch we had with no load. To find this, we simply re-arrange our formula with the new weight and original contact patch:
PSI = (new)Weight/ ContactPatch
This gives us 6,000 lb/ 143 = 42 PSI to match the original contact patch.
Note that every vehicle has a different weight distribution, etc. but for a very rough estimate on how to match what the manufacturer recommends as you increase load, that should help.
I am just using the rear for my example... What I did when I put 70 PSI in the rear was reduce the contact patch of my tires from the original set by Ram. Here were my calculations for the rear PSI:
Let's say my truck weighs 5776 ( for the sake of math I took the GVWR 7100-payload 1324 (I plan on actually weighing it on CAT scales this weekend). Based on Ram's recommendation for the tire PSI (45), I took 5776 divided by 45. That gave me a contact patch of 128.35 sq inches. I added 600 lbs of tongue weight...5776 + 600=6376. Divide 6376 by 128.35 to get 49.676 (PSI)...rounded up to 50 since my tire gauge doesn't read decimals).
When I inflated my tires to 70 PSI here is how the numbers look... 5776 divided by 70 = 82.5 sq inches (new contact patch) which is significantly lower than 128.35. That explains why the truck was all over the road (yes I have a WDH and it is set up properly). It was riding on doughnut tires essentially. Needless to say my inflation was reduced to 50 that night. I pick up the TT tomorrow from the shop and will update the towing feel. I thought this might help others who tow. If I am wrong somewhere in my logic and numbers someone kindly correct me but I won't ever increase my tire PSI back to 70 to tow a 6k trailer. It really was a horrifying experience for me.