tire size on truck effect on towing power/mileage

[pete99]

I have been struggling with a tire size change decision.A little history and info. I have 91 prowler265n fifth wheel and weighs around 7000lbs.I am using 99 ram 2500 5.9L gas powered 4;10 rears to pull it.This seems to work just fine it has maybe 6-7"bed rail clearance.I was recently outjust got back from Knoebels in pa.(very hilly area) I had one occasion where the bed rails and bottom of trailer were so close I cringed.No damage but wow very close. Anyway I mention the hills because my truck has 285/75/16 tires on it and i think it may have come stock with th245/75 on it.I am wondering if towing power milage and general performance would omprove with 245 tires with the added benefit of addotional 1" of bed rail clearance. I have only had this since January and have had no real trouble but wouldn't mind more power and would really like more clearance before I smash top of truck. I can't tell yyou all how many hours I have poured over this forum before making purchase and then finally registering on board. I would appreciate any input from those of you with experience in these matters.

[pete99]

I have been struggling with a tire size change decision.A little history and info. I have 91 prowler265n fifth wheel and weighs around 7000lbs.I am using 99 ram 2500 5.9L gas powered 4;10 rears to pull it.This seems to work just fine it has maybe 6-7"bed rail clearance.I was recently outjust got back from Knoebels in pa.(very hilly area) I had one occasion where the bed rails and bottom of trailer were so close I cringed.No damage but wow very close. Anyway I mention the hills because my truck has 285/75/16 tires on it and i think it may have come stock with th245/75 on it.I am wondering if towing power milage and general performance would omprove with 245 tires with the added benefit of addotional 1" of bed rail clearance. I have only had this since January and have had no real trouble but wouldn't mind more power and would really like more clearance before I smash top of truck. I can't tell yyou all how many hours I have poured over this forum before making purchase and then finally registering on board. I would appreciate any input from those of you with experience in these matters.

[RustyJC]

If you're not sure of your original tire size, check your GVWR/GAWR sticker in the driver's door pillar area. If you go smaller, watch your load range and tire load rating to make sure you don't exceed the tire's load capacity.

Having said that, the 245 will effectively make the final drive ratio lower (numerically higher) relative to your current 285 tire. This will improve towing performance and help your bed rail clearance (with appropriate hitch/pin box adjustments). Fuel mileage effects should be negligable after odometer correction is taken into account.

Rusty

[pete99]

thank you
I was pretty sure that was how that worked but a little confirmatation sure make me feel better about replacing tires with smaller ones.I measured the 285's and they are 32" tall I measured the 245"s and they are 29" tall. 3" inches should make quite a difference in low end torque I would think.Ichecked the door sticker and it says 245 E rated tires also checked owners manual and it says 245 as minimum size for it.I thought that was strange they printed a minimum but no max size. so if I figure right that will make my truck 1.5" lower and it just so happens the 15k reese hitch adjustment holes are exactly that far apart. Woo hoo this should be pretty easy to do and should have all kinds of pull to it. Worry the truck will look funny with the little tires but figure it would look lots worse with smashed bed rails. thanks again.Some one on here helped me out before with umbilical cable and another inverter question. Great having input from folks out there encountering the same kinds of issues really shortens the learning curve.

[Ray,IN]

This tire size calculator will remove the guess-work from your decision. To determine the gearing difference, this gearing calculator is really neat. Click the calculator button at top right of page and enter your data.