I am needing to increase my torque (towing power) on my truck to pull a 28 ft 5th wheel RV with a dry weight of 7,900 pounds.2007 GMC Sierra SLE 4x4 4.8L V8The factory tire size is P265/70 R17 (31" Diameter), with a gear ratio of 3.42 & I am thinking of getting smaller tires (possibly LT or XL 235/65 (29" diameter))to effectively change the gear ratio.I was wanting any info you can offer on this.I already have the truck and the 5th wheel RV, changing them out is not an option I can afford.

My TT is 4500 dry and the 5.3L and 3.42 gears I have are adequate (not great) for flat, open roads but it struggles in moderate hills. I don't know how a 4.8L would even begin to pull 8K much less the additional payload you add for camping. I don't think that is a good combination and spending money to increase torque on that engine will only get you marginal (if any) increases you will probably won't even notice.

I've owned 2 separate 4.8 L trucks with 3.73 gears, and while your idea of going to a smaller diameter tire is a good idea, I hate to be the one to tell you that you simply need more truck. That little 4.8 is a good engine, but it is NOT up to the task of an 8,000 lb 5th wheel. Maybe you can pull it off.....but I sure wouldn't want to try.

the trailer is to be used infrequently & is more for use in searching for a new home/ property, not to tour the country.I can not afford a different truck at this time this one will have to do, so I have to make the best of it with what I have.

Ok:#1. Gear or gearing (tire dia) does not give you more power, just more torque and torque is not power.#2. A drop of 2" on your tires is only going to give you about 170 more RPM. IOW's you will go up from a 3:42 to about a 3:60 to 1 gear.#3. Sorry; but this will do next to nothing IMHO.

2007 GMC 1500 4x4 tire size reduction. | Good Sam Community

Turtle_n_Peeps
Explorer
Jun 04, 2014
Ok:

#1. Gear or gearing (tire dia) does not give you more power, just more torque and torque is not power.

#2. A drop of 2" on your tires is only going to give you about 170 more RPM. IOW's you will go up from a 3:42 to about a 3:60 to 1 gear.

#3. Sorry; but this will do next to nothing IMHO.
TcTheHandyman
Explorer
Jun 04, 2014
the trailer is to be used infrequently & is more for use in searching for a new home/ property, not to tour the country.
I can not afford a different truck at this time this one will have to do, so I have to make the best of it with what I have.
msjdbman
Explorer
Jun 04, 2014
I've owned 2 separate 4.8 L trucks with 3.73 gears, and while your idea of going to a smaller diameter tire is a good idea, I hate to be the one to tell you that you simply need more truck. That little 4.8 is a good engine, but it is NOT up to the task of an 8,000 lb 5th wheel. Maybe you can pull it off.....but I sure wouldn't want to try.
2oldman
Explorer II
Jun 04, 2014
Sure go ahead.
Iraqvet05
Explorer
Jun 04, 2014
My TT is 4500 dry and the 5.3L and 3.42 gears I have are adequate (not great) for flat, open roads but it struggles in moderate hills. I don't know how a 4.8L would even begin to pull 8K much less the additional payload you add for camping. I don't think that is a good combination and spending money to increase torque on that engine will only get you marginal (if any) increases you will probably won't even notice.

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2007 GMC 1500 4x4 tire size reduction.

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