2007 GMC 1500 4x4 tire size reduction.
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 V8 The factory tire size is P265/70 R17 (31...
Forum Discussion
TRAILER LIFE 2014 TOWING GUIDE
Axle Ratio:
Lower gearing (the numerically
higher ratios, e.g. 4.10:1, 4.56:1, as opposed
to 3.31:1, 3.42:1), typically produces greater
tow ratings because of greater torque multiplication.
There is a wide variance in the axle
ratio’s effect on the tow rating, with some
diesel-powered pickups varying only a few
hundred pounds; on others, changing from
a 3.73:1 to a 4.30:1 sometimes increases the
tow rating by 3,500 pounds. In the past, some
ratings have increased by a factor greater than
three (from 2,000 to 7,100 pounds) simply by
using a different axle ratio. Lower gearing will
also make your vehicle accelerate quicker up
to 50-55 MPH. In general, a one-step drop in
axle ratio (4.10:1 to 3.73:1) on an HD pickup
will drop the tow rating and the GCWR by a ton.
Lower gearing has an adverse effect on fuel
economy, but it’s usually not proportional to
the gain in towing ability. Under the best circumstances,
the difference between the highest
and lowest gear ratios offered (say, 3.42:1
and 4.10:1) results in a 1.5-MPG decrease in
non-towing, steady state-highway cruising.
In most normal conditions that change is less
than 1 MPG, and if you tow a relatively heavy
trailer a lot, there’s no question that the lowest
gearing is best.
Axle Ratio:
Lower gearing (the numerically
higher ratios, e.g. 4.10:1, 4.56:1, as opposed
to 3.31:1, 3.42:1), typically produces greater
tow ratings because of greater torque multiplication.
There is a wide variance in the axle
ratio’s effect on the tow rating, with some
diesel-powered pickups varying only a few
hundred pounds; on others, changing from
a 3.73:1 to a 4.30:1 sometimes increases the
tow rating by 3,500 pounds. In the past, some
ratings have increased by a factor greater than
three (from 2,000 to 7,100 pounds) simply by
using a different axle ratio. Lower gearing will
also make your vehicle accelerate quicker up
to 50-55 MPH. In general, a one-step drop in
axle ratio (4.10:1 to 3.73:1) on an HD pickup
will drop the tow rating and the GCWR by a ton.
Lower gearing has an adverse effect on fuel
economy, but it’s usually not proportional to
the gain in towing ability. Under the best circumstances,
the difference between the highest
and lowest gear ratios offered (say, 3.42:1
and 4.10:1) results in a 1.5-MPG decrease in
non-towing, steady state-highway cruising.
In most normal conditions that change is less
than 1 MPG, and if you tow a relatively heavy
trailer a lot, there’s no question that the lowest
gearing is best.
