kbfeip
Well-known member
I've been researching the above subject for some time now and stumbled across an interesting statement made about the effect of 20" OEM wheels on the Dodge Ram 1500.
Although I've been told, and apparently an older version of the Trailer Life Towing Guide also states that the 20" wheel package caused a 1000 lb. reduction in the tow capacity of the Ram 1500.
Not so...according to one poster. Read more below:
Posted 10 May 2010 - 10:32 AM
The 20 inch wheels are only spec'd with 3.92 rear gear ratio.
The 17 inch wheels are only spec'd with 3.55 rear gear ratio.
Unless special ordered with the 3.92 rear gear and 17 inch wheels. Very few trucks came with 17 inch wheels and a 3.92 ratio.
The 20 inch wheels use a 33 inch tall tire.
The 17 inch wheels use a 31.7 tall tire.
This is what the rear end gears feel like when comparing the two against each other. I call this the feel gear. This is a comparasion of the gears and tire sizes.
20 inch wheels with 3.92 rear gear = 3.77 ratio
17 inch wheels with 3.55 rear gear = 3.70 ratio
Dodge allowed the extra .7 tenths to allow the make up of static loss in rolling mass to be equal to a 17 inch wheels with a 3.55 ratio.
Lets say your final transmission ratio is 1 to 1.
Your rpms with 20 inch wheels 33 tall tires and 3.92 gears is 2588
Your rpms with 17 inch wheels 31.7 tall tires and 3.55 gears is 2405
For each pound of rotating weight you lose, it's equivalent to losing 10 lbs of static weight in terms of performance and mileage. 20 inch wheels and tires are heavier than 17 inch tires and wheels. Dodge factored this into to the gear choice.
Since the 20 inch wheels and tires are heavier, dodge specs a bit lower gear to make up the difference with the 17 inch wheel and tire combo to equal static and rolling mass differences and tire height bewteen the 2 vehicles.
People say that using 20 inch wheels create a 5-1000 towing loss. Ive seen people mention both.
This is a flat out myth. Know where in the towing guides or any published specification manual does it ever mention that using 20 inch wheels cause a towing loss.
Every pick up manufacturer offers a small base wheel and a larger upgraded wheel. Every manufacturer then makes the final gear ratio changes to make the both at an exact equal when comparing feel, mass, static weight, performance and fuel mileage. Since the wheels are engineered to the gear. Tow rating remain the same between the two models because of the engineering changes that have been made to make both vehicles equal.
Entire thread found at: http://www.outbackers.com/forums/index.php?showtopic=29961
Although I've been told, and apparently an older version of the Trailer Life Towing Guide also states that the 20" wheel package caused a 1000 lb. reduction in the tow capacity of the Ram 1500.
Not so...according to one poster. Read more below:
Posted 10 May 2010 - 10:32 AM
The 20 inch wheels are only spec'd with 3.92 rear gear ratio.
The 17 inch wheels are only spec'd with 3.55 rear gear ratio.
Unless special ordered with the 3.92 rear gear and 17 inch wheels. Very few trucks came with 17 inch wheels and a 3.92 ratio.
The 20 inch wheels use a 33 inch tall tire.
The 17 inch wheels use a 31.7 tall tire.
This is what the rear end gears feel like when comparing the two against each other. I call this the feel gear. This is a comparasion of the gears and tire sizes.
20 inch wheels with 3.92 rear gear = 3.77 ratio
17 inch wheels with 3.55 rear gear = 3.70 ratio
Dodge allowed the extra .7 tenths to allow the make up of static loss in rolling mass to be equal to a 17 inch wheels with a 3.55 ratio.
Lets say your final transmission ratio is 1 to 1.
Your rpms with 20 inch wheels 33 tall tires and 3.92 gears is 2588
Your rpms with 17 inch wheels 31.7 tall tires and 3.55 gears is 2405
For each pound of rotating weight you lose, it's equivalent to losing 10 lbs of static weight in terms of performance and mileage. 20 inch wheels and tires are heavier than 17 inch tires and wheels. Dodge factored this into to the gear choice.
Since the 20 inch wheels and tires are heavier, dodge specs a bit lower gear to make up the difference with the 17 inch wheel and tire combo to equal static and rolling mass differences and tire height bewteen the 2 vehicles.
People say that using 20 inch wheels create a 5-1000 towing loss. Ive seen people mention both.
This is a flat out myth. Know where in the towing guides or any published specification manual does it ever mention that using 20 inch wheels cause a towing loss.
Every pick up manufacturer offers a small base wheel and a larger upgraded wheel. Every manufacturer then makes the final gear ratio changes to make the both at an exact equal when comparing feel, mass, static weight, performance and fuel mileage. Since the wheels are engineered to the gear. Tow rating remain the same between the two models because of the engineering changes that have been made to make both vehicles equal.
Entire thread found at: http://www.outbackers.com/forums/index.php?showtopic=29961