Tow Ratings for Dodge Ram 1500 with 20" OEM Wheels

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kbfeip

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Dec 24, 2006
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Discovery Bay, CA
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
 
kbfeip said:
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.

Myth?  It depends.  If the truck came stock with 20's than sounds like yes.  If the truck came with 17's and was switched to OEM 20's, then it  probably lowers the towing capacity.  My friend did just that on his 2001 Ram, but he's towing a 2000lbs popup, so he does not care.
 
My Dodge Ram 1500 with Hemi 5.7 engine came with 3.92 rear end and 17 inch wheels.  Not a special order.  It's a 2005 model

Tow rating with 17 inch wheels - 8900 pounds.  Source - Trailer Life Tow Ratings.

As I recall the 20 inch wheels reduced the tow ratings by 500 pounds.  If you have a 4X 4 it also reduces the tow ratings.

Ron
 
Tow rating for same truck, engine , rear axle combo (Quad Cab Short Bed) - with 4 X 4 is 8600
With 3.55 rear axle and 4 X 4 it's - 7600

The rear axle makes a lot of difference.  Can't find where it says the 20 inch wheels lower the tow rating.  Maybe it doesn't?

Ron
 
hoddinron said:
My Dodge Ram 1500 with Hemi 5.7 engine came with 3.92 rear end and 17 inch wheels.  Not a special order.  It's a 2005 model

Tow rating with 17 inch wheels - 8900 pounds.  Source - Trailer Life Tow Ratings.

As I recall the 20 inch wheels reduced the tow ratings by 500 pounds.  If you have a 4X 4 it also reduces the tow ratings.

Ron

Hey Ron,

I'm real curious about the dry weight of your 5th wheel, how long you've been towing it, and what it's like. 

I tow a 30' TT at 4800 lbs. dry.  I originally went that route after being advised that my 1500 with OEM 20"/392:1/QC/2WD had a tow rating of 7750.  The brochure for that year says 8750 and payload of 1760.  (There is no mention of a de-rating of tow capacity for 20" OEM wheel's anywhere in the brochure)

I've stumbled across a new 2007 Fleetwood Lynx 5th wheel model 255RKS, dry wt. is 5910, and pin wt. = 1379 lbs.  It really has my interest, largely due to the potential for shortening up the length of my rig, (My TT is 33.5' overall) and...to be honest I may just have the upgrade bug.  (Which is what keeps dealers in biz)

Would appreciate hearing your thoughts....

Kurt


 
I'm wondering if its not the gear ratio, but the wheel capacity that makes the difference, all wheels are rated for load carrying capacity.>>>Dan
 
I had a 2005 Dodge Ram 4x4 1500 and now have a 2009 Dodge Dodge Ram 4x4 1500. Both came factory with 5.7 HEMI, 3.92 rear end and 20" tires. The tow rating was not reduced for either. 
 
Lowell said:
I had a 2005 Dodge Ram 4x4 1500 and now have a 2009 Dodge Dodge Ram 4x4 1500. Both came factory with 5.7 HEMI, 3.92 rear end and 20" tires. The tow rating was not reduced for either.

Hey Lowell,

Good to hear from you again.  We posted back and forth when I first joined this forum back in Dec 06. 

You bring up a good point.  Haven't had a chance to check the load ratings of the low profile 20" vs. the larger profile 17" tire and wheel package.  However, I suspect that one key may be the resulting overall diameter of the tire which affects the "effective ratio" of the entire drive train package.  (Axle ratio and wheel dia. combined)

From the earlier post: 

"20 inch wheels with 3.92 rear gear = 3.77 ratio
17 inch wheels with 3.55 rear gear = 3.70 ratio

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."


To add to this:

I located both the sales brochure and the Trailer Life towing guide for the 2006 and the 2009 Ram 1500 models.  You have to look closely, but each source does in fact state a lower tow rating for models equipped with the 20" OEM wheels....from 1000 to 1100 lbs. less.

Since it appears by the earlier posting found elsewhere that the overall diameters between the 17" and 20" are almost identical, it makes you wonder if in fact the lower rating is due to tire or wheel capacity.

In contacting a local dealer and Dodge/Chrysler both directly, neither could answer the question directly.
 
Dodge Body Builders Guide shows a 1000-1100 lb reduction with the 20" wheels  in GCWR and tow ratings.  Notice the tow rating change from 1000 lb reduction in '09 to just 50 lbs in '10/'11.  http://www.dodge.com/bodybuilder/year.pdf

Those 20" tires are a P tire and generally P tires in a wide base tire are a poor choice for hauling/pulling a 7k-8k trailer around when compared to a LT tire.
 
My Lincoln truck came with 20 inch wheels.  Though its basically an F-150 it tows a lot more then the 150, not sure why
 
longhaul said:
Dodge Body Builders Guide shows a 1000-1100 lb reduction with the 20" wheels  in GCWR and tow ratings.  Notice the tow rating change from 1000 lb reduction in '09 to just 50 lbs in '10/'11.  http://www.dodge.com/bodybuilder/year.pdf

Those 20" tires are a P tire and generally P tires in a wide base tire are a poor choice for hauling/pulling a 7k-8k trailer around when compared to a LT tire.

A very good point.  Again, makes me wonder if the drop in tow rating for 20" wheels by Dodge was indeed a result of the load rating on the OEM tire.

I've been watching the General Grabber HTS as a potential replacement which has an XL load rating of 1192, vs the Goodyear Wrangler HP OEM tire at 114S.  That's 2908 lbs. load and 51 PSI max vs. 2601 Lbs. and 44 PSI.  Seems like a good replacement for towing applications.  I've got just under 40k on the clock and around 4-5 32ths tread left, so I'll squeak out a few more miles before pulling the trigger on 'em.


 
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