Tag Axle Air Pressure When Towing

[Allen Hughes]

We have a 2006 Patriot Thunder with a C13. We recently acquired a stacker trailer that when loaded totals 14,500 lbs. In our maiden voyage a couple concerns arose. First was the temperature of the tag tires which ran higher than the others, which led me to believe the air pressure needs increased. The second concern was a larger than expected drop in mpg (5.5 to 3..  Any comments or recommendations would be appreciated.  Thanks

[David T. Richelderfer]

Let me lend some comparison statistics and some questions.

1. Our coach weighs 42,500 lbs or so and towing the Chevy Avalanche makes its overall travelling weight about 48,500 lbs.  Do you know your weights for comparison?

2. Our coach has a Cat C-12, 505 hp engine, and gets from 4.5 to 5.5 mpg at cruising speeds from 60 to 70 mph.  We have seen as low as 4 mpg and as high as 6.3 mpg, averaging 5 to 5.5 mpg.

3. Our coach has a 10k lbs rated hitch.  Your stacker weighs 14.5k lbs.  Does your hitch safely support that much weight?

4. A friend with a 2004 Country Coach Magna weighs about 48k lbs without his trailer.  It has a Cat C-12, 505 hp engine and gets 6 mpg.  With a diesel additive - Lynch Diesel Fuel Treatment, $9 per bottle per 100 gallons of diesel - he claims to get 7 mpg.

5. Our coach has an AFE oil-bath type air cleaner.  I think it should be cleaned more often than I clean it, but cleaning it takes a couple hours total with overnight to dry.  The detergent and oil cost $30 per cleaning.  On the other hand I don't have to purchase expensive air filters.  Cleaning the filter more often might yield better mileage.

6.  I run our tags at 110 psi and the tag push-down pressure at about 30 lbs.  I reduced the push-down pressure from 35 to reduce the weight on the steering axle.

Four and one-half years ago when we were first looking at motorhomes, the first coach we saw was a 2006 Patriot Thunder homed right here in Hermiston where we live.  He was asking $165k and it had been for sale for over a year.  He told me his coach had a C-13 and he got about 5.5 mpg.  It was a beautiful coach and we should have bought it right then and there!  But I was afraid of the low mileage.  I guess mileage wasn't such a big deal, eh?  Certainly, diesel prices are not as bad today as four years ago!

Just my opinion... based on my experience with our coach, I think your mileage could be improved some but probably not much more than 1 mpg.  But at 3 to 4 mpg, even a 1 mpg improvement is significant.

[Steve Huber Co-Admin]

Allen,
To add to David's comments, the tongue weight is what is going to help you determine correct tag pressure and tag tire PSI. Suggest you weigh coach (rear corners individually with and without stacker attached. That will give you weight that each tag tier is required to support and yield proper inflation. The higher tire temps are due, in part, to the added tongue weight of the stacker without a corresponding increase in tire PSI. Reduced MPG is probably due to both added weight and added wind resistance (stackers aren't known for their arodynamic design). 
Steve

[Allen Hughes]

David, I upgraded to a 17,000 lbs Super Hitch and just replaced the oversize air filter. Thanks for your comments.  Allen

[Doug Allman]

Allen, Our 40' Marquis with the C-12 505 per CAT SIS report completed by Dave Atherton has gotten 7.79 mpg since it has been in the coach. We have always pulled a full size crew cab F-150 loaded with firewood headed to AZ and total moving weight is right at 46,000 lbs. Might even be a littler more than that as I have never weighed when pulling out to travel. Little over 84,000 miles on coach now.

I had thought that the Aqua hot and the generator used diesel so we should actually be getting better mileage. Dave cancelled that myth as he indicated the SIS system measures only the CAT engine fuel usage for mileage. Not sure if the monitor systems in the coach do it this same way separating engine from aqua (hydro) hot and generator.

Either way I smiled when I read your mileage as I am not doing too bad and is one main reason we have decided to upgrade interior of our coach in lieu of replacing with newer unit. The C-12 is the main reason along with the Roadmaster Chassis and Allison. TY says we already have one of the best on the road and that the 600 Cummins will not do what the C-12 is doing in power or mileage.

As an old racer I still like throttle and brakes. Only reason you got into seat was to go somewhere and stop.

Hopefully you are doing better than you realize.

[Allen Hughes]

Thanks Doug. I had Dave give us a readout this past winter prior to stacker and he indicated our overall mileage was 6.6 which made me feel pretty good because we were hand calculating around 5.5. So I am hopeful the hand calculated 3.8 is more. No matter it still is nice now being able to have both the grocery getter and the toys all in one tow.