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2005 31' funmover Ford V10 Rear End Ratios for mileage


Indian640
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Did the 1st shake down cruise in the funmover.

Everything went extremely well, the ride with the added air bags makes the unit handle very well, (other than needing to realign the front end after shop installed the front bags). Now that I can start fine tuning this rig for the road I need to look at rear end ratios. ( mileage was 6-7 mpg cruising at 70-72 mph) The current ratio is a 4:56. Currently with the added weight this thing has a lot of power that can be traded for mpg. Any thoughts? Art

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6-7mpg is quite good for 70+ mph! Are your tires rated for that speed? Are they new tires or some years old? Some or many truck/RV tires are rated for 65mph. Do you have a TPMS to monitor your tire pressure. On many RV's the weight on the tire is right at or above the max the tire is rated for. Just a few pounds too low in pressure is asking for a blow out.

 

Did you see the video in this topic http://www.rvnetwork.com/index.php?showtopic=117817 about a blown front tire on an RV going between 70 & 80mph?

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Hi Al,

Thanx for your concern.

Tires are new and checked every morning before pulling out. All are 6 x 16 and kept around 78-80 lbs.. I have a friend in NH that has the same model only with a master bedroom in back. He averages around 9-11 and has gotten 12-14 in some instances. I`m researching our vin #`s to find out the rear end ratios. Even loaded ( I added air bag assists to the springs ) this truck has plenty of power, even going 75+ mph.

I would like to trade some of that pulling power for mpg`s. Art

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Did you see the video in this topic http://www.rvnetwork.com/index.php?showtopic=117817 about a blown front tire on an RV going between 70 & 80mph?

 

Watched this video several times and if you look closely at the end, it was the tow vehicle that snagged the barrier cable which in turn pulled back the MH as he was over correcting to the left, forcing the weight to roll the MH. If it wasn`t for that cable he did a great job in the situation given..... you never know..

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  • 5 months later...
  • 3 weeks later...

As greenacres said you need to find out what axle you have. Then go to various gear sites and see what ratios are available. Some have charts yo help you decide. Next size up maybe a 4:30. I would think a 4:10 would be too big of a jump. An alternative would be to go to an overdrive unit between the trans and rear end like a gear vendors unit. That way you can still have the power for the hills and the better mileage.

 

You may want to calculate to see how long it would take to recoop your investment in the rear axle change or overdrive unit to see if it is really worth it.

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  • 2 years later...

That FORD engine was never stingy on fuel.  The builders of your truck put that rear axle ratio in the rear end for a reason. Sure you could put maybe a 3.80…  and lug the engine to death. Only proper solution would be possibly a two ratio set up but you still would gain little in mileage savings to offset the cost of a two speed axle.  If you want better economy you need a diesel engine in a truck that heavy.   You might compare the same trip and keep you speed down to 55 mpg.  You do not decrease fuel consumption in a FORD V10 by pushing it to 72 mph...

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I think that you will find that a E-450 has a 4.56 rear axle ration and the E-350 has a 4.10 axle ratio. That is the main difference in the two. The higher numerical ratio on the E-450 allows the larger payload capacity of that model. If you change that gear ratio, you should drop your payload down to the E-350 level and I doubt that will be possible in 99.999% of the RV's that are on the road today.

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1 hour ago, GeorgiaHybrid said:

I think that you will find that a E-450 has a 4.56 rear axle ration and the E-350 has a 4.10 axle ratio. That is the main difference in the two. The higher numerical ratio on the E-450 allows the larger payload capacity of that model. If you change that gear ratio, you should drop your payload down to the E-350 level and I doubt that will be possible in 99.999% of the RV's that are on the road today.

In addition to the axle ratio, the springs are heavier, maybe parts of the frame are heavier duty to take the extra GVWR for the vehicle.  There could be other changes as well.

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  • 5 months later...

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