Towing resistance, old and new

Red-Rover wrote:
For the past 10 years I have been towing a 1993 Prowler 30 ft with a height of exactly 12 foot. I am about to pull the trigger on a new 29 foot Silver Back of similar weight and pin weight but a foot taller (13 foot) The dealer says that the improved aerodynamics with a nose cap will make up the difference and I should not notice any difference.
Anybody out there that can tell me of their own experience?

Actually the shortest new Silverback is 34 ft. We have the 29 RE and our last fifth wheel was 27 ft. and lower than the Silverback mileage is the same for both, around 10-12 MPG. Ram 2500 CTD. Happy camping:)

like the lizard man in the last star fighter said " theoretically"

prairie camper wrote:

Red-Rover wrote:
For the past 10 years I have been towing a 1993 Prowler 30 ft with a height of exactly 12 foot. I am about to pull the trigger on a new 29 foot Silver Back of similar weight and pin weight but a foot taller (13 foot) The dealer says that the improved aerodynamics with a nose cap will make up the difference and I should not notice any difference.
Anybody out there that can tell me of their own experience?

Actually the shortest new Silverback is 34 ft. We have the 29 RE and our last fifth wheel was 27 ft. and lower than the Silverback mileage is the same for both, around 10-12 MPG. Ram 2500 CTD. Happy camping:)

I can believe that. A larger ratio between height and length tends to improve aerodynamics and the greater length probably balanced out the difference in height.

We have been mulling over a 29IK as a replacement for our Titanium which is 6" lower. My chief concerns with the taller trailer would be overpasses, gas station canopy's and tree branches, not fuel mileage.

My current FW is taller, longer, and much heavier than my previous FW. It is however, much more aerodynamic. I am not a mpg worrier, but didn't notice any real change between the two.

I was more concerned about the ease of towing, with the larger trailer. As it turned out, the new one pulled just as easy as the smaller previous FW.

I would have to agree with the sales person,
Jerry

newman fulltimer wrote:
I would not worry about it a brick is a brick nomatter if you round the corners.if you enjoyed the prowler you will enjoy the creek

Best answer! Those small differences probably matter to trucking companies that put in millions of miles a year...for us, not so much.

Easiest way to improve mileage is, as always: slow down! Fuel use at different speeds calculator

Traveling on the same roads at the same speed and wind temperature conditions you should not see basically any difference in mpg's. The extra foot in height should be offset by the better aerodynamics of the new front cap design. I'm assuming both towables have the same tire size and inflation as a softer 65 psi inflated tire will squat more and have a larger footprint on the road's surface which relates to friction than the same width tire carrying the same weight inflated to 80 psi. A small difference but it is a difference and does alter rolling resistance numbers.

Air resistance actually relates to surface friction.

A simple basic factor to keep in mind is that at 55-60 mph towing, the average air (wind) resistance in your RV example is about 2 times (2.1) the rolling resistance. Towing the same RV unit at 65-70 mph the air (wind) resistance increases it to 3 to 1 (3.1).

The rolling resistance of a given wheeled vehicle remains basically a constant regardless of the speed you could pull it at on a road. However, the air resistance squares itself (multiplies) as the speed increases beginning at approx just under 50 mph. As in approx 2 times for 55-60 mph and 3 times for the 65-70 range. 80 mph would be cloe to 5 times.

This is why "wind tunnels labs" are used to measure actual air resistance. Aerodynamics play a huge part in altering the averages but even a very sharp needle going thru the air still has ever increasing air (wind) resistance as the velocity increases. The angular sides of the increasing needle diameter is forcing the air molecules to move away from the needle surface and thus creates friction and resistance.

Now add in the air forced compacted air behind the end of a needle or an RV being sucked back to fill the void (space) where the needle or RV had occupied and a sucking action pulling backward is the result. This resistance is friction and then sucking and at very high speeds it even creates extreme heat.

That's why the space shuttles must have extreme heat tiles on it's forward surface for reentry and even they glow bright red from the extreme heat that results. They want the sucking action created as it helps the shuttle to slow naturally but you don't want that sucking action pulling your RV unit backwards. The faster, the higher the sucking force is.

Ummmm, what would one expect a sales person to say? :W

Who really cares? Hook up and go have a good time!!!!!!!!!

Yeh, I wouldn't worry about a little more drag. I went from a 15 yr old medium profile 10k lb 5er to a hi profile 15k 5er that has a tapered down roof at the front. The extra weight sure made a difference in acceleration and topping hills and I lost 2 mpg - 14 down to 12. I also had to slow down 5 mph to get 12 but I'm getting used to 65 mph. I can feel more wind drag so I'm sure the mpg loss was part weight and part wind drag but it wasn't the end of the world! Craig