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Truck Canopies or Toppers

I have an ext. cab truck with a 6’6" box and I want to purchase a new canopie for it. I also pull a travel trailer for vacations and weekends. Would a cab high topper help the air flow over the trailer better, or would a cab high at the front and a 4-6" rise at the back of the topper help the air flow over the front of the trailer better?? Which topper creates more drag at highway speeds when not pulling the trailer?

I would guess your root question is “how do I get better mileage”(I don’t think your doing wind tunnel tests) I must ask how much are you looking for? and then whats the make-up of the power unit (what engine,trans,diff,ratio,tire size) You may be at a point that nothing will give a good return for the money (buy gas with it instead) maybe not.Any idea on combined weight. Year and mileage on truck 2wd 4wd single or dual axel trailer? Turbo?

I have an ‘02 Chevy Silverado 2wd, 5.3 V8, auto, 3.73 ratio and 255/70R-16 tires. The mileage is about 80,000 kms. The trailer weighs about 4000 lbs on dual axels and is considered an ultralight, it is about 7.5’ high at the front.Hope this helps!

How many mpg’s are you trying to gain?

The low rise will only lose 3 MPG. The high one will lose more. It may be best to try just the trailer.

I thought he was trying to gain mpg by making his rig more aerodynamic by adding the topper and better directing the air around the trailer, that is what the first part of the post states.

If you’re buying a topper anyway, go with the cab height one. The taller one will only increase drag. If fuel economy is your goal, don’t buy either one. Wind tunnel testing has shown that a pocket of air forms in the bed at highway speeds, and that pocket of air has its own aerodynamic properties that help fuel economy. With either topper, you will be adding weight and disabling that aerodynamic pocket. Now when you add the trailer to the equation, it all depends in the dimensions of the trailer.

Ron-man, I like what you say about the cab high topper and I know that a previous truck I had didn’t get very good fuel economy when I put the topper on it. When I go on vacation, I always keep my blocks of wood, emergency tool kit, etc under the topper for safe keeping. However, maybe a roll-top box cover would do the same thing, weigh alot less and have less drag than a topper. My trailer is 23’ long, 7’4" wide and 7’8" tall and weighs about 4000 lbs when loaded up. Would a roll-top box cover still screw up the aerodynamic properties that help the fuel economy? Joel D. Funk

I wish I knew. My theory, though, is that it too might hurt fuel economy in the same way as lowering the tailgate would. The compartment created by the tailgate and the sides of the bed help create that aerodynamic pocket. In the end, though, this option might be the best one of the three. I believe it will have the smallest impact on fuel economy.

I suppose you want to eat that cake too, eh? Typically, what helps the airflow with the trailer in place will not be beneficial when the trailer is not there. You haven’t mentioned what the profile of the trailer looks like!! We’re left to assume it’s taller than the truck cab roof but we do not know by how much.

Personally, I would want to maximize the performance and usefulness of the truck under the most prevalent conditions. Since you only tow on vacations and weekends, it doesn’t make much sense to make it best under those conditions and sacrifice performance the rest of the time. And some airflow profile that looks good with the trailer might look really goofy when it’s not there. My 4c.

I tow a horse trailer. With the horses in it the weight has to be close to 4,000 lbs. My Toyota Sequoia gets about 18 mpg on the highway which drops to just under 12 mpg when towing.

Whatever you are pulling, your gas mileage is going to go down the toilet. I’d suggest talking to a trailer center and see if they have a “wing” you can attach to the roof of your truck. This can deflect the wind and make a hole for the trailer to pass through. When you are not towing you can take off the wing and get better gas mileage the rest of the time you use your truck.

It seems to me that the wing would have to be fairly close to the trailer. Otherwise, the air would just expand between the wing and the trailer, negating the improved air flow. It sounds like Joe’s original question concerning the height of the cap. But the cap would only inprove air flow around the trailer if it is tall enough to divert the air over the trailer.