Hy everyone,

I am planning on a long road trip next week and I am considerig taking the fiberglass cap/shell off of my truck to improve gas milage and performance. I'm guessing I might only gain 1mpg but anything helps nowadays. Can anyone confirm improvements in mileage or performance without a cap on.

Is there any reason why I should leave the cap on? Can anyone recommend a proper way to store the cap off the vehicle?

Thanks, BB

98 F150 SCAB- 4.6 - avg mpg now @17.8

 

I think that leaving the cap on would be better for gas milage b/c it decreases the amount of drag caused by the bed/tailgate. If you take the cap off then you whould have to put the tailgate down or remove it to get better gas milage. I actually found that I used less gas when I put it on, just my opinion though.

 

thanks for the reply, my friend tells me the same thing about drag . My reply to him is that the truck is tossed around quite a bit with a good crosswind and the weight of the cap can not help either.

on my previos truck, 96 f150 with a 4.9 inline 6, I felt that I had better acceleration without the cap on and about 1.5mpg increase.

 

if you decide to take off the shell put the tailgate down. will help a bit.

 

The streamline benefits of the shell are offset by the additional weight.

 

I can't speak to the cap / no cap issue, but there is some scientific evidence that pretty well refutes the tailgate down / missing theory. The best evidence I've seen was when GM ran a modified S-10 a number of years ago at Bonneville. Since they were going for a speed record, low drag was critical. They actually ran the truck with a tailgate and a partial tonneua cover - over the rear half. This combination was arrived at after man yhours in the wind tunnel - and under very controlled conditions. There, that ought to spark a heated debate. Hope that helps!

As for the cap, I would suggest that if you fill the bed up with a ton of irregularly shaped items, a cap would probably be more aerodynamic. Oh yea, and there's one other draw back to running with a tailgate down. The two cables that keep it from dropping right on your bumber take a whupping on every bump,. Sooner or later they're going to break. How much is that worth?

 

just wanted to add another idea to this topic.....

with the shell off I will have increased visibilty in the rear of the vehicle increasing safety. Good for when the lightning owners are passing (flying) by .

 

Yes, when I owned an 87 Ford Ranger I bought a cap for it for when I moved to New Hampshire from California. From my own personal experience with that particular truck I can tell you that I got WORSE mileage WITH the cap then I did without. I don’t recall just how bad but it was a few mpg. Now that was a 4-banger getting something like 25 – 27mpg without the cap.

You could also feel the drag affect with the cap on as compared to being off. When the cap was not on I had a soft tonneau cover on it and you could feel it move much easier though the wind when it did NOT have the cap.

A truck is already going to have a lot of drag on the rear-end because it is flat (tailgate) when you add a cap you will increase the drag affect. The best gas mileage is achieved with a tonneau cover on and tailgate up (closed). Both a cap and an open bed with the tailgate down cause more drag.

 

on my ride cap on, or cap off no noticable diffreance...


Jim