cartop v trailer

Under normal conditions,

do you get better gas milage by cartopping? or draging a trailer and keeping the roof clean?

If you have a good trailer, wheels,
bearings, keeping the boat or boats off the roof and less exposed to the mainstream will give better mpg.

The difference is likely to be small for a kayak, because if mounted cockpit down, hull up, on the roof, and using a fairing on the rack to control the airstream, it won’t drag the car too badly,

But one tandem canoe on the roof is a drag, and two, more so.

Most of us stick with roof racks because it sames parking and maneuvering problems, and is better for emergency maneuvers. But a trailer imposes a certain discipline, and if you treat trailering as if you were a trucker, you can be quite safe.

a lot of factors will lead to small %
A pointy yak on a rack with thin bars will hardly effect mileage at all. The flip side is that a trailer has weight. If you are in the city and starting and stopping the trailer will have a far greater effect; it isn’t just about wind. You have to buy and maintain the trailer; register, tag and insure it. If the point is to save money a trailer is unlikely to be the answer. I would only think about a trailer if I needed to carry several at a time, had a vehicle that was unsuitable or a really heavy boat.

It depends on how many boats and the car
Two factors - how many boats and the towing capacity of the vehicle.

I have a small car with a very low towing capacity, in fact it is not rated for towing at all. When I put 1 kayak on top of the car I don’t notice much of a drop in MPG. When I have 4 kayaks on top of the car there is a significant drop.

I have a small lightweight Trailex trailer. Towing 1 kayak is not different than car topping 1 kayak. Towing 4 kayaks does not have a significant impact on the MPG, where as car topping 4 does have a significant impact.

I have a friend with a full size fan. 4 kayaks on top or towing 4 on my trailer doesn’t make much difference at all.


– Last Updated: Feb-11-14 9:40 AM EST –

People will tell you anecdotally that one way or thew other is better. Meanwhile they forget to factor in:

Weight of boats and trailer
Towing capacity
airflow WITHOUT kayaks on top

These are not the only factors that could tip the balance in one or the other direction.

So more info.

Jeep or minivan hauling add-on racks and 2 kayaks in saddles.

Brand new Malone Micro-sport kayak trailer with good… well everything hauling said trailer.

So far I am thinking tjhat the wind resistance and high-profile of the rooftop will mess with milage.

Hiding the trailer behind the jeep will save drag but put wear on the engine.

Since the bearings and wheels and suich are new, the trailer hauls like a dream so the wear would be minimal.

Since I am traveling 4 1/2 hours on the freeway, then a hal;f-hour over winding dirt road through mountains…

My instinct is to haul the trailer and save a tank of gas.

But wanmted peoples experiences to confirm this.

on my Kia
I could do tucson to Phoenix and back on a half tank of gas.

Load my racks and a single plastic kayak and my milage drops to a full tank. Put a couple kayaks on the roof and it’s more than a tank.

BUT, I don’t remember how many times I filled the tank when I pulled an old rebuilt bike-trailer with a couple kayaks.

When I replaced the trailer with a Malone micro-sport, I was hauling 2 on the rook and 2 on the trailer and those Hullivator racks DO ruin milage!!!

Putting drag in perspective
You need not worry about wear on the engine with such a trailer as you have. If the trailer is heavy enough that it increases the wear on the engine, that in itself is a form of resistance, which if as you describe, would be worse than the air resistance you’ve prevented (all forms of resistance increase engine wear and reduce MPG, so if there’s a need to be concerned about wear on the engine due to trailer towing but no such concern about engine wear due to air resistance of boats on the roof, by definition there’s more resistance from pulling the trailer and thus no MPG benefit). That said, your trailer isn’t heavy enough for any of that to be true. If you don’t worry about the weight of an additional passenger, you don’t need to worry about the weight of a lightweight trailer either.

This is also the second mention of “good wheel bearings”. Nonsense. Any friction in the bearings will generate heat, and if the bearings provide any real drag at all they’d get mighty hot in a very short time, and if the drag were enough to affect your mileage even a tiny bit they’d overheat and seize before you got far. Even then, the drag wouldn’t be much (there’s only a few pounds of resistance at the perimeter of a tire when the bearings are far too tight for driving - with more resistance than a simple “bad bearing” (anyone can feel this resistance for themselves when seating them prior to adjustment), so even a minor headwind at highway speed must produce much more drag than bad bearings. People should forget about drag from bearings - they either work or they don’t, and if they are cool or only very slightly warm to the touch after highway driving, they work. Just make sure they are clean and greased to keep them out of the “don’t work” category.

On the other hand, larger tires roll more easily than really small ones, especially if there’s some sidewall flex going on (not a big deal with boat trailers usually). Also, larger tires will reduce the chances that you’ll have bearing troubles down the road (due to the slower rotational speed and therefore fewer revolutions overall). I’m not sure that a full-size tire (such as tires for large cars and light trucks) makes any sense though. Surely having each wheel/tire weighing around 70 pounds or more is counterproductive, and that would be even more true for the enormous weight of the kinds of trailers equipped with such tires.

Bearing drag and reality
Clean, decent bearings don’t hurt mpg, but I too am not convinced less-than-optimal bearings make a big difference.

The reason is that I once rented a mountain bike and rode it on a range of trails from flat to mountainous, smooth to rocky/rough. At the end of several days, I by chance spun the wheels and was horrified that they would not even turn freely. At all. The cones had been adjusted way too tight. I had to turn my hand on the wheel to make the thing rotate at all.

Yet all week I’d been riding the bike without thinking anything was terribly wrong. The bike was not as high a quality as my own, but the fact was that as soon as I put even a little effort into pedaling it (or was coasting), nothing stood out as being wrong. My own body weight, the much greater force of feet vs. hand, and momentum hid the poor bearing condition from obvious notice.

Now think how much more torquey an automotive engine is. I doubt you’ll “feel” the car or truck straining because the bearings are not perfect.

Ditto Guideboatguy on the bearing precautions: Just keep an eye out for grease leakage or hot rims. Also check for underinflated tires. Any of those things needs to be corrected ASAP.

Also, the actual wind conditions
If there is strong wind other than a tailwind, mpg will go down, period, regardless whether rooftop or trailer or any kayaks at all. But in those conditions, the lower height of trailered boats plus the fact that they ride behind the rig make it advantageous over rooftopping.

I was surprised to find that on the first day of driving one rooftopped sea kayak from CO to GA, mpg was only down slightly from normal highway driving. But it was a full day of going downhill, and little wind. When I had been similarly blessed while trailering, mpg did not deteriorate at all.

Might be different with a wide, heavy trailer instead of a lightweight kayak trailer and load.


– Last Updated: Feb-11-14 3:29 PM EST –

I am all for getting a trailer. my last trip I car topped and did great on way down but way back the winds were outrageous. making all kinds of noise and at one point 2 foam blocks flew out. and this thing was clamped down tight. so when I got home I started looking for a old boat trailer to fix up and suit my needs.

I do about the same trips as you and love it. plus bearings are easy to replace 10 minutes for each just a little down and dirty work so don't let that scare you just wear some gloves.
here is the before and after trailer pics. total cost was about $300+ trailer was free from my two friends there but cutting the bend out, painting, used tool boxes, bearings, shocks, new lights and weld work. I did all but the welding and am pleased with it. you can find free trailers like that all day long.

Nice work!
That is SO much better than the average do-it-yourself trailer that gets talked about here. You make a good point about how cheap the starting material for such a nice trailer can be too, which is great since most motorboat trailers are already much better suited to the job than those little kit trailers from places like Harbor Freight or Northern Tool (those trailers are too short for boats, and it’s easier to make a long trailer shorter than to make a short one longer).

My only question would be whether you did anything to soften the ride. I think I would have looked to remove two of the four coil springs or find softer ones. Did you do anything like that? The shock absorbers probably reduce the tendency to bounce though.


– Last Updated: Feb-11-14 6:03 PM EST –

Thank you! I love it!

that's why I found an old holsclaw trailer as it had hydraulic shocks as well as springs. new shocks cost $30 and empty or loaded the trailer wont jump around. you can see them in orange on the second picture.

this and also here in Indiana if you buy a trailer that is older than a certain year it wont have a title and its very easy to get one. just let them know the possible year and title it as home made and stamp your vin # in that they give you.

I had one of those
I stripped it, added a flat-deck and some saddles and had a nice trailer… which was too big for my needs.

As i paddle mid-sized boats 10-12’ range, I got a used motorcycle trailer, added the deck and saddles which worked well until it was damaged at the lake.

Now I have the Malone which I adapted by adding a box over the axle (4" space between) plus ammo bozes on the frame and a deck before and after the box to hold B2 bags with gear.

Trailer is 197# bare. Maybe another 10# of mods with a capacity of 355# which I will NEVER reach!

3 boats @ 50# each plus PFDs & straps in the box!

Unfortunatly, my car as a 4-pin plug, Shea’s Jeep a round plug (we got an adaptor) but the forerunner has a square plug and no time to get an adaptor.

So we will be mounting my extra j-racks and car-topping after all.


I really like the low height and convenience of the trailer.

or quartering winds
A (simplistic) way of looking at it is if you want to save gas - buy a small car. If you have a small car with a small efficient engine, towing will make a bigger dent in MPG than when towing with a big powerful thirsty engine.

I towed a small popup camper with a subaru, top of the camper was below the roof of the car. We were all a bit surprised at the reduced range or MPG. But it wasn’t a flat trip.

clean and simple
Well done.

I am a roof topper
Therefore I admit to bias. Fuel economy is a strange phenomenon with loads. I drive full size pickups, and keep track of fuel purchases and odometer reading at every fueling. On short trips, weight make a difference due to accelerating and braking. On long trips air flow is a much bigger factor. The best mileage to date on my current truck, (4X4 Chevrolet) was with my 17 foot 'yak on the roof in the Yakima Mako Saddles, and camping gear and supplies in the extended cab. The weight pushed the front down enough to affect the air flow under the truck. The group I travel with for major outings report various results for fuel usage. Any vehicle hauling or towing close to its capacity will suffer poor economy. With light loading, the larger the vehicle and engine the less difference you will notice. As to roof verses trailer, what you find more convenient to your style will be more important on the long run than a slight difference in fuel economy. Also factor in the cost and maintenance of your method of moving the boat to cost of fuel. A trailer requires license fees, tires, lights, and depending on your policy, maybe more insurance.

There is no wrong answer if it works for you.

Fuel economy factors hard to identify
I’d be extremely doubtful that a load inside the extended cab of a pickup would “push the front end down” enough to affect air flow. Even loaded to capacity, something you simply couldn’t come close to accomplishing just with gear loaded into the cab, you’d be hard pressed to depress the front end enough to notice, let alone substantially affect air flow beneath it (the effect of load on ride height is something I’ve checked a number of times, on a few different light trucks. The front suspension doesn’t change much for interior loads, though it can change a lot when adding things like snowplows, who’s affect is greatly multiplied simply due to where the weight is applied). On the other hand, changes in wind velocity and direction can have an enormous effect on fuel economy, and even very small changes in wind conditions affect fuel economy enough for a person to notice if they do as you do, actually calculating MPG for each tankful.

I agree with all that you say about individual preference, and what vehicles and under what conditions changes will be most noticeable, but I don’t believe you can be certain regarding the reason you had your best MPG on a certain day.

It doesn’t take much

– Last Updated: Feb-15-14 1:46 PM EST –

With my previous truck, 4x2, loading the front of the box heavy, only a small amount closer to the front axle than the rear would give about 1 1/2 more mpg at 75 mph. Regular customers, I have an auto shop, who "level" their new pickups lose about 1/2 mpg at highway speeds. The gear in the cab, plus the boat being centered forward of the center lowers the front a measured 1/2 inch at the fenderwell on my K-1500. "Gear" includes three cases of bottled water on the floor in the passenger front. I pick up less than 1/2 mpg with the boat and gear, but it is measurable.

I just wonder how you can be sure

– Last Updated: Feb-15-14 2:25 PM EST –

Don't you find much more variation than that from trip to trip, even when everything else is the same? I do. I can do the same trip with the same load and get differences of 2, or even 3 mpg. Differences this great are usually due to the affect of wind, but no matter what, if the change you are detecting is no greater than that due to things beyond your control (and probably smaller, most of the time), how can you be sure of the cause? If a strong wind can boost or detract your mileage by 2 or 3 MPG, doesn't it make sense that much lighter winds could change it by 1/2 MPG? The only way to isolate the affect of one variable from the clutter of uncontrolled variables is with properly designed, statistically-valid analysis, which isn't something average folks do, or even know how to do (I used to know how, which is why I understand the principle, but even then I needed an expert consultant to help me). No other method for isolating the affect of a controlled variable within a naturally variable system actually works. If there were no other factors affecting MPG except the things you describe, than your conclusions would have merit. In the real world, cause and effect can't be determined unless the affect of the subject variable is generally a lot greater than that of all the uncontrolled factors, which is why you may see a real difference when comparing MPG for boats on the roof versus not, especially with smaller cars, but that's hardly the case in situations where you are "concluding" that there's a 1/2-MPG change due to the kinds of things you describe.