Roof rack or trunk rack? (solution: none of the above... modded trunk!)
 

Which is better? I drove with a trunk rack with my bike on it for about 400 miles and instantly notice like a 4 or 5 mpg decreas. And when I'm with my friends like the only way to fit our bikes in is to have them hanging out of the trunk with the trunk open. I also notice about the same loss. But what about roof racks? I'm thinking about mounting our bikes on the roof upside down with the wheels off. They would be facing in a straight line with the car as opposed to being sideways on the back. What do you guys think?

The roofrack may be worse than the trunk, although I am not positive about that. Do you have a trailer hitch? If so, looking into a hitch mounted bike rack to get as much of the bikes out of the airflow as possible. Although the cost of a new bike rack may offset the fuel savings.

Roof rack will be way worse than trunk mount.

If you can adjust the trunk mount so that the bikes don't stick up as far you'll be a little better off.

By "trunk mount", do you mean mounted on the rear of the car, behind it? (I'm pretty sure you don't mean on top of the trunk lid itself.)

Your goal should be: (1) inside the car, if possible with the trunk closed; (2) rear mounted behind the trunk (not on top), with as many wheels/seats removed and put in the trunk as possible (3) roof mounted.

The problem with roof racks is they increase both frontal area (A) and drag coefficient (Cd), where a rear rack probably only increases Cd (unless the bikes stick out the sides too). So roof racks are a double whammy.

As Daox says, for a rear mount, you want the bikes riding as low as possible behind the car.

If you are willing to take the wheels off for a roof rack how about taking the wheels off for the trunk rack? That should get the remaining parts of the bike mostly in the car's wake.

Well here is the thing. When it is just me I put it inside the trunk or back seat no problem. But when I'm with my friends and we have 3 or 4 bikes in my like 2door it is really hard to fit all of that in the trunk (though it is possible) but we won't be able to fit other stuff in. We are going on a week long road trip and im Thor sure what the best idea is. A regular trunk rack like I have is kind of out of te question. They are very weak and with 3 bikes, it is one good sized bump away from scattering them all over the freeway in traffic. Really my only options are putting them on the roof upside down and like ratchet strap them on (staying a stream lined as possible) so that we can put our stuff in the trunk OR hanging them out of the trunk with the trunk open. Or of course I can completely disassemble them and fit them
In the trunk the best we can but we may not have enough trunk space for like camping gear and stuff. Here is a pic of how we normally do it. http://i137.photobucket.com/albums/q...1/d8d722fa.jpg

Is that causing to much drag with the trunk open?

It's causing drag, for sure, but it's MUCH better than the whole bike exposed on top of the roof.

Look at the car from the front. How much extra is sticking out? Not much the way you have it now. That's what the air sees, expressed as Frontal Area. How cleanly the air departs the back end is expressed as Coefficient of Drag, or Cd. Multiply those to for total drag. What you have now makes Cd worse, but doesn't change FA. Mounting them on the roof makes both a lot worse. When you multiply those, you get hit twice.

Your current setup actually looks pretty good, I don't think you will get much better with a car like that unless you want to take the trunk lid off (or build a custom one) for when you are using your car as a bike hauler.

I am so used to SUVs and trucks where 5mpg is a big deal, how much extra fuel are you burning with your 5mpg loss? is it actually significant for an occasional trip with friends?

I'd say it explains the decrease you're seeing. I would still bet the roof mount approach would be worse though. You could pretty easily test which is better by doing a coast down test to compare them.

My thoughts are:

1) Make/modify/get a cargo rack for your camping gear to go behind the car instead of the bikes. Cram the bikes in the trunk and close it. The gear could be packed more densely and closer to the rear of the car, which is good.

2) Much harder, but more fun: fabricate some kind of aerodynamic shape that will fill/sit in the void between the rear of the roof arching down to the high part of the trunk lid (when it's in that partially open position, with bikes sticking out). Such a mod may even be favourable for approaching an ideal streamled shape depending on the height of that open trunk. Dealing with side taper from the C-pillar back to the open trunk lid will be trickier though.

That's probably the best you can do there. Nice of you to include a few more facts like 3 friends and the car loaded to the max. Also a Honda Civic huh? So yer mileage drops from 35MPG to 30MPG.

I'd think your SUCC is doing great. (Sport Utility Civic Coupe)

As others indicate, Just Say No to Roof Racks.

If it's that bigga deal, buy a little cargo trailer and modify it to fit in the template area behind your car and put the bikes there. But the expense of the trailer and hitch would probably translate to a 400,000 mile break even financially.

I like this idea! Maybe I can find a messed up trunk for cheep that I can slice a slot for the bikes to stick out and I can close the trunk!


Filling the void between the trunk and back window is a pretty clever idea but I don't think i can pull that off

I would like to get a hitch rack like that, but only if I can borrow one. Id rather not buy it. But that would solve it.

But yah my SUCC is going to kick ass. My friend said his grand parents house in Arizona where we are going has a long windy dirt road that I'm going to rally it on haha. And it is going to be 4 people total. 3 bikes and one skate board and enough spare parts just incase. About 800 lbs total.

I forgot to mention that I once got 43 mpg with the bikes out the back and 3 people. I have no idea how though because the hills were insane! I guess I just used my Bmx skills to pump up and down the hills. Used a lot of EOC. (pickin ip on the terminology ;)

That's a creative idea too.

I would avoid a roof rack at all costs. I used one for a recent trip and took a 15 to 20% hit in mileage.

43MPG ain't bad when you're splitting the fuel costs with 3 or 4 people.

Looks like you had a fairly efficient set-up already.

My own not very rigorous test:

http://www.metrompg.com/posts/photos...y-rack-mtb.jpg

With bike inside (no racks): 55 MPG @ 55 MPH
With bike on roof racks: 40 mpg @ 55 MPH = down 15 mpg or -27%

From: Mini-experiment: the wrath of roof racks - MetroMPG.com

In the hands of someone who didn't know about FE:

96 Esteem sedan- 42 mpg combined.
96 Esteem sedan with a Christmas tree on the roofrack- 20 mpg highway.

I'm not realizing that when I got 43 mpg with all my friends, yes we were on extremely hilly back roads, but they were back roads instead of freeway. I read a lot of the tips last night and saw the speed to mpg graph. Holly crap I had no idea how fuel consumptive 65-80 mph was. We were going way way slower. Normaly on flat highway trips we get like 37 at the best.

Metrompg, is that your car/ bike? 27% decrease is horrible. I'm glad I got this straightened out. I'm curently looking for a trunk to cut holes in and take the handle bars off and nothing will be dragging at all =D

42 to 20????? Holy crap! I would be flooring it in my car with that much drag.

Yeah, that's my car.

Hole in the extra trunk mod sounds ideal. Looking forward to it.

Aweeeeee crap. I just had an idea for a perfect design. I know someone mentioned it earlier but now I got the perfect plan. Taking off my trunk and making one out of couroplast. My friend gets it for free from lowes. Can you say boat tail? Haha more trunk space an even better mileage than with the regular trunk closed. I'm real excited to build this now haha is there anything I should be aware of with the back of it? Does it need to seal shut or can there be an opening ?

Well! I just got one wild hair of an idea.

Leave your trunk alone for weather seal/protection for your spare parts.

My plan only accounts for about 2 bikes, but I still want to share.

They make elongated hitch mounts which several people on here use as support for their boattails.

Picture 2 bikes on their sides elevated/ mounted bunk bed style length wise beyond
the back of your car.

Yes, this would INVOLVE a lot: license plate/tail/brake light relocation/duplication
and custom brackets to secure everything.....but.......!!!!!!!!!!!!!!!!!

Think how trick that an effective boattail could work, and look if you could sleeve
the bikes into a body bag aero looking package!!!!!

A lot of work; but I bet the results could be quite satisfying!!!!

Ok! So I'm less than a week away from my road trip to arizona and I finally got the bike rack situation figured out, my friend gave me a messed up trunk for free and I cut a giant hole in the back for my bikes to stick through. I might get a little bit more creative by building some sort of tail on it If I have some time this week. I also made a little door for it so that i can close it up whenever i shut the trunk, as if the jaged metal edges wouldnt deter theives well enough. Ill have pictures up either tonight or tomorrow. I'm getting really excited.

This is a really creative mod. Please do post the pics.

I'm just testing it. For the trip I will take off the handle bars and front wheels. It can easily fit 3 or 4 more bikes. Overall I think it was a real good solution to my problem. Not to mention it took like 20 pounds off it seems

http://i137.photobucket.com/albums/q...048990307D.jpg
http://i137.photobucket.com/albums/q...048FB70A84.jpg

how cool is that!

That is awesome.

When you get 3 or 4 bikes in there, would you post one more pic? I'd like to put this on the front page - it's a really creative mod.

I think you could put a flexible plastic or rubber 'skirt' around the edge of the hole, that would just bend out of the way for the bike frames. seal it to the trunk lid with some silicone. I bet it would minimize leakage.
That was a huge score, getting a trunk lid that bolts on.

Hell yah! We are leaving Saturday so ill post pics. Ill try and get a ton of pics all throughout the southwest as we are traveling. One small problem is I had it open and the seats folded down you get some exhaust in the cabin and dust if you are driving on dirt. I really want to put some plastic on it to make it a little more aero dynamic but idk. I was thinking about putting something on the jagged edges but I might just be lazy about it instead haha.

The sun's at the wrong angle to clearly see how you cut the lid. 3 or 4 slots 2" wide would suffice. You might fill the hole with a sheet of rubber from an old inner tube (I think trucks still use them).

A vented spoiler like they use to keep dust off the back window of a station wagon might keep the exhaust fumes out. Or a tail-pipe extension that curves down into faster moving air. Don't be lazy about carbon monoxide ha ha.

Yah I just basically cut a hole half the width of the trunk. I cut my tail pipe a little shorter for looks and for the skid plate. Which helps it get in the car lol. So the reason why it gets in is because the eddy of air behind the car. And I'm thinking some form of super sweet coroplast spoiler will fix that problem right up haha

Well, if Saturday sneaks up on you, at least some plastic shopping bags and duct tape.

Ok this is my make shift block off for when it is parked
http://i137.photobucket.com/albums/q...13E6317504.jpg

So I found a way to not take off te handle bars. Which is good because that saves us a lot of time and much needed space in my little trunk
http://i137.photobucket.com/albums/q...13E1E73300.jpg
Built a little couroplast spoiler over it
http://i137.photobucket.com/albums/q...13D2DAF6E2.jpg

Handlebars totally out of the path of the wind
http://i137.photobucket.com/albums/q...13CE4C24A5.jpg
http://i137.photobucket.com/albums/q...13C9F96F81.jpg
http://i137.photobucket.com/albums/q...13C6737E5D.jpg

Although I commend you on yer efforts, you need to be very careful about this mod. Allowing CO (carbon monoxide) into the car interior is very dangerous as it is an odorless gas and if you don't have the proper equipment to detect it, you put yerself and yer passengers at great risk from passing out or dying from the fumes. :(

CO may be colourless, but some people (like me) will taste it when it combines with saliva.

While CO is odourless, car exhaust fumes definitely aren't.
The other smells are an indicator wether exhaust gas is being pulled in.

Crank up the ventilation, and you won't have much of an issue.
I've driven with the rear hatch open numerous times - as do many hatch or break owners ;)
I've never even remotely come close to sucking in CO to a dangerous level.


Visiting old folks with natural gas stoves (literally, a dying breed !) is more dangerous ...
I can - and do - instantly tell them to have their stoves adjusted.


Closest I've ever been, was when an injector seal gave in, and exhaust fumes were being pulled from under the hood by the ventilation system.

Well with the seats folded up I havnt ha any problems with exhaust or cold weather or anything. The sun just came up an we have been driving all through the night. We barely got our stuff to all fit in the car. It's a tight squeeze for sure. But I'll have pictures in a bit.

So fitting four bikes is possible but very very difficult because my friends brought so many bags. But we got it all in haha
http://i137.photobucket.com/albums/q...56A529A43D.jpg

http://i137.photobucket.com/albums/q...56B172CEDE.jpg
http://i137.photobucket.com/albums/q...56CDAA467F.jpg
http://i137.photobucket.com/albums/q...588F1E2E89.jpg
http://i137.photobucket.com/albums/q...56BC9B1DDF.jpg
http://i137.photobucket.com/albums/q...56C31475DA.jpg
http://i137.photobucket.com/albums/q...56C98854AB.jpg

Are those BMW rims? They look great!

^thanks man, my friend just got new wheels on his 328i and we put them on for the trip because my rim is bent.

So I went from avaraging 38-43 to 42-64... Mostly around 47 that is with 1000 pounds of people and stuff. And I figured out how to get them all 4 in nicely

http://i137.photobucket.com/albums/q...AA8BCFF372.jpg

http://i137.photobucket.com/albums/q...AA7EC43449.jpg