How much does a roof rack actually affect fuel economy? - page 3 - IDI Engine - VWDiesel.net The IDI, TDI, and mTDI source.
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#30 by R.O.R-2.0 on 02 Oct, 2012 12:09
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Easy solution to the problem--only put the cross bars on when you need 'em, store 'em in the trunk when you don't. Increased utility on demand, no permanent loss in economy--truly the best of all worlds
just keep in mind.. a SIDE MIRROR is like 6-10% of the total drag your car has..
ROR--do you recall where you got that info? I would be interested in further investigation about how to reduce that--it seems like an easy way to get a noticeable increase in fuel economy, to address that drag. Anyone aware of any potential solutions?
yes, smaller mirrors, and only a mirror on the drivers side..
the info was from a fellow VW junky.. i completely believe him as well..
he built a rocco that got nearly 60mpg with very little tuning!! had shaved everything.. and only one mirror.
and i believe the Yakima racks dont come apart like his does.. so you wouldnt be taking the cross rails off as easy.. -
#31 by 745 turbogreasel on 02 Oct, 2012 12:45
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Quote
10%
Doubtful in a car with drip rails, unless you are rocking some west coast mirrors.
Also be aware local law may require both side mirrors.
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#32 by Blocksmith on 02 Oct, 2012 14:27
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yes, smaller mirrors, and only a mirror on the drivers side..
the info was from a fellow VW junky.. i completely believe him as well..
he built a rocco that got nearly 60mpg with very little tuning!! had shaved everything.. and only one mirror.
and i believe the Yakima racks dont come apart like his does.. so you wouldnt be taking the cross rails off as easy..Quote10%
Doubtful in a car with drip rails, unless you are rocking some west coast mirrors.
Also be aware local law may require both side mirrors.
That's exactly what I was thinking--smaller, pointier mirror(s), perhaps with a clear plastic cone on the back, over the mirror itself, to decrease drag. Unless that was illegal, of course. If it is legal, I'm totally doing it--I don't really use my side mirrors anyway, just my rearview and glances backward over the shoulder to check the blindspot. I'd never even notice if the plastic cone fogged over...
I wonder if putting them further forward on the fenders would help out any?
ROR--any links to this guy's 'rocco build? I'm assuming it's a diesel swap...OR WAS IT GAS ?!
Either way, it'd be great to read more about it.
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#33 by R.O.R-2.0 on 02 Oct, 2012 19:36
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yes, smaller mirrors, and only a mirror on the drivers side..
the info was from a fellow VW junky.. i completely believe him as well..
he built a rocco that got nearly 60mpg with very little tuning!! had shaved everything.. and only one mirror.
and i believe the Yakima racks dont come apart like his does.. so you wouldnt be taking the cross rails off as easy..Quote10%
Doubtful in a car with drip rails, unless you are rocking some west coast mirrors.
Also be aware local law may require both side mirrors.
That's exactly what I was thinking--smaller, pointier mirror(s), perhaps with a clear plastic cone on the back, over the mirror itself, to decrease drag. Unless that was illegal, of course. If it is legal, I'm totally doing it--I don't really use my side mirrors anyway, just my rearview and glances backward over the shoulder to check the blindspot. I'd never even notice if the plastic cone fogged over... I wonder if putting them further forward on the fenders would help out any?
ROR--any links to this guy's 'rocco build? I'm assuming it's a diesel swap...OR WAS IT GAS ?! Either way, it'd be great to read more about it.
nah, diesel rocco.. idk if the guy has a build. i met him at the Double J G2G earlier this year.. had a FF trans in it. n/a too. -
#34 by JBG3 on 11 Oct, 2012 07:49
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2. the fastners are just sheet metal screws. That may be pretty common, but i prefer a nice strong bolt and nut, so im gonna actually bolt them on instead through the roof and discard the sheet metal screws. We are also making rubber feet for the rack.
so what we've decided to do is use nutserts in the roof. There was some debate between the body guy and I, about how best to attach this rack, and since the car will eventually be painted, we really shouldn't just bolt the sucker to the roof under the headliner.
What hes done is used steel nutserts in the sheet metal, and sealed around them. this way I can bolt and unbolt the rack for paint, and overall, its a much more thought out attachment. What I need to do for installation is seal the threads of the screws themselves, instead of making a potentially ugly large foot for the rack.
I think overall, it should look much better and be very strong.
I should have some pics later on
EDIT-
some pics-
here are the nutserts installed, a potential gasket, and the foot for the rack from a few angles. This is way better than the fasters that came with it, and most importantly, (as you can see from the condition of the paint) makes the thing removable for sanding in the not too distant future.
Each rail has 6 screw locations
got to get the correct length grade 8 fastners, but should have it all assembled shortly.
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#35 by ORCoaster on 11 Oct, 2012 19:30
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Slick, Find some nice decorative Chrome or black round Allen wrench type bolts and keep them handy for when the rack is not in place. Otherwise water in the headliner no?
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#36 by JBG3 on 12 Oct, 2012 13:39
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Slick, Find some nice decorative Chrome or black round Allen wrench type bolts and keep them handy for when the rack is not in place. Otherwise water in the headliner no?
got them all mounted, actually, the rails im going to leave on all the time, but yeah, if I left the nutserts open, id have a major water problem.
After installing, I doubt ill be taking it off except for paint, the rack has covers for all hardware, so its pretty sleek once its all on.
Here is the rack installed with the fastner holes covered. it has a deathgrip on the roof, shaking back and forth will rock the whole car without a hair of movement-
Next a few pics of the monte blanc cross bars. These things are pretty gratifying, everything on them seems shaved for air flow, the crank for tightening it recesses into the tower, and the whole thing is low profile. now for some test runs
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#37 by R.O.R-2.0 on 12 Oct, 2012 14:18
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its STILL added drag, no matter how aero-dynamic it is..
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#38 by ORCoaster on 12 Oct, 2012 22:42
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Better to be slick and Aero than that old plywood box bolted to the clip on roof racks we used for going on vacation in the summer. Dad must have hated to put them on as he was all about squezzing every last mile out of a gallon of gas. 7 kids, the box on the top of a Country Squire station wagon and still got near 20 mpg in the late 70's
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#39 by JBG3 on 15 Oct, 2012 11:59
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its STILL added drag, no matter how aero-dynamic it is..
yes. The objective for me is having my cake and eating as much of it as possible.
The full Yakima arrangement dropped fuel economy from mid 40s to high 30s, as much as 7-8mpg. If this setup drops it only a few mpg, that will be worth it to me. So far I have about 360 miles on just the roof rails, not a full tank driven yet.
My plan is to drive a couple tanks with just the rails, a couple with the cross bars, and finally, a couple with the roof top carrier and see the differences. That there will be a decrease I am fully aware, its more of a matter of how much, and whether acceptable -
#40 by JBG3 on 24 Oct, 2012 11:19
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so one whole tank with the roof rails yielded 45.2 MPG with about 30% around town driving and several extended traffic incidents, which is looking like its comparable to nothing on the roof.
Anything above 45 im happy with. Now I will install the cross bars and see what they do. -
#41 by R.O.R-2.0 on 24 Oct, 2012 12:42
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so one whole tank with the roof rails yielded 45.2 MPG with about 30% around town driving and several extended traffic incidents, which is looking like its comparable to nothing on the roof.
Anything above 45 im happy with. Now I will install the cross bars and see what they do.
roof rails hardly create any drag..
the cross bars on OTOH, will bring your mileage down.. they are were the added drag comes from..
i didnt expect there to be a MPG drop with just the lateral support bars.. -
#42 by JBG3 on 24 Oct, 2012 12:53
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so one whole tank with the roof rails yielded 45.2 MPG with about 30% around town driving and several extended traffic incidents, which is looking like its comparable to nothing on the roof.
Anything above 45 im happy with. Now I will install the cross bars and see what they do.
roof rails hardly create any drag..
the cross bars on OTOH, will bring your mileage down.. they are were the added drag comes from..
i didnt expect there to be a MPG drop with just the lateral support bars..
we agree, and I didn't expect a difference either, what I was doing was establishing a baseline to measure against. Now that I have confirmed numbers that point to the rails being essentially no additional drag on the car, I can continue to the cross bars scientifically.
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#43 by R.O.R-2.0 on 24 Oct, 2012 13:00
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so one whole tank with the roof rails yielded 45.2 MPG with about 30% around town driving and several extended traffic incidents, which is looking like its comparable to nothing on the roof.
Anything above 45 im happy with. Now I will install the cross bars and see what they do.
roof rails hardly create any drag..
the cross bars on OTOH, will bring your mileage down.. they are were the added drag comes from..
i didnt expect there to be a MPG drop with just the lateral support bars..
we agree, and I didn't expect a difference either, what I was doing was establishing a baseline to measure against. Now that I have confirmed numbers that point to the rails being essentially no additional drag on the car, I can continue to the cross bars scientifically.
hopefully, being that the bars are actually aerodynamic, i would think it shouldnt even bee too horrible.. -
#44 by JBG3 on 25 Oct, 2012 08:18
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so here are some pics of the cross bars mounted up-
overview-
close up-
Ive decided I really like these Monte Blanc cross bars. Im really interested to see what they do for economy, every feature seems to be designed to limit drag, the handles are recessed, there is a sloped rubber gasket for the attachment to the rails, and all slots for extra attachments come with rubber inserts to conceal them and improve the overall shape. The feature I most enjoy is the lock mechanism, which is a plastic arrangement similar to a wheel lock for a rim, no metal to get corroded and rust. Downside is that its definitely more fragile, locking mechanism and tightening clamp. These seem like things that will be brittle in the winter-
Underneath, there is even a set of 4 plastic parts to fill in the slots used for adjustment-
after its mounted-
the plastic inserts-
and covered up-