roof mounting or rack?

chiefinspector

You would def notice the difference using a roof rack. Sticking the bike in the boot is the best option with regards to MPG but you are limiting what you can put in it. The best thing about a roof rack is that you can still have access to the boot. If you go on long journeys the chances are that you will be taking more gear with you so it is better to have that space.

I live in Aberdeen and drive all over Scotland going biking and am glad for the space and easy access. If one of my friends come along then trying to fit 2 bikes plus all the gear into the back would be very difficult. just something to think about.

Anonymous

So roof rack = better MPG?
BUT, extortionately expensive to set up.

I know full well about the limits of putting stuff IN the car. I've been doing this for quite some time

TuckerUK

Keep the bars on as they can be a bit of a bugger to put on and off but cycle carriers don't take much time at all.

As I think I already posted, I can whip my Thule roof bars with three bikes racks still attached on or off the car in very short order (5 minutes?). I do cheat and use a rechargeable drill to tighten or loosen the mount clamps mind!

blablablacksheep

The bike rack is now mounted and went for a test drive with the bike on it

it was very easy to install and at first i was worried about the front wheel moving too much but after a while i starting to relize the bike isnt going anywhere.

Taking it off also very simple as you can just take off the roof bars with the carrier attached so storage is a peice of piss tbh.

glad i bought thule one instead of Halfords own brand though

diy

yeah I leave my tripple 591s permanently attached to the aero bars and then hang them in the garrage. Its 5 mins for me and the mrs to clamp it on to the rails.

The only down side is that its a two person job getting the bikes on the roof, but on a golf you wont have that problem.

Of course the cheapest solution is to keep the speed down and keep the driving smooth.

chiefinspector

yeehaamcgee wrote:

So roof rack = better MPG?
BUT, extortionately expensive to set up.

I know full well about the limits of putting stuff IN the car. I've been doing this for quite some time

Any attachment that you put onto a car will affect the MPG but with roofrack you def wouldn't notice as much as you do with your rear mounted carrier. Very true, they are not cheap. I paid about £240 in total but while that is quite a lot for what you get, they are very convienient and takes about a minute to put the bike on the roof.

suzyb

chiefinspector wrote:

yeehaamcgee wrote:

So roof rack = better MPG?
BUT, extortionately expensive to set up.

I know full well about the limits of putting stuff IN the car. I've been doing this for quite some time

Any attachment that you put onto a car will affect the MPG but with roofrack you def wouldn't notice as much as you do with your rear mounted carrier. Very true, they are not cheap. I paid about £240 in total but while that is quite a lot for what you get, they are very convienient and takes about a minute to put the bike on the roof.

I don't get this. How can something that is "hidden" behind the car be worse for MPG than something sticking up from the top of it.

Anonymous

suzyb, it's not what I expected either, but I can see some reasons it may be so.
In layman's terms (I don't understand this fully, otherwise I wouldn't have asked myself )
A bike on the roof is pointing in the direction of travel, giving the least possible wind resistance.
A bike on the back is side on to the airflow of the car, exposing more surface area to the wind, giving more drag.

Apart from that, there's the issue of ruining the low pressure zones, and intentional turbilence at the rear of the car etc - but whilst I've seen demonstrations of such phenomena, I don;t understand it well enough to predict outcomes.

quattrojames

I've just bought a Thule 532 carrier to go on top of the Aero bars on my Audi A4. £45 delivered from ebay, a nice carrier and the easiest way to carry a bike in my experience.

paul20v

quattrojames wrote:

I've just bought a Thule 532 carrier to go on top of the Aero bars on my Audi A4. £45 delivered from ebay, a nice carrier and the easiest way to carry a bike in my experience.

im not safe anywhere

chiefinspector

yeehaamcgee wrote:

suzyb, it's not what I expected either, but I can see some reasons it may be so.
In layman's terms (I don't understand this fully, otherwise I wouldn't have asked myself )
A bike on the roof is pointing in the direction of travel, giving the least possible wind resistance.
A bike on the back is side on to the airflow of the car, exposing more surface area to the wind, giving more drag.

Apart from that, there's the issue of ruining the low pressure zones, and intentional turbilence at the rear of the car etc - but whilst I've seen demonstrations of such phenomena, I don;t understand it well enough to predict outcomes.

Without going into the physics of it too much, yeehaamcgee has given a very good answer. Its all to do with areas of exposure and how much resistance that is created because of it.

At the end of the day one way or another, as long as you can get your bike to where you want to go, thats all that matters. How much MPG my car can save isn't high on the list of priorities when i arrive at a trail centre for a days biking.

bearfraser

PITA when you change your motor with roof bars but at least you can keep the cycle racks and move them from car to car. Have got Thule Bike Racks and are now appx 10yrs old and stll Ok. The only problem with roof bars appart from access when your feeling weak is that in the wet weather the oil & crap off your bike gets all over the roof of your motor.

suzyb

yeehaamcgee wrote:

suzyb, it's not what I expected either, but I can see some reasons it may be so.
In layman's terms (I don't understand this fully, otherwise I wouldn't have asked myself )
A bike on the roof is pointing in the direction of travel, giving the least possible wind resistance.
A bike on the back is side on to the airflow of the car, exposing more surface area to the wind, giving more drag.

Apart from that, there's the issue of ruining the low pressure zones, and intentional turbilence at the rear of the car etc - but whilst I've seen demonstrations of such phenomena, I don;t understand it well enough to predict outcomes.

That makes sense.

Daz555

chiefinspector wrote:

Any attachment that you put onto a car will affect the MPG but with roofrack you def wouldn't notice as much as you do with your rear mounted carrier.

I would imagine the shape of the car play a huge part in that. I have a people carrier and the bike sits directly behind the car - I would bet that in my case this is better than a roof rack. Of course cars with van-like rear ends are not the best aerodynamically anyway.

I now have my bike on a towbar carrier which means my bike is even lower down so likey even better than it was before. I have not noticed any increase in MPG from standard since fitting a towbar carrier.

bails87

Daz555
Which carrier, and how do you find it?

Daz555

I have a Thule 970 Xpress. Does not give easy access to the boot as many others do, but this is not an issue in my car as access from the seats is so easy.



Takes about 20 secs from garage to towbar to attach it and the bike is on and locked in a few short minutes and is rock solid. One small issue is the bolts for the hinges - they are not secure so need sorting with new bolts, or rounding/filling with glue etc.

I will definately stick with tow bar mounts from now on - next time however I'd go higher end and get something like this:



That style would also be handy for me on camping trips etc as I could stick extra luggage on the bike rack very easily.

diy

I get that there is a lot of turbulence at the back of the car and that a bike side on is somewhat parachute like. But I'm not convinced the roof is the best place from an mpg point of view. I would have gone tow ball mount if I could have got a ball mounted to the car for a sensible cost.

However, I'm evidence that the roof mount made bugger all difference and for me was the cheapest solution (taking into account the cost of fitting a tow ball and the fact that rear mounts can damage the car and the bike).

However, even on a gas guzzler, you have to do a lot of trips to justify £300 on an improvement.

bails87

diy wrote:

However, even on a gas guzzler, you have to do a lot of trips to justify £300 on an improvement.

True, but you've got to put a price on the convenience, and the fact you're not risking any damage to the inside of the car.

CraigXXL

Coming into this debate a little late but heres my 2p worth.

I have a Mondeo estate and both a Thule 591 Roof mounted rack and Thule Euroclassic towbar mounted rack. I use the roof mounted rack when it's just my bike that I'm carting about as I hate putting a muddy bike in the car. The towbar mounted rack is used for two or more bikes.

With the roof mounted rack on aero bars not only do I get a reduced mpg but a lot more wind noise too. The towbar mounted rack despite carrying more bikes does hardly effects my mpg.

Yeehaa's explanation accounts for the front profile of the bike itself and the turbalance it creates comparing it to the turbalance that is created by a bike on the rear mounted across the car but you also have the roof bars too. Both the rack and bike create more turbalance or vortex that decreases the air speed on top of the car which will decrease further as it hits the second roof bar. The top of the car usually has a higher air speed, the underneath higher still, anything that slows the airflow over the top creates a larger vortex at the rear of the car which creates the drag that holds the car back. The air flow speeds over the top and bottom of the car need to be as close as possible to avoid a large vortex and drag hence the teardrop effect .

CraigXXL

Coming into this debate a little late but heres my 2p worth.

I have a Mondeo estate and both a Thule 591 Roof mounted rack and Thule Euroclassic towbar mounted rack. I use the roof mounted rack when it's just my bike that I'm carting about as I hate putting a muddy bike in the car. The towbar mounted rack is used for two or more bikes.

With the roof mounted rack on aero bars not only do I get a reduced mpg but a lot more wind noise too. The towbar mounted rack despite carrying more bikes hardly effects my mpg.

Yeehaa's explanation accounts for the front profile of the bike itself and the turbalance it creates comparing it to the turbalance that is created by a bike on the rear mounted across the car but you also have the roof bars too. Both the rack and bike create more turbalance or vortex that decreases the air speed on top of the car which will decrease further as it hits the second roof bar. The top of the car usually has a higher air speed, the underneath higher still, anything that slows the airflow over the top creates a larger vortex at the rear of the car which creates the drag that holds the car back. The air flow speeds over the top and bottom of the car need to be as close as possible to avoid a large vortex and drag. Hence the teardrop effect is more aerodynamic as the air speeds are more closely matched creating little drag.