In terms of bike carriers, has anyone gone from a roof rack to a tow-bar mount and noticed any significant changes in fuel economy?
Physics tells me it should be more aero-dynamic and therefore the MPG should increase but is that true?
I like the convenience of the roof rack as once the bike is up there I can forget about it, no matter how stinking it is. But i’d like to change the car for something punchier and having bikes on the roof will probably negate any extra performance gains because of the aero-dynamics, or lack of. So is a tow bar mounted
carrier better?

Had a C250 cdi and had the bikes on the roof = no difference in economy. Got a E350 cdi and huge drop in economy with bikes on the roof, so now have them on a tow bar rack and there’s no reduction in economy…

the convenience of the roof rack as once the bike is up there I can forget about it

quiet.

I much prefer towbar mount – much easier to get muddy bikes on and off without smearing mud all over the car. As far as mpg is concrened there’s an advantage, for ‘performance’ – I’d be reluctant to put ‘high’ sideways g through most roof mounted bikes but for straight line there’s a small difference in throttle response, I suppose with a tow bar mount.

From what I have seen there is marginal difference (C5 estate) between the two – the back end is still designed to be reasonably aero and sticking bikes on that screws it up.

But if you leave your rack on the roof all the time (it is not convenient otherwise) then you loose something in drag whether you have the bikes with you or not. A friend tested this and found a 4 bike thule afair (no bikes fitted), v’s completely removing the roof bars/rack was costing him ~3 mpg at motorway speeds (diesel doing about 60 mpg).

Tow bar 4 bike halfords jobby here. Probably 80kg all in when fully loaded hasn’t made a great deal of difference at all. Easy to use, and saves lifting bikes on the roof which must be a ball ache when you’ve got four to do. Plus I know at some given point there would have been some pedal action down the paintwork.

I think it depends on the car.

On my petrol Vectra I went from bikes on the roof to bikes on a towbar rack and got back 3mpg.

On my previous Mondeo I had both Thule 591 for the roof and a Euroclassic tow bar rack. Using the towbar saved about 2mpg or around 5% but the car handled much better without it and was much queiter too.

When I got the new car I kept the tow bar rack and fitted a detachable tow bar for it. When you have more than two bikes the tow bar rack is much easier to load too. Bikes get slightly dirtier on the back but a lot less flies stuck to them.

It really depends upon the car’s width, type (estate vs. saloon), and suspension setup.

I loose 25-30% in MPG when carrying 3 bikes on the roof, in petrol 3 series estate. In my friends 3 series saloon with 2 bike on a rack on the rear, he’s loosing a similar amount, partially due to the cars nose raising, T’other friends Discovery 3 seems to barely notice that there are bikes on the back of it. but then, it’s more like a building than a car.

I found that a towball rack made little or no difference to mpg or noise, whereas at motorway speeds a roof rack and two bikes knocked a big hole in mpg and was noisy too. (Mondeo estate)

I’ve currently got a VW Golf and was going to replace it for something of a similar size.
Funnily enough, as someone pointed out above, if I have the rack on the roof which is 99% of the time but with no bikes on it, the fuel economy isn’t anything to write home about – probably the same as if I had bikes in them. But if i take the whole system off then I notice better handling, less noise and slightly better mpg.
I’ve a diesel but am doing no where near the miles to benefit from it, so am thinking of going for a car of similar size (A3, another golf, A class) in petrol, but deciding whether to get the tow-bar fitted instead. Sounds like there’s not much difference…

The only time I noticed an ant-roll bar really earn its place was in a loaded estate with bikes on the roof taking avoiding action on a French roundabout. (PP or not?). I think the equivalent, with the extra weight behind, might have been a little more scary, especially on a wet road. But I’m not going to try to be sure. YMMV.

Roof racks are noisier, good point – towbar racks are silent. It’s also MUCH easier to fit a towbar rack (takes me about 2 mins), where as roof racks are a faff to fit meaning people leave them on and put up with the associated noise and fuel economy hit all the time. I have Whispbar aero jobs, advertised as the quietest, and they still make a noise even when unladen and without racks.

In terms of bike carriers, has anyone gone from a roof rack to a tow-bar mount and noticed any significant changes in fuel economy?

Yes, I get better economy with the bikes on the back on a tow-bar mount. Marginal though.

I like the convenience of the roof rack as once the bike is up there I can forget about it, no matter how stinking it is.

What? I’d rather have a dirty bike (if that’s what you mean) on a tow-bar mounted rack on the back, than dropping stuff onto the car roof. Tow bar rack is pretty much more convenient in every way, ime.

But i’d like to change the car for something punchier and having bikes on the roof will probably negate any extra performance gains because of the aero-dynamics, or lack of.

This is pretty much nonsense. Putting bikes on the roof of a Ferrari doesn’t turn it into a Nissan Micra.

Towbar mounted for me, made a huge difference having anything on top of the car (and it’s noisy).

Rack fits in seconds and lives down the side of the garage so there isn’t really a time saving having a rack permanently on the roof anyway.

Gone from Thule 591s to an Atera Strada tow bar rack for our 4 bikes this year.

Only slight benefit on fuel. Better on noise. No panic near car park height barriers. Slight panic when reversing with another meter of wobbly metal sticking out the back. Easier to get bikes on – I’m only 5’9. Sliding rack doesn’t impact access to the boot.

Whether it’s worth the £2-300 or so extra for the towbar is up to you.