For those who carry their bike on their car roof, what difference does it make to fuel economy?
Currently undecided between roof bars or towbar carrier for the bike when we're going away.
Depends, what car, what bikes, how many bikes?
With 4 road bikes on a Big Estate it was about 15-20%.
2 MTBs was about the same. Mostly down to frontal area at a guess.
Usually cruising at 100-110 kph.
The boot rack is (almost) zero difference, i got more variation based on which way the wind is blowing.
Extended motorway run, I'm looking at:
65+mpg with no bikes/bike inside
50mpg with bikes on roof
Hugely dependent on body type but a few friends with coupe/saloon type cars report similar or worse reductions with a towbar rack.
How often will you carry bikes and how far?
For me roof bars were better as I could use them for carrying other things too, not just bikes.
I agree it depends.
We use both on the Leon estate 1.4tsi:
- no bikes, long journey = @52+mpg, more if slower than 70.
- bikes on towbar - @42-44mpg
- bikes on roof - @38-40mpg
The V70 D3 we had was much less affected by them (bug luggy 5cyl diesel) - it did 50mpg on a long run and with bikes on the towbar it made only a couple of mpg difference, roof took it down to early 40's.
Bikes on the roof, massive impact on mpg, it's just science, sorry. But you have to weigh that against the price of a decent rear carrier, and I would only consider a tow bar mounted one, and they aren't cheap. Do the maths.
All that said, I did used to carry a couple of bikes on the roof in the past, but they were the type where you took the front wheel off and locked the forks in. The advantage being I could spin the bars round and lower the seats and reduce drag as much as possible,(I could actually get in a few low clearance car parks).
will depend on car shape
but also total load on car
drive slower, gaster you go the more the extra fuel use multiplies!
Motorway run without bikes (but with the bars and 4 x racks) = ~60-65mpg. With 4 bikes on top (2 adult, 2 kids) = 50mpg.
Years ago I did this exercise and found that at motorway speeds my petrol 2.2i did 33mpg with the bikes on a towbar rack and 30mpg on the roof. And the roof rails (and bikes) were also far, far noisier.
At higher speeds the difference was even greater.
I had a fuel card, for both private & company mileage so no real interest in economy - don't hate me 🙂
Hugely dependent on speed. If your motorway miles are 80mph it will be a lot. 65mph, not so much. Country roads where you may average 40mph, not much at all.
With 4 x mountain bikes on the roof of my Passat I was getting around 30% less MPG at motorway speeds. I ended up fitting a towbar and the difference in MPG was negligible.
It's a lot. But towbar racks also knock some off as well, but a bit less. I have both.
But as above, roof bikes make a noise, rear ones do not.
Upto 10 mpg less with 4 bikes on the roof. Like others, if you drop the motorway speed, the difference reduces. Prefer bikes up out of the way, wouldn't want to get rear ended and having bikes mangled as well as the car.
At 55 on the a93 my fuel consumption on my 3cyl petrol stayed at 55mpg from Aberdeen to braemar and back with a bike on the roof.
With the same bike on the roof on the a90 at 70mpg. It dropped to 43mpg.
Mainly because it's gutless.
The wife's berlingo doesn't seem to care what you put on the roof just returns the same 45mpg wether your doing 50 or 70 bikes or no bikes.
Calais to Alp d'Huez at 130kmh was 54mpg on the towbar, 37mpg with them on the roof - only used the roofrack system once before swapping to towbar type!
Worse than the fuel consumption was the time taken to remove dead, dried in fly parts from my forks & bars.
A couple of years/cars ago in a Mk7 3-door Honda Civic 1.7 cdti going from Newcastle to BPW, two bikes, 2 adults and associated luggage.
In the car on the way there, keeping it at or around the NSL - indicated 66 mpg
6 months later, same direction but on the roof - 45 mpg. Stopped at Leicester to muck about at Western jumps, and after that they went inside for the rest of the journey.
This thread has made me both laugh and cry.
On the plus side I've never noticed a real difference in MPG with a bike on the roof (roof bars are permanently fitted)
On the down side its because I usually consider 23+mpg very good and 19-21 is normal average over a tank full 😂
But that's 20 year old, 3.0 litre, 6 pot Subaru engines for you!
Calais to Alp d’Huez at 130kmh was 54mpg on the towbar, 37mpg with them on the roof – only used the roofrack system once before swapping to towbar type!
I did something similar a few years back with bikes on the tow at on the old car and I can’t remember it affecting fuel economy much at all. I’ve only done shorter journeys on the past with them on the roof but couldn’t remember what the difference was.
As it stands, roof bars and two bike carriers are the thick end of £500. A towabar is about £650 installed and I already have the towbar carrier.
Looks like I’ll be getting a towbar!!
if 'fuel' can be taken to also include electricity, there are various posts on the electric car thread on this too. Seems that a couple of bikes on roof carriers can decimate the range by 25 -30%, towbars generally less than 10% reduction.
Yep, one of the posts on the Electric Car thread was from me - no chance of finding it though.
In a BMW i4 I've found that the consumption was about 25% worse (ish) on a mixed motorway (65MPH) and A/B road journey.
That might be massively inaccurate though as it's just from a couple of trips, but something in that ballpark.
I'd expect an EV to have a larger % efficiency drop, as the car itself is more efficient to start with (generally more aero than an equivalent class ICE as the designers pay more attention to it plus they re-generate power on braking (about 20% on country road driving according the the i4 trip computer) etc, but the aero drag of bikes on the roof is exactly the same as it would be on an ICE, hence a larger %ge of the total.
We used to have four bikes on the roof of an Octavia estate. Didn’t really notice much difference in fuel tbh. Went to a towbar when kids bikes got too big to lift up easily
Long Mway run my car will get 38-40mpg at 70 with just the roof racks on. With bike is 32-ish.
On th French Autoroutes with a bike/bikes it's awful at 130kph, I have to drive at 110kph.
Roof box makes very little difference despite the bulk, MTBs are awful though.
"<span style="color: #000000; font-family: Roboto, 'Helvetica Neue', Arial, 'Noto Sans', sans-serif, -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol', 'Noto Color Emoji';">if ‘fuel’ can be taken to also include electricity, there are various posts on the electric car thread on this too. Seems that a couple of bikes on roof carriers can decimate the range by 25 -30%, towbars generally less than 10% reduction."</span>
Wouldn't "decimate" mean a 10% loss? 😉
I use roof bars for legacy reasons. If I had the choice I’d use a tow bar carrier.
Wouldn’t “decimate” mean a 10% loss?
That’s exactly what it means. The mis-use of decimate annoys me almost as much a the endless mis-use of brakes/breaks.
One MTB on the roof of my old petrol car for long mostly motorway journey was 10-15mpg down.
There are a few threads here if you search about pros and cons of both options. I wouldn't have fuel economy be a major point one way or the other.
I haven’t tried roof bars on my semi-hybrid Octavia but did try an experiment to see if there was a difference between having bikes on a tow ball rack, and having the rack in place with no bikes. Consumption was about the same, leading me to conclude that the difference is likely to be down to a different engine control strategy being used when the car detects something connected to the trailer socket.
My old Skoda 19tdi I tend to trundle along at around 70mph on the motorway. With bikes 2 it's about 3mpg less.
I assume EV's would take a bigger hit to their economy at motorway speeds due to the nature of electric motors Vs ICE. EV's are more economical at slower speeds but ICE depends more one rpm than outright speed. Also tow bar racks will affect aerodynamics as it will disrupt the airflow off the back of the car. It would likely vary quite significantly depending on the car and the rack but difficult to say.
I’ve always ruled out tow bar racks just from the expense of getting a tow bar and rack, and the fact I change cars every 3-5 yrs
Unlike others my roof bars have caused minimal wind noise.
Agree with the rough 25% fuel reduction, but as others have said as the speed increases so does the % reduction at an alarming rate
IMO if you keep your car a long time then tow bar, if you change often then roof. If you might get an ebike then defo tow bar
Unlike others my roof bars have caused minimal wind noise.
The old square roofbars mounted to the massive raised rails on my V70 were loud as hell. The aero bars on the universal/low profile rails on the V60 are almost silent.
Until i get a bike on there.
I used to transport my bike on roof bars, didn’t really notice a big difference. I just found it a lot more stressful than the tow bar rack I now have, mainly due to height restricted barriers. I didn’t actually hit one, but it was always a bit of a concern, however as others have said the cost of the tow bar is quite expensive.
I used to transport my bike on roof bars, didn’t really notice a big difference. I just found it a lot more stressful than the tow bar rack I now have, mainly due to height restricted barriers. I didn’t actually hit one, but it was always a bit of a concern, however as others have said the cost of the tow bar is quite expensive.
To be fair a pair of Thule wing bars are over £300, by the time you add in 2-3 bike mounts I doubt there's much/anything in it cost wise.
Depends on the cost of having the towbar fitted I suppose, especially if you don't need it for anything else.
Why pay £300 for wingbars? There a loads for sale secondhand for a third of that, same with the bike rack for roof or towbar.
The wife’s berlingo doesn’t seem to care what you put on the roof just returns the same 45mpg wether your doing 50 or 70 bikes or no bikes.
Same as my Mini. 45/46mpg regardless of what's on the roof. I leave the wing bars on all the time though, and just load up the bike carrier and bike when I'm gong anywhere with it, so of course it could be that the bars make all the difference, but I doubt it.
Some years back we drove to the south of France and back for summer hols with bikes on the roof of a 3.0 petrol v6... I drove the way out... slowly... On the way back my better half (driving) decided we needed to 'make time'...
...and was later slightly surprised by the economy dropping to around 22mpg.
Clearly more efficient cars are available.
Nevertheless. Drive slow... or suck it up buttercup.
Driving very economically I managed 28mpg with roof box (bag) and roof mounted bike over ~200 miles. Which is very strange as it normally only manages around 26mpg.
Wouldn’t “decimate” mean a 10% loss?
wouldn’t decimate mean a 90% loss 😉
I run a Thule rear rack on a Kia eNiro, maybe 10% increase in electricity consumption.
I would never put bikes on the roof because more than once I’ve seen people make expensive mistakes with roof-mounted bikes and car park height restriction bars…
wouldn’t decimate mean a 90% loss 😉
Historically it was kill 1 in every 10 people.
Why pay £300 for wingbars? There a loads for sale secondhand for a third of that, same with the bike rack for roof or towbar.
Well quite. 2nd hand will always be cheaper, if you can find what you're looking for and it's not located hundreds of miles away.
