 Poster: A snowHead
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Just got back from a great week in the Arlberg. Notice that if I put the skis together in the ski rack versus having a gap between each pair I get about 5 miles per gallon less fuel economy. Suspect that the air finds it easier to go around each smaller ski pair separately than having the equivalent of a single big board around which the air needs to travel?
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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Sfellows, Yes, less drag 
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Well, the person's real but it's just a made up name, see?
Well, the person's real but it's just a made up name, see?
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Years ago I did some research into this. Not your specific scenario but around having roof bars on, having something on them, having a box on - and even having the windows open. And the conclusion I drew was that in grand scheme of things it wasn't a biggie. Your style of driving can make a difference. Obviously the condition, type of car makes a big difference. A lot of people buy SUV's for example and don't consider the fuel economy for that design.
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| Quote: |
And the conclusion I drew was that in grand scheme of things it wasn't a biggie.
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I immodestly feel I could have reached that conclusion without any research or any empirical evidence. 
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Anyway, snowHeads is much more fun if you do.
Anyway, snowHeads is much more fun if you do.
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@Origen, it was a slow day 
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@Sfellows, are you attaching the skis directly to the roof rack without any covering for the journey out and back? If so don't as I've seen bindings ruined due to dirt/salt/exhaust particulate ingress etc. It's also not great for the bases'n'edges.
Wrapping the skis/bindings completely in cling film will avoid any issues.
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I tend to find all these little niggling thoughts disapear when I check my skis and get a beer in the airport lounge.
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What is also clear to EV drivers, and ignored by many ICE drivers despite being established for 40+ years, is that fuel consumption goes up massively over about 60mph. Following the same principle of aerodynamics. But do you hear of people driving down at 62mph?
I still love the anecdote here several years ago of a Skoda diesel being overtaken by an impatient Range Rover. Repeatedly. It would blast past then pull over to refuel…
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You'll get to see more forums and be part of the best ski club on the net.
You'll get to see more forums and be part of the best ski club on the net.
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Yes, knocking a bit off speed makes more difference than almost anything. People who fret about where to get cheaper fuel and then make up for lost time by driving at 135 kph are like the 3 stone overweight cyclist who spends a fortune on ultra light bike bits.
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I just plant the speed control at 60mph, provided you give yourself sufficient time no stress, tune into local rock station and enjoy the journey.
to be fair we do put the skis inside the car.
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snowHeads are a friendly bunch.
snowHeads are a friendly bunch.
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| Origen wrote: |
| Yes, knocking a bit off speed makes more difference than almost anything. People who fret about where to get cheaper fuel and then make up for lost time by driving at 135 kph are like the 3 stone overweight cyclist who spends a fortune on ultra light bike bits. |
You are, of course, completely right ! I once drove to Eindhoven, from Berlin, at an average of 254kph (including the three, nearly four, fuel stops required). So, whilst actually driving, I was averaging just over 270kph. If I recall the consumption was around 11mpg at that speed. So that was about the worst ... and was without skis.
Driving back from Cervinia last year with skis on the roof and 'only' doing about 170kph (as noise and vibration got really unpleasant after that) I was getting around 16mpg whereas if I do around 220kph without skis (my 'normal' cruise speed) then I get about 20mpg. So, not so much difference with skis on/off but a huge difference from speed. Driving through Switzerland, at a strict 120kph due to the insanely high fines, I get around 28mpg.
This with a flat six 3.8 twin turbo engine and reasonably low, aerodynamic car. I suspect that an SUV with it's already much higher drag wouuld be minimally affected by skis but hugely affected by speed.
PS. I am not a nutter; all the high speeds were very early in the morning on deserted German autobahns (so also legal)
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And love to help out and answer questions and of course, read each other's snow reports.
And love to help out and answer questions and of course, read each other's snow reports.
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| spyderjon wrote: |
@Sfellows, are you attaching the skis directly to the roof rack without any covering for the journey out and back? If so don't as I've seen bindings ruined due to dirt/salt/exhaust particulate ingress etc. It's also not great for the bases'n'edges.
Wrapping the skis/bindings completely in cling film will avoid any issues. |
Is it better to wrap a pair of skis together or to put them individually in the rack ? TBH I'd never really thought of this and am guilty of just putting them in the rack ... velcroed tightly together.
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@Sfellows, sorry, I'm not buying this. Whether the skis are together or apart, you are still presenting the same frontal area. And in both cases, it pales compared to the drag of the rack itself (assuming it is perpendicular to the path of travel). Also, a 5mpg delta is massive, as such hard to believe that it is attributable solely to ski position. In my experience, that delta is more typical of the difference between legal speeds and goosing it, or full rack vs. no rack at all.
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You know it makes sense.
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| Scooter in Seattle wrote: |
| @Sfellows, sorry, I'm not buying this. Whether the skis are together or apart, you are still presenting the same frontal area. And in both cases, it pales compared to the drag of the rack itself (assuming it is perpendicular to the path of travel). Also, a 5mpg delta is massive, as such hard to believe that it is attributable solely to ski position. In my experience, that delta is more typical of the difference between legal speeds and goosing it, or full rack vs. no rack at all. |
I second that.
I carry a kayak on the roof of my car and drive for long distance. I barely get a delta of 5mph carrying a giant BOAT on the roof! No way the ski positioning alone is responsible for the difference.
If you have a really odd shape car, you may get a big delta with a roof rack on. But not between the positioning of the skis!
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Otherwise you'll just go on seeing the one name:
Otherwise you'll just go on seeing the one name:
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| Origen wrote: |
| People who fret about where to get cheaper fuel and then make up for lost time by driving at 135 kph are like the 3 stone overweight cyclist who spends a fortune on ultra light bike bits. |
I find it funny how many casual motorsport participants will spend time and money saving grams in the car but tuck into a breakfast bap to start the day and 3 pints to finish it. My answer whenever anyone asks "have you thought about taking some weight out" is to tap my belly
That said, I think weight does have a fairly big impact on fuel economy, my dad's camper gets much worse when loaded up with bikes etc. even on a similar type motorway run
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Poster: A snowHead
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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What is the hull speed of a kayak?
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Well, the person's real but it's just a made up name, see?
Well, the person's real but it's just a made up name, see?
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Is that a European or African kayak?
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You need to Login to know who's really who.
You need to Login to know who's really who.
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Anyway, snowHeads is much more fun if you do.
Anyway, snowHeads is much more fun if you do.
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| abc wrote: |
| ski3 wrote: |
@abc, wouldn't the Kayak example be reasonable definition of absolute drag reduction though ?  that's for the item in addition to the vehicle, and not a reduction in the whole ensemble.
Unless mounted crossways  |
Kayak hull shape are designed to optimize at15 mph. Not at 50mph. Moreover, there're A LOT of "stuff" on the kayak deck that protrude.
Bikes too, have far more aerodynamic impact than skis. Bikes don't cause 5mph reduction either. I call the OP's observation "conflating" contributing factors. Far more likely, speed, wind direction, uphill/downhill were far more significant contributor of the fuel efficiency difference. |
Water has a density about 800 times greater than air, making that comparison relatively invalid for these purpose.
Bikes though, bicycles on a rack crosswise on the back of a our family mpv type car, will easily remove 5 mpg or more. They're a disaster back there in the wake/separation zone of airflow. Anything above 50 mph Road speed it accumulates significantly.
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| ski3 wrote: |
| Bikes though, bicycles on a rack crosswise on the back of a our family mpv type car, will easily remove 5 mpg or more. They're a disaster back there in the wake/separation zone of airflow. Anything above 50 mph Road speed it accumulates significantly. |
Not on my car. 2mph more like.
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I remember having an argument some time back about whether a ski box made a difference to mpg, on our trip to Andorra, we found that the ski box did reduce mpg, but someone was saying it didn't, but then said their average speed on their test was 30mph!. At 30 mph, you could have a garden shed on the roof & get the same mpg!
I drive a L1H1 Fiat Ducato 2.3 diesel van
Normal driving around to local jobs 35mpg
Driving to the Alps, staying off peage 40mpg
Driving on UK motorways at truck speed 55/60mph 45mpg
Driving 250 motorway miles with a 750 kg car trailer 39mpg
Driving back with a 1510kg car on that trailer 2260kg total 36mpg
Driving at 85mph on French autoroutes on a previous ski trip 24mpg
Clearly speed makes a much bigger difference than weight
The 24 mpg was when the van had just 35k on the clock, now it has 143k on the clock, it uses about 10% less fuel
I was actually really surprised by the 36mpg that I got towing a 2260 kg trailer, about 4.5 tonne train weight.
I used to get 25 mpg from a 2.0 Diesel Ford Smax towing a 1.5 tonne caravan 3.5 t train weight, again, wind resistance/speed make the biggest difference rather than weight.
I would expect a few bicycles in a campervan wouldn't make a detectable difference to fuel consumption, more likely the speed that you're doing when on a "bike" trip
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I’ve now reviewed the travel data from my car and the delta is 3.2 mpg.
Travelled from Namurs to the Channel Tunnel, and then moved the skis apart at the tunnel as an experiment as I had noticed the fuel consumption was lower than expected. Then travelled from the tunnel to West London.
Same day, same weather conditions, same average speed and road conditions, similar distance.
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You'll get to see more forums and be part of the best ski club on the net.
You'll get to see more forums and be part of the best ski club on the net.
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Oddly, I found that my Smax had better mpg on UK roads than the quieter French roads, home in the NE to the tunnel always gave better mpg than travelling through France even if I kept the speed down in France, typically we would get into France early evening & drive overnight.
I put this down to the slipstream effect, if the road is busy but free flowing, even keeping a safe distance, there is some slipstream effect, very noticeable in the van
60 mph on a quiet road ~40mpg
60mph following a truck at a safe distance ~45mpg
60mph following a truck a bit too close ,50mpg
(60mph indicated speed)
I might be a bit pedantic about mpg, in my yoof I would see how fast I could get from A to B, this had some associated problems, possibly crashing, speeding fines and generally being a knob, so I switched the challenge to driving as economically as possible without driving excessively slowly when I got a car/van with mpg display.
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This thread deserves to be posted in the Dull Men's Club on Facebook! 
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snowHeads are a friendly bunch.
snowHeads are a friendly bunch.
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@schnitzel_skier, Correct!
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