The Yeti has the aerodynamics of a 3 bedromm semi-detached house. Cd=0.370

Ah. Cd=0.37. Better than those well-known semi-detached houses the Ferrari F50 (0.372) and the Mazda MX-5 (0.38), much better than the Lamborghini Countach (0.42), and the same as that semi-detached house the Jaguar XJ.

The Yeti has the aerodynamics of a 3 bedromm semi-detached house. Cd=0.370

Unfair comment r999, the "bedromm" is a unit which describes the Read only memory of a unit of accommodation.

Sometimes it is also a sign of an illiterate or hastily written post someone who knows little about a sub board he or she is visiting.

The Fabia is a fine example of a car most of us would not find interesting or useful for our purposes, (I'm afraid I don't know if it is aerodynamically efficient or not). I must find time to visit the Fabia forum to say so.

Forgive me having another bite at this one.

A 12-hour drive in the Yeti today, encompassing everything from near-empty motorways to single-track roads with passing places, reminded me that the 1.8TSi 4x4 is almost two different cars when it comes to fuel consumption.

Thee first hour was on the motorway with a tight deadline to meet. Speed mostly 80 to 85. Consumption, according to the MFD, was 27. For a car of the Yeti's size and engine capacity, I find this disappointing verging on poor. The measure of it is that I can do the same journey at the same speed in my 4.8-litre BMW and get equal or better fuel consumption, plus of course vastly better acceleration when required (not to mention a good deal more interior space, etc.)

But taking the day as a whole shows a quite different picture. A couple of hours were on single-track roads where it was seldom possible to get into 5th or 6th gear and stops at passing places were numerous. Then a long section on A-roads cruising at 50 to 60 mph. The day finished with the MFD showing 37.5 mpg overall - and that average included the first hour at 27 mpg, as well as the single-track roads.

So in my view our 1.8 TSI is disappointingly thirsty at 80 mph (27 mpg) and unexpectedly economical at 50 to 60 mph (better than 37 mpg). You're never alone with schizophrenia. Or more to the point, frontal area rules, since air resistance rises as the square of speed.

By the way, I'm aware that MFD figures are not to be taken literally, but I'm using them here for comparative purposes, not absolute accuracy.

You are not really comparing like for like - assuming the BWM is a saloon car. - How well would the BMW fair off road compared to the Yeti? - How does a Range Rover or similar compare to the Yeti at 85MPH?

Do you live in a country with higher speed limits than the UK? To be honest - if you were caught doing 85MPH in the UK the least of your worries would have been the fuel consumption.

Ah. Cd=0.37. Better than those well-known semi-detached houses the Ferrari F50 (0.372) and the Mazda MX-5 (0.38), much better than the Lamborghini Countach (0.42), and the same as that semi-detached house the Jaguar XJ.

Of course clever peoples think the Yeti is more aerodynamic than a Lamborghini Countach!

Cd alone is not a direct measure of drag, but when it is multiplied by effective frontal area to give CdA.

Thus Yeti is to Lamborghini as Semi detacahed is to 2 man tent. (I thought the tent reference might be useful for you Yeti fanatics)

Just trying to say driving a Yeti above 70mph and the consumption will increase like a rocket.

Unfair comment r999, the "bedromm" is a unit which describes the Read only memory of a unit of accommodation.

Sometimes it is also a sign of an illiterate or hastily written post someone who knows little about a sub board he or she is visiting.

And I've obviously strayed into the land of the comically-challenged.

Edited 21 November, 201114 yr by xman

It is always better to bring your sense of humour with you

I'd expect just as warm a welcome if I were to post my opinion of the Fabia in that section. :wonder:

JCP! I like you!

Cd alone is not a direct measure of drag, but when it is multiplied by effective frontal area to give CdA.

Which is the point I was making initally by saying 'frontal area rules', and why I went on to point out that the Yeti's Cd is no worse than that of several sporty or high-performance cars. It is, as you say, the total drag, not the coefficient of drag, that does the damage and explains the Yeti 1.8TSi's economy falling off a cliff over 60 mph. In short, not its shape, but its height. It's one of the key principles of aerodynamics that an abruptly vertical rear is not nearly so bad for aerodynamics as common sense would lead one to expect. Known as the Kamm effect.

In short, not its shape, but its height.

So you agree, its like a 3 bedroom semi.

So you agree, its like a 3 bedroom semi.

Nothing like!!

A 3 bed semi is more like a Land Rover 101"

http://www.google.co.uk/imgres?q=land+rover+101+forward+control&hl=en&safe=active&biw=905&bih=577&gbv=2&tbm=isch&tbnid=qmAV1gHUZbPa0M:&imgrefurl=http://free.yudu.com/item/details/84383/72-FL-06---Land-Rover-101-Forward-Control-Radio-Body&docid=0-3T30CRF3dW1M&imgurl=http://free.yudu.com/item_files/84383/a4a91860d/72FL06.jpg&w=3488&h=2616&ei=ctfKTuHvGpHLtAas-dzCDA&zoom=1&iact=hc&vpx=277&vpy=263&dur=1000&hovh=194&hovw=259&tx=138&ty=120&sig=103621968067596586904&page=1&tbnh=117&tbnw=177&start=0&ndsp=12&ved=1t:429,r:5,s:0

A Yeti might be a dormer bungalow, and a Fabia a pig shed.

So you agree, its like a 3 bedroom semi.

Ah, the Fabia with its Cd of 0.33. That's worse than the VW Golf Mk 3 of twenty years ago, and equal to the Alfa Romeo Giulia of 49 years ago. Maybe in another few decades the Fabia will have been improved enough to compete with the cars of 2011.

I well remember the press expressions of amazement at the time when it was revealed that the Farina designed Austin A40 had a better drag coefficient than the then recently launched Porsche 911.

I agree with R999.

My observations in the 1.8 TSi show that tootling around at speeds below 55mph, using torque rather than revs, produces pretty good consumption figures, even in urban areas, as long as you don't take part in the traffic light Grand Prix. But as your speed rises when you hit the motorway, even at legal speeds, your economy quickly reduces to 28 - 30 mpg, even at steady speeds. Over 70mph (which I never do of course - no, really) and then 27 is a regular figure on the admittedly not totally accurate Maxidot.

a

As others have said, it's all down to aerodynamics. :(

This will be down to the safety aspects of the cars. The raised frontal area to protect those pedestrians that we always hit has made the frontal area much larger, to achieve higher NCAP ratings.

This will be down to the safety aspects of the cars. The raised frontal area to protect those pedestrians that we always hit has made the frontal area much larger, to achieve higher NCAP ratings.

That has got nothing whatever to do with frontal area in the aerodynamic sense of the term.

Not directly r999 but indirectly. Many cars now have higher bonnet lines in order to give distance between the relatively soft/deformable outer skin and the unyielding hard points beneath. This is a pedestrian safety based design and may lead to greater frontal area than would otherwise be necessary. If car bonnets were as low as the engine position would allow the frontal area could be reduced.

Or am I misunderstanding altogether?

You can do what you like with the bonnet shape.

If the width and height of the car remains the same ,so does the frontal area.

I also noticed today in autoexpress ,that the latest astra, which looks like a squashed baked bean to me,has a CD of.....

Yes you've guessed it.......CD .33 ,so not much improvement there over a 1960's Alfa. Pathetic really when you consider the cost of fuel today.

You can do what you like with the bonnet shape.

If the width and height of the car remains the same ,so does the frontal area.

Well said; exactly right. Width times height, in square centimetres. Shape is completely irrelevant to frontal area (that's what Cd measures, among other things).

As the Yeti is not significantly wider than other cars, its large frontal area could be reduced only by lowering the height of the roofline. (As I said further up the thread - 'not its shape, but its height'). Lowering its ground clearance, on the other hand, would reduce its coefficient of drag without affecting its frontal area (except for a few sq cm of front tyre that would then be hidden).

I also noticed today in autoexpress ,that the latest astra, which looks like a squashed baked bean to me,has a CD of.....

Yes you've guessed it.......CD .33 ,so not much improvement there over a 1960's Alfa. Pathetic really when you consider the cost of fuel today.

Yes, though I was cheating a bit when I mocked the Fabia for its Cd of 0.33. The fact is that the smaller the car, the harder it is to design a good coefficent of drag. Same applies to the Ashtray. (What a pair!)

Edited 23 November, 201114 yr by r999

Well said; exactly right. Width times height, in square centimetres. Shape is completely irrelevant to frontal area (that's what Cd measures, among other things).

As the Yeti is not significantly wider than other cars, its large frontal area could be reduced only by lowering the height of the roofline. (As I said further up the thread - 'not its shape, but its height'). Lowering its ground clearance, on the other hand, would reduce its coefficient of drag without affecting its frontal area (except for a few sq cm of front tyre that would then be hidden).

Agreed, but the aerodynamics of a vehicle are significantly altered by adjusting the shape of not only the bonnet, windscreen and rear of the vehicle, but also the sides and underneath. Changing the rake of the windscreen will have a major effect on how easily the airflow passes over the car (ie how slippery the car is), as can the area above (& below) the grille. The creation of high & low pressure areas in the right places on a car is a priority for car design engineers because not only does the car have to cut through the air as cleanly as possible (to give better fuel economy) the engine cooling has to work effectively, the brakes have to have air passing over them , the exhaust gasses mustn't be pulled back into the car, the car has to be stable in cross winds - and in the case of an SUV, it has to have enough ground clearance to go off road. The car's shape must ensure that down-force increases as velocity rises to ensure it doesn't take off at speed, and of course, it must protect both occupants and pedestrians in the event of a collision.

An almost impossible task?

Everything is a compromise. It's just a question of which attributes you are prepared to forgo in order to produce the car that you are happy with. In the case of the Yeti, I think they've almost done the impossible; It's roomy, it'll go off-road, it doesn't look too bad, it's comfortable, it's got loads of kit, it handles superbly, it's collision safety is excellent and it doesn't cost the earth.

(If you can get hold of a copy of Track Driver magazine this month, there is a superbly illustrated article that explains aerodynamics in terms that even I can understand.)

John H

Just trying to say driving a Yeti above 70mph and the consumption will increase like a rocket.

I thought this as well for nearly a year and always pootled along in my Yeti at 70 odd. Then I was late for something and did quite a bit more speedwise with the car fully loaded to the gills... and my consumption was EXACTLY THE SAME as if I had done 70..... See this thread:

http://briskoda.net/forums/topic/216706-yeti-a-brick/

Very perplexing.

Well now. Yesterday I fitted the winter tyres. Today at rush hour my wife took the Yeti (1.8 TSI 4x4 Elegance) on one of her regular journeys: 60 miles, of which the first ten are in heavy city traffic, the rest on motorway. She arrived home with the MFD showing 40.9 mpg. This is nearly 4 mpg better than anything we have seen before, and 14 mpg better than the journey a couple of weeks ago at 80-85 mph that I mentioned further up this thread (which was almost the same route but without the city traffic, and also in warmer weather!)

The tyres are Goodyear Ultragrip 8, which have been reviewed as the pick of this years's new winter tyres. Their rolling resistance, according to the Swiss tests, is good, though actually not the very best of the current winter tyres.

This is a bigger improvement than I expected to see from a tyre change, in view of the fact that at motorway speeds, tyres account for only around 25% of a car's energy use. Of course it is not all down to lower rolling resistance: the narrower section and the slightly taller gearing of my chosen winter tyres will have contributed. Even so, it makes me look askance at the summer tyres that have just been stored away: Dunlop SP Sport 01. I shall have to look up proper (i.e. German / Swiss / Austrian) tests of those and see whether they measure poorly for rolling resistance.

After this experience, we'll switch to proper mpg measurements: brim to brim and never mind the MFD. And let's see whether 40+ mpg is repeatable! Meanwhile my whinges about the 1.8 petrol engine's fuel consumption are on hold, if not yet altogether withdrawn.

I have only had my TSi 4x4 for about a month now, but the 1.8 engine is as everyone highlights thirsty. One positive thing though, the mpg does not seem to be negatively affected by having a 14'6" canoe on the roof at times.b I am currently getting around 30 mpg, but on a run into and out of London on the M4, this rises to 34 mpg, the canoe is generally absent for these runs.