B Class aerodynamics

[Dieselman]

A not very interesting video about testing car aerodynamics, but the figures for the new B-class are impressive, especially with the optional Aero package.

Mercedes B-Class aero paint test | Videos | Auto Express

 

[wemorgan]

0.24 is very decent. Even the 1.2TDi Audi A2 is higher at 0.25 and was quite a narrow car.

 

[Bobby Dazzler]

Remember the width of the car doesn't affect the drag coefficient (Cd) - it's just a coefficient that indicates slipperiness.

The width does have a bearing on the frontal area or cross-sectional area (A).

Together it's CdA that determines aerodynamic drag.

 

[wemorgan]

News - Automotive Engineer

According to Daimler, every 0.01 reduction in the Cd figure can cut fuel consumption by up to 0.4-litres/100km at 130km/h

 

[BTB 500]

Obviously drag reduction is good but 130 kph is a fairly extreme case (81 mph) - not a typical speed for most B Classes! At a more realistic 40-50 mph the benefit is going to be pretty small I think.

 

[Dieselman]

130kmh is that legal motorway speed in most of Europe, so it seems pretty logical to expect drivers to travel at that speed.

I think the saving of 2-3mpg at motorway speeds is a reasonable saving, for no effort.

 

[BTB 500]

The saving quoted was up to 0.4l/100 km, so I think 2 mpg or so at most. Obviously worth having, but I still don't think B Classes will typically spend that much time doing 80+ mph. I suspect weight reduction would be more beneficial overall (stop/start driving).

As an aside, IIRC they got the Cd of the current Vito down to just over 0.3.

 

[Dieselman]

The saving quoted was up to 0.4l/100 km, so I think 2 mpg or so at most.

Given the low drag, I would think that 40mpg should be attainable easily, in which case 0.4 L/100km is 2.2mpg.

 

[BTB 500]

Given the low drag, I would think that 40mpg should be attainable easily, in which case 0.4 L/100km is 2.2mpg.

I make it 2.14 mpg

But that's only if the maximum quoted benefit of 0.4 l/100 km is achieved - could be less.

 

[Dieselman]

I make it 2.14 mpg

But that's only if the maximum quoted benefit of 0.4 l/100 km is achieved - could be less.

But then it could be more, especially if the car achieves more than 40mpg. Either way it's about 5.7% saving, or 600 free miles in every 10,000.

 

[BTB 500]

Either way it's about 5.7% saving, or 600 free miles in every 10,000.

Possibly, but that would only apply when doing over 80 mph. Our Vito is mostly used for motorway runs ... however the average speed over the last 3800 miles (since reset) is actually 39 mph.

 

[Dieselman]

The point is that at that speed the aerodynamic package will save that much fuel. Other factors may irradiate that saving, but it is there irrespective, with no effort from the driver.

Personally, I think it's a good thing. Cars have become less aerodynamic than they used to be due to lack of interest from manufacturers and the consumers.

Other benefits of better aerodynamics are a more stable vehicle, higher top speeds and a quieter passenger cabin.

Hard to see any disadvantages.

 

[markjay]

Found this info:

Mercedes Benz G-Class: Cd 0.54
Mercedes-Benz 190E 2.5-16/2.3-16: Cd 0.32
Mercedes-Benz B-Class + eco-package 2012: Cd 0.26
Mercedes-Benz C-Class Sportscoupe 2001: Cd 0.29
Mercedes-Benz W211 E-Class 2002-2009: Cd 0.26
Mercedes-Benz W220 S-Class 2000-2005: Cd 0.27 (0.268 with Sport Package)
Mercedes-Benz SL (Roof Down) 2001-present: Cd 0.34
Mercedes-Benz SL (Roof Up) 2001-present: Cd 0.29
Mercedes-Benz W203 C-Class Sedan 2001: Cd 0.27
Mercedes-Benz W221 S-Class 2006-present: Cd 0.26

 

[markjay]

What is even more interesting is that the Tatra T77A had Cd 0.212 in 1935....

 

[wemorgan]

What is even more interesting is that the Tatra T77A had Cd 0.212 in 1935....

I had to look that one up to see how it looks. I like, a lot

 

[Dieselman]

I'm surprised you dind't know that Will, it's one of the most famous production cars built.

By going for a rear engine and no radiator grille at the front, the drag is reduced by about 30%.
Tatra were years ahead of the game in many aspects.
They fetch a few £££ now.

http://www.classiccarsforsale.co.uk/classic-car-page/152400/1948-tatra-t87/


The GM precept is another very low drag car (0.163), fully designed, built and tested by yr 2000. Where is it now?