Plus one.
I wonder about were the weight would go. The Roadster has always been a heavy car. Adding in a bigger powertrain (and brakes) is now straining the tub and handling would have to be dealt with. It's a delicate balance setting up a great car and just putting in another XXX horsepower does not equate a wholly superior car.
Add lightness!
Two years ago I went into a lot engineering investigation and mathematical modelling when planning to adapt a modern production car into a pure EV. I've still got the rather attractive 4WD Italian sports car that I bought for the purpose, which is all very nice, but it drinks £4,000 of petrol every year at present and costs way to much to run. It’s a long story why I opted for a Tesla in the end though..!
It was an interesting exercise that sharpened a lot of lost knowledge from university days. The modelling for efficiency / energy usage included many factors such as mass, Cd, Ca, air density, rolling resistance on tarmac and concrete, transmission losses and so on. Below I summarise some interesting overall points regarding what can be done to any car to improve various aspects like better range, better acceleration or better overall efficiency.
(I appreciate that there may well be far wiser people on the forum than I, but others might find this useful. One other caveat - I am sure Tesla Inc spent millions optimising the car, within reason … )
Broadly speaking, there are two factors that drain energy to keep a car moving at freeway speeds, one is rolling resistance, the other is air resistance.
As the speed of the vehicle increases the rolling resistance increases linearly, where as the air resistance increases exponentially.
At above 50+ mph, air resistance becomes increasingly dominant factor. At 100mph air resistance accounts for about 80% of the energy goes into pushing the car forwards.
Big reductions in weight will marginally reduce losses through rolling resistance and improve acceleration, but will not effect losses due to air resistance.
Whereas marginally reducing the coefficient of drag and frontal area (Cd, Ca) significantly improves losses due to air resistance.
Using a freeway speed of 70mph and plugging it into some of those spreadsheets, I can pull out some statistics as follows :-
Loosely speaking, a -20% weight reduction on a Tesla ( = - 250kg !) would improve Wh/Mile efficiency by only about 7%. If this were somehow more dramatic at, say, -40% reduction then still the efficiency improvement is only 15%. So major weight savings would be prohibitively expensive without considering some equally major changes to how the car is made, although the future is looking interesting for this.
However, reducing the Roadsters Cd from 0.35 down to a more reasonable 0.30 would improve the Wh/Mile efficiency by 9-10% straight off, and getting it down to 0.25 would make it nearly 20% better. ( Its worth noting that the Cd for the Model 'S' is apparently 0.27 which is very good compared to almost every other similarly sized car)
So, efficiency benefits through weight savings alone are going to be very difficult. But there's quite a few practical things that can be done that if used simultaneously can improve energy efficiency at speed way more than trying to shed 250kg of weight ! For example :-
- there are tyres becoming available which have almost half the rolling resistance of conventional tyres which will improve the 70mph Wh / Mile efficiency by up to 15% straight off. But to use these will mean some marginal compromises in areas like ultimate grip, road noise and so on.
- pumping your tyres up by 5-10psi will have a worthwhile effect on rolling resistance to the tune of 3-4% of efficiency
- replacing the wing mirrors with bullet cams and small OLED screens on the inside would improve Cd and Ca giving about 3 to 3.5% efficiency benefit.
- if you want range, drive with the hard top on. The Cd goes up considerably with it off.
- You can improve steering responsiveness, acceleration and some weight effects by using lightweight alloys
and tyres, often reducing the unsprung mass by 25kg-30kg. When moving at speed this would have a similar effect to reducing mass of the car by 5% giving about a 2% efficiency saving.
- If you want 4% better acceleration whilst sacrificing top speed, you could reduce the rear wheel size from 17" to 16" but you'd run out of puff a bit quicker. (not actually sure if rear wheel discs/brakes allow this)
- .. I am sure there's loads more.
- … and finally, in my case, going on a diet and eating less doughnuts might save a % or two :biggrin: and make it less of a hernia inducing exercise getting in/out of the Roadster with the lid on !
I've deliberately not touched on other aero dynamic areas of how air flows around/over/under and exits at the rear, as this is way to complex to go into here. These would include the combined effects of flat undertrays, front splitters and lower spoilers, rear wheel covers, wheel spats, rear venturi's, kamm tails, vortex generators etc etc
