What's better? Lighter or more slippery?

gern_blanston

Veteran Member
Joined
Dec 3, 2002
Location
PNW
TDI
Golf, '03, Silver
What\'s better? Lighter or more slippery?

The quick-and-dirty answer is that a better power-to-weight ratio gives lower fuel burn on acceleration, better aerodynamics gives lower fuel burn at cruising speed.
Roughly, it'll be a push.
 

wwhalenc

Veteran Member
Joined
Apr 7, 2001
Location
Boulder, CO
TDI
1991 Jetta with AHU
What\'s better? Lighter or more slippery?

No question lighter is better for city driving... But does .04 difference in drag outweigh a 300 lb difference between two cars up at highway speeds? (The jettaII 4 door conversion I'm driving now is 15% heavier than the '82 scirroco)
 

gern_blanston

Veteran Member
Joined
Dec 3, 2002
Location
PNW
TDI
Golf, '03, Silver
What\'s better? Lighter or more slippery?

I doubt it would make any real-world difference.
 

wwhalenc

Veteran Member
Joined
Apr 7, 2001
Location
Boulder, CO
TDI
1991 Jetta with AHU
What\'s better? Lighter or more slippery?

Anyone have the facing area and coefficients for these cars...I'd love to plug in the numbers and see.
 

delste

Veteran Member
Joined
Mar 25, 2004
Location
Pittsburgh PA
TDI
Jetta Wagon GLS 2004 Black/Black leather
What\'s better? Lighter or more slippery?

The real question is

Great taste or less filling /images/graemlins/grin.gif
 

mgwerks

Veteran Member
Joined
Dec 10, 2003
Location
Texas Hill Country
TDI
black 1999 New Beetle
What\'s better? Lighter or more slippery?

[ QUOTE ]
The real question is

Great taste or less filling /images/graemlins/grin.gif

[/ QUOTE ]
You sure? I have heard that the real question is

-Ginger or Mary Ann

-Munsters or Addams Family

-paper or plastic



(sorry)
 

gern_blanston

Veteran Member
Joined
Dec 3, 2002
Location
PNW
TDI
Golf, '03, Silver
What\'s better? Lighter or more slippery?

If Mary Ann drove a TDI, she'd be perfect...
 

wwhalenc

Veteran Member
Joined
Apr 7, 2001
Location
Boulder, CO
TDI
1991 Jetta with AHU
What\'s better? Lighter or more slippery?

If Mary Anne's the girl I think she is...she'd definitely drive a TDI. Besides...it'd really be the only viable choice w/ the resources on the island. SCO conversion (straight coconut oil)
 

Rammstein

Top Post Dawg
Joined
Sep 3, 2002
Location
Québec city baby, Canada
TDI
Golf 92 D
What\'s better? Lighter or more slippery?

I would suggest to go with the lightest shell as possible.

This shell being a Rabbit pickup.

Try to find a diesel version, it'll be easier.

Weight matters in fuel economy guys.

Look at what I drive: the heaviest 5sp TDI (B5.5 are only available with tip).

My best was 4.31 l/100 km or 54 US mpg.

That was driving at 90 kph (56 mph).

I'll do better this summer for sure, but I'm not getting 60 mpg from stock (like Golf's and Jetta's in stock form) driving at the same speed.

My B4V weigh 1500 kg compared to a 1300 kg Golf 2 doors or a 1400 kg Jetta variant automatic.

The lighter the best economy.

If you could get a light and aerodynamic shell, it would be the perfect match to a TDI engine. /images/graemlins/wink.gif
 

Peter Cheuk

Gasser :P
Joined
Aug 31, 1998
Location
Daly City, Calif., USA
TDI
'06 Jetta GLI
What\'s better? Lighter or more slippery?

Rammstein, different cars, different technologies.

A lighter, more aerodynamic shell is your best bet. I contemplated doing something like this if I ever totalled my Jetta. Take the engine out and drop it into a '85 Golf 2 door shell. Gut the interior and redo it lighter. Then I was thinking of getting a set of forged alloys that came with the Carat models (seven spokes, no VW emblem in the center) and run in super economy mode.

You can always look up an old kit car or make your own. Something like a Bricklin or such...
 

blitzoid

Veteran Member
Joined
Sep 11, 2003
Location
NYC
TDI
Blue '02 Golf GLS TDI
What\'s better? Lighter or more slippery?

Tire rack has 15x6" 4x100 SSR Comps on sale - $230/rim, i think.

They weigh less than 9 lbs apiece. /images/graemlins/eek.gif

And... they look very pretty.
 

VWRacer1

Veteran Member
Joined
Mar 17, 2004
Location
SF Bay Area
What\'s better? Lighter or more slippery?

This is an interesting problem, and I am tempted to agree with Gern that it won't make any real difference. However, just to be a bit anal and prove it to myself, let's do the numbers... /images/graemlins/smirk.gif

Mk2 Golf/Jetta at 2300 lbs, a Cd of .35 and 20 sq ft of frontal area versus a Mk2 Scirocco at 2000 lbs, a Cd of .38 and what, ~16 sq ft (?).

For each, the combined (aero plus rolling drag) power required can be approximated as (8.702 x 10**(-6)) x Cd x A x V**3.

For the Golf at 60 MPH, that's (8.702 x 10**(-6)) x .35 x 20 x 60**3, or 0.000008702 x .35 x 20 x 216,000 = 13.2 hp.

For the Scirocco, that's (8.702 x 10**(-6)) x .38 x 16 x 60**3, or 0.000008702 x .38 x 16 x 216,000 = 11.4 hp.

Two hp at .4 lbs/hr/hp means the Golf will burn .8 lbs more fuel per hour than the Scirocco. Since diesel weighs about 7 lbs/gal, that is an extra tenth of a gallon of deisel an hour, or about 1 MPG.

As we thought, there isn't enough difference to clearly chose between the two. Drop the TDI into whichever car you wish and have a nut! /images/graemlins/grin.gif
 

mgwerks

Veteran Member
Joined
Dec 10, 2003
Location
Texas Hill Country
TDI
black 1999 New Beetle
What\'s better? Lighter or more slippery?

What I am looking for is an old-style VW trike that I could drop a TDI motor behind. Other than the fact it would be nearly impossible to keep the front on the ground during throttle roll-on, I bet that would be and sound fun!

Next project Honda CB500-4 powertrain in a mini-bike. Well, the bike was free!
 

wwhalenc

Veteran Member
Joined
Apr 7, 2001
Location
Boulder, CO
TDI
1991 Jetta with AHU
What\'s better? Lighter or more slippery?

VWRacer.. You da man! Actually I scored an '84 scirocco rolling chassis that's local, so we'll get some empirical data for you in the next few weeks.

TRIKE- Hey, regarding the trike..I remember seeing a 3 wheel vw prototype in the late 80's or early 90s. As I remember the performance was insanely good.

BTW, I weighed my '91 Jetta at the racetrack on Sunday. 2940!!!! I know I had a lot of extra crap in there, but whoooaaaa That's a bit out of hand (i only weight 150 and I had maybe 10 gallons of methanol and bunch of tools)
 

TornadoRed

Top Post Dawg
Joined
Aug 3, 2003
Location
Saint Paul (ex-San Diego)
TDI
2003 Golf GL 5-spd, red; 2003 Golf GLS 5-spd, indigo blue; 2003 Jetta TDI wagon, Candy White (SOLD); 2003 Jetta TDI wagon, silver
What\'s better? Lighter or more slippery?

[ QUOTE ]
A lighter, more aerodynamic shell is your best bet....
You can always look up an old kit car or make your own. Something like a Bricklin or such...

[/ QUOTE ]
Putting a relatively heavy engine like the TDI into a relatively light chassis presents a major weight distribution problem. A rear-engine arrangement is better, a mid-engine arrangement is probably best. If you could solve the placement of the transaxle -- I wonder if it would fit in an older Lotus chassis?
 
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