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Re: MGB aerodynamics

To: MG List <mgs@autox.team.net>
Subject: Re: MGB aerodynamics
From: Max Heim <mvheim@studiolimage.com>
Date: Sun, 08 Apr 2001 15:20:05 -0700
on 4/7/01 10:58 PM, Larry Hoy at larryhoy@prodigy.net wrote:

> I have some questions about aerodynamics.
> 
> Roadsters, no top
> Roadsters, convertible
> Roadsters, hardtop
> GT coupes
> 
> 
> At what general speed does the aerodynamic shape of a car become a significant
> factor?
> 
I believe drag increases exponentially in regards to speed (but don't take
an art major's word for it), so it becomes an increasingly more important
factor at higher speeds (I'm sure you knew that). Drag has an effect on fuel
economy at 55mph (as shown in fuel economy ratings), and it is the limiting
factor on top speed assuming optimal gearing. As for the hypothetical case
of a two cars with equal HP but different drag coefficients racing from a
standstill, my guess is that drag would become a factor somewhere in 4th
gear.

> Of the above configurations, does anyone have any knowledge as to the most
> "slippery"
> configuration?

The fact that the factory raced hardtops at Le Mans indicates that they
considered this setup more slippery than an open roadster (as seems
obvious). The soft top was probably illegal or impractical for racing, but I
think we can assume that it is somewhat less aerodynamic than the hardtop
due to drag-inducing flaps, etc. I would think the MGB GT would have a more
slippery profile than a roadster with hardtop (longer roofline, cleaner
tail), but that may not make up for its larger frontal area due to its
taller windscreen.

R&T reported the following top speeds for various versions, but it is
unclear whether these were actual test results or calculated from gear
ratios:

1963 MGB 106mph
1966 MGB GT 105mph
1968 MGB 104mph

At any rate they are so close that they fail to provide any grounds for a
conclusion.

--

Max Heim
'66 MGB GHN3L76149
If you're near Mountain View, CA,
it's the red one with the silver bootlid.

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