• Hi Guest!
    If you appreciate British Car Forum and our 25 years of supporting British car enthusiasts with technical and anicdotal information, collected from our thousands of great members, please support us with a low-cost subscription. You can become a supporting member for less than the dues of most car clubs.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

Tech question???

Share this page

N

nomad

Yoda
Offline
Wondering if anyone knows the coefficient of friction of a square body spridget with the top up? With a hardtop? How about a bug eye stock and with Costins front end? I think that was the Speedwell bonnet.
Just curious as to which to develop for high mpg. I'm sure that info is out there somewhere.

Kurt.
 
I was going to say probabaly hard top, however; we've all seen convertibles w/ inflated tops going down the interstate. Seems that might be more aerodynamic.
 
I don't have hard data, but

In my experience the hard top is worth about 10%.

Top speed or mpg, but not both at the same time.

Soft top around 6% to 7%.
 
i had a kellison bonnet in my possession for a little while. when i had it i though how much better the aerodynamics of it must be over stock. its was much lower in the front and looked to be about 8 inches longer. if you made some plexiglass covers for the headlights it should be about the best case scenario aerodynamically for the from of a spridget. i have the email of the guy that makes them if your interested.

IMG_3453.jpg


IMG_3455.jpg
 
Thanks for the info folks.

Kellison bonnet does look quite streamlined but I preferr the Costin bonnet like Frank C [Sritenut] had on his car.

Bill, are those your personal tests!?
I've read similiar data in the past that the hardtop increases top speed so therefore would be more aerodynamic.

Has anyone seen the actual figures for Coefficent of Friction anywhere? Be fun to compare to other cars.

Kurt.
 
It's what I've done with the car. With the top off, I get about 30 to 33 mpg on the freeway, with the top on, 35 to 38 mpg, as high as 42, a 3 to 4 mpg difference. This is at a steady state 60 mph for about 100 miles.

with the top off I can get up to about 78 in 5th, (I can go faster in 4th) before I run out of power, but with the top on I've hit about 85 and climbing.
 
It makes that much difference, Bill! That would have to be figured for high fuel mileage.
Apparently no one knows much about Drag Coefficient [correct term]on these cars here. I know that the Lotus elite had a drag Cf of .29 I believe and that is hard to beat even today by modern cars. Seems like I read something about the BE's drag when racing and what the various changes to body accomplished.

Kurt.
 
I've generally put the car together to have low end grunt and good fuel economy, rather than making it a "boy racer". .. 1098 with a very wide angle cam as the only internal mod, 3.9 rear end and a 5 speed. It lumps along at about 3 grand at 60 mph, but runs out of pull in 5th (with the top down) at around 4200 rpm. Still that's over 80 mph. Of course economy goes out the window so i don't do much of that, but sometimes ya just gotta go. .

I see the Prius listed at a .25 cd and the new Ford Fiesta at .33 and the Sprite MK estimated at about .5

I also found this tidbit..
'Road & Track' gives a frontal area for the Mk II Sprite of 14.8 sq ft and a 'total drag at 60 mph: 80lb', though the 1098 notches up 14.3 sq ft for frontal area and 75lb total drag at 60 mph without any bodywork changes

at (https://www.british-cars.net/mg-midget-sp...01001025994.htm)
 
Thanks much, Bill!!

Thats just the sort of stuff I was looking for! So the drag cf is around .49. I was afraid of that. The front is too square and the windshield to vertical on a square spridget. BE with a hard top and a Costin front end should do better. Seems Frank C. got 46MPG on the way to LoTO, as I remember, with his Costin front BE.

My midget with the A15 datsun + 5speed+ 3.9 diff ran right at 40MPG on the way to and from Midget 50. The H89 head that I have on it is what I attribute that to.
So if I swap that into a BE with hard top and Costin front it should be impressive.

Just daydreaming, but I appreciate that info.

Kurt.
 
Aerodynamics are for people who can't build engines

-Enzo Ferrari
:whistle:
 
Then Enzo went on to build some of the most aerodynamically elegant cars ever made...
 
Elegant, yes, but the old ones weren't spectacularly slippery. I don't know which was the last model old Enzo himself designed, but the 512 Berlinetta had a Cd of .35...which is just kinda meh. Surprising for such a pointy car.
 
Back
Top