Friday, April 11, 2008

Comparing Dimensions

I've been reading the excellent Lotus Seven & the Independents, and one thing I'm struck by is how much variation there is in the critical dimensions of various Sevenesque cars.

I've compiled various measurements for the two common Locost platforms as well as for three baseline Sevens and a few lightweight sports cars. I've also thrown in weight and horsepower numbers for reference.

Ride HeightWeightHP
1962 Lotus Super Seven Series II131.55639.547.548.588692485
Haynes Roadster (Gibbs)129.56746


57.5943.91309105 est.
Tanner's CMC Miata-Locost
12865.542.551 est.
56.2 est.924 est.1279175
FM Westfield131.563.455.556.291.55.75 est.1300125
2006 Caterham CSR Superlight129.966.340.059.357.791.13.91245260
1993 Mazda
1974 MG Midget 15001416048.346.344.8804163165
2003 Ariel Atom II134.370.847636392.33.51005220
1957 Lotus Eleven LeMans13960.53145.547884.5136084
2000 Lotus Elise1476745.256.757.990.66.31574143
1964 Austin Mini Cooper S
Click on the car's make and model for the sources for my data.

The first thing that jumps out to me is how tiny the original Seven Series II is. The Caterham is nearly 10" wider than the original car. Of course a lot of this is wider modern tires, but it's still significantly smaller than anything on the road.

The other thing is how much longer the wheelbase is on Gibbs' Haynes Roadster vs. every car in the table. If you look in the Haynes book, the front wheels actually stick out past the front of the nose cone! Since my frame design is based on the Haynes Roadster, reducing the wheelbase to 90-95" is going to be one of my design priorities.

I'm going with the stock Miata front and rear track on my Locost (as of right now), so the width of my finished car should be in-tune with the rest of the pack.

Update 6/22/08 - Chris Gibbs has contacted me with corrections to my table. It appears that the figures I had before for the wheelbase were way off, as many have commented. Now with the correct dimensions, it appears that the Haynes Roadster isn't as big as the discussion forums would have suggested. This makes me feel much better about using the design as a starting point!

Update 4/14/09 - It appears the Haynes Roadster wheelbase figures are in dispute again. I've received word from a reader who very adamantly states that the wheelbase is actually 94". The reader states this is what he got in CAD when modeling up the frame. Gibbs himself on his forum states it is 92", so I'll chalk that up to the book not completely representing the actual car.


JHM said...

Your comparison table makes interesting reading, a question that springs to mind is why did Chris make his chassis so long? Is it to accommodate long people, long engine, IRS, something else? He regularly posts on so not hard to ask him.

My favourite 7 clone is the Donkervoort, its a little longer than Locost or a Caterham with longer overhangs. The longer nose accomodates a ducted rad and the longer tail a cake to go with the Caterhams sandwiches:

Hondaman900 said...

I'm curious why you didn't list McSorley specs in the comparo?

William Conway said...

jhm - I've asked on the Haynes Roadster forums, and he hasn't gotten back to me yet.

Hondaman - I didn't list them because I didn't have a "baseline" McSorely car to take measurements from. Although if you're building a +442, it should be pretty easy to extrapolate the measurements from Keith's locost.

Paul H said...

Your comment re. the wheels sticking out in front of the Haynes Roadster as shown in the Gibbs book is incorrect. The wheels do not stick out in front - I have the book snd car in progress.

Paul H

William Conway said...

Thanks Paul! You were right. The image in the book appears to be a funny coincidence with the camera position. Chris confirmed that my numbers were in error!