Hi,

I'm starting to design my chassis.
But before starting the real drawing I was thinking about what dimensions I should use.
I'm 203 cm tall and it's not easy to find the right dimensions for a mid-engined car.
Dimensions are in mm.
Explanations for the drawing. The smaller outside boxes at the bottom are wheel case dimensions I will have to consider.
The long boxes are driver and passenger. The line behind those is where the engine compartment should start.

The only thing I don't know is if I'm having enough place in the engine compartment for an engine.

Thanks in advance.

Geoff
Rescued attachment mid-dimensions.JPG

when i did my midi (now deceased) i sat on the floor and measured around my body/legs etc,you take up more space than you think

Yeah if you're designing from scratch, you measure every component, including you and the seat, put them into either the computer or down on paper, then start moving stuff around. For my mid-engine Mini, the outer dimension was already fixed. If you're starting from scratch you just arrange the parts where you want and you're done. I found the car will pretty much design itself once all the major components are placed where they have to go; everything else just holds them in place.

[Edited on 8/21/05 by kb58]

also if you havent already, get plenty of literature on the subject. i got "reace car chassis design and construction" by Fores Aird and "competition suspension design" cant remember who by though and both are very informative.
to get the measurement for the cockpit it may be best to have a sit in a seven and see if it is comfortable then measure the length and width.
then as kb says, sort out what parts you are using and measure them to use in your design since the positioning of bulkheads and tube convergences all depends on what they have mounting on them.

I'm using a wheelbase of 2550mm and should fit someone of 6'4". This measurement allows 815mm from the front of an LS-2 motor to the G50/52 driveshaft centreline, and 1000mm from floor to roof.

I know you're way taller than this, but to fit in a reasonable sized mid-engined car, you can play around with lots of things including engine setback, lowered floors, roof height (open top"), front wishbone layout (to give you more pedal room) etc.

I echo the other advice you've got so far about mocking up your critical measurements full size. Once you know your wheelbase, cockpit width and basic body shape you can fine-tune your front & rear track. Your ratio of wheelbase to track should be about 1.6:1.

Design is difficult. I have just wasted 2 days on 3 iterations of pushrod and bellcrank for my rear suspension before I got it right, all because of not grasping the fundamental interconnectnedness of the connected things (my tribute to Douglas Adams).

Read all the chassis/suspension design books you can get your hands on, particularly everything by Carrol Smith.

All the best with your build.

Regards
Richard

I think your dimensions should fit you as I am also building a big mid engine GT car and have engineered it to have maximum space in minimal dimensions.
It should comfortably take someone of well over 6ft.

My wheelbase is 2610 and full car width is 2000 at the rear. Your passenger area is 150mm longer than mine and same width.
I'm fitting a V12 so my rear axle C/L to rear bulkhead is 1050 but that allows 80mm engine clearance (mainly down to dry sump pulley).
However I have a sloping bulkhead which extends the passenger compartment 60mm.
Front of the passenger area to front axle C/L is 200mm.
Like Richard my roll bar is 1000mm high (fronm base of chassis) and this would have been lower but I like my seat very upright AL-LA rally style and I have plent of clearance above my head.

I used the approach kimi recomends in as much as I had my basic dimension and components which I possitioned on a flat board, I then tweeked them so that I got the exact driving possition I wanted.

What engine etc are you planning?

[Edited on 8/9/05 by andygtt]

Thank you for all for your replies until now.

I still have 2 possible designs.
The first one is with a smaller engine (eg Honda 2.0)which is transverse mounted engine and which will need less space at the back. The other design is a Big longitudinal design with a V8 - V12 engine with a G50 or similar gearbox.

A roll bar at 1000mm will not be enough for a upright position in my case. Look at another post of mine.
http://www.locostbuilders.co.uk/viewthread.php?tid=30290

Maybe I have to make my design a little bit wider. It looks a little bit disproportionate.

Geoff

[Edited on 8/9/05 by geoffreyh]

I don't think you need to worry about making it wider, I have allowed normal ground clearence and with my chassis being 1000mm high it still makes it a few mm lower than ther Porsche GT and Zonda (both around 1150mm). But I'm also wider than these cars so I could go higher without it looking silly.

I guess it all depends on your design but with mine we have built strength both sides of the driver and thus have a large central tunnel..... This has a knock on effect of limiting my driver footwell as if I extended it forward it would compramise the wishboness etc.
If I removed the central tunnel the driver could go over 150mm and then it might be possible to gain another 200mm leg room between the wisbones (its not recomended to go beyond the front axle centreline due to crush zones then being required).

Gotta say though that I have found designing and building my own chassis (with professional help admittedly) huge fun and extremelly satisfying.
I've spent hours sitting on the base chasis planning my driving position, pedals, steering column etc etc.

Geoffreyh, are you designing one car to use either the Honda or the V8-V12, or are you trying to decide between 2 different designs?

If it's only the one chassis, and you would prefer a V8 or V12 - and who wouldn't - they can be moved back in the chassis so the driveshafts run forward to the hubs. I don't remember the maximum angle for the Porsche CV joints, but you should be able to find out on the www. Even a small angle of 6 degress will give you several extra inches (bad choice of words)!

Using a longer wheelbase like Andy will help, and remember that a V8 is shorter than a V-12. I'm not sure of the length of a Viper V10, but it may be another option (US$15K as a crate motor).

If you're not settled on the design, what about a convertible or targa for the extra headroom? With a bit of planning, I'm sure you can make something really nice that fits you perfectly

Andy, I ended up narrowing my tunnel from 300mm to 200mm to give a bit more footroom, because I decided I didn't like offsetting the pedals to the left. I'm using a larger sill cross-section to compensate.

quote:

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Originally posted by Richie Revs

Andy, I ended up narrowing my tunnel from 300mm to 200mm to give a bit more footroom, because I decided I didn't like offsetting the pedals to the left. I'm using a larger sill cross-section to compensate.

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