i am building a custom middy with fwd donor, what i want to know is whether to keep with the donors wheelbase and track or is it not that important.

for info
wheelbase is 2580 mm
track is 1453mm (measured from tyre centres)

Liam,

I'm building with Corolla running gear. I don't even know what the donor wheelbase is (I could look it up I suppose). I've set my wheelbase at about 2350mm as a matter of packaging and proportion as much as anything. I've got scope to change the wheelbase by +/- 50mm or so by making different front wishbones.

The track is pretty much set by the running gear unless you want to start making custom axles (expensive!). The Corolla is 1440mm - I'll have about 1480 because the wheels I'm using are 20mm offset to suit the front suspension rather than the ~40mm FWD offset the Corolla would normally have. The offset change isn't a problem (hopefully!) because the rear wheels aren't steering.

Dominic

It's not important. In fact, don't even look at it, wheelbase that is. Just design your car and whatever it ends up being is "correct."

Track on the other hand does matter, but only to the extent that if you make it different then stock, you need custom axle half-shafts made, about $300-$400. Also, I learned the hard way what happens if you make the track a lot less then stock; the CV angularity increases very quickly! That is, making the axles, say, 30% shorter, doesn't mean CV angularity increases by 30%... it's a lot more. It's something that should be modeled.

[Edited on 12/7/04 by kb58]

Those are nice dimensions for a sports car, about the same as Graber's, I think.

Not to be argumentative, but I wouldn't go as far as saying that wheelbase is unimportant. It isn't critical and offers a wide range of options, but does have an effect on pitching moments and thus load transfer. Again, not a huge deal as long as it will almost inevitably fall within the "norm," but something to keep in mind just because. Cheers!

A good guide for a sportscar is to use a wheelbase to track ratio of around 1.6 (as found on most high-end racing cars).

I would agree that you should keep the stock track-width to save yourself a lot of problems and unnecessary expense.

quote:

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Originally posted by crbrlfrost
Not to be argumentative, but I wouldn't go as far as saying that wheelbase is unimportant. It isn't critical and offers a wide range of options, but does have an effect on pitching moments and thus load transfer. Again, not a huge deal as long as it will almost inevitably fall within the "norm," but something to keep in mind just because. Cheers!

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quote:

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Originally posted by pbura
Those are nice dimensions for a sports car, about the same as Graber's, I think.

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I'm pretty certain I have the same track as Steve (we are both far too frugal to go for custom axles...LOL)

My wheelbase is 2337mm (92 inches)...a little less, but similar...

[Edited on 12/7/04 by Alan B]

i was going to stick to standard locost fron suspension geometry because i have cortina uprights, butwhat is the track of a bookcar? compared to the (tyre centre to tyre centre) track of the nubira at 1453mm

"My wheelbase is 2337mm (92 inches)...a little less, but similar..."

[Edited on 12/7/04 by Alan B]

Liam,
Regarding your request for a chassis design my thoughts on a middy chassis for transverse engines is now in the photos section. The thoughts are preliminary but I have done a quick FEA analysis and the stiffness is good. The details need to be filled in to suit a specific build. I know this is a bit off thread but I hope it helps.

Constructive comments welcome on the middy chassis btw.

cymtricks,

this is fantastic its exactly what i wanted,
after deciding to do a middy i began to design my own chassis and what i came up with is very similar.

the only differences being that i included a simple transmission tunnel for routing cables and hoses,
also i wanted to use my original locost nosecone so i designed the front with suitable dimensions in mind. With your help i now have a good idea about what tube sizes and bracing to use


after looking at the model i was wondering about the "2x1 dashboard frame side" you mentioned on the drawing. i am not sure i understand what you mean. is the hand drawn view the junction at the front of the sills?
i don't understand where the shaded part, the 2x1, is going to or from

please forgive me if i am being dumb its been a long day!

[Edited on 15/7/04 by liam.mccaffrey]

Liam,
The design is unfinished. By which I mean that details specific to a build need to be worked out.

The 2x1 tube runs vertically up the side of the scuttle/dashboard frame and closes the end of the sill. The view shows the sill meeting it from the left and the dash top joining it from the top of the hand drawn view. It is shown shaded to highlight it in the picture.

The 4x2 tube down the side of the seat is end on.

The sill has ready made ends of the right width. the small face of a 4x2 at the back and the wide face of a 2x1 at the front.

The footwells will probably need tubes running from the ends of the 2x1 tubes to the front suspension region to stiffen up the panels. Triangulation may not be necessary if the panels are all welded in place.

If you scroll back through my posts I have put a middy seven design on this forum. It has a very similar engine bay structure to my above post with the rest being locost book inspired.

[Edited on 21/7/04 by cymtriks]

hi cymtriks

i have seen your drawing, without realising you were its source, i have drawn a cad version of this drawing which you are welcome to, when i saw it i thought it was so cool, it just looks really balanced,

i am about to scale my drawing up, as at the moment it is a scale cad drawing(i know this is wrong but i did a vector convert of the jpeg)

at the moment i it looks as though i'll build the engine bay as per you model with a locosty front. am doing chassis next week so i can post some pics and info if you are interested!

liam

[Edited on 22/7/04 by liam.mccaffrey]

hi liam, just a few comments since ive been thinking middy myself at times!

firstly, i would drop the transmission tunnel, as there is no need for strength here. Any brake pipes and wiring i would just make a minimal fibreglass cover for. I would use foam instead of seats, glued directly to the floor, to keep weight both minimal and low. you can afford to be low cos theres no engine to see over. ditto book front suspension dimensions, it makes life much easier. without a transmisson tunnel and with basic seats you can have a narrow cockpit, leaving more room for reinforcement (if thats your priority) or intakes for the radiator/engine.

if i think of any more, i'll add it later!

I'm not sure if the tunnel doesnt add strenght in terms of twist,could be wrong though

when i saidtransmision tunnel i meant minimal, as per you suggestion of fibreglass cover, also i am making a seat out of foam as you suggest i am a big guy i need all the room i can get.

this is really good ie lots of feedback and thoughts from others, it feels like the plan is really coming together, coupled with the fact that i have collected virually all of the required components all that is left now is a lot of blood sweat and tears!

thanks

quote:

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Originally posted by Cita
I'm not sure if the tunnel doesnt add strenght in terms of twist,could be wrong though

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That's one reason why I build an enclosed car, since a roll cage structure is much more resistant to twist since the tubes are so far apart.

today i printed out a full size cad side elevation of the car to put on my garage wall. its the seven based middy cymtriks designed, will post photo soon

i think this will help me design the chassis as it has given me some overall dimension as well as wheelbase
which is 2323 by the way