Hi all
I have pretty much made up my mind and decided to scratch build my next car. I think my welding and fabrication are upto it and i'm fairly happy that i understand the basics of chassis design (basics) but i think i may have fallen at the first hurdle.
How do you decide on the following

Wheelbase
Ride Height ( manhole safe )
Front and rear Track width




thanks agin

quote:

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Originally posted by Julian B
Hi all
I have pretty much made up my mind and decided to scratch build my next car. I think my welding and fabrication are upto it and i'm fairly happy that i understand the basics of chassis design (basics) but i think i may have fallen at the first hurdle.
How do you decide on the following

Wheelbase
Ride Height ( manhole safe )
Front and rear Track width




thanks agin

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for the sake of an argument you may as well have the same track front and rear unless donor items force differently. 'they' say that 1.6 is the ideal ratio for wheelbase to trackwidth, no idea as i didnt work it out myself. Ride height depends on your local conditions. I feel round leeds i could get away with 100mm at the front, 125 at the back (bit of rake is good).

Don't know if its still in print, but if you can get hold of a copy of:- "Designing and Building Special Cars" by Andre Jute, it will answer all of your questions. Deals with all aspects of design very fully. HTH Ray

Local library may be able to get you a copy.

[Edited on 26-3-07 by Chippy]

You can still pick copies up for between £10 and £25 plus postage form various sellers. Mainly in the States.

The wheel base - track issue is not that big a deal.
Just choose an existing vehicle that you think is close and use that to start.
In the end it will end up as wide as you think is sensible and no longer than you need to fit everything in and try and get the C of G where you want it.

Difference in front to rear track is used to typically to try and promote under steer in vehicles that want to over steer which is most middies. The difference typically is not that much I think it is ~20mm for the Ford GT for example. So its within the range of adjustment that can be achieved with different offset rear wheels if required when it comes to testing.

Ground clearance at ~125 appears to be the way to go but with the car you already have you have an ideal way to test this by gluing polystyrene or some such to the bottom of it and see if it gets knocked off.

quote:

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Originally posted by Julian B
Ride Height ( manhole safe )

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Wheelbase and track will depend on what you want from the car....

Odviously both are dependant on the size car you are planning however the longer the wheelbase in relation to the track the more stable the car will be at speed..... however the small it is in relation to the track the more pointy it will be in the twisties (as well as more twitchy example is a lotus elise).

There are however a complete ream of other things that are also going to effect the dynamics so you really want to decide what kind of car you are going for before you settle on anything as some things will be a compramise.

Ride height will be practicality driven and also dependant on you body shape.... a long nose = more ride height for example.

My Ultima had 90-100mm under the front splitter... my car is going to be 110-120mm.

ride hight in concern to speedbumps is very much dependant on wheelbase.

a long luego needs to be much higher than my litle striker,

I have 90mm in the front (sump sticking out 1.5cm below that) and 105mm in the rear, only once had a problem on bottoming out but the steel sumpguard caught the damage perfect, minor scratches)
I can go over pretty high speed bumps with 55km an hour without touching

grtz Thomas

Thanks for all the info

Just one other question. If i'm using donated uprights does the anle of the track arms matter?

I remember at school we built a gocart in metalwork ( Showing my age now ) and the track arms were pointing to the centre of the rear axle. If this is true then is the wheelbase set by the uprights you use?

Cheers again

My next project will be 75mm
I am waiting for it.....
At times it will be up to 150mm or even 0mm !
I am fitting air shocks with a compressor plus titanuim blocks under the chassis incase I spring a leak!!!

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Julian B

I believe what you are referring to there is Ackermann steering basically no you don't need to worry about that for any thing other than slow speed vehicles.