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Old 29th October 2011, 10:09 AM
hyperbodger hyperbodger is offline
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Default Chassis Design

This could well be a "light the blue touch paper and retire" thread, and apologies if its covered elsewhere (I'm new to the forum, just starting the build and am still finding out where things are located on the site)
I'm intending to use round rather than RHS tube - I know its more difficult but I've got a milling machine and linisher so fishmouthing the tube is just effort rather than cost.

Out of interest I've done some analysis of chassis designs and was wondering what the position on "chassis development" is. There's a really good argument for "if it ain't broke don't fix it" and that the current chassis design works well, is relatively straight forward to build and is cost-effective. My question is - Is anyone developing or thinking about designs which could increase stiffness, reduce weight etc? The question arose in my mind after I'd hired a Caterham for the weekend (just to prove that my 40-odd year unfulfilled interest in Lotus 7 type cars shouldn't just be left as a pipe-dream) and discovered that there are substantial differences in their latest offerings and earlier ones.

Just for the record - I'm using round tubing mainly because I think its slightly stiffer for a given weight, have spent a considerable amount of time learning to weld it and (main reason) have always wanted to and want to see if I can do it.

If anyone is interested in looking at chassis design, weight, stiffness, actual results compared with design calculations etc. I'd be interested in working with them.
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Old 29th October 2011, 10:29 AM
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twinturbo twinturbo is offline
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I think the weight saving will be marginal as you will have to increase the tube diameter to match the strength. If not already done then I would look at data to find out what diameter and wall thickness of tube matches or exceeds that of the 1.6mm 25box.

Apart from that, and the complexity of ensuring the dimensions are correct the only other major issue is that round tube is more difficult to fix things to.

There is scope for development of the design, and in a way that has already hapend with the MX5 chassis. If using round tube there is also a lot of scope for using 1 piece tube bend sections for various parts of the chassis reducing the number of welds required.

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Old 29th October 2011, 11:05 AM
robo robo is offline
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Cant think of any advantage there. Stuff like all the ali panels are far easier to attach to square as are suspension brackets ,nose cones , engine /gearbox mounts and just about everything else. Nice thought though

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Old 29th October 2011, 11:12 AM
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vmax1974 vmax1974 is offline
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I seem to remember a while back someone was talking about this and when they calculated the weight saving on the chassis alone it would have been about 25 percent lighter for the same stiffness but like twinturbo said hanging things off it may be a different matter I was thinking of just using round tube for the bracing parts did a search a while back for tube benders that you could make yourself and came across a contraption that uses the rear hub off a mk3 fiesta and a long length of bar dont know how well it would work but may be worth a try I will post a link when I get home tonight
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Old 29th October 2011, 01:17 PM
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I agree with you Talon, To make a car go faster, just add lightness. Colin Chapman.
Be Lucky, Mike.
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Old 29th October 2011, 09:26 PM
MarkB MarkB is offline
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Bent tubes are bad, short welded tubes are stronger. For an example look at a Ducati 916 frame.

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Old 1st November 2011, 11:11 AM
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vmax1974 vmax1974 is offline
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sorry i was slow in this been busy here is the link http://www.thefont.info/tubebender/tube_bender.htm
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Old 4th November 2011, 04:50 PM
Tilly819 Tilly819 is offline
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I wrote a program that compares tube and box sections for stifness in bending and torsion also restance to tension and compression and a comparison of weight. if you want direct comparisions between various tubes/box's let me now the sizes and i will enter the figures

hope this helps

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Old 16th November 2011, 04:34 AM
danilo danilo is offline
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Do a wee bit of research and you will find that Lotus and Caterham use 16ga and 18 ga tubings.
Much lighter than the DIY crowd typically uses for their builds.
Apparently the demonstrable benefits of chassis designed by good Engineers
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Old 16th November 2011, 12:11 PM
TQ_uk TQ_uk is offline
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There's a section in this book:

about square/tube comparison - will see if I can remember to have a look tonight & paraphrase it.

Tilly, if you can put up tube 'equivalents' for the usual box section(s) used that'd be great e.g 25mm @ 1.6mm = ?, 25mm @ 2mm = ? etc. Though rest assured we won't hold you accountable
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