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Old 14th November 2010, 08:44 PM
Wynand's Avatar
Wynand Wynand is offline
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Default Custom Front Suspension

My build is McSorley 442E and except for the basic plans freely available on the net, I build my car from bits and pieces of info found and common sense. The rear suspention is an IRS Rorty design (drws in error - another thread on that later)
Since I had no "book" to help out on the front suspension, I designed my own and quite happy with the results. I had to scarp a set of top WB's though to get things perfect

The front uprights are Mk5 Cortina units and the bushes and inserts I made on the lathe since I made all the WB brackets a bit wider than the normal 42mm ID ones at 50mm ID for more meat to weld on the tubing.
Although I have a 200A inverter MIG, 180A inverter TIG welding machines in my garage, I opted to weld all the WB's with an Inverter DC arc welder using E316 welding rods. This in my opinion is much stronger than TIG if well executed. All the welds on my WB's are untouched by a grinder.

Here are the logic and numbers achieved with the suspension - measured with a very sensitive and accurate magnetic master ProMac level.

Since I used Cortina uprights and they have a large scrub radius and relatively little KPI, a lot of though had gone into the end result.

Camber: Wheel set at 1 degree negative with rim / tire fitted and 155mm ground clearance.

0 - 50mm bump: zero camber gain or loss
60mm bump: camber gain 0.3 degree negative

0 - 50mm droop - camber static with no gain or loss.





Caster:

Set at 7.25 degree positive which gains negative camber rather quickly but not excessive when cornering and in my personal view the only time one would want camber gain/loss. Should track straight and true with the caster and trail with easy self centering.



Steering:

Zero bump through the 60mm up and 60mm down range - measured with sharp fixed rod to inside of tire going up and down.
This took a lot of effort to achieve - three brackets rejected, tacking, loosing etc. A software program gave the height of rack centre from chassis 73mm and actual is 76mm. What influenced the bump quite a bit was the forward or backwards movements of the rack at the set height and software does not give this. BTW, an Escort 2 rack is used.

The wheel in the pics is a temporary 14 inch whereas the car will sit on 15 inch rims when completed

No shocks/springs fitted yet since Im not paying the close to 800 pounds asking price for a set of GAZ units here....
Im fabricating my own adjustable coil over gas shocks and will post pics of how to and results later when its done.

Below a few pics of suspension parts attached.

Can I have opinions on this suspension and like to hear it straight. I consider criticism as constructive to improve upon.
Attached Images
File Type: jpg Lotus 7 002a.JPG (63.6 KB, 72 views)
File Type: jpg Lotus 7 004a.JPG (64.0 KB, 62 views)
File Type: jpg Lotus 7 006a.JPG (67.8 KB, 55 views)
File Type: jpg Lotus 7 008a.JPG (58.4 KB, 57 views)
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  #2  
Old 14th November 2010, 09:06 PM
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HandyAndy HandyAndy is offline
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Default

Hi Wynand,

I think the work you have achieved without the "book" is very impressive indeed, to work from plans only available on the "net", which having looked at the said drawings sometimes don,t give vital info, the result of your construction is to be highly commended

I,m not a suspension set-up expert, but may I say the one thing that caught my eye was the angle of the steering rack outer arm position appears quite extreme, thats not said in a negative way, as I,m just comparing it to the position in the "Book" for the Roadster, do you have adjustment of the actual steering rack main body where its clamped to the chassis to lessen the extreme angle? just a thought.

Look forward to seeing more photos of your build

cheers
andy
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Old 14th November 2010, 09:36 PM
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Wynand Wynand is offline
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Thanks Andy,

The steering rack arms do look a bit odd, but that is the position I achieved zero bump. Moving it forward - and it can only go about 30mm then against the frame front upright - induces toe out when bumped.

I thought of modifying the steering rack bracket to move forward or backwards and will perhaps do it just in case...
The chassis is only primer coated after blasting since I still have to fit engine mountings, the gearbox tunnel (done) etc before epoxy coating the frame for final assembly.
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Old 14th November 2010, 09:49 PM
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HandyAndy HandyAndy is offline
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If you have that much adjustment then maybe you could find a "happy compromise" of the bump versus toe out, I would imagine from looking at the photos only ( not with measurements to hand etc) that even a small adjustment wouldn,t create a too extreme on the toe out, maybe could be dialled out a little with some clever steering rack extensions .

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andy
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