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Learning how to build Lotus Seven replicas...together!
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PostPosted: Mon May 19, 2008 11:01 pm 
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Joined: Mon Aug 15, 2005 10:13 pm
Posts: 7048
Location: Charleston, WV
This is something that gets asked about a lot. I thought I would start this thread to condense the knowledge we have about it from different threads. Feel free to add to it if you have useful knowledge.

Specs:
Wheelbase 56.8"
Weight: around 40 lbs. (est)
Weight with A arms: 60lbs. (est)
Roll Center: 2.6"
Chassis points:
Upper: 15.12 Width, 15.25 Height
Lower: 9.75, 8.0
Upright points:
Upper BJ: 24.85 Width, 16.21Height
Lower BJ: 26, 8.0

Considerations when using the Miata rear SF:
It will lengthen your wheelbase, how much depends on ride height.
See pic below for a visual explanation.


Attachments:
longerwheelbase.jpg
longerwheelbase.jpg [ 66.84 KiB | Viewed 2452 times ]

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PostPosted: Tue May 20, 2008 12:30 am 
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Joined: Fri Aug 10, 2007 12:05 am
Posts: 601
Location: Champion, Ohio
I never thought of measuring the rear end of my build until it was too late. Basically, anyone using the Miata subframe has to consider the fact that they will be fabbing the entire back end themselves. I just built what looked right; I saw some pictures of Mark Rivera's build, and the Rorty plans, and from looking at those, I plowed on, simply measuring to make sure everything was identical on both sides.

One thing you might want to consider is using hard differential bushings--I bought an steel set from Rivera after seeing them on his photo site.

http://www.locostusa.com/forums/posting ... ply&t=3843

http://kit-car.org/Files/suspension/Ror ... sembly.pdf

Although the wheelbase might extend a little (Mine is 97.5", if I remember correctly), I think the overall length is about the same, as I have a pretty short back end.


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PostPosted: Tue May 20, 2008 12:33 am 
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Joined: Fri Aug 10, 2007 12:05 am
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Location: Champion, Ohio
Oh... one thing that would be nice to know is what thread pitch those four mounting points on the bottom of the subframe are. Mine is welded inside the frame, and I have no clue what thread they are. I have an aluminum plate covering the bottom of that and bolts to those four points. I currently just have smaller nuts and bolts holding it in, but it'd be nice to utilize the nuts welded there from the factory.

Anyone?


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PostPosted: Tue May 20, 2008 1:27 am 
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Joined: Fri Feb 29, 2008 7:15 pm
Posts: 151
Location: Denver, Colorado
Actually, if you look at my chassis pictured above, I welded the rear bulkhead upright flush with the outside instead of moving it in an inch for the rear live axle set up, so I have room to move the Miata subframe in if I would like to. I am still working out the details...


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PostPosted: Tue May 20, 2008 1:10 pm 
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Joined: Fri Feb 29, 2008 7:15 pm
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Location: Denver, Colorado
OK, I figured out what you meant. The subframe can't protrude into the cabin past the rear bulkhead, which it would need to do to get book wheelbase.

So then the question becomes, does it matter? I know the classic Mini did better in pick-up form as an autocrosser because of the longer wheelbase. Does anyone have experience comparing both types?

Randy


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PostPosted: Tue May 20, 2008 2:22 pm 
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Joined: Mon Aug 15, 2005 10:13 pm
Posts: 7048
Location: Charleston, WV
From reading Staniforth I recall a longer wheelbase being good for stability, especially at speed. (probably good for an open track car) However it should also make the car a bit less nimble through the autocross course as shorter wheelbases are good for transitional maneuvers.

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