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 Post subject: Fwd struts in the rear
PostPosted: April 24, 2018, 9:01 pm 
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Anyone using fwd strut assemblies in the rear for an IRS setup?


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PostPosted: April 24, 2018, 9:34 pm 
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Colin Chapman used them in quite a few different cars. When struts are used in the back I believe they are called Chapman Struts for that reason.


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PostPosted: April 24, 2018, 9:44 pm 
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That’s a nice bit of history info. Yeah, i knew they were used in the Elans but was wondering if anyone had integrated any into Locost chassis. Thinking about doing just that with Miata fronts and 323 fronts used in the rear with a coil over style strut.

J


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PostPosted: April 25, 2018, 11:01 am 
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It has been done on a few Mid engine builds but I cannot recall seeing it in a traditional locost frame. The biggest problem that people run into is that production car struts are too tall. if you look at the height from the top of the tire to the top of the strut tower and compare that to the height from the top of the rear tire to the top of the frame on a Locost you will see the issue. If I remember correctly om my Locost it is only around 4". That is about where the bottom of the spring starts on a normal strut. You would have to find a vehicle that has extremely short struts and also aftermarket coil overs that would allow an appropriate damping and spring rate for the rear of a Locost, maybe around 180-200 lbs/in vs 400-500lbs/in for a stock FWD car. That is why people tend to stay away from using struts. If one can find a strut that matches that description then I don't see why it wouldn't work.

Looks like some of the aftermarket rear struts for a mid 90s Protege are pretty short. I'm not sure if they would be short enough, or which one in the photo is the front or the rear.


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PostPosted: April 25, 2018, 12:11 pm 
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Going back to 2009 with our site's search engine....... You will see the obvious packaging problem if applied to a traditional Locost body.

viewtopic.php?f=18&t=6280&hilit=chapman+strut&start=30


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PostPosted: April 25, 2018, 12:15 pm 
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Right, just seeing if anyone has done one for reference. Funny you should post the Ksport assemblies as I’ve been talking with them on a custom setup. Never ran any Ksport suspension though and questioning durability and function.

J


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PostPosted: April 25, 2018, 12:17 pm 
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rx7locost wrote:
Going back to 2009 with our site's search engine....... You will see the obvious packaging problem if applied to a traditional Locost body.

viewtopic.php?f=18&t=6280&hilit=chapman+strut&start=30


Yeah, that’s the problem I’m facing is overall height of the strut assembly and shortening of the rear Miata axles.

J


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PostPosted: April 25, 2018, 1:57 pm 
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Strut height I can't help with.

As for shortening the rear axles, Not a problem. I'll suggest you read my build linked below. I cut out 2" of my rx7 axles and spliced with a sleeve. This same technique or slightly modified, has been used successfully by a few builders here.

viewtopic.php?f=35&t=4145&start=37

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PostPosted: April 25, 2018, 2:56 pm 
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Nice, i was thinking about sending them out to be cut down and resplined


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PostPosted: April 25, 2018, 4:19 pm 
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Daddyj, I think you're in luck as to the FWD struts in the rear. Take a look at the "Goblin" http://dfkitcar.com/ ! It's a middy that uses the drivetrain, along with the struts, from a Chevy Cobalt. We have a couple of guys bringing a Goblin to the gathering in Mountain Home, Ar next Month!

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Last edited by ngpmike on April 25, 2018, 11:27 pm, edited 1 time in total.

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PostPosted: April 25, 2018, 6:54 pm 
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Daddyj wrote:
Nice, i was thinking about sending them out to be cut down and resplined

Cut and resplining works only if there is enough meat on the axle to cut new splines into. If the miata axles reduce the diameter as soon as it clears the CV boot, then it will not be possible to cut and spline. My RX7 axles were like that. You can see the transition in my pics.

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PostPosted: April 25, 2018, 7:15 pm 
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See OzGecko's build log at

viewtopic.php?f=36&t=3241

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PostPosted: April 29, 2018, 3:31 am 
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Daddyj wrote:
That’s a nice bit of history info. Yeah, i knew they were used in the Elans but was wondering if anyone had integrated any into Locost chassis. Thinking about doing just that with Miata fronts and 323 fronts used in the rear with a coil over style strut.

J


If you are planning on using Miata front hubs in the front, why not just use Miata rear hubs in the rear? This is the most popular/common way to get an IRS setup on a Locost, and there are many builds doing it this way, which are also using the Miata rear differential, and sometimes even reusing the Miata rear lower and upper control arms.

Just to clarify, are you planning on building a conventional front engine Locost? The examples given above which use FWD struts in the rear of the car are typically for mid-engine applications, where the entire FWD drivetrain and strut suspension is moved to the rear.

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PostPosted: April 29, 2018, 3:38 am 
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Daddyj wrote:
rx7locost wrote:
Going back to 2009 with our site's search engine....... You will see the obvious packaging problem if applied to a traditional Locost body.

viewtopic.php?f=18&t=6280&hilit=chapman+strut&start=30


Yeah, that’s the problem I’m facing is overall height of the strut assembly and shortening of the rear Miata axles.

J


Is the reason why you are planning on shortening the rear axles to prevent the rear wheels from sticking out too far from the body? If so, is widening the body an option for you, such that you could use unmodified full length Miata axles and not have the rear wheels stick out too far from the body?

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PostPosted: April 29, 2018, 10:00 am 
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I’m still in the planning/parts gathering stage. I do have Miata and 323 knuckles as well as Miata viscous lsd. Yes, I’m running into issues of having to shorten the axles and running beg offset wheels due to strut mounting and knuckle design. I want to use the fwd 323 knuckles and strut in the rear as to simplify the rear with struts and 2 control arms instead on 4 plus shock mounting. As well I’m going to be using the Westgarage MX5 chain driven conversion as not only for weight savings but to also use the LH offset of the chain for more cockpit space. I’m using a blueprint of a 7 S2 (small chassis) rh drive but using “book” building techniques.


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