WTH Spider Rear Racing Suspension!

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ST3Racer
Posts: 81
Joined: Mon Jul 09, 2018 12:34 am
Last Name: McMahan
First Name: Bill

Re: WTH Spider Rear Racing Suspension!

Post by ST3Racer » Mon Aug 12, 2019 11:23 pm

Andy,
Mounted how, exactly? Inboard of the long arms? Attached how? Or concentric? I am having trouble concepting this.
Bill McMahan
Parker, Colorado
'69 124 Spider 2L ex EP racer, ex Volumex NASA ST3 Racecar - retired
'69 rebodied with '79 backdated chassis as '72 DP 1.8L Vintage Racer
'74 124 Abarth Stradale Replica
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rridge
tremila club
Posts: 3609
Joined: Sun Jan 24, 2016 9:18 pm
Last Name: ridge
First Name: richard

Re: WTH Spider Rear Racing Suspension!

Post by rridge » Fri Aug 16, 2019 5:05 pm

The double trailing arm mod was popularized on the West Coast by Dave Voss and others. A second set of lower arms is mounted on the inside of the stock arms by doubling the length of the mounting bolts and cantilevering the additional arm on those longer bolts off the inside mounting brackets.

I ran the set up on my street Spider for several years to reduce the understeer in a way similar to a rear anti-sway bar. The bushings in the trailing arms absorb and resist the twist created by the body rolling side to side while the axle remains parallel to the ground. Most of that resistance is generated by the bushings. Twice the number of bushings gives twice the resistance to rolling.

I found the mod made a nice reduction in understeer for the stock suspension in my '81. After I lowered my car moderately and went to stiffer shocks the rear end became a little too loose for street work. The nice thing about the mod is that it is completely reversible. There is a picture and more info at this link: https://www.flickr.com/photos/rridge/69 ... 018311651/
Richard
'81 Turbo Spider
Rockville, MD
ST3Racer
Posts: 81
Joined: Mon Jul 09, 2018 12:34 am
Last Name: McMahan
First Name: Bill

Re: WTH Spider Rear Racing Suspension!

Post by ST3Racer » Sat Aug 17, 2019 1:41 am

NOW, I understand. Interesting. Using stiff springs, and stiff adjustment on the KONIs, gives me the balance I need on both the street car, and the racer. On sweepers, both cars are neutral, and on tight corners, it can be made to drift a bit to get the rotation needed to make the corner. Power on the street is calculated at about 150 crank, and the racer is about 200 crank. I run a 25mm front bar, and no rear bar, on both cars. I have found that any rear bar makes the handling unpredictable, so I make sure that the stiffness and balance of the springs gives the handling that is needed, for quick laps, or fast mountain driving.
Bill McMahan
Parker, Colorado
'69 124 Spider 2L ex EP racer, ex Volumex NASA ST3 Racecar - retired
'69 rebodied with '79 backdated chassis as '72 DP 1.8L Vintage Racer
'74 124 Abarth Stradale Replica
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