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In the 1960’s, when I was racing my GT350 R Model, we started improving the suspension in 1966, the second year that I had the car. Changes to the front alignment were experimented with. We only ran Firestone bias ply road race tires. Mostly, we worked with the rear end. Tire size, spring rates, sway bar & panhard were changed & tested. And, of course, we tweaked the front & rear Koni shocks. But, before we were done, the car had completed its mission and was gone.
Starting in 1987, when my son, Chip, & I got into the vintage race game, we built the first three cars essentially following-on from the 60’s set up. Since we decided to build the cars to the 60’s SCCA rules, it didn’t take long to realize that we would need improved performance to be competitive against other vintage cars. Since the 289cid engine and brakes were frozen to the 60’s rules, we looked to the suspension to make the cars more competitive. Having been an experimental test engineer back in the 50’s at Ford, specializing in ride & handling, helped.
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The key to being competitive, with less horsepower and original type brakes, was to improve speed in the corners, or “ maintaining good momentum”. I insisted that we end up with a front suspension that would be optimum, but meet the 60’s rules. Therefore, we couldn’t use modern bolt-on goodies and spherical bearing joints. The control arms and strut rods had to be original 60’s.
Following are some of the other front-end criteria that had to be optimized:
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- System that provides minimum driver effort, necessary for this ”Ole Kooter”.
- Tracking under acceleration with front-end rise.
- Steering stability & tire to pavement adhesion during braking and front-end dive.
- Ease of initial turn in to corner.
- Balance of oversteer/understeer during entry into and exit from corner.
- Maintaining maximum adhesion during front-end dive, roll & lift, while in the corner.
- Lateral weight transfer in corners & its effect on front tire to tire temperature balance.
- And, all of the above, while in both high speed sweeping and slow speed tight turns.
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We did a number of things to get a base line of data from which to base our work. We acquired a G Analyst in the early 90’s to give us lateral and in-line acceleration. And we picked up a portable set of alignment tables.
At the track, we varied tire pressures, alignment and tire pressures, checking results with the G Analyst.
Probably, the most important things done, were determining the limits of frontend rise and dive and roll angle. We got this information by taking measurements from photos taken at the track tests and then duplicating the positions in the shop without the front springs on the cars. This information gave us the attitude range that we were working within. Outside these limits, we didn’t care what happened to the alignment.
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In addition to all the above, we wanted to run up to 8 ½ inch wide wheels as allowed in the SCCA PCS and GCR for the Shelby GT350, starting in 1966. We also had to consider both radial and bias ply tires. Due to the higher weight, the coupes used Radial tires. They also ran on 8-inch rims.
In an effort to reduce variables, early on we decided on front springs. We use these to this day. It was also decided that the original Shelby front sway bar size was fine. The sway bar torsional stiffness varies drastically with minor changes in diameter. A change from 1 in diameter to only 1 1/8 in will cause a 60% rate increase. We kept working with alignment till we arrived at optimum settings. Then we slightly modified the control arms so that the desired alignment was obtained with no bushing bind. This worked great with poly bushings. Most have been in for years with minimal wear. On the 1965/66 cars it was decided to use modified 1967 strut rods. This allowed using the strut rods for caster adjustment, leaving the upper control arms shims for camber adjustment only. This design has varied little since the early 1990’s. We did adapt the late 60’s heavy-duty spindles with same performance. A freebie benefit from all this was that bump steer had essentially no change over the operating range. We did end up with different alignment for bias ply and Radial tires.
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The proof of our success in this endeavor is in the performance of the cars.
In 1993, we completed the rear suspension design. It has undergone very little since then. Mainly, we only beefed-up some parts to improve wear life.
Walt Hane
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