I walked 2.29 miles (3.68 km) going to get my toes done, buy breakfast sausage for cheap$1.67/lb, drop by the ATM for Mrs. the Poet, and get a Whataburger and fries. Then I took a nap. Whoo! living the life.😑
Still thinking about the TGS2 because what else would I think about if I wanted to stay sane? Since the part I didn’t have totally nailed down before I was still thinking about getting that upper coilover mount figuratively nailed down in every plane and triangulated against flex. Basically the plan is to run tubes from the upper and lower frame rails to the upper mount from two verticals between the rails, one vertical right in front of the firewall, and one just in front of the axle. The bottom of the upper rail will be 1.5″ (3.81 cm) plus the thickness of the bump stop, that I haven’t sourced yet, above the tube of the axle. The bottom rail will be 7.5″ below the center of the axle at intended ride height, or 6″ (15.24 cm) measured to the top of the rail, with a bracket coming from the rail to support a droop stop 1.5″ from the bottom of the axle at normal ride height. Yep, that comes to 3″ (7.62 cm) axle travel at the frame, which is normal for a T-bucket front suspension. What’s not normal is to control the axle with both bump and droop stops, normal is to use the shock absorbers for this function. But it really tears up a shock to use it as a droop stop and even worse to use a shock as a bump stop without an external stop fitted over the shaft. Basically without an external stop the shock piston slams into the foot valve and after a couple to a few times of that happening you no longer have any dampening control over the axle travel. So belt and suspenders there will be a bump stop on the coilover, and another on the frame.
Now where the frame leaves the front of the body the top of the top tube is 17″ (43.2 cm) from the bottom of the bottom tube, leaving 7″ from the top of the axle to the bottom of the top tube, lots of space to mount a bracket and bump stop and still leave 1.5″ for travel up. In fact good design principles require less than 1.5″ clearance between the bottom of the bump stop and the top of the axle so that there is enough travel to cushion the axle before reaching the limit of the shock and slamming into that foot valve. It might touch the valve but if I do my job as an engineer there shouldn’t be enough force to damage anything.
Now one of the problems I’m having is getting springs light enough for the front end because there is so little weight on the front end with the mid-engine configuration, without installing ridiculously long shocks. The shortest shocks I can find that will hold the springs are nearly 20″ long extended and 13″ compressed. The issue is the free length of the springs, and there has to be enough extended length to get the spring in place without compressing it so the adjustable seat can be spun on by hand so it doesn’t get cross-threaded. The problem is the shock has to mount as close to the kingpin as possible to control the single-wheel motion, and I need to limit wheel travel to keep the TGS2 from turning into and off-road buggy and to control camber, body roll, and prevent the frame from crashing into the ground. And the weight situation is we are talking about a car with a race weight around 1300-1400 pounds with more than 60% of the weight on the back and about 240 pounds per wheel on the ground and less than 25 pounds on the spring. It doesn’t take much spring to control that little weight, but a lot of shock dampening to control the unsprung mass. The sprung/unsprung ratio is almost off the chart for this car. It’s not bad in back, but there is just too much previously bought parts weight up front that isn’t resting on the springs. And seriously, all that weight just in the front axle and suspension does a serious negative to polar moment.
Looking at the numbers makes me seriously question my tire choices for the street setup because each tire weighs 31 pounds, without the 24 pound wheel. Fifty-five pounds is a ridiculous amount of unsprung weight per corner for a 1300 pound car with more than 60% rear weight distribution. Seriously the wheels and tires together weigh more than the rest of the front end minus suspension.🤯 Also I need to move more stuff forward of the center of the wheelbase, to keep the weight more forward and also keep the polar moment low. Also, seriously, this will probably raise the car weight more than a little. The race tires are a little better at 23 pounds each and the aluminum wheels are about 20 pounds going by shipping weight. So that’s a huge chunk off the unsprung weight.
And I have been thinking about the TGS2 in street rod parameters rather than mid-engine sports car parameters because Goodguys is a street rod and muscle car sanctioning body. Thinking in the proper terms gets the tire weight down to 20 pounds and the wheels are a smidge lighter at about 18 pounds. Still more than the sprung weight for each corner… I seriously need to redo my weight estimate because of how heavy the front axle, brackets, and spindles are. I’ll ponder my calculator and weight charts more now that I have weighed the parts I have on hand and use known weights whenever possible and get back to you later.
Witch on a Bicycle 