Daily Archives: November 9, 2021

Forcing myself to actually care about something

I think that’s something old people have a problem with, finding something to actually give a shit about as they get older. Also I’m dealing with something that’s making my damaged hip hurt, so there’s that, too.

What I have been thinking about for something to do is looking up stuff that might be useful for building the Sprint-T. The price of that upgraded T5 transmission is $3600, this week. But it only weighs 77 pounds, 2 pounds more than the stock T5. That’s pretty good for a 67% increase in rated torque capacity from 300-500 pound-feet. Most of the increase in capacity comes from upgraded materials, with the rest from slightly larger gears.

While I was it it I also looked up the weight difference between the straight axle and the independent front suspension. Actual weight on the tires is about the same, but the ratio of sprung to unsprung weight change is huge, mainly because each wheel only has half of the unsprung weight as opposed to both wheels having all the unsprung weight with the straight axle. If I got my sums right the independent suspension is 5 pounds more than the straight axle, with most of that in the frame where the suspension attaches, brackets and bracing not needed with the straight axle.

There’s also a bit more weight for the moving parts in my design because I like to have the lower arm almost a center pivot with pretty much no change in track with suspension movement. That means there will be some bump steer as the instant center moves during suspension travel and the tie rod can’t point at the point where a line drawn between the upper and lower control arms intersects so it has a different arc than the place where it attaches to the spindle. That also means the lower control arm goes halfway across the car, which makes it heavy. I’m still thinking I want to make the lower arm shorter than that just to reduce weight because it doesn’t make that much difference for the geometry of the front wheel travel. But I’ll have to buy some suspension CAD program to play around with the suspension arms to see where the crossover point between long and short control arms is for the Sprint-T.

And for everybody who reads the tags, the weather today has been wonderful, warm enough to not require heat, but cool enough to not require AC. We get about 2 to 3 weeks like this twice a year here, and we just bask in it. The electric bill is almost nothing as we only have to pay for keeping the water heater going for showers and dishes and washing hands.