Daily Archives: September 25, 2020

More thinking about the Sprint-T

Just because I’m not working any more doesn’t mean I can’t stay awake at night and think about things on the Sprint-T. On the contrary, now that I don’t have to think about working, I can think even more about the Sprint-T. And because I don’t have any budget to build things I can think about how to do things as cheaply as possible.

I was thinking about how many turns lock-to-lock the steering will have with the shorter steering arm on the spindle compare that to other methods of changing the ratio. OK with just changing the steering arm on the spindle the turns lock-to-lock won’t actually change unless something in the steering hits something before the steering box hits its internal stops, but the front wheels will turn twice as far for each turn of the steering wheel. But since the front tires can’t turn anywhere near as far as the box can try to turn them, assume a stop in the system limits the travel, so how many turns lock-to-lock can we get from the system instead of the box?

The 20:1 box has 5 turns lock-to-lock by itself, moving the pitman arm 90° of arc. That’s 45° left and right of center, which is pretty decent angle but not great. But 5 turns lock-to-lock is terrible. So the problem then becomes how much angle to allow vs. steering wheel turn. Doing the steering arm half as long as the pitman arm gets 180° of movement which has already been categorized as “too much”, but the total ratio is “not quick enough”. Seriously this will be a huge improvement, but still not quick enough for the autocross racing the car is intended for. But at the double throw, the overall ratio is 10:1 at the tires, with 2½ turns to get the stock 45° of steering movement. Now if I restrict the angle at the front wheel to 120° of lock which is way more than what I get with the steering arms from Speedway (which are designed for freeway driving and cruising around a fairground car show, not racing autocross so nothing bad about that) I still get 31/3 turns lock-to-lock, which gives the equivalence of a 131/3:1 box with everything set to “out of the box” in the steering linkage. The really annoying thing about making this post is I have one word “wheel” that refers to two completely different things, and trying to disambiguate the difference between the steering wheel and the wheels the car drives on. I had to go back and change a few words back and forth.

Anywho, I can rapidly change the overall ratio at the front wheels by making a new arm with the distance from the steering axis of the spindle to the pivot point of the arm closer or further away. I should probably make at least one arm with several pivot points to see how the turn-in of the car changes, then build one arm to not have a bunch of holes in it and be neater for appearance. And I should also be looking at what’s available in angle iron to see what I will be working with to build the final arm. But this seems a good place to put this to bed, and maybe myself as well.