Steering turns issue

[dreracecar]

Caster changed when the tires changed--front runners will work with less because of their flat profile and compound verses an Avon speedmaster which has a round profile and needs the extra caster to roll around the tread.

[32bantam]

40.......man that is a BUNCH!!!! I don't think a shopping cart has that much!!! lol
15 is usally enough for most cars...but I will let Roo chime in.
Steve

[wideopen231]

All three of my P & S boxes  must be different then as when I center the arm inside the box, turning the sector shaft until it runs out of travel turns the input shaft the same amount in either direction--starting at 12 o'clock it ends up at 10 and 2 o'clock. If the pitman arm is mounted at 90 degrees to the steering column rather than at 90 degrees to the drag link, that will have an affect on the amount of right and left lock depending on the angle of the steering column relative to the drag link.. Not having the steering arm on the spindle at right angles to the drag link will have the same effect. I did not pull the worm gear out of the box to check the helix on the worm but even it that varied from end to end it would simply change the steering rate, not the total travel.

Roo

So wich woul give best steering RoooMan 90 to shaft or 90 to link?

[rooman]

I used to watch the big show cars back up after burnouts and see some pretty alarming-looking front-wheel wobble. At the time I wondered why no one seemed to get all upset about it, just went on about their business and made the pass without the fronts falling off. Upon getting my FED bout 10 years back, and having the wobble thing happen to me I understood what was going on, that the caster that made it stable going forward did the opposite in reverse, especially if you let speed build and get too far from straight at the same time. "Oh-Sh*t" moment but no broken wrists or otherwise. So just keep speed moderate and no wild steering and all is well. It's not like I'm backing up from half-track, anyway.
 Just for grins, (not feeling the need for sh*ts), me and the kitten just went and measured the caster on my car, it reads 25' on one side, 28' on the other.
 Evidently, old-school thought was that more was gooder, seems modern thought might be that less is more, or at least that less is enough.
 Any expert opinions on what is optimum? And any relation to wheelbase or anything else?

I normally run 20 degrees on dragsters (front or back motor)and have used anything from 10 to 15 on altereds etc depending on engine placement. FYI most modern top fuel cars are in the 18-20 range and the JFR funny cars were 6 degrees when I was working there.

Roo

[rooman]

All three of my P & S boxes  must be different then as when I center the arm inside the box, turning the sector shaft until it runs out of travel turns the input shaft the same amount in either direction--starting at 12 o'clock it ends up at 10 and 2 o'clock. If the pitman arm is mounted at 90 degrees to the steering column rather than at 90 degrees to the drag link, that will have an affect on the amount of right and left lock depending on the angle of the steering column relative to the drag link.. Not having the steering arm on the spindle at right angles to the drag link will have the same effect. I did not pull the worm gear out of the box to check the helix on the worm but even it that varied from end to end it would simply change the steering rate, not the total travel.

Roo

So wich woul give best steering RoooMan 90 to shaft or 90 to link?

Normally having the link at 90 degrees to the arms is the correct geometry to have symmetrical steering. As the arm moves off center (90 degrees) it will move the link less per degree of travel the further it is around the arc. With a typical 5" pittman arm the effect is not that much but it is there. Most standard steering arms are 6" center to center and thus are a little more sensitive to the angle.  If the link is not square with the arm at the starting point the  travel will initially accelerate in one direction before slowing down while in the opposite direction it will be falling off right from the start.

Roo

[wideopen231]

What I was thinking.I must have miss read post earlier on subject.Man that neve happens!

[janjon]

It would seem to me that the system does not know or care what angle the pitman arm might be to the steering shaft, it cares somewhat or greatly whether it's 90 degrees to the link, with the wheels pointed straight ahead, as regards equal rates and equal travel left and right. Same with front bellcrank, if equipped.
John

[rooman]

It would seem to me that the system does not know or care what angle the pitman arm might be to the steering shaft, it cares somewhat or greatly whether it's 90 degrees to the link, with the wheels pointed straight ahead, as regards equal rates and equal travel left and right. Same with front bellcrank, if equipped.
John

Exactly

Roo

[slingshot383]

Should be able to adjust your radius rods to bring the caster in, and set it the same on both sides.  Once you've done that, recheck your toe-in, try for 1/8" in at front.

[rooman]

Should be able to adjust your radius rods to bring the caster in, and set it the same on both sides.  Once you've done that, recheck your toe-in, try for 1/8" in at front.

With most radius rod set ups it is hard to reduce the caster more than a few degrees through adjustment. Major changes usually mean longer tubes so that there is still sufficient rod end engagement in the radius rod.  The taller the axle brackets are the less effective lengthening the rods will be. With a tube axle, if the caster varies from side to side you are stuck with that variation as moving one side will move the other the same amount.
 On the subject of toe, if you run a bellcrank to turn longitudinal motion into lateral and have an articulated front end (i.e. suspension) you must run from the bellcrank to one steering arm and then from there to the other arm with a link (like an early Ford beam axle car). If you run links from the bellcrank to each steering arm and you have any significant suspension travel the bump steer (toe in-out) will be diabolical. Ask me how I know

Roo

[buickfed]

if I lengthen the rods, it will make the spindle c/line higher, therefore the front end will sit higher. correct? is this a bad thing?

[rooman]

if I lengthen the rods, it will make the spindle c/line higher, therefore the front end will sit higher. correct? is this a bad thing?

Lengthening the rods will actually make the center part of the axle sit lower as the ends of the axle will be swinging up in an arc. Your wheelbase will also increase a bit as the spindle moves forward as well as up (say from 2 o'clock to 1 o'clock). In other words if the wheel/tire diameter stays the same and the spindle is raised relative to the lowest part of the axle the axle has to be lower for the wheels to still be on the ground.

Roo

[janjon]

Ain't geometry wonderful? And widely misunderstood?

[Geri]

I have P&S  steering as well, before I attached the pitman arm I rotated the steering full left to full right ,found the center and marked the steering box and shaft  next to the same spot so I know when the box is centered.
 the pitman arm cannot be straight down unless the steering box is horizontal with the ground-this means I had to have the pitman arm somewhat angled to the rear of the car so the steering box was centered as the wheels were at dead straight ahead, this allows me equal turning raduius left and right, but it's also only a 150" car.
 another issue I dont see many address is the angle of the steering arms off the front spindles.
 the proper  angle should be- draw a straight line through the center of the king pin to the center of the rear end, that string line will show you where the steering arm should attach to the tie rod.
 this ensures  the inside wheel will always turn the proper radius of a shorter turn than the outside wheel. dragsters dont turn? ever see a car a bit loose, turn to correct  and peel the front tires off? ever wonder why?

[denverflatheader]

This red I sold last year to friend of mine.  If you look at right front wheel you can see steering arm does have double bend in it, possibly done to align it with rear end (what Geri wrote)  Don’t know for sure, bought car from second owner in 2003 at chrr, then picked car up in LA on way home, his friend who was there said he had it made for him by Don Long.  That car was so smooth running down the track, straight as an arrow, no steering required.  Probably could have made a pass without a driver in it  : )  DF