Steering linkage set up!

[Scott Hanisch]

Hi to all. I have (from what other members have told me) a 1962 Rupp A-Bone kart that I am currently restoring to lets say "driver" status, and by no means a period correct resto and would like to ask some questions about the steering linkage. As you can see in the pic I have the, what I call short/long tie rod steering and would like to know the pros/cons of this set up compared to the more conventional equal tie rod length set up? How do I and what do I need to convert to the more conventional setup? Thanks for all your info.

[steve miller]

hey thats a good question .. i think its got something to do with akerman ?? or somethin like that ..i no on my karts the ones with two same lenght rods one tire always steers more than the other and it looks funny to me..!!! but maybe its better ..?? i like the short and long set up better ..!! hope someone can clear this up for you ..

[Rob Voska]

Judging by the angles I would leave as is. You have the early kart with a 1/2" steering shaft. Looks like the ratios & alignment would be out of wack if you went to 2 short tie rods.

[Scott Kneisel]

Scott,
Maybe it is an illusion but that rt hand front axle looks like square tubing. Is it square or round?

I agree with Rob, keep the drag link set up on the kart, that is what it was set up with so I would keep it.

Also, Darts never had ackerman steering which causes one wheel to turn more than the other. McCulloch karts have it and most modern karts have it but Rupp didn't utilize it. Ackerman would require two equal tie rods, either mounted in two different positions on the steering shaft OR spindle arms angled in toward the center of the kart. Either one creates the ackerman effect which was made popular for indy cars.

I don't know if it really helps handling any on drifting karts like yours but ackerman does help even out tire wear.

My 2 cents.....Also, Rupp specifies a little bit of toe OUT in the front, try 1/16-1/8". It really helps the handling in my experience.

Have fun and be safe,
Scott Kneisel

[steve miller]

Scott K. when you say rupps didnt utilize ackerman you mean just dart karts . ?? i have few rupps with ackerman .??? (two equal lenght rods ) .my 64 grand prix ,couple a bones and a 300 ... i restored them all by pictures outa magazines .?

[steveohara]

Scott H.

You may or may not have ackerman steering even with a single tie rod connecting the spindle arms.
You can determine if you have it with a tape measure and a couple simple measurements.
Start by measuring the distance between the kingpin bolts. If the kart has no kingpin inclination the measurement will be the same at the top as it is at the bottom. I believe that the Rupp front ends have a little KPI so you should measure the distance between the kingpin bolts in both positions, top and bottom.
If the top measurement is shorter than the bottom you have KPI. Add the two measurements together and devide by two to get the distance between the kinpins at the center of their height.... note that dimension.
Now place the kart so that the front wheels are pointing straight ahead with no toe in or toe out and measure the distance from the center of the hole that the tie rod bolts to on the spindle arm across the front of the kart to the center of the hole in the other spindle arm. (With a single tie rod this will be the same distance as you would get measuring the tie rod from eye to eye in the rod ends) Now compare the two dimensions.
If the center to center distance between the spindle arm holes is less than the average center to center distance between the kingpin bolts that means the arms are pointing in toward each other and would eventually intersect if they were long enough. With the arms facing forward as they are on your kart you would have negative ackerman if the arms point in. Obviously, negative or opposite ackerman is not a good condition.
If the center to center distance between the holes in the arms is longer than the kingpin dimension you would have ackerman which is good and will help the kart steer a little better in most circumstances.
You could split the single tie rod into two sections like you see on the newer karts and it won't change the ackerman effect you currently have (if any) so long as the two tie rods use a common pivot in the middle where they connect to the steering shaft. Modern karts use two pivot points that seperate the ends of the tie rods by about an inch and a half. To increase the ackerman effect on a front steer kart the tie rods have to overlap each other at the point where they connect to the dual mounting positions on the steering shaft.
Even with a hard skinny tire on the old chassis, ackerman can make a dramatic difference in the handling characteristics of your chassis and there is really no way to say you should do one thing or another since tire choice and condition, weight distribution, power levels not to mention driver skill all play a major part in determining how the kart handles.
Try it like it is first and if you don't like it then you can start tweaking it.
OBTW... from the picture it looks like the left front has a bunch of positive camber. If so, you'll want to fix that before you mess with anything else. If you have to bend the axle to get the camber out of it that will effect your measurments from kingpin to kingpin so make sure the front wheels are standing up straight or have very little negative camber before working on the rest of the settings.
last comment... the A-Bone I drive each year at Adams ( Jay Mensoza's kart) had a lot of slop in the kingpin to spindle fit and also in the fit between the kingpin and the holes at the top and bottom of the C brackets. I don't know if that is a common condition on the Rupp chassis but if you have that you'll want to find a way to fix it. We upgraded the bolts on Jay's kart and removed a lot of the problem. Still not perfect like a modern kart with bearings but better than it was.
Regards,
Steve O'Hara

[Andy Symons]

Hi Scott-

Steve is correct but you needn't go to the trouble to measure for Ackermann with your forward steering, single tie rod set up, since the only way you could have any real amount of positive Ackermann would be if your spindle arms were angled outward noticeably. With your setup, lines drawn through the spindle arms (from the tie rod mounting holes, through the center of the kingpins at the same height, back to the rear axle) would have to meet and cross in the center of the rear axle. It's obviously not the case.

Now if your arms are, through design or wear, angled slightly outward, they would provide a tiny bit of Ackermann but perfect Ackermann means that the radii of all 4 wheels' turning circles begin from one point and that can only happen with a single connecting tie rod if the geometry is there as described above. In practice, I don't think there would be room for the spindle arms to angle out that much on a forward steering kart before interference with the wheel/tire would occur.

On a rear steering kart however, with the spindle arms behind the kingpin, the angle of the arms necessary for full Ackermann is away from the wheels, toward the inside of the kart, and 100% Ackermann can be easily obtained with a single tie rod end or an equal length pair originating from a single central mount. In this case, it is very easy to see that the angle of the two spindle arms, if they were extended, would have them meet in the center of the rear axle.

As others have pointed out, with a race machine which has to deal with tire loading, slip angles and traction losses, full Ackermann steering at speed isn't a big deal.

[Dick Teal]

Guys,

Just Google Ackermann Steering and you will find everything you ever wanted to know including how it effects race vehicles.

The Fox satellite seat karts have reasonable steering geometry and we found that they work best with 1/16th toe-in.

What's really interesting is something called bump-steer and most independent front suspension steering is effected by it. It sure is fun keeping things simple with vintage karts. Google bump steer and you will understand.

Dick Teal

[Tom Smith]

What's really interesting is something called bump-steer and most independent front suspension steering is effected by it. It sure is fun keeping things simple with vintage karts. Quote
Like this one? It was the first kart a buddy of mine built. He didn't actually know how to build or run a kart but that didn't stop him.

IFS kart .jpg

(440.87 KiB) Not downloaded yet

[steveohara]

Andy is correct if you apply the traditional definition to the term Ackerman Steering, however the motorsports world and especially modern karting have bastardized the term to refer to pretty much any configuration that produces a tighter turning radius for the inside front tire compared with the outside front tire. Modern sprint kart chassis use a combination of slightly angled spindle arms and split tie rod pivot points on the steering shaft to produce extreme Ackerman "effects" but the geometery does not generate Ackerman as it was originally defined. It is pretty much impossible to engineer a steering system that will generate pure traditionally defined Ackerman over any kind of meaningful range of steering input. Modern karts have such extreme geometry that the inside front wheel turns dramatically sharper as the steering input is increased and then it reaches a point where the inside wheel begins to move back toward straight as the steering input is increased. If you find that you are using enough steering input to get in to that condition you have already lost control of the kart so it isn't an issue.
It should also be noted that using toe out as a static setting is basically a poor mans Ackerman setup which results in a tighter turning radius on the unloaded (inside) front tire relative to the loaded (outside) front tire.
The downside to using toe out is the added drag the engine must overcome when the kart is going straight and each front wheel is trying to turn the kart to the side it is mounted on.
Last, except for Tom's friends cool suspended kart design, bump steer is not a factor in kart chassis unless you are talking about the kind of "bump steer" Kathy Hartman was famous for using with her "roller" front bumper
Steve O'Hara