|09-02-2012 11:35 AM|
Bruce Cambern as I noted can take 3 or 4 hours explaining the New Geometry and setups he uses on his Cobra for different tracks, but doesn't like traveling all over the country any more, stays mostly in Calif races any more.
|09-02-2012 11:25 AM|
|09-02-2012 11:22 AM|
castor and kingpin
Castor angle and king pin inclination have to work together. bend a paper clip into a T shape, to simulate kingpin and spindle at 0 castor . rotate the spindle end, it stays the same height as the wheel turns. (Some heavy equipment geometry) Now tilt it back to simulate castor with a 90 * kinpin inclination. as you turn the spindle end moves closer to the ground in one direction and farther away the other direction, as the spindle tries to move closer to the ground it raises the vehicle, the weight tries to move the wheel back straight ahead and the inertia can move the wheel past straight and it will lower that side, The Front end can start to "dance". now bend the paper clip to simulate king pin inclination, at 0* castor. as you turn either direction the end of the spindle tries to move closer to the ground, raising the vehicle, vehicle weight tries to return the wheels to straight ahead whether you turn left or right. Now with your king pin inclination add in some castor, as you turn you will get differents amounts of lift depending which way you turn , with a rigid chassis the weight on that side will help point the wheels back straight. as you add more castor you can reach a point where you will get a lot of lift in one direction and Drop in the other direction. that tire will try to "float" no directional stability when turned one direction for that wheel.. Some of the 70's drag cars had new spindles made with around 15 degrees king pin inclination so they could run a lot more castor before reaching the "float point". I the early 60's I tried to explain what was wrong with the local engine builder's Studebaker Bonneville racer front end geometry. as I left I said you will get that thing upside down !!. Two weeks later He ran 5 MPH over the record , then on his back up run it started to "dance" rolled several times, The hemi stayed under the hood but the bellhousing broke apart and the 4 speed went out the backwindow breaking his arm on it's way thru.
|09-02-2012 10:29 AM|
In that photo I don't see anywhere near 7 degrees, so either you changed it from the photo or it's just an odd angle and I can't see it. But 7 degrees is quite a bit and you WILL see that just looking at an axle in a car.
The ackerman angle is a basic principle that when you round a corner the inside tire is following a tighter radius than the outside tire.
Like at a track meet, the inside runner has to have their starting point back from the outside running because they are going to be running on a shorter lane, right?
The inside lanes are noticeably shorter than the outside lanes.
Just as the track when your car goes around a corner, the inside tires are taking a shorter route. The rear end differential allows the inside tire to roll slower than the outside. If you had a locked rear end the tires would be squealing skidding on the ground fighting against each other as you went around a corner right? The front is doing the same thing on your car. The not only is the inside tire not turned sharper than the outside but it is literally not turning as much! Your left tire is is turning LESS than your right tire when you make a left turn!
This can make a car do all kinds of odd things as you are going in a straight line as your wheels are wanting to to in different directions every so slightly but that is what is happening with just a little turn of your steering wheel.
There are tons of cars out there with the setup as you have so it "works" for some people, maybe with wider tires it is less noticeable? It may "work" but it is NOT correct, it is a horrible mistake when we talk about steering geometry, it is WRONG.
On the caster issue, most old cars have very little caster, 1-3 degrees. The more caster the more it likes high speed in a straight line. The more caster, the less it "likes" to make turns. As an example a high end BMW seven series which is made for those high speed autobahns will be 6 or 7 degrees while a little BMW 3 series will have only 3-4 because it is more of a "canyon carver" kinda car.
So the more faster the straighter it should go and the less rolling resistance. A land speed record kinda car will have as much as 18 degrees. I remember the old rails use to run so much caster the tires would flop over side to side instead of turn! But you don't see that anymore so they must have learned that is just isn't worth the loss of control for the little less rolling resistance they gave up with less caster.
How are you measuring the angles?
|09-02-2012 08:22 AM|
You can improve the handling with the front mounted tie rod by heating and bending or cutting and re-welding the steering arms to move the pivot -attachment of the tie rod ends as close as possible to your wheel spokes. Ackerman needs to have the wheels pointed straight ahead, and a line drawn thru centerline of the king pin, the tie rod end pivot and intersecting the center point of the rear axle., draw a V, the rear axle center is the point of the v and the tie rod and king pins are on the lines, When you get into racing with IRS and IFS things start to change, A good friend of mine, Bruce Cambern, Retired head of Ford Racing, Had all 4 wheels on his 427 Cobra pointing different directions when he set a road course record at MIS, and won 3 firsts and one second, overall first place at the 2009 optima, good Utubes, the incar shots will make you dizzy on a big screen.
|09-02-2012 08:03 AM|
Mounting the tie rod in the front on spindles designed for rear mounting is a problem,when making turns, the Ackerman is backwards. My brother used to race gocarts and I could feel the cart slow down in corners when the geometry was wrong. With backwards ackerman, in a turn the wheels are fighting each other, Scrubbing the tires, not perpendicular to the center point of the turn radius. If you hit a bump in a turn the tire that has the most traction takes over and the front end will dart to one side. Mustang II and other most other front steer suspensions have Pivot points, geometry design locations to produce akerman geometry. The exception was 80's Ford trucks with front steer. ackerman was only close.
(BS auto engineering, 15 years as an Auto engineer, 5 years Teaching Auto college courses).
|09-01-2012 07:31 PM|
|wayneooo||thanks for the answers guys ill go over it till i like the way it rides any way i thought the tires were supposed to lean more like when u ride a bike not like a passenger car tire and im not sure what i have the toe in set at i just sorta eyeballed them making them in a straight line|
|09-01-2012 05:52 PM|
I'm at 7 degrees on my Bucket and it's working great. I also have my toe-in at .5".
Where you mount your tie rod isn't the cause of your problems if all is setup correctly, just a matter of choice, mine is in front on a Total Performance kit, the only issue is bending it if you bump into things.
|09-01-2012 08:40 AM|
In my post about dragster linkage , The swing pivot location is above the REAR mount of the FRONT hairpin ..The swing pivot simulates normal steering gear location on a T bucket .
|09-01-2012 08:35 AM|
First "steers like crap" isn't very descriptive.
Second , Pretty hard to tell what's going on from a pic. of the beginnings of a car.
5-9* degrees neg caster is usable but, it depends on the setup of the rest of the car.
|09-01-2012 08:32 AM|
I was given an unfinished T bucket project with a tube front axle and Harley spokes like yours, Chassis needs radiator mount brackets, Trans cooler mounted then Paint and final assembley I wonder how it will handle ? ? There are things not easy to fix. Theoretically center lines are supposed to line up and some have off sets. Line thru king pin, line thru tire center, thru tire contact point on road . Line on road parallel to direction of travel thru contact point. Using different size tires and wheel offsets that the suspension was not designed for can cause problems.
|09-01-2012 08:27 AM|
angle of a dangle
yet 7° is correct.. my last 2 buckets were done that way and had not problems.. going down the road u can steer it with a finger. ck everything else.. don't forget 1/4" toe in too..
|09-01-2012 08:21 AM|
and bald tires
We built a 31 chrysler roadster with a 49 olds, hydro and olds rear end. Fastest thing in the vallley. A buddy found an almost new wrecked 55 olds that he swapped into his 46 merc, He gave us a ride and asked if we thought the merc was as fast as the roadster. blasted up to 110 on a back road, and as he slowed down to make a U turn a Bald front tire blew out., he had burned all the ruubber off all 4 tires, Our guardian angel was looking out for us. "Don't drive faster than your Guardian angel can fly ! "
|09-01-2012 06:09 AM|
|08-31-2012 10:57 PM|
In the 50's My brother had long shackles on his 40 Ford coupe, the cheap way to lower it, He had to add a panhard bar to get the front end sway to stop . As Rwenuts noted, The shakles should be about a 45* angle in the completed car. engine installed, radiator installed etc.
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