I want my twin fed to handle best it can, so should the ackerman angle be built in to the front end, will it help in a straight line ?
I doubt that ackerman is used in any dragster but toe-in and excessive caster are used. That's why the wheels tip radically with a sharp turn. Ackerman is employed in a turning situation, caster/toe is for straight line geometry.
I believe as long as the car is square from the motorplate back and the front wheels are pointing forward with an acceptable amount of caster, you should be fine.
It does sound silly when you put it like that, just wondered if it would help in any way, its for this if pics help
I have always built ackerman into my dragsters. The reason is to reduce tire wear around the edges. Running a spool pushes the front end and without it the tires will scrub while turning.Running a lot of weight up front makes it harder to turn. I ran 14 years on the same Avon front tires before I had to put another set on and that was because there was no tread left evenly across the tire.
Oh I dont mean that comment as a slam .... but just imagine the havoc of FEDs on the roundy track! LOL ... nice project.
Yes this is absolutely true. While it would be helpful for "correct" suspension geometry it is not necessary for a vehicle that does 90 percent of its driving in a straight line.
When the wheels are pointed straight ahead, Mr. Ackerman goes on vacation. However, even though it's not as critical as on a street driven vehicle, you can still design some into your geometry to make maneuvering easier in the pits and on the return road. Bob
I doubt that it is something that most digger or drag car builders worry about as they aren't usually too worried about how the car tracks in a turn but anyone who has been around drag racing for a while has seen dragsters almost slide a front tire when making a simple turn in the pits or staging area. Dreracecar's comment in post # 8 makes a lot of sense when you start thinking about scrubbing the tread off front tires.
My thought is that the longer your chassis the harder it is going to be to build Ackerman into it. The farther from the rear the wider the points will be. I can think of some scenarios where your points would land outside of the tire. I like dreracecar's thoughts on it. It would make it easier to manuver in the pits or getting ready to stage, although if you build a lot of caster into your front suspension it is not going to steer well anyway. I guess every little bit helps and his statement on tire life would be enough for me.
I am certainly no dragster chassis set up expert, but my take on it would be this. if it's not any harder to set up the Ackermen correctly, go ahead and do it. Beyond handling in the pits and such, if you ever HAD to drive out of a situation on the track, F.E.D.s have such a small contact patch for directional control, I personally would want every bit of what I could get. We have all seen pictures of front motored cars crossed up, why not use every bit of contact patch you have instead of dragging one side in an emergency?
Cool lookin' FED - twin motors will always make a statement. With all that weight on the front wheels, too much caster will make it more difficult to steer, but going straight will be the key - I'd be leaning that king-pin back so she runs straight. Awesome look by the way. Can we have some more pics?
Caster and toe, I lost a roller Jr. Fueler off a flatbed trailer years back coming down from Reno, it simply rolled off because of a poorly secured tie down and a RR crossing. By the time I realized it was gone and got turned around , a jillion terrible scenes played in my head . There that car was parked in the middle of the highway with not a scratch on it, jut like it had just made a pass and was waiting for a tow back to the pits ! It was an old Kent Fuller chassis with a ton of caster in the axle.
My thoughts EXACTLY. If you got loose and had to "wheel" that thing back into the groove at high speeds, you sure wouldn't want your front wheels "scrubbing"
I have a cad drawing system (Mastercam) on my computer which allows me to configure the steering arms to acheive akerman (wheelbase-front trac-caster) and a cnc mill to cut them out so that is why I do it. Huge amounts of caster is not nessasary if you are using the latest front tires, but when you chose to use bicycle type tires then you increase the caster. Caster alows the bicycle tire to roll over the tread because the tire profile is round. Later type dragster tires are flat almost like narrow slicks and dont require a lot of caster.
The question is, if you are building the front end, why not put it in?? Cool looking dragster though!
In the original post it said FED. I assumed he aws referring to a dragster, as in alcohol/fuel dragster. Looks like a competion coupe or the such with a "normal" chassis/ front susp. configuration
Found this scan in another thread. Don't know who's chassis drawing, or where it came from. In the top view, see where it says "TO DIFF. CENTER" ? That is the classic method of achieving Ackerman.
I recently moved the tie rod for my champ car from in front of the axle to the rear of the axle. I placed it in front originally because it was going to interfere with the hairpins and frame rails if I placed it in the rear, even though I knew the ackerman angle would be all wrong. When I decided to correct the situation by moving ther tie rod to the rear I lengthened the steering arms and dropped them below the frame. Now the ackerman angle is correct and I sleep better.
By the way, you don't need 40 degrees of caster as in the dragster print above. Ten degrees will be plenty.
Page #351 of Hot Rod Chassis Construction by the editors of Hot Rod Magazine from '67. It's a Don Long car, Pink's "The Old Master"...
The Jalopy Journal
