front axle alignment specs

[30dodgeboy]

What are the recommended specs for the front axle alignment (caster, camber, toe)?

My car is a 144" wb, pretty stiff chassis, with 2.25S17 Avon Speedmaster (ribbed tread) front tires.

Thanks in advance.

[dreracecar]

Camber is fixed unless building a new axle and not super critical with the avons.
Because the avons have a round conture (not flat like frontrunners) I like at least 20deg of caster so that the tire rolls around the tread when turning which helps drive the tread into the pavement.
toe @ 1/8"
The biggest issue is that for tire life and to keep the avons happy(you cant buy them anymore) is that you must have ackerman built into the steering arms. This when turning will allow the inside tire to turn sharper during a turn and will not scrub off the tire tread as it would if both tires turnd the same amount.

  I need to know how wide the front axle is at the middle/center of the kingpin bosses in order to tell you how much the offset is (I already know the w/b). Depending on what you have you may have to make new arms.  The pic shows .691 offset for a 120"w/b chassie and a 42" wide axle and a 4" arm

[rooman]

The ackerman principle is fairly simple--the attachment point of the linkage to the steering arm should be on a line drawn between the center of the king pin boss and the center of the rear end housing. You can run a string from point to point and figure out where the hole in the end of the arm needs to be. If you are running the drag link to the spindle and simply using the steering arms to connect the front wheels the length of the arm is not a factor. If you are using a bell crank style linkage that opens a whole new can of worms relative to steering angle related to input from the box and arm length can be a factor.

Roo

[ricci32]

1/8 in or 1/8 on toe im and old dirt racer.

[30dodgeboy]

I don't have the axle width handy, but will measure it next time I am working on the car.

I do completely understand the ackerman principle, I learned and applied it when building go-karts as a kid.  Thanks for bringing it up.  Tires appear to have some wear from excessive toe (saw-toothed towards center of car).

Steering is with a bellcrank at the front.  The tie rod is one piece connecting both steering arms.  A second link connects the right steering arm to the bellcrank.  I have already learned how sensitive the steering linkage kinematics are to the various link lengths.  You are certainly right about that Rooman!  We used 1/2" EMT electrical conduit sections with 3/8"NF nuts tacked inside to determine what the lengths needed to be in order for it to steer properly.  Even pitman arm position is a factor - balancing frame clearance, header clearance (early hemi), steering angles, etc... its quite a balancing act.  Then I made the tie rods to the correct lengths.

Thank you guys for the replies.

[JrFuel Hayden]

30dodgeboy,
 I hope not to alarm you, but are you aware the very newest those Avon's could be is 35 years old. Once an Avon rep saw a SoCal dragster builder was using their light weight motorcycle/ moped tires on 200+mph dragsters they freaked and went back to England and destroyed the molds. I tried to buy the molds but got a big NO.
So look closely at your Avon's, look for cracks in the tread and sidewall, there is a good chance they are cracked, and hard.
I, Hayden Wheels, sell some Avon tires, but ONLY for show/ cackle cars, NOT for racing.  We do sell new Avon "looking" rib tires that are not old.
If you have any questions, feel free to call 800-624-3803
Jon Hansen

[BK]

Mine were feathered also. I thought it was toe in until I noticed they were feathered in the same direction. What turned out to be was, car would fade a little right, I would counter steer left but tires would mostly skid until about half track when there was enough weight to steer.

[JrFuel Hayden]

So BK, you added 10 lbs to the axle, so you can steer it ?

[BK]

 It already had 40lbs on the nose. I didn't want to add any more. I just lived with it. It would steer after 1/2 track or so.

[janjon]

"It would steer after 1/2 track or so."

FED guys are nuts...

[JrFuel Hayden]

So BK, you have never had to lift because your FED was headed for the wall or center-line ?
If so, I guess you don't need anymore weight.  How much do you think an extra 20 lbs would slow your car down ?
We added 20 lbs to our NHRA Heritage Jr Fuel car at a race because my tune-up gave us more power, only to have the driver lift because it was drifting.
Funny thing the car ran better ET's after we added the 20 lbs, and it went straight.
I know of a fast JrFuel team that carries about 80 lbs of lead on the front, but still set the A/ND record of 6.77.
Are you racing 8.60 or 8.50 brackets ?

Included is a picture of my mid 60's nitro Jr Fueler that I raced in the midwest for 5 years.

[BK]

Never had to lift it wasn't darting around or making any crazy moves.
It wasn.t the ET I was thinking of it just didn.t seem right to put all that weight on the tires and steering linkage. I had 40 bolted on and there was shot in the front axel tube, I don't know how much. I'm sure it wasn't 80lbs. If I had put that much up there I could have left the line wide open and probably picked up 11/2 to 2 tenths.
It was Saturday night super pro class.
I didn't know anyone to get advice from when I was running it. I was kind of making it up as I went.