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Ackerman? We don't need no stinken Ackerman

B

Bill Blue

Platinum Level Sponsor
I hope! Finally got the front end (Tiger copy, using MGB parts) totally installed and adjusted. I was curious as to what was happening to the Ackerman. Bolted a couple pieces of angle iron about two feet long onto the brake rotors and measured. From dead ahead to full left turn lock, no change. The rotors remained at 1/8" toe out.

How this happened. My front brakes are not stock. They use GM "Metric" calipers, which mount very differently from the stock calipers. The MGB steering arms are (almost directly) bolted onto the back of the spindle forgings. The steering arm has to be backed away from the rotor to gain clearance for the knuckle.

Bill
 
DanR

DanR

Diamond Level Sponsor
Mr Bill, It has been a long task thus far and I'm glad you have it done!
 
260Alpine

260Alpine

Silver Level Sponsor
Tiger's have terrible Ackerman. Zero would be better than Negative. Ideally steering arm angles meet at center of rear axle like this diagram. ackerman.jpg
 
Barry

Barry

Diamond Level Sponsor
Remember that the factory Tiger steering system results in reverse Ackermann as the steering angle goes off-center. Instead of increasing toe-out, the factory Tiger steering system produces increasing toe-in.

Bill has a highly modified Tiger-ish steering system with a different steering rack, a different steering rack location (not as far forward) and different steering arms. Achieving neutral rather than reverse Ackermann is a major accomplishment!

 
B

Bill Blue

Platinum Level Sponsor
Toyanvil said:
Are you saying you do not have any ackermann angle at all?
Click to expand...
Well, not that I was able to measure. The measurement was taken about two feet in front of the spindle. It did not change from straight ahead to full left lock
husky drvr said:
Full droop or ride height?
Click to expand...
Ride height. I guess that I have a lot of Ackerman angle, just enough to nullify the Tiger style steering setup, not enough to overcome it.
Bill
 
spmdr

spmdr

Diamond Level Sponsor
It sounds a bit like this:

BMGBArm6.JPG

In this case, the main goal was bigger brakes. But if you can improve the steering in the process... DW
 
B

Bill Blue

Platinum Level Sponsor
spmdr said:
It sounds a bit like this:

View attachment 27866

In this case, the main goal was bigger brakes. But if you can improve the steering in the process... DW
Click to expand...
Very much, except I was able to marry 11.25 X 1.0" GM rotors onto slightly modded stock hubs. What size rotors do you have? Are the steering arms stock Tiger" My rig places a portion of the rod end slightly ahead of and in front of the rotor. So much so that I'm going to have to retract the arms a bit to clear the 15" X 5.5" wheels. And I thought I was done.

Bill
 
Barry

Barry

Diamond Level Sponsor
Bill Blue said:
Very much, except I was able to marry 11.25 X 1.0" GM rotors onto slightly modded stock hubs. What size rotors do you have? Are the steering arms stock Tiger" My rig places a portion of the rod end slightly ahead of and in front of the rotor. So much so that I'm going to have to retract the arms a bit to clear the 15" X 5.5" wheels. And I thought I was done.

Bill
Click to expand...



A critical factor is that Bill moved the front brake rotors appreciably outward relative to the factory Series Alpine location which in turn allowed the outer tie-rod end pivot points to be moved outward and forward which in turn reduced the off-center steering toe-in gain (aka, reverse Ackermann).

Moving the outer tie-rod end pivot points inward (toward the longitudinal centerline of the vehicle) and backward (further to the rear of the extended axis of the steering rack) for wheel clearance will almost certainly cause the off-center steering toe-in gain (aka, reverse Ackermann) to return.

As often happens, fixing one problem causes or aggravates a different problem. 16" wheels ???
 
Last edited:
B

Bill Blue

Platinum Level Sponsor
Barry said:
Moving the outer tie-rod end pivot points inward (toward the longitudinal centerline of the vehicle) and backward (further to the rear of the extended axis of the steering rack) for wheel clearance will almost certainly cause the off-center steering toe-in gain (aka, reverse Ackermann) to return.

As often happens, fixing one problem causes or aggravates a different problem. 16" wheels ???
Click to expand...
No, I just bought a set of beautiful 5.5 X 15's that will make do. It appears that 1/8" spacers will do the trick. 16's would allow better geometry, but not a whole lot. I think that if things were rearranged, it would a significant change. The rotor would have to move out at least 1/2".
Well what do you know, found a way to make the program work. This is about the best pic I can make with everything on the car. It will help if I identify components. The calipers are GM "Metric". They have been in service since the Orange Car was built in 2007. Rotors are 11.25"X 1" GM. The angle iron is what I used to set the toe and measure toe in change. The cement block "floats" on a plastic moving pad. Allows the wheel to move out and assume the proper set as weight is applied.
IMG_8259.JPG
 
Barry

Barry

Diamond Level Sponsor
Bill Blue said:
No, I just bought a set of beautiful 5.5 X 15's that will make do. It appears that 1/8" spacers will do the trick. 16's would allow better geometry, but not a whole lot. I think that if things were rearranged, it would a significant change. The rotor would have to move out at least 1/2".
Click to expand...


A simple and effective solution to a very complex problem.
 
B

Bill Blue

Platinum Level Sponsor
No, I've decided to see if I can live with it. I need to get this damn ting back on the road before I check out. Not many in my family tree survive their early eighties. But tell me about bump steer, how to diagnose and eliminate it. Should the tie rod be turned upside down?

Bill
 
P

PROCRAFT

Donation Time
Bill Blue said:
No, I've decided to see if I can live with it. I need to get this damn ting back on the road before I check out. Not many in my family tree survive their early eighties. But tell me about bump steer, how to diagnose and eliminate it. Should the tie rod be turned upside down?

Bill
Click to expand...
Bill
Bump Steer what I do plate bolted to the spindle. two dial indicators f/(remove the shock spring) cycle up and down checking the toe change.
toe should not change when traveling, if so, usually corrected by moving the steering arm up or down whichever corrects changes the arc which changes the toe. call me some time if your inclined and I'll explain more! Joel
 
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