1966 Barracuda X's 2
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so since i'm going to be playing with the steering converting it to RHD and fitting a power rack I need to check the steering geometry.
so I knocked up this v
just a quick check. I just undid the torsion bar but need to remove it to get full bump, that said there is enough info to show the steering in standard form really sucks.
from full droop
to an inch away from full bump
a dramatic caster change and a minimum of 6mm of steering movement worked out at the tread diameter on just one wheel. i'm sure I can get much better bump-steer even with modifing the steering system. caster change is unavoidable with the antidive top arm set up but running a much stiffer torsion bar will limit movement.
now I can play with different track rod lengths and positions to see what happens.
so I knocked up this v
just a quick check. I just undid the torsion bar but need to remove it to get full bump, that said there is enough info to show the steering in standard form really sucks.
from full droop
to an inch away from full bump
a dramatic caster change and a minimum of 6mm of steering movement worked out at the tread diameter on just one wheel. i'm sure I can get much better bump-steer even with modifing the steering system. caster change is unavoidable with the antidive top arm set up but running a much stiffer torsion bar will limit movement.
now I can play with different track rod lengths and positions to see what happens.
ok so I messed around by undoing the torsion bar fully and took measurements.
then I shortened the track rod by one and a half inches and redid the test with the what would be the road wheel in the same position. (the rack i'm thinking of using is three inches longer than the drag link)
quick quiz, what do you think happened?
then I shortened the track rod by one and a half inches and redid the test with the what would be the road wheel in the same position. (the rack i'm thinking of using is three inches longer than the drag link)
quick quiz, what do you think happened?
Last edited by Bozwell on Sun Dec 11, 16 6:47 pm, edited 1 time in total.
no one want to guess what the bump steer did then (this is one wheel remember so figures would need doubling for total toe-in)
so in totally standard form, taking ride height at zero, two inches of bump caused 50 thou (1.1mm) of toe out to three inches of droop at 120 thou (3mm) of toe in (170 thou tracking change over 5 inches). if you take just one inch each way at ride height, which is where the suspension will spend most of its time, it went from 35 thou toe out to 40 thou toe in. (that's 75 thou of tracking change over two inches)
maximum recommended is ten thou per inch of movement
and with the 1.5 inch shorter track rod measured one inch either side of ride height. 5 thou toe out to zero at ride height to 5 thou toe out! thats right, it has virtually eliminated bump steer not what I expected either. (that's 5 thou of tracking change over two inches)
even at two inches either side of ride height it only moved 18 thou. only at full droop on the last inch it moved to 60 thou toe out.
so the Jag rack will work and work very well
so in totally standard form, taking ride height at zero, two inches of bump caused 50 thou (1.1mm) of toe out to three inches of droop at 120 thou (3mm) of toe in (170 thou tracking change over 5 inches). if you take just one inch each way at ride height, which is where the suspension will spend most of its time, it went from 35 thou toe out to 40 thou toe in. (that's 75 thou of tracking change over two inches)
maximum recommended is ten thou per inch of movement
and with the 1.5 inch shorter track rod measured one inch either side of ride height. 5 thou toe out to zero at ride height to 5 thou toe out! thats right, it has virtually eliminated bump steer not what I expected either. (that's 5 thou of tracking change over two inches)
even at two inches either side of ride height it only moved 18 thou. only at full droop on the last inch it moved to 60 thou toe out.
so the Jag rack will work and work very well
so i did some more measurements. Caster, camber and bump steer on lock.
I can see why the standard suspension and K frame gets ditched, the readings are a joke.
nine degrees of Caster change over the full range. four degrees in just the one inch either side of ride height change. Camber changes by a degree over the same two inch range
also anything other than straight ahead the bump steer goes all to pot. reason for that is the drag link is held in place by the steering box and idler arm which are angled. basically the track rod changes angle by five degrees. when just a few 10's of thousandths can affect bump steer that much angle movement made too much difference. from 5 thou over one inch straight ahead to 50 thou over one inch on 15 degrees of lock.
at least a steering rack moves in a linear motion so that wont be an issue to change bump steer on lock and for the rest i'll just have to do what I can and put up with it.
I can see why the standard suspension and K frame gets ditched, the readings are a joke.
nine degrees of Caster change over the full range. four degrees in just the one inch either side of ride height change. Camber changes by a degree over the same two inch range
also anything other than straight ahead the bump steer goes all to pot. reason for that is the drag link is held in place by the steering box and idler arm which are angled. basically the track rod changes angle by five degrees. when just a few 10's of thousandths can affect bump steer that much angle movement made too much difference. from 5 thou over one inch straight ahead to 50 thou over one inch on 15 degrees of lock.
at least a steering rack moves in a linear motion so that wont be an issue to change bump steer on lock and for the rest i'll just have to do what I can and put up with it.