jimny steering wobble, Maths has the solution
by andre christiaan cloete
(Garsfontein, pretoria, south africa)
....this is an issue the plagues all classic car enthusiast, including the modern day suzuki jimny. you have heard solutions from thicker shims on the steering joints to wheel alignment and kingpin change and the standard; steering damper. etc.
Although there is no doubt that some of these or a combination of, will in certain cases assist with treating the symptom or in some case inadvertently solve the problem with different rims and 3mm difference, I have yet to come across the solution in all of these cases.
Seems to me that even the technicians at the Suzuki garages, have forgotten a very very important point. Not to even mention the classic car enthusiast. I have looked at many american car shows where larger tyres and rims are standard practice. many technical things are explained. however, seems to me it is a hit and miss. if you go large enough, you will not come across the steering wobble. the fix the problem when they change for wider rims.
if you study it out, the reason is clear and the solution even easier.
LARGER DIAMETER TYRES STUFF THE STEERING INCLINATION ANGLE AROUND. that is right. when you increase the tyre size on the same rim, you move the virtual steering pivot point outward. now it is positioned on a meta stable point that causes the vehicle to hunt at certain speeds. in other words, this virtual point can not decide if it is left or right of the tyre center line. or the center line of the contact patch
you have to put this point either left or right of the center line. you can not sit in the middle. sure, if you put it inward, the steering will be vague and loose. sure if you put it outward, the steering will be heavy and less vague with larger scrub radius and more tyre wear. but there will be no wobble.
if you do the calculations, you will see that going for the standard larger Jimny tyres, you need to push the rim outward by at least 3mm (further will require longer studs on the hub). i had 3mm spacers made and problem solved. the previous owner had steering damper on, but it did not solve the problem. my spacers corrected the inclination angle and problem is GONE, completely.
just a side point. If you ran with your current tyres for a long while, they have worn in a certain way that the spacers might not help completely as the tyres have a skew contact patch, replace the tyres. also, tyres with a ridge or inline set of blocks the mimic a center rib, will track straight, much more easily than tyres with no rib. like the AT of bf goodridge (no rib), will hunt much faster as there is nothing that points them in a certain direction, under rotation.
just do the calculations and study the steering inclination angle and you will come to the same conclusion. can someone please post this solution around to help all the suzuki enthusiast around the world. does not seem that my local enthusiast in Pretoria, wants to listen. maybe I am talking above their hat as they never heard anything like this. what do i know.
your jimny friend