TA22 + rack and pinion

[Rob KE25]

LeeRoy and oldcorollas, you both make some good points.

Oldcorollas, I don't know how bump steer would be affected when the wheel is turned in my notion of how to set up the steering. I'll have to think about that. Good food for thought.
I would be very keen to see your diagrams of steering geometry.

LeeRoy, I guess you know, but it is possible to have toe out (or toe in) in part of your suspension travel, despite having a shorter (0r longer) tierod.

By raising the rack(in relation to the LCA inner pivot point), bumpsteer can be minimalised a fair bit, even if you have shorter tierods.

I have an AE86 crossmember with p/s knuckles, and this is a case of this in action. The tierods are 277/278mm long, and the LCA is 294 mm long. The rack is 7mm higher than the LCA innerpivot point.

As you suggest,(in rear mounted racks) short tierods will cause toeout in compression and droop when wheel alignment is set at ride height. Long tierods will cause toe in in bump and droop.
Different lengths cause archs of different radius. Think of it as the letter C and c, tightening radius.(Pural is it radii?)

Mounting racks higher will cause toein on bump, toe out on droop.
Mounting racks lower will cause toeout on bump, toe out on droop.
But this doesn't work in as straight line. Eg at 1inch you get 2mm toe change, so at 2inch
you get 4mm. Rather, it works exponentially, both ways. So at some point in wheel travel, there is not much change of toe. This may not be at ride height either. Think of it sort of as a strange letter S. And this strange letter S has also been stretched. (Wish I could do drawings, would save some confusion). This letter S would be reversed if the rack height was swapped to the other side of the crossmember, either horizontally or vertically.


Anyway, by mating these two concepts (rack height and differing lengths), it is possible to counteract each other in some parts of travel, resulting in very little bump steer in that particular part of suspention travel. OR you could get them to work together, and have heaps of bump steer. Don't know why you would though.

From what I understand- could be wrong- this is how most car manuracturers are able to have little bump steer for the first few inches of travel, but then purposely create toeout on greater amounts of bump. So cars don't suddenly turn in when Mr. Wally behind the wheel panics and turns a bit too much when his car is already having a fair bit of turning force. (Understeer being stable, oversteer not).

Where am I going with this?
Just wandering if you guys think this match or mismatch of tierod length can be properly mated with rack height for a good steering geometry pattern. Because that is what I have recently been thinking of doing.
But reading this thread I have decided to not rush ahead too fast.
Appreciate your opinions...
Cheers, Rob.

[jeffro ra28]

errrrrrm, If you read my posts on page 12 please disregard the information i posted. I had a major mis hap with my epc program. The information was misleading if not incorrect.

Apologies.

[oldcorollas]

From what I understand- could be wrong- this is how most car manuracturers are able to have little bump steer for the first few inches of travel, but then purposely create toeout on greater amounts of bump. So cars don't suddenly turn in when Mr. Wally behind the wheel panics and turns a bit too much when his car is already having a fair bit of turning force. (Understeer being stable, oversteer not).

Where am I going with this?
Just wandering if you guys think this match or mismatch of tierod length can be properly mated with rack height for a good steering geometry pattern. Because that is what I have recently been thinking of doing.
But reading this thread I have decided to not rush ahead too fast.
Appreciate your opinions...
Cheers, Rob.

Heya Rob,
that is something i had not spent time thinking about as yet
but a very good point about manufacturer intentions....

yup, i agree with your method.. it works particularly well when the lower arms angle down as in stock application, but with lowered cars, these angle changes start becoming issues...

thansk to Derekjay (send the boy some rep!!! ) i got my hands on the Maxima free math software and to out it bluntly.. is bloody brilliant
http://maxima.sourceforge.net/

so, i am one step closer to modelling

the first thing i want to do is model the original castor camber and track curves for different bump/droop for stock cars... then see where steering bits go and what the changes are... and then go on to simulate racks and their different positions...

i'll make up a diagram for ppl to measure stuff in the next couple of weeks...as the relative positions of things is vitally important for the results..

[LeeRoy]

I've also been giving all of this some thought over the past few days so ill spit out a few thoughts im having.

Castor will affect rack placement. Greater castor means rack placement can be lower.

Steering arms that angle down will also allow rack to be mounted lower.

On the 22 a combination of both of these appear to allow the drag link to be mounted horizontally equal (or damn close to) the LCA pivots.

Now i have a few questions. Say you have 5deg castor, if you could turn your wheel 90deg then would the camber be 5deg - im assuming it would be. So my question is; am i right in assuming the increase in camber is linear as the wheel turns but dependant on the amount of castor.

Also, as castor is increased it will angle steering arms down correct? and this angle down combined with steering arms which also angle down allow the rack to be mounted lower. However, the rack will still be mounted with an distance equal distance above or below the line of LCA pivot as that of the distance between the ball joint and the tie rod end.

Basically what im saying is if you increase castor you either need to mount your rack lower or use less angled down (not in. Angle in = ackerman) steering arms in order to have the rack mounted in the same position as it would be with less castor.

Some people also seem to think ackerman will be changed through rack position. Ackerman is not changed by moving the rack. Ackerman only exists in the steering arms - nothing else. Also, longer tie rods wont provide extra lock. Lock is determined by rack length (well the part of the rack with teeth anyways).

Oldrollas whats the chance of getting a formula that works out the impact of bump steer whilst turning using the inputs of camber, castor, LCA angle and length, and tie rod angle and length?

[oldcorollas]

thats the plan. but it will be complicated...
anyone here good with vectors?

ackerman should be affected by rack placement.. but really only due to length of the tie rods and their angle to the steering arms..

you can check this easily by drawing a diagram... with the rack mounted inline with the steering arms, and then with it mounted say.. 2x steering arm length behind...

when inline.. the steering arms move the same angle almost (not quite. depend on lengths you choose) but when you move rack back, there is bigger difference in angle between th wheels

[ChrisO_ke11]

Here are some scanned diagrams in my copy of the mechanics bible, Hope they help in understanding steering geometry

[oldcorollas]

anyone got a TA22 crash manual (or other cars also) with the following info?

http://toymods.net/forums/showthread...454#post751454

[TA22 1MZ]

i have recenlty undertaken the KE70 rack & pinion conversion into my TA22.
also made use of the KE70 steering column, or the bottom half of it at least.
Will update as I make further progress

[stidnam]

How did you get the ta22 top and ke70 steering shafts to stay together? Been thinking of how I will do it and haven't come to any great ideas yet. Maybe weld it will be the best option for strength.

[LeeRoy]

Shortened AE71 x member is currently in mine. Rack shortening will be in the not too distant future.

[stidnam]

Shortened AE71 x member is currently in mine. Rack shortening will be in the not too distant future.

Seen yours at lindens. Can't remember did you chop out of the middle of the x member or the ends? If only the ends how will you mount the shortened rack properly as the mounting points will be too wide

[TA22 1MZ]

once you split the two shafts and use the top of the 22 shaft with the bottom of the KE70 shaft, then put the unit back into the modified ta22/ke70 column, the circlip that holds the top bearing in and the bottom bracket tht holds the bottom bearing in keep the shafts from splitting. I am also going the drill a hole and insert a pin thru the 2 shafts where they meet just to make sure.

obviously this all sounds a bit strange without the photos. I am going to purchase another ke70 r&p with x-member and refine it again.

basically, with the steering cloumn/shaft assembly, if you lay the TA22 and Ke70 setup side by side and pull it all apart you start to see how the 2 can be grafted together for a factory looking setup.

the only welding I did was the bottom half of the KE70 column to the TA22 column, so you can retain the KE70 bottom bearing to keep the shaft centralised.

I also cut out the flange from the KE70 floor mounting bracket and welded it onto the TA22 item so you can retain the factory mounting position to the floor.

The only thing left to refine now is mounting the column back to the 3 locating points near the dash surround. I'll get some pics up when I get a chance

i have recenlty undertaken the KE70 rack & pinion conversion into my TA22.
also made use of the KE70 steering column, or the bottom half of it at least.
Will update as I make further progress

[old_school_jap1]

any chance of this happening with an ra23 column ? as the headlight switch on the stalk is a good thing

[TA22 1MZ]

Shortened AE71 x member is currently in mine. Rack shortening will be in the not too distant future.

LEEROY, what control arm setup have you gone with? which holes in the rail did you use to mount the x-member? Just trying to align mine at the moment and looking for any tips if you have some
Cheers

[TA22 1MZ]

any chance of this happening with an ra23 column ? as the headlights on the stalk are good

The RA23 column still shares the same bottom shaft as the TA22 so will still need modification to make work.

Adapting the indicator/light assembly would be a far simpler conversion in its own right.

Here are some pics with the x-member in place
http://www.toymods.net/forums/showth...875#post776875