TA22 + rack and pinion

[Ashh]

bugger.
This just doesn't seem to want to work at all. Are AE86 struts able to take higher offset?

Just recalculated with 5" wide wheels, they should be able to give about a 50mm offset if 7" ones can only get 25mm. They'd also push the track further inwards than the 7" ones anyway since it's measured from the center of the tyre, or according to my engineer. This is all just conjecture though..

Would the best bet just be to shorten a LCA in such a way that it 'looks' standard. Get it passed engineering and then just swap in a KE70/TA22 one and live with the extra track with some flared guards or something?

[Ashh]

Switching my direction to shortening the rack (this can apparently cause it to get really close to the sump, but I'm thinking that shifting the engine sideways by 10mm or so won't be a problem.

Now given that I have a ke70 rack and that the ke70 LCA mounts are 80mm wider than on the Ta22, should I shorten the Ke70 rack by 80mm to suit the ta22 LCA spacing? Is it that simple?

[TA22 GT]

I shortend my LCAs by 20mm as a permenant mod and cant see why it will be an issue. I also have XT130 struts in my TA22. Why do you think shortening them is a problem?

[stidnam]

shortening the LCA without shortening the rack the same amount means that you make bumpsteer worse.

[Ashh]

^incorrect.

Your rack has to basically match your LCA mount to LCA mount distance.

If you shorten your LCA all that will happen is the angle change of the LCA occurs faster so geometry problems are amplified.

The problem with shortening the LCA the required amount (40mm each side to remain engineerable) is
A. Welded suspension components is hard to get through engineering
B. It will be a really short LCA and amplify the imperfect setup.

That's my current thinking, happy to be called wrong

[WDE_BDY]

No, the rack width compared to LCA mount width is not your key concern and you generally find the rack is narrower than the LCA's due to the shape of the steering arms. To minimise bumpsteer the LCA's should match the distance between rack ends and the steering arms. Macpherson strut is far more sensitive to this than wishbone setups.

Callum

[Ashh]

That's just a tie rod distance. Which is adjustable? /for it to be perfect the rack end needs to be in the same plane as the LCA mount.

In an ideal world the rack would the same width as the LCA mounts. However the geometry changes when you turn, and through the suspension travel so manufacturers err on the side of toe in under compression (braking).

[WDE_BDY]

Tie rod distance is only adjustable to set toe in and allow for manufacturers tolerances. Perfect world you set the rack the same distance above the LCA mounts as the tie rod mount on the steering arm is above the balljoint and the LCA the same length as the rack end to the steering arm. This means they are then moving in the same arc and you minimise toe in and out with suspension movement. The actual width of the rack is just a product of the offset of the steering arm which tend to sit the tie rod mount inwards from the balljoint mount, so if it is set in 15mm the rack end would need to be 15mm inwards from the LCA mount. Factory setups are not strictly like this for other reasons such as toe in under braking etc.
Generally you want to keep LCA and tie rod length relationship similar to factory, you also want to keep them as long as possible as you get less angle change for the same vertical movement. So in your case, narrowing by 80mm will work IF you use KE70 steering arms and LCA's or if the offset and length of the TA22 steering arms and LCA's is pretty close. As the factory KE70 geometry has a limited travel range to remain optimum then if running low you may need RCA's to put you back into that range

Callum

[Ashh]

Cheers for that

Turns out that if I shorten the rack by 80mm then the spline to attach the column to will be somewhere under the sump as with an unshortened rack it's already mighty close to the sump (according to TA22 GT).

So the options are either to shorten the LCA by 40mm each side (which is really not ideal...), abandon the KE70 swap in and find a different car with a more suitable track or abandon the rack and pinion conversion completely.

- This is because I want to engineer it and the track increase restrictions are mightily annoying.

[stidnam]

Basically what I was getting at but may not have worded it right. I have that shortened KE70 crossmember & rack I was talking to you about the other day you can try and see if it works for you if you like. Reason I am not using it is that it hits the side of the T series block when engine is mounted centered. If you offset it as you suggest it may work for you.

[Ashh]

Oooh how'd you shorten the cross member? cut and shut? I'm definitely keen. I don't think mounting it over 10 or 20mm will pose any huge clearance issues with the gearbox.

[trdee]

Have you investigated whether there is any rack out there with a similar rack length to the distance between TA22 LCAs? Maybe something from a small narrow car like a mazda 121 or a barina or a micra or something?

[Ashh]

Have you investigated whether there is any rack out there with a similar rack length to the distance between TA22 LCAs? Maybe something from a small narrow car like a mazda 121 or a barina or a micra or something?

Personally no but it has been done earlier in this thread. From memory the AE82 rack is only 10mm longer than the LCA mounting points of the TA22 so it wouldn't take much to shorten it. However I think the basic rack dimensions when they're shortened will be the same so the potential problem of the spline/column interfering with the sump will be the same. Also I already have a KE70 Rack and Cross member.

[TA22 GT]

Personally no but it has been done earlier in this thread. From memory the AE82 rack is only 10mm longer than the LCA mounting points of the TA22 so it wouldn't take much to shorten it. However I think the basic rack dimensions when they're shortened will be the same so the potential problem of the spline/column interfering with the sump will be the same. Also I already have a KE70 Rack and Cross member.

I looked at a heap of options when I did this upgrade on my TA22. I measured up racks from AE82, AE86, Mazda etc etc. My conclusion is that the KE70 is the best fit as anything narrower will hit the T series sump. the KE70 rack in the correct position just clears the T series sump by approx 10mm. I wouldn't go any closer than that as you need to allow to engine movement and engine mount sag over time...

[Ashh]

I've been playing around with stidnam's shortened rack and crossmember (80mm taken out of both).

With my 2T and W58 gearbox it's not possible to shift the engine over enough to clear the knuckle without having a serious party with a mallet on the firewall/tunnel.

My new line of thought is to take my unshortened KE70 rack and shorten the rack and the housing by differing amounts. The rack *needs* to be shortened by around 80mm so that you don't get horrendous bumpsteer, the housing however only has to be shortened enough to allow the rack enough travel to get the wheels from lock to lock. To reduce the amount of travel required I'm planning on using shorter steering knuckles.

By eyeballing it/basic guestimation I think the housing needs to be at least 30mm longer on the knuckle side to clear the engine. From memory at full lock the rack extends around 130mm out from the housing to the rack end. Reducing it by 30mm is a ~23% reduction. To get the same steering angle with the reduced rack travel the steering arm (distance between outer tie rod ball joint and LCA ball joint) would need to be reduced by the same percentage (or more).

Tried googling AE86 power steering arm lengths and the like but no one seems to have posted that sort of data up. Anyone got access to it? I know T3 will probably manufacture an arm to a custom length but I'd like to confirm the theory before ordering expensive bits

inb4 the steering arm length does NOT affect ackerman, as long as the steering arm angle remains the same.