Two Measurements Required on Steering Rack for TR4A Please

[Z320]

What the @&€!!?@ is a TR6?

[stuart]

This is how the rack sits on a TR5/6

Stuart.

 

[Z320]

Hi Malcom,

with some ideas I‘ll be out at my 4A tomorrow to do some measurements

to come to a more realistic sketch and calculation.

Until this, don’t worry, now I know you do nothing worse than the Triumph engineers did on the TR6.

Ciao, Marco

 

Edited February 18, 2022 by Z320

[Malbaby]

11 hours ago, stuart said:

This is how the rack sits on a TR5/6

Stuart.

 

Thanks Stuart...your pics show the tie rods exiting the rack angling forward. I have seen other pics of TR5 chassis that shows the tie rods exiting towards the rear.

Am I correct in assuming that all the steering arms on these cars the same length??

[Drewmotty]

You probably already know so It may….or may not be useful to know that the fore and aft position of the rack makes little if no difference to the steering geometry but even small vertical increments make a big difference to bump steer. 
Off now as my granny is sucking eggs and I want to make sure that she does it correctly:-)

[Ralph Whitaker]

10 hours ago, Malbaby said:

Thanks Stuart...your pics show the tie rods exiting the rack angling forward. I have seen other pics of TR5 chassis that shows the tie rods exiting towards the rear.

Am I correct in assuming that all the steering arms on these cars the same length??

How did you arrive at that based on those pictures. To my eyes it appears that the tie rods are dead inline with the rack, only the downward angle because the suspension is fully dropped gives the appearance of them pointing forwards.

Ralph

Although this shot of the lube chart for the TR4 does show them pointing forwards, but if the rack was moved forward for the 6 cyl engine it would straighten out the tie rods, unless the steering arms were lengthened too !!

Edited February 19, 2022 by Ralph Whitaker
Additional thoughts

[Ralph Whitaker]

Looking again at the TR6 pics of Stuarts the hub steering arms are certainly longer than the TR4 items.

[Lebro]

Probably to improve the Ackerman angle

Bob

[Z320]

Making it longer will be very close to grind on the rim of the wheel….

TR4A and later 6 are the same due to the  Rimmer order number.

Edited February 19, 2022 by Z320

[stuart]

43 minutes ago, Z320 said:

Making it longer will be very close to grind on the rim of the wheel….

TR4A and later 6 are the same due to the  Rimmer order number.

Yes but prior to that for TR4 and earlier there are several different arms.

Stuart.

[Z320]

view 90° angle to the wheel

view 45° to the wheel

 

[Z320]

Hi,

this is from the TR4A workshop manual, I have the TR6 maunal too, but can't find this sketch there

I checked this some years ago when I gave some thoughts to an electric power steering.

The "wheel" is in the correct position, winded up with my spring compressor.

The result was 1.5° less - but mainly confirmed the manual.

Is there somebody out there who checked the TR6 wheel angle, I can't find any data?

By moving the steering rack 40 - 50 mm foreward on the 6 cylinder can't be the same? It must be "different".

Ciao, Marco

Edited February 19, 2022 by Z320

[Z320]

My TR4A without wheels today - but in the axles (please see the jack under the center crossbar for safety)

Shroud and fan I had to dismantle for the cord

Offset to the steering rack on my TR4A is 50 mm in the driver and passenger side

Distance from ball joint to ball joint is about 1,085 mm

This is a drawing (!) from the TR6 manual

My tie rods are about vertical, but my TR4A has 20 mm lowered front springs.

Very interesting is this to realise: the ball joints are "over" the axis of steering rotatio!

In my opionion this is a "disadvantage" for the outside wheel - and a hudge benefit for the steering geometrie!

On which heigh measure and determain the distance? 15 mm could be correct (but I don't know).

The steering lever is about 160 mm long (from the axis of steering rotaion)

By this opportunity I put out the Mintex brake pads and fitted cheap standard pads which I used before....

Ready for some CAD work this weekend, the results will not me absolute.....

Ciao, Marco

Edited February 19, 2022 by Z320

[Malbaby]

Marco...thanks for taking the time in measuring your TR4A steering

[Your tie rods being horizontal at rest would preclude any noticeable bump steer].

As we know, the TR5/6 rack placement puts the rack forward of the 4A position [due to the 6yl engine].

My guesstimate is about 75mm.

Looking at "Stuart's" pics again, the TR5/6 rack is probably in line with the tie rod ends position.

Other pics [from a TR250] that I have seen definitely places the rack about 13mm forward of the tie rod ends.

 

[Z320]

Hi Malcom,

this is my result:

moving the rack closer to the engine makes the inner wheel steer more, the outer less.

Moving the rack away from the engine the inner wheel steering decreases and the outer wheel steering increases.

With the rack straight to the tie rods the Ackermann starts to become negative.

In my opinion the TR builters had to fit a 6 cylinder engine in a 4 cylinder frame and

did worry the consequences on the steering or found a position for the rack with accepable effect.

I'm conviced the TR6 must have less Ackermann than the TR4A, I can't judge if this has any effect, on driving straight ahead shure not.

Allow me to relativise the result: it will be relative correct - but not absolutely.

Now a TR6 owner must help.

Ciao, Marco

[Z320]

This are 2 more photos for Malcom,

the rear side of the steering rack is 50 mm in front of the frame cross member.

You plan is 95 mm in front of the crossember, this is abot 5 mm before the tie rodas are straight.

Ciao, Marco

[Z320]

I can hear some of you doubt, so I had a closer look what happens.

In Malcoms case the steering rack still has the same "TR4A lenght" in his TR6 mod. frame.

And the track of the front axle will be further the same (is the TR6 track different / wider?)

He has to make the lenght / radius / circle of the tie rods shorte / smaller (blue) when he moves the rack foreward.

Moving the rack 80 mm to the left makes the wider circle (magenda) steer more degrees than the blue one on the inner wheel,

BUT the wider circle (magende) steer less degrees than the smaller blue one on the outside wheel.

That's Ackermann, but why different?

I also needed some time to understand and had to take a very close look.

On the inner wheel the circle pushes the wheel "80 mm" PLUS the way of the tie rod circle outwards, this is more with the longer tie rod.

On the outer wheel the circle plus the wheel "80 mm" MINUS the way ont the tie rod circle outwards, this is also more (but in the result less) with the longer tie rod

Triumph could have cured the disadvantage of the shorter tie rods by a shorter steering rack, or more track of the axle.

Or they did nothing at all? All not asked aswers are anwerd now.

Ciao; Marco

 

 

 

 

[stuart]

The steering rack and track rod ends are the same on 4a/5/6 just screwed on a different amount on the inner rod ends. This is particularly noticeable on some of the cheap repro racks where when fitted to a 4a theyre not screwed on that many turns

Stuart.

Edited February 20, 2022 by stuart

[BlueTR3A-5EKT]

Slow down

i have just mooched through my copy of Racing and Sports Car Chassis Design by Costin & Phipps and noted mentions on Ackerman Angles and perfect set ups.

The reason your steering ball joint centre is outside the kingpin centre is to obtain Ackerman angle in the forward to backward plane.  
 
You’re currently only addressing the side to side angles.
 

We sidescreen car owners understand the requirement of that ball joint position, and Revington supply modified steering levers that move the ball joint centre out so the joint almost touches the disc.   It improves the car control and handling immensely.  In standard form the imaginary line drawn through the steering lever ball joint and the king pin centre goes outward not toward the car centre/rear axle.  The lines cross in the centre of the car in front!   I would guess sidescreen steering levers were made for a car that had the steering rods behind the front axle centre line not ahead of it.

Here is an internet link (beware-it is internet so uncontrolled information) to same info on Ackerman.  https://en.m.wikipedia.org/wiki/Ackermann_steering_geometry

Edited February 20, 2022 by BlueTR3A-5EKT

[Malbaby]

This is all very interesting.

[Z320]

Indeed it is!

Before your question I not gave much thoughts on that.

I hope a TR6 owner can help with some measurement from his car.

Edited February 20, 2022 by Z320

[Malbaby]

From the above diagrams, it would seem that for the TR5/6 cars that when turning, the outside wheel will turn more than the inside...TR4 is opposite.

Cannot understand that.

[Z320]

With shorter tie rods

- the outer tie rod pulls the outer wheel closer to the rack --> steers more (than the a longer tie rod)

- and holds the inner wheel closer to the rack --> steers less (than a longer tie rod)

The result of a shorter (or longer) tie rod on one wheel is the opposite result on the other wheel.

Edited February 23, 2022 by Z320

[Z320]

Hi Malcom,

is your question answered?

Did you get „TR6 help“ by PM?

How did you continue / will you continue?

Ciao, Marco

 

[Malbaby]

Hi Marco,

Not completely.

I am happy with the forward/back position, but not convinced on the height as yet.

Would have liked to have found the theory that determines the ideal height of the rack compared with chosen ride height

Have seen a post where the bump steer was measured by mechanical means with a graph, determining that the rack height required to be increased slightly from the factory position....Cannot understand why this is so....The tierod arm angles down from the rack in the factory position....So even more angle if the rack is raised...Seems to me that ideally the tierod should be close to horizontal to minimise bump steer...Apparently this is false, but I would like to know why.