New stub axles

[strat6v]

Just had a look on wilwoods website. They have started producing a stub axle thats very similar to the fiat 132 part, Seems the kingpin inclination angle is 79 deg where the fiat part is approx 85 deg tho, :confused:

[jadefarms]

Can anyone tell me the correct kingpin inclination for a Hawk HF3000?
Published figure for Fiat 132 is around 6° plus or minus 20', but machined extension will alter the geometry.
I have got 7° one side and 9° the other. I guess one is a bit out....

[Martin K]

Can anyone tell me the correct kingpin inclination for a Hawk HF3000?
Published figure for Fiat 132 is around 6° plus or minus 20', but machined extension will alter the geometry.
I have got 7° one side and 9° the other. I guess one is a bit out....


Colin Artus will know the answer to that I am sure.

[guy mayers]

Kingpin inclination? Isn't that castor angle? The shorter the leading link the bigger the castor angle and the more self centering you'll have on the steering. Wind it on!

Guy

[jadefarms]

No, kingpin inclination is different, set by the suspension uprights. There is no adjustment, short of hitting it with a hammer!
It is the angle of inclination of the kingpin to the vertical. For a system with swivel joints also called steering axis inclination.
Having scratched my head, I don't think the machined extension affects the angle, so I guess it should be 6°, the same as a Fiat 132, but does anyone know better?
What effect will it have if it is out by 1-3 degrees? :confused:

[guy mayers]

It's all adjustable on the Hawk! The upper wishbone has a rosejoint on the outer end and another on the inner end of the lower arm so that the camber can be adjusted. The leading link also has a rosejoint at the front so that the castor angle can be adjusted. You ought to be able to get the kingpin angle identical on both sides. Or am I missing something very technical? :confused: :confused:

Guy

[jadefarms]

Yes you can adjust the rose joints top and bottom, but they will only affect track and camber, not kingpin inclination. The front tie rod controls castor angle.
If you adjust the rose joints the whole hub/stub axle assembly moves, without changing KPI. Easier to see from a diagram... not that I'm an expert.. :confused:
Struan

[John]

Kingpin inclination, scrub radius. Not adjustable as I read it. Set by the said stub axles and the offset on your wheels so it has to be got right from the outset. Yes, you can adjust camber and castor, but the first two you are stuck with.

[strat6v]

If you used a stub axle with a different kpi then it would throw everything else out too, probably causing some nasty bump steer. Best explanation is in
'Competition car suspension' by Allan Staniforth. Goes hand in hand with design, roll centres, steering rack position etc etc.

This is a good book to put on your christmas prezzie list ;)

[John]

Exactly where I did read it, John!!
Don't think I'm going to make it saturday, the weather forecast is too good and I'll be laying flags!
If it rains get Ralph to save me a sausage roll. Have a good one.

[CorseChris]

...and there was me thinking I wouldn't be going 'cos the forecast is pants!

[Martin K]

I remember Colin Artus showing me an original Lancia drawing which showed a modification to the 132 upright to increase the KPI for the Stratos - so KPI should be more than a 132 but I don't know by how much.

The 'modification' was an bend downwards of the upper part if the stub axle where the extension piece bolts in.

This was probably done to correct the scrub angle with the Stratos running larger diameter wheels and with a different offset to the 132 - but this is just my guess.

[jadefarms]

Can anyone tell me the correct kingpin inclination for a Hawk HF3000?
Published figure for Fiat 132 is around 6° plus or minus 20', but machined extension will alter the geometry.
I have got 7° one side and 9° the other. I guess one is a bit out....
I agree that KPI is non-adjustable, but to return to my query can anyone confirm the correct KPI.
If it is 2-3° out how much does it matter?
Guess the only way to change it would be to get a better spec upright/extension assembly. :(
Struan

[jadefarms]

I remember Colin Artus showing me an original Lancia drawing which showed a modification to the 132 upright to increase the KPI for the Stratos - so KPI should be more than a 132 but I don't know by how much.

The 'modification' was an bend downwards of the upper part if the stub axle where the extension piece bolts in.

This was probably done to correct the scrub angle with the Stratos running larger diameter wheels and with a different offset to the 132 - but this is just my guess.
Thanks Martin!
So if KPI were say 8°, it might be not far out on that thinking, perhaps.... :)
Struan

[Martin K]

Thanks Martin!
So if KPI were say 8°, it might be not far out on that thinking, perhaps.... :)
Struan

I don't think that is far out. The thing is, even changing your front tyre diameters and wheel widths/offsets from the original could require a different KPI so working from the Stratos KPI angle is only a starting point.

You could try drawing up your wheel/tyre and hub arrangement (as accurately as possible) then you can work out very accurately the KPI you need for zero scrub radius.

[strat6v]

Wasn't the original Allora criticised for having excessive scrub radius?

[Chris J]

Wasn't the original Allora criticised for having excessive scrub radius?

I think they were ok if you didn't space the wheels off, John.

[chris.richard]

And for us numpties, what would the driver detect if the KPI or the scrub radius was sub-optimal? :confused:

[strat6v]

Probably some hefty contact with the local flora and fauna :D :D

[chris.richard]

So that's what caused it!

[jadefarms]

I don't think that is far out. The thing is, even changing your front tyre diameters and wheel widths/offsets from the original could require a different KPI so working from the Stratos KPI angle is only a starting point.

You could try drawing up your wheel/tyre and hub arrangement (as accurately as possible) then you can work out very accurately the KPI you need for zero scrub radius.
I was hoping that someone else might have done the calculations! I am using coffin spoke wheels.
Guess I'll have to get out the tape measure and fire up the Cad program....
Trouble is bending the stub axle to 'correct' any errors could be a problem. Big hammer or scaffold pole might not give the required precision, not to mention fatigue issues.... :eek:
Struan

[mudhut]

Don't think you'll get too fatigued if you use a long enough scaffold tube...

:rolleyes:

[chris.richard]

:D :D :D

[jadefarms]

Don't think you'll get too fatigued if you use a long enough scaffold tube...

:rolleyes:
Indeed, a fine labour-saving device..... ;)

[Arthur]

If I've read Mr Staniforth correctly, what we want is for the steering inclination (KPI) (angle to the vertical through the centres of the upper and lower swivel joints on the front hub), when a thoeretical line is drawn through them, to meet the road at the exact centre of the tyre tread in contact with the road.
This will give the lightest steering.
But as the steering turns, any inclination in that axis will either add or subtract camber.
If the axis is vertical, there's no change in camber with steering angle, but with any rational assembly, the axis will be offset inwards by two or three inches due clearance for brakes and such. The extended line is therefore a distance from the tyre centre contact with the road (scrub radius), and rolling resistance (force) now acts on the distance (scrub radius). In a straight line, forces left and right cancel out. When you try to turn the car, left and right change, one up, one down, and act to oppose the steering movement. You feel this as heavy steering.
Add some silly castor to that, and you end up with wrestler's arms.
Which also why fitting wider tyres without additional inset on the wheels, or fitting hub spacers to push out the track, also cause heavier steering feel.
You could also alter the inset (more new wheels) to reduce the front track, and move the tyre centres inwards, to correct a scrub radius problem, but generally it will look a bit odd with the wheels buried in the arches - mind you, a lot of the real competition strats used much narrower rubber than I would have expected, and also seemed to have a rather narrow front track...........

Now then, I haven't spent my life rebuilding uprights to test the theory, so I've no idea "how much".
The advice is generally to keep KPI to as low a value as possible at design stage, while managing to get everything in the hub, for lightest steering feel. Therefater, view the resulting camber change in turns as an element of tuning - you can't change it without physically altering the upright, but if the steering is over-heavy, you can lighten it by reducing the castor.
You may lose some of the self-centring feel, but remember that a chunk of the self-centring, and the feebdack you feel in the wheel, is caused by "pneumatic trail" (Carroll Smith), as the centre of force reaction moves outward and aft in the tyre rubber under load, so you'll have more self-centre the more you load the tyre. Until you overload the rubber, of course, when it all goes light and airy-fairy, and Lo! we have found the understeer limit!

I appear to be preaching again. Not intentional, apologies if it sound that way. I'm at the rag end of my mental capacity when dredging this stuff from memory; hope it makes some kind of sense. As pointed out abve, Mr Staniforth and Mr Smith are the bibles for this kind of stuff as far as I'm concerned.

[CorseChris]

Topical this. I've had an issue with my car pulling to the left under heavy braking since I built it. I've tried pretty much everything and was starting to consider checking KPI & hub/rim measurements to see if I had somehow ended up with some un-matched components.

I specified the rim widths & offsets (inset actually) based upon the published KPI spec for the 132 upright so it should be correct (or at least balanced). Must dig out my calculations and double check them as well. Hubs where a pair of brand new FSO/Polonez items but uprights where the usual scrap-heap challenge. Rims should be easy enough to double-check but perhaps it's time to buy that proper castor/camber/KPI gauge rather than my DIY plumb-line unit.

I'm quite sure one thing you'd detect with different KPI on each side would be some degree of pull under braking.

Speaking of spacers....anyone see that program Chop Shop???? 6" spacers on the front wheels of a 3 series BMW. Mmm.

[strat6v]

I have had mismatched or should i say bent uprights before. Maybe it would be worth building a simple plywood jig to check them? You could have a baseboard with a rigid hub mount set at 90 degrees then the correct dimensions actually drawn on the base board?

[CorseChris]

Neat idea John. I was thinking a quick way might be to swap the uprights left to right....but that's not really very quick.....

Getting the centres of the the balljoint axis is hardest, but a pair of used joints could provide the neccesary tapers and centre-points.

[strat6v]

Or a piece of bar turned down to pass through the tapers snug, maybe with a point on each end?

[chris.richard]

(KPI) (angle to the vertical through the centres of the upper and lower swivel joints on the front hub), when a thoeretical line is drawn through them, to meet the road at the exact centre of the tyre tread in contact with the road.

If the KPI is the angle relative to vertical, then it is adjustable - both the top and lower swivels can be independently adjusted in, out, front & back.

The angle relative to the wheel axis is fixed, becausy the hub and wheel are bolted together and the only adjustment of contact patch centre relative to axis through the swivels is by adjusting the wheel offset.

I think.

[strat6v]

KPI is fixed. It's a line, 90 degrees from the angle of the stub axle, in relation to another line drawn through the centres of the ball joint tapers ( in our case)

Does that help?

I'll scan a pic from the book later. ;)

[CorseChris]

I had a great drawing of the upright...but can't find it at present. It clearly showed all the pertinent details. Seem to recall it was in a post by Jeff Davison way back...I'll go have a look.......

[CorseChris]

this picture hints at the angle in question... http://www.stratossupersite.com/forum/attachment.php?attachmentid=2077

Draw a line through the balljoint holes, draw a line through the stub axle. KPI is the angle between them (or 90 - that angle, depending on how you want to specify it). Supposed to be 6 degrees for the 132.

Can't find that diagram though...come on John, get scanning.....

[strat6v]

This should help :)

[jadefarms]

Exactly right, but Stratos/Hawk has machined extension mounted on top so the angle needs extending to the top rose joint. If, as Martin has suggested, the top mounting of the Fiat 132 stub axle could be bent, the angle would be changed to give more (or less) KPI, to maintain zero scrub radius with wider (coffin spoke?) wheels.
I wonder if one could machine a slight angle to the base of the extension, to achieve the same effect.
As Martin says, some accurate measurements and drawings of all the dimensions, offsets etc are required.
My brain hurts...
Struan :)

[jadefarms]

Something like this...

[chris.richard]

It's possible that the extended upper swivel position is still on the same line as the one through the stub mounts.
I wouldn't think that machining a new taper in a different position onto the stub is going to be easy/strong enough, but I'm no engineer, as is frequently obvious!

[jadefarms]

Yes, in the normal way the machined extension should not alter the angle which should travel through the same line, but any bend or manufacturing tolerance in the top mounting will affect it.
Martin raised the point about Lancia introducing a bend to increase KPI.
Struan :)

[Chris J]

I just assumed the centre of the top rose joint on the Hawk extension would be on the same line as the top and bottom ball joints.

So that's not the case?

[jadefarms]

Yes I think they should be in line, but any bend in the top stub axle mounting, intentional or otherwise could alter things.... The machined extension would magnify the error/alteration.
Going back to my original query I have 7° KPI one side and 9° the other. I guess my 132 uprights are slightly bent and the machined extension magnifies the error. On a 132 the effect would be hardly noticeable as the top mount bolts directly to the upright.
Struan :)

[Steve Poole]

Very interesting thread this. Maybe this will help

http://www.offroaders.com/tech/Steering-Geometry.htm

Steve

[Martin K]

I wonder if one could machine a slight angle to the base of the extension, to achieve the same effect.

Then you would have to make certain the angle was in the correct plane - careful assembly would be required as any misalignment would affect castor!

[CorseChris]

Finally found that diagram...but although it shows good cutaway detail, it doesn't really give much more info than we already have. Can't find my drawings and calculations I did for my wheel specs either, which is a shame.

I've attached a poor rendition of the 132 diagram for interest.

[strat6v]

Does show an element of scrub radius. Is that acceptable for our cars or should it be nearer zero?

[jadefarms]

Then you would have to make certain the angle was in the correct plane - careful assembly would be required as any misalignment would affect castor!
Quite so, I was thinking theoretically rather than practically! It would be essential to have alignment markings, for assembly.
Struan :)

[CorseChris]

Does show an element of scrub radius. Is that acceptable for our cars or should it be nearer zero?

That it does.....roughly 40% of the height of the upright (whatever that is) so quite a bit really. I aimed for as near to zero as I could get with mine...but can't recal what I managed to achieve. Trying to work it out again now. Could you measure top to bottom on that upright please John?

[Chris J]

Does show an element of scrub radius. Is that acceptable for our cars or should it be nearer zero?

I'm guessing a typical Hawk has more scrub radius than a typical Corse?
(That is, if there's such a thing as typical examples of either type?!).

[jadefarms]

That it does.....roughly 40% of the height of the upright (whatever that is) so quite a bit really. I aimed for as near to zero as I could get with mine...but can't recal what I managed to achieve. Trying to work it out again now. Could you measure top to bottom on that upright please John?
164mm on mine...
Struan :)

[CorseChris]

Cheers Struan. Nice one for the numerologists....

Having done a drawing based on those figures, it seems I have a scrub radius of about 56mm on my car. Assumes the wheels where made to spec. with a 25mm 'inset'.

Any comments on that from the experienced/knowledgable most welcome!

[colin artus]

The kpi for the 132 upright is 6 deg (as already mentioned) and for the Stratos it's 10 deg.
http://i17.tinypic.com/6z5yick.jpg

The Stratos stub axle has been modified by bending the top slightly to achieve more inclination and therefore to reduce the (+) scrub radius. I imagine this was done by heating the forging and applying force. It might sound a bit blacksmithy but the steel is quite ductile. However doing this mod on a commercial basis was not practical and so Transformer/Hawk did not change the kpi from the Fiat spec. Of the two original Stratos stub axles I measured one was 8 deg and the other 13 deg kpi - they were spares so they weren't necessarily off thre same car.

[CorseChris]

Interesting diagram Colin.

Based on a quick measure-up, and assuming a 15" rim(?) I get about 68mm scrub radius for that setup. If it's a 14" rim then scrub radius would be 63mm (roughly).


Good old tweak on the upright isn't it!



....unless I got it very wrong.....

[colin artus]

Chris
The diagram will be a 14" rim - I made the scrub radius 62mm. However the lower kpi/sai for the 132 means that the radius figure will be higher given that the wheel and hub are the same - if you measured from the 132 manual drawing this would explain the discrepency (different hubs and wheel offsets). A quick scribble indicated that (given all else is equal) the change from 6 to 10 degrees kpi decreases the positive scrub by approx 10%
I should also mention that whatever kpi you have, you most definitely want it to be the same on both sides of the car!

[jadefarms]

Chris
The diagram will be a 14" rim - I made the scrub radius 62mm. However the lower kpi/sai for the 132 means that the radius figure will be higher given that the wheel and hub are the same - if you measured from the 132 manual drawing this would explain the discrepency (different hubs and wheel offsets). A quick scribble indicated that (given all else is equal) the change from 6 to 10 degrees kpi decreases the positive scrub by approx 10%
I should also mention that whatever kpi you have, you most definitely want it to be the same on both sides of the car!
How close does it need to be, do you think? :(
Struan

[colin artus]

I would expect anything more than 1/2 a degree difference to exhibit pull in a straight line and this condition would worsen under braking. The Fiat manual gives +/- 20' which is little more. If your stubs are beyond this then you should see about replacing them with a pair that match or modifying one to match the other ( match to the one closest to 10 degrees).

[Sando]

...So going back to Johns original post, the ones he's seen that could be adapted would be 11deg? and nearer the mark than initially thought? especially if you use wheels with a lot of inset or with spacers?

Rob

[colin artus]

The Wilwoods would give 21 degrees kpi (90 - 79). Not necessarily a problem, but further away from the Stratos spec.

[chris.richard]

The Wilwoods would give 21 degrees kpi (90 - 79). Not necessarily a problem, but further away from the Stratos spec.

Maybe it's a bit late at night Colin, but up here 90 - 79 = 11 :D

[colin artus]

Doh! Arghh!
I'll just get me hat.

[strat6v]

Wilwood upright pic.

Could make a good replacement if the fiat part supply dries up

[CorseChris]

That Wilwood upright looks an awful lot like the Fiat item doesn't it.
Colin, thanks for the info - I wasn't far out with my 63mm figure then. All based on scribbling on a print of that diagram you posted so not too accurate!

The scrub on my car is based on the 132 upright and hub, no spacer, 16" rim 205/50 section tyre with a nominal rolling radius of 12" and 1" offset on the rim.

I'm wondering if I could have a KPI problem as the brakes always perform perfectly when on test rollers. Very closely matched. One other major factor I've not checked is corner weights.

...but to avoid hijacking the thread even further.....those Wilwood uprights do look promising....and I think Struan needs to tweak one of his uprights ;)

[jadefarms]

That Wilwood upright looks an awful lot like the Fiat item doesn't it.
Colin, thanks for the info - I wasn't far out with my 63mm figure then. All based on scribbling on a print of that diagram you posted so not too accurate!

The scrub on my car is based on the 132 upright and hub, no spacer, 16" rim 205/50 section tyre with a nominal rolling radius of 12" and 1" offset on the rim.

I'm wondering if I could have a KPI problem as the brakes always perform perfectly when on test rollers. Very closely matched. One other major factor I've not checked is corner weights.

...but to avoid hijacking the thread even further.....those Wilwood uprights do look promising....and I think Struan needs to tweak one of his uprights ;)
Yes I guess I do, but how? They were a pair supplied by Gerry with the kit.
Back to the scaffold pole I suppose and some heat! Just tricky guessing how much is 2°... :o

[strat6v]

Big jig marked with degrees, attached to a big vice :)

[John]

What is the correct procedure after heating a component to bend/adjust it?
Surely the uprights would then need further heat treatment to normalize them and or put some strength back into them?
I'd take some serious advice before you do this, Struan.

[jadefarms]

What is the correct procedure after heating a component to bend/adjust it?
Surely the uprights would then need further heat treatment to normalize them and or put some strength back into them?
I'd take some serious advice before you do this, Struan.
Gerry says that the Lancia Team did it as a matter of course, in a crude way between events, different angles for different setups and tyre widths. Simply heat up the upright and adjust as required.
Scarey stuff I will admit and I think I will limit any changes to the minimum to balance the two sides...
There is really nothing to go by in the way of angles on the upright, in any case. Kingpin angle is dictated by the centres of the upper and lower joints, which are not accessible for accurate measurement, only indirectly by the kingpin alignment gauge.
Alternatively, just change the uprights and hope for a better matched pair... :( Struan

[CorseChris]

Some kind of jig for sure. John's idea of a bar turned to snugly fit inside the tapers would be a good way to get a true line down that axis and establish one reference. You might even fix the problem there. The plywood cutout accurately made would do the other. Then tweak with a fly press perhaps? Not as easy as straightening out a set of forks though :(

An alternative might be my notion to use the ball & taper sections from some dead joints and use the machining marks in the ball to locate centre. That would leave the area between the lugs free so you could use the same trick to locate the stub axle axis (machining marks east to get at).

...IYSWIM!

It might be rash but I'd think a bar through the tapers should give a quick go/no-go check if you are looking at replacements. I'd expect that an upright where the bar goes nicely through would be true & straight. Looking at the Stratos diagram, it looks as though it takes a fair old tweak to get much of a change, so you could probably get fairly close with the Mk1 eyeball???

Thinking about how the things might be made could help - how would they hold the parts during machining?? Identify those points and it should be pretty simple to establish measurement datum points.

Dunno, just rambling really.....but thinking I might need to make some measurements myself......

[CorseChris]

Finally made a start on looking into this problem on my car...swapped the front wheels - no change. Went to fit a replacement pair of hubs only to discover they aren't right. Couldn't fit the new bearings as the inner one is smaller than the 132 upright. The correct bearing ID is 32mm IIRC, the 'replacement' hubs had a 25mm bore bearing. Anyhoo, decided to just swap the hubs left to right and will see if that makes any difference.

[CorseChris]

....no change, so the hubs are fine. I'll swap the uprights left for right next......maybe a pair of those Wilwood items will find their way onto my car soon......

[CorseChris]

Think I might investigate this option a bit further....Rally Design are doing them for £125 a pair, so not too painful. I'll have to check, but it looks as if the Fiat hubs might fit.....probably too good to be true, but from memory, they look about right....

[strat6v]

Think I might investigate this option a bit further....Rally Design are doing them for £125 a pair, so not too painful. I'll have to check, but it looks as if the Fiat hubs might fit.....probably too good to be true, but from memory, they look about right....

Ever the optimist :D