How much castor?

[greenamex2]

Parallel at the front. Keep meaning to try some toe out but worried about losing straight line speed, the cars only good point, or damaging the tyres.

Five link live axle at the rear so whatever the axle ended up with when it got the wack that caused this particular one to have over 1/4 of a degree of negative camber!

I suppose at this stage it might be worth pointing out that me rear axle suffers from a form of 'roll steer' owing to the angle of the lower arms (the top ones, owing to them being a third of the length of the lower ones, just stop the top of the diff nodding backwards and forward. Oh to be able to extend into the passenger compartment, or at least move pickup points about). I have thought of a way of 'interpreting the regulations' to sort out the arms, just trying to decide whether it is worth the effort.

The 'roll steer' twists the axle in the same direction as the front wheels, sort of negating some of the effect. I have always assumed this would just confuse me a bit whilst I was turning in and them become irrelevant once in the corner.

Any thoughts.

[dtype38]

Originally Posted by Denis Bassom

The 'roll steer' twists the axle in the same direction as the front wheels, sort of negating some of the effect. I have always assumed this would just confuse me a bit whilst I was turning in and them become irrelevant once in the corner.
Any thoughts.

If I'm understanding that correctly then it sound like your car is trying to crab in at back when you turn in. That may not be such a bad thing if your car would otherwise have a tendancy to oversteer. If you get understeer though, that might be the cause. Pesonally I'd not like to have to fight my rear axle to get my car to turn.

Is the effect changed by ride height? Could it be minimised by running with the lower wishbones horizontal (the pivot points that is) so that both wheels are pulled by the same amount as one goes up and the other goes down?

[johnny yuma]

Originally Posted by johnh875

For the benefit of those outside Australia, the year should be 1971 not 1951

nah I have a 1951 FX holden with EH179 ,4 SPEED,LSD,HT DISCS FRONT But on all original front end available geometry.With full trim 55s oran park,64s amaroo have driven it interstate,nice to steer,bit hard in the springs on backroads though! I THOUGHT OUR BRITISH COUSINS MAY HAVE HEARD OF XUIs,but not 48-215s

[Al Weyman]

Lets see a picture Johny sounds interesting.

According to our old friend Fred Puhn in How to Make Your Car Handle, Rear axle Roll steer is designed into a car by some manufactures to induce understeer which is reconed to be safer in a road environment.

[greenamex2]

Interesting Al, what page number? And yes, I do have pretty much every technical motorsport book ever!

Of course mine wasn't designed in by Toyota but caused by me lowering the car. Well guessed dtype38. As I can't move my pickup points I have come up with a way of using the standard pickup points but not necessarily in the manner Toyota intended, to paraphrase Eric Morecombe.

[Al Weyman]

There is a section deatiling a Pinto leaf sprung rear end and the angle of the front and rear spring mounts, I have not got the book in front of me and am too lazy to look for it but it is in there.

[dtype38]

Nice one Al. I didn't read that bit of Fred's book because I don't have that sort of axle.... but he is the reason I don't have anti-roll bars. I just got out my welding gear started at the front of the book (index says p23 and p92 for roll steer)

Graham, are you allowed extra linkages in your suspension, so long as you keep all the original ones in the original places? Reason I ask is that you may be able to get control of the movement by effectively adding additional radius arms to counteract the change in ride height. It would also very much depend on what is being stretched/flexed/pivoted for the "roll-steer" to occur. If you're fully rose jointed it wouldn't work, but if the movement is bush compression, then an angled radius arm linked to the existing one might sort it

[Peter Mallett]

Originally Posted by Denis Bassom

Parallel at the front. Keep meaning to try some toe out but worried about losing straight line speed, the cars only good point, or damaging the tyres.

Used to run parallel but got so much understeer on braking and turn in (good in FWD though). Now run 30" toe-in. You still need to nail the corner but no understeer at all.

[dtype38]

Peter, now I am confused... I use toe-out at the front to get it to turn in. I thought it was toe-in that caused understeer (ie stability... wants to go straight and all that)

[Al Weyman]

According to Mr Puhn you are right dtype, I was just about to ask the same thing. That is why I reduced my 1/8 toe in to zero to try to reduce the understeer,

[greenamex2]

Graham, are you allowed extra linkages in your suspension

Not sure if you meant to aim this at me but it is applicable to my regs. The scrutineers interpretation of this reg was if you could still drive the car round the paddock WITHOUT the extra links then they were fine by him. As you said, this opens up a whole raft of tuning possibilities!!!

[dtype38]

Sorry, yes Dennis I did mean you.

And yes I meant an additional linkage. I was thinking of something along the lines of a high level radius arm angled down at the reverse inclination of what you have effectively pointing up because of lowering the car. It would revert to exactly what you have if it was removed, but you would need to rubber bush the new one quite softly to allow the correct articulation of the suspension but with enough "push" to counteract the "pull" causing the axle twist.

[graham bahr]

[QUOTE=dtype38]

Graham, are you allowed extra linkages in your suspension, so long as you keep all the original ones in the original places? QUOTE]

dtype you had me going for a minute there, i was trying to work out where you might possibly fit an extra link to an E30 beemer with its independant trailing arm rear suspension and well located front arms and struts, then i wondered if you were refering to T+R regs for when i have my committee hat on,

i gave up... and carried on reading the posts, then i saw the light

[graham bahr]

Originally Posted by Denis Bassom

Not sure if you meant to aim this at me but it is applicable to my regs. The scrutineers interpretation of this reg was if you could still drive the car round the paddock WITHOUT the extra links then they were fine by him. As you said, this opens up a whole raft of tuning possibilities!!!

hmmm, thats a pretty free regulation

[Al Weyman]

Does'nt that just mean that the original links are all fitted and functioning? Much the same as CTCRC which says you can add devices like anti roll bars and watts linkages.

[dtype38]

[QUOTE=graham bahr]

Originally Posted by dtype38

i gave up... and carried on reading the posts, then i saw the light

There was light ??

Actually, I have absolutely no idea what your back end looks like and went way out on a theoretical limb base purely on my imaginings of what your problem might be. Sorry... got carried away

[greenamex2]

Just read the bit in Fred Puhn's book, whilst I prefer not to take too much notice of American books on handling it does make a lot of sense.

Between a bit of extra castor and some fiddling with my links I should have my slow corner entry problem fxed. Hopefully this will also mean less bodywork caused damage by pug 205 drivers not expecting me to be slow into a corner despite having me a faster lap time than them!

[Al Weyman]

After reading this thread and having a few handling problems after having to raise the ride height and run smaller diameter wheels to comply with CTRCC pr 73 regs and looking at a long distance shot if the car on Neil Brays site where I swear you can see masses of camber on the nearside as turn in I decided to check my caster and camber this weekend as it is definitely well out of whack (I know I should have checked it before taking it out again but there you go). Anyhow I also checked the camber gain at full bounce and droop and when turning the steering.

Shock horror on the nearside I had a static camber of 5.5 degrees going up to 8 degrees on full droop with positive camber gain in full bounce. On the turn it actually reduced camber by 1.5 degrees. The other side was not a lot better the static camber was only about a 2.75 degrees but the postive camber gain was the same as the nearside. I checked the castor and the nearside was going the wrong way by 1 degree (negetive) and the off side was about 1 degree the right way (positive).

Anyhow after a fair bit of work and messing about I managed to set the camber on both sides to around 3 degrees and the caster about 4 but that was it and without cheating was as good as I could get it. I rechecked the camber at turning (and it does not turn the absolute full way because of the 6 pot calipers) it now gained about 1.5 degrees which is a hell of a lot better than loosing about the same so a net gain of 3 degrees camber gain on turn in, very handy.

So how bad lets hope it works it must be better than it was, still have no camber increase on full bounce and increases camber on full droop but there you go that is the way the suspension is designed I guess and again without cheating and moving the mounting points is as good as it is going to get.

So thanks to Dennis for starting this thread or I would have not noticed the problems lets hope it does the trick, good one!

[graham bahr]

nice one!

[greenamex2]

Originally Posted by Al Weyman

So thanks to Dennis for starting this thread or I would have not noticed the problems lets hope it does the trick, good one!

This was supposed help ME go faster, not anyone else!