simon's learning what to do with the polo thread

[simon k]

The electronics are simpler but the suspension is multiple times harder to get to do what I want it to do. Try getting a Mini to have greater than 1 to 1 camber change to roll ratio, or heaven forbid a sub terrainian rear roll centre

erk.... do they even have a rear roll centre in the first place???

A bit of action happened on the rear bar on the weekend. I think I'm going to make an adjustable blade type bar for it... the standard one was going to be just as hard to mount without the original brackets.

I was also putting adjustable bottom arms on the front to get some more caster and Jason showed up, he looked at the top arms and said "Why don't you swap them from one side to the other???". We measured a spare one and I think it'd come up with something like 34° - I've no idea what a practical maximum caster is, but I reckon that's too much. I couldn't find any references to anyone else doing it, in 60 years of mini racing, if someone had thought it was a good idea it would be published somewhere

[simon k]

simon these Ground Control adjustable tops are for sale in the parts section. Probably wouldn't fit but is a good parts breakdown iin case you were to make something. I do know that Greg (Kaanage) fitted some to his Tdi that he tracks. He runs at Phillip Island a fair bit. He might be worth contacting re some advice for tops.

thanks Sam - I checked it out last night and wrote you a reply, but shut down my computer before hitting "Post" - duh... the parts breakdown is handy. Will talk to Greg when it's time - another run at Phillip Is. would be fun actually, I did a regularity there in the mini once

[sambb]

Don't mercs have like 20+ degrees of caster dont they? Would be hard to hande without power steering if there was any steer offset/scub radius.

[Sydneykid]

erk.... do they even have a rear roll centre in the first place???

Yep, typical trailing arm roll centre, to lower it (which we absolutely need on a FWD car) we need to raise the outer trailing arm pivot on the body. Or lower the inner. The problem is there isn't enough room to get the roll centre even to ground level, let alone below it. The other issue is the camber moves at the same time as the roll centre and to get the roll centre low enough we end up with a lot of (too much) negative camber. Plus of course we want to toe it out a bit and that also means moving the inner and/or outer pivot points for and aft.

There's this one control arm that looks after roll centre and toe plus static and dynamic camber. This is the common "old" car problem, we can't fix one thing without screwing something else up.


Cheers
Gary

[Sydneykid]

Don't mercs have like 20+ degrees of caster dont they? Would be hard to hande without power steering if there was any steer offset/scub radius.

18 degrees of caster is not unusual on BM's and Merc's, but they have built in alignment between their SAI and scrub radius. Which is hard to do after the fact. Control arms, steering rack, steering arms, ball joints etc all have to designed for that geometry. I had a Falcon that I managed to get 10 degrees of caster on and it was fun to drive, once you got used to it.


Cheers
Gary

[Water Boy]

Is this Ipra Gary?

[simon k]

I took one of the rear stub axles off on the weekend to see about this spacer plate.

1. extra holes to rotate the standard caliper (I'm not brave enough to chop the original lugs off)
2. extra set of holes to mount a second caliper for a hydraulic handbrake (I'll do some motorkhanas with mine at some point)

anyone who wants some can cut the extra bits off

how thick - 10mm?
what should I make it out of? the plate on the end of the bar is really hard, like chome moly or something...

I reckon I'll make it look something like this...

[sambb]

Legend. Every time I'd walk past my beam that sits against the garage wall because its too heavy to get under the house, I'd think I hope that industrious Simon does those spacers because I'm too lazy at the moment.
Yeah I think 10mm would be a good thickness for Et40 6.5-7in rims with 205's. I space my ET40 7in rims 20mm at the back on the track which is just ok on 195's but on 205's the tyre is out under the guard lip and would easily be hitting it if it weren't for such stiff rear springs. Even 15mm spacers in that instance is pushing it a bit, so 10mm spacers would be good. Measure your standard front track and I think you'll find its about 20mm wider at the front so 10mm spacers at the rear (20mm wider track) could stay in there all the time making the car square tracked, and then when you go on the track you could space the front to eek the widest possible track width there. Definitely measure the front though to confirm that though.
RE materials I think Gary had said which grade of aluminium they'd done it in, but I cant find that little discussion on my build thread.

[simon k]

I'm seeing lots of people saying 6061, and others saying 7075 - I might need some convincing about making them out aluminium and not steel - there is a good chance that they'll never be removed from the car, and only be looked at when changing rotors, so I'd prefer to make them out of something that can be ignored and trusted to do its job...

[Sydneykid]

RE materials I think Gary had said which grade of aluminium they'd done it in, but I cant find that little discussion on my build thread.

I'll confirm it with the machinist but from memory our caliper brackets are 6082 T6.

Cheers
Gary