17 replies to this topic

[vvcmetro]

How on earth do you calculate the rear roll centre for a mini? I race a metro and am in the process of making a tubular front end/wishbones etc for it and cutting the front end off - like you do for a flip front mini. I can calculate the front roll centre easily enough, but how do you calculate the roll centre for a swing arm like mini's and metro's have?
If anyone on here has had any experience with this your help would be greatly appreciated.

cheers

jason

Edited by vvcmetro, 31 January 2011 - 01:30 PM.

[Wil_h]

You can't. It dosen't have one.

[vvcmetro]

Ok, thankyou very much. I was thinking maybe you dealt with it as a 4 link live axle or solid axle/coilspring?


I must add, I have converted to coilover suspension and rear beam as well

Edited by vvcmetro, 01 February 2011 - 03:09 PM.

[vvcmetro]

Or alternatively I did think about 205 torsion beam

[vvcmetro]

Ok, bit more digging now. for swing arms the roll centre is at ground level

[Wil_h]

That's interesting. If you look at semi-trailing arms and extrapolate to a parallel radius arm I guess you could conclude that the roll centre would tend towards being on the floor but isn't actuallty there. But wherever it is you can't move it.

Do you mean a swing arm by the way? I thought that these were what an imp has on the front. i.e. big long arms pivoted near the centre of the car.

Edited by Wil_h, 01 February 2011 - 06:24 PM.

[MRA]

If the pin is inclined at 2 different angles.... would this not create a roll centre ?

When you say you haver a rear beam do you mean "beam frame" or "beam axle" 2 completely different things, unfortunately the tendency to call beam frames beam axles is misleading and confusing.

Beam axle has both wheels linked by a beam, hence beam axle, whilst a beam frame is just another name for a subframe, and would probably be best called a box section sub frame.

[Wil_h]

If the pin is inclined at 2 different angles.... would this not create a roll centre ?

Yes, it's called a semi-trailing arm.

This rear suspension on a mini aparently has adjustable roll centre.

http://www.flickr.co...in/photostream/

Not sure how it works, but I presume it is semi-trailing.

Edited by Wil_h, 16 February 2011 - 05:48 PM.

[MRA]

lol

[matt large]

If your still struggling drop me a line as have just had to do some roll centre calculations for a baja buggy with rear trailing arms, is a lot more simple than you would think but easier for me to show you some drawings than to try and explain it,

matt : )

[vvcmetro]

If the pin is inclined at 2 different angles.... would this not create a roll centre ?

When you say you haver a rear beam do you mean "beam frame" or "beam axle" 2 completely different things, unfortunately the tendency to call beam frames beam axles is misleading and confusing.

Beam axle has both wheels linked by a beam, hence beam axle, whilst a beam frame is just another name for a subframe, and would probably be best called a box section sub frame.

I've got a beam frame, the pivot points are the same as a mini. cast steel trailing arm with roller bearings and rod at the pivot point bolted the subframe/beam frame.

[Wil_h]

lol

I don't understand. That rear suspension is not all it seems. It looks like a standard radius arm in alloy in that photo, but it isn't.

[bmcecosse]

The Metro has a 'beam frame' as standard. The suspension must have a roll centre! I always thought with trailing arms it was through the line of the trailing arm pivots. But I can't find my suspension book at the moment - so I can't check.
Edit - been looking into this and it seems general opinion is that the RC is ~ at axle height - which on a Mini (esp if lowered slightly) is more or less at the trailing arm pivot height. And since the Cof G of an unladen Mini is also nice and low down - it's the main reason the car doesn't roll very much.

Edited by bmcecosse, 16 February 2011 - 10:30 PM.

[Sprocket]

Not really knowing enough about this, I shouldnt comment but I will since I'm sure I read some where that with trailing arms, the roll center if calculated would be below ground level

[MRA]

The only way for that to happen is if the pivot pin intersects with the other pivot pin under ground, the lines of intersection are that the pivot pins intersection point (IP) and the centre of the tyre where it meet the road would be your theoretical RC point, however it is my understanding that this really is only relevant to Semi Trailing Arms, and they would be at a compound angle... such as Mondeo rear suspension... and X type Jaguar, both of which have pretty good handling and relatively low roll in corner.

I would have to agree with bmcecosse on the axle centre line being the RC for Classic Mini

Edited by mra-minis.co.uk, 16 February 2011 - 11:48 PM.