12 replies to this topic

[JCmini]

I just checked my rear left tyre and the outer third is bald. The center is 1.6mm and inner 1.6mm.

 

So getting new tyres tomorrow.

 

I looked at an old alignment result from last year. Driven about 4k since then. 

It looks like both rear cambers are positive left 0.38  and right 0.58. I think it should be zero. And the back left is toeing in too much 0.41.

 

Would this be the reason for the bald outer edge?  The rear off side has no issues. Its on 12" wheels. 

 

Just deciding whether to buy shims and if so how much or try the mini spares adjustable brackets. 

Attached Files

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Edited by JCmini, 30 March 2020 - 08:07 PM.

[cal844]

Personally I'd try simply loosen the radius arm pivot pin and gently lever it forward slightly.

[unburntfuelinthemorning]

Positive camber and toe in will wear the outer edge.  The camber is only slight so it's probably the toe especially as there's twice as much on the left.  Either that or it's driving round that roundabout for an hour at the grip limit although this would show on the front more.

[weef]

Hi  the rear wheel alignment should be:

 

Toe in   1.5mm to 3.0mm

 

Camber   Negative  0.5mm.

 

I don't know what this equates to in decrees but the rear camber should be negative not positive as in your case. Positive camber will  give the tyre wear pattern that you describe, as would an excess in the toe in.

The toe in setting can be adjusted by the use of shims behind the outer radius arm mounting but the camber setting is more difficult to adjust. There is no way engineered in the standard make up for this adjustment, so you may have to slot the outer mounting bracket hole to allow some adjustment. A large heavy duty washer can be fitted between the bracket and the nut and once the correct parameters are set tack weld this washer in place to maintain this setting.

It goes without saying that before any settings/adjustments are made the radius arm components must be in perfect condition.

[unburntfuelinthemorning]

Hi  the rear wheel alignment should be:

 

Toe in   1.5mm to 3.0mm

 

Camber   Negative  0.5mm.

 

Where did you get your figures from?

[GraemeC]

Rear camber is +ve as standard.

[nicklouse]

some settings to aim for. and yes positive camber is standard.

 

[JCmini]

Ok think I will leave the positive camber for now. Just going to add shims.
Minispares shims reduce toe by 0.8mm so 2 or 3 seems about ? I think 0.41 degree is about 3.6mm.
Does that sound right?

 

Here is  some photos just for reference of the Tyre. 

 

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Edited by JCmini, 31 March 2020 - 10:39 AM.

[unburntfuelinthemorning]

Not sure but go conservative with the shims, you don't want any toe out as it's rather dangerous on a road car.

[GraemeC]

Firstly - be careful.  The figure on the print out isn't 0.41 degrees - it is 0 degrees 41 minutes.  So with 60 minutes in a degree it is 0.68 degrees.

Secondly - alignment figures in mm are specific to wheel size, given the reading is taken at the edge of the rim.

 

So for a 12" rim:

12" = 304.8mm

Alignment in mm = sin0.68 x 304.8 = 3.62mm

(Note: this is per wheel, so would need to be doubled (or each wheel calculated separately and added together) to give overall toe).

 

So you would want to approximately half the toe in on that wheel - a reduction of 1.8mm.

I would use no more than 2 shims and re-measure (the MS quoted figure can only be a ball park).

 

 

For reference for a 10" rim the same angular alignment would give:

10" = 254mm

Alignment in mm = sin0.68 x 254 = 3.03mm

Edited by GraemeC, 31 March 2020 - 02:47 PM.

[imack]

The shims I bought from minispares measured 20 thou, not the advertised 28 thou.

[JCmini]

thanks everyone for your contribution. And Graeme for that maths lesson. Just about kept up. I did not know about the degree and minute difference. Makes  more sense now. 

 

Minispares confirmed to me that each shim reduces toe by 10 minutes or 0.167mm. Which makes total sense now to only add 2 shims to equal the other side. Hopefully this should sort the tyre rubbing out with the new tyres. 

 

Do you think I need to do any thing about the positive camber or just leave it? 

Edited by JCmini, 31 March 2020 - 03:40 PM.

[GraemeC]

Personally I'd leave it for now and see how you get on.

To change it later is either a file and welder job (free-ish) or buy some adjustable rear brackets (expensive and you'd need to get them set up).