Wheel Offset Calculation

[MK1_Oz]

I am trying to calculate the wheel offset I need on my new build - Mk1 Escort with bubbles and Hilux axle. I have looked at a few manufacturer's websites to find calculation methods but none suits my incomplete car.

What I have tried to do is to install the axle and measure the space I have between the bubble arch and the hub mounting face (on the thinking that I want the wheel as far out towards the arch with only an allowance of 5mm (enough??) from the tyre to the arch). From there I know the position of the outside edge of the wheel. Using the known width of the wheel I can then work out the centreline of the wheel and from there I can work out the offset. Its sorta backwards from how the manufacturers suggest calculating it but should get the same figure. Anybody disagree?

OK. Axle alignment. I tried various ways to work out the centreline of the chassis but as we all know, Escorts were not built with small tolerances!!!! I ended up centering the axle between the chassis rails as measured inline with the axle location. Doing that meant that the axle mounting face was 113mm from the arch inner edge on one side and 117mm on the other. Is this an inaccuracy in my measurement of the centreline OR are the bubbles put on a fraction different each side. Hard to tell me thinks!!! My question then becomes, when centering the axle would you centre between the bubbles or to the centreline of the car? (I haven't measured the front suspension mounting points to see if they are centred)

The two ways will vary the offset by a few points - either 0.5+ or 3.5-, when using the chassis rails to align the axle, as shown in the pic of my AutoCAD model below or it would be 1.5- if I centred between the arches.




I need to order my Compomotive MLs ASAP to ensure they get to be in time.

[M11rf]

If you give the length of the axle i am sure someone will be able to tell you what offset wheels you want... What are the options for the offsets?

I have a Mk1 with bubbles and an AE86 axle fitted and ET-12 8" wide wheels, maybe it will help as a reference... I could probably get ET-16 to fit and it would be almost touching the arch.

As for the axle not being central... I think it's pretty normal! If you want to try and move it at all, i would try and get it central with the chassis rather than having it central between the arches (although it should be central with arches if central with chassis )

[Miniliteman]

The difference between the 2 measurements is just 4 mm i.e. if you shift the axle 2 mm it will be cebtral between the arches.
So the measurement then is 115 mm. The 5 mm space between arch and tyre is not alot I would go for 10 mm.
That means the ET for the wheel should be +3.5 .

[MK1_Oz]

I was contemplating a larger wheel to arch clearance. COuldn't quite think through how much the wheel 'moves' outwards when one side of the spension gets compressed.