Rear track width

[Howard Wright]

Hi All

I’m about to shorten two long wheelbase axle tubes and believe that I need to take one inch out of each. This falls in line with the difference in half shaft lengths 22 1/4” for the SWB cars and 23 1/4” for LWB cars.

However something is bothering me.  The SWB track is quoted as 3’ 4” whilst the LWB track is quoted as 3’ 7”.  3” difference. 

Where does the extra inch come from?

Cheers

Howard

[Alan]

Because track is correctly measured between centrelines of tyres where they touch the ground?

[Steve Jones]

If you're narrowing a wide axle to fit a short chassis then you need to reduce the overall width by a total of 2 5/16". That means taking half of that, 1 5/32", out of each side tube.

Steve

[Howard Wright]

Hi Alan

This must mean that there is difference in offset in the wheels.  At the time of change between short and long wheelbase the wheels changed from closed centre to open centre.  The tyre size remained the same. 

Cheers

Howard

---

Thanks Steve

Useful info as is your photos of the procedure on an earlier thread.

It still doesn’t explain why the half shafts changed by an inch rather than 1 5/32”?

Cheers

Howard

[Alan]

Howard. You are right. I hadn’t thought that through.

[Colin Morgan]

Sorry, probably doesn't help, but the lengths are quoted as:

short – 22 1/4" x 0.890" dia, standard taper, 1930-31
long – 23 1/2" x 0.890" dia, standard taper, 1931-38

on the A7 Components site...

[Howard Wright]

Hi Colin

Thanks and a slight correction to my first post this thread

https://www.austinsevenfriends.co.uk/for...133&page=2

Shows the original Austin ledgers and quotes 22 1/2”. and 23 1/2” for the two axle shafts.

I know David has done a lot of research on half shafts so perhaps his figures relate closer to actual measured shafts. 

I am certain Steve is correct in there being 2 5/16” difference between the lengths of the axle cases but that still leaves 11/16” to make up to get the difference in track.  Is it possible that the thickness of the 1 1/4 brake drum and open centre wheel material could account for some of this?

A bit pedantic really.  I’ve got the answer I really wanted from Steve (thanks)

Cheers

Howard