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MG Midget and Sprite Technical - Minimum Centre Bore Dimension for 13' Alloy Wheels

Dear All,

Please bear with me while I try out all this BBS stuff before I introduce myself properly!

The BRG Morry is "Little Dog I", a car that my late dad and I occasionally raced in the SA National Saloon Car Championship Class W (1000cc) in the late 60s/early 70s, sadly no longer in existence.

The white Morry (Little Dog II) is currently undergoing restoration and modification as a "Street Legal Concours Classic Racer" (my terminology in order to stay focused); basically a replica of its predecessor but with a little bit more development

The blue A-H Sprite Mk II (The Ruum) is currently undergoing restoration and modification also as a "Street Legal Concours Classic Racer"; basically a replica of a SCCA F/G/H Production race car, and will share identical components with the Morry wherever possible to ensure more "bang for my buck"...

And now for my question:

I am 6000 clicks from home working in the Niger Delta and urgently need forum help with the minimum centre bore dimension that can be used for 13" alloy wheels fitted to a BTA1254 Spridget hub with/without spacers.

Thank you.

Cheers for now,

Rob T


K R Tissington

edit as confused myself!
David Smith

Sorry, I tried to introduce myself and ask a question all at the same time! Here is my question again:

Can anyone help me with the minimum centre bore dimension that is required for 13" alloy wheels fitted to BTA1254 disc brake Spridget front hubs, with/without spacers. I don't have the hubs yet to measure as these are being sourced from Mini Mania (USA) and I would like to order my wheels which are Compomotive 7J x 13" TH1370 ET02. My measurement of both the Morris Minor and Sprite drum-braked steel wheels indicate that 65 mm dia will work...

Thanks for any assistance.

Rob T


K R Tissington

Here is a composite picture of the bare hub, and with a measurement across it's narrowest part.

At it's narrowest, the hub diameter is approx 57.25mm.




Lawrence Slater

However, there is a fillet radius at the bottom as shown here in this composite.

The diameter at the largest is about, 66mm.

As can be seen here.

So your wheels will need an internal chamfer to accomodate that radius.

PS, mine are DISC hubs.




Lawrence Slater

Pretty much as Lawrence says, but:
The center protruding part of the hub is an uncontrolled (diameter) dimension, and the hub itself is a horrid lumpy casting, inside and out. They are frequently way out of balance. If you are spending that kind of money on wheels to run at high speed, you should look at doing some machine work on the hubs to help out.

The minimum possible on the hub centre is 55mm, with a radius at the root. That should give you a clean spigot, and you could (just) turn the outer half down to 54mm, which is the smallest commonly found wheel centrebore = Mazda. Anything bigger will probably give an incomplete spigot, hence still out of balance, and NOT suitable for hub centred wheels. If you want hub centred wheels, then you need to turn an accurate spigot, then sleeve to size desired. At 65mm+, any wheel should fit, but check for seating at the radius.

FRM
FR Millmore

Hi Lawrence,

Thank you so much for taking the trouble to measure a hub for me. The info provided is exactly what I needed to make a decision.

All the best,

Rob T

------------------------------------------------------
Hi FRM,

Thanks for the cautionary information. Compomotive have advised me to use lug-centric mounting and since I might be obliged to run a thin spacer to cater for backspace interference, I could reduce the centrebore dimension to say 60 mm or a bit less, leaving a bit more metal around the stud holes.

Cheers,

Rob T
K R Tissington

You're welcome. :)
Lawrence Slater

This thread was discussed between 01/02/2012 and 02/02/2012

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