Good morning all,

I've been told by the local constabulary that the wheels on my baja are too big! I have to return the wheel size to no greater than 15mm larger overall diameter than original, which apparently is the law (haven't checked the RTA website yet tho).

Can anybody please tell me what the original tyre size would be for a '68? I've never had original tyres on it so have no real idea. I know they were 15" rims but I want to be able to make sure that when I get new tyres fitted, they match the overall diameter numbers.

Many thanks,
Marc.

Original wheels should have been 4J x 15", with 5.60 X-plys. If these were 80profile? (not sure for Xplys, thought some were 78?), diam. would be 24.0" or 609mm.
The metric equivalent today is probably 145 x 15, which for standard 80profile radials would be 24.1" or 613mm OD.

You could probably argue that those old 5.60 Xplys were superseded by 6.00 x 15: OD= 24.6" or 625mm.
The metric equivalent should be 155 x 15: OD= 24.8" or 629mm.

Similarly today 155 would probably be replaced by 165R 15, with OD 645mm or 25.4" (for 80profile). So you may be able to argue your way up to 645mm from 609mm, as both 145 and 155 are probably "discontinued" (by almost all makers).

The biggest specified diam. I can see in a published document for 165R15 is 26.00", ie. 660mm.

{You may even be able to argue that "original wheels" also includes 4.5" x 15" (if they are 4-stud)...? And to push it even further, 175 radials may have been allowed fitment on them...?}

You can easily calculate theoretical tyre OD as follows [example for 165mm x 15"]:
(0.80 x 165 x 2) + (15" x 25.4) = 645mm.
where 0.80 is the tyre profile (80% = 0.8), 165 is the width (mm), and 15 is the rim diam. (inch).
[Real tyres may vary by a mm or so from this.]
E&OE.

In Oz you can't get 145 or 155x15 tyres at 80 profile so 165/80 is the best you can do. Every Beetle owner will have this dilemma in Oz.

For QLD only 15mm in tyre diameter is allowed from the largest tyre fitted to that vehicle. I think later GT beetles had 175/70's fitted and you may be able to swing that one as it is the largest tyre fitted as a manufacturers option due to the beetle not changing in design by much after going to BJ suspension.

So there ya go. Heres qld mods page
QLD Mods

and NAtional code of practice pagesNCP pages

Unfortunately a Baja would rarely fit in the confines of these rules so maybe your only option is to transport the tyres to where you go off road and then pop the std size wheels on to go home. Even an engineer should NOT approve outside of these rules and so the rossers are in the right

Going back a way weren't early beetle fitted with a 16" somewhere back there? Theres one option.

Also weren't GTs fitted with 6" wide wheels...?

At that rate couldn't you argue to legally fit 17x7 or something to that effect... Wasnt there some rule about not changing the track by x amount... As for the rolling diamater of the wheel. Is it a braking issue? Could you install type 3 rear drums to compensate for bigger wheels and tyres?

Anyway i dont have any reserarch on the topic so good luck. Just what ive heard over time.

Thanks for the input guys.

After I made the post (I always ask here first!) I did some reserach on various rolling diameters and came up with numbers around the 628.5mm so that seems to be in the ballpark of your comments, Brutus. I've decided on some 205/60-15's which are well within the overall diameter numbers and according to the guy at the tyre shop, who is also the Blue Slip guy, they will be legal.

Thanks for the help!

Cheers,
Marc.