tyres what size

Hi Steve,

Are you changing rims too? I am very interested in seeing your calculations as I want to put 16x8 rims and either 265/75/16 tyres or 285/75/16 tyres on my Landcruiser. Its a DX Landcruiser and come with 7.5R16 as standard on 16x6 rims. According to the RTA here in NSW that modification is outside the legal amount of tyre and wheel size increase allowed and will need an engineers report to make it legal. So, I look forward to seeing your response. The RTA have sent me a document explaining what is allowed and what isn't. Send me your e-mail address and I can e-mail it to you.

In answer to the original question, as far as I know, 7.5R16 were the same size at 235/85/16's. At least that is what many tyre sellers have told me..

Cheers,
Alan.

Alan,

I assume you're referring to the Vehicle Standards Information sheet 9 (Guidelines for Alternative Wheels and Tyres)?

My Cruiser is a GXL, already running 16x8 rims, so I am not changing the rims.

The maximum permissible diameter for a 750R16 (with 'traction tread') is 812mm. There's a 3% variance allowed on the tyre (not the rim), which takes the max to 824.17mm. Add the 15mm increase you're allowed, and you get 839.17mm as the biggest tyre you can have.

Using the 'official' measurement (285 x 0.75), a 285/75R16 tyre has a diameter of 833.9 which is less than the 839.17 from the 750R16 tyre.

A member from here (who's also on another forum I frequent) has confirmation from the RTA that this +/-3% variance is allowed in the calculations.

By my calculations, a 235/85R16 tyre would have a diameter of 805.9, which is pretty close to a 'standard' (i.e. highway tread as opposed to 'traction tread') 750R16 - which is 804mm.

Both diameters listed above for a 750r!6 tyre are the official sizes taken from the 'Rims and Tyres Standards' booklet that the tyre industry use.

Hi Steve,

thanks for your time to sensibly answer my question. will be waiting for your post of the spreadsheet. many thanks.

Bob

Hi Steve,
Yes, that is the sheet I was talking about.

I didn't realise that a GXL Landcruiser would have a tyre placard for a 7.5R16 tyre on the door. I always thought the GXL models came with 275/70/16 tyres as standard and as such would have a matching placard on the door.

Yes, the GXL came standard with 275/70R16 tyres, however my placard covers both the 275/70R16s and the 7.50R16s.

I don't have access to send personal messages, so will have to find some other way to get the spreadsheet out.