Thread: Tyre placard

Originally Posted by sean c

Thanks for replies all. I have purchased Gordon's 18" wheels and was planning on fitting 265/60R/18 tyres. This size is not on the placard and for me the placard makes no sense stating different load ratings for the same vehicle.
Reading through the replies there is enough doubt for me to ask the regulator for an interpretation of what the minimum load rating should be.
Logically it should be 109 as this is the minimum on the placard and the vehicle mass does not change with different wheel size.
Will advise when I get a reply from Qld government department responsible.
The other way I was thinking, if I get no sensible, response is to get an Engineer to sign off on change. Any thoughts on how this might go?
Sean

I have just ordered the silent armours for the D4 and they are arriving this afternoon, so i share your concern re loading.
Speaking from a position of complete ignorance, could the different specified load ratings for each rim/tyre combination reflect different patterns of stress/strain distribution according to the different geometries of the tyres?

Confusing Placard ain't it!!

I have been trying to get clarification on this issue from Qld Dept of Main Roads & Transport. After politely getting passed between various offices I believe I have now solved the mystery myself.
On the cover page of the Qld Transport’s guide to vehicle modifications http://www.tmr.qld.gov.au/~/media/c792a0c9-92b1-43ee-933b-7bdd8b20842f/pdf_modification_motor_vehicles2.pdf it has the disclaimer below;
The contents of this publication are a guide only and cannot be used as a reference to a point of law. For a detailed explanation, refer to the Transport Operations (Road Use Management - Vehicle Standards and Safety) Regulation 1999.
I then looked up the regulation it pointed to and there is no reference to tyre placards at all!!
The only reference to tyre load is text below;
˙Wheels and tyres—size and capacity
35. The wheels and tyres fitted to an axle of a vehicle must be of sufficient size and capacity to carry the part of the vehicle’s gross mass transmitted to the ground through the axle.
The Land Rover manual also lists on page 248 the ‘Original wheel and tyre combinations’ The load index varies from 107 to 112.
I now believe Qld Transport took the easy way out in their guide book by referencing the tyre placard, which most manufactures, except for Land Rover, have the minimum load index listed.
I will follow the Qld regulations and ignore the guide book which ‘cannot be used as a reference to a point of law’, according to the disclaimer.
Don’t know what other states have but may pay to check the actual legislation rather than the guide books published by the relevant authorities.
Sean

Of note is that the information required about a vehicle for Australian compliance aproval as shown on the Road Vehicle Descriptor record, does not include tyre load ratings. The tyre and rim information section only provides for tyre sizes, rim diameters and widths, offset, front and rear tracks and applicable vehicle model designations (eg S, SE, HSE).

When selecting tyres, particularly for something as specialized as the D4, there are a couple of other numbers besides the Load Index or Rating, (an up to 111 number on the D4). There is also Load Range which is most often XL and Speed Rating, the V letter for the most part. My view is that the load index number, as long as it is close is not a big deal, but the Load Range is. In short, it is the difference between car tyre construction and heavier truck tyre manufacture. The speed rating is more of a heat buildup sort of thing related to load and speed.

The links below are from the Tire Rack USA site and are I think provide pretty good explanations of the three factors.

Tire Tech Information - How to Read Speed Rating, Load Index & Service Descriptions

Tire Tech Information - Load Range/Ply Rating Identification

Tire Tech Information - Sidewall Markings