AT tire profiles vs AS tire profiles

[popeye427]

I'm working on a design for an SUV chassis that will be sold in markets that include extreme snow and off road. The tire assumptions that came with the proposed vehicle only show metric AS tires. I'm insisting that we need to have AT tires in the mix for this vehicle, and that requires accurate tire profile assumptions for packaging and clearances.

I have an older version of a T&RA program that provides a calculated profile for P-metric AS tires. Is there a formula for predicting tread diameter, width, and shoulder profile changes from the same size AT vs AS tires? The T&RA yearbook data indicates about a 6mm diameter increase for deep traction treads in the sizes I'm using. I can simply add the tread depth difference, but I'm hoping for a more structured approach. Any information would be greatly appreciated.

 

[CapriRacer]

Popeye427,

First, there are no laws or regulations that say that tires have to meet certain dimensions. That means they can be any size the tire manufacturer decides. They usually follow TRA or ETRTO or JATMA, but not necessarily.

But vehicle manufacturers can specify the dimensions. A good place to start for a vehicle manufacturer is TRA, etc dimensions (which ought to be the same regardless of the standardizing organization.)

Now, allow me to answer your question: In theory, All Terrain tires are dimensioned according to "Deep Trac. Tread" column listed in the TRA Yearbook - and not the "HWY/Trac. Tread" column. Doing a quick survey confirms what I thought to be true - the only difference is the AT is 0.23" larger in diameter (for P metric tires). This makes sense if you consider that difference is 3.7/32nds difference in tread depth. (about 3 mm)

But I'll bet your real question has to do with the page labeled "Definition of Maximum Envelope Dimensions.......". I think that drawing is calculated to include ALL tires, including All Terrain and Winter tires.

But you can survey the proposed tire suppliers for this vehicle to see if they agree. Again, there are no regulations that require compliance with any particular set of dimensions.

 

[popeye427]

Thanks Capriracer,

You are correct in your assumption that the critical point was the definition of maximum envelopes. I had already adjusted the projected dimensions to simply reflect the deeper tread, but its always useful to see an assumption confirmed.

As for suppliers, well there really aren't any at present. This is an overseas vehicle, destined for that market, and I'm a subcontractor to the guys contracted to do the ADAMS modeling and package layout.

Thanks again