2008 A4 Avant 2.0 6MT

The factory 17 x 7.5 rims have tires with Load Cap of 94H or 1477lbs (235/45/17).

I am looking to switch to 18"x 8.5-235/40/18

The tires I am looking at tirerack are 91H 1356lbs. But Tirerack pulls them up as OK.

Max load of vehicle(vehicle weight + max cargo load) divided on the 4 tires (even taking uuneven fore/aft weight distribution into account) puts the max load at 1356 or 91H per tire.

-What is the minimum load that is OK?
-Is Audi putting 94 because of extra rim protection?

-Is 91 OK as per Tirerack recommendation? Or should I stick to 94?

--Anyone done 91?

Any insight would be appreciated.

Any ideas?

Thanks.

 

How many applicable tires actually carry 94H?

 

As long as the Gross Axle Weight Rating (GAWR) on the driver door placard is 2712lbs or less front and 2712lbs or less rear then these tire will indeed meet the maximum load capacity that your axles are designed to carry. From my experience 91 load tires are pretty common to use and work with no problem on the A4 2.0T cars.<ul><li><a href="http://www.tirerack.com/a.jsp?a=AR8&amp;url=/tires/index.jsp">Tires</a></li></ul>

 

The load rating of a tire is more-or-less proportional to the amount of air in it. You can increase the load carrying capacity of a tire by either making it's internal volume physically larger (wider tire, taller sidewall, smaller wheel) or by increasing air pressure; and, of course, the reverse is also true. As a result, the specific load rating of a tire is only achieved at a specific pressure, which <a href="http://www.tirerack.com/a.jsp?a=AR4&url=%2Ftires%2Ftiretech%2Ftechpage.jsp %3Ftechid%3D55">Varies from 35-42 PSI</a> depending on the construction of the tire.

Heat is the enemy of a tire. Running a tire overloaded or underinflated results in higher operating temperatures from the additional flexing of the sidewall and tread. At excessive temperatures, the tire can fail at speed, usually from tread or ply separation (think <a href="http://en.wikipedia.org/wiki/Firestone_Tire_and_Rubber_Company">Firestone 500</a>).

So ... If you're running a tire at it's actual physical load limit, you <b>must not</b> run the tire below it's specified air pressure, and specified by tire manufacturer standards, not the pressure specified by Audi on the gas tank door. Other than excessive tire wear on the center of the tire, there's no safety risk from running the tire overinflated up to the maximum stamped on the tire. As long as you don't overload the tires, there's no minimum load rating. Using the 94 load rating as specified by Audi rather than 91 gives a bit of a safety margin and/or allows running lower tire pressures for a softer ride.