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      06-26-2011, 07:55 PM   #1
TN_3
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Tire Load Rating?

I am in the process of researching replacement tires for the RFTs on my incoming X3, and noticed that the factory tires have a load rating of 102. Most of the tires I am looking at have a rating of 98. I looked through the X3 manual and didn't see a minimum load rating recommended by BMW. Anyone know if there is one?
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      06-26-2011, 11:07 PM   #2
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Originally Posted by TN_3 View Post
I am in the process of researching replacement tires for the RFTs on my incoming X3, and noticed that the factory tires have a load rating of 102. Most of the tires I am looking at have a rating of 98. I looked through the X3 manual and didn't see a minimum load rating recommended by BMW. Anyone know if there is one?

Where did you find a specification for the factory tires having a "load rating of 102". The standard 35i tires are 245/50R18's with a load rating of 100V (meaning 800kg load and max speed of 240 kph (149 mph).

Are you sure you're comparing tires of the same size?

I checked ratings of (30) different tires in the 245/50 size (all I could find that fit the X3 35i standard wheels) and every single one had a 100 load rating. the more expensive "summer only" tires usually carried a 100Y or 100W rating, while the least expensive versions were rated at 100H (same 800kg load, but max speed reduced to 210kph (130 mph). Every single tire carried a "100" load rating.

A fully loaded X3 (carrying 903 lbs of passengers and cargo) has a gross vehicle weight of 5136 lbs, with about 58% on the rear (most loaded) axle.

That means that each tire must carry a load of 1490 lbs. A modern tire must have a minimum load rating of at least "95" (690kg - 1521lbs) for a fully loaded X3. Any tire with a "98" rating (750kG - 1653 lbs) would provide a nice safety margin. All the above assumes that tire pressures are increased appropriately for the higher load.
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      06-26-2011, 11:13 PM   #3
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I've ordered the M-sport package which comes with the 245/45-19's. OE tire is the Goodyear Eagle LS-2 RFT with a load rating of 102.

I, too, did the math and a tire with a load rating of 98 should be sufficient, but didn't know if BMW had a recommended value.
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      06-26-2011, 11:30 PM   #4
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Originally Posted by TN_3 View Post
I've ordered the M-sport package which comes with the 245/45-19's. OE tire is the Goodyear Eagle LS-2 RFT with a load rating of 102.

I, too, did the math and a tire with a load rating of 98 should be sufficient, but didn't know if BMW had a recommended value.

Congrats on the M-Sport on order. Hope the wait is over for you soon.

I wonder if all M-Sports will be delivered with the Goodyears, or if they will change depending on supply? The standard 35is were coming with Pirelli P7's for a long time and then all of a sudden people were getting Goodyears and Dunlops. The Pirelli RFTs do have a 98 rating and I wouldn't be surprised to see some M-Sports wearing them upon delivery.

Since BMW does not seem to have a minimum (load) spec. it looks like the actual load calculations are the best way to go. Since even the "98" ratings gives a large safety cushion (3306 lbs rear axle load) and since the speed ratings are way above what any stock 35i can do, you should have no problems whatsoever, unless you drastically overload the car (which we know you won't do).
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      06-27-2011, 10:50 AM   #5
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Basically I have narrowed my choices down to either the Conti DWS or the Pirelli P Zero Nero A/S. The Contis have a load rating of 98, which is sufficient for the vehicle like we stated earlier. The P Zero is available at a standard load rating of 98, but they also have a XL rated tire in the proper size that is rated at 102. I'm wondering if the XL rated P Zero might be better suited to the X3, as it matches the load rating of the stock tires.
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      06-27-2011, 06:51 PM   #6
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Load rating does seem to affect stiffness of sidewalls (all else equal), so factor that in.
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      06-27-2011, 07:07 PM   #7
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That is part of my dilemma...the DWS is known for soft sidewalls, and if I add into that a lower load rating than stock, I'm worried they might be too unresponsive.
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      06-28-2011, 04:53 PM   #8
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Also noticed the Pirellis have a speed rating of H vs Y for the DWS. Think this will cause much of a noticeable difference in handling characteristics?
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      10-29-2011, 07:49 AM   #9
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I've done extensive research on tire minimum load way back 1990. No tire manufacturer has this specs. Neither did SAE gave reference to this in their standards at the time. Well, since I needed this data to fix a tipping problem in a fully loaded tow truck, I performed actual weighing experiments and engineering calculations and determined the permissible tire minimum load. In correcting the truck's flawed weight distribution using tire min. load, I installed just enough counterweight that eliminated the tipping and restored tire traction without causing tire overloading when the truck carries no load.
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