Front tires load index

[Maroon 6.2L SS]

Is anybody running front tires with a load index of 99 or 100? Is this enough load or do you have to run the XL (extra load) tires?

[CamaroCracka]

I believe 100 equates to about 1800# per tire. That is plenty.

[Maroon 6.2L SS]

Thanks!

[Pearlj10]

100 load does equate to 1764 lbs. GM went with load 103 (1929 lbs) on the fronts and 106 (2094 lbs) on the rear for the staggered setups to allow a buffer for passengers and cargo, I believe. From an old post by Tire Rack:

What you should do is identify the Front and the Rear Gross axel weight ratings. In the case of a 10 Camaro SS these #s are Front 2203 lbs and Rear 2468 lbs. Take the tire load rating and multiply it by two and this number needs to exceed the higher of the two #'s. In this case they would need to exceed 2468 lbs. Normally the factory tires will exceed this # by a good safe margin.

[Norm Peterson]

Originally Posted by Maroon 6.2L SS

Is anybody running front tires with a load index of 99 or 100? Is this enough load or do you have to run the XL (extra load) tires?

Cliff's Notes version - 99 is really too small to use as replacement for 103 SL tires. 100 is at best marginal.

The real tech here needs to reference the Tire & Rim Association inflation pressure vs load index vs rated load capacity tables.

What you want to do for load rating purposes is match the load ratings rather than the load indexes directly.

Maximum load rating as shown on the tire sidewall is irrelevant here. That's a tire maximum that does not care about the car it may be mounted on.

Important note - the XL tables differ from the SL tables, and not in the way you'd expect.

A 103 SL tire at 32 psi inflation is rated to 1742 lbs. 1742 would be the number you need to match. But you can adjust inflation pressure to achieve this, at least over small ranges of Load Index numbers. In SL tires, a 100 LI tire would need to be inflated about 3 psi more (35 psi in this case). A 99 LI would need about another psi (36 psi).

Substituting an XL tire would require about 42 psi in either 99XL or 100XL. Remember that I said that the tables don't line up the way you might expect. XL tires at any given LI number are actually smaller than SL tires of the same LI number, and gain their capacity by being allowed to run at higher inflation pressures (up t0 42 psi rather than 36 psi for SL).


Norm

[AlanRubin]

20s are 103, 1929 lbs
18 and 19 are 102, 1874 lbs.

99 is fine, that is not SMALL. The tire is the same size, at 1709lbs. I ran 99s on my
20s, and it was fine. Lower speed rating too...

The curb weight is ~ 3,750 lb for the entire car.

Let’s pretend your tire has a load index of 84. Using their charts, we find out that
means it can support 1,102 pounds at maximum air pressure. Multiply that by four
tires (4 tires x 1,102 lbs = 4,408 lbs) to find out your car’s maximum load carrying
capacity.

I think 99 is just fine, the manufacturers always over estimate, based on the
total cargo, passenger, and towing capacity.

Tire load index tells you how much weight your car can safely carry based on the
correct tire size and pressure. I don't, nor do I plan on, towing, so I run whatever tire
is on sale, and I could care less about the load index being anywhere near 1700lbs per
tire.