What do the letters SL or RF mean?

I know the basics, Speed Rating, Aspect ratios treadwear etc. and these arent part of that, for example they appear here in the tire rack chart:

http://www.tirerack.com/tires/Spec.j...model=Ecsta+MX

Thanks,

-Bill

 

Bill,

Generally, here are some special tire markings:

XL - Extra load capacity (offers higher load capacity than standard in this size)
RF - Reinforced (offers higher load capacity than standard in this size)
SL - Standard load capacity (trucks, this is assumed on car tires unless otherwise noted)
C - 6 ply rating (trucks)
D - 8 ply rating (trucks)
E - 10 ply rating (trucks) and so on...