I have 2 different styles tri ribs.
Deerstone tires:
Notice the center rib is wider. This tire was purchase from Miller tire at a tractor show:
http://www.millertire.com/
This is the other style tri rib that is on my 149
All 3 ribs are the same width. The name on the side of this tire is GBC. This tire was purchase on ebay.
Both tires are good handling-steering tires. Neither tire is hard on the lawn.