Hey there Bob. It very well could be an 87. You said yours is a diamondback? Maybe Specialized used the chainstay u-brake longer? I don't now.

The rear is actually a 126mm, but I'm running a 7spd wheel in it right now. Soon it will match the front, a bombproof 26" with XTR hubs and Mavic A231 wheels. VERY strong.

I have though about getting a 50 or 52 tooth chainring, but I have been under the impression that the narrow wheels and tires (700C's) are what really bring in the speed because of less rolling resistance. Is that note the case, as you say? Maybe I have a big misconception here.

PS- went and looked and I have a 30-13 cassette now.