The "T" in all those bikes stood for "Trail" because they were all enduro models.
So, the TT-R models are essentially updated versions of the old TT models of the 70s, 80s, and 90s. The "R" designation simply means "Racing" because these particular TT models share parts and engineering with the two-stroke YZ and four-stroke YZF full-on motocross machines.
Essentially, all TT-R models are classified as playbikes by Yamaha, much the same way that the previous-iteration TT models were. But, while the original TT models were pretty heavy and bulky, the TT-R models are comparatively lighter, higher-tech, and easier to ride.
Well, just got back a few hours ago and have some awesome photo's, when I get to sort out the accidental shots of thumbs, sky, shoes or the just plain boring I'll post some links to Photobucket, I took 809 photo's all up
Cheers
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2004 TTR250 - Highway Dirtbike Hand Guards, 38mm Bar Risers, D606 Front & Rear, Opened up Airbox with Twin Air Filter, Re-jetted Carby, B+B Bash Plate & Frame Guards, DIY 3mm Alloy Tail Tidy, 14/47 Gearing.