The R3 is the 2.3L version. The RIII is the 2.5 version.
I guess the 2008 RIII Touring I just bought is really a 2.5 liter!!! Because it says on the speedo
Whatever it is, I changed it a bit and put the Nell's tune in and I'm really enjoying it, I did a little research on the tires and put the Metzler's on it as Triumph recommended them or the Avon's, I have no problems with them but I haven't pushed it too much, getting up to 100mph feels a little shaky, but I think it's the windshield and bag's, will try it without and see if it's better, I just normally Cruise anyway, but it's a lot different than my old kz 1000 above 100, it's been a long time sense I've really been riding, got rid of the Old Ball and Chain time to live again, I called Bridgestone about matching a front bias tire to put on the back cause I couldn't find the size in a bias tire, they said they don't make a tire for that bike, some guys on here mix and match different manufacturers and sizes, I trust the engineers that recommend something know more than me, the only time I locked up the back tire now is in the rain. I replaced a Bridgestone on the rear that was at the end of it's life but still had tread and I locked that up twice on a dry road, I hear the Metzler's only last about 5,000 miles and the Avon's more I think 7 or 10,000, I keep the air psi at the recommended also, I hear if you Carry 2 up or more than avg. Weight you can up it 1 or 2 lbs, but that's it, and for better traction up to 2 psi less, I haven't experimented with that to know, but I do know the manufacturer's of the tires and bike say you can adjust up to 2 psi either way and be okay, but I've seen an under inflated tire just disintegrate on an SUV, the whole sidewall was blown out, but that was extremely low probably like 20 psi in a tire that required 35, surprised my X stayed on the road.
But it's Big and I like Big, better too big than too small, I'm 6'4" 300lbs I was looking at Harley ultra glides with a 114 cu.in. and couldn't find many choices and they were all $20,000 + . I don't have a garage so I couldn't see leaving a $20,000 hunk of metal outside even with a cover on it so I googled what is the biggest production motor made and found the Rocket, I was hooked, than I saw the price and went to pick it up that weekend and haven't regretted it yet, gl in your search, I found mine on cycletrader.com. The test drive was shaky cause I found out when I went to take it out the first time the front had 22psi and the rear 25psi, I even commented to the seller it wobbled going around the turns at 45mph a little, glad it was only a 45mph zone. Gl have fun and remember Murphy's Law anything that can go wrong will go wrong then you'll be ready for anything like crazy drivers in a mad rush just to get a few feet in front of you, it's a cruiser easy does it and get there, gl