I live in Humboldt County, CA, and I work as a healthcare chaplain for hospice/palliative care people in their homes. It's a rural, hilly, coastal county. A chaplain travels to where they are needed, which includes high mileage and the occasional dirt road. For years, I wanted to make my Seca II more offroad capable, though I've ridden the Seca Tourer on street tires to Saline Hot Springs in Death Valley on several occasions--it's a Jeep road, and the signage recommends at least 10" of clearance for 4X4's. With due respect to our fearless leader, Radare, and his awesome Scrambler, I didn't want to mount rears on fronts, have off sizes, or (heaven forbid!) to use TUBES! (If you are going to use cast wheels, you at least ought to be able to avoid the hell of tubes, which heat tires up (increasing wear), are a pain to mount, are more likely to fail catastrophically, and can't be plugged when a nail punctures the tire. The result of my research is the basis for the Yamaha Seca II All Road motorcycle.
Idly researching last (rainy) winter, by trial and error, I came up with a weird tire mix: A Continental TKC 80 front, sized 120/70-17, and a Mitas E-07 rear, sized 120/80-18, BOTH TUBELESS. The TKC 80, despite being labeled a 120 (instead of the stock 110), is very slightly SMALLER than the stock Avon Roadrider on the other bike. It's 107mm wide (at the knobs) to the Avon's 110mm. The TKC has a 34mm gap to the fender (great for clearing mud or debris), while the Avon has a 32mm gap. Speedo inaccuracy is unnoticeable.
I compared sizes to the road tires on my other Seca II. (Yes, I have two II's.) The Mitas E-07, though also stamped as a 120, is 133mm wide--25mm wider than the front TKC80. The Kenda Cruiser 130/70-18 on the back of my other bike is 131mm. No meaningful difference. HOWEVER, the Mitas is certainly TALLER. I wouldn't try to run it with the stock shock, but I happen to have a one-off Fox shock with remote reservoir, which was built for the short-lived Seca II racing class, and is a TAD taller than the stocker (to steepen the steering and make it quicker), and much stiffer and better damped. It almost never bottoms out. The YSS shock (available on ebay for $400 or so) on the other bike is the same length, however, and also much better sprung and damped than stock. To keep the front tall enough for a real rear shock, you really do have to do a Progressive or Race Tech front spring (with or without Gold Valve cartridge fork emulators), but you should do that anyway, and especially if you intend to thrash it offroad.
The bike works well on any gravel or forest roads. I go as fast on these roads with the Seca II All Road as I do on my sprung and shocked Kawasaki KLR650. It won't do single track, but that's because the exhaust header is only five (or so) inches off the ground (like a Versys or a V-Strom), and nobody makes a bash plate (or a high pipe!) for our machines. On pavement, I ride it as hard as I ever have, and it stays planted, turns in beautifully, brakes hard, and looks--utilitarian. (Caveat: I haven't ridden it in rain, but I ride quite conservatively in the wet anyway, so I'm pretty confident it will work fine for me.)
I highly recommend these tires, though they are not cheap. The TKC80's wear out on the rear of big adventure bikes, but seems to be lasting quite well on the front of the Seca II. The Mitas E-07 has a reputation for being very hard-wearing on big adventure bikes, so I expect it to last well on my 60bhp machine. I'd post pictures, but that doesn't seem to be an option here....
