A great post, good information. Can you help me? My stock 69 K0 CB750 has a brand new Dunlop Roadmaster K81 TT100 4.25/85H18 Nylon which I had fitted to the rear. I have done a couple of hundred miles on it so it is good to use properly. I like a ribbed front tire as that is how I always remember them years ago here, so can you recommend which brand or type to fit as mine is nearly worn down. I can't get IRC tires in this country (New Zealand). I'm just getting back to riding after a 30 year layoff and although my confidence is right up there I just can't bring myself to lay the bike right over, something feels like it isn't right yet. I used to scrape the pipes on my CB250 and other bikes I owned years ago but this bike says to me 'just go easy now son!'...maybe I'm just older and wiser? Any ideas? Regards, Mark
My first thought: the 85-series rear is light on load rating, unless you're riding a cafe racer and only single-up. That profile is more suited to bikes weighing 500 pounds to 350 pounds. I always used the 4.25/110H size rear, 3.25/110H front on mine. If you put one on front, make it the same profile, but mind the weight.
Second, if you're running a TT100 on one end, run it on both ends.
The V-profile of the TT series is designed for increasing patch contact with the road as the lean angle increases. The trade-off for this is a slight instability at about a 5-10 degree lean angle if you have round-profile on one end and V-profile on the other. If the TT100 is on just the front, then the bike feels like it "dives" into the corner "ahead of schedule" (compared to what you are telling it to do). Then, as the tire loads in the turn, the caster changes (reduces) suddenly because the rear tire does not match the "squiggle" on the ground. The result is wobbly lines in corners, especially sweeping turns.
If the V-profile is on the rear only, and a round-profile tire on the front, the caster goes the other way as you start to lean over. The increased caster then tries to make the bike "climb" to the outside of the turn. When you straighten back up, it tends to overcorrect, making you "wobble" the other way.
Not that I'm against TT tires, you understand - they are my favorites (except when installing those steel beads) for overall mountain riding and wet traction. But, with touring loads, they wander all over the lane because they don't hold a heavy load vertically as well as round-profile tires. And, the block pattern on the front accentuates the decelleration "head shake" (K2 and later) unless you fix that problem (well, I see you're lucky enough to have a K0, so yours probably doesn't shake, anyway!).
The "big four" is one of the most top-heavy bikes in the world. The gas tank "feels" like it's solid lead when compared to other bikes. This requires a different riding sense, but one that will reward you with far better riding skills than, say, someone who only rides CB500 or BMW, etc. This high center requires you to "cross-steer" into a turn, then correct when you hit the angle you want. You don't realize you're already doing this, but since you rode lower-center bikes before, it feels different to you. To understand what I mean, go into a nice, empty parking lot and try this: ride about 5-10 MPH and push the bars slightly to the right. The bike will immediately go into a left turn. "Catch" the turn at the angle you want, then steer INTO that turn to stand the bike back up. Do LITTLE turns at first, then you'll get it. Once you get the hang of this, you'll ride everything else (especially bikes with lower center masses) with much greater ease and confidence.
I used to teach this in Motorcycle Safety classes. We saw 2 customers get killed and one seriously hurt when they jumped onto big bikes after riding 100cc-class putters. So, I talked the boss into sponsoring a Safety class one Saturday per week during the Spring and Fall, for free. We always had a big class, and no one got killed for clumsiness in their riding in the following 3 years. The most important thing I could teach was the "cross-steer" concept, because it makes your brain stop thinking about what you're doing and start reacting according to how the bike "feels" under you. Very important, especially with tall bikes.
