Hayabusa Rear Profile and Magnetic Field | Ask the Geek

Hayabusa Rear Tire Size and Profile
I've read on Hayabusa sites about the benefits of XXX/55 profiles over the standard 190/50. Would it really be worth the effort to change ride height for geometry and gearing? The 190/55 profile is 16mm taller (8mm on the radius) than the 190/50 Battlax BT-016 Pro. There are those claiming that using a 180/55 has other benefits: The tire's taller, narrower profile lays down a lot more rubber when banked over, improving traction. It's lighter, so it accelerates and stops faster. The reduced gyroscopic effect makes the bike feel lighter and flick quicker, requiring less steering effort. It's slightly taller, increasing your top speed slightly. And it costs less. They also go on to state that as 190/55 street compounds become more available, they offer many of the same benefits. To me the difference between comparable-compound 180 and 190 sizes is mainly tire weight. I know there have been other similar questions about this, but what are the definitive pluses and minuses in reference to fork angle and geometry, ride height, the obvious gearing difference, handling gains or losses and any possible fitment interferences?
Steve Saunders
Cleveland Heights, OH

Before the 190/55 tire profile was common, a popular modification for literbikes with OEM 190/50 rear tires was a swap to 180/55 rear, with some of the benefits you mention in your question. On your Hayabusa, replacing the stock 190/50 rear tire with a 190/55 will raise rear ride height by the difference in radius, 8mm in your case. That’s a pretty significant change, enough that you would feel quicker and lighter steering. Gearing will change in proportion to the circumference, about 2.5 percent or equivalent to a one-tooth change in the rear sprocket. This you would not notice so much, especially if the majority of your riding is on the street. As for the differences between the 180/55 and 190/50, in our last tire test (“Both Sides of the Fence,” April ‘09) we saw a difference of just half a pound between the Bridgestone BT-016 in those two sizes, and even though that weight is at the very edge of the circumference, again I don’t think you’d really notice that. Note, though, that among other brands we’ve seen as much as a two-pound difference between the sizes, a fair amount. Even though the 180/55 is taller than the 190/50, the wider rear tire typically has more actual tread width as well, and I doubt the 180 puts down “a lot more rubber” at the lean angles you’d typically encounter on the street. The biggest fitment concern when fitting a taller tire is clearance to the swingarm pivot area. Given all the above, I think in your case the 190/55 would be a better option. In the Bridgestones, the difference in weight is negligible, and the Hayabusa certainly could use lighter steering from the taller profile.

Magnetic Bigfoot Field
** I have been riding 25-plus years. I have been told over the years by old-timers about motorcycles producing or having a small magnetic field involving the frame/motor. The old-timers would suggest doing the following: "Change out every bolt, nut and washer to stainless steel. Stainless steel is not magnetic, so it does not hold a charge. It helps the motorcycle run better with less electrical interference." I have heard this countless times, from different people, from different parts of the country over the years. Any truth to this? I understand that stainless steel is better than the OEM steel used in the bikes from the factory, but magnetic field and running better? This question has always bugged me. I'm 40 years old now, I do not want to be an "old-timer" spreading more myths. Please, help me with this urban legend.
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Kevin Darcey
Saint Augustine, Fl**_

I have never heard anything like this before. Yes, the ignition system on your motorcycle makes an electromagnetic field, but interacting with the steel around it will not affect how your bike works. There are some very isolated examples where you can get interference with some modifications, but that is all related to wiring and signals jumping wire to wire. Even if steel on your bike did cause problems, just changing hardware would have little effect. You would only be removing a small portion of steel as you would still have all the engine internals, fuel tank, axles, chain and much more left. SR

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