My track-day bike is a '99 Yamaha R6 and my street bike is a '10 Ducati Streetfighter. I don't ride on the street anywhere close to the way I ride on the track, so I end up wearing out my Streetfighter tires in the middle and I wear the R6 tires on the edges. I change/balance the tires myself and I go through at least two sets of Michelin Power Ones on my R6 per year depending upon the number of track days. What are your thoughts on putting the track-day take-offs onto the Streetfighter? I realize these Power Ones have little siping and are primarily for the track, but tires are expensive and my Streetfighter is for weekend rides and not commuting or sport touring where there is a higher chance of encountering rain.
They both use the same front tire size (I've got a 70-series front on the R6) but rear sizes are different - the R6 uses a 180/55 (5.5 inch rim) and the Streetfighter uses a 190/55 (6.0-inch rim). Michelin's fitment guide shows that the 180/55 will work on a 6.0-inch rim and the Streetfighter has a ride height adjuster to allow me to compensate for difference in circumference (I assume the 180 on a 6.0-inch rim will be smaller in circumference than a 190/55). I would think that the Streetfighter would turn better with slightly narrower tires assuming ride height is properly adjusted but I may be (theoretically) giving up some cornering traction with the narrower rear. Is there any reason why I shouldn't consider doing this?
According to Michelin, the Power One is a street/track tire recommended for "30 percent hypersport street riding, 70 percent track days." And that's assuming you're using the "street" version of the Power One and not the DOT race tire. This would be an OK choice for your Streetfighter ridden on weekends, but maybe a bit too track-oriented with only 5 percent siping on front and rear. Compare this with, for example, the Power Pure. It has at least 10 percent siping, and is recommended for "85 percent hypersport street riding, 15 percent track days."
Michelin and most tire manufacturers do state that a 180/55 tire will fit on a 6.0-inch rim, and in past years it was a popular replacement for the 190/50 tire (before the 190/55 was readily available) to quicken steering. The difference in diameter between the 190/55 and 180/55 is, surprisingly, only a few millimeters and you could easily adjust your rear ride height to account for that. This too would be an OK choice for your Streetfighter, although again not optimal.
The big problem I see is using what is essentially a worn-out track tire on the street, even though it may have plenty of tread left in the center. Tires intended strictly for street use are designed to work over a broad range of temperatures (carcass and ambient) and withstand many heat cycles. At the other end of the spectrum, DOT race tires are intended to work at a specific temperature (again, carcass and ambient - that is why different compounds are offered). Additionally, they are typically more reluctant to reach that temperature (hence tire warmers) and lose much of their performance after just one heat cycle. While the Power One is a street/track tire, in our experience tires in that category typically exhibit at least some of the traits of their track-only counterparts. That means relatively slow warm-up time as well as reduced performance after a few heat cycles. This was one of our main findings during our tire test of a few years ago when we compared the different categories of tires within two brands ("Jeopardy", Dec. '06).
While used track-day tires may look fine in the center of the tread, if you've worn most of the tread from the edges they've likely been through quite a few heat cycles at the track. In my own experience, this wear on a track-oriented tire ends up equating to an even longer warm-up time and further reduced performance at the lower temperatures generated on the street. And one more issue: If you do end up in trouble and using the edge of the tire, now you've got no tread and no siping when you need it most. To put things in perspective, in your letter you are worried about any loss of traction from using the narrower tire; I would suspect that the degradation in performance from being used up on the track is much more than any difference due to size.
There are two aspects to consider when selecting tires for your bike. First, tire manufacturers go to a lot of effort to match a specifically sized tire and rim to a particular model, and have in recent years catered to an increasingly segmented market with various street/track hybrids. Deviating from what the tire manufacturer recommends for size and/or usage will in most cases result in less than optimal performance. Second, the tires on your bike impact not only performance, but also safety. Why risk that - or your beautiful Streetfighter - to save some money?
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