a TZ250 is much more a race bike then the NSR250, as is the RS250.
After riding, and racing NSR's for five or more years, and getting on an RS250 I can say they are very different in so many ways. They only thing they share is the fact that they are motorcycles.
The NSR is actually a much easier bike to go fast on, but you run into a limit of the NSR in power, and handling. The RS is so much beyond that!
Having said all that? Every once in a while I will get feed up with the RS and my trying to get up to speed on it, and go back to the NSR. After one session, I will be back out on the RS, cause the NSR makes me lazy in my riding
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Charles Gallant