Your tire size will make a huge difference in speed. When I got new tires on my 240, it calls for a size that is no longer made, I asked the guy if the new tires were going to throw off the speedo. He said no. He was wrong. When the needle is at 55 I'm going closer to 62 or 63. My tires are a little too big. But it give me a little more speed from my 240.

In your case slightly larger tires might correct the error.

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