Tachometer Guessing Game
Over the years I've been racing a two-stroke motorcycle, I've noticed people make some interesting assumptions about what that involves. Usually the first erroneous assumption I have to clarify is that I'm road racing, not riding a dirt bike.
The next most common inaccurate assumption is that a two-stroke revs to very high RPM. This confused me at first, since my two-stroke redlines at the same RPM as my four-stroke street bike, but I've come to accept that this is a commonly held misconecption.
In an effort to clear the air, so to speak, I came up with this Tachometer Guessing Game... have fun!
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Question # 1
Which one of these four tachometers belongs to a two-stroke motorcycle?
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This Honda has a 10,500 RPM redline
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This Honda has a 12,000 RPM redline
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This Honda has a 13,500 RPM redline
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This Honda has a 18,000 RPM redline
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Question # 2
Which one of these four tachometers does NOT belong to a 250 cc motorcycle?
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This photo was taken of myself and my friends at North Bay, the VRRA's Runway Romp event in 2009. These four happy women all race vintage Honda motorcycles, and I've given you some hints for the Tachometer Guessing Game with the model names and displaments of the various motorcycles.
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Answers to the Tachometer Guessing Game...
Answer # 1
The tach reads 10,500 RPM redline on the Honda NS 250 F - the only 2-stroke in the group.
Answer # 2
The tach reads 12,000 RPM redline on the Honda CBR 600 - the only bike in the group that is NOT a 250
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More information on RPM
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Andrea
VRRA # 418
1983 Honda NS 250 F
V-twin liquid cooled two-stroke
10,500 RPM Redline
The general assumption that two-stroke bikes rev higher than four-strokes is not supported by this group of bikes. With a bore and stroke of 56 x 50.6 the NS has over-square dimensions. The lowest revving bike in the group is the NS250, the only two-stroke in this row of Honda motorcycles, the piston is traveling about 3,486 feet per minute at redline, which is slower than the pistons of the other 250's. Considerably slower than the CBR 250's tiny pistons.
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Jen
VRRA # 343
Honda CBR 600 Hurricane
Inline 4 cylinder 4-stroke
12,000 RPM Redline
The largest displacement of these four bikes, but with four cylinders, each cylinder on the CBR600 displaces only marginally more than the cylinders of the two twins, the NS and the VTR, even though they are 250's. The size of a piston is one of the factors limiting the speed at which it can move, hence the RPM that can be attained.
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Mel
Honda VTR250
V-twin 4-stroke
13,500 RPM Redline
A liquid cooled v-twin Honda motor, but unlike my NS250, Mel's VTR is a 4-stroke. The VTR revs somewhat higher than the NS, although the cylinders are the same displacement, the bore and stroke dimensions (60 x 44.2 for the VTR250) are different, and so the pistons are different sizes. Both the NS and the VTR were originally built to be sport oriented street bikes, and have since been converted into vintage race bikes.
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Laura
Honda CBR250 Hurricane
Inline 4 cylinder 4-stroke
18,000 RPM Redline
This little Honda revs to a spine tingling 18,000 RPM. With four tiny (62.5 cc - about 4 tablespoons!) cylinders, very small pistons, and valves smaller than some body jewellery I've seen, this bike can rev high. With a bore and stroke of 48.5 x 33.8 this motors dimensions are over-square like the other 250's, but the potential for high rpm operation for this motor is far greater than any of the other motors whose tachometers are pictured above.
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Jen, Mel, Laura and I with our four race prepared vintage racing Honda motorcycles, in this photo we've just finished our last racing round of the season, and we're all pretty happy and excited.
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