How fast is 8,500 RPM's on a seca turbo?

I think the topic speaks for itself

 

In what Gear ?

 

I'd guess he's asking about whatever his last gear is (not sure if it has 5 or 6 gears).

 

Calculating it out from the gearing, your rear wheel is turning 1498rpm at that speed. If we take the 18" rear wheel, and add 10" to the diameter for the sidewall and rounded tread thickness, we have a 28" wheel outside diameter.

Circumference = Pi X diameter = 28" X 3.14159 = ~88"

88" X 1500 = 132000" per minute / 12" = 11,000 ft per minute / 5280ft = 2.082 miles per minute X 60 minutes = 125 mph, which sounds about right.


That is probably a bit off, since you must factor in the slight flattening of the rear tire under load, which would cause the effective diameter to be a little less in practice. The 10" added to the rim diameter is also a guesstimate, and will vary depending on the aspect ratio of the tire. To get a better result, you should get someone to measure from the exact center of the rear axle to the road surface while you are sitting on the bike, then multiply by two. I don't know how much, if at all, the tire diameter would grow when spinning at 1500rpm due to centrifugal force.

 

Yeah 5th gear.