What is the exact MPH at 3000rpm?

ROCKETHEAD

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May 15, 2008
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Location
Yorkville, IL
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2015 Triumph Trophy SE
I need to calibrate my VSS input on the Innovate LM2 datalogger and need the actual MPH/3000rpm to do it. Not because you have a GPS or a bicycle trip computer but based on the actual gearing and stock Wheel and Tire in 5th gear.

Thanks for the help.

HEAD
 
Hmmm... how accurate is that calculator?

It's asking for sidewall height, but on an MC tire, it's significantly rounded past the sidewall (vs a car tire) which gives it a larger overall diameter, directly impacting speed at RPM.

Sidewall height is irrelvant in this calculation, the math would be off unless they are assuming a fixed number to add to the sidewall height to compensate for a generic MC tire shape. Which would make it useless to darksiders.

The only piece of tire information that you'd need in this calulation is the overall diamter of the tire, the width, sidewall height and what size wheel it fits on don't mean anything.

Or did I miss something?
 
Last edited:
3ngin33r1 said:
...
The only piece of tire information that you'd need in this calulation is the overall diameter of the tire, the width, sidewall height and what size wheel it fits on don't mean anything.

Or did I miss something?
Click to expand...

I believe you are correct! The tire pressure (at extremes) would be the only other factor.
 
Why do you need to get the circumference of the tire when you can figure it with the tire size?

First of all 50 is not sidewall height. It is aspect ratio or a percentage of tire width. It is figured height / width x 100. Or 120mm/240mm x 100 = 50

The "tire height" as you describe for a 240, 50 series, is 120 mm which is 4.7 inches. The sidewall on the Metz is 2 inches. Measure from the ground to the rim and it is 4.7 inches.

So instead of measuring the circumference of the tire, you take the wheel diameter (16 inches) plus the tire height 4.7 inches and get the overall diameter of wheel and tire. Then you do the whole 3.14 thing and get the circumference. Then the other ratios are used to figure how far the tire rotates with each revolution of the crank.

That is why they need wheel diameter and that is how they are able to compensate for the radius profile of the tire.
 
Last edited:
Cool.

That was my misunderstanding then. I was under the impression that the aspect ratio was the height of the sidewall from the bead to where there tread begins when that number was divided by the width.
 
Last edited:
Sorry to drag up an old thread, but I will anyway.

When I used the calculator (which I like, thanks for posting it) the answer seemed a bit high to me. I think that this is because the RIII has a primary AND a secondary reduction gear. I multiplied them the ratios (1.034:1 & 1.043:1; p. 1-30 or 38/627) to get 1.078 and put that number in. The answer given by that for the stock tyre at 3,000rpm comes out to 76.8mph, which seems more accurate to me. For my 225/55 it works out to 77.5mph. Again, this seems to reflect reality better.
 
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