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I was wondering if anyone might be able to compose, or find a conversion table that could tell us the difference between what the speedo reads, and what actual speed should be, corrected for different sprocket sizes. For instance, I have gone down one tooth in the front, and my speedo reads 178 in 6th. What would true speed be? (with,or without correcting for factory speedo error.) Or, if I did the -1+2, and top speed is 159, then true speed should be... etc. I hope that made sense.
 

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A -1/+2 is a 15.5% error. -1 is a 11.5% error. 100mph x .155= 15.5. Meaning you're doing 100-15.5=84.5.

Now you can do the rest.
 

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Here's an Excel spreadsheet that does what you want.

I don't remember where I found this spreadsheet originally but I entered all the correct gearing information from the 07/08 service manual so all you have to do is put in the gearing you want and it will tell you at what RPM you get what speed in what gear.

It even draws a graph for each gear with each gear in different colors and each 1000 rpm with the speed listed.

There's one tab with the stock gearing and one tab to do changes to the gearing (though you could change either). I did that so one tab would always be the stock for reference.

Enjoy.
 

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If you want to be really mathematically anal about this I can calculate it down to .0000001 mph lol. The required variables are rpm, primary and secondary reduction ratios (what gear your in and your sprocket arrangement), and the exact circumference of your rear tire. Give me some values and watch me go!:D
I work with these calculations on a daily basis.

edit: I can do the same with pulleys too.




oh and get a spedohealer!
 

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if the tire circumference (under rpm and full expansion), ratios provided and input rpm are exactly precise. The answer will be exactly precise. There are NO other variables other than those mentioned above that will influence. Try me.
 

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if the tire circumference (under rpm and full expansion), ratios provided and input rpm are exactly precise. The answer will be exactly precise. There are NO other variables other than those mentioned above that will influence. Try me.
Not to the level of precision that you're positing.

You're talking about one ten millionth of one mile per hour. You'd need to take into account such factors as wind resistance, tire rolling resistance, tire compound, weather...hell probably cosmic radiation would play at that small of a speed. In short...You'd probably be able to calculate to the hundredths of a mph but much past that and the math and physics get crazy quickly.
 

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Not to the level of precision that you're positing.

You're talking about one ten millionth of one mile per hour. You'd need to take into account such factors as wind resistance, tire rolling resistance, tire compound, weather...hell probably cosmic radiation would play at that small of a speed. In short...You'd probably be able to calculate to the hundredths of a mph but much past that and the math and physics get crazy quickly.


Phobos; we don't have the same background/understanding of physics.
Wind resistance, tire rolling resistance, tire compound and weather along with cosmic radiation have nothing to do with input and output rpms given fix ratios. They do come into account if we were to attempt to calculate absorbed horsepower/ efficiency. This is not what I am talking about. Lost power, aerodynamic drag cosmic radiation, have nothing to do with this.

WHAT I AM SAYING.. is that if you have a known input rpm to a driver gear, if you have a known amount of teeth to that driver gear, a known amount of teeth to the driven gear; you can bet all you own that it is very simple to calculate the EXACT output rpm. PERIOD. THAT IS WHAT I'M SAYING. How much resistance is not pertinent to this by any means whatsoever. If we are talking about actual speed traveled there is only one other variable to take into consideration which is wheel slippage. Assuming NO slippage, if you have a tire of 1 meter in circumference, and it does 1 revolution, you will advance by exactly 1 meter. How much power this took, or how much resistance or drag is not pertinent.
Now having said that I do agree that it is hard to get close to real life numbers down to the specs I'm talking about. There is only one other variable which is slippage. I have to go, at work, but I will check in latter bitches.


Edit: Ok I'm at home now. To make it perfectly clear; the calculation will be DEAD ON ( to .0000000 till infinity) when talking about rear wheel rpm. I do agree that actual speed would be off slightly due to wheel slippage. Assuming no slippage it would be dead on as well.
 

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your speedo is not going to be off by a single number. it is not going to be a linear equasion. example, if your speedo is off at 5 mph at 30, then 5 is not the magic number, because what is it off when you are doing 1mph? still cant be off by 5, so its not a linear. best bet is to have a friend pace you, when they are doing 70 have them give you a signal and then see what your speedo said, same with other common speeds like 40,45,60 etc.

or just buy a speedo healer.
 

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your speedo is not going to be off by a single number. it is not going to be a linear equasion. example, if your speedo is off at 5 mph at 30, then 5 is not the magic number, because what is it off when you are doing 1mph? still cant be off by 5, so its not a linear. best bet is to have a friend pace you, when they are doing 70 have them give you a signal and then see what your speedo said, same with other common speeds like 40,45,60 etc.

or just buy a speedo healer.
this reminds me of my JDM cluster(JAPAN) for my Integra..It only show KMP instead of MPH..
 
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