Alright, we have no stock tach on our bikes. Folks have posted charts to tell us our speed vs. rpm in all gears. But if you, like I have changed final drive ratios, and or tire sizes, you just have to make a guess at your rpm at speed. NO MORE! I have done the math to get the ''magic numbers'' for each of the 5 gears.

1st - 44535
2nd - 30200
3rd - 21790
4th - 18349
5th - 16820

They don't make any sense on their own, but here is how to use them.
First, measure the circumference of your back tire. Blow it up to normal pressure, and have a friend layout a tape measure 7 feet. While sitting on your bike, start with the valve stem straight down at 0 on the tape. Roll forward till the valve stem is all the way around to bottom again, have your friend read the number, this is the circumference of your back tire, write it down.
Second, write down the final drive ratio on your bike. If you are running stock pulleys, they are 23 and 68  for a ratio of 2.96 to 1.
Third, divide the tire's circumference in inches to the second decimal point by the gear ratio. Write this number down. It is the key number for your bike as setup.
Example= My bike's tire is 73.50'' and my final drive ratio is 2.60 (Kaw. pulley conversion) giving me a key number of 28.27.
Now divide each gear's magic number by your bike's key number. This will give you the engine rpm at 10 mph in each gear.
Example for my bike is -
5th gear- 16820 / 28.27 = 595 rpm at 10 mph x 6 = 3570 rpm at 60 mph
Do each gear,
Example for me-
1st = 1575
2nd = 1068
3rd = 770
4th = 650
5th = 595
You can now multiply these numbers to see your rpm at different speeds for each gear, or divide your selected rpm by these to see your speed at that rpm.
Example= Say I want to shift at 4,000 rpm,
1st - 4,000 / 1575 = 2.53968253968, or basically 25 mph
2nd - 4,000 / 1068 = 3.745, or 37 mph
3rd - 4,000 / 770 = 5.194 or 52 mph
4th - 4,000 / 650 = 6.153 or 62 mph

Now you can ''try'' different final drive ratios or size tires by making a new key number.
My bike's stock tire was just 73'' and with the stock pulleys at 2.96 to 1 the key number was 73 / 2.96 = 24.66.
So at 60 mph my old rpm was 16820 / 24.66 = 682 x 6 = 4092
My current key number is 28.27 - 16820 / 28.27 =  595 x 6 = 3570
So the Kaw  pulley conversion  and tire change has dropped me 522 rpm at 60 mph cruise. (Hey, I'm old and live in south Florida = no hills or twisties. I am on the Superslab a LOT and always have to throw away rear tires with the sides looking like new.)
Now you can make-up charts and graphs CORRECT FOR YOUR OWN BIKE till your heart is content.
This is in relation to REAL SPEED, not the stock speedo. Get a GPS app for your phone and you can see how much your stock speedo is off, but that is for another post.

Disclaimer...I have worked the math several times for this, and it will give you a good idea of the numbers for your bike. If someone wants to go to 29 decimal points and re-figure it they may find it could be off by a fraction. BIG DEAL!!  We aren't plotting the path of the Space Shuttle here. I am giving you a way to figure how changes in your final drive and tire size will affect your rpm on YOUR BIKE.  

Best wishes,  Badwolf

Take a look at this:

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1341162964

Best regards,

There's an app for that...
http://www.gearingcommander.com/

Justin, You have to figure how many times your tire rotates to go 1 mile then use your gearing to see how many rotations of the engine that is. 60 miles a hour is 1 mile a minute so there is your rpm. Other people's charts work fine if your bike matches there set-up. Some brand tires vary in size to others, along with tire pressure, loading, and rim size. My tire is on a 3.5'' wide rim. If I put it on a stock rim the circumference and profile would change. This method allows you to see what effects changes in gearing and tire size does to your rpm on paper where it is a lot cheaper. My 4th gear almost matches what my stock 5th was so 5th now is like a extra gear compared to stock. Yes I have a higher 1st gear now, but I got used to it quick.(south Fla. = no hills) I was in north Ga. in Sept and It never bothered me. Now a little bigger tire and I should hit my target of peak torque (3400) at 60 in 5th.

I understand, I think, I think I get it, but, coupla beers and a few cocktail napkins, a few
What if we used this tire?
analyses, and a coupla more beers,, I'd have it.
I slapped the Dunlop on it, the Speedo and reality started to agree and the bike ran well, some days better than others, and I started understanding the racers back in the old days, ripping into their carbs, changing jets, based on temperature and humidity and, I guess, barometric pressure. I'm pretty sure it broke the 100MPH Mark once. Right conditions, long straight stretch of cement on I 20,
I just ran it, had fun, practiced in certain corners, working on exit speed and knowing whatever RPM it was turning at a given speed was just outside of my ability. I can see how knowing that could help with choosing the Right gear to be in at an apex, to get the best acceleration from apex to exit.

4-speed:
1987-95
1.888 (68/36) Primary
2.956 (68/23) Secondary

5-speed:
1996-2015
1.8108 (67/37) Primary
2.956 (68/23)   Secondary


4-speed:
2.2143 (31/14)
1.5000 (27/18)
1.0952 (23/21)
0.8750 (21/24)


5-speed:
2.3333 (35/15)
1.5789 (30/19)
1.1429 (24/21)
0.9565 (22/23)
0.8846 (23/26)

Your way works except you have to know the "magic number" for each gear.

I provided the above info for anyone who wants to do the math.  

Really you only need to know your RPM at 10 mph in top gear. That way you can, hopefully, multiply your speed (divided by 10) times that RPM to know how fast you're spinning the engine.

Ex.:
10 mph in top gear with a 5-speed and stock 140/80-15 tire is approx. 668 RPM.

Multiply your speed divided by 10 (65 mph=6.5) by this number.
ex. 668 * 6.5 = 4342 RPM

You'll be real close.

You'll only need to remember 1 number: 668.  


45 mph = 4.5 * 668 = 3006 RPM
50 mph = 5.0 * 668 = 3340 RPM
55 mph = 5.5 * 668 = 3674 RPM
60 mph = 6.0 * 668 = 4008 RPM
70 mph = 7.0 * 668 = 4676 RPM

etc.