question about gear calculations

can anyone tell me how what the mathematical calculations are to convert engine rpms over to rear wheel rpms given a certain gear.

i was thinking:

engine rpms/middlegear ratio/gear(x) ratio/final drive ratio = rear wheel rpms?

im creating a spreadsheet that will be used to create a nice little speed calculator given rpms, gear, speed it will be slick i just need to figure out the math first.

any ideas???

 

You have it right. You multiply the ratios to get rear wheel rpm.

 

ok this is what i have it seems about right

(RPM's) / (primary,spur,middle,final gear ratios(6.997)) / (gear(X) ratio) * (diameter of wheel (26)* PI(3.1459)) * (60 minutes) / (63,360 inches in a mile) = MPH's

so for a xj650 seca @ 4500 rpms we have:

Gear 1 = 18 mph
Gear 2= 26 mph
Gear 3= 34mph
Gear 4= 42mph
Gear 5= 61 mph

so for a xj650 seca @ 9400 rpms we have:

Gear 1= 48mph
Gear 2= 69mph
Gear 3= 90 mph
Gear 4= 112 mph
Gear 5= 128mph

sound about right or am i off??

 

Close probably. Lots of variables though; not all tires are exactly 26" in diameter for instance, it might be 26.8" or 25.4" depending on mfg.

There is an "on-line motorcycle speed calculator" out there somewhere, you plug in your bike and if it's in the DB, it fills in the chart. If not in their files, you have to plug in your gear ratios, etc.

I'll try to find the link.

 

Also, a difference between the Seca and Maxim rear tire size is made up for in the "primary set" which is the crank-to-cluch basket gears.
And the 900 has a "taller" middle gear set.

So, I figured there are 9 (nine) variations possible with some ambitious parts swapping.
1 - Stock Maxim
2 - Stock Seca
3 - Maxim with Seca rim = "tall"
4 - Seca with Maxim rim = "PainterD"
5 thru 8 - install the 900 middle gear in 1 - 4
9 - install 750 middle gear in a 900 = drag racer??