Speed calculation

My question is about how to calculate speed on the KZ 700/750. On a long ride I noticed my speedometer was going erratic on me and that the odometer and trip counter stopped. I got it home and opened up the cluster to find the speedo gears melted and stripped. I tried to fix it by removing the odometer gear and clean off the plastic that was gumming up the gear but that only made the odometer and trip counter non functional. I then noticed the speedometer was reading at least 10 mph or more faster than it feels like I'm going but the erratic behavior stopped. the next thing I did was add a bicycle computer to the dash so I can record miles somewhat accurately but with it set up as per the instructions it says I'm doing about 77 mph when the speedo says I'm doing 90 and the rpm is at 7000.
I used the formula with tire size, final drive ratio and rpm just came up with 191 mph at that rpm. I KNOW I'm not going any where near that fast... or even half that fast...

The formula I'm using is RPM X tire diameter divided by Gear Ratio X 336. the formula tells me 191 mph which I Know is wrong.

The thing I was wondering is what's the ratio between the engine and the transmission at the rpimary chain or clutch basket. I know there's no way a 700cc bike can hit the speeds the calculations say I'm doing and the bicycle computer is telling me I'm going a lot slower than I'm really going cuz at 75 mph on it's scale I'm blowing by traffic as if they're standing still... everyone here drives around 75 to 80 on the freeway.

If anyone here knows the Proper math formula to use it'll help me out big time getting the bicycle computer calibrated correctly until I can find a new gauge cluster for my bike.

You should consider using a GPS unit to check your speed. I think if you maintained a steady speed on a straight piece of highway for a mile or two, you could compare the speedo with a GPS reading....
(This isn't my idea, someone else here suggested it a while back.)

Out on the internet are a few sites that have Excel charts to calculate speed. I have downloaded two of them to my pc, but I cant post them here because the site settings wont accept Excel uploads.

The strange thing is, I must have the rare speedometer that is right on the money. At 4500 rpm (half of redline) I am at indicated 58mph in 5th. The chart said at 9000 rpm my top speed would be 116, exactly double what I get at 4500. When I enter 4500 as a "redline" my top speed is 58mph

Sorry I don't have the website links anymore, try a google search for "Excel gear ratio speed" and see what happens.

True the GPS is a good idea, I'm also considering that option.
OKC_Kent, can you send me the charts at ddavis30@satx.rr.com ?It will definitely help.