Gearing & Speedo Question
 

I just purchased a '98 SH, the previous owner replaced chain and sprocket with -1 on countershaft and +2 on the rear. This change has made the speedo useless. If you have done this can you give me a "hint" as to a correction factor--for instance, the speedo now reads 15 mph fast or whatever.:eek:

I have same gearing as you do exept i run a 190 reat tire. My speedo was 15 mph off at 70 mph actual and 85 mph indicated. Best thing i ever did was buy a Speedohealer and it is accurate as hell.

One problem that I've heard a lot is that the Superhawk speedometer (even stock) isn't that accurate. That said, the -1/+2 mod changes the ratio of turns between the front sprocket and the rear sprocket from 2.56 to 2.86. What that means is that the front sprocket used to turn 2.56 times each time the rear tire made one revolution. Now the front sprocket turns 2.86 times for each wheel revolution. So the speedometer "thinks" you're going 11.7% faster than you are since the pickup is on the drive, not on the wheel. If the stock setup had been accurate, you are now roughly 11.7% off on the high side. It's not going to be a fixed MPH off, but a consistent percentage off. At an indicated 70mph, you would now be traveling only 62.67mph.

This also means that at the top of 6th gear, you'll redline at a lower speed since your engine is turning 11.7% faster than stock at the same speed. I prefer to give up some at the top in order to have more pull lower in the rev range, but changing back to stock will return the speedometer to it's original margin of error and give you an 11.7% higher top speed.

The Speedohealer is a good option and should be pretty accurate (as k-d-williams said). I decided to go with the RX-2 Speedometer from Koso North America. It's digital and looks awesome...but it's $400.
http://ep.yimg.com/ca/I/motostrano_2063_23385458

The cheap alternative, that also gets you a digital readout, is a bicycle speedometer. Reasonably easy to install (some creativity is necessary), easy to calibrate, especially if you have a GPS. Mine looks like this.

https://www.superhawkforum.com/forum...&pictureid=803

It doesn't fix the odo, if you care about that. But the speedohealer still has you squinting at tiny numbers. Tradeoffs. Here's a thread about it:

https://www.superhawkforum.com/forum...dometer&page=2

I am installing a similar bike speedo but it also has temperature. I hope to get a speedo healer to slow down the crazy milage that builds up quicker too. Oh yeah, & lowering the gearing doesnt necisarily lower top speed as most bikes are fighting too much wind to ever reach redline in top gear.

Each tooth added to the rear changes final drive about 2.5%. Each tooth down from front changes it about 6.25%. Speedo should read about 11% more than before at any given real road speed.

Just knock 10% off whatever the speedo says and you'll be close enough.

I have a speedo healer and it works great and you can reprogram it whenever you change gearing. It's so easy to reprogram even I can do it;)

Thank you for the assistance, at least I have a "ball park" point of reference. I think I'm gonna purchase a ram mount for the front of the tank and use my 12 y/o Garmin eMap to mentally calibrate the speedo.

Just to add to my previous post, i used my Garmin 496 gps out of my airplane to calibrate my speed. The end result was 17.3%. My speedo is perfect now from 35 mph to 145 mph per my gps.