Speedo switch out question

[Skievryday]

Now I know the mechanical speedo on a 28 year old bike isn't going to be perfect, but here is my question.
I scored an 83 GS 850 L set of gauges from mortation to put on my gaugeless 1980 750 E. Sweet. But I question the speedo rating- 25 mph in 1st at about 7k rpm? So was the wheel size different on these bikes? IF so anyone want to try and caluculate the percentage difference? Am I reading it right?

I used to have a 650L so it could be the gearing on a chain with 100 more cc's that is making me go faster in lower gear, but it seems high.

[rustybronco]

find a highway with mile markers ride at an indicated 60 mph, 1 mile=60 seconds, best to average it over 5-10 miles.
how slow or fast are you?
3mph @ 60mph=5%
6mph @ 60mph=10%

you now have the correction factor for your speedo.

[Skievryday]

How fast or slow?

Ask my fiance.

A lot of variables in there like being able to maintain speed, while watching my watch, etc. but I get the idea. Thanks

I don't think fo these things, but then I go. Holy crap that makes sense...

[rustybronco]

strap her next to the speedo (the watch!).

[robertbarr]

Just duct tape a Garmin (or similar GPS) to your handlebars.

[SqDancerLynn1]

Or ride along side of a vehicle with a digital speedo

[rustybronco]

Go very fast past a cop, he'll tell you with high accuracy.

[Skievryday]

Renobruce- you are no fun. Three bungee cords a wad of duct tape, and I could totally get her on there.

Robertbarr- I am a map kind of guy. Can't justify the money, but I know people who have been able to and I thought about this. Just have to convince them that the tape will hold.

Lynn- Another good idea... I have a friend with a prius which should have a digital speedo.

Man I thought someone would be excited to figure it out mathmatically, but I guess I ahve to go do the work.

[Clone]

http://www.suzukicycles.org/
You can check the spec. of the two different models on that site, to see if the wheels were different sizes, and go from there.

[Steve]

Or ride along side of a vehicle with a digital speedo

Just because it's digital, does not mean it's accurate.

I am sure there's a difference between bikes and cars, but my Kawasaki Voyager 1300 was ALL digital (including the fuel injection) except for the odometer. The odometer was rather accurate, it was only off about three tenths of a mile over a 100-mile stretch of freeway mile marker signs, but the speedometer was off by just over 10%. :shock: When I got my GPS to show that I was doing 70, the bike's speedometer was somewhere between 77 and 79.

.