How fast am I going?

I have a xj1100 and just got my speedometer working but am I really going that fast? It seems to be off on the fast side. I think I am going about 10 mph slower then the speedometer says. I get 70 mph at 4k in fifth gear. I think it reads 52 mph at 3k in fifth gear.
Anyone with a xj 1100 that can let me know if that is correct?

 

Got a xj1100? next time you take it out can you see how fast your going at 4k in fifth gear?

 

I think you are going about half. I heard somebody say there go's that half fast rider.

 

What the #### are talking about? If I am looking for a wise asssss I will refer to my own.

 

I'm not sure how different the gearing is between that and my 650, but In 5th gear my speed (in kph) is about double my rpm / 100. i.e. 5500 rpm = 110kph

 

Here is what my XS and XJ 1100 do
5000 rpm= 70mph in 5th
max speed : 135mph = 8500 rpm in 5th
I'll make some more noted on my next ride

 

Interesting my 650, 5K=70mph in fifth.

 

Yeah thats strange? I did install a drive gear that I got off ebay. The ad said it was off a 1982 xj1100. It looks the same as the one that came with the bike. I was thinking maybe it was off a 750 or some other bike with different rear gearing. I read somewhere that if you use a 750 rear you can get a higher final drive gearing. Not a easy task as it takes cutting, machining and wielding. So I thought that the speedometer drive would be diffident on the smaller bikes. I just don't know what's going on with it. Maybe if I try to put the original one back in it will be correct. I replaced it at the same time I figured out that the tang in the wheel was bent and not catching.

 

Well the ratio of the speedomter itself on most old metric bikes is the same.
ie you can swap pretty much any speedo out from an old metric.
So I would guess the drive gears are the same, even if the wheel is taller the center is still the same.
I mean if it fit properly it is the same size as the original.

 

I have clocked the bike now and I am about 10mph fast on my speedometer.
Can you adjust the speedometer? What would make this happen.
I have spent a lot of money and time on the speed tac assumability and a new cable. I would like to get the thing rite if possible.
Not because I care how fast I am going.. It's because the police do!

 

There are many different drive gears as yamaha had several different size tire/wheel combos. All japanese bike speedos from the 70/80/90s are the same ratio so the gears have to be different. How else would they be remotely close to being accurate?

 

Good point, I rethought what I wrote and came to the same conclusion.
My thinking was that 2 inches at the center would always rotate the same speed no matter the diameter of the tire.
But later I thought no that's not right the diameter directly affects the speed at which the center rotates too.
Thanks for pointing it out.

Jaming, are you running stock tire and wheel?
Along the same lines as above, when I put 235's, up from 205's, on my old Buick it changed the speedo reading.

 

I don't know It looks stock. I think the gear drive I got off ebay is the wrong one for my bike. I will have to change it out before I will know for sure. I will get around to it soon and let you know if it worked.
I did take the speedometer apart to set the odometer to the actual millage for the bike. I had to remove 4k miles because I got the speedometer off ebay. But I did not play with the mechanics for the speed and the needle runs smooth. It must be the gear drive.

 

i use a $20 bicycle speedo good to 125 MPH and dead simple to install. I forget the name but I found it on this forum. Tracks ride time, max speed, current temp, etc.

 

I took one of the magnets off the bike when I got it. The guy had one of thous bike speedometers on it at one time. I looked and the tire is the rite size for the bike. I think its my speedometer that is off somehow. Can you calibrate it? If not I will just live with it.

 

Yeah -- you will have to find the manual or instructions online. Basically you mark the tire and the ground, roll the bike a revolution and mark the ground. Then you measure the distance between the marks and enter that. Mine is a protege (http://ecom1.planetbike.com/8002.html but i didn't pay that much) and you press a button on the back and enter the distance in millimeters. extremely accurate.

 

Well my xj 1100 at 5000 rpms runs at 120 kmh = 74 mph and thats with 2 people on bike... Hope it helps you out

 

All metric bike speedos from the era have the same RPM-speed ratio, even Hondas, etc.
Virtually all the maufacturers did the same thing: had one speedo drive box for a 18" front wheel and one for a 19" front wheel (and later for a 17") and nothing much else was different. The speedos all read the same RPM-speed, and the only calibration difference was between say, an 80-mph and 125 or 150mph gauge. That's why I can use a 150mph XJ900 speedo in my 550 Seca in place of the original 80mph unit and it's perfectly accurate.
You might have the wrong drive gear box for your size wheel, OR your speedo itself and/or the cable might need a good cleaning and lubricating. If it's bouncing appreciably I would suspect the latter.

 

OK- - my 900 reads 118 MPH at a GPS true reading of 104 MPH.
The 900 has a smaller front tire than a 750.
Is it possible that I have a 750 speedo drive box ?
What would be my fix ?

 

You could use a handheld GPS such as TOM TOM or Lowrance to see how fast you are really going. If the tire is the correct size for the bike it should be accurate at least as accurate as the original.


If you find that it is inaccurate it may be a simple gear change at the cable drive. In the Automotive world there were different speedometer gears to calibrate speedometers (b4 compukers). Had a quick look in bike bandit but didn't see any in the parts listing. Maybe someone else knows if such a gear selection is available.

After re-reading the thread, I see that has already been addressed. Again it appears I'm so cheap I won't pay attention.

 

My xj700 speedo is also of.
I had the wife clock me with her car and determined that it is off by 4 mph at 60

 

This is why you seldom get stopped for 5 - 10mph over at highway speed. No system is 100% accurate and variation of 10% is fairly common. If that's all you are off, don't worry. The inaccuracy of the bike and coupled with that of the car, could mean one or the other, or neither is accurate. Even tire pressure can affect it.

Police speedometers were checked and calibrated so that when they paced a speeding car, documentation could be presented into evidence. Now they use radar or laser which can be used in all circumstances.