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Speedo calibration?

Ducdude

Well Known and Active Forum Website User
VOC Member
Good day all,

I took the Shadow out for a 100 mile cold (3C) romp to a local show today and did a bit of the trip on the motor way. I also had an aux digital speedo running to check the big old 150mph unit. What I found is that the faster I go the larger the delta is between the actual road speed and the reading on the bikes 150mph unit. The old speedo always reads high.

So at an indicated 30mph on the bike the actual road speed is 28-29mph at an indicated 50mph the actual road speed 47-48mph (not 42-43mph) and at a straight up 80mph I am actually doing 75mph and so it goes up to at least 100mph...

The needle's action is smooth and it always goes to zero when stopped. The speedo was cleaned and lubed (professionally) 3 years and 2500-3000 miles ago

Is there an easy/painless way to bring this unit into calibration on my own?

Much Thanks,
Eric
 
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mercurycrest

Well Known and Active Forum Website User
VOC Member
Is there an easy/painless way to bring this unit into calibration on my own?

Much Thanks,
Eric

Hi Eric,
Yes, if you have a good eye and a steady hand. There are balance wheel weights in various thicknesses you can replace to either speed up or slow down the balance wheel. That's if, you can find some, or.. you can have a Smith's expert do it for you. In any event, they are adjustable.
Cheers, John
Try this place for parts.... http://www.speedograph-richfield.com/
 
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Albervin

Well Known and Active Forum Website User
VOC Member
Eric, it appears the % variation is all over the place.3% at 30 mph, over 10% at 50 mph and then 6-7% at 80 mph. As it is not linear a different front tyre won't fix it. Now this is a bit naughty but...... post a similar question on that other VOC forum, Dennis Quinlan is very active on it. He has a worldwide reputation for knowing nearly everything about chronometrics. Our own Andy Rackstraw is also very knowing but I don't think he is a regular forum poster. One advantage of your speedo is that you should never get booked for speeding. Both my 3" and 5" speedos were serviced by Dennis & I can say they are 100% accurate at 60 mph. Courtesy of the NSW Police Department!
 

Ducdude

Well Known and Active Forum Website User
VOC Member
Fit a bigger front wheel?

LOL I had though of that .... I was thinking it may be cheaper and easyer to adjust the speedo.:D I am still running the stock 20" ft wheel and for now I like it that way...Besides the tire is still new-ish...

Thanks,
Eric
 

Ducdude

Well Known and Active Forum Website User
VOC Member
Eric, it appears the % variation is all over the place.3% at 30 mph, over 10% at 50 mph and then 6-7% at 80 mph. As it is not linear a different front tyre won't fix it. Now this is a bit naughty but...... post a similar question on that other VOC forum, Dennis Quinlan is very active on it. He has a worldwide reputation for knowing nearly everything about chronometrics. Our own Andy Rackstraw is also very knowing but I don't think he is a regular forum poster.60 mph. Courtesy of the NSW Police Department!


Thanks Alyn,

I miss read my notes:

an indicated 30mph actual road speed is 28-29mph 3.3 - 6.6% off
at indicated 50mph actual road speed is 47-48mph (not 42-43mph) 4 - 6% off
at indicated 80mph actual road speed is 76-75mph 5 - 6.25% off

So I am 5-6% off most of the time ..The variation is pretty linear and only seems dependant on where I am catching the Smiths at its reading and the resolution of the measurement at the low end. Still I am not changing the FT wheel size to adjust, thinking that a tweak on the speedo will do the job better for me...

Much Thanks for the help. Now all I need to do is figure out how to change the weights on this thing...:)

Thanks,
Eric
 

bmetcalf

Well Known and Active Forum Website User
VOC Member
I liked my 19" because I could mumble"indicated" when I was bragging about how fast I rode and not feel guilty at all. With my 21", I lose that shred of honesty and have to just exaggerate. :rolleyes:
 

Peter Holmes

Well Known and Active Forum Website User
VOC Member
I liked my 19" because I could mumble"indicated" when I was bragging about how fast I rode and not feel guilty at all. With my 21", I lose that shred of honesty and have to just exaggerate. :rolleyes:
What is your preferred 21 inch tyre 3.00-21, 80-90-21, 90-90-21, and what manufacturer?
 
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