Jcgranier
New member
How to adapt a bike speedometer to a Go Kart?
Bike speedometer adaptation to go kart
- Thread starter Jcgranier
- Start date
gegcorp2012
Active member
I would agree with @redflash that the quickest and easiest speedometer would be an app on a GPS enabled cell phone. I tried a few mounts and have not found one that work good enough to see while I am driving. Most car mounts are fragile or expensive and wil let the phone shake loose on bumps, so be aware your expensive phone could get damaged.
Now I use a pouch to hold my phone and protect it at the same time (hands free, but out of sight),,, it's a bummer when I put it there and the GPS app is asleep or not recording, but it's easy to get the GPS going and take another lap.
To use a bicycle speedometer, you will have a couple of mods to make.
The bike speedometer has a drive tab that sticks in between two of the spokes and turns the speedometer cable (?) time(s) per 1 tire rotation. The problem is that bike speedometers that I have seen mount on the end of the front axle.
My first thought would be to drive the speedometer at the base of the rear axle sprocket, but that may not be possible because the cable is supposed to mount on the end of an axle, and a bike axle is like 3/8" while a kart axle is 1" or more.
If you can figure out how to drive the speedometer, you will also need to re-calibrate the speedo head for accuracy because the speedometer is meant for a specific wheel diameter (like 24" or 26") and go-kart tires are smaller diameter, so the speed will appear faster because the speedometer iwill probably be overdriven.
Smaller tires = more revolutions for the same distance
One way to fix that is to re-draw the numbers on the face plate. You would have to use some math skills or measuring skills to figure out the % overdrive (% error) and re-draw the scale.
Best way to calibrate it would be to compare to a GPS app on your phone (ha ha)
Good luck.
Hands-free phone mount sounds better, right ?
I hope you can show some pictures of what you end up using.
I am showing a picture of a phone mount that fits in a CD player slot. I drilled holes and mounted it to my steering wheel bracket, but it eventually broke with the weight of my android phone on a yard track. For reference you may need something sturdier than this.
Ive been having good results with a tool pouch that I got at the hardware store. Just tie wrap it somewhere and slip in the phone or tools, etc.
Now I use a pouch to hold my phone and protect it at the same time (hands free, but out of sight),,, it's a bummer when I put it there and the GPS app is asleep or not recording, but it's easy to get the GPS going and take another lap.
To use a bicycle speedometer, you will have a couple of mods to make.
The bike speedometer has a drive tab that sticks in between two of the spokes and turns the speedometer cable (?) time(s) per 1 tire rotation. The problem is that bike speedometers that I have seen mount on the end of the front axle.
My first thought would be to drive the speedometer at the base of the rear axle sprocket, but that may not be possible because the cable is supposed to mount on the end of an axle, and a bike axle is like 3/8" while a kart axle is 1" or more.
If you can figure out how to drive the speedometer, you will also need to re-calibrate the speedo head for accuracy because the speedometer is meant for a specific wheel diameter (like 24" or 26") and go-kart tires are smaller diameter, so the speed will appear faster because the speedometer iwill probably be overdriven.
Smaller tires = more revolutions for the same distance
One way to fix that is to re-draw the numbers on the face plate. You would have to use some math skills or measuring skills to figure out the % overdrive (% error) and re-draw the scale.
Best way to calibrate it would be to compare to a GPS app on your phone (ha ha)
Good luck.
Hands-free phone mount sounds better, right ?
I hope you can show some pictures of what you end up using.
I am showing a picture of a phone mount that fits in a CD player slot. I drilled holes and mounted it to my steering wheel bracket, but it eventually broke with the weight of my android phone on a yard track. For reference you may need something sturdier than this.
Ive been having good results with a tool pouch that I got at the hardware store. Just tie wrap it somewhere and slip in the phone or tools, etc.
most bicycle speedometers are not capable of taking go kart sized wheel circumferences as their reference.
(some do, however)
So, just check that first if you intending to buy one.
If you already have one, check how low you can go on the wheel diameter setting.
if it takes a small circumference as reference it's just a matter of placing
the pickup and the , which usually is just a small magnet
that can easily be glued to a wheel (I'd buy a small neodymium magnet that is registered by the pickup)
if you got a mechanical speedometer you'll have to make your own pickup I'm afraid (doable... with simple hand tools)
best if you post pics and more infos about the speedometer you'd like to use
ideal if you also add the rear and front wheel circumference (use a taylors tape measure around the wheel)
if it cannot be set to that small of a diameter wheel, maybe we can cheat if it can be set to show either miles or kilometers per hour.
'sid
(some do, however)
So, just check that first if you intending to buy one.
If you already have one, check how low you can go on the wheel diameter setting.
if it takes a small circumference as reference it's just a matter of placing
the pickup and the , which usually is just a small magnet
that can easily be glued to a wheel (I'd buy a small neodymium magnet that is registered by the pickup)
if you got a mechanical speedometer you'll have to make your own pickup I'm afraid (doable... with simple hand tools)
best if you post pics and more infos about the speedometer you'd like to use
ideal if you also add the rear and front wheel circumference (use a taylors tape measure around the wheel)
if it cannot be set to that small of a diameter wheel, maybe we can cheat if it can be set to show either miles or kilometers per hour.
'sid
Jcgranier
New member
Guys, Thanks for all the input. My grandson is old school and wants an analog speedometer that's why I was trying to adapt a bike or mini-bike speedometer to this Go Kart.
and he's right about that
and I'd just have the perfect speedometer for that kart
Anyways, analog speedo means analog pickup, those are quite tricky to get right unfortunately.
the trick is to get a known pickup which in itself can be troublesome sometimes.
but once you found one
you can work your way from there.. this is one for a 27" wheel I think
count the notches (say 32) since a 27" bike tyre has a rolling circumference of ~ 224 centimeters
you then know every notch measures 7cm (~2.75")
Now you need to know the circumference of the wheel you want to attach the pickup to.
(say an 11.5" kart wheel and it's rolling circumference is ~91cm divided by the 7cm per notch you need a 13 notch pickup disc.
to get a reading in this example
(it'd be a metric reading since that made the conversion in this example easier... but it'd suffice to get an idea I hope
)Now, you can also make a new pickup wheel together with the new disc to adjust the ratio,
say you need a bigger disc to reach around an axle stub of a frontwheel spindle for example
just make a 39 notch disc and increase the toothcount of the pickupwheel by a factor of three as well.
(say 6 to 18 teeth)
or whatever you need to dial in the ratio closer to your actual wheel size.
it's only important to get a known and reliable base value for the pickup value,
so that you can calculate and make your new pickup based on that.
'sid
Jcgranier
New member
Thanks for the info, Sid. That speedometer would be perfect except it's registers in Kilometers. Hope to update all soon
madprofessor
"Loose Cannon Creations"
Speaking of GPS speedometers: I recently found the app in my very cheap Android phone, set it up, and tried it against the speedo in my van. It consistently read out only about 80% of what the van's read. Van's tires are basically factory size, so it must be pretty accurate, the GPS not.
Point is this, don't count on a GPS from your phone until you check it against a known factor.
That being said, my free GPS app always asks me to buy their upgrade. Not at all confident it would read any closer. Anybody recommend a proper GPS app that doesn't require me to send a credit card number out over the airwaves where it can be intercepted? Maybe I could buy it from my hard-lined computer to transfer to my phone?
Point is this, don't count on a GPS from your phone until you check it against a known factor.
That being said, my free GPS app always asks me to buy their upgrade. Not at all confident it would read any closer. Anybody recommend a proper GPS app that doesn't require me to send a credit card number out over the airwaves where it can be intercepted? Maybe I could buy it from my hard-lined computer to transfer to my phone?
yeah well... but since you'd have to mess with the ratios anyways, it'd be easy to change that.
'sid
PS I wonder how you guys still don't get it that this topic is NOT about phone apps
gegcorp2012
Active member
Popular analog speedometer setup showing dimensions in Imperial and Metric.
I have not seen any speedometer heads that show MPH yet, but this one looks like the faceplate could be changed. (could put the 'Vette logo on it too)
However, this pickup has a worm gear and would be harder to modify than the example that @itsid showed.
I have not seen any speedometer heads that show MPH yet, but this one looks like the faceplate could be changed. (could put the 'Vette logo on it too)
However, this pickup has a worm gear and would be harder to modify than the example that @itsid showed.
Jcgranier
New member
Yeah thanks. This has been a challenge. Which makes it worst is that this is a fixed axle go kart so the pickup would have to be mounted on the frame and rear pulling wheel. If this were a rotating axle, I could use a minibike speedometer.
a worm drive pickup would be difficult to make... true, but there's no need to do so,
it's only important that you have a known wheel to flexshaft rotation ratio for a given wheel diameter
so that you know how fast the flexshaft needs to rotate for your wheelsize.
with that you can make any style pickup you like that has the needed ratio.
even a simple friction roller if you like.
I think I'd rather suggest the front wheel over the rear axle anyways..
mostly because the flexshafts tend to be short and rather unwilling to take corners really..
so a direct line of sight between the pickup and dial is advantageous
but sure you can use any rotating part that has a fixed ratio with the wheel
so you can (if you include the sprocket ratio) also pick up from the engine shaft itself if it's just a cent clutch.
if you accept a moving hand when the clutch isn't engaged yet.
(1:1 like axle rear sprocket or brake disc are trivial of course... )
or you can add another let's call it "chain tensioner" sprocket that picks up the chain speed for you.
as long as you do the math right, that can also serve as a nice source for the pickup.
changing the dial isn't too difficult on mine either btw..
as long as it's not a glued plastic case I bet you can swap the dial on all of them more or less easily.
mini bike isn't a bad idea actually... the RUPP minibikes had a front pickup as far as I remember...
also worm gear just like the one gegcorp posted.. just made for small diameter kart sized wheels...
maybe they fit as is?
if you want a true and sole mph dial, you could try to find vintage speedometers alike
(VDO made them in 45 and 100mph for example)
rupp had one as mentioned.. and google shows a ton of alternatives.. some made of metaphorical gold though.
'sid
it's only important that you have a known wheel to flexshaft rotation ratio for a given wheel diameter
so that you know how fast the flexshaft needs to rotate for your wheelsize.
with that you can make any style pickup you like that has the needed ratio.
even a simple friction roller if you like.
I think I'd rather suggest the front wheel over the rear axle anyways..
mostly because the flexshafts tend to be short and rather unwilling to take corners really..
so a direct line of sight between the pickup and dial is advantageous
but sure you can use any rotating part that has a fixed ratio with the wheel
so you can (if you include the sprocket ratio) also pick up from the engine shaft itself if it's just a cent clutch.
if you accept a moving hand when the clutch isn't engaged yet.
(1:1 like axle rear sprocket or brake disc are trivial of course... )
or you can add another let's call it "chain tensioner" sprocket that picks up the chain speed for you.
as long as you do the math right, that can also serve as a nice source for the pickup.
changing the dial isn't too difficult on mine either btw..
as long as it's not a glued plastic case I bet you can swap the dial on all of them more or less easily.
mini bike isn't a bad idea actually... the RUPP minibikes had a front pickup as far as I remember...
also worm gear just like the one gegcorp posted.. just made for small diameter kart sized wheels...
maybe they fit as is?
if you want a true and sole mph dial, you could try to find vintage speedometers alike
(VDO made them in 45 and 100mph for example)
rupp had one as mentioned.. and google shows a ton of alternatives.. some made of metaphorical gold though.
'sid