Kawasaki Vulcan Forum banner

1 - 20 of 22 Posts

·
Registered
Joined
·
150 Posts
Discussion Starter #1
So browsing the forums earlier I found out that the speedo was off on our bikes which surprised me but also kind of made sense. Also after some more reading some people in the of the other forums had mentioned changing tire size can potentially bring the speedo closer to an accurate reading, is there any or is it anecdotal. I guess my main concern is I wanna keep the bike around 65-70 to avoid another speeding ticket but I'm not really sure exactly how fast the speedo should read.
 

·
Registered
Joined
·
166 Posts
Unsure about in the states but assume it's has to be the same as we have the same bike here in Aus but the Speedo is allowed to be out by 10%.

This being the case the manufacturer generally puts the speed in the under 10% (you are travelling slower than the Speedo says)

No you can change your tyres to make the Speedo change but to make a speed that reads slower than actual speed read faster you would need to put smaller wheels on the wheel the Speedo reads from (I assume it's the rear wheel on most bikes)

This can create another offence (here in Aus at least) in that your vehicle now longer conforms with the design regulations of the bike.

Best option is to use a GPS to get a true and either remember what is out by or I believe there is a way to change the calibration on the 900 Speedo (unsure but recall you have to pull the Speedo out and re adjust the needle)
 

·
Registered
Joined
·
243 Posts
I checked my speedometer against a police radar billboard with the stock rear tire - it was off by about 10%. After I replaced my rear tire (darkside 195/65R15), speedometer is right on. Checked against GPS and it's confirmed. I really don't care what the manufacturers think, I want to know for sure how fast I'm going. If I'm going over or under the speed limit, it's my decision using accurate information.
 

·
Registered
Joined
·
155 Posts
Yep, a friend who was the police for a while had his Suzuki tested with an official radar gun. He found pretty much the same, that it was off by about 10 percent. It reads on the low side. That would partly explain when we were riding on the freeway with an indicated 80 mph people were still passing us.
 

·
Registered
Joined
·
166 Posts
Best bet to use a GPS as those billboards and radars have working tolerances also.

Unsure in the states about offences regarding going outside manufacturer guidelines but they are made this way to stop you from speeding.

What was the size of the original tyre you had on the bike?
 

·
Registered
Joined
·
675 Posts
Cant remember how/why but I believe the gist of it was they are designed to display HIGHER than accrual speed so that you dont get a ticket for going to fast. Same was true with cars years back to.

Some get really bugged about this, and others just subtract about 5 mph from the speedometer and go on with life.
( 5 is a nice round number to work with)
 

·
Registered
Joined
·
243 Posts
best bet to use a gps as those billboards and radars have working tolerances also.

Unsure in the states about offences regarding going outside manufacturer guidelines but they are made this way to stop you from speeding.

What was the size of the original tyre you had on the bike?
oem 180/70-15
 

·
Registered
Joined
·
243 Posts
The new tire was a General Altimax 195/65R15. The OEM was Dunlop 180/70-15 MC 76H TL. If I recall, after mounting it on the rim, it was about 1 inch taller.

[/IMG]
 

·
Registered
Joined
·
166 Posts
The new tire was a General Altimax 195/65R15. The OEM was Dunlop 180/70-15 MC 76H TL. If I recall, after mounting it on the rim, it was about 1 inch taller.
That change won't really effect your readings.

It's all about the rolling diameter of the wheel. The look of the tyre wall height can be very deceiving sometimes.

Check out https://tiresize.com/speedometer-calibration/ for an idea. Screen shot attached.
 

·
Registered
Joined
·
166 Posts
Yeah I've gathered it's around 10% off so 75mph on the speedo should translate to around 67ish?
Don't count on it being 10% and just guessing. Could be spot on and you add your 10% and begin speeding.

Also at certain speeds the Speedo can be out different percentages. Example 10% at 100 but 2% at 40.
 

·
Registered
Joined
·
39 Posts
Also at certain speeds the Speedo can be out different percentages. Example 10% at 100 but 2% at 40.
Rare cases; This is wrong information in most cases

Speedo should be off that exact % all the time..

45 indicated = 41.5 actual
100 indicated = 90 actual

My 1600 nomad is off 8%

Ive rode plenty of bikes with wrong speedometers to get used to doing math
 

·
Registered
Joined
·
166 Posts
Rare cases; This is wrong information in most cases

Speedo should be off that exact % all the time..

45 indicated = 41.5 actual
100 indicated = 90 actual

My 1600 nomad is off 8%

Ive rode plenty of bikes with wrong speedometers to get used to doing math
Not as rare as you think.

I do this stuff as part of my job and use a calibrated Speedo in my work vehicles everyday. Along with other speed measuring tools I can confirm that a Speedo is not normally constant with the same percentage from stop to full blown. It's is generally pretty close but sure isn't the same.

The faster you go the more the percentage tends to become out, but your Speedo speed always reads faster than your true speed. Yet to drive a vehicle where it's the opposite (unless it's been modified)
 

·
Registered
Joined
·
243 Posts
That change won't really effect your readings.

It's all about the rolling diameter of the wheel. The look of the tyre wall height can be very deceiving sometimes.
On paper, it looks like the tires are almost the same size, but you don't take into the account of the wheel size. The more narrow the wheel, the taller the tire will be in the center of the tread. With all the tire manufacturers, their listed height is based on a wheel width. They also have a recommended range of wheel width for that particular tire. In the real world, if you put multiple brand tires of the same size, you will notice that they are different heights (I've been selling tires for over 40 years).
 

·
Registered
Joined
·
16 Posts
My Vulcan 1500 is off by 8 MPH when above 50 MPH, when in town I cut it in half. I've checked it a few times with a Magellan GPS and with an IPhone app.


Sent from my iPhone using Tapatalk
 

·
Registered
Joined
·
166 Posts
On paper, it looks like the tires are almost the same size, but you don't take into the account of the wheel size. The more narrow the wheel, the taller the tire will be in the center of the tread. With all the tire manufacturers, their listed height is based on a wheel width. They also have a recommended range of wheel width for that particular tire. In the real world, if you put multiple brand tires of the same size, you will notice that they are different heights (I've been selling tires for over 40 years).
I have only run with paper figures and mostly I deal with car tyres. Good to know that cycle tyres are different.

So what's the best way to ensure the tyre you are buying will be the correct size for a bike?
 

·
Registered
Joined
·
243 Posts
I have only run with paper figures and mostly I deal with car tyres. Good to know that cycle tyres are different.

So what's the best way to ensure the tyre you are buying will be the correct size for a bike?
I would start Here. It's a database of real people running different tires on different bikes.
 
1 - 20 of 22 Posts
Top