Speedo Correction

[caddy425_imp]

The problem: Speedo reading 10-15% optomistic.

Theory - speedo reading off the rear wheel sensor - so any sprocket changes should (in my mind) make no difference to the speedometer reading

What I did: I went one tooth down on the front sprocket and one tooth up on the rear sprocket in order to get easier launches when riding two up. Which is most of the time lately. So that geared the bike down about 10%
As per the above assumptions is didn't expect to see any difference in the speedometer reading

Anyone know of an easy correction - or do i just live with it?

[pekingduck]

The problem: Speedo reading 10-15% optomistic.

Theory - speedo reading off the rear wheel sensor - so any sprocket changes should (in my mind) make no difference to the speedometer reading

What I did: I went one tooth down on the front sprocket and one tooth up on the rear sprocket in order to get easier launches when riding two up. Which is most of the time lately. So that geared the bike down about 10%
As per the above assumptions is didn't expect to see any difference in the speedometer reading

Anyone know of an easy correction - or do i just live with it?

You are correct that the speedo speed reading takes its input from the rear wheel speed sensor, and gearing does not change that. Only rear tire diameter can affect that. I assume you are checking against GPS on your phone. I am curious if the inconsistancy is steady, or the % changes with speed.
Honda and the other Japanese manufacturers' speedometers read fast, usually somewhere between 5-10%, so that no blame can be assigned to them for speeding tickets. Any instrument has a margin of error, including GPS, so you may have a normal situation. I assume the speedo inconsistancy was there before any sprocket change.
You can get a Speedo Healer v4 ftom Healtech, or another aftermarket device like a Speedo Tuner.

[caddy425_imp]

The problem: Speedo reading 10-15% optomistic.

Theory - speedo reading off the rear wheel sensor - so any sprocket changes should (in my mind) make no difference to the speedometer reading

What I did: I went one tooth down on the front sprocket and one tooth up on the rear sprocket in order to get easier launches when riding two up. Which is most of the time lately. So that geared the bike down about 10%
As per the above assumptions is didn't expect to see any difference in the speedometer reading

Anyone know of an easy correction - or do i just live with it?

You are correct that the speedo speed reading takes its input from the rear wheel speed sensor, and gearing does not change that. Only rear tire diameter can affect that. I assume you are checking against GPS on your phone. I am curious if the inconsistancy is steady, or the % changes with speed.
Honda and the other Japanese manufacturers' speedometers read fast, usually somewhere between 5-10%, so that no blame can be assigned to them for speeding tickets. Any instrument has a margin of error, including GPS, so you may have a normal situation. I assume the speedo inconsistancy was there before any sprocket change.
You can get a Speedo Healer v4 ftom Healtech, or another aftermarket device like a Speedo Tuner.

You are correct that the speedo speed reading takes its input from the rear wheel speed sensor, and gearing does not change that. Only rear tire diameter can affect that. I assume you are checking against GPS on your phone. I am curious if the inconsistancy is steady, or the % changes with speed.
Honda and the other Japanese manufacturers' speedometers read fast, usually somewhere between 5-10%, so that no blame can be assigned to them for speeding tickets. Any instrument has a margin of error, including GPS, so you may have a normal situation. I assume the speedo inconsistancy was there before any sprocket change.
You can get a Speedo Healer v4 ftom Healtech, or another aftermarket device like a Speedo Tuner.
Before I changed the sprockets it seemed that speedo was about 5km/h optimistic across the board vs my Garmin GPS. And the limiter kicked in at an indicated 5km/h over the hard limit. Now it seems to be exponential leading to about 15km/h by the limiter. very odd sort of result when nothing else had changed. As to your point - won't be getting any speeding tickets. Thanks - just wondered if anyone else had seen this effect.

[flynrider]

That's definitely odd. I check my speedo against my aviation GPS every year or so and have found that the electronic speedo on the CB11 has always been within 2 mph of the GPS speed. Same can't be said for the old mechanical unit on the CB750. It's within 4 mph at highway speeds and the error increases as speed increases.

Since your problem seems to cropped up recently, I'd suggest inspecting both the ring and the sensor. Since the sprocket change involved working in the vicinity of the ring/sensor something may be loose or out of place.

A tried and true diagnostic technique is to go back and check the last thing you worked on, even though seemingly unrelated.

[chync_imp]

Did you change the tires from stock?

I found going from a 50 profile ratio to a 60 caused a 10% difference in my speedo compared to gps.

I switched to 17" rims and installed a speed-o-healer to correct the speedometer.

They report that speedometers can be off as much as 15% from the factory but I have never heard from a cb owner of anything that far off without modifying something.

Keep in mind your mileage will be off too.

[Nortoon_imp]

My CB1100 EX is 6% optimistic. My CB500X was the same.

What the CB500 forum members found was that speedometers in the US measure in miles and were accurate. The rest of the world measures in kilometers and their speedometers were 6% off.

[apex1_imp]

My CB1100 EX is 6% optimistic. My CB500X was the same.

What the CB500 forum members found was that speedometers in the US measure in miles and were accurate. The rest of the world measures in kilometers and their speedometers were 6% off.

My 2017 EX is very accurate, within 1 or maybe 2 mph at 70 mph. It is as accurate as my Harley which has a “certified” speedo meaning it is accurate enough to be used in court by law enforcement. My Ducati, on the other hand, is wildly optimistic and I often ride with gps just so I know how fast I’m going.

[peterbaron]

Worry less, ride more...speedometer is not micrometer ..will always show more than actual speed due to legal matters..