Topic: CB750K6 Speedo Running Fast

[M 750K6]

Hi,

I'm used to bikes and cars reading slightly above actual speed. It's always been within 5%. However, I'm finding my CB750's speedo is reading 10% above actual speed. It's a stable needle, doesn't waver. I have stock wheels and a 3.25 x 19 Avon Roadrider on the front.

Is this usual? 10% feels too much, I'm adjusting it in my head, rather than accepting it, as I do with my other bikes. Is there any way to bring it nearer to actual speed.

[newday777]

Hi,

I'm used to bikes and cars reading slightly above actual speed. It's always been within 5%. However, I'm finding my CB750's speedo is reading 10% above actual speed. It's a stable needle, doesn't waver. I have stock wheels and a 3.25 x 19 Avon Roadrider on the front.

Is this usual? 10% feels too much, I'm adjusting it in my head, rather than accepting it, as I do with my other bikes. Is there any way to bring it nearer to actual speed.

Back in the 70s most all bike speedos were figured to be 10% fast reading.

[M 750K6]

Hi,

I'm used to bikes and cars reading slightly above actual speed. It's always been within 5%. However, I'm finding my CB750's speedo is reading 10% above actual speed. It's a stable needle, doesn't waver. I have stock wheels and a 3.25 x 19 Avon Roadrider on the front.

Is this usual? 10% feels too much, I'm adjusting it in my head, rather than accepting it, as I do with my other bikes. Is there any way to bring it nearer to actual speed.

Back in the 70s most all bike speedos were figured to be 10% fast reading.

I wondered if all Hondas of the era do it. Is that the case?

My 1975 Norton is almost spot on, so was hoping there might be a fix. I've checked my tyres and they appear to be a recommended fitment, but maybe the modern ones are a little bit smaller circumference?

[HondaMan]

Most of the Japanese bikes of the era read fast, but that one's a little higher than I'm accustomed to seeing?
If your Avon 3.25x19 front tire is like the last one I had, it is small on its OD as compared to the old Bridgestone OEM tires of the same size designation. This is due to modern tire carcass construction: today all bike tires are laid over molds designed for radial cores, even when the tires are not radial. This is simply due to the costs of tooling in manufacturing plants these days. I've noticed (and measured) the "inch-marked" tires on these carcasses to be smaller OD and height than their original designs. To help "fix" it on my own 750 I used a 100-90/19 front tire this last time around (instead of the supposedly cross-referenced MT90-19 that was once prescribed) and it put the numbers much closer to reality. I check mine using a sweep-second wristwatch and several mile markers on interstates: I don't have a smartphone with satellite linkups, that's just so wrong for a 1970s bike...

[PeWe]

My K6 speedo show around 2.5%, definitely less than 5% too much when I have checked when passing speed warning devices with a sign showing the speed that flash when driving faster than allowed.

I usually drive faster then to check. They are sometimes  placed on 50 kmh roads.
I prefer to pass it in 100kmh to get better reading with less error.

Only thing that other cars in front of me brakes hard when they think it has a camera.

3.25-19 tire. I might have had 100/90-19.

[M 750K6]

100/90 19 looks interesting. Is the front rim 2.5" width?

[PeWe]

100/90 19 looks interesting. Is the front rim 2.5" width?

I used have used 100/90 on stock rim 1.85"
My K6 has now that size on 2.15-19.

[Galactica]

My 2019 Subaru speedometer is bang on.
My 2006 Nissan Frontier reads 3km high right fro zero.
My 2019 Yamaha Tracer900 reads 7% high
My various Kawasakis; Z1, kz900, kz1000s were all over the place.

Legislation allows speedometers (from new) to be in error up to 10%, but must not read low.

[CycleRanger]

I don't think the speedos were particularly accurate even when new but one thing that can make them run faster over time is if some of the dampening oil has leaked out.
The speedo on my K5 is reads about 10% fast.
I haven't bothered to check my other bikes.

[PeWe]

I need to check my speedos again when riding season arrives.
Possible mid April.
My old Garmin navigator from 2009 if I can attach it so I can read the small numbers.

Maybe time for a bike navigator for my rides?

[PeWe]

Thanks for the idea to verify speedo.
And with GPS $$$

I realized that I need a new one, for motorcycles.
Searched and found:
Garmin Zumo XT2.
One shop had $100US discount so I could not wait.

My 24 rides 2024 can be planned in advance, riding on unknown roads with visible alternatives to new for me restaurants and gas stations.

[CycleRanger]

Thanks for the idea to verify speedo.
And with GPS $$$

I realized that I need a new one, for motorcycles.
Searched and found:
Garmin Zumo XT2.
One shop had $100US discount so I could not wait.

My 24 rides 2024 can be planned in advance, riding on unknown roads with visible alternatives to new for me restaurants and gas stations.

I have a GPS app on my phone. There's many of them. For as often as I use it it was cheaper than a Garmin.

[PeWe]

Thanks for the idea to verify speedo.
And with GPS $$$

I realized that I need a new one, for motorcycles.
Searched and found:
Garmin Zumo XT2.
One shop had $100US discount so I could not wait.

My 24 rides 2024 can be planned in advance, riding on unknown roads with visible alternatives to new for me restaurants and gas stations.

I have a GPS app on my phone. There's many of them. For as often as I use it it was cheaper than a Garmin.

The Garmin is cheaper than my  phone I do not want to suffer the elements while riding  

The phone can be used in car finding one address, though. Google map, no GPS app.