Author Topic: Honda speedometer accuracy (Read 9021 times)

pjlogue · « **on:** October 20, 2016, 06:07:32 AM »

I was wondering how accurate the speedometers on the Honda bikes are. I have a 75' 750K I just restored. While riding, my perception is that the speedometer is indicating slightly higher than actual speed. Looking back to when I bought the bike in 76' I remember having the same perception. Has anybody checked the calibration of their speedometers on a bike that's all stock?

-P.

Grabcon · « **Reply #1 on:** October 20, 2016, 06:26:26 AM »

Throw a GPS/phone unit on the bike and check your speed and see what the variance is. My guess it will be off from the GPS value. Most likely reading fast. The odometer may be another story. That might be right on or be a different percentage off.

evanphi · « **Reply #2 on:** October 20, 2016, 06:26:32 AM »

Plenty of old and new bikes will indicate higher than their actual speed. Grab you cell phone with a GPS speedometer app and tape it to your tank, then go for a ride. See how far off your gauge is.

EDIT: Damn so close! 6 seconds apart, Grabcon!

flybox1 · « **Reply #3 on:** October 20, 2016, 06:52:22 AM »

pjlogue · « **Reply #4 on:** October 20, 2016, 07:46:34 AM »

I'm guessing the speedometer will be on the +10% side. Back in the 70's it always seemed the cars from Japan had errors in the speedometers. I always figured it was either the metric conversion thing with wheel diameter or it was on purpose so their vehicles looked like they got better gas mileage.

-P.

Darren Jakal · « **Reply #5 on:** October 20, 2016, 07:55:23 AM »

I read on another forum (car) that there is a closely guarded formula that each individual manufacture uses to drop the needle down from the actual speed.

He thought himself an expert and insider (so take it for what it's worth) and said that it was to stay clear of blame when someone was caught speeding: "honest officer my speedo said I was doing only xxx".

There are numerous radar spots around here that give you speed feedback on a lit screen and when it says I'm doing 50 kph my speedo will read 48. So when I think I'm doing 130 the car maybe only going 122 or so.

Not sure if this was part of product planning in the 70's it sure seems to be true for my 1994 mitsubishi.

Duanob · « **Reply #6 on:** October 20, 2016, 09:48:35 AM »

I found the accuracy can depend on tire size. When I went from the stock pizza cutter tire to a 110/90-19 my speedo was off by about 4-5MPH at highway speeds according to my GPS. It's just like a car, if you change the diameter of the tire it will affect the rotational speed and throw the speedo off.

el pachuco · « **Reply #7 on:** October 20, 2016, 10:29:19 AM »

I recently verified the accuracy on my '75 750k. It was only 2 mph optimistic at 35 mph, 1 mph optimistic at 60 mph and spot on at 80 mph. after about 83 mph the needle began bouncing very bad and climbing slowly as the gps mph continued to climb to 95ish, before I let out of the throttle.

BobbyR · « **Reply #8 on:** October 20, 2016, 10:30:58 AM »

All of these are great. The roadside radar signs are pretty decent. Mine reads low since I found a friendly Cop.

rocket johnny · « **Reply #9 on:** October 20, 2016, 10:38:34 AM »

my 76 k6 is about 5 mph off . 55 is 50

pjlogue · « **Reply #10 on:** October 20, 2016, 12:48:26 PM »

This is about what I was guessing mine is. I'll have to use a GPS and verify.

-P.

Desert-SOHC · « **Reply #11 on:** October 20, 2016, 01:01:05 PM »

I run a 110/90-19 on the front of the 78 and while I havent done a GPS run but the local radar sign indicates that my speedo is about 4mph slow. Indicated 65mph is actually 61mph on radar and there is another on a 35mph street that also shows the same thing. I just assume that mine reads 5mph faster than my actual speed.

Geeto67 · « **Reply #12 on:** October 20, 2016, 02:38:10 PM »

Quote from: pjlogue on October 20, 2016, 06:07:32 AM

I was wondering how accurate the speedometers on the Honda bikes are.

Not very.

I have had three fail on me in almost 20 years on the same bike. There are a lot of factors that could contribute to them not reading correctly because they are old mechanical systems that aren't typically serviced.

drumstyx · « **Reply #13 on:** October 20, 2016, 02:45:01 PM »

On other cable driven speedos I've used, the speedo is magnetically driven of course, but the odo is gear driven. This should mean the odometer is precise, but the speedo cam be anything depending on spring tension...usually somewhere around +5-10%

jonda500 · « **Reply #14 on:** October 20, 2016, 03:32:08 PM »

8% higher than actual speed
John

pjlogue · « **Reply #15 on:** October 21, 2016, 01:25:37 AM »

Thanks for the responses. They kind of point to what I suspected that the stock gage/wheel reads higher than actual speed. I'm a stickler for things being accurate (especially gages) so I'll use a GPS to verify the error. I don't suppose there are different pinion gears for the speedo pick up in the front axle to make adjustments are there?

-P.

Geeto67 · « **Reply #16 on:** October 21, 2016, 03:49:58 AM »

Quote from: pjlogue on October 21, 2016, 01:25:37 AM

Thanks for the responses. They kind of point to what I suspected that the stock gage/wheel reads higher than actual speed. I'm a stickler for things being accurate (especially gages) so I'll use a GPS to verify the error.

That's a huge waste of time. The unit was designed to be inaccurate when new, you aren't going to fix that without replacing it or re-engineering it completely. You are better off just getting something like a new electronic speedo that you can calibrate and dressing it up to look like the old gauge than you are trying to get the stock one to read correct.

Another option, if you can find it, is to find the speedo from a police model. They are rare, look nothing like the stock speedo, and I think they even mount differently, but they are a calibrated speedometer that can be used for speed enforcement. There were very few police models made and the last one I saw sell was a couple years ago for $600, but they are out there.

Quote

I don't suppose there are different pinion gears for the speedo pick up in the front axle to make adjustments are there?

No there are not. Since you mentioned the speedo drive, one of the reasons for further inaccuracy is they are basically a sealed bearing, but the grease inside them gets old and stiff and puts resistance on the drive. Sometimes they even wear out of tolerance.

Honestly, you are trying to solve for a problem that really isn't crying for a solution. Almost Every civilian vehicle made has a speedometer that reads fast. If you really need to have your speed be "accurate" a supplemental gps speedometer or a bicycle speedometer with magnetic pickups on the wheel will tell you how fast you are going.

PeWe · « **Reply #17 on:** October 21, 2016, 05:46:05 AM »

My speedometer is rather accurate. About + 5% too much or even less when I checked a radar with sign to inform people how fast they drive. Many car drivers slow down when they see this and do not understand a perfect chance to test various speeds

Speedo show 105km/h- real speed 100km/h or 105mph -100mph

This with std 19" rim front, tire Dunlop StreetSmart 100/90-19
Bike, avatar CB750 K6

Darren Jakal · « **Reply #18 on:** October 21, 2016, 08:30:20 AM »

Quote from: jonda500 on October 20, 2016, 03:32:08 PM

8% higher than actual speed
John

This is exactly what the "expert" claimed. For the vehicle in question he was sure it was 7%

RAFster122s · « **Reply #19 on:** October 21, 2016, 08:52:29 AM »

I have a 2000 Ford Crown Victoria with a factory calibrated speedo, it is a ex California unmarked police car. Its speedo which states at the bottom it is factory calibrated reads LOW! ONCE I pass 60mph it becomes off by about 5-7 miles an hour. That is with the same rolling diameter and same brand and size and inflatiin pressures recommended for the model. GPS indicates I am doing about 75-76 by the time I see 70 indicated and it reaches 65 just a needle's breadth past 60. I don't care to lose my car to impound or map the speed variance so I do not push it to 100 and above to the typical top speed of 140.

It can reach it, I hear

via gps and past that indicated

Considering you are travelling what is it, 90 ft per second at 60mph...anyone want to do the math on 100-120-140?
It is scary the amount of ground covered and your reaction time to anything would be impossible at very high speeds and all turns or changes in direction have to be done gradually if you don't want to be rolling out of control. That is why high speeds are not safe on public highways. Other traffic is greatly affected as is yo or less ur car by the wind deflection of the different velocities of the vehicles. Someone changes lane in front of you 1/4 mile away you have very little time to slow to avoid them.

PeWe · « **Reply #20 on:** October 21, 2016, 10:09:32 AM »

GPS to check the speed. It's bad if speedo show less than real when it can end up in a speeding ticket.

strynboen · « **Reply #21 on:** October 21, 2016, 12:16:49 PM »

mine is register 160 KMT but is only running150.
.so its hard do the ton..have to run 175 KMT to real brakethrough the ton

BomberMann650 · « **Reply #22 on:** October 21, 2016, 12:34:55 PM »

My 550 is over reporting by about 6 mph.

So my needle lives at 80-84 when I'm on the freeway. Still getting passed by easily offended washington drivers.

Ichiban 4 · « **Reply #23 on:** October 21, 2016, 02:01:48 PM »

I've ridden many Honda bikes since the 60's..from Cubs to the 750's. All seemed to be a little high on their speedo readings..around 5%. I always felt that was on-purpose by Honda..so that rather than going too fast..a rider would be safer going a little slow. Also saw that on British bikes I rode.
Also have had several Toyota cars..and they also have been high on their speedo readings. As mentioned on this thread..I've measured that against what the readings on roadside speed signs have been..mainly.
Never felt it an important issue for me..or the average rider/driver.
Ichi

Crack On · « **Reply #24 on:** October 21, 2016, 05:28:51 PM »

I noticed no one has answered the question of replacement gears available to adjust the reading so I'll ask again:

Does anyone know if there are different toothed gears available for the stock speedos? If there are where if you know.
Thanks

(Yes this won't make a bad system better. but I would like to set mine to be as accurate as possible at 65mph for freeway riding here in SoCal.)

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Author Topic: Honda speedometer accuracy (Read 9021 times)