Speedo's: The untold story???

Message

ngsalvo · #1 Unread post by **ngsalvo** » Thu Jul 12, 2007 6:49 pm

Hey.
Took my bike (Hysoung GT250R) in for a service the other week, and mentioned that I felt the speedo was out by a couple of K's.
The guy asked why I thought this, and I explained to him that when I go the speed limit according to my speedo, I get overtaken as though I'm standing still.
My wife was driving behind me the other day, and when we got to where we were going, she asked why I was riding so slow. As far as I knew, I was doing the limit.

The guy at the service shop said that they sometimes set the speedo a little slow so that you don't speed. I thought that this was weird, but he seemed pretty sure, and said that a few people lately had the same problems. I asked him to put it in writing that in his educated opinion, I can do 70kp/h and be under the speed limit which is 60kp/h. He wouldn't do this, and somehow his GPS was 'broken' so he couldn't test the speedo's accuracy (how does a GPS get broken? You hold it in your hand, or it sits on the dash in a purpose built bracket. What was he doing with it to break it???

)

I am wondering if there is any truth to his comment that they factory set the speedo a little slow so that we don't speed. Has anyone heard of this, or was he just not interested in looking at the dash of my bike?

#2 Unread post by **t_bonee** » Fri Jul 13, 2007 12:15 am

I've heard the same thing. I've never tested it cause I've never felt the need. I rarely drive/ride the speed limit anywho though. So it's kinda moot for me.

jstark47 · #3 Unread post by **jstark47** » Fri Jul 13, 2007 1:04 am

I've heard of a lot of motorcycle speedometers being set a little slow - each of the 5 bikes we've had has been a little slow, the worst being the V-strom. According to it, I'm riding 90mph when I'm just easing past traffic in the morning. It's about 7-8 mph high.

But yours sounds more than a little off. And yeah, I'd say that mechanic isn't interested in adjusting instrumentation. Is this at the dealer that sold you the bike?

Nibblet99 · #4 Unread post by **Nibblet99** » Fri Jul 13, 2007 1:26 am

Bike speedo's are renowned for being a bit off, but anything that changes the circumference of your tyres can have an additional impact, from a different set of tyres to under inflating them.

Just add it to the other list of the quirks you get on MC, like inaccurate fuel gauges

BMK · #5 Unread post by **BMK** » Fri Jul 13, 2007 1:27 am

I'm not buying it.
It would seem to me that a manufacturer that would knowingly and intentionally set the speedometer inaccurately (fast or slow) would open themselves up tp all kinds of legal problems and lawsuits. It doesn't make any sense for them to do it....theres nothing for them to gain and quite a bit to lose by such a practice.

I'm not saying your speedo is accurate, I'm just saying I don't believe the manufacturer modified it to be inaccurate.

Just my opinion.

Nalian · #6 Unread post by **Nalian** » Fri Jul 13, 2007 1:54 am

It's pretty well known that most of them are off. Google for "speedo healer" and you'll see all kinds of fixes for it.

Gadjet · #7 Unread post by **Gadjet** » Fri Jul 13, 2007 2:09 am

My bike speedo is off by 10%, as calibrated with my GPS. I don't consider this to be a problem though, as I'm used to it and I now use my GPS for speed readouts.

A 'Speedo Healer' won't work on my bike, even if I wanted to try one, as my speedo is cable driven, not electronic.

#8 Unread post by **Sev** » Fri Jul 13, 2007 2:20 am

Something occured to me just now.

If you were to measure the circumference of the wheel at the widest point - right down the middle. Then the circumference to one side (as if you're leaned over). Wouldn't they be two different numbers. Which is to say because of the profile of the tire when you make a single revolution of the wheel while turning (leaned over) you would have travelled a shorter distance then if you were straight up and down.

Manufacturers might take that into account when they calibrate the speedos? If that's even close to being possible/true. And yes I realize it's a small small number. But we all know how much even going up a size on the back can throw off the speedo if it's not driven off the front wheel.

jonnythan · #9 Unread post by **jonnythan** » Fri Jul 13, 2007 2:21 am

BMK wrote:I'm not buying it.
It would seem to me that a manufacturer that would knowingly and intentionally set the speedometer inaccurately (fast or slow) would open themselves up tp all kinds of legal problems and lawsuits. It doesn't make any sense for them to do it....theres nothing for them to gain and quite a bit to lose by such a practice.

I'm not saying your speedo is accurate, I'm just saying I don't believe the manufacturer modified it to be inaccurate.

Just my opinion.

They're off, and the manufacturers know it. Sport bikes are notorious for "optimistic" speedometers.

The one on my bike is off by about 7%. When I'm doing 60 indicated, GPS says I'm really doing around 55-56.

jonnythan · Fri Jul 13, 2007 2:22 am

Sev wrote:Something occured to me just now.

If you were to measure the circumference of the wheel at the widest point - right down the middle. Then the circumference to one side (as if you're leaned over). Wouldn't they be two different numbers. Which is to say because of the profile of the tire when you make a single revolution of the wheel while turning (leaned over) you would have travelled a shorter distance then if you were straight up and down.

Manufacturers might take that into account when they calibrate the speedos? If that's even close to being possible/true. And yes I realize it's a small small number. But we all know how much even going up a size on the back can throw off the speedo if it's not driven off the front wheel.

There will be a difference, but it won't be anywhere near the difference you see on most speedometers.