Top speed frustration

[670cc]

It might be easier to make an instrument that measures miles per hour more accurate than an instrument that measures kilometers per hour.

Think of measuring distance with a ruler using units of half and inch. You can only be accurate to within half and inch.

Compare the accuracy of that same ruler with one using units of a thousandths of an inch. You can be accurate within a thousandths of an inch

Miles and Kilometers are a similar situation:


A speedometer that is off at 100 mph by 5% will only be traveling at 95, an error of 5 mph.

A speedometer that is off at 100 kmh by 5 % will only be traveling at 95 km/h, an error of about 3 mph

Both will have the same percentage of error, but one is significantly more accurate than the other.

Don’t confuse the term accuracy with resolution or precision.

No one said we were limited to whole numbers. On the speedometer, simply display either the English or the metric speed to a resolution of one decimal place and the English units have no practical advantage over metric units. Accuracy (displayed vs actual speed) on the other hand, is all in the hands of the speedometer’s design and implementation.

 

[ld_rider]

Don’t confuse the term accuracy with resolution or precision.

Or percentage of error with accuracy ;-)

 

[Dennis M]

When I had my Burgman 650 it's speedometer read 10% high at all speeds, and most everybody on the Burgman forum reported the same. Both from checking against GPS and those "your speed is" signs that are periodically placed out on the road to try to get people to slow down.

 

[ld_rider]

Or percentage of error with accuracy ;-)

Ok, here I am replying to my own reply ..how weird it that?

Upon further review my posts make zero sense and even less logical sense. An error of 5 percent is an error of 5 percent. Makes no difference if Km or Miles. In my long winded reply one of my errors was using two different speeds and comparing the errors. 100 miles per hour isn't the same speed as 100 Km an hour. Obviously, the faster vehicle will cover more miles and have a larger "error distance" than a slower vehicle. Duh!

With equal speeds the distance errors would be the same.....and their accuracy.

Back to your regularly scheduled thread .....

 

[New Commuter700]

When I had my Burgman 650 it's speedometer read 10% high at all speeds, and most everybody on the Burgman forum reported the same. Both from checking against GPS and those "your speed is" signs that are periodically placed out on the road to try to get people to slow down.

I worked for a rental car company in the '90s and I noticed that every single Dodge Dynasty was off by around 10 percent. I am convinced to this day that they did that not for the speedo but for the odometer, so that the warranty miles would go by faster.

 

[dduelin]

I worked for a rental car company in the '90s and I noticed that every single Dodge Dynasty was off by around 10 percent. I am convinced to this day that they did that not for the speedo but for the odometer, so that the warranty miles would go by faster.

The odometer often exhibits less variance than the speedometer. Error of 4% or less is considered within bounds of convention.

 

[dreamer]

The EU legislature on speedometer accuracy for motorcycles:

The production shall be deemed to conform to this Regulation if the following relationship between the speed indicated on the display of the speedometer (V1) and the actual speed (V2) is observed:

in the case of vehicles of categories L3 (i.e. motorcycles), L4 and L5:

0 ≤ (V1 – V2) ≤ 0,1 V2 + 8 km/h;

So what that means is that the speed indicated can never be less than the actual speed and cannot be higher than 10% of actual speed + 8 km/h. All motorcycles (stock) I had to date were within this spec.

 

[Junkie]

I worked for a rental car company in the '90s and I noticed that every single Dodge Dynasty was off by around 10 percent. I am convinced to this day that they did that not for the speedo but for the odometer, so that the warranty miles would go by faster.

I know on Suzuki SVs there's a significant difference between what speedo says and what odo says (approximately 8% between the two), with odo being essentially spot on. Wouldn't surprise me if the Dynasty was similar.

The EU legislature on speedometer accuracy for motorcycles:

The production shall be deemed to conform to this Regulation if the following relationship between the speed indicated on the display of the speedometer (V1) and the actual speed (V2) is observed:

in the case of vehicles of categories L3 (i.e. motorcycles), L4 and L5:

0 ≤ (V1 – V2) ≤ 0,1 V2 + 8 km/h;

So what that means is that the speed indicated can never be less than the actual speed and cannot be higher than 10% of actual speed + 8 km/h. All motorcycles (stock) I had to date were within this spec.

Wow, that's a massive difference.

Do you know what odo is allowed to be off by?

 

[dreamer]

Yes, it is huge. On my Aprilia scooter I was doing max speed of 149 km/h indicated, 135 km/h GPS. The difference was 14 km/h, which was still within spec according to this ((135+8)/10=14.3).

I could not find any info on odometers, but I always believed, that speedometer is related to odometer. I know this may not be true in all cases, but at least for NC isn't there only one sensor for speedo/odo?

 

[Junkie]

oh, it's .1 (speed+8) rather than (.1 speed) + 8?

While there's only one sensor, that doesn't mean they can't program them differently.

On Suzuki SV650, the speedometer reads about 9% high while the odometer reads about 1% high. I assume this is because there are different standards for the two.

 

[dreamer]

oh, it's .1 (speed+8) rather than (.1 speed) + 8?

That would be ridiculously high. From the notation in the document it is not clear, so I assumed that what they meant was the more sensible calculation method.

You may be right about the possible programming difference. However, I could not find any regulatory data on odo for that matter.

 

[Junkie]

Back to the bike itself, I was a little surprised at just how little extra power it has in 6th with the gearing I have (16/39). At freeway speed if I stand on the pegs it slows down, even at WOT.

 

[Jt105]

Back to the bike itself, I was a little surprised at just how little extra power it has in 6th with the gearing I have (16/39). At freeway speed if I stand on the pegs it slows down, even at WOT.

Any motorcycle will slow down if you stand on the pegs. WOT is at the edge of the speed-torque curve. Any change in drag will cause a change in speed.
Tuck in and you will go faster. Sit up and you will go slower. Stand up and you will go even slower.

I’m sure Honda could have designed the valve timing differently to make more HP at speed, but that was not the goal. I’m happy with how it is and it fits well with my intended use.

JT

 

[Junkie]

I'm aware that more drag will slow you down, I'm just not used to having little enough power and tall enough gearing that it can't do freeway speed with me standing up. I'm not that close to WOT at freeway speed normally. Even my WR450 will do freeway speed standing (but then again, it's geared way lower).

 

[New Commuter700]

I know on Suzuki SVs there's a significant difference between what speedo says and what odo says (approximately 8% between the two), with odo being essentially spot on. Wouldn't surprise me if the Dynasty was similar.

Most cars of that era (and earlier) used the same sensor (or mechanical cable) to the instrument head to turn the speedo and the odo. I was not even aware that any motorcycles would be different as space is usually at a premium. That may be why I could never track down the problem with the speedo on my Yamaha Virago

No, the Dodge's odometers were all off by a lot as well. I drove the same routes often and had to note mileage on different vehicles.

 

[Junkie]

Most cars of that era (and earlier) used the same sensor (or mechanical cable) to the instrument head to turn the speedo and the odo. I was not even aware that any motorcycles would be different as space is usually at a premium. That may be why I could never track down the problem with the speedo on my Yamaha Virago

No, the Dodge's odometers were all off by a lot as well. I drove the same routes often and had to note mileage on different vehicles.

There's only one sensor on SVs. The firmware on the gauge is set up to display the wrong speed.

 

[Jt105]

I'm aware that more drag will slow you down, I'm just not used to having little enough power and tall enough gearing that it can't do freeway speed with me standing up. I'm not that close to WOT at freeway speed normally. Even my WR450 will do freeway speed standing (but then again, it's geared way lower).

I rarely ride mine on the freeway so it doesn’t bother me. It pulls great past 80mph and that is the top I really need in my area.
I am glad to have a second bike. My ST1300 into the wind across flat North Dakota was a blessing last summer. Plenty of reserve power on hand. I couldn’t imagine doing that on the NC for the exact reasons you said.

JT

 

[Junkie]

It's possible that with stock gearing it would pull it, I don't know. I have the DCT rear sprocket which is 4 teeth smaller than stock, so RPM is significantly lower than most NCs.

I try to avoid freeway but sometimes there aren't any other reasonable options. The NC is good enough on the freeway that I won't trailer it, the WR450 is a different story (although part of that is the maintenance - I'd rather not waste an engine that's only good for 20k miles on the freeway, but it's unpleasant too).

 

[dduelin]

I’m glad I don’t have to stand up while riding on the freeway.

 

[Junkie]

it's nice to be able to stretch every now and then on long trips, without adding time by making stops