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Pretty dang satisfied with my GTV so far (only picked it up Saturday). I know fully well that every scooter on the planet has a slightly ambitious speedometer, and I've heard most of them are around 5-7% inaccurate. I've had 4 scooters prior to this one, so I'm used to mentally judging my real speed versus what the speedo thinks it is.

But I've noticed that my GTV seems to be waaaaay more off than 7%. My boyfriend estimates its up to 25% off. There are 2 speed limit signs in our neighborhood that have speed detectors in them, along with digital readouts to tell you how fast you're going past them. With my boyfriend having verified long ago that his own SUV's speedo is about 3% off, we know that the signs' readings are pretty accurate.

I go past these signs with the GTV speedo indicating about 45mph. The sign pegs me at 36. Like I said, I'm used to mentally compensating for the discrepency, but not nearly this much. I don't think I should be getting passed so fast when my speedo indicates I'm 5 over the limit, and I'm really several under.

Is anyone else's speedo off by nearly this much? I'll probably go in for my break-in service at the end of next week, so I'm definately planning on mentioning it. Not that I've heard of any fix for such a problem.
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UTC quote
My 07GTS ie is way off too. I saw 32 on a radar sign that the county puts up and my speedo indicates 40. That's ridiculous!
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UTC quote
Got a GPS? It's the single best way to do a speedo comparison.
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jess wrote:
Got a GPS? It's the single best way to do a speedo comparison.
Nope, spent all my money on the Vespa. I know my comparison isn't terribly scientific, but I also know it's way more off than what's generally considered "normal."
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UTC quote
Witch wrote:
Nope, spent all my money on the Vespa. I know my comparison isn't terribly scientific, but I also know it's way more off than what's generally considered "normal."
Dunno. I haven't seen on be off by more than the usual amount before, so it's hard to say. Does the needle jump up and down a lot, or is it smooth?
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It would be nice to think, its off by 5mph, but its not, at least not mine.

Maybe up to 40mph Ive seen it off 5mph, using traffic monitoring systems (ie Vcalm) used by citys. But at higher speeds its off a lot more per my GPS.

Its strange that Piaggio would be allowed to ship a scooter to the US with such a poor speedo.

BTW, my needle doesnt jump, its smooth like my freshly shaved head.

Manny
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snapshot05 wrote:
It would be nice to think, its off by 5mph, but its not, at least not mine.

Maybe up to 40mph Ive seen it off 5mph, using traffic monitoring systems (ie Vcalm) used by citys. But at higher speeds its off a lot more per my GPS.

Its strange that Piaggio would be allowed to ship a scooter to the US with such a poor speedo.

BTW, my needle doesnt jump, its smooth like my freshly shaved head.

Manny
Generally a speedo will be off by some percentage of speed, not a set number of MPH. This is why it becomes more optimistic as your speed increases. 10% is typical on a GT/GTS/GTV/GT60, so 40 is really 36, 60 is really 54 and top end of 90 is really 81. Ish.

25% seems wrong--have it checked now while you're under warranty. The fix is a new speedo.

P.
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UTC quote
My speedo on my GTV is a little off but definitely not 25% - 10% at the most I would say. I would have your speedo looked at by the shop like you mentioned.
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UTC quote
Based on my Garmin Nuvi, my MP3-500 is at least 10-12% off (faster) than actual
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The needle moves very smoothly. No jumps at all. Actually, it seems even smoother than all my other scoots were.

I will definately have the dealer check it out. I'm a little bummed to have such a problem right from the start. But I'm also glad it's nothing serious that could actually affect the handling or anything. And yeah, I would imagine it's covered under warrenty.
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All my speedos have been way off, with the exception of the X9 500SL, which was fairly accurate.

I use a cheapo cycle 'computer' to calibrate speedos with 30, 40, 50, 60 and 70 mph marks, made of 1mm strips of white tape about 1cm long. Thereafter I ignore the dial marking entirely!
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I know it'll still be off somewhat, even if they fix or replace the whole speedo. But I just feel it should be a whole lot closer than it is, ya know? I mean, my little Yamaha Razz was actually fairly close to accurate, and I paid like half the cost of a Buddy 50 for that thing. For what I'm paying for the Vespa, stuff on it should work well.
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Molto Verboso
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awdnut wrote:
Based on my Garmin Nuvi, my MP3-500 is at least 10-12% off (faster) than actual
Mine's on the order of 12% as well, as compared to my Zumo. It's actually a bit higher than that. I haven't bothered to do a careful comparison yet. But it's definitely more than 10%. When it says 75mph, I'm at around 64mph. I do check my tire inflation routinely. Plenty of tread left on my tire too.

Some people argue that it's overstated to be on the "safe" side. Personally, I think it's just as friggin' unsafe to grossly overstate the speed as it is to grossly understate the speed. You have no idea how many risky situations I put myself in under the assumption that I was able to do 75mph, before I put the GPS on the scoot. Then there's the story about the fellow in Colorado who got slammed by a truck on the interstate...something tells me he thought he was going faster than he actually was.

I've also heard the argument that it's asking too much of the speedo to be practically accurate, citing a bunch of variables like the small tire diameter accentuating the tire inflation, tire compression, treadwear, factors, as well as the tire radius changing due to steering inputs. While those factors are truly more significant given a smaller tire radius, the notion that you can't make a speedo that does a better job at telling the true speed because we've got 11" rims is a load of bull. At its worst, the variance of full tread depth versus bare tread depth is enough to take a dead-on accurate reading of 60mph and drop it down to 57.7mph. That's a variance of under 4% (that's under +/-2%). And I'm using a very sizable tread depth of 8.4mm for that! The variance of various weight loading on the front tire is barely perceptible, because the vast majority of the weight variance is on the rear tire. It just doesn't add up. And being an engineer, I can attest to the fact that if we can send a friggin astronaut to the moon, it's pretty friggin trivial to make a functional speedometer with 11" rims if we were really trying.

For the record...Yamaha managed to get my Vino's speedo dead-on accurate against the GPS.
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Those speed signs use doppler radar which accurately measures the rate at which an object is DIRECTLY approaching the sign. If you are not driving directly at the sign, there will be some error (the sign will UNDERESTIMATE your actual speed on your true path). So... the farther the sign is off the shoulder of the road, the farther you are toward the side of the road away from the sign, or the closer you are to being alongside the sign, the greater the error in the sign's reading.

If you want a truly accurate reading from one of those signs, you'll have to find one that is located so you can drive directly at it for a second or two (depending on the display's refresh rate), and then the sign will only display accurately during the second or two immediately after you've driven directly at it. If the sign is sensitive enough that it can pick you up at a great distance, you will likely be driving nearly straight at it (assuming it is not on a curve) and the error produced by the geometry will be negligible.

Dave
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UTC quote
The GTV speedo is a purely analogue eddy-current one isn't it, no Hall effect sensor, just a rotating cable? If so it may have a calibration adjustment available. Adjusting the return spring to pull slightly more will result in a slower speed displayed. I may be way off-beam though!
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UTC quote
TheWasp wrote:
Some people argue that it's overstated to be on the "safe" side. Personally, I think it's just as friggin' unsafe to grossly overstate the speed as it is to grossly understate the speed. You have no idea how many risky situations I put myself in under the assumption that I was able to do 75mph, before I put the GPS on the scoot. Then there's the story about the fellow in Colorado who got slammed by a truck on the interstate...something tells me he thought he was going faster than he actually was.
Small edit:

Precisely why I will not ride on the interstate. Even if you can do 70 MPH many of the cages out there are speeding by at least 10 MPH and a lot of them more than that.

My speedo is probably off, but the max I get is about 59 which is near what Piaggio claims for the top speed of the Leader 150. Maybe the gauge is off by 3 or 4 %.
⚠️ Last edited by Louisiana_Geezer on UTC; edited 1 time
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I carefully checked my S150 with GPS, and it's 10% optimistic. I like 10% - makes it easy to calculate true speed in your head: Speedo says 50, 10% of 50 is 5, so subtracting 5 from 50, my true speed is 45. Easy.

I'd be really upset if it were 7%, much harder math.
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Mine is off too but just think of all the speeding tickets we are avoiding! Be happy it isn't reading less than actual...
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Molto Verboso
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In the 50 to 60 MPH range, my speedometer reads 14% high. Pretty bad performance in view of the cost of the GT200.
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Silver Streak wrote:
Those speed signs use doppler radar which accurately measures the rate at which an object is DIRECTLY approaching the sign. If you are not driving directly at the sign, there will be some error (the sign will UNDERESTIMATE your actual speed on your true path). So... the farther the sign is off the shoulder of the road, the farther you are toward the side of the road away from the sign, or the closer you are to being alongside the sign, the greater the error in the sign's reading.

If you want a truly accurate reading from one of those signs, you'll have to find one that is located so you can drive directly at it for a second or two (depending on the display's refresh rate), and then the sign will only display accurately during the second or two immediately after you've driven directly at it. If the sign is sensitive enough that it can pick you up at a great distance, you will likely be driving nearly straight at it (assuming it is not on a curve) and the error produced by the geometry will be negligible.

Dave
Speed is a function of the COS of the angle of travel to the sign and really isn't a factor at the small angles where they first register. The ones I use are always parked at roadside and I don't see the speed drop due to angle until I'm fairly close. Also, load and inflation don't really affect the reading as it's the circumference that really counts and while a squashed tire may look smaller, the distance around is the same. I agree with the poster who said that for the money, we ought to be more accurate. Piaggio simply needs to get their act togther on this.
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What puzzles me is that there are a number of members who claim speeds of ~ 70 MPH with their 150 LEADER engines, while mine has only seen 60+ MPH on the speedo a very few times. If my speedometer is 14% off that means that my top speed is about 51 - 52 MPH.
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Molto Verboso
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TheOldSquid wrote:
Also, load and inflation don't really affect the reading as it's the circumference that really counts and while a squashed tire may look smaller, the distance around is the same.
Actually, a squashed or under-inflated tire actually does have a reduced *operating* circumference, even if it appears to have the same distance around as it goes around the top of the wheel--albeit, not by much. It's the effective radius--and thus circumference--felt at the road surface that counts, and that is reduced if the tire is squashed or under-inflated. That much is true. But as I previously mentioned, it is entirely possible to estimate a useful median value for tire radius of a properly inflated and loaded front tire, and having a large rider load versus a small rider load on the scooter changes that value little if properly inflated, because the majority of the weight is on the rear tire. That's also why the recommended tire inflation values stated by the manufacturer for various loads do not change much for the front tire. It simply does not dramatically change the contact patch of the front tire.
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I was wondering,are speedometers required by law? Just curious.Obviously their accuracy doesn't have to be correct by law.

Tim
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The most innacurate speedometer I've ever seen was in a '77 Lancia Scorpion that belonged to a friend of mine, it was at least 20% optimisitic. Looked really cool though. I wonder if it's some sort of Italian thing? Like they like to think they're going faster than they really are. I know people who set their watches fast intentionally so they aren't late to appointments...
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Quote:
Speed is a function of the COS of the angle of travel to the sign and really isn't a factor at the small angles where they first register. The ones I use are always parked at roadside and I don't see the speed drop due to angle until I'm fairly close.
Agreed... but I think that is pretty much what I said. I was simply trying to avoid using mathematical terms, as I'm always being accused of using too much "engineer-speak". My point is that many folks do not understand this and assume that the reading on the sign is Gospel, regardless of the geometry involved. If the sign is more than a few feet off the edge of the road, you are riding in the far lane, and are looking at the reading 50 feet before you pass the sign, the error will indeed be significant.

Dave
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Richard H. Lemmon wrote:
In the 50 to 60 MPH range, my speedometer reads 14% high. Pretty bad performance in view of the cost of the GT200.
Yep mines off that much, at one point my speedo says 60mph but a straight away check on a Vcalm system said I was doing 45mph. I was the only vehicle at the time.

As for having the dealer fix it, I doubt they know how. I like Jimc fix.
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I don't know about my speedo...I was riding the GTS alongside my buddy on his 1200 Sportster, and I yelled at him (over his pipes) "My speedo says 55, how about yours?" and he said "55".
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Well, regardless of how accurate the speed sign is, my speedo is obviously off by quite a lot. I was mainly using the sign to get an idea of how much it might be off. The cars passing me like I'm a restricted 50cc when my speedo indicates 5mph over the limit, while I'm in city traffic, is enough to tell me that something is pretty wrong.

Scheduled my break-in service, and they said they'd be happy to check it out. In the meantime, I'm pretty much ignoring my indicated speed, and just riding to keep up with traffic. I know I'll eventually get a feel for what certain speeds are anyway, but I haven't had this particular scooter long enough.
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I simply stopped wearing speedos when I ride. Razz emoticon
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They also don't realize that our scooters are too small to be accurately clocked by a radar.

My dad used to be a cop and the chief of police told him not to even clock motorcycles.

Apparently laser is the only accurate way to clock something as small as a scooter or motorcycle.
Silver Streak wrote:
Quote:
Speed is a function of the COS of the angle of travel to the sign and really isn't a factor at the small angles where they first register. The ones I use are always parked at roadside and I don't see the speed drop due to angle until I'm fairly close.
Agreed... but I think that is pretty much what I said. I was simply trying to avoid using mathematical terms, as I'm always being accused of using too much "engineer-speak". My point is that many folks do not understand this and assume that the reading on the sign is Gospel, regardless of the geometry involved. If the sign is more than a few feet off the edge of the road, you are riding in the far lane, and are looking at the reading 50 feet before you pass the sign, the error will indeed be significant.

Dave
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How come everyone puts so much stock in what a GPS tells you for speed? It is my understanding that the US military, who put the sattelites into orbit, built in a 30 meter fudge factor so it could not be used for weapons delivery. The manufactureres made DGPS that uses a computer in the unit to bring it in to within 10 meters for navigation.

If you run a GPS in your car on level hwy with the cruise control on, you see the speed go up and down as you travel.

I'm with jimc, only by running on a known distance can you accurately calibrate your speedo.
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I've never been on a scooter where the speedo hasn't been off by at least 5 MPH. I think they do that on purpose.
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Molto Verboso
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UTC quote
Guess I got lucky, mine is only 1 or 2 mph off, even with new tires!
Now, my gas gauge is something else....I stored my scoot today, and the low gas light was on for at least 10 miles, the gauge reading empty....and still, when I drained it, it had over 1/2 gallon in it!
Wish my dash lights still worked....the copper printed panel was all corroded.....
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Although I don't own a portable GPS, I just go with the flow of traffic. I remember once riding on PCH into Long Beach coming over the Long Beach Freeway and there was a speed trap about a block from the downhill portion. I looked down on my speedo an it was at 55mph but the officer with the laser or radar g.u.n just kept pointing that thing at the cars behind me. I believe the speed limit is 40mph. He just ignored me, even though I almost pooped in my pants.
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UTC quote
jimc wrote:
All my speedos have been way off, with the exception of the X9 500SL, which was fairly accurate.

I use a cheapo cycle 'computer' to calibrate speedos with 30, 40, 50, 60 and 70 mph marks, made of 1mm strips of white tape about 1cm long. Thereafter I ignore the dial marking entirely!
This really does solve the problem. Where did you come up with the 1mm wide white tape?
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UTC quote
You can use some extra pinstriping tape if you have some laying around. It works very well for this, and is made to last in the elements. As for my GT200, I notice the slight wobbling of the needle as its main nuisance. I have ridden side by side with my truck, and had my daughter flash her hand at 50...55...60, etc. and found that mine is not off by much. When she flashed 65, I was centered on 61 or 62...(remember the speedo needle wobble). I tend to just ride withe the traffic, or even lead it when I fell like it. Even on the highway, I'm comfortable in the left lane at times...its fun to see the looks when a scooter passes cars and trucks!!
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UTC quote
maybe, the speedos are all on Italian "time"... you get there when you get there, enjoy the ride, not the speed...

ciao
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Molto Verboso
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UTC quote
ScooterRep wrote:
How come everyone puts so much stock in what a GPS tells you for speed? It is my understanding that the US military, who put the sattelites into orbit, built in a 30 meter fudge factor so it could not be used for weapons delivery.
If I recall correctly...they stopped doing that a few years ago, except for a few obviously sensitive areas.
ScooterRep wrote:
The manufactureres made DGPS that uses a computer in the unit to bring it in to within 10 meters for navigation.
Keep in mind it is a global *positioning* device, not a global *speed* device. It very well does have some variance moment by moment, and there is of course smoothing algorithms involved. But by the fact that it is a tool to measure *position* and not speed, and that the *position* is measured within 3m (or whatever number you believe in) accuracy means that even though the momentary speed calculation might fluctuate around the real value, it can only be off in one direction for a brief time, which is smoothed out in the smoothing algorithms. If it consistently under/over-reported your speed...it wouldn't be a particularly good global *positioning* system would it? The positioning errors would be cumulative. and your position would be way way off. In reality, it is definitely a way way more accurate measure of speed in a flat-out highway cruising scenario than either the side-of-the-road speed trap option or the speedometer itself. And it is simply a physical impossibility for a positioning system to consistently under-report or over report the speed.
ScooterRep wrote:
If you run a GPS in your car on level hwy with the cruise control on, you see the speed go up and down as you travel.
by about a mile or two, in either direction for a moment or two. It's not pefect. But compared to methods that systematically under-report or over-report your speed, this is way more accurate. But I agree...running known distances on flat terrain and in controlled scenarios...that's the scientist's bestway to stick to his/her stochastic guns, so to say.
⚠️ Last edited by mandarinia on UTC; edited 1 time
@skip avatar
UTC

Member
Motobecane Mobylette, Honda Metropolitan, Vespa S 150
Joined: UTC
Posts: 40
Location: Connecticut
 
Member
@skip avatar
Motobecane Mobylette, Honda Metropolitan, Vespa S 150
Joined: UTC
Posts: 40
Location: Connecticut
UTC quote
Here is my data for an S 150:

GPS...Speedometer
30...........33
35...........39
40...........44
45...........49
50...........55
55...........60
⚠️ Last edited by skip on UTC; edited 2 times
UTC

Molto Verboso
'05 Vespa Granturismo
Joined: UTC
Posts: 1610
Location: Rancho Cordova, California
 
Molto Verboso
'05 Vespa Granturismo
Joined: UTC
Posts: 1610
Location: Rancho Cordova, California
UTC quote
If size of the target was a factor causing radar to be unable to accurately check the speed of a scooter, how is it able to check the speed of a pitched baseball?
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