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72mph gps with a high compression piston and cam kit at 10k rpm.
 

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67 on the rev limiter with a slight down hill. It took a long time to get there as I weigh 225.馃榿
 

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I can maintain an indicated 56 up hill, untucked, 200 lbs, with LS2 Subverter.
 

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I've hit 62 but I've never really pushed to get into the 60MPH zone anyways. I'm perfectly fine hitting it right at 50-55 since that seems to be the sweet spot and can be fun racing up to that speed. Anything beyond is mostly a crawl anyways in terms of acceleration unless you're just going straight downhill.
 

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63kg rider, Hindle exhaust. I can hit 107km/h (67mph) indicated on a flat, full tuck or just under 100km/h (62mph) seated upright.

I really should verify the accuracy of the speedometer with a GPS though.
 

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85 mph... in the back of my pickup.

I've hit 68 on a flat, indicated speed, bouncing off the limiter with DIY intake mod. I'm about 175 in full gear. Tucked.
 

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it's actually not possible to know ACCURATELY how fast you are ACTUALLY going on a Z125 because:

- The OEM speedometer is very optimistic - about 6% on mine, and I understand that is typical of the Z125 speedo

- The OEM tachometer is even MORE optimistic, so you can't use the tach instead of the speedometer either

- For those who think speed calculated via GPS is more accurate at the speeds we are talking about, forget it - a university research team has proven that it is not anywhere close to being accurate at these speeds because of the sampling methods and mathematics involved

It's driving me nuts, as I try to figure out the "right' gearing for my Z125, so I have gone to the next obvious stage of remedial action:

- I've ordered a small engine digital tachometer that claims really good accuracy (way under 1% error) and attaches simply by looping a signal wire at least 5 or 6 times around the sparkplug cable. Also a mount to hold my iPhone 6. The tach is tiny enough to velcro to the top of the front brake master cylinder. The combination of tach and iPhone with GPS-based speed app will enable me to:

- do comparison testing of this tach versus the cheap OEM tach

- calculate the REAL speed by using the accurate engine RPM and the known primary, gearbox and final drive ratios, and the actual ROLLING diameter of the rear tire (which is NOT Pi times static diameter, but rather a smaller number because the tire's actual rolling diameter is less than static diameter because of the tire contact patch acting to reduce the ACTUAL rolling radius).

- Compare the real properly calculated speed to the speed reported by the GPS-based speed app

After I have everything in place to do the testing accurately, I'll post results.

And by the way, I do NOT expect a stock Z125 to hit even 60 mph = 97 KPH with just 8 rwhp, let alone anything higher as claimed by a few here, especially since I wear a size XL jacket, and weigh 200 lb , plus 26 lb extra of safety and winter warmth gear at this time of year, and it is impossible for me to "tuck in": on this tiny bike. :)

I'm projecting 55 to 58 MPH = approximately 89 to 94 kph with me on the bike, on a certified (not estimated) level road, with no significant headwind nor tailwind, and sitting in the normal riding position.

Jim G
 

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it's actually not possible to know ACCURATELY how fast you are ACTUALLY going on a Z125 because:

- The OEM speedometer is very optimistic - about 6% on mine, and I understand that is typical of the Z125 speedo

- The OEM tachometer is even MORE optimistic, so you can't use the tach instead of the speedometer either

- For those who think speed calculated via GPS is more accurate at the speeds we are talking about, forget it - a university research team has proven that it is not anywhere close to being accurate at these speeds because of the sampling methods and mathematics involved

It's driving me nuts, as I try to figure out the "right' gearing for my Z125, so I have gone to the next obvious stage of remedial action:

- I've ordered a small engine digital tachometer that claims really good accuracy (way under 1% error) and attaches simply by looping a signal wire at least 5 or 6 times around the sparkplug cable. Also a mount to hold my iPhone 6. The tach is tiny enough to velcro to the top of the front brake master cylinder. The combination of tach and iPhone with GPS-based speed app will enable me to:

- do comparison testing of this tach versus the cheap OEM tach

- calculate the REAL speed by using the accurate engine RPM and the known primary, gearbox and final drive ratios, and the actual ROLLING diameter of the rear tire (which is NOT Pi times static diameter, but rather a smaller number because the tire's actual rolling diameter is less than static diameter because of the tire contact patch acting to reduce the ACTUAL rolling radius).

- Compare the real properly calculated speed to the speed reported by the GPS-based speed app

After I have everything in place to do the testing accurately, I'll post results.

And by the way, I do NOT expect a stock Z125 to hit even 60 mph = 97 KPH with just 8 rwhp, let alone anything higher as claimed by a few here, especially since I wear a size XL jacket, and weigh 200 lb , plus 26 lb extra of safety and winter warmth gear at this time of year, and it is impossible for me to "tuck in": on this tiny bike. :)

I'm projecting 55 to 58 MPH = approximately 89 to 94 kph with me on the bike, on a certified (not estimated) level road, with no significant headwind nor tailwind, and sitting in the normal riding position.

Jim G
馃槀, way too much free time, and way too serious......
 
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馃槀, way too much free time, and way too serious......
Oh, you like to develop an engine performance improvement plan based on wrong displayed rpm, wrong speed, and thus a completely incorrect understanding of the current engine power and torque curves?

Let me know how well that works out for you! :)

or maybe you just like to THINK you have a 70 MPH bike . . . :)

Jim G
 

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Oh, you like to develop an engine performance improvement plan based on wrong displayed rpm, wrong speed, and thus a completely incorrect understanding of the current engine power and torque curves?

Let me know how well that works out for you! :)

or maybe you just like to THINK you have a 70 MPH bike . . . :)

Jim G
Like I said,"way to serious" Jim.
But you go ahead and enjoy your little project and analyze and develop to your hearts content.
In the end, after all the time and money spent, it's still a 125cc with barely double digits hp.
As far as "how well that works out for you", I am not doing any mods for more power/speed.
My mods are to lose some of my extra body fat, to make me go faster. :grin2:
 

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- For those who think speed calculated via GPS is more accurate at the speeds we are talking about, forget it - a university research team has proven that it is not anywhere close to being accurate at these speeds because of the sampling methods and mathematics involved



Jim G
You are going to have to quote the source on this one. Even at 5hz sampled over a minute or so, this should produce a more than accurate enough reading to measure the average speed of something this slow! Even the slow 1hz receivers in most phones would do a good enough job after a minute "at speed".

But it is also not 100% accurate to use speed radar to get the speed of an object because we don't know the speed of the signal in the air density at that given moment, and that the radar device must be absolutely inline with the object due to cosign error. Also the clock sources used are not 100% accurate because they do have drift, and the do have a tolerance that is many decimal places out. Ultimately you can call GPS not 100% accurate, but that is a leap based on the number of decimal places we really NEED for this example. But I think this is being pedantic. For our uses a single decimal place is good enough for our needs and this can be had easily at 5hz gps sampling and any decent calculation speed. Work in a receiver that uses GLONAS and GPS and you get finer accuracy.
 

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You are going to have to quote the source on this one. Even at 5hz sampled over a minute or so, this should produce a more than accurate enough reading to measure the average speed of something this slow! Even the slow 1hz receivers in most phones would do a good enough job after a minute "at speed".

But it is also not 100% accurate to use speed radar to get the speed of an object because we don't know the speed of the signal in the air density at that given moment, and that the radar device must be absolutely inline with the object due to cosign error. Also the clock sources used are not 100% accurate because they do have drift, and the do have a tolerance that is many decimal places out. Ultimately you can call GPS not 100% accurate, but that is a leap based on the number of decimal places we really NEED for this example. But I think this is being pedantic. For our uses a single decimal place is good enough for our needs and this can be had easily at 5hz gps sampling and any decent calculation speed. Work in a receiver that uses GLONAS and GPS and you get finer accuracy.
Here is that reference you asked for:

https://scialert.net/fulltextmobile/?doi=jas.2005.1518.1522

Note that the researchers discovered that the average GPS error was about 7%, and got down only to 5.3% at the most favorable speeds. That is actually as bad or worse than the cheap Z125 speedometer.

Jim G
 

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- For those who think speed calculated via GPS is more accurate at the speeds we are talking about, forget it - a university research team has proven that it is not anywhere close to being accurate at these speeds because of the sampling methods and mathematics involved
You are going to have to quote the source on this one. Even at 5hz sampled over a minute or so, this should produce a more than accurate enough reading to measure the average speed of something this slow! Even the slow 1hz receivers in most phones would do a good enough job after a minute "at speed".

As someone who makes their bread and butter doing GPS design, I would also like to see the source for this. Seems like a broad generalization.


Top speed on a Z125 is 67(ish). What does it really matter if you are riding at 35 or 32 MPH? Unless you are riding like an idiot, you aren't going to get pulled over.... so what does it matter?
 

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As someone who makes their bread and butter doing GPS design, I would also like to see the source for this. Seems like a broad generalization.


Top speed on a Z125 is 67(ish). What does it really matter if you are riding at 35 or 32 MPH? Unless you are riding like an idiot, you aren't going to get pulled over.... so what does it matter?
There are at least 2 good reasons why it matters:

1. If you believe the factory speedometer you will think you can ride on a 60 mph highway without impeding other drivers

2. You cannot intelligently make engine and sprocket changes to optimize performance for your specific riding needs or wants if your measurement instruments are lying to you.

3. This thread is all about "how fast have you had your Z125 going". If you answer that question by quoting your lying speedometer or tachometer, you are lying to everyone who wants to know the REAL answer to the question. If we are going to post lies, why bother to even ask the question?

Jim G
 
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