Actually hitting 28mph

[drewberz]

Hi silver. Found a way that might get you just a tad closer to the 28mph. Unscrew the sensor on your rear tire spoke and try moving it out (towards the tire) by 2 inches. If the display errors out, then that was too much, so make it 1.5 inches and so on. For me, I was able to move it 2 inches, as it was set inside the sensor receiver (on the hub side) to begin with. My 18.9 to 19.5mph motor cutoff speed became a real world 20.5mph max. The cutoff seems to have changed to closer to 19.5mph on the speedometer as well....the motor doesn't seem to cut out as early, as often as it used to.

Why does this work? Is the sensor then picked up every 2nd revolution or something of the sort? If so your distance would be off.

 

[tomjasz]

Do we consider that our 20 MPH bikes are capable of safe stopping distances at 28 MPH? Have we ever tested our panic stop distance?

 

[rich c]

What’s wrong with just pedaling harder to reach the speed you want? The bike doesn’t turn on the brakes to keep you under any set speed.

 

[NeilJ]

Hi silver. Found a way that might get you just a tad closer to the 28mph. Unscrew the sensor on your rear tire spoke and try moving it out (towards the tire) by 2 inches. If the display errors out, then that was too much, so make it 1.5 inches and so on. For me, I was able to move it 2 inches, as it was set inside the sensor receiver (on the hub side) to begin with. My 18.9 to 19.5mph motor cutoff speed became a real world 20.5mph max. The cutoff seems to have changed to closer to 19.5mph on the speedometer as well....the motor doesn't seem to cut out as early, as often as it used to.

Please explain the physics behind this, in my book a rotation is a rotation no matter where the magnet is on the spoke, or is there something I'm missing?

 

[The duke]

Th

Please explain the physics behind this, in my book a rotation is a rotation no matter where the magnet is on the spoke, or is there something I'm missing?

Think about a skateboard wheel. How far would it go in 10 rotations? Then think about a car tire. Wouldn't that travel farther on the same 10 rotations? If rotations equal speed....

 

[NeilJ]

Th
Think about a skateboard wheel. How far would it go in 10 rotations? Then think about a car tire. Wouldn't that travel farther on the same 10 rotations? If rotations equal speed....

Yes, but on the bike the tyre remains the same radius therefore a rotation is the same irrespective of the magnet location.
If you buy a cheap speedo they don't say put magnet @ "X" distance from the axle centre. You just input tyre circumference.

Imagine looking at your bike wheel, you place a magenet 10cm below the tyre valve and another magnet 20cm below the valve, spin the wheel they all rotate the same.

 

[The duke]

Yes, but on the bike the tyre remains the same radius therefore a rotation is the same irrespective of the magnet location.
If you buy a cheap speedo they don't say put magnet @ "X" distance from the axle centre. You just input tyre circumference.

Imagine looking at your bike wheel, you place a magenet 10cm below the tyre valve and another magnet 20cm below the valve, spin the wheel they all rotate the same.

Oh, I get it. The sensor is geared for a certain wheel circumference. That makes sense!

 

[drewberz]

Yes, but on the bike the tyre remains the same radius therefore a rotation is the same irrespective of the magnet location.
If you buy a cheap speedo they don't say put magnet @ "X" distance from the axle centre. You just input tyre circumference.

Imagine looking at your bike wheel, you place a magenet 10cm below the tyre valve and another magnet 20cm below the valve, spin the wheel they all rotate the same.

This is where I'm guessing that the sensor is picked up on most rotations, but not all rotations. If it's picked up on less rotations, then the motor is being tricked into thinking it's going slower than it actually is. If the sensor is too far, it errors out.

 

[04fuxake]

I have a US model Quick-E, so it's supposed to hit 45kph/28mph. However, I can never hit that on the flat. The assist usually cuts out somewhere between 26.5-27mph according to the speedometer. I'd love to actually get what it's supposedly capable of, and it really started to sting when I measured the bike with GPS and found that 26mph on the spedo is 24-25mph real world depending on tire inflation.

Does anyone have an idea of why? Do the 20mph models hit 20mph, or do they cut out at 18mph?

I wondered if it could be a units thing, e.g. the bike can do 45kph but that doesn't work out to be 28mph. But when I put the bike in metric mode, it can't go over about 41-42kph either.

My Fathom E+3 has a 32km/h limit but the assistance seems to really fade out from 30km/h. I wonder if that's how they handle the transition from assisted to non-assisted without it being a sudden drop.

 

[Volt Dolt]

I've owned two "Level I" Giant e-MTBs. Per documentation found online, they are supposed to start reducing assist at 19 MPH, tapering down to zero assist at 20 MPH. I suspect they use that same design philosophy for the Level III bikes.

For no reason other than I like gadgets, I ride with two GPSs. On both bikes, I found the same as you: The Giant speedometer reads 20 MPH when you are going about 18.5 MPH. I've tried both extremes of tire pressure and it made negligible difference. I mentioned it to my dealer and he said "maybe your GPSs are off". Sorry, no.

I suspect Giant does this on purpose to reduce their potential liability (they don't want anyone to be able to demonstrate that the motor produced power when the bike was going 20.1 MPH when their specs say it cuts off at 20 MPH).

I have a US model Quick-E, so it's supposed to hit 45kph/28mph. However, I can never hit that on the flat. The assist usually cuts out somewhere between 26.5-27mph according to the speedometer. I'd love to actually get what it's supposedly capable of, and it really started to sting when I measured the bike with GPS and found that 26mph on the spedo is 24-25mph real world depending on tire inflation.

Does anyone have an idea of why? Do the 20mph models hit 20mph, or do they cut out at 18mph?

I wondered if it could be a units thing, e.g. the bike can do 45kph but that doesn't work out to be 28mph. But when I put the bike in metric mode, it can't go over about 41-42kph either.