odometers and speedometers ... why aren't our two bikes the same?

[ebikemom]

Calling all physicists!

My husband and I ride together on ebikes of the same make, different models, that have the same PAS system. My bike rides faster than his in all PAS levels. Why, I wondered ....

When riding side by side, his bike speedometer says he's going faster than I am. When we noticed this, we stopped and reset our trip odometers to zero. We rode either 8 or 9 more miles, depending on whose trip odometer you look at. Mine showed less mileage.

So, my bike goes faster in each PAS because even though our bikes are set to the same mph for each PAS cut-off, my bike thinks it is going slower than it is.

We checked all of our settings, and they are identical. We both have 26" bikes, both are set at 26". So, I measured the radius of my wheel and his, from the center of the axle. I just used an ordinary tape measure, so not highly accurate, but my bike wheel's radius is about 1/4" larger. I think this is due to my bike's balloon tires. My husband's bike tires are a bit thinner.

Would this slightly larger radius create the effect we are noticing?

 

[larry-new]

And there is of course weight. Your bike has it easier...and wind resistance for a larger profile, and tire pressure.

 

[ebikemom]

My husband's explanation is that my bike is "juiced"!

 

[indianajo]

The software of any controller is subject to change day by day. Those are very sophisticated computers were are buying in a $25 controller module. I've looked inside mine that wouldn't (perhaps) run more than 13 miles. inside my controller, the chip with a lot of legs (probably the microprocessor) didn't even have a revision sticker on it, which is standard practice in items like printers (lowrey) that need to be supported by the factory for years to maintain customer respect.
There appears to be no financial incentive to be "accurate". Certainly not at the low end of the market. Getting through the 31 day "free return" period without an actual return of money is the main incentive in this market.
The quality level of anything sourced from ***** is very hit and miss. My electric bike purchases have been mostly miss. When my power wheel and battery actually worked, the speed and odometer were about 25% too high. The market is intensely competitive, and suppliers come and go rapidly. See mike's suggestion about buying two of everything the same day, as any later day the repair parts may not actually replace ones of the "same" make and model.
Various organizations can get good quality from that country, but it depends very much on who the QA people are, when they were last paid off, and whether they are likely to be there Sunday morning at 3AM when the contents of the reject bin is traditionally put into shipping crates so everybody can party early. My yubabike from that country bought in January was superb. No electronics were involved, I'm adding them later.
I spent the spring trying to buy a power wheel kit designed and built in Switzerland, at about 700% of the price of a ****ese one, when last stocked in San Diego. None of the 3 representitive shops in the US listed on the manufacturer's website would even answer my email.

 

[harryS]

If both bikes have the same electronics, my assumption, then the difference would be due to wheel diameter, but your husband's wheel would have to be 2" smaller to get the 10% difference in miles reported.

Many controllers can be used for different size bikes, so it is possible that your husband's bike was mistakenly programmed for a 24" wheel instead of a 26" wheel.

 

[mrgold35]

I've had the same exact issue with my fat tire Radrover -vs- Radcity Step-Thru. Both ebikes use almost the exactly same controller with limited settings for wheel size from 14" to 28" in 2 " increments (also 700C setting). My Radrover was set to 26" with 26" rims; but, it has 26"X4" tires. It wasn't until we rode side-by-side for an extended ride I noticed my Radrover was off from her mph/odo readings. Her readings seemed more correct and matched those neighborhood mph radar signs.

We are very close to the same mph/odo once I changed my Radrover to 28" tire size.

A better way to measure the tire is to mark a point on the ground using the valve stem at staring point (make sure PSI is where you want it), sit your full weight on the ebike and do one tire rotation, and measure the distance covered between the valve stems. I had to do this when my mph/odo sensor in the rear hub failed on my Radrover and I added a wired speedo/trip computer. The speedo needed the circumference of the tire in mm to calculate proper data. On-line tires size calculators and doing the roll test without weight didn't produced accurate results until I sat on the bike (270lbs).

 

[Trihonda]

Wheel circumference is certainly the issue with speedometer differences. Ive experienced that even having a few psi tire inflation change can change the actual circumference somewhat, which in turn affects the distance travelled per wheel revolution.


The actual speed difference issue can be attributed to rider weight differences and rolling resistance of a different size tire.

 

[ebikemom]

Thanks everyone! The bikes are both Pedego—When is a city commuter and one is an interceptor. The controllers are set up exactly the same.And we have our settings set up exactly the same. I think everything you guys have mentioned such as wheel diameter including the tire, the tire inflation, etc. would certainly make sense.

 

[harryS]

Amy, what is the precision on your odometers? Our only production ebike is an EG, and it only reads to the nearest mile. In that case, one reading 8 and the other at 9 is understandable.

 

[Volts]

Just a guess: is there a magnet bolted to the rotor? Many bikes do. Maybe a rotating magnet is a sensor and its covered in particles to where it's gone fuzzy.

 

[6zfshdb]

Another factor you need to keep in mind is the actual track the bikes are taking. Every time you move the handlebars, you deviate off the straight line track and add a very small increment of distance. Even riding side by side, one bike may move laterally more than the other. This alone won't account for a 10% difference but can be a contributing factor along with tire pressure and wheel circumference.

Using a handheld GPS receiver will help determine which bike has the most accurate odometer. While there is some error in measuring distance with a GPS, it is consistent when riding the same path and immune to the above factors.

 

[PDoz]

I'm putting my money on the difference being your weights - ie his tyre compressing more than yours. Easiest way to confirm this is swap bikes for a while. Or carry a bit more weight on your bike to test the theory?

A few months ago someone tried to explain tyre compression made no difference because the outer contact patch still travelled the same distance per tyre revolution - just across a flatter route. So I went out and let down a tyre and confirmed that's not correct for a 3 dimensional tyre - it bulges / stretches outward as well as flattens forwards so DOES travel less per revolution.

Ps ask your son , I'll bet he comes up with the answer surprisingly quickly - the box doesn't exist for people with asd

 

[6zfshdb]

A few months ago someone tried to explain tyre compression made no difference because the outer contact patch still travelled the same distance per tyre revolution - just across a flatter route. So I went out and let down a tyre and confirmed that's not correct for a 3 dimensional tyre - it bulges / stretches outward as well as flattens forwards so DOES travel less per revolution.

The term is referred to as "rolling circumference" and it does indeed make a difference in the distance traveled.

 

[Over50]

...We rode either 8 or 9 more miles, depending on whose trip odometer you look at. Mine showed less mileage...

My wife and I rode our Bosch bikes together for lunch a few weeks back. Both Terns with 20" wheels. On return I noticed her trip odometer was at 9 miles and mine at 8. The Purion display doesn't show fractions so I don't know how much of a difference there was. Perhaps one bike was at 9.0 and the other at 8.9....

 

[ebikemom]

The term is referred to as "rolling circumference" and it does indeed make a difference in the distance traveled.