Hi Chuy and
to the forum.
I don't have any experience with the EggRider display but I would expect the speed and odometer readings to both be effected equally by the wheel size/circumference settings.
As your mileage is reading too low, I suggest that you try increasing the wheel size/circumference until the speed and odometer readings matches the GPS speed and distance figures.
To measure your tyre's actual circumference do the following;
Make a chalk line on the ground and place your front wheel with the valve stem at the bottom of the wheel directly above the chalk line.
Roll the bike forward in a straight line one complete wheel revolution until the valve stem is again at the bottom of the wheel.
Make another chalk line directly below the valve and then measure the distance between the two chalk lines in mm.
(if you don't have a metric tape measure you can convert inches to mm by multiplying them by 25.4.)Make sure that you measure the same wheel that the speed sensor is attached to.
If entering the correct circumference does not cure the problem
(i.e. the speed reads correctly compared to the GPS figures but the odometer does not) then you would need to enter the required offset value into the "ODO Offset" field to correct the odometer readings
(make sure you also click the "Write" button to save it).
Example: If a 10 mile trip shows only 9.2 miles on the odometer, try entering an ODO offset value of 1.087
(10/9.2) and see if it sorts the odometer readings.
If this offset makes the odometer reading even lower, try entering a value of 0.92 instead
(9.2/10).
Please let us know how you get on.
Alan