Is my math correct?

Kaleidopete

Kaleidopete

Well-Known Member
Math is not my strong point.
My bike computer calculates my miles off a magnetic sensor on the wheel that was set up by the factory. Trek.
My Tomtom watch calculates my miles from satellite reception. I believe the bike would be more accurate.
My bike say I rode 13 miles, while Tomtom says it's 12. Calculating the difference would be 1.08% says google.
That would mean my 2018 Tomtom mileage which was 3729, was really 4027. Or am I wrong?
 
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13 is 108.333333 % of 12 (13 / 12=1.08333333) which means a 8.333333 % difference

If your bike says 3729 than your Tom Tom mileage should be 3442 (3729 / 1.08333333)

If your tom tom says 3729 instead than your bike mileage should be 4039 (3729 * 1.08333333)
 
my .02....I assume the accuracy of the computer will depend on how accurately it is programmed to the circumference of your wheels/tires. That aside, my math came to 4039 miles also, but I did (3729/12)*13....My brain works funny
 
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pkovo said:
my .02....I assume the accuracy of the computer will depend on how accurately it is programmed to the circumference of your wheels/tires.
Click to expand...

This...Garmins will calculate your wheel size based on satellite reporting, when you first connect a speed sensor/go for a ride, then preferentially use the speed sensor to calculate distance.

However, the most accurate way of doing it is to, with a helper, put the valve on the wheel at the 6 o'clock position, mark the ground at that spot, then--with you on the bike, and your tire pressure set to what you ride at--roll the wheel one-to-several-times, ending, with the valve at the 6 o'clock position, and again, marking the ground. Measure the distance between the points, and divide by the number of revolutions, if greater than one. It goes without saying, you must roll the bike in a straight line. You'll end up with a number in mm/cm/in, which you then input into the computer when it asks (usually in mms).
 
Karate Monkey said:
However, the most accurate way of doing it is to, with a helper, put the valve on the wheel at the 6 o'clock position, mark the ground at that spot, then--with you on the bike, and your tire pressure set to what you ride at--roll the wheel one-to-several-times, ending, with the valve at the 6 o'clock position, and again, marking the ground. Measure the distance between the points, and divide by the number of revolutions, if greater than one. It goes without saying, you must roll the bike in a straight line. You'll end up with a number in mm/cm/in, which you then input into the computer when it asks (usually in mms).
Click to expand...

I have an easier way to do this - no helper required.
1. Open can of white trim paint
2. Place dot of paint on center of tire
3. Ride bike in straight line in driveway
4. Measure distance between 2 white spots on driveway
 
pkovo said:
my .02....I assume the accuracy of the computer will depend on how accurately it is programmed to the circumference of your wheels/tires. That aside, my math came to 4039 miles also, but I did (3729/12)*13....My brain works funny
Click to expand...
I think the accuracy of the computer would be spot on since there are no aftermarket add ons here, it's all original factory assembled.
No changes in tires or wheels, meaning I think Trek has it figured out.
 
Kaleidopete said:
I think the accuracy of the computer would be spot on since there are no aftermarket add ons here, it's all original factory assembled.
No changes in tires or wheels, meaning I think Trek has it figured out.
Click to expand...

I would check the settings. Wheel circumference, especially on a mountain bike, is dependent on tire pressure. Do the above and see if the number jives with whatever trek used.
 
rick81721 said:
I have an easier way to do this - no helper required.
1. Open can of white trim paint
2. Place dot of paint on center of tire
3. Ride bike in straight line in driveway
4. Measure distance between 2 white spots on driveway
Click to expand...
How long would it take to erase the paint marks from the driveway?
 
Kaleidopete said:
My bike say I rode 13 miles, while Tomtom says it's 12.
Click to expand...
I think what is being overlooked here is that the sensor is mounted on the front tire (I presume),
and hence that extra mile you are getting from the computer could reflect the extra revolutions when you do a wheelie, manual or otherwise send it aerially.
I think this 8.3% should simply be considered the rad-factor,
and so the further off your computer and GPS are, the radder you are.
 
jmanic said:
I think what is being overlooked here is that the sensor is mounted on the front tire (I presume),
and hence that extra mile you are getting from the computer could reflect the extra revolutions when you do a wheelie, manual or otherwise send it aerially.
I think this 8.3% should simply be considered the rad-factor,
and so the further off your computer and GPS are, the radder you are.
Click to expand...

All my speed sensors are on the rear wheels. I don't do wheelies but compensate by doing burnouts
 
jmanic said:
I think what is being overlooked here is that the sensor is mounted on the front tire (I presume),
and hence that extra mile you are getting from the computer could reflect the extra revolutions when you do a wheelie, manual or otherwise send it aerially.
I think this 8.3% should simply be considered the rad-factor,
and so the further off your computer and GPS are, the radder you are.
Click to expand...
actually it's on the rear wheel
 
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