# accurate tire size set



## peaceful1 (Sep 27, 2012)

I have a tahoe 2.0 2012 & using a  bike computer  it's wheel size is :

26*2.20
54-559

but the attached manual doesn't have this size what should I do ?


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## jjaguar (Oct 6, 2011)

Measure rollout. Using the valve stem for reference, sit on the bike and ride in a straight line for one complete revolution of the wheel, then measure the distance between the start and finish points. For more accuracy, ride farther (two or three revolutions) and take an average.

It's the most accurate method anyway, because actual tire circumference will vary depending on tire model, pressure, and bike and rider weight.


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## shiggy (Dec 19, 1998)

peaceful1 said:


> I have a tahoe 2.0 2012 & using a  bike computer  it's wheel size is :
> 
> 26*2.20
> 54-559
> ...


Do a roll out. Been discussed here many, Many, MANY times.


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## peaceful1 (Sep 27, 2012)

thanks guys for helping me out just fore making it clear 

when I find out the exact tire circumference what should I do with it?

it suppose to make a special number in the chart right ?


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## Bluechip (Feb 17, 2006)

Enter it directly as wheel circumference after adjusting it to the correct measurement asked for (cm or mm).


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## shiggy (Dec 19, 1998)

peaceful1 said:


> thanks guys for helping me out just fore making it clear
> 
> when I find out the exact tire circumference what should I do with it?
> 
> it suppose to make a special number in the chart right ?


To quote your attached chart: "wheel circumference in mm"
Clear enough?


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## peaceful1 (Sep 27, 2012)

hey! in the top it says "wheel circumference" why I haven't seen that before !

by the way is the magnet placement important in the accuracy (*answered*)

you guys are great I appreciate all the help


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## shiggy (Dec 19, 1998)

peaceful1 said:


> hey! in the top it says "wheel circumference" why I haven't seen that before !
> 
> by the way is the magnet placement important in the accuracy (*answered*)
> 
> you guys are great I appreciate all the help


Only in that the magnet needs to properly align with the sensor.


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## Harold (Dec 23, 2003)

shiggy said:


> Only in that the magnet needs to properly align with the sensor.


yup. that is all. the sensor is simply a reed switch that only ticks off revolutions. the computer head unit counts those revolutions and converts them to a distance using the wheel circumference.


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## peaceful1 (Sep 27, 2012)

when I ruled out it was 2100 mm but when I calculated with its radius it was 2136 mm


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## Harold (Dec 23, 2003)

peaceful1 said:


> when I ruled out it was 2100 mm but when I calculated with its radius it was 2136 mm


a proper rollout accounts for tire pressure and rider weight compressing the tire as you ride, while using the radius does not.


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## DennisF (Nov 4, 2011)

Ride several revolutions and get an average.

Put a zip tie around your wheel & tire so it marks the ground as you ride -- have also heard of people using a dot of paint.


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