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Old 03-26-14, 07:53 AM   #1
popcorns
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Tires & inches

Hello, I just bought a Bike Computer but I've stuck at the part with the inches. My tire has so many numbers.. But i've no idea what all these mean. If you could help me by telling me which of that is the inches.. I googled it but I didn't find a solution..
So, here is the numbers:
Pressure 40-65PSI 2.8-4.6kgf/cm2 280-460 KPa (56-559) 28x1.95 k-849-010
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Old 03-26-14, 07:58 AM   #2
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28x1.95. If your computer doesn't have that size in the menu, you'll have to look at the book for manually entering, and (for the computers I've owned) measure the circumference and manually enter that number.
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Old 03-26-14, 09:13 AM   #3
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Sheldon Brown has a bike computer page that might help

Harris Cyclery articles about Cyclecomputers by Sheldon Brown
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Old 03-26-14, 09:49 AM   #4
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some allow a wheel radius that you measure, to be input.
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Old 03-26-14, 10:58 AM   #5
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Something is wrong...

Looking at 56-559

559 = 26"
56 = width (in mm) or about 2.2 inches

So, I would expect to see something like 26 x 2.2

I have noticed that some tire manufacturers are confusing things by applying measurements, and who knows, theirs may be more sensible, but if you look at Sheldon's site noted above, you'll see we already have enough different ways to get confused.

However, the 56-559 should be the most "standard" thing related to size in what you show.
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Old 03-26-14, 01:00 PM   #6
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The manual/instructions that came with the computer should have a list with tire sizes and the corresponding number you'll need to enter into the computer when setting it up.

If you don't have the manual/instructions they're probably online. What computer did you get? Brand and model.
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Old 03-26-14, 01:16 PM   #7
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Yes, I have the direction paper and it says that I can calculate the tyre circumference by multiplying my tire diameter by 3.1416
And then there's a list of mosto common cicle tyres circumferences..

20'' = 1598mm
22'' = 1759mm
24'' = 1916mm
26'' (650A) = 2073mm etc.

But what I should multiply? My computer accept 3 numbers to fill it. The 2 first are big and the third smaller.

Last edited by popcorns; 03-26-14 at 01:22 PM.
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Old 03-26-14, 01:31 PM   #8
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I searched for: circumference of 56-559 tire

And found this: http://202.215.251.86/data/resources...e_chart_v2.pdf

And it lists 2068 for 55-559 and 2070 for 57-559, so you can use 2069
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Old 03-26-14, 02:13 PM   #9
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Quote:
Originally Posted by Little Darwin View Post
I searched for: circumference of 56-559 tire

And found this: http://202.215.251.86/data/resources...e_chart_v2.pdf

And it lists 2068 for 55-559 and 2070 for 57-559, so you can use 2069
Aw thank you very much!!
Thank you all for your help!
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Old 03-26-14, 03:28 PM   #10
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the easiest and most accurate way to figure out your wheel circumference
is a roll out test

put the bike with the valve on the front wheel at the bottom of the rotation
and put a mark on the ground beside it
then roll the bike forward until the valve is at the bottom again and mark that point
then measure between the two marks

this is most accurate if you are sitting on the bike during this test
but i dont think it makes a noticeable difference
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Old 03-26-14, 08:18 PM   #11
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Quote:
Originally Posted by Wilfred Laurier View Post
the easiest and most accurate way to figure out your wheel circumference
is a roll out test

put the bike with the valve on the front wheel at the bottom of the rotation
and put a mark on the ground beside it
then roll the bike forward until the valve is at the bottom again and mark that point
then measure between the two marks

this is most accurate if you are sitting on the bike during this test
but i dont think it makes a noticeable difference
+1 roll it out to be sure
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Old 03-27-14, 07:16 AM   #12
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you might have to hunt for a metric tape measure but they are out there
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Old 03-27-14, 09:44 AM   #13
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A difference of a few mm is not a big deal for most riders. Assuming a true measurement of 2000 mm entering any random number between 1980 and 2020 is less than 1% off....

However, if accuracy is critical, you should measure the rollout of several revolutions, while sitting on the bike with any equipment and accessories you normally carry. If you do as an example 7 revolutions, measure total rollout to the nearest mm and divide by 7. To ensure even closer accuracy, this should be done at the usual riding speed on the usual surface you ride, and should be redone periodically to allow for tire wear.

Then after that, you should still realize that it is just an estimate, since a bicycle trip involves a little side to side motion which will reduce accuracy.
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Old 03-27-14, 10:45 AM   #14
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Its all about circumference. all the computer does is count rotations ..

measure .. mark the sidewalk when the valve stem is at the bottom

roll the wheel once . ideally you are sitting on it. to compress the tire.

and then measure the difference between the 2 marks on the sidewalk .


you can ride thru a dog poo-pile and then the next time that deposit on the tire
marks the sidewalk again would do the same..
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Old 03-28-14, 07:23 AM   #15
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You've already gotten the correct answers. 56x559 is a regular 26" mountain bike tire, with a width of 56mm or, actually, 2.2 inches. A roll-out will be the most accurate method of determining the actual circumference, which is what the bike computer will need. Most roadies try to get within 1%. IMHO being 10% off would render the speedo almost useless; but maybe for a mountain bike it's all you need, which can be done by calculation.

The wheel's height will be the diameter of the rim plus twice the diameter (roughly, although different rim widths will affect that measurement.) So, 559mm + 112mm = 671mm. The circumference is that times pi, or 671 X 3.14 = 2107 (the computer won't accept fractions, even if tenths of millimeters would be too small to measure with a tape.)

Where the accurate measurements become a problem is in tire deflection, which depends on pressure and load. A properly-inflated tire will compress by about 10-15% with the rider on it. Even more than that if you run your tires soft for extra traction or flotation. Not only can it can be tough to get an accurate roll-out unless you have someone helping you; if your tire pressure varies, so will your speedo's accuracy.
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Old 03-28-14, 09:55 PM   #16
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Quote:
Originally Posted by popcorns View Post
Hello, I just bought a Bike Computer but I've stuck at the part with the inches. My tire has so many numbers.. But i've no idea what all these mean. If you could help me by telling me which of that is the inches.. I googled it but I didn't find a solution..
So, here is the numbers:
Pressure 40-65PSI 2.8-4.6kgf/cm2 280-460 KPa (56-559) 28x1.95 k-849-010
Simply measure the diameter of your rear tire in inches, multiply that diameter by 25.4, then multiply that by pi (which is 3.141592653) and it will derive the required 4 digits to enter into your bicycle computer.
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Old 03-29-14, 03:35 PM   #17
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Quote:
Originally Posted by popcorns View Post
Pressure 40-65PSI 2.8-4.6kgf/cm2 280-460 KPa
These are all various measures of Inflation Pressure:

PSI = Pounds/Sq. Inch
KGF/CM2 = Kilograms of Force/Sq. Centimeter
KPa = KiloPascals
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