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Old 05-19-17, 08:35 AM   #1
dyson42
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tire sizes

I"m new to racing and know really nothing about it. my son is racing he is 9 years old and has a older redline fight expert. My questions are:
what is with the skinny tires he has and all other kids his age seem to use there 20" 1 3/8? can I change to a thicker tire like 1.4 etc.? do they have to use the 1 3/8 tire? what is the difference between the skinny tires the younger kids seem to use and a thicker tire?
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Old 05-20-17, 05:14 PM   #2
rhenning
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I believe the 1 3/8 inch tire uses a bigger rim then the other you see. There are 2 sizes of rim diameters. 406mm and 451mm. Usually the decimal sizes are 406 rims and the fractional sizes are 451 rims. You will have to ask where he is racing to see the tire size rules that apply in your area. Roger
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Old 05-23-17, 12:06 PM   #3
pickettt
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Quote:
Originally Posted by dyson42 View Post
I"m new to racing and know really nothing about it. my son is racing he is 9 years old and has a older redline fight expert. My questions are:
what is with the skinny tires he has and all other kids his age seem to use there 20" 1 3/8? can I change to a thicker tire like 1.4 etc.? do they have to use the 1 3/8 tire? what is the difference between the skinny tires the younger kids seem to use and a thicker tire?
He doesn't HAVE to use one size or the other. It is preference. Once guys and girls start to get a little heavier, they make the transition to a wider tire.
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Old 05-23-17, 12:15 PM   #4
mihlbach
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IF you are racing in the USA, the USABMX rulebook can be found here....
http://s3.amazonaws.com/bmxwebserver...7_Rulebook.pdf

Here are the relevant rules.

2. Bicycles for competition in the Intermediate / Expert
/ Girl / Pro classes can have no larger than a 20”
nominal wheel diameter. 12”, 16” & 18” bicycles are
acceptable for competition. The total diameter of the
wheels, inflated tires included, shall not exceed 22 1/2”
(57 cm).
3. Bicycles for competition in the Cruiser / Girl Cruiser
shall have wheels where the total diameter of the
inflated tires included shall measure more than 22 1/2”
(57 cm).


There are no wheel restrictions in the Novice class.


There are two rim diameters that are nominally called 20", as described by rhenning above.
Smaller kids generally use fractional sizes (eg. 20 x 1 1/8 or 20 x 1 3/8). Larger kids and adults use decimal sizes (eg. 20 x 1.75). Again, the rim diameters of these two 20" systems are not the same, so the tires are not interchangeable. However both are legal in all classes (excluding cruiser) in USABMX sanctioned racing.
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