Tip & How-To about Cycling

I has to change my WTB Velociraptor 44/50 tyres last week due to age and wear bu

I soon found out that the 44/50 on the tyre is a two-number system introduced by Wilderness Trial Bikes who make the Velociraptor tyres, and is called the GMS both sizes are in millimeters and refer to the size of the inflated tyre, I don't think that it was a popular sizing system I couldn't find much about it but this is what I found out.

  1. The first number is the width of the inner casing in this case 44mm
  2. The second number is the width of the outside tread 50mm
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These measurements are taken on a standard rim which is 20 mm wide at the bead-capturing point (inner measurement) , with a tyre inflated to 60psi (4 BAR) and maintained for 24 hours.

The recommended pressure range is from
40-75psi on most WTB tyres. Download the PDF on tyres sizes for all the WTB range.

NOTE: > 14.50 psi = 1 Bar


Common BSD (also in inches) vs Actual Wheel Diameter check out my GMS Tip HERE for more information on this critical Bead Size and Tyre size relationship

622mm (24.5") = 29" - Large MTB
622mm (24.5") = 28" - 700C
590mm (23.3") = 26" - Standard MTB
520mm (20.5") = 24" - Childrens MTB
451mm (17.8") = 20" - BMX

NOTE: The BSD of the tyre is always 15% smaller than the Actual Measured Wheeel Diameter

The WTB tyres also have one rotation for the front tyre the treads usually point in this direction and a rear tyre can be used in both directions depending upon its use either Dry Mud OR Cross Country Downhill

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Front tyre continuously having flat tyres? After 2 or 3 hours driving appears to brake the stem of valve ? Happened 5 days in a row? Thanks


If you are using it for its' designed purpose, then this is going to happen. Off road riding has its' drawbacks, and you have found one of them. This is why most off road riders use tubed tyres and bolted tyres (to the wheel). You may need to adjust the tyre pressure to stop the tube creeping in the tyre. It will be trial and error to get the pressure right for your style of riding.

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Yup nice question. For any vehicle accurate tyre pressure will give you better tyre life, low running cost, etc. Here is a chart for car tyres click here.
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