question for greyracer or someone with displacement knowledge

4 replies to this topic
  • belongaj

Posted April 10, 2009 - 03:33 PM


I want to make sure I am legal in a class. I bought a kx 100 with a 2mm stroker crank in it. My daughter can race up to a 105 in the girls class. I want to make sure the bike is legal. The bore is stock at 52.5 and the stock stroke is 45.8 so the stroke must be 47.8

Can someone tell me what the cc's are for the bike. I do not know how to figure the displacement. All help would be appreciated. Thanks

  • Brad_Aus

Posted April 10, 2009 - 03:58 PM


Looks like you are at 103.5cc.. There is lots of displacement calculators readily available online

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • grayracer513

Posted April 10, 2009 - 05:33 PM


Multiply half the bore by itself (square the radius), multiply that by Pi (3.1416), then multiply the result of that by the stroke.


The number you will come up with is cubic millimeters. Divide it by 1000 (move the decimal 3 places to the left), and you have your answer in cubic centimeters.

  • belongaj

Posted April 12, 2009 - 05:26 AM


I went and used an online calulator and came up with 103.5cc also. That was awesome. Thank you to those who responded.

  • trailman006

Posted April 12, 2009 - 05:42 AM


Thats cool. I learned something new today. This place is great.

Related Content


100 hrs on 2014 yz450f, shim valves or replace them? by ttr230rider6

Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • Hot  79 replies

YZ450F 03 Sparks driving me crazy by SirAttard

Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • 5 replies

Chubby dad, looking at bikes , First trip to the orange/black forum ! by Slow_ride

Dirt Bike   Make / Model Specific   KTM   250-530 EXC/MXC/SXC/XC-W/XCR-W (4-Strokes)
  • Hot  28 replies

Thinking about Yamaha 250... by Arctic Pride

Dirt Bike   Special Interest Forums   Pro Racing
  • Hot  491 replies

yz400f throttle bog by yz400fmaniac

Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • * * * * *
  • Hot  28 replies

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.