Figuring the Numbers – MTB Frame Geometry w/ @thebikecompany

LiteVille 301 w/ test wheels

With increasing frequency we are asked to relay frame geometry data as finite, singular, almost as though it is gospel carved in ancient stone.

Ideal MTB geometry certainly sits in a window – however some manufacturers seem overly committed to hitting a “magic” number on each of their published dimensions.

301 with test wheels closeup

Recently we had a variety of 27.5” wheel and tire combos in the back of our shop.  We also had a LiteVille 301 test bike which arrived with the largest 27.5” rear tire I have seen so far.  It was a great chance to show one of the ways that geometry numbers can be easily manipulated.

bottom bracket & head tube comparison litevill

For ease of a quick test we mounted an angle finder on the headtube of the 301.  We changed between the high volume Schwalbe Hans Dampf, the mid-sized Maxxis Ardent, and the smaller Kenda Karma measuring bottom bracket height and reading the angle finder.

We found that we could manipulate the numbers approximately 3/8 inch on bottom bracket height and 1 3/4 degrees on the angle reading simply with tires.

bottom bracket comparison

headtube comparison mountain bike

What makes this interesting is how easy it is to move the numbers around with a simple tire swap.  While the Hans Dampf isn’t a rear tire that would typically hit my radar – I see all three options utilized by riders.  Even the bottom bracket and angular change between the Karma and Ardent was notable.  How far will some companies go to make sure their geometry numbers are in the “magic” area?  I have heard of bikes being measured with 1.9” commuter tires to manipulate their published numbers.  Forks are another easy way to manipulate your numbers.  Crown to axle, rake, and trail all play a part in a bikes geometry layout.

Where is this leading?  MTB is a market where bike capacity is often argued essentially on published numbers headtube, bottom bracket, top tube, travel, etc.  An industry with such an eye on precision that it offers 1/2 or 1 degree adjustable headset options, what if the listed geometry isn’t accurate to a trail built bike to begin with?  A market where clients who are otherwise enamored with a particular bike tell me its headtube is 1 degree off – they can’t ride it.  Are you able to understand how a particular bike will ride on trail from numbers (and possibly manipulated) alone?

You have options.

Work with a top tier resource.  Your resource should be able to explain a bike’s trail personality and how it will pair with your riding characteristics.  I can’t tell you the personality of a beach cruiser – but I go through steps with my clients to insure they are on the right MTB platform.

Work with your suspension.  Properly setup and tuned suspension will allow riders to temporarily manipulate bike geometry for given terrain with body positioning.  Think of how a bike will slacken headtube angle if you squat the rear end down.

Someone once told me “Figures don’t lie, but liars can figure.”  Be wary of information that doesn’t seem to add up.  Even if the published numbers are entirely accurate and equal various suspension systems ride incredibly different.  Manufacturers of lesser suspension systems are notorious for mating geometry numbers to more acclaimed platforms and marketing a “how different can it be” mantra.  Don’t settle for less – in the end it costs you more.  Demand More from the beginning.

See you on the trails –


  1. Chris Archer says:

    Thanks for the article. As the pictures arn’t quite clear enough, can you advise was this BB test done with the bike in 140 or 160mm travel mode? I can’t make out the writing on the linkage plate. Interesting to read though, as they all come in under the ‘official’ published information.


  2. Thanks for the comment Chris. That bike had 140 chips on it I believe (it was a test bike that is out of the shop with a team rider at the moment). Geometry is such an interesting thing to see how the different companies interpret it all… see you on the trails –

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