Seat Tube Angles and BB Offset
The topic of seat tube angles (STA) appeared in the spotlights over the past few years. Steeper STA’s have made their way to enduro and trail bikes. Growing reach numbers made bikes roomier and created an opportunity for the STA to be steeper, resulting in a better position for comfortable and efficient pedaling, without feeling cramped. Welcome to 2020, it’s great.
But the topic of STA’s has always come with a lot of confusion. That is because there are two different ways to measure the STA.
Put your phone against the seat tube, and you’ve got the ‘actual STA’, simple. And if your seat tube would go straight to the BB, it would also be the virtual STA. The virtual STA is measured from the bb, to where the seat tube meets the horizontal top tube.
On most full suspension bikes, the seat tube doesn’t point straight to the BB and the virtual STA will be somewhere around 3 to 12 degrees steeper than the actual STA.
In theory, the virtual STA will tell you where your saddle is. But only for the specific case of having your saddle on the height of the horizontal top tube. In reality most people ride their saddle much higher. And anyone with slightly long legs will be so far off, that the virtual STA completely loses its purpose.
Some companies have gone as far as showing virtual STA’s for different seat height, which is great, but also makes it even more confusing. We provide both seat tube angles, but also add in the offset from the seat tube to the BB. The BB Offset to the ST is simple to understand and great to compare between bikes.
The actual STA and the BB Offset define the full picture and are simple to understand, measure and compare. The virtual STA can help to understand where your saddle is but depends on the length of your legs. We provide all three dimensions and would love to see the actual STA and BB Offset across the bike industry for more transparency.