If you're new to bikes, understanding bike sizes can be difficult. There's no perfect size for any specific height and a lot of it is personal preference. It's important to note that this guide does not replace an actual test ride. It's only here to educate you on the terms and ideas.
First, let's start with the terminology.
Traditionally, frame size was based on the seat tube length when bike geometries were somewhat similar. Road bikes had that classic silhouette of a high and straight top tube and mountain bikes were all hardtail. The drawing above is of a modern full-suspension bike of a very different design.
As bike design evolved and manufacturing techniques progressed, bikes now come in a variety of shapes and basing the size purely on the seat tube length has become irrelevant. The industry now sizes frames like underwear - small, medium and large.
Effective Top Tube
Effective top tube is a better way to compare bikes as your reach to the handlebars has the most impact on how the bike feels. It's called effective because it takes into consideration the seat tube angle and it's measured parallel to the ground. Taking that even further, there are measurements called Stack and Reach, but that's more advanced stuff for another time. For now, we'll stick with effective top tube.
If you like how your current bike feels, compare its effective top tube length to the new bike you're considering.
Example - You have a large Trance trail bike that fits well and you're considering buying a Reign 2. The large Trance is 24.4" effective top tube. The new Reigns are long, being designed for short stems, with the medium being 24.4" effective top tube, same as the large Trance. In this case, going down to the medium Reign might fit well. While this isn't often the case, we do see some people size down when moving to the Reign because they are so long. Of course, there are other factors to consider, like stem length, etc., but a quick look at geometry of the two bikes gets you started.
If this is your first bike, we can look at you and give you a good idea of what size is likely to be best.
When you throw a leg over the bike and are straddling the top tube, with your feet flat on the floor, this is where standover height matters. You need at least 1" of clearance between your junk and the top tube. If you can't safely touch the ground with both feet then the frame is too big, even if the reach is fine. Most modern mountain bikes have a sloped top tube design to give you more standover height, like in the drawing above.
Height and Body Type
People's proportions vary quite a bit. Some people have short legs and a long torso with gorilla arms. Some have long legs and a short torso with little T-rex arms. Most bike size charts are based on height, which is a good place to start, but it can still be hard to know what size bike you need over the phone or internet. On top of that, there's overlap between sizes so you might fit well on both a medium and large. Again, it's preference.
Here is Giant's general sizing chart.
Come into the Shop
The best way to know your bike size is to come into the shop and go for a test ride. We've given you a lot of information here, but if this is your first bike, you still won't really know which size is right for you. You'll have a better understanding of how it all works, but our best advice is to come into the store and test ride.
We stock the common sizes of most of our range, so finding your bike should be easy.
Laser Bike Fits
Once we've got you on the right size bike, there are adjustments that can be made to make it fit perfectly. This is usually more relevant with road cycling, but can still be useful for mountain bikes, too.
We offer a comprehensive professional bike fit for $150. They usually take about 90 minutes. We'll properly align your cleats, put you and your bike on the trainer, take current laser measurements, make changes and offer recommendations. We'll give you a chart of all your measurements. Road bikes offer quite a bit of adjustment with the handlebar configuration. We can get you sorted for hours of comfortable riding.
To book a bike fit, please contact us.