 Today I wanna show you what I believe is the simplest way to selecting the right frame size for your next bike purchase. And I've brought in expert bike fitter, Neil Stambry, who will be providing us with some further insights into what we should be looking out for. The tool we're using today is a 100% free website called Geometry Geeks. A business or website I have no affiliation with but a tool that I use all the time when making my next bike purchase which averages out to be, I reckon every three months as we speak. This website was established in 2017 and has quickly become the world's biggest open access bike geometry resource. Now one caveat before we get into it is in my opinion, this tool is mostly useful if you've got a bike or you've had a bike in your journey and that bike has fitted you well or you know where the fit fell down for a specific bike that you've had before. For example, maybe the reach was a little bit too far in and we can use that previous experience as the benchmark. So if you haven't purchased a bike before and you're confused about sizing, can I suggest you watch this video instead? So what I'm gonna do here is show you a real world example of how I would go about purchasing a bike like that when that bike behind me fits me perfectly but before I show you the example itself, let's hear from Neil about the top three things you need to look out for. So three things you need to be most wary of and then two things need to be slightly more, slightly careful of as well. The first two are the reach and the stack. So these two numbers, the reach refers to the horizontal dimension from the center of the crank to the center of this steering tube. This basically tells you how long the bike is. The stack refers to dimension taken from the center of the crank to this point here vertically. This basically tells you how high the bike is in the front end. So you've got the length and the height. These two numbers need to fall within a range that is gonna work for you and by a country mile, usually the stack, the height is the single biggest consideration. With aero bikes, race bikes, endurance orientated bikes, the stack height here will vary quite dramatically with them. In this case, for example here, I have got a 20 millimeter spacer stack underneath my stem. So I would not want to purchase a bike with a significantly lower stack because that spacer stack is gonna get real big. It's gonna get out to 30, 40, 50 millimeters if the stack was much lower and that would be a bit of a problem. You need to also be careful that it's not too tall. If it's too tall, if the stack is too high, you will basically not be able to get your bars low enough. So you need to take into account the stack height when you're referencing off the two bikes to make sure that you're gonna fall within a range which is actually doable. Ideally, you wanna aim for something with a 10 millimeter spacer underneath. That would be bang on, gives you a bit of room to go down, gives you room to go up as well as long as your steerer tube isn't cut. The reach, basically, the way to think about this is imagine that you've got your next bike, the one that you're looking for has got a 10 millimeter longer reach and you're running a 100 millimeter stem. That just means you're gonna need a 90 millimeter stem on the new bike to make the reach to the bars identical. The third consideration is the seat tube angle here. This bike has a particularly slack seat tube angle, 72 and a half degrees. This basically dictates the clamping point of the seat. As you can see, this is a great example here. I've got this seat shoved as far forward as it can possibly go, which if I was looking at a new bike, I would very carefully then wanna make sure that I purchased a bike with a steeper seat tube angle just so that that clamping point move forward. If the seat is shoved as far back as it can possibly go, for example, you would probably wanna go for something with a slacker seat tube angle to move the clamping point more towards the center of the rail to give you a bit of play there. So I don't typically look at the next two, Neil is about to mention, although I might do that moving forward, but let's look at these three using my real world example. So I know the BMC team machine, SLRO1, medium 54, fits me perfectly with a 110 millimeter stem that makes the reach dialed in. So if I type BMC team machine SLRO1 into geometry geeks and make sure you select the right model for me being the 2021, and if you don't see say the 2022 model, just do some research on that particular make and model. Most brands update their design and subsequently the geometry can change as well every three to four years. I know with the BMC team machine, it was updated in 2021. So the 2022s and even 2023s will stay the same. So now we have the team machine SLRO1 in a medium. I can go and compare it to another bike that I needed to purchase recently, which was the Seeker Xseed. And I had a lot of people, and this often happens with bike purchases, because I tend to sit in the middle of a number of sizes, being 179 centimeters in height, asking me why I didn't go the large in the Seeker, why I went in the medium. So I'm gonna show you exactly why that was the case in this example. So if I grab a medium and grab a large, I can now independently compare to the BMC team machine. I'll leave it on the BMC team machine and looking at these three areas, Neil was discussing, I have no seat clamp maxing out issues on the team machine. I'm kind of in the middle. So the 0.5 degrees either way isn't a biggie. And from there, I can immediately see that the standout is stacked. So if I was to go a Seeker large, I'm gonna be a lot more upright unless I slam that thing, which I don't necessarily want to do particularly for resale. What I am better off doing is given the variables at hand, purchasing a medium and going with potentially a 120 millimeter stem versus a 110 mil stem that I use on the BMC to make up for that seven millimeter shorter reach. So here's Neil to share the other two considerations. So those are the three big numbers. You need to also be slightly wary of the height of that bearing cap does vary between bikes and it varies between models of bikes as well. And then the layback of the seat post is your last consideration. So a zero offset clamp, for example here would solve a lot of my problems by clamping that saddle in the center of the rails, but I can't purchase a seat tube insert that's got a zero offset clamp for this particular bike. So most of them will be 20 or 25 millimeters laid back and you just need to be a bit wary of that when you're considering the next bike versus the current one. Those bits of information, those last two, the height of the bearing cap and the layback of the post are not on websites like Geometry Geeks. You will need to look at the manufacturer's website to just triple check those ones.