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Does Reach = Hip to Shoulder Length?

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12/13/2020 7:01 AM

I was inspired by some of the other geometry discussions going on in the forum to think about my own setup and what works and what doesn't. At first I was thinking about body position with respect to handlebars and how I have been working to more actively weight the front end (as others have discussed/found, I ride very off-the-back to the detriment of front end grip especially in corners). Thanks to the forum thread on handlebar height for that discussion! I thought about the other component of the front-end-weight equation, reach, as someone else mentioned it in that post, and how my previous bikes have handled. After my first ride on my current bike it felt instantly better all around, even though the head angle only changed slightly, the BB went up a touch, but the reach increased by ~15mm to 475mm. I could imagine riding something longer for a more descent-oriented build but this works well on the rolling terrain of my local trails.
I was still thinking about front-end weighting when I thought about how reach is derived. It's an imaginary straight line from the stack height over the BB to the headtube:
Photo
Which, if you think about those lines as a person, looks suspiciously like the 'ride tall/ride strong' neutral position that is talked about in World Cup DH. You see it a lot in riders that 'look slow, ride fast' like Luca Shaw or Troy Brosnan. It's not a perfect photo, but hopefully you get what I mean.
Photo
So then I thought: is the 'ideal' reach somehow related to your torso length? That length being from where you hinge at the hips to your shoulders. In that way, when riding tall on flat terrain, you would make the perfect L-shape on your bike with your arms straight down (or thereabouts). If you ride mostly downhill (aka DH bikes) you could figure out the average grade and math out the difference in that triangle.
Yes, there are a lot of other things to consider like angles, chainstay lengths, ape index and torso-leg ratios, but when I measured my torso, the length was... just about 47.5cm, or about how long my reach is now. Intriguing! For reference, I don't think my arms are super long and I am a185cm total height.
So let's here it, VitalMTBers. What do you think? Is my bike fit a coincidence or is there more to this?

Are you comfortable on a bike where Reach = Torso Length?

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12/13/2020 10:15 AM

Where on the shoulders? Is it on the ends or next to you neck? Are you shrugging to any degree, trying to just relax them, or push them toward the ground (I've also heard that motion referred to as "packing.")

I don't think reach is a number to focus exclusively on, but is one that can help someone find the right size frame to build the right set up with. But I'm curious if my torso will get close to the reach numbers I'm considering for future bike purchases.

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12/13/2020 11:26 AM

taldfind wrote:

Where on the shoulders? Is it on the ends or next to you neck? Are you shrugging to any degree, trying to just relax them, or ...more

Good point on how to measure. I was imagining hinge points, so ideally hip hinge point to centre of shoulder (i.e. shoulder socket). I measured this in a neutral stance, but I suppose pushing shoulders towards the ground would be better.
I'm sure there is some variability in here - if I measured my torso length off by even 5% that could change my reach substantially. I agree that reach isn't the only number to look at, but it just struck me that my current bike is very close to my torso length.

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12/14/2020 12:13 AM

Well you are probably right to some degree, but proper bike fit is affected by a lot more factors, like leg lenght ( as you pointed out). Just for the sake of chatting, does your new bike have longer chainstays? Longer chainstays will deliver more front end traction.
BTW the graph you posted is not perfectly accurate, as chainstay lenght must be measured parallel to the ground, because what matters is the distance between wheel axle and bb, which is the rear center.

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