Modern Geo Talk: Chainstays, Stack, Reach, and Bitching About It

Thats true, which is ultimately why  I went with the Chisel. It responds so well on the pedals, which is really what I need for the local stuff. I also wanted something that rode in stark contrast to my Prime, which it for sure does. 

Unless you bend over and pull yourself far over the bars, use a setforward seatpost, etc. etc., using a longer reach bike is exactly the issue we are talking about balance. No, it will not move the balance forward, it will make the front/back balance even worse. You're not meaningfully moving the weight away from the rear if you keep the chainstay the same, but you are moving the front further away. Imbalance 101.

It actually makes more sense to go with a smaller size to improve the balance. 

@jeff.brines  touches on the tips vs. tails of bikes topic in his Spire review: https://www.youtube.com/watch?v=7ldmkydwn7U

I keep seeing people mention a front to back ratio (usually in the 1.8ish range) how is this calculated?

(front center) / (rear center)

Also gets you an approxiate estimate:
(Wheelbase - CS length) / CS Length

If you have a high pivot bike, take into consideration how much the CS/Rear center grows throughout its travel to adjust your WB length and calculation accordingly.

How do you calculate front center and rear center?

They're like virtual, draw a vertical line that intersects your BB, and then draw a horizontal line from your axle to the BB line. They would be your centre measurements.

Full agreement in regards to what @jeff.brines is saying about FC/RC ratio for modern bikes. Luckily I can ride medium and small sizes, so the RCs can be pretty good as long as the FC isn't super crazy.

A recent Transition Spire project::

Alloy frame (medium) with 27.5 rear wheel and +2 angle cups. 190mm fork, 180 rear travel with cascade link. HA 63, BB 342mm (in the high shock position), WB 1256mm. 

It's a bit over my preferred max FC/RC of 1.75 (around 1.8), but the front doesn't "feel" long. It still turns quite well. Maybe something to do with the smaller rear wheel? First mullet bike I have had that was not a full DH sled.

Sick build. It's crazy that the HA is still 63 after using a +2 cup and in high position, but perhaps its because of the 190mm fork.

So for XL bikes what’s out there for enduro bikes close to the 1.8 ratio?

Banshee Titan with long dropouts, Forbidden Dreadnought, anything else?

From what I’ve been able to find there’s no options in DH bikes anywhere close with the exception of the Forbidden Supernought and some short-reach XLs like the Banshee Legend 29. Even a Santa Cruz V10 with 465 chainstays winds up around 1.88 FC/RC. 

You’re starting to see why there is a very vocal group pushing for more balanced bike geo…

I’m in the market for both an enduro and DH frame and now I have an excuse for why my buddies who ride mediums are faster than me. 

The only two meat bikes that fit this bill that come to mind is a Kavenz VHP16 in its sagged position with the +20mm chainstay thingies and the Mistress Cycles GoodOnYa, which is a unique approach to geometry, and quite new and obscure. 

The new Forbidden Druid CorE e-bike also fits the bill. It would be cool to see a corresponding meat-propelled equivalent. 

Limited options for the meat brigade, but we'll keep hope alive. 

The Kavenz could actually fill both roles with the proper linkages, two shocks and two forks. Ideally, probably wheels as well. 

They also intend to release +30 dropouts in short(ish) order, if their socials are to be trusted. That would let you get even longer out back, should you desire that. 

You could then direct the savings to sick, custom-tuned suspension components and/or various conspicuous bling!

G1 can get close ~1.83 and it’s a big xl

Exactly the struggles I’ve been feeling. As an XL guy, my trail bike is 1.86 and my DH bike is 1.88. It’s a struggle!

Not many options out there at all. You named most. Kavenz getting closer. New Geometron can messing with mutators and trying to remember a couple others. 
DH is basically only Forbidden Supernought and Enduro has the few that have been listed here and by others. 

Sure hope for more options soon… ready to build up a new trail and DH soon and really wanting closer to or at 1.8 

What are the ratios of medium and small bikes? 

My medium Strive is 1,9 by using the geo chart.

When using real measurements its 1,88.

I saw a list of bikes with ratios on a forum somewhere. Not sure where 

Was thinking of making a spreadsheet with all bikes in all sizes that’s ongoing and added to that shows all the ratios for everyone to have access to and be able to scope 

Be fun to put pros set ups in it as well for nerding and stuff like that

As an example, the Santa Cruz Hightower is: 1.7764976959 (S), 1.8348623853 (M), 1.8792710706 (L), 1.9298642534 (XL), 1.9842696629 (XXL).

Out of curiosity - where did the rhetoric come from that medium bikes have the best ratios and ride the best? 

Just an assumption as most people ride mediums and logic says that geometry should be optimized for most people if it is for anyone. Considering the chainstays are basically the same for every size, mediums are where it's at. 

Honestly, it could be just as out of whack as all the other sizes. Maybe front to rear ratio of 1,0 is the best? 

Paul Aston's style may not be for everyone, but it seems like he's on the front of this balanced geo for bigger sizes wave. Here's the geo chart for one of his custom bikes. 490mm chainstays, 510mm reach, 1.84 F/R ratio.

Some quirks in his setup since he's running an ultra-short Rulezman stem and the bottom bracket is 10mm above the hub-hub line at full extension.

I think it comes from preference and trying different things. I ride size large and have ridden 1.88, 1.86, 1.85, 1.84, and 1.83 f/r ratios.

I have a much easier time maintaining speed over rough terrain but turning is relatively more challenging for me - so I prefer bikes closer to 1.83.

This might be of interest to some, this is how rolling your bars 10 or 20° backwards affects the geometry of the bar if you have a 35 mm riser bar with 8/5° of sweep. The stack and setback (negative reach) are somewhat specific to the case, but it still gives some good insight on how some values are barely affected (backsweep), while others are greatly affected (the setback basically makes your bike almost a size smaller reach wise):

More backsweep and less upsweep both contribute to pushing your elbows inwards, giving you a less attacking position.

Is this part of the reason why Jackson is running his bars rolled so far forward?
 

The other piece of the equation that I was told about cockpit setup and elbow position is that brake angle also dictates it. Flatter brakes want to move your elbows in, and steeper brakes move your elbows out. Given that viewpoint as well, someone like Goldstone who runs flatter brakes needs more forward bar roll to get the elbows in the right spot vs someone (like Loic and Richie from what I can tell) run a bit steeper brakes and probably less forward bar roll because of it. 

I've personally moved to a bit of "backwards" bar roll and steeper brakes. So my bar roll is "mostly" in line with headtube angle and my brakes are at a 42 degree angle down from level on the bar.