Understanding Advanced Bike Geometry Pt 2 - Tuesday Tune 26

In part 2 of this episode we look at Front Centre to Rear Centre (FC:RC) ratio and why it's a seriously important factor in bike handling that's rarely discussed. We compare numbers between a few different bikes, all of which have notable geometry for one reason or another:
1. Deviate Guide 2018, size large - the best cornering bike we've tried
2. Transition Patrol 2016/17, size L and XL - Pinkbike's Bike of the Year in 2016 (same geometry in 2017), and an all-round great bike
3. Pole Machine 2018 - inthe vanguard of "long/low/slack with a steep seat tube angle" and geometrically an absolute weapon in a straight line, with some caveats
4. Nicolai/Mojo Geometron G16 - even more extreme geometry than the Pole
5. Nukeproof Mega 2018/19 - radically "conventional" geometry compared to the rest... and the overall winner of the Enduro World Series in 2018 under Sam Hill. Phenomenal skills aside, why is he winning on seemingly old-school geometry?

Note: there's an error in our spreadsheet, where the RC for the Mega is shown at 446mm instead of 437mm. The FC:RC ratio there should be 1.64 rather than 1.61.

[archetypex]

This two-part Series has to be one of the best if not the best videos tutorials exclamations you've ever produced Steve. Very technical and some of it over my head but it has made me break out the Physics for Dummies and also try and understand the mathematics and physics behind the geometry. There are only really a handful of people who are making videos that force people to think, analyze and comprehend what's going on with regards to machinery and components. Thanks again, your Insight your knowledge and Goodwill for making these videos, t is much appreciated.

[StructureCycleworks]

Steve, we would love to see an update of this video including the SCW1. To say that your logic resonates with us is an understatement.

[MTBguide]

Love these more in-depth Tuesday Tune video's. Keep up the good work!

[tylergentry]

Good stuff Steve! I think you're absolutely right in your calculations and coming to the conclusion that if you have a shorter bike, or a bike like the mega with a FC/RC ratio closer to 1, that it will be easier to weight the front wheel. This probably does result in better/easier cornering for most. The downside should also be added though that longer bikes are more stable going straight, easier to plow through stuff, and you have more room to maneuver which is why too long or too short gets bad as well.

I've also ridden a Machine and while I loved it, I did notice I was weighting the front more to corner effectively. Cheers!

[mirceaandreighinea]

i feel like saying two thinks: finally somebody within the cycling world knows what talking about & we think alike ;-) thank ya!

[jamiemacmahan]

Thanks Steve for the many informative and educational videos! This is outstanding and fun to think about and explore!

[soulzerosix]

Very interesting videos, thanks for putting the time and effort. Late to the party here, but since I was looking for a new bike recently I did some tables myself and noticed this: As mentioned, the FC/RC ratio changes across sizes for the same model. Some brands keep the same rear center across their sizes, and others make it longer as sizes grow. Comparing two examples on their smallest and largest sizes the numbers show that even when the RC changes for each size, the ratio isn't kept constant enough. The length added to the RC for each size up relatively short. I used the Privateer 141 as an example of a model that varies rear centres across sizes. The ratio is 1.75 for the P1 and 1.87 for the P4. I used the '22 Giant Trance X 27.5 as an example of a model that gets the same rear center across sizes. The S is 1.72 and the XL is 1.91. So the Privateer 141 gets closer ratios across the range compared to the Giant TranceX but it's still far from being constant. Is it because brands are being conservative and don't want to scare people away with huge rear centres on the larger sizes? Or is it something else (related to rider position/measurements) that makes up for the non-constant ratios? BTW Paul Aston has been experimenting with a custom DH bike with a 500mm RC. Maybe he's onto something?

[Cyclingabout]

Great commentary, Steve. This is the kind of stuff I'm always thinking about, but have never explored in-depth. Based on my own riding experiences I don't think I can fault your conclusions at all. 👍🏻

[barefootmtb]

Loved the vid. Geeking out over this info keep it coming.

[persistentconsistency]

Exceptional explanation and reasoning. Definitely thinking about this info as I chose my next rig.

[alexnelson]

Great information as usual. As a big guy on bikes over 500mm reach I have first hand experience with rear stays being too short. It sucks to lose front end grip and run you bars low trying to get some grip. Just build up a XL Ripmo and even though it feels a little small with a 60mm stem, the balance is amazing. Finding a bike that fits and is balanced is a beautiful thing. I don't know if I would give up easy manuals for longer rear stays and higher bars.

[michaelhirt]

Very well explained, thanks for the research. Opened up a new perspective on Body-Positioning for me!

[maxwella]

Thanks for doing these. An additional parameter that might be interesting is angle of inclination. I would seem that declines will increase the front wheel bias. Rather than optimizing for flat ground, many riders will want to optimize for the down slope because that is when you are more likely to be standing on the pedals. On flat found, a steeper seat angle might make up for the longer front-center.

[nickhanni]

Wow- awesome video and explanation. Thanks!

[syammimarifin]

Interesting stuff as always. This reminds me of the kinematics & compliance test that we do to characterize a ground vehicle in terms of the suspension performance in quasi-static condition. All those theoretical ride conditions that you listed may certainly be numbers that bike makers should report alongside the current geo numbers.

[Polebicycles]

Hi Steve! It's Leo here. I think you were asking me to answer this one :D Cool crushing numbers! Kudos for that, but you fell into the "static vehicle design fallacy". We did similar graphs a few years back before we started to change the geometry. One of the assumptions was that if we make the reach longer, the rider might get more tired if your reach goes further in front. The numbers don't really take in count the reality where the rider position of riding is not static. The optimal rider moves up and down on the bike rather back and forth. The riding stance is not very static, and the rider kinematics, the bike kinematics, and braking need to take into account. So, just trying to calculate the numbers on a sheet for a bike is not worth it because you start jumping into conclusions without thinking about the rider. Many bike designers seem to follow motorcycle and car design principles and that is a big mistake on bike design. What you need to do is start to stand on a scale and lean to a desk and bend your knees. ;)


A longer wheelbase is quite different when you ride downhill as you are not in a steep angle on drops. The longer wheelbase front wheel reaches the drop bottom before the rear. This means that the rider does not have that much flexibility and therefore he saves energy by moving less. With all designs, there are drawbacks though. On a longer wheelbase, the front end is not that easy to manual on a road. You need more effort on that. But on the other hand, on the trail, you can get your front wheel up anytime you want and you can also plow through stuff and save energy like that. Also, the longer wheelbase makes the ride calmer because there is less movement on both ends of the bike. Our conclusion is that with a longer bike you save more energy and you are 2-3% faster on an Enduro track.

I think comparing Sam hill and the reach number is a bit far-fetched because if you look at his riding on ANY BIKE, he hardly seems to do anything. The reason he looks like he's not doing anything is just that he has mad skills and he is strong as a horse. On EWS, the pedaling is a very crucial part of the winning ;)

On the grip issue you had on the Machine: If you remember, we had to use the same rear shock spring rate that I did, and the reason why you did not have enough grip on the Pole you rode was mere that your shock did not have the right spring rate. I weight roughly 73kg, and you are somewhat 90kg? I think it's fair to say the bike setup was far off for you.

Your tech vlog is cool! Actually, I was just about to email you about the hysteresis on shocks. I'm still thinking if the hysteresis on shocks is useful or not because we can create a similar effect with the leverage ratio and a low tune as well. I would love to chat again soon and change thoughts because I think that you are one of the smartest guys on the bike industry!

[Bruisewillies]

Really interesting stuff! Generally, I've always stuck with rigid bikes, but I'm sure the same rules apply. Some of the information seems to confirm what a lot of people actually "feel".

[aliikane]

Great Geo video. Now after this video, perhaps the new trend of bike manufacturers is going back to smaller FC/RC ratios, so you won't to shift weight as much and for less pressure on hands to keep the front tire traction. Both small and higher FC/RC ratios can be good depending on style of riding and physical characteristics, but of course there are trade offs. Currently, I have a short FC/RC frame and like it, but having a higher FC/RC ratio can be good as well just for more room and bigger margin of error.

[smoothmoose]

I see the major takeaway here is FC:RC ratio is important and with most bike manufacturers designing around a single chainstay length (RC) to be a serious design compromise to reduce costs, standardize tire clearance, and speed time to market. I'll like to see more brands (especially boutiques like Pole) to consider proportionate chainstay lengths to size on their bikes.

[tobiasdonner]

I ride said Nicolai G16 Large for 6, 5 years now and can confirm that there is weight on the hands also the stack is super low compared to the reach. I‘m 192cm and should be riding XL, but I‘m glad I went for L at that time. I had switched to 38mm fork offset early on to get more weight on the front wheel and I also brought the bars up quite a bit.

My takeaway is that FC/RC balance is key. That means if you want to have a easy manualing bike that is also balanced you‘ll have to go for a shorter reach as well. Assuming a manual benefits from shorter chainstays, shorter reach and higher stack it seems to me that the shorter reach approach can easily backfire by overdoing it.

It took the Black Friday sales opportunity to buy two Propain Spindrift 27, 5“ frames M @ 450mm reach and L @ 475mm reach both @ 435mm chain stays to figure this out.

I will also go with a 75mm riser bar because I’m 192cm tall with a rather normal 86cm RAD, and I think shorter reach with a high stack fits me better.

Thanks a lot for the superb content!

BR Tobias