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 at Vorsprung have ridden
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 - in the 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?
MENTIONS: @VorsprungSuspension
A medium with "short chainstays" (425-43cmm) may very well have that ideal RC:FC ratio whereas the same bike in XS or an XL may have a non-ideal ratio and will behave substantially different.
I think this is a prime example why the "superenduro" bikes like the firebird and the spartan were reviewed negatively due to their short chainstays (with 6'+ riders) whereas the length of those chainstays may be perfect for a person who rides a medium where the RC:FC ratios are better.
Personally, I reckon the FC:RC might be relevant there, but the RS shock in the Spartan's is really poor, which has more to do with the harshness reported.
That is the general consensus, but why? Short chain stays mean shorter wheel base when compared to the identical axle placement for the front wheel. I like to think of it in motorcycle terms since I ride daily. A razor sharp handler like an R6 has a relatively short wheel base and steep steering head angle when compared to a cruiser. The sport bike turns in like nobody's business and the cruiser turns like a pig. One is meant for highest performance the other for long sessions in the saddle. Neither one does the other's job well at all, but are purpose built.
I expect that we'll see more of the same for general consumer bikes, ie: short stays, longer/relaxed fronts so that the average rider gets a nice middle ground. For DH specific bikes, I would expect longer wheel bases to aid in stability, but there is a point where too long becomes cumbersome. Interesting to watch for sure!
1. The Geometron was the best climbing bike I've ever owned.
2. It was hard work to bunny hop because of the massive weight shift involved. I found this especially when riding a trail blind and having to react quickly to an obstacle. If I knew in advance that I needed to bunny hop something, it was fine because I could plan ahead.
3. On steep trails it was extremely fast and cornering was not a problem (due to weight being naturally forward)
4. On more mellow trails, the bike would understeer in corners unless I consciously weighted the front. Never had too much of a problem losing the front wheel, just ran wide a lot on turns.
In the end, because of the type of trails I ride most often (in Ireland), the more conventional geometry is a better compromise. It's not as fast on the steeps (but not far off), but that's probably about 25% of my riding - and faster everywhere else.
In the end IMO, it comes down to the terrain you ride most often.
In picking my most recent bike I laid all the frame numbers out to help and the tried them. The bikes I disliked the most had really short rear centres. SCHTLT being the worst as it felt like I was riding on the rear axle.
In the end I picked Banshee as their frame had long chainstays and adjustable drop outs too. I'll never pick a bike with one size fits all across the range or no adjustability.
Frankly, I'm amazed bike manufacturers get away with this slackness. It seems like they just can't be bothered, Norco and YT I believe notwithstanding.
There are so many dynamic factors affecting ride, and geometry is just one of the variables. A good rider adapts riding style very quickly to ride most bikes at a very similar pace. Terrain, braking, tire choice, suspension setup and even the intangibles like committment and confidence play equal or bigger roles. It’s a whole package, and the sum is more than just the parts.
I’m as guilty as the next at looking at geometry tables and specs, making assumptions. But damn if
I haven’t gotten out on trail just to find that the latest greatest rig is just a dog for me... and often the other way around, I’m surprised how great a ride goes.
Have fun with charts, numbers and theory but never give up the chance to ride someone else’s bike. You might be surprised how much it can open your mind.
I think the Geometrons and Machines of this world suit the taller guys more but that main issue with the front end weight is also about ride style and steepness too....if you drop your chest to the stem, bend elbows and knees into a decent attack position and are shredding steep shit then they weight shifts to the front a lot anyway. Riding a slack bike last summer on greasy green runs was hideous, front end washout and i just couldnt load it up at all. Hit the black runs and suddenly it was easy to rail shit with grip and the bike came alive.
Slack n long for fast steep ripping, more conventional for trail and pop. If you dont care about climbing or climbing is everything to you then choose accordingly.
At least we have the choice now....5-8 yrs ago there was little between full suspension bikes (excluding DH bikes) compared to today. good times
Shouldn't the endo angles on the Pole/geometron be shallower and not steeper than the other bikes due to the increased FC? (the angle was defined from the horizontal in the frst video)
Cheers!
What I like to mention and I am speaking from experience you have to respect different rider dimensions and rider weight in this model as well.
I (195cm / 95kg) love this "modern long" geometrys a lot. The extra weight shifts on long bikes are no problem, the weight the body and the room are there.
It is or was way more exhausting to keep the balance on a "shorter" bike how often did i found my self hanging over the bar under heavy braking or at steep stuff. And at jump or climing with to much weight on the rear getting into trouble.
What i like to say, there are not just different bike geometrys there are different riders and riding styles too.
I feel central and relaxed like175cm Sam Hill on his Nukeproof, when I ride those long bikes.
Maybe it is helpfull to add a variable for rider size to the model and put it into realation with the rider weight.
This new factor need to be taken into account to calculate the rider forces for example on the handle bar and CoM.
It is clear that your model 80kg rider will need less force on the bar to get the 50% an an size M Nukeproof Mega, than on a size L Geometron. But the model rider will probably also never fit on all of those bikes.
The other way around a 100kg rider who is hopefully taller, should put how much force on the handlebar of a Size M Nukeproof Mega to get 50% ? Is he even allowed to touch the bar ? ;-)
At 195cm I have no doubt that you'll benefit a lot from a bike that fits you well first and foremost, and I think the current trend of longer bikes overall is very good in that regard.
Longer reach does not require you to shift your weight forward more, it automatically forces you to do so. Your natural riding position (and cog) will be more forward, so you don‘t need to shift. Just a longer reach makes me struggle in the steeps, too much weight on the front. To unweigh the front you do need to shift your cog a lot. Me no liky. A slacker head angle helps to compensate in the steeps, bit the front unweigh problem remains. Just my thinkin and experience. But I do like the fact, that you are not a fan of those cruise ships...
I wouldn't say I'm not a fan of the long bikes. I'd actually personally like to try something with geometry fairly similar to the Machine but with a longer RC and slightly shorter (not much, just a bit) FC. It's not that the bikes suck, it's that their obvious advantages in a straight line (basically, better endo/looping angles) can in also make some things more difficult.
Though I'm curious about one thing. You mentioned that Sam Hill doesn't have to move very much to keep his weight balanced. While this is true, you seem to present it in a positive light, but I wonder if it might also be a negative?
Since the weight distribution on a short bike is more sensitive to CG motion, a rider on a short bike has less margin for error when moving, and might inadvertently transfer too much weight to either wheel. So a longer bike might be easier to ride, simply because the rider has more margin for error when moving around on the bike.
The point however was more to do with highlighting the fact that some bikes require you to load up your hands/arms more heavily to get weight on the front wheel than others do. Whether you see that as positive or negative is up for interpretation for sure, but I think we can all agree that higher load on the arms leads to more arm fatigue more quickly. As Leo pointed out in the Youtube comments though, that isn't necessarily the first thing to limit the rider though, like if your back or legs are getting tired before the arms then who cares about the arms - and that is also hugely dependent on the rider's physical strength, riding style and ability.
Ive been advocating for long chainstays for years, its all true.
This is why I love that the industry is trending towards the short seat tube model so people can choose a bike more on total fitment rather than just their leg length.
1. Steepen STA for better climbing --> effective top tube now too short
2. Lengthen reach to get ETT back to realistic numbers --> FC now really long
3. FC really long --> now harder to get enough weight on front wheel
4. Longer chainstays to get more weight on front wheel --> now it's hard to hop/manual
5. Raise BB to make manualling easier? --> now it feels less planted and doesn't corner as well
6. ????
7. Profit
Wondering if the rider would actually have to move his body less far forward to achieve the hand load required for 50% grip and if the rider might even have to move rearwards on the shorter reach bike to keep the 50% number.
Thanks!
Started riding a Turbo Levo a month ago, with short offset Lyrik 160 up front and I can’t get over how well it corners. 1230mm wheelbase, 455 chainstays static, so FC:RC = 1.7
Suspension feels incredible too, which I suspect is due to the much higher sprung:unsprung mass.
Hi Steve,
Did you feel like you gained anything in steep, straight line 'plow-ablity' going from the L to XL Patrol? What about when you went from the XL Patrol to L Deviate Guide; did you loose something?
It seems to me that the FC /RC ratio would be a trade off / continuum between these two traits: steep straight 'plow-ability' and flat cornering grip or is there a combination that you feel provides the best of both worlds in one package?
(I personally think for me part of the 'unicorn' factor also has to do mixed wheel size - 29" front and 27.5" rear but that's a whole other topic!)
Another great series!
Is there any method to find whether the spread is proper size?
Agree to not change arbitrarily between bikes however short stems are part of the concept of the new geometry. The stem length should be there (together with bar width and height) to adapt the spread of the bike to your height. It would be great to see a version 2 of the spreadsheet where those variables are adjusted to get a similar spread (which is what a tester would do in reality) and see the impact of the longer wheelbase/FC/RC while comparing bikes that all "fit" the same standard rider.
Cheers!
Could explain why people thought 29ers couldn't jump, or manual (front-heavy - long CS and steep HA). I personally dislike how the front wants to dive back to the ground if I don't "compensate" by shifting my weight way back on a drop, while others insist that all it takes is speed and the bike naturally flies straight...
I suspect that it's much more important to get everything centered around a rider's CoG when standing comfortably. The spread from this point determines freedom of movement as the bike pitches up and down (rider forward for climbs, rearward for descents). Move the seat forward to match the standing position, and optimize kinematics for that CoG... wouldn't this be the end game, becoming more about choosing wheelbase length and travel to adjust for the trail, your skill, and overall challenge levels?
Critical flaw in most designs could just be how designers plot the rider CoG to be forward of the hips while seated, rather than standing, also ignoring the bike's CoG. The M Spider 275c I rode had a nice bike CoG, forward of the BB just behind the forward shock mount, helping to feel balanced. Friend said similar of the Intense Primer. Despite how great I thought the Spider felt out of the saddle, I thought the saddle got in the way and didn't like how it rode in the saddle. Same with the med Jekyll 27.5, except the Jekyll sorely needed a steeper STA. Got my eye on a large La Sal Peak, after all I learned.
It's convenient that a lot of side photos of bikes have the cranks level, so I can measure the pixels from the forward pedal threads to each wheel axle, preferring the front to be a bit longer to account for the front shortening under compression, and the rear lengthening from the point 175mm forward of the BB.
I only have theories regarding where to place the handlebars and saddle, to also make it so I can save energy in the seated position too, able to switch to a more ideal position to adapt to the trail, minimizing the movement necessary to get into that new position. Practically means that the saddle is moved forward to under the standing position, so your butt is hovering over it. With droppers, you can just get that out of the way if you want to unlock your leg suspension travel. Also means more clearance for rear wheel travel. The reach # is what it is... don't need to have it at conservative numbers, like 440mm, since the need to position your weight back won't be necessary with a bike that is no longer nose-heavy. What matters is that you're relaxed in your neutral upright position, until you do need to shift back for an explosive technique--hard to do that when you're already stretched behind the saddle. Basically how I understand how this forward-geo trend is going.
Basically, need more bikes to gravitate towards this sweet spot. Some bikes, in certain sizes, are close. Tall people on medium travel 29ers might be comfy on their bikes that are already in the sweet spot. A lot of enduro bikes in Large hit the sweet spot. Would like more options to hit it...
CS length has gotten a lot of flak. People demand short, but I think if you can't get it any shorter, you can make the front center longer to balance it out. It's a waste to give these bikes traditional reach and head angles, just because those #s are what people are familiar with. 450mm chainstays would work great on a 1300mm WB bike. 460 maybe on a 1350mm WB bike. 420mm worked well on 1150mm WB bikes, just as 435mm CS 160mm FS bikes seem to be getting positive reviews with 1230mm wheelbase.