How do you like your chain stays? Do you prefer short chain stays or a longer rear center? The chain stay debate is a never-ending quarrel, the dispute is heated, and the camps seem entrenched. Is there no middle ground? It is time to reconcile.
But first, let us draw the line (with a wink): The short chain stay stereotype is a rider who loves to pop off every trail feature he can. He will take every opportunity to manual and wheelie his bike, even in front of the proverbial ice cream parlor. He has a shrugging attitude towards crashing, and thinks that a more progressive geometry is a crutch for people who can’t handle their bike on the edge. He’s likely to have a BMX background or have spent his youth on a slope style bike. If he’d have a poster above his bed, it would feature Sam Hill.
The long chain stay stereotype is a rider who likes to go fast, really fast. He enjoys straight line shredding, but he’ll insist his bike corners better than yours, too. He’ll take every opportunity to point out that if you go fast (really fast), you need the stability his bike’s geometry brings to the table, and he thinks that if you’re not preferring long rear centers, you’re just a slow rider.
Of course, we’ll never know, but maybe the first (short chain stay) stereotype is a bit shorter in height than the second (long chain stay) stereotype – because, if you’re smaller, you’re likely on a smaller frame, and on a smaller frame, the short chain stays are less severe: The smaller your frame, the shorter your front center, and even if your chain stays are short, their less short in relation to the bike’s front center. But the larger your frame, the longer your front center – and, in turn, the shorter your rear center is in relation. So to some extent, this may be a debate of tall people and not-so-tall people, or, to put it in a better way, between people who tend to ride smaller frame sizes and people who tend to ride larger frame sizes.
Yes, we need a balanced ride – and the relation between front center and rear center length determines weight distribution. Your center of gravity is applied to the ground on a perpendicular path that extends from the bottom bracket. This means the steeper the terrain, the more the center of gravity shifts forward (on a descent), or backwards (on a climb). Mountain bike coaching has always emphasized adjusting body position to balance center of gravity, i.e. the steeper the climb, the more forward your body position, and the steeper the descent, the further backward you move. While that is good advice in general, it is more tricky than this. If you’re hanging off the rear on your bike, you lose control, front-wheel grip and braking traction. To alleviate this, geometry has evolved towards long-reach, slacker bikes – but it only works if your riding style fits: You have to deliberately work the front on a long-reach bike, and the shorter the chain stays in relation to the front center, the more aggressive your position has to be on the front.
Just when I was working on this article, I got an email from Neil, who rides a longest (= frame size large) Nicolai Geometron, a super slack bike with a 520mm reach, a 1313 wheelbase and 445 chain stays. He wrote he’s actually getting his chain stays switched to 450 – so he’s going even longer. If you look at the relation between rear center and front center, his idea starts to make a lot of sense, because in terms of balance, the Geometron’s rear center does not seem that long, actually:
|Bike||Frame Size||Rear Center||Wheelbase||RC % of WB|
|Specialized Enduro 26"||L||419||1183||35,4%|
Geometron’s rear center accounts for 33,9% of its wheelbase, and the Enduro’s chain stays make up 35,4% of its wheelbase. In terms of balance, the Enduro’s chain stays are slightly longer in relation to the bike’s overall length. Of course, the Enduro is a lot shorter than the Geometron, which has a massive wheelbase at 1313mm.
For quite some time, bikes have been getting longer in reach and slacker in head angle. Designers kept chain stays short to keep wheelbase in check and maintain slow-speed agility. Short chain stays have been the rave in bike design, and proponents argue they quicken cornering and provide a more playful and lively ride experience. Ever since, it seemed to be consensus that short chain stays are a desirable trait. Only a few people (e.g. Chris Porter of Mojo Suspension) spoke up, pointing out potential drawbacks and emphasizing the advantages of longer chain stays. Chris is actually one of the really lucky people who not only spoke out, but also got a bike specifically designed to fit him – Mojo teamed up with German Nicolai brand to create the Geometron, which set a new benchmark in the slack & long department.
Recently, the long rear center proponents get heard a lot more, which may be attributed to a side effect of the current bike geometry trend: We now have the slacker, longer bikes, and if you leave chain stays unchanged, they become shorter in relation to the whole bike. Perhaps it is time to embrace balance and design rear centers with front centers in mind.
Yes, you can enjoy short and long rear centers – both come with strengths and weaknesses, and in my opinion, it is not fair to claim otherwise – there’s still no silver bullet in mountain bike geometry, and what works for one rider’s style and terrain may be less ideal for another.
But geometry always pursues an ideal (not only referring to bikes), and in my opinion, the ideal should aim at balance and weight distribution. It is common sense that in order to maintain balance, if you increase front center, you need to increase rear center, as well. Which brings us back to rider height and frame sizes:
I firmly believe that chain stays should grow with frame sizes: As you step from an M frame to an L frame, front center increases, and so should rear center. What Norco calls „Gravity Tune“, and what only a few other companies (e.g. Liteville and YT Industries lately) are doing should be the standard for all mountain bikes.