Thought Experiment: Where Is It Worth Saving Weight on a Trail Bike?

Trail bikes can be a strange proposition. The days of the sub-30lb goal seem to be shrinking into the distance in our mirrors as we move away from the notion that weight is one of the main parameters of performance.

The problem, if it even is a problem, is that the modern trail bike is simply so capable. Adding slightly heavier components to keep up with the bike's capabilities can be a slippery slope. First, it might be a burlier fork, then heavier tires, and maybe an insert. Before you know it, your trail bike is more of the broadsword than the rapier you imagined.

But where, if anywhere, is the place to save weight? What components yield the greatest ratio of performance per gram? For this article, I’ll be working within a certain brand's range to try and keep things consistent. Also, I’ll also often be going for top of the line equipment if only because it removes a variable when it comes to trimming excess weight. Also, for argument's sake, I’ll consider the total weight of the bike to be a respectable 14.5 kg (32 lb). I know it is something of a contradiction to have a set weight for a bike when we're talking about the changing components to alter the weight.

My last caveat is that this bike will be a trail bike that might be shorter on travel than its enduro counterparts but it’s still meant to be ridden aggressively on technical trails.

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Forks


In my experience, the trouble with aggressive trails bikes is that they often soon outstrip their fork, especially for heavier riders or those who have choppy terrain on their doorstep.

Of course, the slacker the head angle the more it requires in terms of stiffness. I've found that it tends not to be torsional stiffness that gets affected, so much as fore and aft stiffness and the front wheel wants to come underneath the headtube under heavy braking.

So, how much weight is added going from a RockShox Pike Ultimate to a Lyrik Ultimate?

Based on a 29” model, the weight penalty in itself is 238g. Going to a Zeb, should you really want to, would be a 398g increase. The travel can be adjusted internally, although it should be noted the Zeb would be at 150mm, where the Pike tops out at 140mm in the 29er.



What about Fox’s range? This time, let’s look at the claimed weight of their range going from the 34 to 38, again in 29”.

Starting with a weight of 1820g for the non-StepCast 34, going to a 36, would be a 330g increase. Should that not be aggressive enough it would be an additional 190g to go to the all-out 38 enduro fork. Again, you may well have issues with too much additional travel. The 34 has a maximum of 140mm, whereas the 36 has a minimum travel of 150mm and the 38 160mm.

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Shocks


Working with a 210x55mm shock, a Fox DPS, which is a particularly light monotube shock, weighs 278g. To add a piggyback with their Float X model would add 175g. If you wanted to go to a Fox DHX coil from the DPS, including an 450lb SLS spring, you would be looking at adding 485g.



And with RockShox, how do their weights stack up, especially within the trail-friendly Deluxe line? Working with a 210x50mm shock, a Deluxe Ultimate weight 340g. To add a piggy-back would add 113g. If you wanted to go to a coil shock, including 400g for a spring, you would be looking at 806g.

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Wheels


Using Hunt’s alloy wheel range and starting with their XC Wide 1647g wheels could be an option for trail riders trying to shed some weight. To go to their Trail Wide wheels would see a weight increase of 184g. To go all the way to the Enduro Wide wheelset from the XC Wide would be a difference of 503g.

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Tires


For the sake of simplicity, we’ll talk about tires as a pair. A pair of 2.4” Nobby Nics in the Super Ground casing weighs 1780g. To go for something more aggressive like the 2.35” Hans Dampf in Super Trail would see a weight increase of 370g. If you wanted to prioritise grip even further then a set of 2.4” Magic Marys, also in Super Trail, would see a weight increase of 660g over the Nobby Nics.

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Brakes


Some Shimano XT brakes, again as a pair but not including rotors come in two versions with two or four pistons. A set of two piston BR-M8100 weighs 571 grams.


With brakes, there is another large variable to change - rotor size. So, assuming we kept the weight the same but changed the rotor size what difference would there be?

Assuming the trail bike has 180mm as standard then a set of 180mm rotors is not only the smallest you can run but also means there is no need for adaptors. A set of Shimano XT RT86 six bolt rotors would weigh a combined 290g. A 200/180mm set up would weigh 63g more. A 200/200mm setup would weigh 126g more than the 180mm rotors.

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Drivetrain


Drivetrains are a little bit different in that they’re not so specific to a bike's intentions. If you do care though, how much weight can you save with a different drivetrain?

Of course, with drivetrains weight is far from the only indication of performance. Unlike the other products compared, where they all hold a similar place in the brand's product hierachy and cost similar amounts. But if you were interested, what would the difference be if we compare weight increase to cost reduction? For reference, a Deore groupset retails for $296, SLX for $410, XT for $612 and XTR for $1,375.



What about SRAM - what are the price and weight differences between mechanical and electronic gearing? Let’s look in particular at the recently released SRAM GX AXS and its mechanical counterpart.

The GX AXS derailleur and shifter weigh a total 522g and have an RRP of $600. The mechanical GX shifter and derailleur weighs 462 grams, including cable and housing and cost $170.

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Frame


So, what if you’ve gone for the burliest, and heaviest option for each part so far. If you were to change the frame itself what kind of weight differences are there typically? In this instance, let's look at a 29" Nukeproof Reactor in a size Medium.


So, essentially, going from a trail bike frame to a all-out super-enduro frame represents half of the change, in the context of the total weight of our bikes, from going between XTR and Deore.

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Where and why?

If it were my 14.5 kilogram trail bike, where do I think is the most efficient place, performance per gram, to make a bike more capable? It's a bit of a cop-out, but it really depends on where you're riding. Somewhere steep, my answer is brakes, somewhere rough, that changes to suspension...

If we set ourselves to goal of an aggregate 5% total weight gain then I would opt for:

Stopping Power (0.4% - 63g) - I think adding larger rotors improves the most performance for the smallest trade-off. 200/180mm rotors are a great compromise of power and heat management, even on two pots. They'll also combine with my next choice to yield greater performance yet. There's no point in have large amounts of braking power if you don't have any grip. I know four-piston brakes benefit those on long and arduous descents, but hopefully my large rotors will do a lot of the heavy lifting in that regard.

Goldilocks tires (2.6% - 370g) - Without a doubt, tires are one of the areas that can dictate a whole bike's performance. They're the bike's sole contact patch unless you opt to use your face, and all the burliest componentry in the world won't save you have no grip. However, they're also heavy and the weight can quickly add up. For general trail riding a middle-of-the-road tire, in this instance, a Super Trail Hans Dampf, offers a good blend of security, platform and tread depth. Trail bikes can end up chasing their own tail with heavy wheels and tires and lose the sharpness that makes them such a pleasure to ride in the first place.

A Stiffer Fork, in this case a Lyrik (1.6% - 238g) - With heavier braking and more grip, it might not be too long before you want a stiffer fork. I think that a burlier fork goes a long way to helping a bike feel consistent and planted on rough fast trails, especially when applying the front brake. However, I don't think any of the new larger-stanchioned enduro forks are ever really needed on a trail bike. Something such as a Lyrik or 36 is ample, especially with the Charger and Grip2 dampers being as good as they are. At just 1.2% a piggyback shock would be the next on the list but sadly it would take me outside my 5% weight change.


What didn't I chose?

I haven't gone for the most extreme option in any case. I know there is an argument to say that "travel weighs nothing", and although it's not something I disagree with, often the choices made to enable larger amounts of travel do add up in terms of weight. Although interestingly enough, not always on the frame.

This problem can be approached two ways - if you're somebody that runs downhill tires, inserts, a 38 and the biggest brakes you can find, then I see little point in opting for a shorter travel frame. By that point you've already chosen all the heavy bits, you may as well lean into it.


However, if you're never going to open the floodgates and run that sort of equipment then a trail bike with heavier parts as needed can make a wonderfully versatile bike.

When running heavier wheels it often isn't a noticeable performance change that you're chasing, and the benefit is normally increased resistance to damage. However, adding rotational mass can really compromise a bike's feel and turn a bike from a pleasure to a chore. For me, on a trail bike, I'd rather just take a measured approach when riding particularly rough trails and enjoy all the benefits that they can yield.

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Special thanks to Competitive Cyclist for helping me fill in the gaps for the one or two product weights that we didn't have on PB record.

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So, if we're trying to keep our weight as low as possible, where to spend and where to save? What has the bigger impact on performance? A large change like aggressive tires? Or a combination of changes like a piggyback shock, big calipers on larger rotors and a burlier set of wheels?

With 5%, or around 750g, what would you add to beef up this trail bike?

At what point are we selling ourselves short and start to think about looking at a more aggressive frame? Or are we looking for short-travel-pop rather than the brutish charms of a longer travel bike?