All-new BMC Fourstroke XC race bikes add magical “Autodrop” seatpost

By jpmigny2020@gmail.com

October 5, 2022

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The brand new BMC Fourstroke household of cross nation bikes isn’t only one bike, it’s three analog bikes, from a World Cup-winning pure XC race machine to a correct path bike, with an reasonably priced XC mannequin sitting between them, plus a fourth mannequin to but to come back.

The headliner is the Fourstroke 01, with 100mm journey entrance and rear and an incredible new Autodrop built-in dropper put up that each raises and lowers on the press of a lever. Under which can be the usual Fourstroke (100mm journey) and the Fourstroke LT (120mm), which use customary dropper posts and decrease grade carbon, however share the identical geometry.

The purpose with the brand new vary was to hold ahead the innovation launched with the 2018 fashions, however enhance their capabilities for contemporary riders. For racers, that meant maximizing effectivity. For path riders, the brand new Fourstroke LT turns into extra user-friendly, higher geo, and longer dropper journey.

The prior Fourstroke XC bike was progressive for the time, with a 67.5º head angle, and launched an built-in dropper put up that was not solely distinctive for placing a dropper on an XC race bike, but in addition for being built-in into the body. It was additionally one of many first full suspension bikes making common rounds (and notching wins) on the World Cup circuit.

2023 bmc fourstroke LT light trail bike being ridden

The Fourstroke LT provides journey, retains the racy geometry and dealing with.

There was additionally the Fourstroke LT, which bought wider bars, greater tires, and totally different builds. It was meant for extra aggressive riders, however saved the RAD dropper, which restricted its utility as a correct “path” bike. It had 120mm journey, but it surely bought that from merely placing an extended stroke rear shock on there with a 120mm fork, which meant geometry wasn’t optimized for the longer journey.

The subsequent technology expands and improves upon the light-weight, race-oriented intentions with absolutely fashionable XC race bikes and one other actually distinctive built-in dropper seatpost…

2023 BMC Fourstroke 01

The brand new Fourstroke 01 is supposed to reinvent the cross-country class with up to date suspension kinematics, twin bottle cage mounts on the downtube, and … Autodrop, a dropper seatpost that may drop by itself, no want so that you can sit on it.

There are a variety of challenges with placing a dropper seatpost on an XC bike.

The primary is weight. Racers need the lightest weight system attainable, with some high execs even ignoring sponsor commitments to experience components (like a dropper) which can be lighter than what their sponsor might supply. By integrating the design into the body, BMC can scale back the burden by 50-100g (or extra) in comparison with a typical dropper.

2023 BMC Fourstroke 01 XC race bike tech details

The Autodrop seatpost saves weight and makes use of pressurized air to drop by itself.

The burden financial savings come by utilizing the body as a part of the put up, but in addition by going with an ovalized form. Moreover stopping it from rotating, it additionally saves weight as a result of they’ll reinforce it within the route of the load, however save materials elsewhere.

The opposite downside with droppers on XC bikes is that squatting to compress the put up wastes vitality. With fashionable programs and rivals pushing everybody to their absolute restrict, utilizing any quantity of vitality to regulate the bike is vitality not getting used to win.

Working with the athletes, like Titouan Carod, they discovered that racers would drop their put up 70 to 100 instances per race. That’s loads of squatting. He stated that not solely does the Autodrop put up save the legs that additional effort, it additionally lets them drop the put up on the final minute, letting them pedal proper up till it’s wanted.

internal parts for BMC Fourstroke 01 autodrop integrated dropper seatpost

Left to proper: The unique “air chamber” bottle subsequent to the carbon fiber chamber utilized in manufacturing; prototype dropper internals; and the ultimate manufacturing components.

So BMC checked out different vitality sources, and compressed air was the clear winner. It weighs nothing, and it really works. The trick was getting it into a motorbike’s body and making it work.

Their first check posts used a plastic soda bottle because the air chamber. As soon as that proved each dependable and purposeful, they labored on becoming it into the body.

Not like the previous Shimano Airways pneumatic shifting, BMC’s pneumatic system places the air tank contained in the body. In reality, it’s a carbon fiber tank that’s co-molded as a part of the downtube, saving weight. However sure, you’re basically inflating your downtube.

The tank could be crammed as much as 14 Bar (~200psi), so, sure, you’ll desire a good highway or observe flooring pump that may go that top if you wish to fill all of it the way in which up), however there’s a stress regulator to cut back it to 4 Bar (~58psi) to stop it from damaging the dropper meeting. The put up solely wants 4 Bar to drop itself.

How does the Autodrop seatpost work? What if I run out of air stress?

The very first thing to know is that this: It features like a standard dropper put up should you don’t pump up the Autodrop tank. Push the distant thumb lever and it releases so you may drop it by placing your weight on it. Press it once more and a coil spring pushes the put up up.

Or, pump up the tank and it’ll drop it for you should you push the distant lever only a bit additional.

The system will work all the way down to 4 Bar, and a totally inflated tank gives you about 100 drops. The air stress is ONLY used to drop the put up by itself. Principally, if you push the dropper lever all the way in which in, air fills a secondary chamber that presses towards the coil spring to compress it, and the put up drops.

The lever beneath the bar is the dropper distant. Push it calmly and it features like a standard dropper. Push it a bit farther in to activate the Autodrop.

Whenever you press the lever to boost the put up, the air in that second chamber is launched and the coil spring pops the put up again to full top. It’s a two-position system – up, or down, no intermediate stops – and it has 80mm of journey, which they discovered was acceptable for XC bikes.

Sure, they might have given it extra drop, however that may have used up extra air per drop, so the choice was made to restrict it to 80mm for all body sizes. That additionally permits a wide range of seat top adjustment, which is finished with a single Allen bolt set decrease on the seat tube.

And should you run out of air, the put up will drop and lift like a standard dropper put up, utilizing your weight to drop it, and the coil spring to boost it.

Can I service it?

Yep. Simply disconnect the air line by eradicating the rear wheel and come out the mini mud flap, launch the air stress, unscrew the stress discount valve, pull it out, lower the tube (don’t fear, there’s loads of additional tube, and so they promote it as a spare half) and you may pull your complete seatpost out to wash and lubricate it.

Or simply take it to your native store and ask them to comply with the easy 60+ step tutorial video. However severely, they are saying it’s not that sophisticated.

The entire thing solely weighs about 350g, which is on par with a number of the ultralight droppers on the market, however none of these can do what Autodrop does.

Dialing within the Geometry

After constructing a check mule with adjustable geometry, BMC settled on a 1-degree slacker (66.5º) head angle and barely longer attain.

The outcomes have been the anticipated longer, decrease, slacker updates. However the greatest change is a dramatically decrease BB drop of 53mm (9mm decrease than earlier than).

Their racers stated the decrease BB improved cornering on off-camber and flat sections and was definitely worth the commerce off of some extra pedal strikes right here and there.

Up to date Suspension Kinematics

For an XC bike, the Fourstroke’s really useful 30% sag is loads, but it surely permits them to supply nice small bump sensitivity.

The remainder of the design is lighter than earlier than, however they have been in a position to try this whereas preserving a twin linkage design. The place many manufacturers have gone to a linkage-driven single-pivot bike to avoid wasting weight, BMC examined that towards their APS twin linkage and the clock. Combining lap instances and energy meter knowledge, they discovered that their APS was a greater resolution, being loads environment friendly and sooner general.

Till now, BMC has used a vertical shock design, shifting inline with the seat tube. However they wished to provide riders the choice to run two bottles contained in the entrance triangle. So, they engineered round a horizontal shock working beneath the highest tube, which, usually, might permit some body sizes to suit a small bottle on the seat tube.

BMC is a design-driven firm, so not solely do the bikes have to carry out rather well, they should look good.

Two bottle mounting positions on the downtube FTW.

The brand new Fourstroke has a really low high tube and standover. And so they wished an almost straight downtube, with out making a “stomach” by having it jut out straight ahead from the underside bracket so as to add room.

Seems, they have been in a position to put 5 bottle bolts on the downtube to create room for 2 brief bottle stacked inline. Or, for the reason that decrease mount has three bolts, you may run a bigger bottle a bit of increased as much as make it simpler to achieve.

The entrance shock mount is alloy, bolted beneath the highest tube. This was intentional.

Slightly than bonding it or molding it out of carbon, utilizing a separate alloy half allow them to future proof it towards totally different shock designs, which they are saying they’ve already taken benefit of throughout improvement. All they should do is machine a brand new half to accommodate totally different shock volumes or lengths, and so they say that is one thing you’ll respect quickly due to issues they know are coming however received’t inform us about but.

The highest tube flattens on the underside to make room for distant cable attachment factors, adjustment levers, and so forth.

Making the Fourstroke extra attainable

With the prior technology, the RAD seatpost added appreciable value, however was the one choice. So, to make them extra reasonably priced, they needed to actually downgrade the spec.

With the 2023 Fourstroke, they’ve the 01 degree with three fashions (plus a frameset) that get the built-in Autodrop seatpost, and a normal vary that will get a normal spherical dropper seatpost with a decrease degree carbon fiber grade to provide riders on a price range the identical suspension and dealing with, however at extra attainable value factors. See full mannequin and spec lists at backside of this put up.

2023 BMC Fourstroke LT

Take virtually all the pieces in regards to the Fourstroke, tweak the higher APS linkages so as to add 20mm journey, give it barely extra aggressive spec, and you’ve got the Fourstroke LT.

The LT, for “lengthy journey”, has 120mm journey entrance and rear, however with geometry that’s 99% the identical because the Fourstroke. And that’s as a result of fashionable XC geo has gotten so aggressive, and plenty of manufacturers are pushing their XC race bikes to 120mm journey, so the LT is for that buyer that desires fast dealing with with a bit extra suspension.

Which means, it’s XC geometry and XC-efficient suspension, with XC weights, however with a bit extra journey. Suppose, marathons and epics and all day rides. Or, should you should, you may name it a quick “downcountry” bike.

bmc fourstroke and LT suspension linkage comparison

The 100mm Fourstroke’s higher linkage on the fitting, and the 120mm LT’s on the left.

And so they try this totally with the higher linkage – the entrance and rear triangle are the identical because the 100mm Fourstroke. The important thing distinction within the geometry is that it has a 38mm BB drop, 15mm increased than the 100mm journey model, serving to it deal with the additional journey with out taking the pedals too low. However they might hold the opposite angles equivalent, all by adjusting the place of the rear shock’s decrease mount.

It doesn’t get the Autodrop dropper seatpost of the Fourstroke 01 fashions. And, not like the prior mannequin’s RAD seatpost, which was restricted to 80mm drop, the brand new LT makes use of customary spherical dropper posts. Relying on body dimension, you’ll get 125mm to 150mm of dropper journey.

Key spec variations & body weight comparability

The entire bikes get 30mm inside width rims aside from the Fourstroke 01 TWO, which has alloy rims with a 25mm inside width…to avoid wasting weight on that mannequin, all others are 30mm inside no matter whether or not the edges are alloy or carbon.

The 100mm bikes include 29×2.35″ tires, the LT will get 29×2.4” tires. The utmost really useful tire width on any mannequin is 29×2.4″.

Different spec swaps for the LT embrace a low rise handlebar, angled stems, and 180mm brake rotors entrance and rear with four-piston brakes, and greater forks – Rockshox SID 35mm and Fox 34 Stepcast, relying on the mannequin.

In contrast, the 100mm bikes get SID SL or 32 Stepcast forks, flat handlebars, and 160mm rear/180mm entrance rotors on the entrance of the L/XL body sizes, however 16omm entrance and rear on S/M sizes (saves weight), with 2-piston brake calipers.

Each 100mm Fourstroke mannequin comes with twin distant lockouts for fork and shock, however the execution is totally different relying on spec. The Fox-equipped bikes get a DT Swiss three-position distant lever on high of the bar, above the dropper distant.

The Rockshox-equipped bikes get a a lot sleeker TwistLoc distant, a transparent win for each aesthetics and ergonomics.

Claimed body weight for the 01 frames is 2,172g, and claimed weight for the usual/LT frames is 2,130g. That’s with all {hardware}, however with out rear shock or rear axle.

Which means that the integral carbon fiber air tank constructed into the downtube with the pneumatic meeting solely makes the 01-level body 42g heavier. The result’s a module weight with dropper seatpost that’s almost the identical between fashions, so that you’re getting that superior function at no weight penalty.

2023 BMC Fourstroke Geometry, Fashions & Pricing

Full specs and particulars for all fashions are on BMC’s web site. The Fourstroke 01 TWO would be the first accessible and is delivery now. Others will come out all through the rest of this 12 months and even into Q2 2023…as a result of provide chain points.

Value noting is the inclusion of Prologo and Fizik saddles throughout the vary…no housebrand or generic brand’d saddles on any of the fashions at any value level. Vittoria tires are a pleasant contact on increased finish fashions, too.

BMC Fourstroke 01 fashions

Fourstroke 01 LTD
Spec highlights:

Fox Manufacturing unit 32 Stepcast fork and Float DPS shock
SRAM Eagle XX1 AXS
SRAM Degree Final brakes
DT Swiss XRC 1200 carbon wheels
€ 12,999.00 / CHF 13,499.00 / $13,499.00

This paint scheme can also be accessible as a frameset with the identical fork, shock, and the Autodrop system for €5,499.00 / CHF 5,999.00 / $5,999.00