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Spotted: Giant Propel Disc prototype at the Tour de France

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The new Giant Propel Disc for Sunweb's Michael Matthews

The new Giant Propel Disc for Sunweb's Michael Matthews (Image credit: Ben Delaney/Immediate Media)
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Matthews' bike has Di2, but it looks like the Propel Disc could handle mechanical systems, too

Matthews' bike has Di2, but it looks like the Propel Disc could handle mechanical systems, too (Image credit: Ben Delaney/Immediate Media)
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Removing rim-brake calipers opens up frame design

Removing rim-brake calipers opens up frame design (Image credit: Ben Delaney/Immediate Media)
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Check out the enormous frame area above the bottom bracket

Check out the enormous frame area above the bottom bracket (Image credit: Ben Delaney/Immediate Media)
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Giant builds a speed/cadence sensor into the chainstay on many of its road bikes

Giant builds a speed/cadence sensor into the chainstay on many of its road bikes (Image credit: Ben Delaney/Immediate Media)
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Dura-Ace rotors only recently began to surface for the new 9170 group

Dura-Ace rotors only recently began to surface for the new 9170 group (Image credit: Ben Delaney/Immediate Media)
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Disc front wheels require more substantial spoke lacing than comparable rim-brake models

Disc front wheels require more substantial spoke lacing than comparable rim-brake models (Image credit: Ben Delaney/Immediate Media)
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Matthews' bike gets topped off with a portable charger plugged into junction box inside the handlebar's right end

Matthews' bike gets topped off with a portable charger plugged into junction box inside the handlebar's right end (Image credit: Ben Delaney/Immediate Media)
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The length of Matthews' stem nearly overshadows the substantial aero profile of the bar

The length of Matthews' stem nearly overshadows the substantial aero profile of the bar (Image credit: Ben Delaney/Immediate Media)
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What size is that stem? It's marked 120, but seems longer

What size is that stem? It's marked 120, but seems longer (Image credit: Ben Delaney/Immediate Media)
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Giant was one of the very first brands to use an integrated seatmast with the TCR

Giant was one of the very first brands to use an integrated seatmast with the TCR (Image credit: Ben Delaney/Immediate Media)
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Thru-axles with Allen bolts make for a clean look, but perhaps not the fastest wheel change

Thru-axles with Allen bolts make for a clean look, but perhaps not the fastest wheel change (Image credit: Ben Delaney/Immediate Media)
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Giant isn't yet talking about the new bike, but it's pretty clear what it is

Giant isn't yet talking about the new bike, but it's pretty clear what it is (Image credit: Ben Delaney/Immediate Media)
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See any wires or hydraulic lines? Neither does the wind

See any wires or hydraulic lines? Neither does the wind (Image credit: Ben Delaney/Immediate Media)
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Matthews was just setting up his bike Thursday, with a ride on bare bars to dial in the lever position. Note the Di2 junction box in the bar end

Matthews was just setting up his bike Thursday, with a ride on bare bars to dial in the lever position. Note the Di2 junction box in the bar end (Image credit: Ben Delaney/Immediate Media)
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It appears the top of the stem comes off for access to routing shift and brake lines

It appears the top of the stem comes off for access to routing shift and brake lines (Image credit: Ben Delaney/Immediate Media)
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This massive stem on Matthews' bike is alloy. It could still be in prototype form

This massive stem on Matthews' bike is alloy. It could still be in prototype form (Image credit: Ben Delaney/Immediate Media)
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While the frame is branded and looking to be production-level, the stem and handlebar reamin blank

While the frame is branded and looking to be production-level, the stem and handlebar reamin blank (Image credit: Ben Delaney/Immediate Media)
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Slam that stem

Slam that stem (Image credit: Ben Delaney/Immediate Media)
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The head tube looks wider than that of the current Propel

The head tube looks wider than that of the current Propel (Image credit: Ben Delaney/Immediate Media)
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Shimano Di2 sprint shifter clip onto handlebars, and can be wired into the shifter or a junction box

Shimano Di2 sprint shifter clip onto handlebars, and can be wired into the shifter or a junction box (Image credit: Ben Delaney/Immediate Media)
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Matthews checking out his new rig

Matthews checking out his new rig (Image credit: Ben Delaney/Immediate Media)

This article first appeared on BikeRadar.

Giant appears poised to launch a disc version of its Propel aero bike, given the machine that Team Sunweb's Michael Matthews is dialing in for the Tour de France.

The Giant Propel Disc frameset looks to be production-ready. The Propel Disc's striking stem – which encases the Shimano Dura-Ace Di2 wires and hydraulic lines – is unmarked and alloy, and may or may not be in final form.

While both Sunweb and Giant were tight-lipped about the bike, there are a few discernible points about the bike worth noting.

The original rim-brake Propel features a very slender, hourglass head tube. The Propel Disc has a stouter head tube, presumably for more front end lateral stiffness.

The down tube on the new Propel Disc is massive, as is the junction above the bottom bracket. Hello, frame stiffness.

And the top tube/seat tube junction takes on a larger, curving shape than that of its predecessor.

But perhaps the biggest change aside from the addition of hydraulic discs is the internal integration of shift and cable lines. On Matthews' bike, both the Di2 wires and the hydraulic hoses enter the handlebar just behind the hoods, then run through the stem and into the frame.

BMC's latest Teammachine SLR01 Disc has a somewhat similar design, where the shift and brake lines are secured and covered underneath the the stem before running into the frame. With the Propel Disc, the stem appears to have a top cover, accessible with four bolts. It seems likely that the bottom portion is the structural stem, with the lines sandwiched in between.

An Le, Giant's global marketing director, was vague when asked for details about the new bike.

"Giant is constantly working with our athletes to develop the best products to help them perform at the highest level," Le told BikeRadar. "For this year's Tour de France, we have worked with world-class riders like Team Sunweb's Michael Matthews to engineer and test the next generation aero race bike, with the goal of delivering a clear aero advantage in the sprints."

BikeRadar photographed Matthews' bike two days before the start of the Tour de France, just before Matthews and his teammates went out for a training ride. Mechanics had not yet installed handlebar tape, as Matthews wanted to make sure the levers and sprint shifters were positioned just right. And mechanics had not yet installed a power meter.

Stay tuned for more details as they become available.