What is the Giant Propel?
The Propel is Giant's latest aero road bike.
It is the product of Giant's constant pursuit of lighter, faster, stiffer and smoother.
Buzz words? Yes, we know.
But true and applicable to the latest Giant Propel nonetheless.
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Giant Propel Advanced Disc Fork 2018 OD2 Aero Black Green (Used)
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![Giant Propel Advanced SL (2025) Frameset]()
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Will you love the Propel?
Yes, if you love to ride fast and red-line it.
Can we also just add that it won't make you significantly faster (definitely a little though).
It's not a reverse aging potion.
It won't make you feel 18 years old again.
It won't make you feel like you've got quad-zilla legs.
But if you've already got good bike handling skills, flexibility and
strong foundational fitness, the Propel will compliment your riding and help you reach the next level.
More versatile than ever before.
One gripe with the old Propel is that it's so specific in what it could do and where you could use it.
Not this one.
Slightly dropped stays and thinner tube sections help reduce road buzz.
And the ability to fit wider tyres (up to 30mm) paired to wider rims makes it so much more comfortable to ride.
Plus, with a frame weight of 845g (Propel Advanced SL, MD) it's one of the lightest aero bikes too.
This makes riding the occasional ride with serious vertical far more enjoyable.
In all, it's a far better all-rounder than the old Propel and most other aero bikes.
Look. It's very aero.
Giant’s approach to aero for the new Propel has been a holistic “system” approach.
The system includes the wheels, tyres, bars, stem, brakes, water bottle cages (yup, you read that right) and frame.
Each of these components had to help minimise drag - NOT just the frame.
Step #1
Create a CFD (computational fluid dynamics) model to simulate airflow and determine areas of drag.
Truncated ellipse airfoil shapes used in the downtube, seat tube and seat stays help make the new Propel faster.
Step #2
Create physical forms so that above CFD models can be tested in a wind tunnel.
Let’s pause here for a sec.
Giant uses a dynamic mannequin that is pedaling at 90rpm to get close to real-world conditions.
Most brands use a static mannequin.
Your (moving) legs create a very different airflow pattern that needs to be accounted for.
Additionally:
The wheel speed is kept consistent at 40km/h and drag was measured at different wind (yaw) angles ranging from +20 degrees (rider’s left side) to -20 degrees (rider’s right side).
Step #3
Work with aerodynamicist at Immenstaad (Germany) at the GST Wind Tunnel to create the final form.
More aero stuff.
The frame done, Giant moved to peripheral components:
- The water bottle cages are 2 different sizes - one specifically designed for the seat tube and down tube.
- SLR (carbon) Aero bar and stem are redesigned for smoother air flow (and easier adjustability).
- Even the wheels - the latest CADEX Aero 50 and CADEX Aero tyres - help reduce drag.
These use beautiful bladed carbon spokes and ultra low friction hubs and a super fast 40T engagement system (only on the SL 0 model).
Stiffness + Weight makes (or breaks) Efficiency
Efficiency here relates to the new Propel stiffness and weight (or stiffness-to-weight ratio).
Stiffness first.
There’s Bottom Bracket stiffness and Frame stiffness.
Bottom bracket stiffness measures how much this area flexes under power.
More flex = more wasted energy.
Frame Stiffness:
Takes into consideration the frame and front fork.
It measures how much the total frame flexes.
More flex = bad handling - especially in corners where the frame is loaded the most.
BB Stiffness is 7.5% higher. Frame Stiffness is 9.2% higher.
Both significant increases.
Then there’s the Propel’s weight - or lack of it. It’s 225 grams lighter than the outgoing version.
A brand new carbon layup and architecture + the best carbon Giant can make (Advanced SL) and new tube profiles has resulted in such a significant weight reduction.
The bare frame weighs 845 grams - phenomenal.
Add the increase in total system stiffness of 20.26 N.m/degree.
All this stuff results in a 26.4% improvement in the Propel’s stiffness-to-weight ratio (or its Efficiency).
Comfortable (for an aero bike).
Speed at the expense of comfort is not sustainable - even for the Pros.
The complete backend looks nothing like its predecessor.
A slimmer top tube, seat tube and chain stays deliver a lot more compliance from the rear of the bike.
More frame clearance is added to accommodate 30mm wide tyres (more air volume).
It’s an 85% increase in compliance compared to the old Propel.
The extra compliance not only delays the onset of fatigue, it also improves road handling (think micro-suspension).