Bike purchase Howto’s¶
These are excerpts from AI chatbot, helping me choose my next bike.
🚲 The Situation¶
I wanted a fast, durable bike that could handle occasional loads and rough roads, and I was stuck between two models: the Giant FastRoad 1 and the FastRoad SL 1. What started as a simple A vs B comparison quickly evolved into a deep dive — gearing, cadence, bike geometries, gravel vs road options, warranties, and even internal cable routing.
Here’s how the conversation unfolded. It’s not a polished buyer’s guide — it’s a record of a real Q&A. You might find it useful if you’re in a similar spot.
🤔 Initial Comparison: FastRoad 1 vs FastRoad SL 1¶
Q: What are the key differences in specs and reliability?
A:
FastRoad SL 1:
50/34T chainrings, 11-speed Shimano 105 drivetrain
Lighter ALUXX SL frame (~10.2 kg)
Internal cable routing
FastRoad 1:
50/34T, 10-speed Shimano Tiagra
Standard ALUXX frame (~10.5–10.8 kg)
External cable routing
Verdict: SL 1 is a bit lighter and has a higher-end drivetrain. Both are good in terms of durability.
⚙️ Speed vs Cadence: Where Do I Stand?¶
Q: I currently ride a 700c, 42T crankset, 7-speed Shimano Tourney setup. I can hit 39 km/h — what cadence does that imply?
A: We modeled it:
With a 42/13T gear at ~95–100 RPM, you hit 39 km/h
Confirmed with speed-vs-cadence plots (see below!)
📊 Plot: Speed vs Cadence for Current Bike¶
(Your current setup vs potential upgrade scenarios)
⚖️ Formula Used to Estimate Cadence:¶
Cadence is calculated using:
Cadence (RPM) = (Speed * 1000) / (Wheel Circumference * Gear Ratio * 60)
Where:
Speed in km/h
Wheel circumference in meters (700x28c ≈ 2.096 m)
Gear ratio = front_chainring / rear_cog
♻️ What Happens With a 50T Chainring?¶
Q: What if I switch to 50/11T like the FastRoad SL 1? How much faster can I go at the same cadence?
A:
At 96 RPM (your estimated peak), you’ll hit ~55 km/h with a 50/11T
That’s ~16 km/h faster than current setup, without spinning faster
📊 Plot: Speed vs Cadence (Including FastRoad SL 1)¶
🔢 Formula Used to Estimate Speed:¶
Speed (km/h) = Cadence * Gear Ratio * Wheel Circumference * 60 / 1000
🤭 Exploring Drop-Bar Alternatives¶
I also wanted drop-bar options with:
Crank size ≥ 50T
10+ speeds
Rear rack option (even if occasional)
Slightly wider tires for rough roads
📋 Models Considered¶
| Model | Gearing | Weight | Notes |
|---|---|---|---|
| Giant Contend AR 3 | 50/34, 11-34 (2x8) | ~10.4 kg | Endurance geometry, rack mounts, disc brakes |
| Trek Domane AL 4 | 50/34, 11-speed Tiagra | ~10.3 kg | Hidden routing, full rack/fender mounts |
| Cannondale Synapse 1 | 50/34, 11-speed | ~10.2 kg | Alloy, endurance ride, rack-ready |
| Genesis CDA 20 | 46/30, 9-speed Sora | ~11.4 kg | External cables, steel frame, touring-ready |
🏷️ Warranty Considerations¶
| Brand | Frame Warranty | Notes |
|---|---|---|
| Giant | Lifetime | For alloy frames, original owner |
| Trek | Lifetime | Alloy & carbon included |
| Cannondale | Lifetime | Must register within 30 days |
| Genesis | Lifetime | Steel and alloy frames covered |
All offer solid lifetime warranties for original owners. ✅
🔧 Internal vs External Cabling¶
| Type | Pros | Cons |
|---|---|---|
| Internal | Clean look, aero, protected | Harder to service, costlier repairs |
| External | Easier maintenance, DIY-friendly | Exposed, messier appearance |
If you value aesthetics and don’t mind shop servicing: internal. If you’re more hands-on or going long-distance: external.
📃 Racks & Load Handling¶
Even the performance models like FastRoad SL 1 support:
Rear rack mounts on seatstays/dropouts
Fender mounts
✅ All shortlisted bikes support rear rack use — suitable for occasional loads.
📊 Sizing: What Fits a 171 cm Rider?¶
| Model | Suggested Size |
|---|---|
| Giant FastRoad (1/SL 1) | Small |
| Giant Contend AR 3 | Small |
| Trek Domane AL 4 | 52 cm |
| Cannondale Synapse | 51 or 54 cm |
| Genesis CDA 20 | Small / 52 cm |
Try before buying if possible — some brands size large (like Giant).
🧠 Final Takeaways¶
✅ FastRoad SL 1 offers better speed at same cadence, lighter frame, and mounts.
🛠️ Genesis CDA 20 shines for self-maintainers, simplicity, and steel comfort.
📏 At 171 cm, you’re comfortably in Small/52 territory across brands.
💡 All options allow some form of light touring or rack setup.
📂 Appendix: Cadence to Speed Code (Python)¶
import matplotlib.pyplot as plt
import numpy as np
# Cadence and gear setup
cadences = np.arange(40, 130, 5)
wheel_circumference_m = 2.096 # 700x28c approx
# Gearing options
gear_ratios = {
"42/13": 42/13,
"42/12": 42/12,
"50/11": 50/11
}
# Plot speed vs cadence
for label, ratio in gear_ratios.items():
speed_kmh = cadences * ratio * wheel_circumference_m * 60 / 1000
plt.plot(cadences, speed_kmh, label=f"{label} (ratio {ratio:.2f})")
plt.title("Speed vs Cadence")
plt.xlabel("Cadence (RPM)")
plt.ylabel("Speed (km/h)")
plt.legend()
plt.grid(True)
plt.tight_layout()
plt.show()
📢 Share the Ride¶
I hope this conversation helps someone else starting their cycling journey — feel free to fork it or reuse it! 🚴♂️
Got suggestions or corrections? Open a pull request on GitHub or reach out on the discussions tab!