AXL vs CSL vs RSL: Where the Real Gains Start

TL;DR:

• CSL vs RSL: ~7% lower physiological cost on the same routes—this is the first big “you can feel it” step change.

• AXL vs CSL: ~2% additional gain (TSS and heart rate) — smaller on paper, but it shows up late in hard rides and in head/crosswinds.

• If you’re upgrading from RSL, CSL is the point where the bike suddenly feels faster for free. If you want every last watt and more stability at speed, AXL is the move.

  
  

Why We Ran This Test

No fluff here. We used the same rider, same roads, and the same tires with matched power targets. Our goal was simple: where does the performance curve actually bend? Is the jump from RSL to CSL bigger than from CSL to AXL? The short answer is yes. The 7% improvement we observed with CSL marks the beginning of the real gains. AXL adds another 2% on top—small, consistent, and meaningful.

What We Measured (And Why It Matters)

• TSS (Training Stress Score): This serves as a proxy for total load. A lower TSS for the same terrain and targets indicates a less physiological cost to go equally fast (or faster for the same cost).

• Average Heart Rate: While blunt, it is honest. A lower HR at matched power/pace means higher efficiency (aero + stability = fewer spikes).

  
  

Results (Headline): AXL delivered ~2% lower TSS/HR compared to CSL. CSL delivered ~7% lower TSS/HR compared to RSL.

If your typical long ride lands around 200 TSS, that’s ~14 TSS saved with CSL vs RSL, and ~4 TSS more saved with AXL vs CSL. It may not sound huge, but when stacked over blocks of training and races, it can be the difference between hanging on and having something left.

How We Tested (In Plain English)

• Routes: We selected repeatable mixed terrain with steady segments and exposed sections for crosswind handling.

• Control: The same rider position, same kit, identical tires and pressures, matched normalized power targets.

• Environment: Rides were completed in similar temperatures and wind conditions; outliers were excluded.

• What We Looked For: Changes in TSS, average HR, and the shape of the HR trace (spike control in gusts, surges out of corners).

  
  

CSL: The First Big, Feelable Step (≈7% vs RSL)

This is where the “wow” begins. Moving from RSL to CSL cut about 7% off the physiological cost for the same work. On the road, this looked like:

• Lower drift in HR as the ride progressed (less fade in the final hour).

• Fewer spikes when the wind shifted or the pace lifted—less “stomp and sit back down.”

• Easier to hold aero position because the front end wasn’t getting pushed around as much.

  
  

If budget or simplicity dictates “one upgrade,” CSL is the upgrade. It’s the point at which the bike starts feeling fast rather than simply light.

AXL: The Marginal Gains That Stick (≈2% vs CSL)

On paper, 2% doesn’t create a buzz on social media. However, on the road, it’s the difference between riding the line and owning it:

• Micro-spike control: In rolling terrain and gusty crosswinds, AXL smoothed the HR trace even more. Less wrestling means fewer anaerobic dings.

• Late-ride efficiency: That small percentage shows up when you’re already tired—making it easier to close moves or take longer pulls.

• Stability at speed: The calmer the front end, the more time you actually stay in position. That’s free aero.

  
  

If you’re chasing every watt or racing into the wind, AXL is worth it. It turns good days into banked days.

“What Do 2% and 7% Actually Feel Like?”

• 7% (CSL vs RSL): You notice it within 20 minutes. The same power feels easier; the bike surges cleaner; your HR isn’t climbing as quickly.

• 2% (AXL vs CSL): You notice it in the last 20 minutes. You’re still able to respond, and your HR doesn’t punish you for staying aero when the wind kicks.

  
  

Which One Should You Choose?

• RSL — Solid, durable, cost-effective. Great for training and rough conditions.

• CSL — Best value jump. If you’re on RSL and want to feel fast without stressing your wallet, start here.

• AXL — Top end. The last 2% that helps in real speed, crosswind stability, late-ride resilience, and—yes—race day.

  
  

Notes on Setup (The Boring Bits That Decide Results)

• Keep tires the same across tests; change the wheel, not the system.

• Pressure matters. Re-check between sets; a 5–7 psi swing can fake a “win.”

• Match the fit. If the front profile allows you to stay tucked longer, that is free speed—log it.

• Look at the trace. A calmer HR and fewer spikes are as important as the average.

  
  

Where We Go From Here

• We’ll publish the anonymized ride files with AXL, CSL, and RSL overlays so you can see the TSS and HR drift side-by-side.

• Next round: repeat the protocol in windier conditions and a short-course threshold loop to show the high-IF picture.

  
  

Honest Take

If you’re moving up from RSL, CSL is the redefining upgrade. It’s the first place the watts start “sticking.” If you’re already on CSL and you care about every marginal watt—especially in real-world wind—AXL earns its keep. The gains are smaller, but they’re there, and they show up when it counts.

Suggested Meta

• Title: AXL vs CSL vs RSL: Where the Real Gains Start

• Meta description: Our field data shows ~7% lower physiological cost moving from RSL to CSL, and another ~2% with AXL. Here’s what that means on real roads—and which one you should ride.

  
  

Optional Callouts to Drop in the Post

• Data bite: “On a 200-TSS long ride, CSL vs RSL saved ~14 TSS; AXL shaved ~4 TSS more—small numbers, big legs at the end.”

• Rider quote: “AXL didn’t feel ‘faster’—it felt calmer, which made me faster.”

  
  

PLUS AERO Testing: Videos + Open Data Start Now

We’re not guessing. We’re doubling down on testing—on camera—and releasing the raw files. The first insight already paid off: tyre pressure is a bigger lever than most riders think. Small changes there consistently moved TSS and average HR in the right direction across our loops. We’ll show it, not sell it.

What’s Coming (Short List)

• Tyre Pressure Series (3 videos): How we set it, how we verify it, and what it does to HR/TSS and speed on real roads.

• Hill-climb Protocol: Matched power, repeat climbs; time gaps + HR drift; CSL vs RSL vs AXL overlays.

• Wind Days / Crosswind Control: Calm vs gusty runs; stability notes + “HR spike count” as a fatigue proxy.

• Crit-style Loop: Short accelerations, corner exits; how each wheelset handles micro-spikes.

• Race Files Breakdowns: Anonymized laps with overlays for position time (how long you actually stay aero).

• Open Data Drop: .FIT/.CSV + a one-pager explaining exactly how to read the fields we reference.

  
  

The Tyre-Pressure Piece (How We’ll Show It)

• Same rider, same loop, same tires (width/compound), matched power, only pressure changes.

• Pre-ride calibrated gauge, post-ride hot pressure check (to confirm deltas were real).

• Report: avg speed at matched NP, TSS, avg HR, and spike count (>90% of max HR or >120% of target power).

• We’ll include rim/tire limits on screen—never exceed manufacturer caps; if you’re on hookless, respect your spec.

  
  

Bottom line: Pressure is “free speed” and “free freshness.” We found consistent reductions in physiological cost at sensible pressures without wrecking handling. Full numbers and files will be in the video description.

Conclusion: Where the Real Gains Start

The line is clear: CSL is the first big step—~7% lower physiological cost than RSL on the same routes, which you feel early and often. AXL adds ~2% more on top of CSL; smaller on paper, but it shows up when it counts—late in hard rides and in crosswinds—by keeping you calmer and in position.

What This Means for You

• On RSL and want a jump you’ll feel right away? Go CSL.

• Already on CSL and care about every marginal watt or windy-day speed? Go AXL.

• Don’t ignore tyre pressure—it’s free efficiency and stability when set sensibly.

  
  

We’ll keep publishing open numbers and files so you can see exactly what changes and by how much. If you’ve got a course, race, or setup you want us to test next, tell us—real roads, real data is the plan.