Summary of "The Fastest Tyre Width is NOT What You Think"

Overview

You arrive at the Silverstone Sports Engineering Hub for controlled tests comparing 28, 30, 35 and 40 mm road tires. Two main test methods were used: a wind tunnel (front wheel only) for aerodynamic drag, and a pedaling-efficiency rig to measure rolling losses and system power loss. Tests were run at two representative speeds: 30 km/h and 40 km/h.

Test setup

Tire model: PO Race TLR (with TPU inner tubes).
Pressures set using Silca’s pressure guidance optimized for speed.
Two rims used to explore rim/tire interaction:
- D50 rim — 21 mm internal (used for the 28 mm tire).
- Elite G45 — wider internal width, shallower depth (used for 30, 35, 40 mm).
Cross-tests: 28 mm was also tested on the wide rim; 30 mm was tested on the narrow rim to assess rim/tire pairing effects.
Speeds tested: 30 km/h and 40 km/h.

Wind-tunnel (front wheel only)

Why front-wheel-only tests

Removes rider motion noise.
Isolates the single biggest contributor to drag (front wheel).
Avoids the incorrect assumption that one-wheel results can be simply doubled for two wheels.

Key aerodynamic results

Lowest drag recorded: 28 mm on the narrow rim at 30 km/h — 7.857 W.
Order of increasing drag at 30 km/h:
1. 28 mm (narrow)
2. 28 mm (wide)
3. 30 mm (narrow)
4. 30 mm (wide)
5. 35 mm
6. 40 mm
Absolute differences at 30 km/h:
- Less than 1 W between 28, 30 and 35 mm.
- 2.4 W total increase from the best 28 mm setup to the 40 mm.
Results at 40 km/h:
- Same order, but penalties increased with speed.
- 28 and 30 within ~1 W of each other.
- 35 mm ≈ +2 W penalty (vs best).
- 40 mm ≈ +5.1 W penalty (vs best) — a magnitude that matters in racing.
Averaged aerodynamic penalties reported (aero only):
- 28 → 30 = +0.7 W
- 30 → 35 = +0.6 W
- 35 → 40 = +2.3 W

Pedaling-efficiency rig (rolling resistance + system losses)

Method

Logged rider power input and rear-wheel output.
Swapping tires isolates incremental losses attributable to the tire while drivetrain/system losses remain constant.

Key rolling-resistance results

Surprise finding: the 30 mm tire had the lowest measured power loss (better than the 28 mm).
Differences quoted:
- At 30 km/h: 30 mm lost 0.56 W less than the 28 mm.
- At 40 km/h: 30 mm lost 2.06 W less than the 28 mm.
Ranking by rolling losses: 30 (best) → 28 → 35 → 40.
Important: rolling-resistance differences scale to the bike (i.e., double for two wheels), so they have a direct and larger effect on total power than single-wheel aero numbers.

Combined (aero + rolling) — practical impact

On smooth roads at everyday speeds, aerodynamic differences between 28–35 mm are negligible; rolling resistance tends to dominate total losses.
Representative combined numbers reported:
- A pair of 30 mm tires versus a pair of 40 mm tires required about 19.5 W less power at 30 km/h.
- At 40 km/h the same comparison required about 24.3 W less power.
- The presenter also factored in aero differences depending on configuration: approximately +1.8 W at 30 km/h and +4 W at 40 km/h in some comparisons.
Practical takeaway:

A 30 mm tire strikes the best compromise for typical smooth-road riding at the speeds tested — matching or beating the 28 mm in total-efficiency tests while adding grip and comfort.
For rougher surfaces:
- Wider tires run at lower pressures will likely offer a net advantage because they absorb vibrations and reduce effective rolling losses on uneven roads.
- That effect is consistent with existing research but was not directly tested in this specific session.

Caveats and context

Results depend on many variables: rim/tire pairing, system weight, speed, road surface, tire pressure, puncture protection, and grip trade-offs. Small aero gains can be overwhelmed by wrong pressures or poor fitment.
Real-world corroboration: a previous 7 km on-road comparison (Connor and Ollie) reportedly showed a 28 mm tire beating a 40 mm by 18 seconds at equal power, indicating that large gaps can appear in certain setups and conditions.
Practical recommendation:
- If a 30 mm tire fits your frame and you ride mostly on smooth roads at moderate speeds, try 30 mm tires for a balance of speed, comfort, and grip.
- Use wider, lower-pressure tires for rough surfaces.

Presenters and sources

Video presenter: GCN Tech host (unnamed in subtitles)
On-site collaborators: Ollie (on-site collaborator); Connor (referenced for prior road test)
Testing partners/venue: Elite Wheels (wind-tunnel/testing partner); Silverstone Sports Engineering Hub
Equipment and tools: pedaling-efficiency rig; Silca tire pressure calculator (used to set pressures)
Tires/wheels tested: PO Race TLR (TPU inner tubes); D50 (21 mm internal) rim; Elite G45 rim