---
title: PLUS Aero Wheels blog hand built in South Africa
description: "Here it is to copy:\n\nTips, tech and ride tests from PLUS Aero Wheels. Hand-built carbon road and gravel wheels, made for South African roads."
image: https://www.plusaerowheels.com/hubfs/Snapshot_20261109074843.jpg
---

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# From our earlier development context, this may relate to your PLUS wheels, but I haven’t assumed that is the target.

![Snapshot\_20261109074843-1](https://www.plusaerowheels.com/hs-fs/hubfs/Snapshot_20261109074843-1.jpg?width=2000&height=1125&name=Snapshot_20261109074843-1.jpg "Snapshot_20261109074843-1")

# Executive summary

- **Rim depth alone does not determine aerodynamic performance.** Rim profile, outer width, tyre profile, measured mounted width, spoke design, yaw angle and tyre surface all matter.
- **The tyre–rim interface is critical.** A nominal “28 mm” tyre may measure materially wider or narrower depending on the rim’s internal width, casing and pressure.
- **Deeper rims generally increase side force as well as reducing drag**, so the fastest wind-tunnel result is not automatically the easiest or safest setup to control.
- **Front and rear wheels should not necessarily use identical priorities.** The front wheel is more influential on steering feel and crosswind confidence; the rear can often accommodate a wider, higher-volume tyre for comfort and surface performance, provided compatibility and clearance are verified.
- **There is no universal “best” tyre width, rim depth or 105% rule.** The suitable combination depends on speed, wind exposure, road surface, rider mass, tyre construction, rim geometry and handling preference.
- The PLUS Aero background article correctly emphasizes these interactions, but its indexed contents do **not** constitute independent aerodynamic test evidence.1

| Topic | Evidence type | Main finding | Important limitation |
| --- | --- | --- | --- |
| Tyre width, rim width and rim depth | Measured wind-tunnel test | Crane and Morton tested six wheels and five tyres; drag linked to tyre-to-rim width ratio; side force mainly from rim depth. | Only tested combos; not for modern wide rims or other tyres. |
| Tyre surface and yaw | Measured wind-tunnel force and PIV test | Jux et al. tested 62 mm rim with three tyres; tyre surface changed separation, stall and drag (0.96, 0.67, 1.11 N). | One rim, one speed, isolated wheel; best setup uses a seam that would wear. |
| Rim design and crosswind | Measured wind-tunnel test | Tew and Sayers: aero wheels cut axial drag up to 50% vs tested spoked wheel, but side force rose. | Historical designs; not a ranking of current carbon wheelsets. |
| Whole bicycle and handling | Measured wind-tunnel test | Barry et al.: wheel type changed drag, side force, yawing and roll moments; drag alone is insufficient. | Applies to their bicycle, mannequin, wheels and tunnel only. |
| Wheel and ground modelling | Validated CFD study | Ground-contact modelling alters predicted wheel forces; their model needs ≤10 mm wheel–ground clearance. | Methodology result, not a consumer wheel comparison. |
| Mounted tyre width | Manufacturer technical documentation | Continental: 28 mm GP5000 S TR measures 28.8 mm on 21C, 29.6 mm on 23C; width shifts ≈0.4 mm per 1 mm rim change. | Manufacturer-specific; width still varies by model, pressure, casing and use. |
| Nominal versus actual size | Manufacturer technical documentation | Schwalbe: tyre width varies with rim width, pressure, time and casing; pressure and casing affect final width. | Guidance only; not an aerodynamic measurement. |
| Compatibility and pressure | Manufacturer safety documentation | Continental, Schwalbe and ENVE require checking tyre and rim limits; lower pressure limit rules; hookless needs compatible TLR tyres and widths. | Maker-specific instructions; do not prove compatibility for a PLUS wheel model. |

## Commercial interests

- **Crane and Morton:** academic wind-tunnel study; the abstract identifies NSERC funding.
- **Jux et al.:** university research from TU Delft; the work uses a commercial DT Swiss wheel and Continental tyres but is not presented as a manufacturer product ranking.
- **Tew and Sayers / Barry et al.:** academic or research-group testing with specified test equipment.
- **Continental, Schwalbe, ENVE and SILCA:** commercial technical guidance. Useful for compatibility and explaining design principles, but their recommendations and marketing claims should not be treated as independent validation of a universal aerodynamic rule.
- **PLUS Aero:** its public product pages list wheel dimensions and “tubeless ready” status, but I found no independent wind-tunnel dataset for the current PLUS models.

Rim depth, rim profile and external width

### **Rim depth**

A deeper rim can reduce aerodynamic drag by presenting a more streamlined shape to the flow. However, the same additional area can increase lateral force in crosswind.

The strongest direct evidence is not “deeper is always faster”; it is:

1. Different rim geometries have different drag curves.
2. Side force generally increases with the aerodynamic depth and projected area of the rim.
3. Drag and handling vary with yaw angle.
4. A wheel that performs well at one yaw angle may not be best when evaluated over a realistic distribution of yaw angles.

Tew and Sayers measured reductions of up to 50% in axial drag compared with their tested conventional spoked wheel, but also reported increased side force. That is a **wheel-level, test-specific comparison**, not a claim that every modern deep wheel saves 50% against every shallow wheel.

### **Rim profile**

Labels such as “U-shaped,” “V-shaped” or “toroidal” are not sufficient to predict performance. The relevant geometry includes:

- maximum external rim width;
- location of maximum width;
- curvature from tyre to rim;
- tyre protrusion above the rim;
- spoke and nipple shape;
- brake-track or bead-seat geometry;
- surface texture;
- front versus rear wheel environment.

A wide rim can help smooth airflow from the tyre into the rim, but only if the particular mounted tyre produces a compatible shape. A wide internal rim may also make the tyre wider, which can reduce the aerodynamic benefit if the outer rim is no longer sufficiently wider than the tyre.

### **Internal versus external rim width**

These dimensions must not be confused:

- **Internal width:** bead-seat or bead-hook spacing. It changes tyre volume and mounted width, and affects tyre support and pressure behaviour.
- **External width:** the outside width of the rim. It is the dimension more directly relevant to the tyre-to-rim aerodynamic transition.
- **Measured tyre width:** the actual width of the inflated tyre on that specific rim, at a stated pressure and after allowing for casing settling.

A “28 mm tyre on a 25 mm internal rim” is not enough information to determine the aerodynamic shape. You also need the tyre model, measured width, external rim width and pressure.

### **The “Rule of 105”**

SILCA describes the 105% rule as a rule of thumb from earlier wind-tunnel work: external rim width should be at least 1.05 times the **measured** tyre width.

This is useful as a screening criterion, not a law of physics. Its limitations are important:

- it originated from particular historical wheel and tyre combinations;
- it does not describe the complete rim profile;
- modern rims and tyres may behave differently;
- compliance does not guarantee low drag;
- violating it does not establish a specific watt penalty;
- the rule should use measured mounted width, not the tyre’s sidewall label.

Tyre width, measured fit and pressure

### **Nominal width is only a starting point**

A tyre marked 28 mm may measure approximately 27–30 mm or more depending on rim internal width, tyre casing and bead construction, inflation pressure, tyre age and casing stretch, tread or sidewall shape, and manufacturing tolerance.

Continental’s published example illustrates how rim internal width affects mounted tyre width:

| **Nominal tyre** | **Rim internal width** | **Published mounted width** |
| --- | --- | --- |
| GP5000 S TR 28 mm | 19C | 28.0 mm |
| GP5000 S TR 28 mm | 21C | 28.8 mm |
| GP5000 S TR 28 mm | 23C | 29.6 mm |

This is why aerodynamic comparisons should identify the measured inflated width, not simply refer to a “28 mm tyre.”

### **Recommended measurement protocol**

For a meaningful setup comparison:

1. Confirm the tyre and rim are compatible.
2. Mount the tyre on the exact wheel.
3. Inflate to the intended operating pressure.
4. Allow the tyre to settle, preferably for at least several hours or overnight.
5. Measure at the widest point using calipers.
6. Record front and rear separately.
7. Record pressure, rider mass, tyre age and whether the setup is tubeless or tubed.
8. Recheck clearance at the frame, fork, brake and mudguard.

Pressure can change both tyre width and aerodynamic behaviour. SILCA reports that, for some older combinations, pressure changes caused differences of roughly 1–9 W at 10–20° yaw. This is a commercially published, setup-specific result, not a universal pressure penalty; its main value is to show that pressure can alter the tyre–rim geometry enough to matter.

### **Front and rear tyre widths**

There is no general evidence-based rule that the same nominal tyre width should always be used front and rear.

A practical starting principle is:

- **Front:** prioritize steering feel, crosswind confidence, fork clearance and a clean tyre–rim transition.
- **Rear:** consider a slightly wider or higher-volume tyre where extra load support, comfort and rough-surface grip matter more, provided the rim and frame are compatible.

A wider rear tyre may bring rolling-resistance or comfort benefits on rough surfaces, but it should not automatically be assumed to be aerodynamically faster. Conversely, narrowing the front tyre solely to meet a ratio can reduce comfort, grip or confidence.

The PLUS Aero background material makes the same practical distinction: width, casing, pressure and surface should be considered together rather than treating width alone as decisive≥

Yaw angle and crosswind handling

## **What yaw means**

Yaw angle is the angle between the bicycle’s direction of travel and the apparent wind.

For example, with:

- riding speed: 40 km/h;
- direct crosswind: 10 km/h;

the approximate yaw angle is:

β = tan−1(10/40) ≈ 14°

That is why a wheel tested only at 0° yaw does not represent all real riding conditions.

Yaw depends on:

- bicycle speed;
- wind speed;
- wind direction;
- gusts;
- terrain exposure;
- rider direction changes.

At higher riding speed, the same crosswind generally produces a smaller yaw angle. At lower speed, the same wind can produce a larger yaw angle and stronger handling disturbance.

## **Drag versus side force**

A wheel can show low axial drag while producing substantial side force. Side force can create:

- steering torque at the front;
- yawing and roll moments on the complete bicycle;
- sudden changes in rider correction demand;
- reduced confidence in gusts or exposed roads.

Barry et al. explicitly found that wheel type affected not just drag but also side force, yawing moment and roll moment. The practical implication is that “fastest in the tunnel” and “best for the rider’s route” are not necessarily identical.

No wheel can be guaranteed to be crosswind-safe for every rider or weather condition. Rider mass, grip position, road camber, gustiness, backpack or clothing, and experience all affect handling.

Rolling resistance, comfort and surface conditions

Aerodynamic drag is only one part of real-world performance.

At roughly 40 km/h on flat terrain, aerodynamic drag can dominate total resistance, but this does not mean that an aerodynamic tyre–rim combination is always fastest over a complete route. Rough surfaces introduce vibration and tyre deformation losses. A tyre that is slightly less aerodynamic may be faster overall if it:

- reduces vibration;
- maintains better contact over broken surfaces;
- permits a lower pressure without rim strikes;
- improves grip and cornering confidence;
- allows the rider to maintain position and speed.

Evidence on rolling resistance does not support the simple statements “wider is always slower” or “wider is always faster.” Rolling resistance depends on tyre construction, compound, pressure, vertical load, casing losses and surface.

A field-oriented test by Wheel Energy, reported by Velo, compared tyres of different widths and pressures on a Zipp 303 setup. It is useful as practical testing but is not a peer-reviewed universal model.

The current evidence supports this practical tradeoff:

- smooth, high-speed road: aero matching may be more valuable;
- broken urban tar: pressure and casing compliance may offset a small aero difference;
- rough gravel: comfort, puncture protection, support and control usually deserve priority over a narrow aero target;
- wet or loose surfaces: grip and predictable handling take precedence over marginal drag reduction.

6\. Watt comparisons: what can and cannot be claimed

### **Reported measured comparisons**

The studies above mostly report:

- drag force;
- coefficient of drag area;
- side force;
- wind-averaged drag;
- force or moment curves.

They do **not** provide a universal “this wheel saves X watts” answer.

Examples:

- Tew and Sayers reported up to 50% lower axial drag than their tested conventional spoked wheel, but also higher side force. The comparison is wheel-only, with specific historical wheels and test conditions.4
- Jux et al. reported wind-averaged isolated-wheel drag values of 0.67–1.11 N for three tyre configurations on a 62 mm rim. These are forces at 45 km/h with a specified wind-averaging method, not whole-bike power savings.5
- Their 33% wind-averaged drag difference between the best and smoothest tested tyre configuration is a **wheel-only comparison under the study’s modelled wind distribution**, not a 33% reduction in total bicycle power.5

### **Converting a measured CdA difference to power**

If a study reports a change in aerodynamic drag area, the aerodynamic power difference can be estimated using:

\\\[\\Delta P = \\frac{1}{2}\\rho v^3 \\Delta C\_dA\\\]

where:

- \\(\\rho\\) = air density;
- \\(v\\) = ground-relative air speed;
- \\(\\Delta C\_dA\\) = measured change in drag area.

**CLEARLY LABELLED ILLUSTRATION, NOT A TEST RESULT**

Assume:

- air density: 1.225 kg/m³;
- speed: 40 km/h, or 11.11 m/s;
- wheel-only \\(\\Delta C\_dA\\): 0.005 m².

Then:

\\\[\\Delta P \\approx 4.2\\text{ W}\\\]

If the wheel-only \\(\\Delta C\_dA\\) were 0.010 m² under the same assumptions:

\\\[\\Delta P \\approx 8.4\\text{ W}\\\]

These values are **illustrative calculations**, not claims about a particular PLUS, ENVE, Zipp or other wheelset. They also omit:

- rider and frame drag;
- drivetrain and rolling resistance;
- yaw-angle distribution;
- gusts and turbulence;
- acceleration and climbing;
- changes in rider position;
- differences between isolated-wheel and whole-bike testing.

A wheel-level power saving cannot be presented as a whole-bike saving unless the test reports the complete bicycle system or the wheel’s measured \\(\\Delta C\_dA\\) is explicitly inserted into a whole-bike model.

### Compatibility and Pressure Requirements

Before giving specific tyre recommendations, verify all of the following for the exact wheel model:

1. Hooked or hookless rim construction.
2. Tubeless-ready requirement.
3. Approved minimum and maximum tyre widths.
4. Rim internal width.
5. Rim external width, if evaluating aerodynamic matching.
6. Maximum rim pressure.
7. Maximum tyre pressure.
8. The lower of the tyre and rim pressure limits.
9. Frame, fork, brake and mudguard clearance.
10. Rider-plus-bike system-weight limit.

Manufacturer guidance is consistent on the key safety principle:

- Continental: check tyre and rim limits separately; follow the lower pressure limit.3
- Schwalbe: hookless rims require compatible TLE/TLR tyres and specified minimum widths; the rim pressure limit must be followed.6
- ENVE: approved tyre lists and pressure limits vary by wheel model and internal width; an unlisted tyre is not automatically confirmed compatible.7

PLUS Aero’s public product pages identify several road and gravel wheel dimensions and state that its wheels are tubeless ready. For example, the PLUS gravel range lists:

- GSL: 45 mm deep, 36 mm external, 30 mm internal.8
- GSL-54: 54 mm deep, 38 mm external, 32 mm internal.8
- GSL-R 59: 59 mm deep, 42 mm external, 36 mm internal.8

The road range includes 40–50 mm wheel options. However, the public pages I found do not provide a complete tyre-by-tyre compatibility table or pressure chart for each model. Therefore, those dimensions should not be treated as sufficient confirmation for a specific tyre setup.

## Qualified setup recommendations

**Fast road riding on smooth surfaces**

A reasonable starting strategy is:

- choose a moderate-to-deep front rim if the rider is comfortable with its side-force behaviour;
- match the rim’s external width to the measured inflated tyre width;
- measure the tyre on the actual rim rather than relying on the sidewall label;
- use a fast, compatible tubeless road tyre;
- set pressure for rider mass and surface, not automatically at the tyre’s maximum;
- compare front and rear results separately if possible.

For a PLUS wheelset, the text does not prescribe an exact tyre size or pressure without the exact model, tyre model, rider mass and manufacturer limits.

## **Wind-exposed road riding**

Prioritize:

- predictable front-wheel steering;
- moderate side-force behaviour;
- rider confidence in gusts;
- sufficient tyre volume for the road surface;
- a tyre–rim profile that remains compatible at the intended pressure.

A shallower or moderate-depth front wheel may be the better practical choice for a lighter rider, a rider who is sensitive to steering torque, or routes with frequent gusts and exposed sections. This is a handling recommendation, not a claim that a shallow wheel has lower drag in every condition.

## **Mixed road and gravel**

Prioritize:

- tyre and rim compatibility;
- tubeless reliability;
- puncture resistance;
- measured clearance;
- pressure low enough for control and comfort but high enough to prevent rim damage;
- an external rim shape that is not excessively narrow relative to the actual tyre.

A deep road rim paired with a large gravel tyre may be mechanically compatible but aerodynamically mismatched. Conversely, a wide gravel rim is not automatically slow: the complete tyre profile, tread and pressure determine the result.

### **Front/rear width strategy**

A modestly wider rear tyre can be reasonable where the route is rough or rear load is higher. A narrower front tyre may reduce frontal area only if it still creates a suitable tyre–rim transition and does not compromise grip, comfort or handling. There is insufficient evidence to recommend a universal front/rear width pair across all rims and tyres.

Rider-experience evidence versus measured evidence

## **Measured evidence**

These should remain separate:

- wind-tunnel force measurements;
- whole-bike yaw and roll moments;
- field testing with power measurement;
- rolling-resistance drum or instrumented-road testing.

## **Modelling evidence**

- CFD flow predictions;
- wind-averaged drag models;
- power calculations based on a reported CdA difference;
- assumed yaw distributions.

### **Rider experience**

Rider reports can reveal:

- whether the front wheel feels nervous in gusts;
- how much steering correction is needed;
- whether the rider can hold an aerodynamic position;
- comfort and confidence on rough surfaces.

They cannot independently establish a watt saving. “Feels fast” should remain a handling or subjective-performance observation, not be converted into watts.

### Unresolved Evidence Gaps

1. Few independent tests of current wide-rim road and gravel wheel–tyre combinations.
2. Limited whole-bike evidence separating front and rear wheel contributions.
3. Insufficient field data linking wind-tunnel side force to individual rider confidence and steering correction.
4. No universal validation of the 105% rule across modern hookless rims, tubeless tyres and large gravel tyres.
5. Sparse data on rough-road performance where aerodynamic drag, rolling losses and vibration interact.
6. Limited independent testing of PLUS Aero’s current wheel models.
7. Incomplete model-specific PLUS tyre compatibility and pressure information in the public pages reviewed.
8. Watt claims are often reported without all of the required conditions: baseline, air density, speed, yaw distribution, wheel-only versus whole-bike scope and uncertainty.

### Bottom line

Choose the wheel and tyre as one system. Use rim depth as a starting descriptor, not a performance verdict. Confirm the exact rim’s compatibility and pressure limits, mount the intended tyre, measure its actual width, and evaluate the result at realistic yaw angles and surfaces.

For most riders, the best real-world setup is not the one with the lowest isolated drag at one wind-tunnel angle. It is the combination that provides a favourable tyre–rim shape, acceptable crosswind behaviour, low enough rolling losses, adequate comfort and grip, and enough rider confidence to maintain speed consistently.

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