A measurement of a material's resistance to indentation. TPU filaments are rated on the Shore A scale (typically 85A–95A for printing filaments), where lower numbers indicate more flexibility. PETG is rigid and would be measured on the Shore D scale. Higher Shore A = stiffer TPU.
Why Traction Spikes Exist
Robot mowers with rear-wheel drive often struggle on wet grass slopes above 15°. The OEM rubber tires lack the grip to maintain forward motion when dew, rain, or frost reduces friction. The mower detects "No Movement" (via wheel encoders), triggers a fault, and either returns to the dock or sits stuck until the owner intervenes.
Aftermarket traction spikes are small inserts or overlays that add mechanical grip to the mower's wheels. They are the most common 3D-printed robot mower modification, with hundreds of designs available on Printables, MakerWorld, and Thingiverse for Husqvarna, Mammotion, Segway, Worx, and other brands.
PETG vs. TPU: Head-to-Head Material Comparison
| Property | PETG | TPU (95A) | Winner |
|---|---|---|---|
| Rigidity | High — holds spike shape under load | Low — flexes and absorbs impact | PETG for spike retention |
| UV Resistance | Good — 6–12 months before yellowing | Excellent — 12–24 months outdoor use | TPU |
| Impact Resistance | Moderate — can crack on sharp rocks | Excellent — absorbs impact without fracture | TPU |
| Wear Rate on Grass | Low — hard surface resists abrasion | Moderate — softer material wears faster | PETG |
| Wear Rate on Concrete/Pavers | Moderate — hard surface grinds down | High — soft material wears quickly | PETG |
| Print Difficulty | Easy — standard settings, no enclosure needed | Hard — requires direct drive or slow Bowden setup | PETG |
| Layer Adhesion | Excellent | Good — but can delaminate under shear stress | PETG |
| Heat Resistance (HDT) | 80°C | 60–80°C depending on formulation | PETG |
| Chemical Resistance | Good — resistant to lawn chemicals and fertilizer | Good — resistant to most garden chemicals | Tie |
| Cost per kg | $18–25 | $25–40 | PETG |
When to Choose PETG
PETG is the correct choice when your mower operates primarily on grass-only surfaces and rarely crosses concrete paths or stone pavers. The rigidity of PETG means spikes maintain their shape and sharpness over time, providing consistent grip across wet grass. PETG is also significantly easier to print — any FDM printer with a heated bed can produce quality PETG parts with no enclosure required.
Recommended print settings for PETG spikes:
- Nozzle temperature: 230–245°C
- Bed temperature: 70–80°C
- Layer height: 0.2mm
- Infill: 80–100% (spikes must be solid for structural integrity)
- Wall count: 4+ perimeters
- Print speed: 40–50mm/s for spike tips
When to Choose TPU
TPU is the better option when the mower must cross hard surfaces — driveways, concrete paths, brick pavers — between mowing zones. The flexibility of TPU absorbs impacts that would crack or chip PETG spikes. TPU spikes also produce less noise on hard surfaces and are less likely to damage decorative pavers.
The tradeoff is printability. TPU requires a direct-drive extruder or a very short Bowden tube. Standard Bowden-tube printers (like the Creality Ender 3) struggle with TPU because the flexible filament buckles in the tube. If you have a direct-drive printer (Prusa MK4, Bambu Lab X1C, Voron), TPU is a viable option.
Recommended print settings for TPU 95A spikes:
- Nozzle temperature: 220–235°C
- Bed temperature: 50–60°C
- Layer height: 0.2mm
- Infill: 100% (critical for spike integrity)
- Wall count: 4+ perimeters
- Print speed: 20–30mm/s (slow is essential)
- Retraction: minimal or disabled
The Hybrid Approach: PETG Base + TPU Tips
Advanced modders have developed two-material spike designs that combine PETG structural rigidity with TPU contact surfaces. The PETG forms the mounting base and spike body, while a TPU cap or overlay is press-fitted onto the spike tip. This approach provides:
- Structural rigidity from the PETG base
- Impact absorption from the TPU tip
- Reduced noise when crossing hard surfaces
- Replaceable tips without reprinting the entire spike assembly
The main disadvantage is the additional assembly time and the need for precise tolerances so the TPU press-fits securely onto the PETG spike.
Materials to Avoid
- PLA: UV-degrades in weeks. Heat deflection temperature of 55°C means spikes deform on hot summer days. Not suitable for any outdoor application.
- ABS: Better UV resistance than PLA, but prone to warping during printing and layer delamination in outdoor humidity cycles. PETG is superior in every relevant property.
- Nylon (PA): Excellent mechanical properties but absorbs moisture aggressively. Spikes printed in nylon will swell and soften after days of lawn exposure, losing dimensional accuracy.
Frequently Asked Questions
Most manufacturers do not explicitly address aftermarket wheel modifications in their warranty terms. However, if a warranty claim involves the drive system and modified wheels are installed, the manufacturer may deny coverage. Best practice: keep the original wheels and swap back before any warranty service.
PETG spikes typically last 1–2 mowing seasons before UV degradation and mechanical wear require replacement. TPU spikes last longer due to their flexibility (less brittle fracture) but wear faster on hard surfaces. Both materials significantly outlast PLA, which can degrade in weeks of outdoor use.
No. PLA has poor UV resistance and low heat deflection temperature (55–60°C). It becomes brittle after weeks of sun exposure and can warp on hot days when the mower sits in direct sunlight. PETG and TPU are the minimum acceptable materials for outdoor robotics accessories.
5–8mm spike height is the sweet spot for most lawns. Shorter spikes (3–4mm) provide minimal improvement. Taller spikes (10mm+) increase the risk of the mower digging holes when it loses traction on slopes, which defeats the purpose of the modification.
Printables, MakerWorld, and Thingiverse all host free designs for popular mower models including Husqvarna Automower, Mammotion LUBA, and Segway Navimow. Search for your model name plus "traction spikes" or "wheel spikes."