Free 

Trx4m all-terrain wheel lets you grip at any loose surface like snow, gravel, dirt, small rocks, and mud. Each little spike is approximately 13mm tall, so you have some fender clearance.
UPDATE: Ski wheel. ONLY FOR FRONT WHEELS!!! Disconnect front driveshaft from the axle to make this possible. Use only for snow.
UPDATE: Made bigger spikes to grip powdery and wet snow












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