From ditch + finder.
ditchfinder (plural ditchfinders)
- (UK, automotive, slang) A poor-quality tyre for a car, usually one made and sold cheaply.
2009 August 5, Mike P, “Re: Rear wheel drive”, in uk.rec.cars.misc[1] (Usenet):My MX-5 was *ace* in the snow in February round here. I went where other cars couldn't go with no problem at all. It was on Avons, and felt a whole hell of a lot safer then the FWD Puma on Pirelli ditchfinders did.
2012 February 26, Chris Bartram, “Re: tyres”, in uk.rec.driving[2] (Usenet):The better half's Lupo was transformed when the cheap and nasty Nankang ditchfinders came off (and they were well above the legal limit) and mid-price Kumhos went on. The cheapos compromise on grip and can become noisy.
2016 June 7, Adrian, “Re: Tyre noise”, in uk.rec.cars.maintenance[3] (Usenet):Sure, mismatching isn't ideal, but I'd much rather have mismatched decent tyres than matched AliBaba-brand-it-yourself ditchfinders.