Loading ramps

To get a ride-on on a trailer, you could lift it (only ~260kg) or get some ramps.
For a few years I've used 2m long, 40mm thick low grade timber, for a lighter mower (170kg)
With the new mower, plus me driving it on (ever tried pushing 260kg up a 20% grade?) you're talking ~340kg. A bag full of grass on the back adds another 50kg or so. The planks worked ok, but did deflect around 40mm. Pretty heavy too at 10kg each

I saw these folding ramps for €52, made by Arebos (China). They are good for 300kg each. 1.8m long/~95cm folded (even came with a CE certificate ;-). Build quality is firmly average, with an hour spent removing sharp edges, plus, more annoyingly, little metal spikes on the grip pattern. The tread/grip is great, and is manufactured by punching upwards with a W shape. Unfortunately if the tool is off a bit, you end up with pointed 2mm spikes at the ends of each tread piece. With good tyre tread, I doubt it would puncture the tyres, but with ride-on tyres costing almost as much as car tyres, I'd prefer them to not have tiny knife cuts. That, and I might use these to load the motorbikes. 
These deflect around 10mm with the ride-on rear axle and me at the hinge (~120kg), and the sides bulge a little. 8kg each. They don't appear to be galvanised (not mentioned in advert when I bought them, but others state this) Time will tell.