I like the look of those tyres! I reckon you might need to rethink the valve spring idea as by the time you put 4 springs for stability I reckon it would take a fair bit of weight to get any movement from the springs. Perhaps some springs from a bike seat?
Bunnings had some decent compression springs that would do the job but were too dear. I found an old boat seat at work which did the job.
The tyres are great! I wheelied the damn thing through a puddle today and flipped. Such a great mower. Glad I was able to give it a second life so the mighty rover can live on.
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