I am seeking some wisdom here, having failed to discover much online.

I have just acquired a small plywood boat (4.5 metres long 1.5m wide) and also managed to find a small boat trailer to fit both the vessel and the 'driveway' alongside my house (possibly just wide enough to fit an Austin 7, back when the house was built).

The boat is light - 120kg all up. The trailer is also light at 100kg, but it is equipped with toy wheels - 8 inch cast alloy with integral bearings, and tyres rated for 80kph max - so a wheel upgrade is on the agenda.
In doing that it would be good to consider how to give the boat the best ride quality, and my hope is to increase the wheel diameter but try to keep the unsprung weight low. Boats like this can be damaged if the ride is too hard, so springs, tyre type and inflation pressure also need to be considered.

If 13" wheels can be fitted under the welded-on mudguards, the boat should have a better ride quality due to bigger rolling diameter and lower tyre pressure than required for the 8" wheels. However it's hard to guess how much the increased unsprung weight (due to adding iron hubs and 13" wheels/tyres) would offset the ride quality benefits expected. Alternatively I could choose 10"x 4.5" cast alloy wheels with integral bearings to minimise unsprung weight - a smaller rolling diameter but quite a bit lighter. Any thoughts on this?

10 inch trailer wheels are usually fitted with light truck tyres which seem to run on quite high inflation pressures, at least at the max load rating. I am aware that tyres for trailers and cars have different operating conditions, but suspect that with the light load to be carried in this case either type of tyre would be well within its operational capabilities, and suspect car tyres would probably give a softer ride. Re tyre inflation pressure for the load to be carried, I have not found load/inflation charts for some of the tyres on offer: is there a general rule that can be used for this?

Also, perhaps someone can advise how the spring load rating should relate to the load supported. The current 2-leaf slipper springs appear to be the consequence of starting with a 3 or 4 -leaf spring and removing 1 or 2 leaves (the leaf clips having been lost in the process). Compared with similarly sized 2-leaf springs advertised, my estimate of the current springs load capacity is about 250kg per spring, or 500kg total. The total load to be carried by the springs is probably about 200kg.

I should say I have had a number of boat trailers over the years and towed them on long trips and indifferent roads without a problem, but they have been a bit bigger. This one has me wondering.


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