Questions about trailer wheels and suspension

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.

Bill

What about some old original mini wheels.
Ive seen them thrown out in the council clean up
They were 10” and you could get radials for them.
Datto wheels were 12” from memory.
On my 3 bike trailer I used widened Cooper S wheels after I lunched the lightweight at Amaroo in 72.
H.

Thanks Henry,

Hope I remembered your name correctly, it does not always happen.
I have absolutely scoured the usual sources for second hand options, and the only ones I can see on offer are either priced very high, or beaten to death.
A trailer I once built for a plywood dinghy used Mini wheels; 'good ride' was not an issue because the trailer was built around a Mini rear suspension assembly - smooth as silk compared with most trailers, but you would never get that registered these days.
Amazingly there are some 10" alloy wheels with integral bearings on Gumtree in Canada Bay (of all places) but as yet no response to my contact.

Keep well.
Cheers,
Bill

Found these on fleabay and gumtree, the first ones are in Sydney. I think there's one lot there that include hubs to suit.
https://www.ebay.com.au/itm/Morris-Mini-10Inch-Rims-undercoated/303535006186?hash=item46ac18a1ea:g:USoAAOSw-~NbQxzp
https://www.gumtree.com.au/s-ad/tingalpa/wheels-tyres-rims/mini-wheels/1245173084
https://www.gumtree.com.au/s-ad/pear...rim/1244601957
https://www.gumtree.com.au/s-ad/camb...rts/1244179469
HTH
Kryn

Hi Kryn,
Thanks for those links, it helps to see costs and where they are located.
Today I was looking at what is needed for a Mini wheel solution, and it turns out that the costs of wheels (cheap used), tyres and galvanised hub kits to fit the existing axle there's not much saving compared with just buying new light alloy wheels with integral bearings (separate hub not required), which also have the functional advantages of lower unsprung weight and good corrosion resistance (those little wheels are going to see a lot of salt water).
Cheers,
Bill

Hi Bill, glad to help. If you go that way, make sure that the seals are of the marine type, or get a bearing buddy kit as it keeps the hub grease under pressure and prevents the ingress of moisture which is the biggest killer of boat trailer bearings. The design of ordinary seals allow moisture to be sucked in when the hubs are suddenly cooled.
https://www.couplemate.com.au/how-to...e-bearing-seal
The other important thing is to rinse off the salt water on your rims, even though they're alloy, they can still create problems.
To get a smoother ride from your springs, get a screwdriver, prise apart the springs and put a thin smear of graphite grease between the leaves, particularly on the ends where the springs rub, paddlepop sticks are great for this.
A little bit of rust between the leaves can effectively be like a solid bar, there's no slippage, hence the grease trick.
Use to do a lot of this on leaf springs on 4WDs to get a better ride.
HTH
Kryn

Kryn,

Thanks, that's a really helpful link to marine seal fitting.
I do use bearing buddies on my boat trailers, and marine bearing seals are on the purchase list.
Suppliers of small alloy wheels with integral bearings fit tyre tubes because salt water can cause slow air leaks by getting between the wheel rim and the bead of a tubeless tyre, presumably due to corrosion. You would think rubber grease when fitting the tyre would fix that.

The existing springs will be used for the time being to see how they go.
I took the springs apart (only 2 leaves and no keeper clips) to chip off the worst of the rust, and put some anhydrous lanolin grease on them near the U bolts. Graphite grease sounds good for the slipper contact surfaces. As mentioned it looks like one or more leaves were discarded to soften the springs and the keepers were discarded, though they would be good to stop the leaves skewing which had happened on one of them -will see what I can do.

Cheers,
Bill

Bill, the U bolts should keep the springs from skewing. I doubt that you'll find a keeper on any 2 leaf spring set, the way to get around that is to find a set of springs and rob the keeper leaf out of it, and throw away the bottom one of the original set.
Kryn