After serious thinking Steve Walker wrote :
If you are only really struggling on that one hill, there are some temporary,
spray on solutions to increase grip. I have no idea whether they work or not,
as have luckily never needed anything.

They make a normal tyre slightly sticky. Yes it does work, but only a
little better than the untreated tyre. If you are stuck, but could
almost become unstuck, the spray might be enough.