The TB20 IPC specifies only these options (for the main landing gear)
Goodyear: 15x6.00x6 6PR Flight Special II P/N 156E61-3
Michelin: 15x6.00x6 6PR Aviator P/N 061-501-0
However many owners use different brand tyres, or same brand tyres of the same size and general specs but not the exact P/N. It seems the Goodyear Flight Custom III is fairly popular.
Is that legal?
It has been suggested that it isn't, without a Major Alteration process (337 etc).
The type certificate data sheet (or STC data sheet) is by my understanding the only legally relevant document. For my aircraft the TCDS lists the tire size(s) and ply rating. Obviously they have to fit within the wheel fairing etc and that's where the manufacturer's brand & P/N suggestions can be useful provided they aren't 70 years out of date... which some day they will be.
For one of my aircraft the TCDS specs an obsolete size tire (5:50 x 5), discontinued probably 25 or more years ago. However the airframe manufacturer at that time released commercial documentation (I think a service bulletin or similar) suggesting the use of the next best size. I think in the event of an insurance claim, this would be OK for my use with the insurance company and it also works fine to get annuals signed off by my IA.
To the best ofmy knowledge the answer is Yes.
I know of a Comanche that was grounded by an FAA inspector for having the wrong tyres on it. The FAA Type Cert. (or whatever it is called) specifies 4x6 all round while he used 6x6, latter models are being specified as 6x6 for the mains and 4x6 for the nose.
Hope that this helps.
I agree with that view; I said "of the same size and general specs" and that is what the owner you refer to didn't do.
I don't think anybody would suggest one could vary the general tyre specs.
Let's face it - you wouldn't put the wrong size tyres on a car, but the manufacturer's name doesn't matter unless you are doing something special.
The Q (which I might not have phrased well) is whether the exact manufacturer P/N must be used.