stapfam

Didn't realise how old your bike is, but 126 to 130 is just a good tight fit for a wheel to get into, so might be possible to fit a 130 in there, without having the frame respaced to take a 130.

For the last 10 years or so- Mountain bikes have had the same spacing of 135 and so we do now have some standardisation. 6 speed must put it to a freewheel hub where the sprockets screw onto the hub instead of being a cassette. Even some 7 speeds are like this and they are not a good idea on a bike that is being used with gusto. Problem is that to go 7 speed, with a cassette onto the splined freehub sysyem now used- is finding a 7 speed hub. None have been made for years, so the norm is to fit an 8/9 speed freehub and to fit a spacer for the one less sprocket. Hardly seems worth it when an 8 speed cassette is only a little more expensive, and 8 speed changers can be cheap. Then it seems even less worthwhile when you can go 9 speed with just the cassette, changers and chain. This is despite all the blurb that chainrings are different and a different derailler is required. I have run 8 speed chain rings and deraillers on my 9 speed bikes untill the full upgrade was necessary so I know they work together.

So now look at the cost. Currently you have to buy a wheel- that is the reason for the upgrade. 126 spacing may limit your choices on what else you can do, but a new cassette, changer and chain are also going to be required. On an old bike, I would say look around the shops for an old wheel that will fit, and use that to get the bike roadworthy. Then sell it. With the money from the sale, and the amount not spent on upgrades, you can buy a better bike secondhand than the one you have got.

That is me though, but if you have to stay with your current bike, or you just do not want to part with it, look at the cost of the upgrades and think what is possible.