Bicycle Mechanics - Best way to upgrade wheels

I have a good set of shimano 105 wheels (36 spoke). They are old but low miles and excellent condition. The rear wheel is the screw on hub type and 5 speed cassette.
I am building a new bike for my son and want to update the cassette to a 9 or ten speed. Am I better off getting a new hub for the rear wheel and rebuilding the wheel or buying a new wheel. Time is not an issue.
Thanks

If the cogs are "screw on" and 5-speed they are almost certainly a freewheel, not a cassette, and you can't upgrade to 9 or 10-speed as freewheels were never made that wide. You could get a 7-speed freewheel to replace the 5-speed and these are available. If you want to go to 8,9 or 10-speed you will need a new rear wheel with the appropriate freehub configuration.

The way components are priced these days, buying a complete wheel is almost always cheaper than buying the parts and building your own. In fact, it's often cheaped to buy a complete wheel even if you already have a suitable hub. Such is life.

BTW, your 5-speed hub is probably spaced 120 mm. Any 6 or 7-speed hub (freewheel or cassette) will be 126 mm and 8/9/10-speed hubs are 130 mm so be sure the frame is compatible with what you buy or can be cold-set to a wider spacing. Steel can be. Al and carbon can't.

Thanks for that. I was aware that the hubs were different and not compatible, that is why I asked about changing them. Maybe I will just buy a new rear wheel with the correct hub.

Thanks for that. I was aware that the hubs were different and not compatible, that is why I asked about changing them. Maybe I will just buy a new rear wheel with the correct hub.

Check out Ebay but, first read Sheldon Brown's tutorial on Shimano hubs and cassettes...very informative. You would do well with a Shimano 105. I am a Campy guy and I recently rebuilt a friend's 105 wheels with new spokes and CPX33 rims...now they are like new. I rebuilt the hubs and they are very well built.

The wheel set you have is most likely 27 in. If you only buy only a new rear wheel 9-10 speed compatible it will most likely be 700 C (4mm shorter). You will then have to mix and match tires.

Also spreading a frame more than on size might be asking for trouble. 120-126-130.

Brake reach might also be an issue. They can either modified with a round file or you can buy long reach calipers

Friction shifting also ends with 8 speed