Can I swap out to any Freewheel/ ratio?

dorsetclimber

I have a cyclocross bike, I use it as my main bike for near everything. Its great on hills etc, However its not cross season,

I am planning to have two wheelsets, 1 for offroad , and one for road use.

the ratios are a little weird, and I don't fully understand them. before I purchase a second wheelset, I was interested to see if I could put on a different ratio on the rear wheel and to what effect it may have. Maybe a benefit for top end road speed, /N.B I LIKE the BURN

at the moment its
SRAM Force groupset, Chainring 42/38
Freewheel sprockets Shimano Ultegra 12/25

so I would be thinking about getting a second wheelset for use on the road, with a new Freewheel for that, or whatever it needs?
Do I need to change chainrings or ?

If anyone has a link the numbers explained, in terms of how a rider if affected , that would be great

Anonymous

I assumed the chainset was that way because you do not go as fast or as uphill (get off and carry ?) When using for cyclocross?
If the deraileur can take an 11-28 cassette then I would have thought it would give you a highest and lowest gear nearer to that of a 50/34 12-25 of a standard compact road bike.
Guess it depends how often you want to swap between the two set ups. Much easier to keep it to the wheel rather than have to swap chainrings.
Try typing gear length inches in to google to get a site to compare ratios.

Wirral_paul

A 42/38 chainset?? Well i've never heard of anything with such a close ratio between 2 chainrings - they're hardly any different really. Thats not a typo? Most i've seen lately run something like a 46/36 on the front.

I'd expect you could swap the chainrings out for any ratio compact rings - 50/34 or 50/36 might be more useful to you than changing the cassette.