Must replacement crankset have the same number of teeth? I have a Giant Boulder 520 (1996) and I am upgrading it bit by bit.

I bought a new Shimano 7 speed cassette 11-28T. Now, I want to replace my crank set, however I do not know which size to buy.

Does it have to have the same number of teeth as my current one or does it not matter? I currently have a 42/32/24 crank set, do I have to replace it with a 42/32/24 crank set to avoid having to replace the derailleur or anything else? 

I am currently thinking of getting a Shimano crank set FCTY501 42/34/24 compatible with 6/7/8 speed. Will it work with my new cassette and will I need to adjust my derailleur?
You are not changing the largest and smallest chainring sizes, so if nothing else has changed a 42/32/24 crank would be compatible with the rest of your drivetrain.

However, I looked up the specification of your bike on Bicycle Blue Book. The original cassette was a 7-speed 13-28 tooth. You may have problems with the 11 tooth small sprocket. 

If you want to check, you can look up the specs for whatever your rear derailleur is. You can find technical documentation for Shimano products on the Shimano Bicycle Components Site.

Rear derailleurs typically have the following specifications:


Minimum rear sprocket size
Maximum rear sprocket size
Maximum front chainring tooth difference
Total capacity


You'll need to ensure that your derailleur can handle an 11 tooth smallest rear sprocket, and a slightly increased total capacity.

The total capacity is the difference between the numbers of teeth on the largest front ring and rear sprocket, and the smallest front ring and rear sprocket. I.e., a measure of the extremes of chain slack the derailleur has to accommodate.

For an 13-28 cassette and 42/32/24 crank: (42+28) - (24+13) = 33, 11-28 cassette : (42+28) - (24+11) = 35.