Marin Fairfax Alp 2011 - Can I fit a 11-32t Cassette I currently have a Shimano LG50 12-25t 8 speed cassette and am finding it a real struggle on steep hills - I am around 13 stone (82kg). This is the first time I have looked at changing the original gear ratios on any bike I have owned.

I want to change to the 11-32t or another cassette but I am wondering if I need a new chain i.e. to lengthen it and also if the rear mech is OK. I ask this as stuff on the interweb says both can possibly be an issue. I believe there may be normal and long leg versions.

The rear derailleur is the original Shimano Sora 8 Speed Rear Derailleur (GS Long Cage). 

Current chain is the Shimano Altus HG40 6-7-8 Speed Chain.

Crankset is Truvativ Touro 52-42-30t.

Using the link below it says the rear derailleur will take 37T to 39T or less.
So the current cassette is (25-12) + (52-30) =35T
11-28 is (28-11) + (52-30) = 39T
11-30 is (30-11) + (52-30) = 41T
11-32 is (32-11) + (52-30) = 43T

From this it looks like my only option is the 11-28, which would only give a minimal improvement. Am i wasting my time trying to fix this particular bike as it stands?????

Thanks in anticipation. Kev

Many thanks to you all for your responses. I hope I have learnt a lot around this area and it sounds like I was hoping to achieve too much. I have ordered a 11-28t cassette and new chain as this stays within the guidelines from Shimano for the Sora rear mech. I will be v interested to see the difference it makes.

As suggested by someone, I did a lot of shopping around for a slightly smaller 5 bolt chain ring than the 30T that's on there, but hit a massive blank in finding a Truvativ ring that was smaller. Thanks again to all......UR*s
I think a disadvantage of the 11-32 cassette are the large gear steps. Also consider that switching from 25 to 28 already makes it 12% easier.

You could (additionally) install smaller chainrings, 52 is quite large and instead of 30 you could go down to 28 or 24. 

You will need a new (longer) chain if you increase cog size, unless you decrease chainring size at the same time or the chain is currently a bit longer than necessary.  A worn chain will work badly on new cogs or chainrings though.