Advice needed: Want to upgrade bike to be a better climber

[Mavii]

My current set up is a standard 2011 Merida Ride 91:
Speeds 18
Frame Ride Speed-Single
Colour Anthracite(white)
Fork Road CF-S
Front Derailleur Shimano Sora 34.9 Double
Rear Derailleur Shimano Sora SS
Shifters Shimano Sora
Brake Levers attached
Brakes F/R Shimano Sora
Crankset Shimano Sora 50-34
BB Set attached
Chain Shimano CN-HG53
Hubs F/R Shimano 2200
Rims Alex Race24-White-NC
Freewheel Shimano CS-HG50-9 11-25
Spokes Black stainless
Tyres Maxxis Detonator 25 60
H-Bar FSA Vero Compact OS
Stem X-Mission Comp Lite CEN OS -8
Head set M10 Neck
Seat Post XM Comp D SB15 27.2
Saddle X-Mission Side-2

I want to upgrade my Cassette/Freewheel to something that will make it easier to climb hills. I am going to be doing a very hilly 90km race and want to make it a bit easier. What is the best cassette to upgrade to? 11-28T or can I go as far as an 11-32T cassette? Also I believe I will have to upgrade my rear derailleur, what would you recommend I upgrade to and do I then need to upgrade my front derailleur or will it be okay? Any advice would be great, including actual model numbers if possible..

Cheers

[GeorgeET]

Going to 11-32T would help but you may need a longer chain. Granny gear at crank would be good like a 24t small gear, but that would require a tripple crank at front and different dereilleur.

For now the 11-32 is your simplest option.

[Painkiller]

I would certainly look in to the the tooth capacity of the Sora ss rear derailleur before the 11t - 32t.It may be to short a cage. If he had to change to the gs or even move up to Tiagra or so no big deal. I am with George on that it would be cheaper to grab what you can on the rear and get it better shape!

[nfmisso]

You have a cassette, not a freewheel.

At the extreme, you could go with:
Sunrace 11-36T 9 speed cassette
Shimano M591 rear derailleur (needed for 36T)
and a new 9 speed chain (longer).

Your present shifters as long as you stay with Shimano (or Shimano compatible) rear derailleurs rated for 9 speed (or 10 speed road, but not 10 speed mountain) will be fine.

You may need to replace the RD cable at the same time as the RD, depending on the condition of the cable end.

I would not change the FD.

Note that there is a much larger jump between the gears than you currently have. Depending on your riding style this might be barely noticeable to very annoying.