Gearing ratio far too light

[Dvntie]

Folks
I'm looking for some advice
I have a boardman team c 2010 spec and I fond that I run out if gears on a descent.
The set up is as follows front and rear mechs SRAM rival rear is short gauge
Shimano hg 5600 10 SPd cassette 12-25.
Shimano hg5600 chain
Chainset is the SRAM gxp 50/34
And SRAM rival shifters
So what I'm looking to find out is a possible set up that's a bit more meaty
Any suggestions would be greatly appreciated

[nameused]

I would try a bigger ring in the chainset. I have a 28/38/48 on my mountain bike. Most of the time I hear of people having 54 teeth in the front.

[Painkiller]

you need to spec the maximum teeth your front derailluer can handle between rings
15 to 22 on most setups
53/39 for example
you should be running an 11t on the rear also
but remember you will probably have to replace your chain

[nfmisso]

As mentioned above, get a cassette with an 11t smallest sprocket.
http://www.sheldonbrown.com/k10.shtml#shimano9

The GXP is offered in 53/39.
http://www.sram.com/sram/road/products/s900-gxp-crankset
The Red group goes to 55/42
http://www.sram.com/sram/road/products/sram-red-crankset

I don't know the BCD, 130mm maybe ? Harris has 54T chainrings in 130mm BCD
http://sheldonbrown.com/harris/chainrings/130.html
and 110mm
http://sheldonbrown.com/harris/chainrings/110.html

See here for how to measure BCD:
http://sheldonbrown.com/harris/chainrings.html

53/11 is 15% taller than the 50/12 you currently have.
55/11 is 20% taller than the 50/12 you currently have.

You will need a new longer chain if you change the chain rings

[Dvntie]

Folks
Thanx a million for the advice
Looks like I've a little bit of work to do then
I'll let you know how I fare
Thanx