12-25T to 11-28T cassette?

[Crankichick]

Hello, any advice please on lowering the gearing on my 2008 Specialized Vita.

It has 48/38/28T chainrings and a 12-25T 8 speed cassette. The rear derailleur is a Shimano Sora long cage.

I would like to have a gear inch below 30 to help with steep hill climbing.

Would it be possible to do a straight swap from a 12-25T to a 11-28T or would it be best to change completely to a mountain bike derailleur and cassette?

Thank you.

[beardy]

Yes your rear derailleur will accept the straight swap.

Or you could spend £16 on the new Sora which will allow you to use an 11-32 with your set up.

The medium cage version here.

http://www.chainreactioncycles.com/shim ... -prod84819

The medium cage has a 41 tooth capacity, ie 20 teeth on the front (48-28) and 21 on the rear (32-11).

You could buy the cassette alone first and try with your existing mech, it may just work if you are lucky.

[Crankichick]

Thanks beardy. So I can use a 9 spd derailleur on my 8 spd set up?

[beardy]

Yes no problem on the rear. So long as it is with one manufacturer (Shimano)

You can not use a 10 speed MTB derailleur (Deore etc) with any of the others.
I dont know about 11 speed.

[markfh]

Just to add to beardy's response I am currently running a 48/38/28T crankset with a 11-28T cassette and a Sora 3500 GS (medium cage) with no problems all be it that on that bike I have downtube friction shifters so indexing is not an issue for me.

Depending on your current chain length you will probably need to replace/lengthen the chain to allow for the larger rear cog.

[TonyR]

You could buy the cassette alone first and try with your existing mech, it may just work if you are lucky.

As its a long cage it will almost certainly work and anyway you can usually go a bit above the specified range without problems.

[beardy]

I was thinking more of the problem that the old Sora mech from 2008 was only designed to cover 28 tooth cassettes, so it may not clear a 32t sprocket.
On the other hand I have seen it done before.

The new mech is designed to clear 32t sprockets.

[andrew_s]

A 24t chainring will fit straight on and require no other changes. Available from Spa for £7 in steel or £13 in zicral.
You can fit a 28t cassette later if 26 inches isn't low enough, or maybe a 32.
I've been using 48/38/24 any time this last 20 years with no problems.

[fatboy]

A 24t chainring will fit straight on and require no other changes. Available from Spa for £7 in steel or £13 in zicral.
You can fit a 28t cassette later if 26 inches isn't low enough, or maybe a 32.
I've been using 48/38/24 any time this last 20 years with no problems.

+1 This is what I did. Dead simple, don't even need to lengthen the chain (which you'd need to do if you change the cassette).

[Crankichick]

A 24t chainring will fit straight on and require no other changes. Available from Spa for £7 in steel or £13 in zicral.
You can fit a 28t cassette later if 26 inches isn't low enough, or maybe a 32.
I've been using 48/38/24 any time this last 20 years with no problems.

Would a 24T chainring work ok with my front derailleur? It's a Shimano T301 and according to the following link it says "the small ring should not be smaller then 20 teeth of the large rings size":-

http://bandlbicycles.com/about/shimano- ... -pg359.htm

[Tigerbiten]

Put the chain small-small and measure the gap between the chain and the bottom of the cage.
You need 2mm per tooth reduction.
So if the gap is around 4mm, you can fit a 2 tooth smaller chainring and if the gap is around 8mm, you can fit a 4 tooth smaller chainring.

[fatboy]

Don't need to do small small, just the smallest cog on the cassette that you reckon you'll use

[andrew_s]

Being 4 teeth past the limit means that you won't be able to use rear sprockets within about 5 teeth of the smallest without the chain dragging across the bottom of the front mech cage (always assuming the limit is accurate}.
I only ever use the 24T chainring with the larger sprockets, on account of not changing onto it until I want a low gear, so I've never bothered worrying about front mech capacity

[Crankichick]

Thanks Guys for all your help, it's great to see all these options. I can't wait to be zooming up those hills at 20 metres per hour instead of 10!

[Valbrona]

Getting bigger sprockets at the back will only lower your gearing so much. Might be an idea to get a new chainset with smaller chainrings, like 24/36/46 or similar. Spa Cycles will put you straight. They do a Sugino XD2 triple chainset and a Stronglight Impact triple chainset which both take smaller chainrings than the standard Shimano road type.