Help I need smaller gears - what can I do? A GUIDE

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boileroo
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Re: Help I need smaller gears - what can I do? A GUIDE

Postby boileroo » Sat Sep 22, 2012 18:52 pm

Hey all

Another (no doubt annoying) gearing question for you all.

I've been riding for a few months now, absolutely loving it. However, I've just moved from Norfolk to Bath, and suffice to say I'm more than struggling with the hills!! I'm riding a spesh allez compact (50/34) with a 13-25 8 speed cassette. I feel as though I should be able to ride hills with this, but I'm really not very strong! Also, to my admittedly limited knowledge, it seems that a 12-25 cassette is fairly stupid?

Anyway my question: I'd love to change to a triple but can't afford to right now. My current plan is to change the cassette to something that'll help me in the climbs. I've been looking at the shimano 11-32 8 speeds with this in mind. What do I need to be aware of with this? Will any shimano 8 speed be compatible? Any tips would be hugely appreciated. Cheers all!

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John.T
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Re: Help I need smaller gears - what can I do? A GUIDE

Postby John.T » Sat Sep 22, 2012 19:15 pm

Fit a MTB mech and new chain with the 11/32 cassette. All this has been covered many times on here.

boileroo
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Re: Help I need smaller gears - what can I do? A GUIDE

Postby boileroo » Sat Sep 22, 2012 20:07 pm

Heya
-
So just to clarify, if I put on something like an alivio m410 rear mech I could use a cassette with anything up to 34 teeth? Only change would then likely be a new chain? Just wanting to clarify before I do anything!

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drlodge
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Re: Help I need smaller gears - what can I do? A GUIDE

Postby drlodge » Mon Sep 24, 2012 09:10 am

Basically:
- fit new cassette with gearing of your choice e.g. 12-34T
- find RD with "capacity" that suits. This comes in two forms (a) largest rear sprocket (needs to handle 34T in this case, most 32T max RDs would probably do it OK IMHO) and (b) total chain capacity, in this case its (50+34) - (34+12) i.e. 22 teeth (large front + large rear) - (small front + small rear).
- you'll likely need a new chain too as it'll need to be longer than the old one.
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Pross
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Re: Help I need smaller gears - what can I do? A GUIDE

Postby Pross » Wed Sep 26, 2012 10:04 am

drlodge wrote:Basically:
- fit new cassette with gearing of your choice e.g. 12-34T
- find RD with "capacity" that suits. This comes in two forms (a) largest rear sprocket (needs to handle 34T in this case, most 32T max RDs would probably do it OK IMHO) and (b) total chain capacity, in this case its (50+34) - (34+12) i.e. 22 teeth (large front + large rear) - (small front + small rear).- you'll likely need a new chain too as it'll need to be longer than the old one.


Are you sure that's correct? Shouldn't it be (large chainring - small chainring) + (largest cassette sprocket - smallest cassette sprocket) i.e. (50-34) + (34-12) = 38?

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drlodge
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Re: Help I need smaller gears - what can I do? A GUIDE

Postby drlodge » Wed Sep 26, 2012 11:09 am

Actually both equations are the same, just I got my calculation wrong. The right answer is 38, which is achieved via either method

(large front + large rear) - (small front + small rear) == (large front - small front) + (large rear - small rear)
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gazhilla
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Re: Help I need smaller gears - what can I do? A GUIDE

Postby gazhilla » Fri Sep 28, 2012 08:57 am

Can I just say a massive thank you to the folks contributing to this thread, as an 18stone returning rider the advice has been great for someone who lives on the edge of the lake district :)

tenagadalam
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Re: Help I need smaller gears - what can I do? A GUIDE

Postby tenagadalam » Fri Oct 05, 2012 09:55 am

thanks a lot. It's very useful :)

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sandwats
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Re: Help I need smaller gears - what can I do? A GUIDE

Postby sandwats » Tue Oct 16, 2012 08:39 am

Me too - incredibly helpful. Only thing that could improve it would be for the world-weary types who complain "this has been covered so many times before" to save their breath!

ChrisAOnABike
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Re: Help I need smaller gears - what can I do? A GUIDE

Postby ChrisAOnABike » Tue Oct 16, 2012 08:40 am

Sorry if I'm repeating stuff that's been covered - I've been through most of this thread and I'm still not sure.

I have Tiagra, compact chainset (50/34), and a 12-28 10-speed cassette.

As others, I don't want to switch to a triple, but although it's early days, I am considering how to achieve a little more range at the back.

AIUI, there's no option for 30 or 32 instead of 28 without changing the rear mech and chain. Is this right?
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drlodge
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Re: Help I need smaller gears - what can I do? A GUIDE

Postby drlodge » Tue Oct 16, 2012 11:40 am

You need a RD with adequate capacity (36 links), so it depends on what your current RD is...?
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ChrisAOnABike
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Re: Help I need smaller gears - what can I do? A GUIDE

Postby ChrisAOnABike » Tue Oct 16, 2012 12:33 pm

drlodge wrote:You need a RD with adequate capacity (36 links), so it depends on what your current RD is...?

I looked at the back of the RD, and it says RD-4600 I think. Can't be quite sure it's a 6 not an 8 - is there such a thing as an RD4800? Can't find any ref to one??

Edit: I've now found this PDF, but I'm not sure how to interpret the bits that refer to number of teeth.
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John.T
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Re: Help I need smaller gears - what can I do? A GUIDE

Postby John.T » Tue Oct 16, 2012 14:42 pm

That mech will officially only take a 28 sprocket as the largest but you would probably get away with a 30. 32 would be pushing it but depending on your hanger length (they do vary) you might be OK. If you really want a 32 then a 9sp MTB mech will be fine.

ChrisAOnABike
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Re: Help I need smaller gears - what can I do? A GUIDE

Postby ChrisAOnABike » Wed Oct 17, 2012 20:24 pm

Hmm... the more I read, the more confused I get.

I've found this thing called 'capacity', which seems to be:

(chainset tooth difference) + (cassette tooth difference), which in my case is:
(50-34=16) + (28-12=16) = 32

From the spec on that PDF, it seems that the capacity needs to be 39T or less (so Ok there), and max big cog size = 30T (so Ok there too).

Which suggests that I'd be Ok with a 12-30 cassette. Ok, so 2T more doesn't sound much, but it's still a 7% change in gearing from 28T to 30T.

Can someone shed any light on how I'm reading the spec?
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John.T
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Re: Help I need smaller gears - what can I do? A GUIDE

Postby John.T » Wed Oct 17, 2012 21:14 pm

I should have read the PDF before answering. I was assuming a 28 tooth max. You have it right. Total capacity is as you think. It is 34 teeth with a SS (short cage) mech and 39 with a GS (long cage). At 32 you are fine with either. The extra capacity on the GS is for a triple chain ring set up. Your safe max (officially) is 50/34 with 11/30. You should be safe with up to 32 with care in setting the B screw and chain length. If unsure then don't go this far. If you want to get a slightly lower gear you can fit a 33 inner ring.

ChrisAOnABike
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Re: Help I need smaller gears - what can I do? A GUIDE

Postby ChrisAOnABike » Wed Oct 17, 2012 21:46 pm

John.T wrote:I should have read the PDF before answering. I was assuming a 28 tooth max. You have it right. Total capacity is as you think. It is 34 teeth with a SS (short cage) mech and 39 with a GS (long cage). At 32 you are fine with either. The extra capacity on the GS is for a triple chain ring set up. Your safe max (officially) is 50/34 with 11/30. You should be safe with up to 32 with care in setting the B screw and chain length. If unsure then don't go this far. If you want to get a slightly lower gear you can fit a 33 inner ring.

Great, many thanks for clarifying.

It's early days yet - I may find I can get up the hills easily enough in time (I've only had the bike 10 days, after all :) ) - but I think, given how cheap the cassettes are, if I go for an upgrade I'll play it safe and go for a 12-30 initially, and see how I get on.

Thanks again.
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JamesB5446
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Re: Help I need smaller gears - what can I do? A GUIDE

Postby JamesB5446 » Wed Nov 07, 2012 08:28 am


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TheFD
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Re: Help I need smaller gears - what can I do? A GUIDE

Postby TheFD » Fri Dec 28, 2012 12:33 pm

Ok - one quick question. I have a 53/39 front and 12/27 rear. 105 (2010 model - 5600?). Can I just swap the front rings for 50/34 and will it work?
2013 - R872
2010 - Spesh Tarmac

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John.T
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Re: Help I need smaller gears - what can I do? A GUIDE

Postby John.T » Fri Dec 28, 2012 13:14 pm

The smallest ring that will fit on those cranks is 38 teeth. For 50/34 you will need a new chainset.

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TheFD
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Re: Help I need smaller gears - what can I do? A GUIDE

Postby TheFD » Fri Dec 28, 2012 14:48 pm

John.T wrote:The smallest ring that will fit on those cranks is 38 teeth. For 50/34 you will need a new chainset.

So I would need to change the cranks as well? Would the front mech be ok?
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