Lowest number of teeth on a crank

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jibberish
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Lowest number of teeth on a crank

Postby jibberish » Tue Nov 20, 2012 11:18 am

Hi

I'm signing up to do a crazy road mountain thing and need to lower my gears.

I've got a compact and wondered if there were any options for changing my crank. I currently have

Crank - 50/34
Cassette 11/28

I'm not bothered about missing out on high gears for high speed as I'm happy to free wheel once the descent is steep. It's the up-hill I'm worried about.

I can go to a triple, but then I have to get a new derailleur etc and I won't use all the top end gears. I've been looking at Sram and Shimano, but can't find any crank that has less than 34 teeth on it (other than MTB). Is using an MTB crank an option? Bike is a Scott CR1.

Thanks for any help.

Jibb

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Grill
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Re: Lowest number of teeth on a crank

Postby Grill » Tue Nov 20, 2012 11:24 am

That combination of a compact chainset with the 11/28 cassette will get you up anything.

What crazy road mountain thing is it exactly?
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ugo.santalucia
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Re: Lowest number of teeth on a crank

Postby ugo.santalucia » Tue Nov 20, 2012 11:26 am

I think that's as far as you can go without having to make changes... a 30 T cassette will require a long cage derailleur. I am not aware of < 34 T chainrings... with 110 spacings, that's as low as you can go, I fear.

What's the crazything you have signed up for?

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Gizmodo
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Re: Lowest number of teeth on a crank

Postby Gizmodo » Tue Nov 20, 2012 11:30 am

There is a 14 page sticky thread in Road Beginners called Help I need smaller gears - what can I do? A GUIDE
Last edited by Gizmodo on Tue Nov 20, 2012 11:44 am, edited 1 time in total.

chanjy
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Re: Lowest number of teeth on a crank

Postby chanjy » Tue Nov 20, 2012 11:36 am

Front derailleurs won't play nicely if there's more than a 16t difference between the big and small, so you don't have many options at the front.

SRAM Wifli will get you a 32t dinnerplate at the back but you need the rear mech too.

There's no shame in it - even pros use them going up the Angliru (had a standard double at the front, mind)

http://www.bikeradar.com/news/article/c ... lta-35156/

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Grill
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Re: Lowest number of teeth on a crank

Postby Grill » Tue Nov 20, 2012 11:42 am

chanjy wrote:There's no shame in it - even pros use them going up the Angliru (had a standard double at the front, mind)

http://www.bikeradar.com/news/article/c ... lta-35156/


Absolutely. I'm just wondering what event round these parts would necessitate lower gearing. Tour of Wessex perhaps?
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jibberish
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Re: Lowest number of teeth on a crank

Postby jibberish » Tue Nov 20, 2012 11:46 am

Thanks guys - I'm gonna have a look at these links now. I'm doing the Fred Whitton Challenge and then Marmotte.

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Grill
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Re: Lowest number of teeth on a crank

Postby Grill » Tue Nov 20, 2012 11:51 am

Nice. They've got some beefy climbs, but I reckon if you're in half-decent shape your current setup will be absolutely fine.
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shmooster
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Re: Lowest number of teeth on a crank

Postby shmooster » Tue Nov 20, 2012 12:08 pm

The Fred Whitton exceeds 30% so low is good. I'm doing the same rides as Jibberish and spent this morning looking at the options :-)

Options on 105 are:

Change Rear to higher range:
Up to an 11-32T using HG81 MTB cassette from Shimano with a new chain and and a 5701-GS medium cage rear mech, still staying on a compact double at the front. Or 12-30T on Ultegra CS-6700.
7% - 14% lower ratio vs 11-28 cassette
Cost around £80 for parts.

Change to a triple chainset, leave the cassette
Change crankset, to a 50-39-30T 5703 with a new front derailleur, new rear derailleur and maybe new front shifters (some compacts like my Roubaix use triple compatible shifters, some don't).
13% lower ratio vs 34-50 chainset
Cost around £200 for parts

Change to a triple chainset, change the cassette
As above but also change the rear cassette to a 12-30T Ultegra (12-32 isn't supported on a Shimano 105 triple)
21% lower ratio vs 11-28 cassette 34-50 chainset
Cost around £250 for parts

verloren
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Re: Lowest number of teeth on a crank

Postby verloren » Tue Nov 20, 2012 12:45 pm

You can get a 110BCD inner ring of 33T, though the improvement over 34T is marginal (and you'd probably have to switch to a 48T outer to keep shifting reasonable). Otherwise WiFli if you run SRAM or an MTB rear mech and cassette for Shimano is your best bet. Or shift weight from the rest of your body onto your thighs :)
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chanjy
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Re: Lowest number of teeth on a crank

Postby chanjy » Tue Nov 20, 2012 13:10 pm

So have you guys actually done a recce and decided 34-28 isn't enough? If you're decent riders you'd probably manage and are just scaring yourselves into buying things you might not need :)

jibberish
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Re: Lowest number of teeth on a crank

Postby jibberish » Tue Nov 20, 2012 13:19 pm

I did Etape Cymru this summer on 34-28 and it was doable, but I watched other people on the granny gears going up the hills. I was faster than a lot of them, but there will come an angle where that's not the case. I also felt myself reaching for a lower gear when I was already in the lowest one going on many occasions.

racingcondor
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Re: Lowest number of teeth on a crank

Postby racingcondor » Tue Nov 20, 2012 13:45 pm

Stronglight do a 33 tooth Compact inner -

http://www.stronglight.com/stronglight/page.php?nom=produit&keyProd=11_10vitessesCompact

However if you need smaller than a compact and a 28 on the rear even for the Fred Whitton then I doubt you'll finish (wanting it is different!). I got over Hornister on a 36-23 when I was a long way off race fit (and since I'm a 3 that's not very fit at all).

mroli
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Re: Lowest number of teeth on a crank

Postby mroli » Tue Nov 20, 2012 15:44 pm

To be fair, just getting over Honister and getting over Wrynose and Hardknott at the end of the Fred are 2 very different things. I'm not bad at hills and Hardknott is a grind - I had 34-25 and the OP could be fine getting around a "normal" sportive with that gearing but find himself pushing at the end of the Fred.

@jibberish - have a look at my blog (in my sig) - it has most of the hills in the Fred in it and you'll get some idea of what faces you. I don't know where you're based, but if you can find a 20% hill plus near you and work out how you do up it, it'll give you a good idea. The Marmotte and Fred are different types of climbing...

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pb21
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Re: Lowest number of teeth on a crank

Postby pb21 » Tue Nov 20, 2012 15:58 pm

If my maths is right a cadence of 80rpm with a gear of 34x28 means you will be going at 5mph, which should be OK for anything?

verloren
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Re: Lowest number of teeth on a crank

Postby verloren » Tue Nov 20, 2012 16:08 pm

If you can keep a cadence of 80, yes. As hard as it is to believe, there are at least two hills near me where I can't maintain that cadence. You might conclude that I'm a poor cyclist, and you'd be right, but I still want to get up those hills!
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'10 Tifosi CK7 Audax Classic with assorted bits for the wet weather

'08 Boardman Hybrid Comp for the very wet weather.

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PeteMadoc
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Re: Lowest number of teeth on a crank

Postby PeteMadoc » Tue Nov 20, 2012 16:37 pm

The simplest thing to do is just go for a 30 cassette on the back, those two extra teeth will make a big difference and are far easier to get than messing with the front rings.

Most rear mechs will say 28 is the max but you will most likely get away with 30. A friend fitted 30 on the rear for a trip to the alps (Marmotte route incidentally) on an ultegra mech.. no problemo

Here you go

http://www.tweekscycles.com/Product.do? ... 0Cassettes

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drlodge
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Re: Lowest number of teeth on a crank

Postby drlodge » Tue Nov 20, 2012 16:42 pm

pb21 wrote:If my maths is right a cadence of 80rpm with a gear of 34x28 means you will be going at 5mph, which should be OK for anything?


34x28 at 80rpm is nearer 8mph, when my cadence drops up Whitedown to around 60, speed is around 5.5/6mph. So speed = cadence/10 in that gear, roughtly speaking.
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pb21
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Re: Lowest number of teeth on a crank

Postby pb21 » Tue Nov 20, 2012 17:09 pm

drlodge wrote:
pb21 wrote:If my maths is right a cadence of 80rpm with a gear of 34x28 means you will be going at 5mph, which should be OK for anything?


34x28 at 80rpm is nearer 8mph, when my cadence drops up Whitedown to around 60, speed is around 5.5/6mph. So speed = cadence/10 in that gear, roughtly speaking.


Oh yeah :oops:

shmooster
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Re: Lowest number of teeth on a crank

Postby shmooster » Tue Nov 20, 2012 17:14 pm

As in my post above, a Shimano RD-5701 allows a 32T on the rear with a compact chainset

http://www.chainreactioncycles.com/Mode ... elID=85966

I did some climbing in the alps in the summer, and on Col de la Forclaz there were a couple of bits where I would have liked something lower than 28/34. That was a lot less steep than the hills on the Fred Whitton.


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