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Rear cassette for a 29er


Plastic Hadeda
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Sorry if this has been posted before - but a search on the forum reveals no results. At the risk of scorn being poured on me by the SS brigade - anybody tried fitting a 12-36 cassette on a 29er - for those (long) very steep climbs? Shimano say that torque is an issue - puts too much pressure on the freehub body - but I was wondering if there was anybody out there who had tried it?

Plastic Hadeda2010-02-15 08:44:32

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If you are running a 2 blade crank with 29/42 chainrings then a 12-36 would probably be suitable but for normal cranks and climbs its overkill.

 

 

 

I run a 11-32 on a 26/36 crank.

 

The Thug2010-02-15 08:54:25

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I hear you - but my knees beg to differ at a 20% gradient.Unhappy

 

By way of explanation - Sheldon Brown's Gear calculator shows that, on a 26" bike, with a 22 front / 34 rear combo you get 16.8 gear inches per rev. On a 29er that goes up to 18.8 gear inches.

 

Using a 22/36 combo on a 29er gets you back down to 17.7 - about halfway back to the 26er gearing.

 

Put another way - a 22/34 combo on a 29 er is almost the same as a 22/30 on a 26er (19.1 gear inches), Which is a bit too much for me over a long haul, gettting the same ratio on a 29er would mean a 38t cassette!

 

Plastic Hadeda2010-02-15 10:18:43

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But how often & for how long do you hit a 20% gradient?

 

 

 

On the Sani Transfrontier race we hit 25% a couple of times but it wasn't for longer than 10 - 20 metres or so.The Thug2010-02-15 12:52:32

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But how often & for how long do you hit a 20% gradient?

 

 

On the Sani Transfrontier race we hit 25% a couple of times but it wasn't for longer than 10 - 20 metres or so.

 

 

I was being a bit facetious Thug - hence the explanation on gear inches and the emoticon. What I was getting at is that a 22/34 on a 29er is roughly equivalent to a 22/30 on a 26er and I was just trying to get some info on how best to get back to the same gearing.

 

I find that on long climbs I was battling to manage my HR after the short sharp climbs - couldn't get back to a more restful gearing to recover after the hard efforts and don't particularly want to try the pharmaceutical route for this  Sleepy

 

Anyhoo - moot point now - the 12-36 arrived. Jayd(Jade/) at Shimano was more than helpful in explaining what to look out for on the hub and all is fitted and working.

 

Now to work out how to fit in all that skipped training before March 2nd! Dead

 

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