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Swapping MTB rear for hill climbing(5 posts)

Swapping MTB rear for hill climbingElefantino
Mar 18, 2002 9:47 PM
Tell me what you think of this. I've heard of a trend, be it old and me just ignorant or new, where road riders are avoiding the dreaded double-to-triple dance by temporarily replacing and DA or Ultegra rears with an XT or some other MTB rear derailler along with a fairly wide (13-34-ish) cassette and still running a double.

I'll admit it hadn't occurred to me. What are the pros and cons, at least one obvious con being that when you try to reprogram your FlightDeck for this configuration you will appear to travel at roughly the speed of sound?

Thoughts, techies?
FWIW,
Mike
Been there, done that.Len J
Mar 19, 2002 5:21 AM
It works well. The only other thing you have to do is lengthen the chain. Both the XT & XTR rear der are compatible with your existing STI shifters. The only two downsides are:

1.) Lots of gaps in the shifting (13/34 is not a corn cob) &

2.) Everyone you ride with will give you s##t.

But it is definatly cheaper than a conversion to a triple & gives you almost the same gearing. (A 30-27 is 30 gearinches/8.9 mph at 100rpm/7.1 mph at 80 rpm, a 39-34 is 31 gearinches/9.2 mph at 100 rpm/7.4 mph at 80 rpm)

Len

p.s. shifting on a 12-23 with an XTR rear der is pretty smooth also
common quick fix for randonneurs/ultramarathonerscyclopathic
Mar 19, 2002 7:01 AM
34t on doubles is equivalent of 26t on triples with 30t granny
the MTB cass you can get is either in 11-34 or 12-34 size (XT or XTR). As previous post stated you'd need longer chain and MTB rear der, all works fine.

Pros: lower gearing, cheap fix (esp if you have MTB with cass to borrow)
Cons: gapping.

On supported rides (like Furnace Creek 508) you can have best of 2 worlds bring extra rear wheel with MTB cass. You use your main 12-23 for flats and swap rear wheel for climbs.

All this is pretty theoretical in flatlands you live. I can't see anyone needed small ring in Fla ;)

anyways after experimenting with different setups I found triples with 12-27 rear being much better overall gear. 42/27 is equiv to 39/25 and it's enough to climb grades pushing 20%. Granny on other hand is a bailout gear it allows to sit down on same 20-25% climbs.

I've only used my granny once on 22% climb (which reminds me I need to adjust FD to shift into it). To my excuse at that point of time I had about 90mi/12,000' in my legs. Things start looking quite different after you get a few hundred miles in your legs you know 8-P
I'm a lousy climber; been doing it for yearscory
Mar 19, 2002 7:55 AM
Actually I'm a better climber now...but when I WAS a lousy climber, I ran a 30-tooth in back for years, sometimes a 32 (I live in the mountains, and climbs over 7,000 feet are common). And now that I'm an old, mediocre climber, I'm doing it again. No problems aside from the obvious gaps between gears, but the advantage of actually having the granny you need outweighs the drawbacks of being one tooth off in the middle of the range for me.
re: Swapping MTB rear for hill climbingLC
Mar 19, 2002 10:34 AM
I found the only way to really not feel like your getting the gaps is to lose the 11 and 12 cogs and have the big gaps at the largest cogs since they are for steep hill only. I used a 13,14,15,17,19,21,23,28,32 and found it had all the gears i needed. The stock MTB cassette felt like I was always searching for the right gear when on the flats.