Can I modify the gearing on a 2009 Jamis Aurora?

Question

I have a stock 2009 Jamis Aurora.

I'm looking to modify my gear set-up to make climbing hills with large loads a little easier on my knees, as I constantly find myself wishing I had one or more low gears. The specs say the crankset is an FSA Vero Forged 50/39/30 with a length of 175mm. The casette is a 9-speed SRAM Powerglide 950 (11-32). I read on a couple forums that some people had switched out their 30 tooth front sprocket for a 26 or 24, to help out with steep climbs and heavy loads. However, when I called a couple bike shops, they expressed concern that it wouldn't be possible and compatible with the front derailleur.

So I had a couple questions for bike experts since this is my first time really looking at gear systems -

1) Would changing from a 30T to 24 or 26T make a tangible difference on climbs?

2) How do I figure out whether the rest of the bike components will tolerate a 24 or 26t sprocket in the front?

3) Finally, any other solutions for this problem that one might try?

Thank you!

UPDATE 6/19

After incredibly helpful advice from folks in this thread, as well as consulting a number of LBS, I have successfully swapped out the 30 for a 26, without losing my STI levers and without any other problems. The secret lies in adding a 'chain watcher' to help guide the chain back onto the granny if it comes off. Some other adjustments to the front derailleur are also necessary. But with a competent bike shop, it's doable. I haven't climbed with a load yet (this weekend), but from use so far, it shifts smoothly into the granny (but you have to take care you're somewhere in the middle of the rear cassette when doing so), and shifting back up to the middle is also not an issue, though it takes a little longer than before and must be done delicately. With the granny, you shouldn't use the smallest 3 or 4 cogs in the back. Otherwise it works like a charm. Bike shop said it'd probably work just fine to switch the cassette to a 12-34 instead of 11-32 if I wanted lower gearing, too.

Answer 1

You can easily put a 26t chainwheel on the front crank. I've done that on a couple bikes, because 30/39/52 makes for a stupidly redundant set of gears with anything like a wide range cassette on the back.

It will likely take some tweaking of the front derailler setup to get it working properly, switching to a 50 from a 52 can help with that.

It isn't an out of the box recommendation since you are slightly exceeding the manufacturers specifications for both front and total ranges, but in practice it works just fine. I would recommend installing some kind of chain keeper like the Deda Dog fang. This will help avoid dropped chains when shifting from the middle to small chainring.

As far as changing the rear cassette goes, you should be able to use a Shimano 9speed HG 12-36 and it's generally just cheaper to buy the whole cassette than individual rings. If your current cassette isn't worn, you can mix and match rings to build a custom cassette. However, switching cassettes doesn't really solve the problem as well as a smaller chainring would IMHO. A good granny will give you a few choices in climbing. If you go to just the 36t in the back, you've only added one lower gear and you'll be "stuck" there.

If you are doing a lot of loaded touring, I would recommend replacing the entire front crank altogether. Standard road triples 130/74 BCD don't make a lot of sense for touring. A 110/74 or even a 9 speed MTB crank 22/32/44 will give a more useable set of gears. Personally, I would take a long look at the Surly Mr Whirly crank for touring. It uses modern bearings and you can get a replaceable spider to allow for whatever front gears you like.

IMHO, the old MTB standard 58/94 is ideal for loaded touring. 20/30/42 allows you to use a relatively close range on the back and still get all the gears you need. If you do go this route, you might need to replace the front derailuer as well.

Keep poking around on Sheldon Brown's pages, there is lot's of good info there.

Answer 2

Swapping chainrings would definitely help on climbs. Your current 30-32 bottom gear is reasonably low by touring standards, with a development of 30/32*π*0.68 = 2.0m, where the 24T chainring will give you ... 1.6m (20% reduction). You'll really notice that. 26T will shift easier and still be significantly lower.

Really the only reliable way to find out whether the rest of the components will work with it is to try. At worst you'll find that the front derailleur isn't really long enough to cope with the small chainring and the chain runs on the bottom of it for some of the smaller cogs on the cassette. Which is workable for many people - you end up with the granny ring only working with the biggest 3 or 4 cogs on the rear cassette. Shifting will likely be more difficult than you expect, especially getting out of that chainring back into the middle.

Doing that shift while climbing will be tricky, and that's what kills it for many people. You only get one chance, and if you don't make the shift you have to drop back, recover the bike, speed up and try again. Which is annoying.

To mitigate that it can help to change front derailleurs (basically buy the front triple derailleur with the widest range you can find), and drop a few teeth on the middle chainring to make the shift easier. That is at the cost, obviously, of harder shifts from the middle to big chainring since you've increased that gap.

If you can afford it, I think it's well worth buying a 26T cog and seeing what happens.

Other options

You can get some benefit from a bigger cog on the cassette, but the jump from 32T to 36T is not particularly large and you will probably struggle to shift that with your current rear derailleur. The obvious fix is a Rohloff hub :)

Answer 3

I'd start by swapping the rear cassette so that you have lower gearing (i.e. bigger gears in the back). The rear derailleur is what determines the biggest cassette (set of gears in the back) you can put on the bike (since they have to have enough tensioning ability to regulate the chain change for big gears). There are wide range (SGS), medium range (GS) and narrow range (SS). In this case, its a Shimano Deore derailleur, which is SGS. Thus, you can stick on a bigger rear cassette if you can't handle the climbs as is. Maybe a 12-36t or something.

I don't think I'd swap the chainrings out - 30t and 39t are already pretty low for most applications, and you need to swap the other chainrings out to smaller things in that case, since the front derailleur can approximately only do jumps of 10t reliably at a time. This is also pricey. That being said, the Surly LHT ships with a 26/36/48, so it might be worth a shot. But I'd start with a bigger cassette.