Author Topic: Advice for choosing components to reduce gear inches  (Read 1762 times)

0 Members and 1 Guest are viewing this topic.

Offline DavidJohnD

Advice for choosing components to reduce gear inches
« on: October 11, 2016, 05:26:37 pm »
Hello,

I have just purchased myself a new touring bike Genesis Tour De Fer 20 (2017 model).  I love the bike but I have one problem, the gear inches are too high with a 30T on the small chainring with a 32T on the cassette with a 700C wheel giving about 25 gear inches and I would like to ask you all to provide the best options which I can use to reduce the gear inches to below 20.  I plan to use the bike which will most likely involve a lot of steep hills with a lot of weight.  The bike is 10 speed and comes with Tiagra 4703 groupset and I like the STI levers (I don't want to change these), it has Deore rear hub and I am confused with the chainline and what components to use as it is currently all road components but I realise that I possibly need to mix road and mtb components to achieve this?

I believe I need to keep the tiagra front mech (as this works with the STI shifters), use a mtb crankset, have a mtb 9 speed xt rear deraillure and a mtb 36T cassette - the problem I foresee will be the chainline - how can I maintain the chainline of 45mm since the front mech works to this, but most mtb cranksets are 50mm?  Would I need to choose a crankset which uses the tapered BB or is there a way that I can use a hollowtech 2 BB?

I would welcome any advice you can help me to choose the components to reduce the gear inches while keeping my STI shifters.

Thank you in advance.

David.

Offline DavidJohnD

Re: Advice for choosing components to reduce gear inches
« Reply #1 on: October 11, 2016, 06:54:49 pm »
Is there a simple solution which I could be overlooking, like using a small chainring in replacement for the 30T or another solution?

Offline mbattisti

Re: Advice for choosing components to reduce gear inches
« Reply #2 on: October 11, 2016, 08:31:59 pm »
I had the same situation with my Burley Hudson.  I replaced the 30 tooth chainring with a 24, and added a N-gear chain keeper to prevent the chain dropping off when coming down off the middle ring (it's a big jump).  Then I replaced the 30 tooth cassette with a 36.  You will need a long cage derailleur to take up all that slack chain, but even a 32 or 34 tooth cassette with that 24 tooth chainring will give you some pretty low gearing.  And relatively cheaply.

Offline RussSeaton

Re: Advice for choosing components to reduce gear inches
« Reply #3 on: October 11, 2016, 10:39:04 pm »
Unfortunately, you seem to have picked the most messed up crankset Shimano makes.  A FOUR bolt crankset that uses 110/74mm bcd.  Until now I had never heard of such a thing.  And looking around, there are ZERO chainrings available for this goofy size.  So it looks like this crankset is stuck with the factory 50-39-30 configuration.  Maybe the simplest and cheapest solution is to just replace the crankset with a Sora triple.  See following links.  It has a 74mm bcd FIVE bolt inner chainring.  You can cheaply and easily put a 24 tooth inner ring on it.  Then your low becomes 24x32.  Should be low enough.  You could also try a 11-34 cassette.  Get a little lower and probably not much chance your rear derailleur will not work with that.  If you go nutty and try a 36 rear cog, then your derailleur hanger my not be low enough and the rear derailleur will not fit underneath the 36 cog.  So that will not work.  34 most likely not a problem.  But you have to try it to know.  Going with a mountain bike triple crankset will allow you to get a 22 tooth inner ring.  Little lower than the Sora 24 inner ring.  Not sure it makes much difference.  Safest is to go with the Sora.  Positive it will work 100% fine.  24 inner ring is low enough.  I rode the Dolomites and Alps with a 24x32 low gear and four panniers and other bags.

http://www.jensonusa.com/Shimano-Sora-FC3503-Triple-Crankset
http://www.ribblecycles.co.uk/shimano-sora-triple-3503-9spd-chainset/pid=19642?currency=USD&location=USA

http://www.genesisbikes.co.uk/bikes/adventure/adventure/tour-de-fer/tour-de-fer-20

My current touring bike has Shimano 105 triple STI 10 speed shifters, Tiagra triple front derailleur, and 9 speed Deore rear derailleur.  10 speed cassette 11-32.  Shifting is 100% perfect always.  Crank is old 7 speed Deore with TA 44-33-20 rings.  Inner ring is down to 20 through a Avid Tri-Adaptor thing that allows me to replace the separate spacers and bolt on a 58mm bcd inner ring.  Perfect shifting always.  Doubt there is enough room to allow the rear derailleur to get under a 34 ring on the cassette.  No way in He-- it could ever fit under a 36 ring.  Rear derailleur hanger length will decide if your bike can fit a 32, 34, or other rear cog.  32 cog always works. 34 may or may not work.  36 is very doubtful unless the bike was specifically built to work with that pie plate.
« Last Edit: October 12, 2016, 03:30:03 pm by RussSeaton »

Offline Pat Lamb

Re: Advice for choosing components to reduce gear inches
« Reply #4 on: October 12, 2016, 09:52:26 am »
I think Russ has the best solution, just replace the crank.  I've seen reports of the Tiagra front derailer handling a 24 low, I don't know if it'll work with a 22.  Sticking with the stock Sora 24 is easiest, and will give you a decent low gear.

Sounds like OP is a mechanical newbie; if that's the case, you're probably best off finding a bike shop with a decent mechanic and letting him (or her) do the switch.  The FD can probably handle the MTB triple, but its position may have to be tweaked -- much better to let the pro do this right off.

Offline dkoloko

Re: Advice for choosing components to reduce gear inches
« Reply #5 on: October 12, 2016, 11:23:11 am »
If you go nutty and try a 36 rear cog, then your derailleur hanger my not be low enough and the rear derailleur will not fit underneath the 36 cog.  So that will not work. 

No trouble for me changing to 36 rear cog. I add that changing components to get below 20 gear inches can be much more challenging than being satisfied with a 20 inch low.

Offline RussSeaton

Re: Advice for choosing components to reduce gear inches
« Reply #6 on: October 12, 2016, 03:39:06 pm »
If you go nutty and try a 36 rear cog, then your derailleur hanger my not be low enough and the rear derailleur will not fit underneath the 36 cog.  So that will not work. 

I add that changing components to get below 20 gear inches can be much more challenging than being satisfied with a 20 inch low.

24x32 low gear with 700C wheels gets you down to 20 gear inches.  It used to be very easy to get a triple crank with a 74mm bcd inner ring.  Put a 32 cassette on the bike and you are at 20 gear inches.  Very easy.  Every touring bike ever made can fit this.  Going to a mountain bike triple with 22 inner ring gets you another 1-2 gear inches lower.  Going to a 34 or 36 cassette gets you another 1-2 gear inches.  All very small changes.  Once you get to 20 low, you are low enough.  Everything else will probably not even be noticed.

Offline DavidJohnD

Re: Advice for choosing components to reduce gear inches
« Reply #7 on: October 12, 2016, 06:01:48 pm »
Hello everyone,

Thank you for taking time to reply to my message, I am going to look at the Sora crankset as it seems the easiest, simplist and cheapest solution.  Since I currently have 50, 39 and 30, I would like to change all of the chainrings to give me something like: 24, 34, 44, which then makes me think that an mtb crankset should work with a road front mech?  I am also aware that on SheldonBrown's website the difference in teeth between the middle and large chainring should be no more than 13 teeth.

As a thought which I had considered is choosing an mtb crankset with a road front mech feasible, would I need to chose a mtb crankset which gives a chainline of 45mm, or would I need to use a road hollowtech II BB to force the mtb chainrings to give me a chainline of 45mm?  Or am I potentially opening myself upto a whole world of pain?  Have any of you done this before? I would like to evaluate the different options before I make my decision.

I am planning on doing the changes myself and using it as a learning exercise, I have previously replaced the crankset on my old 8 speed mountain bike and regularly service and maintain the bike.  The gap in my knowledge is road components and potentially mixing road and mtb components together as I think it could be very easy to get this mixture wrong?

I think I will also aim for 24x32x700c to get the 20 gear inches to keep things simple to start with so that I can start doing test rides with a fully loaded bike and steep hills! :)

Thank you.

David.

Offline Pat Lamb

Re: Advice for choosing components to reduce gear inches
« Reply #8 on: October 12, 2016, 07:49:00 pm »
Your chainline questions illustrate why I recommend letting a bike shop change things for you.  Let them figure out what you need; often the price of the part (crank) will include installation and adjustment.  If it were a cassette, I'd say go for it.  But you may need a couple of tools, which will eat up any savings from buying online (even if you get it right the first time and don't have to eat shipping).  Besides, a learning exercise is better used on something you're likely to repeat -- like changing cassettes or chains when they wear out.  You may never need to replace the crank, although you may need to replace the BB after 5-10 years.

Offline dkoloko

Re: Advice for choosing components to reduce gear inches
« Reply #9 on: October 12, 2016, 10:25:35 pm »
Hello everyone,

As a thought which I had considered is choosing an mtb crankset with a road front mech feasible, would I need to chose a mtb crankset which gives a chainline of 45mm, or would I need to use a road hollowtech II BB to force the mtb chainrings to give me a chainline of 45mm? 

Thank you.

David.

I don't understand fixing on chainline of 45mm. With a triple crankset, middle chainwheel should align parallel with frame with middle cog. BB needs to match crank. I wonder if front derailleur is that critical; I have a number of times used a double racing front derailleur with a touring triple crank. Pat Lamb recommends letting a bike shop make the changes. I suspect, given your inexperience, that whatever components you buy, you will be making many adjustments, maybe changes in components, afterwards, to get everything working. Whether you want to hazard this, as a learning experience, is up to you.

Offline DavidJohnD

Re: Advice for choosing components to reduce gear inches
« Reply #10 on: October 13, 2016, 09:30:48 am »
Thank you for your advice.

I am going to look at the Sora crankset.

Many thanks,

David.

Offline GusHauck

Re: Advice for choosing components to reduce gear inches
« Reply #11 on: August 12, 2017, 09:35:54 am »
Question: If one can achieve the gear-inch target range of 18 - 110 by either changing the chainrings or the cassette (similar cost), is there a preferred option?

I'm in the process of outfitting a Cannondale Hybrid with MTB component set to be my touring cycle. I can get to a gear-inch range of ~18 to ~110 by changing the crankset and chainrings (staying within the 20 tooth capacity for the front derailleur) OR changing the cassette cogs (rear derailleur will adjust to accommodate the largest cog). Cost and effort are about equal.

The one advantage of the crankset change is that I could go with a longer crankarm (175mm rather than keep the current 170mm).

Opinions?

Online John Nelson

Re: Advice for choosing components to reduce gear inches
« Reply #12 on: August 12, 2017, 02:02:15 pm »
Very interesting question. One deserving of its own thread. No need to dredge up an old one.

Offline TransAM2010

Re: Advice for choosing components to reduce gear inches
« Reply #13 on: August 16, 2017, 02:25:24 pm »
Question: If one can achieve the gear-inch target range of 18 - 110 by either changing the chainrings or the cassette (similar cost), is there a preferred option?

I'm in the process of outfitting a Cannondale Hybrid with MTB component set to be my touring cycle. I can get to a gear-inch range of ~18 to ~110 by changing the crankset and chainrings (staying within the 20 tooth capacity for the front derailleur) OR changing the cassette cogs (rear derailleur will adjust to accommodate the largest cog). Cost and effort are about equal.

The one advantage of the crankset change is that I could go with a longer crankarm (175mm rather than keep the current 170mm).

Opinions?

For me I split the difference and do some of both. Cassettes are relatively cheap but you often need to swap derailleurs as well to get the gearing you want on the low end. I like triple cranks with a 24 or 26 small cog and rear cassettes that are 11/12-34 with a 9 speed drive train. This gives me (with 26 inch wheels) very close to the range you are indicating with the fewest other compromises in other ways for my riding style. I think different riders have different considerations based upon other factors so there's no simply right or wrong answer. 

Offline RussSeaton

Re: Advice for choosing components to reduce gear inches
« Reply #14 on: August 16, 2017, 09:09:24 pm »
Question: If one can achieve the gear-inch target range of 18 - 110 by either changing the chainrings or the cassette (similar cost), is there a preferred option?

I can get to a gear-inch range of ~18 to ~110 by changing the crankset and chainrings (staying within the 20 tooth capacity for the front derailleur) OR changing the cassette cogs (rear derailleur will adjust to accommodate the largest cog). Cost and effort are about equal.

Depends on where you are starting from.  And what components you are starting with.  If you are starting with a triple crankset that allows 64 or 74mm bcd, then its real easy to just put a 22 or 24 tooth inner ring on the crank and you are done probably.  If you are starting with a 11-28 cassette and a crank that only allows 30 tooth inner ring, then its easiest to put a long cage rear derailleur and 11-36 cassette on the bike.  Generally its a hell of a lot easier to change derailleurs and cassettes than cranks and bottom brackets.

When setting up my loaded touring bike, I changed the chainrings AND the cassette.  Sort of.  It was really just the chainrings.  But I went from a seven speed 12-32 cassette to a ten speed 11-32 cassette.  And changed chainrings from a 48-45-24 to 44-33-20.  So my decrease on the low side came only from the chainrings.  High gear stayed exactly the same.  But I picked up a LOT more usable middle gears from the cassette change.

20 tooth capacity for a front derailleur?  That's a good one.  Is it April Fools Day?