madsen

So I have a new to me bike that I need to change the gearing on. It is a 99 co motion with a 145 rear spread. The front chain rings are new FSA 52 39 30. Rear cassette is an 8 speed Shimano with like 12 30.
I have 2 thoughts/ questions. I am wondering if I can / should get a sheldon Brown Cycloturist 13-30 9 speed ?
What problems will that cause with the rest of my system if I go to a 9 speed ?

Second can I just change the inner 30 to a 24 , Obviously change chain and then will it shift ok ? Derailleur looks to be a long

Or should I go with a different chain ring set with new crank arms. Bottom bracket looks new Crank arms are old Shimano.

Any thoughts ideas are very welcome.

JOHN

fietsbob

BCD, bolt circle diameter, determines how small the 3rd chainring can be 74mm BCD, its 24t.
58mm, its 20t

A 145 is a Tandem standard , Shimano's current tandem hub will take the 9 speed stuff ..

the steel 10mm axle is common to both hubs, so if you want 36 rather than 40 or 48 spokes
they can be modified..

now that cassettes are 12t, 48t big ring should be large enough, 11t, a 44t will do..
so many touring rigs, adopt MTB drivetrains..

Chris_W

If you change the cassette to a 9-speed then you'll also need to change the chain and right-hand shifter (unless the current shifter is not indexed, but 8-speed stuff normally is indexed).

You can certainly change the inner ring to anything down to 24 teeth, and nothing else needs to be changed to do this (not even the chain, which you suggested). I would recommend a 26 tooth ring, 24 tooth might be a bit too big of a cadence jump between small and middle rings. It would be a good idea to add an anti-chain-drop device inside the inner ring if you change it to prevent derailments. I like the N-Gear Drop Stop the best, but the Deda Dog Fang might be more readily available.

For the middle ring, 39 teeth should be fine. The big ring is not really needed on a touring bike - I actually got rid of mine and replaced it with a chainguard, and so now have a 26-42-chainguard crankset.

fietsbob

Had a 7 speed F/W 13:50 high 24:34 low, 700c wheels .. 50/40/24 triple, worked fine .

friction bar end shifters on drop bars.. 110-74 crank

found a 58-110 crank, then a 22/36/48 was the kit.

the cadence change is coped with by a double shift, down on the crank and up on the hub.

tape the gear ratio chart on the frame if you need to be reminded which ratio combo,
is the next lower one.

seeker333

Most Shimano FDs are designed to handle a maximum 22t change from high to low, ie 52-39-30, 44-32-22, etc. They usually have a min and max ring spec as well, because the curvature of the FD cage is designed to match the diameter of intended ring sizes. If you're not real handy at improvising mechanical solutions, then you should stick to the specs to avoid trouble.

A Sugino 26-36-46 or similarly geared "trekking" crankset works well for loaded touring, especially combined with a std 11-32 or 11-34t 9s mtb cassette. Most tourists aim for a gear-inch range of ~20 to ~120. The Sugino crank and a 11-32t casette on a 700c wheeled bikes yields a range of 21-117. I go even lower on my bike, about 19-112 using a mtb crank. Many Sugino XD600 owners swap the 26t for a 24t inner ring.

As mentioned in #3, you will also need a chain and 9s shifter. Shifters are normally sold in pairs, and may not cost much more than the odd right hand shifter from ebay/craigslist/lbs/etc. Also you'll need a mtb RD to handle 11-34t cassette, or the newer 11-36t. Otherwise you're stuck with whatever range your current RD will accommodate. Also note there is a capacity spec for the RD, since it must take up slack from both the tooth range of cassette plus tooth range of the crankset. Mtb long-cage RDs often have a 45t range, meaning they can handle a Shimano std crankset (22t) plus a std cassette (another 23t). Specs are usually stated for min cog, max cog, and capacity, like here on a 761 RD:

https://techdocs.shimano.com/media/te...9830676130.pdf

Just a few choices force you to buy other components, and before you know it you've replaced most (all) of the drivetrain. This is why it's important to know this stuff before you buy a used bike, thinking you can perhaps get by just changing an inexpensive ring, then finding out later it's not that simple. If you can tolerate less-than-perfect shifting then you can ignore some of these rules to some extent and jury-rig component combinations. The problem here is it's hit-or-miss, and there's usually no one that can tell you with certainty that parts a + b + c + d + n will work together as desired.

LeeG

John, what is it you want with new gearing that you aren't getting now?

madsen

Gearing is way to high. I am old and fat and carry a heavy load. So at a minimum I need a low of 20 gear inches and probably nothing over 90 - 95 at the top. I did a trip last year with another bike of 550 miles and had a great time but I had frame wiggle and walked way too many hills and had hub problems but I still had a great time and will do at least 750 to 800 this summer
So I bought a bike that wont wiggle and hubs with rims that wont go bad" Phils " with 36 spokes. Having ridden it a few times and done the gear calculations.I know that it is not low enough and is higher than I would use 99% of the time.

ClemY

Concur. For me, the gearing is much to high, but I am old and heavy. I like a 20-32-42 chain ring set with a 12-36 9 spd. cluster. I can't imagine myself needing more than a 95" top gear, and there really isn't such a thing as too low a granny, at least for me.

dwmckee

I had same gearing on my comotion tandem. First I dropped the 30 front to a 28 (you can maybe go to 26, but it starts to affect shifting performance if you go too far...) That was a cheap first step. That was not low enough for us so next we went to a larger rear cassette. You probably can stay with an 8 speed with a larger cog which is way easier and cheaper than changing to a 9 speed. You generally can do it with no adjustment changes or shifter changes as long as you have a long cage derailleur and stay 8 speed; the cassette will cost you $25 - $50 on eBay and can be changed yourself very easily with a $5 tool. The 8-speed drivetrain is really bomb proof and way more tolerant of minor mis adjustment of gearing. When you go to 9 and 10 speed you will find it takes finer and more frequent adjustments to keep it in tune. Your 8 speed may not need adjusting for several years; a 9 or 10 speed may need a few fine adjustments during the season to keep it running perfectly!

Here are two 8 speed 34 tooth cassettes that may work for you in your current drivetrain:

https://www.ebay.com/itm/SHIMANO-CS-H...item56547db8fe
https://www.ebay.com/itm/Shimano-Cass...item3360ade61d

Both are $25.00ish in price...

You MAY need to go to a slightly longer chain, but I would try just the gear changes and see how it runs for you first.

BTW we found with the larger rear cassette we were able to do a lot more riding staying on the middle front chain ring, which was really nice!

Tourist in MSN

Start with a 24t instead of the 30t chainring. You probably have a road triple crank, so a 74mm bolt circle diameter 24t ring should work. From this link you can click on the crib sheet to verify if you have a 74mm circle.
https://www.sheldonbrown.com/gloss_bo-z.html#bcd

You might want to get a chain catcher too.

You will probably lose the ability to use your smallest chainring with a couple of the smallest sprockets in the rear. The issue is that the cage probably won't take up all the slack, but you should not be that cross chained anyway. Thus, this is not a problem, but you should be aware that you have to work harder to avoid those gears.

But if you really want a lower lowest gear after trying a 24t ring, you could either get a mountain crankset with a smaller than 24t ring or a new cassette with a larger biggest sprocket. Or both.

I suggest one step at a time instead of buying new cassette, cranks, etc. You might find that one new 24t chainring is enough.

I am happy with an eight speed 11/32 rear cassette with my 24t granny gear on a road triple, I run a 52/42/24 front. I built up my first touring bike with this gearing in 2004, was happy enough with it that I replicated the gearing on my second touring bike that I built up in 2010.