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understanding new drivetrain component gearing

Old 05-06-22, 07:51 AM
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rumrunn6
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understanding new drivetrain component gearing

I had the drivetrain components replaced on an older, entry level MTB. it seems fine, the gearing feels fine on a known hill I'm used to. however, I see a difference in the gearing when I look at specs on the paperwork. I don't think I need to be concerned, but it would be good to hear from someone, with actual knowledge, tell me it wasn't a bad move

I bought the bike 2nd hand (in the Spring of 2019), I don't know exactly what year it is. the only specs I could find easily are on the REI website

GT Timberline 1.0 29er Bike - 2014
https://www.rei.com/product/867504/g...29er-bike-2014

OEM - Rear Cogs Sunrace, 11-34, 8-speed (I can't confirm that it was an 8 speed not 7speed, I think it was a 7 speed)
NEW - SHIMANO CS-HG200 12-28 7 Speed Cassette

OEM - Crankset Forged Alloy, 42/34/24
NEW - SHIMANO ALTUS FC-M311 CRANKSET (BLACK) (3 X 7/8 SPEED) (SQUARE TAPER) (175MM) (42/32/22T) (RIVETED)

I'm hoping that losing some teeth in the back is compensated by also losing some teeth in the front? am I looking at this correctly?

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Old 05-06-22, 08:05 AM
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You can look at a gear-inch calculator such as https://www.bikecalc.com/gear_inches to see how close the gearing is. The 24/34 combination is about 18.7 gear-inches; the 22/28 combination is about 20.8 gear-inches. Not sure what the next largest cog was on the old cassette, but if it was a 30T, then the new gearing is close to that - basically you've lost just the very lowest gear.
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Old 05-06-22, 08:26 AM
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Originally Posted by nathand View Post
You can look at a gear-inch calculator such as https://www.bikecalc.com/gear_inches to see how close the gearing is. The 24/34 combination is about 18.7 gear-inches; the 22/28 combination is about 20.8 gear-inches. Not sure what the next largest cog was on the old cassette, but if it was a 30T, then the new gearing is close to that - basically you've lost just the very lowest gear.
thank you. I think I now have a smaller small front chainring. so maybe I didn't lose so much? I rode a known steep hill last night that seemed fine. it's about the steepest hill I ever climb. in the past I've been known to stop 1/2 way to catch my breath. I've been doing better on it the past year or so, but I haven't ridden it in several months. I was worried I wouldn't be able to climb it, but I was able to climb it
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Old 05-06-22, 09:04 AM
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using that calculator (700c/29er w/ 2.25" tires)
I think my OEM smallest gear inches was 20.58
& with the new stuff I think it is 22.90
so I think it is harder to pedal, but not much harder?
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Old 05-06-22, 09:35 AM
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Originally Posted by rumrunn6 View Post
so I think it is harder to pedal, but not much harder?
Right. It's probably equivalent to losing only the largest cog off your old cassette.
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Old 05-06-22, 10:17 AM
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Everything depends on how often you used the old 24/34 and if it was not low enough, or barely, on some climbs.

If there are no issues climbing with the new setup, you may have improved the gap between ratios; unless the old one was a mega with a 24 to 34 jump. If that is the case then you substituted the 34t for a 28t and the rest of the cassette might be identical.

But using smaller inner and middle chainrings lowered the overall ratios of the 11-24 cogs when in those chainrings.

John
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Old 05-06-22, 10:51 AM
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THANK YOU
losing my lowest gear is a drag. kinda important @63 with old joints, etc. I can fudge around with the other mid gears, but when you need LOW nothing else will do, except walking up the climb
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Old 05-06-22, 10:52 AM
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Originally Posted by 70sSanO View Post
Everything depends on how often you used the old 24/34 and if it was not low enough, or barely, on some climbs
THANK YOU it was livable as it was, but I had been thinking something lower would be nice
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Old 05-06-22, 10:55 AM
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Originally Posted by nathand View Post
Right. It's probably equivalent to losing only the largest cog off your old cassette.
THANK YOU wish I discussed it at the shop when I was dropping it off. I asked about it when I picked it up. they gave me the only thing they had in the shop & didn't save the old one. I'm a little disappointed in myself & the shop. I'll live with it for a while & see if it really matters. mostly today, I was just trying to understand what happened with the switch
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Old 05-06-22, 12:06 PM
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what derailler do you have? you cold put a 12/32 cassette on for $20 if the range of the derailer will handle it https://www.rei.com/product/737175/s...E&gclsrc=aw.ds
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Old 05-06-22, 12:18 PM
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Originally Posted by squirtdad View Post
what derailler do you have? you cold put a 12/32 cassette on for $20 if the range of the derailer will handle it https://www.rei.com/product/737175/s...E&gclsrc=aw.ds
THANK YOU!, from the spec sheet above it only shows "Shimano Acera" another website was more specific: "Shimano Acera, RD-M360"
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Old 05-06-22, 12:28 PM
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Originally Posted by rumrunn6 View Post
THANK YOU!, from the spec sheet above it only shows "Shimano Acera" another website was more specific: "Shimano Acera, RD-M360"

acera spec are 11 min rear cog, 34 max rear cog
43 tooth change wrap

so you would be good with the 12 -32 in terms of cog capacity

and you would be good with chain warp as you need 40 and derailer can handle 43 (see below)

might need a new/longer chain

change wrap = Difference between hi/lo front rings + difference between hi/lo rear cogs

change warp = (42-22 = 20) + (32-12 = 20)

chain warp = 20+20 = 40
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Old 05-06-22, 12:31 PM
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Originally Posted by squirtdad View Post
acera spec are 11 min rear cog, 34 max rear cog
43 tooth change wrap

so you would be good with the 12 -32 in terms of cog capacity

and you would be good with chain warp as you need 40 and derailer can handle 43 (see below)

might need a new/longer chain

change wrap = Difference between hi/lo front rings + difference between hi/lo rear cogs

change warp = (42-22 = 20) + (32-12 = 20)

chain warp = 20+20 = 40
very cool, thank you so much for taking the time to help! I'll put this on my bucket list & maybe have my LBS (not the shop that just installed the new stuff) do the swap if/when I decide to.
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Old 05-06-22, 12:38 PM
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I'm a little perplexed here. You, Rumrunn6, have been around BF a very long time. This seems like such a basic question.
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Old 05-06-22, 01:56 PM
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Originally Posted by zacster View Post
I'm a little perplexed here. You, Rumrunn6, have been around BF a very long time. This seems like such a basic question.
the older I get, the more respect I have for others' expertise. I may be on here a lot & for many years, but one learns what's relevant to themselves. I've never had an entire drivetrain replaced & as a visual artist I shy away from math problems. even when I was SCUBA diving I struggled w/ dive tables, but could swim like fish. when I was in my teens, I asked a bike shop for a smaller rear cassette on my 10 speed, cuz I wanted to go faster. hehe kids on the street, eh? I remember 1 killer hill that got tougher. but at that age, I could still climb it. don't have those legs/knees 46? years later

anyway, even when I know something, asking an expert for a fresh explanation, can educate me a little bit more
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Old 05-06-22, 02:48 PM
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Originally Posted by rumrunn6 View Post
the older I get, the more respect I have for others' expertise. I may be on here a lot & for many years, but one learns what's relevant to themselves. I've never had an entire drivetrain replaced & as a visual artist I shy away from math problems. even when I was SCUBA diving I struggled w/ dive tables, but could swim like fish. when I was in my teens, I asked a bike shop for a smaller rear cassette on my 10 speed, cuz I wanted to go faster. hehe kids on the street, eh? I remember 1 killer hill that got tougher. but at that age, I could still climb it. don't have those legs/knees 46? years later

anyway, even when I know something, asking an expert for a fresh explanation, can educate me a little bit more
Usually it's the other way, when you get older you become a stubborn old cuss. "That's how I do it and that's they way it is". Good to hear a different perspective. I'm getting older too and feel like a little of both sometimes.
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Old 05-06-22, 03:46 PM
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I have to agree with everyone else that a 12-32 7 speed is a good choice.

John
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Old 05-06-22, 04:48 PM
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Originally Posted by zacster View Post
Usually it's the other way, when you get older you become a stubborn old cuss. "That's how I do it and that's they way it is". Good to hear a different perspective. I'm getting older too and feel like a little of both sometimes.
oh definitely. old guys know stuff
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Old 05-08-22, 01:36 PM
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Originally Posted by squirtdad View Post
acera spec are 11 min rear cog, 34 max rear cog
43 tooth change wrap
so you would be good with the 12 -32 in terms of cog capacity
and you would be good with chain warp as you need 40 and derailer can handle 43 (see below)
might need a new/longer chain
change wrap = Difference between hi/lo front rings + difference between hi/lo rear cogs
change warp = (42-22 = 20) + (32-12 = 20)
chain warp = 20+20 = 40
thank you.
- if I change the cassette myself
- can I just see how the chain does on all gears before deciding about replacing? I don't ever see myself using large front to large rear gear
- I'll figure out the Rear Der. adjustment. do you think maybe I'll get lucky with just a cable/barrel adjustment? or the chain tension (for "B" adjustment)

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Old 05-08-22, 08:57 PM
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Originally Posted by rumrunn6 View Post
thank you.
- if I change the cassette myself
- can I just see how the chain does on all gears before deciding about replacing? I don't ever see myself using large front to large rear gear
- I'll figure out the Rear Der. adjustment. do you think maybe I'll get lucky with just a cable/barrel adjustment? or the chain tension (for "B" adjustment)
IMHO never safe to not be able to run big/big, no matter how much you tell your self you won't use it, there will be a situation where it happens, and that can mean every stops, with potential breakage of parts and body depending on speed, been there, done that, will not repeat New chain if needed is cheap insurance

Here are 2 great videos for chain sizing and derailler adjustment. both are pretty easy if you follow the steps IME

chain sizing small/small is my favorite

park tool derailler adjustment video

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Old 05-08-22, 11:18 PM
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You have compacted your ratios slightly, more on the top than on the bottom.

old: 11 34
42 103 33
34 83 27
24 59 19

new: 12 28
42 95 41
32 72 31
22 50 21

If it works for you, you can just keep using it!
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Old 05-09-22, 03:48 AM
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Originally Posted by squirtdad View Post
IMHO never safe to not be able to run big/big, no matter how much you tell your self you won't use it, there will be a situation where it happens, and that can mean stops, with potential breakage of parts and body depending on speed, been there, done that, will not repeat New chain if needed is cheap insurance
OK thank you. yeah I've had enough of that this year. thanks for there vid links
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Old 05-09-22, 03:51 AM
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Originally Posted by Fredo76 View Post
You have compacted your ratios slightly, more on the top than on the bottom.

old: 11 34
42 103 33
34 83 27
24 59 19

new: 12 28
42 95 41
32 72 31
22 50 21

If it works for you, you can just keep using it!
thank you. I don't totally understand that. my only concern is losing my lowest gear & getting it back or improving it, getting it lower. I rarely ever use the big ring up front

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Old 05-09-22, 08:43 AM
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Originally Posted by rumrunn6 View Post
I had the drivetrain components replaced on an older, entry level MTB. it seems fine, the gearing feels fine on a known hill I'm used to. however, I see a difference in the gearing when I look at specs on the paperwork. I don't think I need to be concerned, but it would be good to hear from someone, with actual knowledge, tell me it wasn't a bad move

I bought the bike 2nd hand (in the Spring of 2019), I don't know exactly what year it is. the only specs I could find easily are on the REI website

GT Timberline 1.0 29er Bike - 2014
https://www.rei.com/product/867504/g...29er-bike-2014

OEM - Rear Cogs Sunrace, 11-34, 8-speed (I can't confirm that it was an 8 speed not 7speed, I think it was a 7 speed)
NEW - SHIMANO CS-HG200 12-28 7 Speed Cassette

OEM - Crankset Forged Alloy, 42/34/24
NEW - SHIMANO ALTUS FC-M311 CRANKSET (BLACK) (3 X 7/8 SPEED) (SQUARE TAPER) (175MM) (42/32/22T) (RIVETED)

I'm hoping that losing some teeth in the back is compensated by also losing some teeth in the front? am I looking at this correctly?
This calculator is one of the best I’ve run across for comparing drivetrains. Below is your old and new drivetrains. The number above the triangles are gear inches. The calculator also allows for those values to be speed or development or gear ratios. You’ve lost both high end and low end with the 12-28 cassette.


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Old 05-09-22, 09:25 AM
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Originally Posted by cyccommute View Post
This calculator is one of the best I’ve run across for comparing drivetrains. Below is your old and new drivetrains. The number above the triangles are gear inches. The calculator also allows for those values to be speed or development or gear ratios. You’ve lost both high end and low end with the 12-28 cassette.
thank you!
considering they also changed the front chain rings, what effect will installing a 12-32 rear, do for me? (which I am leaning toward doing)
I expect my low will be lower than OEM, (which I would welcome for the rare need) I'm not too concerned about the high gear, I rarely used it if ever

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