anga

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Added Nov 21, 2022Will 6/7 speed RD-TY300-SGS and appropriate 9-speed shifter work with 9-speed cassette CS-HG400-9, 12-36T?Max capacity of RD is 34T. link to cassettehttps://bike.shimano.com/en-EU/product/component/alivio-m3100/CS-HG400-9.html ​​​​​link to RDhttps://bike.shimano.com/en-US/product/component/tourney/RD-TY300-SGS.html
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Hi

Two combinations.

Added: Shimano

1. 7-speed shifter, 8-speed cassette, 7-speed derailleur
Can above combo use 7 out of 8 cogs in the 8-speed cassette?

2. 8-speed shifter, 8-speed cassette, 7-speed derailleur
Will above combo use all 8 cogs in the cassette?

Thanks

dedhed

Brand?

anga

Edit first post. Shimano

bboy314

1. No (not reliably at least)
2. Yes

cyccommute 

If you are using Shimano HG or SRAM 8 speed, the thickness of the cogs are close enough (1.85mm for the cog and 3.15mm for the spacer for 7 speed vs 1.8mm and 3.0mm for 8 speed) that they can work.

Yes, that will work. For the derailer, the number of speeds doesn’t matter for 7, 8, or 9 speed for the derailer. Once you get to 10 speed, Shimano changed the pull ratio so that it won’t work with the lower number of speeds.

veganbikes

2 is going to work I am running 7 and 8 speed derailleurs with 9 speed shifters (cassette and chain as well) and they work just fine. 9 is the way to go as you can still find decent serviceable 9 speed stuff.

hokiefyd 

I have experience with both situations described above and both have worked acceptably well to me. This is with Shimano "mountain" stuff, though I think mountain and road are pretty interchangeable in 7- and 8-speed land.

I'm currently using an 8-speed Microshift thumb shifter on a 7-speed Shimano cassette with an 8-speed Acera derailer on one of my bikes and it works very nicely.

hokiefyd 

Did you mean to say Shimano IG (Interactive Glide)? I think the sprocket thickness on those is pretty thick (with thin spacers). I think it's Shimano HG (Hyper Glide) that's compatible with SRAM, right?

https://sheldonbrown.com/cribsheet-spacing.html

(Having said that, I think IG's sprocket spacing itself...center-to-center...is compatible, so should work similarly as long as the chain will support it.)

cyccommute 

Sorry. I mistyped. Read HG and typed IG.

dedhed

10 speed road is compatible but not mountain.

"In general" Shimano 6 - 10s road and 6 - 9s mountain rear derailleurs all use the same ratio. There are a couple outliers in Dura Ace

anga

Thanks guys.
Will upgrade to a 8-speed cassette from a 7-speed. The additional low gear will help.

HillRider

10-speed is the dividing line. For road rear derailleurs 10-speed is backward compatible with 7,8 and 9-speed components. For MTB derailleurs 10-speed is not backward compatible. 11-speed and above aren't backward compatible at all.

cyccommute 

I assumed that anga is using mountain derailers. That may have been a wrong assumption but someone using 7 and 8 speed equipment at this date is probably not using road equipment. No point in muddying the already muddy waters.

cyccommute 

Just to be clear, your system will work better if the shifter and cassette are matched. You can make a 7 speed shifter shift an 8 speed cassette but you’ll get better results if you make the 7 speed shifter shift a 7 speed cassette and an 8 speed shifter shift an 8 speed cassette. If you have a 7 speed shifter and need lower gears you can get wider range 7 speed cassettes like this one.

anga

I have an 8-speed shifter.

70sSanO

If you can fit an 8 speed cassette onto the freehub, that is the best way to go.

I’ve lived in the 7 speed cassette with 8 speed shifters for a years due to freehub body/frame limitations. Still have one set up that way.

I’ve read many posts saying it is possible as is, but in my opinion, the only way I would run it is to:
Use a cassette with full length cogs,
Take it apart, and
Sand the plastic spacers to get the correct center to center spacing of 4.8mm.

Depending on the freehub body and lockring, you might need a slightly wider spacer behind the cassette, or shim washer(s) between the lockring and the 1st position cog. This is only necessary if the lockring bottoms out against the freehub body.

You need to block out one shift. The only caveat doing this with any pawl/ratchet index shifter, front or rear, is make sure to set the end limit screw doesn’t cause the pawl to wedge against the ratchet. Actually this holds true regardless of blocking a shift.

John

cyccommute 

That’s the best way to go. Your 7 speed derailer will work with it.

Hondo6

Generally true, but there is one exception.

Shimano's current 10-speed road group (Tiagra 4700) uses the new Shimano 11-speed road pull ratio. The Tiagra 4700 RD won't work with Shimano 6-9 speed shifters, or other Shimano 10-speed road shifters, for that matter - including Tiagra 4600.

I understand the same is true of the Tiagra 4700 double FD, but not the triple. Can neither confirm or deny this from personal experience, though.

anga

Will 6/7 speed RD-TY300-SGS and appropriate 9-speed shifter work with 9-speed cassette CS-HG400-9, 12-36T?
Max capacity of RD is 34T.

link to cassette
https://bike.shimano.com/en-EU/produ...S-HG400-9.html

​​​​​link to RD
https://bike.shimano.com/en-US/produ...TY300-SGS.html

cyccommute 

Maybe but probably not. The shifter and the cassette aren’t the problem. The rear derailer is. It just doesn’t have the capacity for the 36 tooth cog and likely can’t be pushed to make it work. You’d be better off with an Acera M3000 which has the capacity for a 36 tooth cog. It’s about $30 and is worth every penny when compared to the Tourney.

anga

Keep reading that max rear capacity for Shimano RDs is conservative and can easily handle a couple of more teeth.

Other point I recall is that front difference in chainring sizes is binding while rear difference in cog sizes is not as long as total capacity is not exceeded.

Here front difference is 18 (40 - 22), rear difference is 24 (36 - 12) and total difference of 42 is less than total capacity of 43.

I have zero practical experience on this issue.
So, experienced users are welcome to comment.

cyccommute 

The capacity…which you have correctly calculated and is relate to the amount of chain that can be wrapped around the cogs and chainwheels…is different from the maximum cog size. Capacity is very conservative. The size of the max cog usually isn’t. The Tourney has a maximum low cog size of 34 teeth. The Acera I suggested has a max cog size of 36.

anga

​​​​​​Total capacity of RD is 43
Low sprocket_Max is 34T
Low sprocket_Min is 11T
Max front difference is 20

What I recall reading is that the derailleur can handle a sprocket 2T larger than the Low sprocket_Max as long as the total capacity is not exceeded.
cyccommute are you saying this is not the case?

If above RD doesn't work, will go for RD-M2000 or RD-M3100 that support 36T. RD-M3000 is unavailable here.

cyccommute 

Some derailers can, some can’t. It’s hard to predict but, if there was one that probably won’t handle it, it would likely be the Tourney. That derailer is just too poorly designed to do much with it.

Yes, the two rear derailers you listed would work.

anga

CS-HG400-9 12-36T is sold out!