Drive train set up too ambitious?

[Milzy]

I’m thinking of putting a semi compact on my compact chain ring bike and changing the rear 32T to a 34t.
Thinking is I can get extra speed down hill as I tend to spin out a lot on compacts but also on the super steep technical stuff we like doing I can easily twiddle away without the rear wheel slipping. I know to sit down & be smooth etc but we ride lots of these tiny steep back roads that are damp and mossy.
I have a long cage mech it’s just would the ratios run properly thinking of chain length and angles. In my mind you should just get away with it but I don’t want the chain dropping or drooping in lower gears. What do you think?

 

[HLaB]

Go for it. I've swapped out chaingrings and cassettes a few times over the year and AFAIC as long as you have your chain length right (Park tools have a good guide there) there's not to much to it.

 

[sleuthey]

It worked well for me when I put an 11-40T on the rear and a 38T on the front. I did need a hanger extender but don't think you will for 34T

 

[Milzy]

It worked well for me when I put an 11-40T on the rear and a 38T on the front. I did need a hanger extender but don't think you will for 34T

No the R8000 long cage mech is suited to 34. Probably unofficially take a 36. I will try it, should be good for all terrain. I was trying to chase a mate down in a decent tail wind and frustratingly span out, it was only slightly down hill too.

 

[Dogtrousers]

If I've understood right, you want to put a subcompact (something like 46/30?) onto a drivetrain that already has a compact (50/34). If I've got that right, then you might want to have a look at this thread here. https://www.cyclechat.net/threads/mullet-drivetrain-conversion.285302/ in which @rivers went one step further put 46/30 on the front and 11-42 (I think) on the back. So significantly more extreme than what you want to do but interesting reading on the art of what's possible.

If I've not understood right. Just ignore me.

 

[ColinJ]

SEMI compact; something like a 52/36?

 

[Dogtrousers]

SEMI compact; something like a 52/36?

Ah ... I mis-read it (as Sub, not semi) Ignore me. It all makes a bit more sense now. The references to spinning out seemed a bit weird, but they don't any more.

Anyway, just figure out the required mech capacity (big ring+big sprocket-small ring-small sprocket), compare it with the published capacity of the mech, and if your mech is OK, then OK. If it's just a bit short, then cross your fingers.

 

[fossyant]

Spinning out on a 50 x 11/12 ? Is that what you are saying ?

 

[Dogtrousers]

Spinning out on a 50 x 11/12 ? Is that what you are saying ?

50x11 @100 rpm is 57.3 km/h 35.6 mph
50x11 @110 rpm is 63.0 km/h 39.2 mph

50x12 @100 rpm is 52.5 km/h 32.6 mph
50x12 @110 rpm is 57.8 km/h 35.9 mph

Assuming spin-out is somewhere over 110, but 100 is controlled.

 

[Milzy]

Yes 50/34 great for up hill but bad for down hills and tail winds. Especially chasing a big powerful club mate.

 

[fossyant]

You need to spin more. I rarely use 53 x 13 or 14.

 

[Jameshow]

You need to spin more. I rarely use 53 x 13 or 14.

I have to use a 54/10 all the time don't you know!🦵🦵🦵🤣🤣🤣

 

[Venod]

I have one bike with 52/36 and 12- 34 11speed on the back, I never spin out, but I wouldn't with a 50 - 11 either.

 

[Milzy]

I have one bike with 52/36 and 12- 34 11speed on the back, I never spin out, but I wouldn't with a 50 - 11 either.

My bike will be same as yours then. Find some long steep hills and try to sprint down. Easy to spin out. I know many who don’t like going down fast though, and some are very strong riders.

 

[Sharky]

I have one bike with 52/36 and 12- 34 11speed on the back, I never spin out, but I wouldn't with a 50 - 11 either.

50x11 is a higher gear than 52x12