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Discussion Starter · #1 ·
The current set-up is a 52-39 with 12-23. My terrain is virtually flat with a few gentle rolling hills. As it is now, the 23, 21 and 19 are unused gears. I'd like to put a 42 tooth inner so that it will bump me into the 19 at times. Here's the issue.

My Ultegra has the type B chainrings and the 42 is only available in type A.
The tech at Shimano told me I'd lose shifting performance on the big ring because the shift ramps are designed for the 39 tooth and chain pick-up will be different using the 42 tooth A type.

I fitted one of my old 6-7 spd 42 tooth chainrings and I could see the ramps miss it and instead catch on the following ramp. Sadly, due to the spacing on the drop from 52-42, there is about a .5mm difference so the chain does not catch when going to the lower. So much for the old chain rings.

Now...it seems the "official" way to get the 42 inner is to go 53 for the A-type. The cost of this is about $75. A 11-21 cassette will also substitute though 11-21's seem scarace.

Advice on which direction to pursue: Mix the 42 A type with 52 B, go 42-53 A, cassette...???
 

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Personally, if you're not using those top easy gears, run an 11-21 and have the tightest spaced block out there. Would seem lots easier than having to deal with an entire new crankset to slap on a 42.

Just my opinion.

mike
 

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Shimano A-B.

I've mixed Shimano A and B rings for as long as I can remember and have never had any shifting issues. The A-B thing is a shift aid design to help those who do a lot of their shifting under full power and at low cadences. If you shift with a little more finesse, mix away.
 

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If you use mis-matched rings, it will slow front shifts while standing.
Rolling hills are a good time for the 53X19 and even 53X21.
 

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Discussion Starter · #5 ·
Thanks guys!

I'll give the chainring a shot since it is the least expensive route.

I'm curious what the ramp difference are between the A-B types...I'll have to take a look next time I get by a shop.
 
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