Mixing chainrings?

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tonyxcom said:

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Thanks anyways. Funny you mentioned Universal Cycles, since they are here in Portland and where I buy most of my stuff locally even though there are a big online retailer as well. I was going to order the 26t SLX ring tonight, but was really wanting a 24t instead.

yeah I reread your post and realized you wanted 24t.

anyway, you shouldn't have any problem with mixing chainrings. I currently have a 24/36 combo on my M970 cranks and don't have any shifting problems. I think some of the fancier chainrings (like XTR) have different shift ramps for 22 or 24t inners.

And Universal is great. Prices aren't always the best, but they are ultra reliable, only 2 days to San Fran and I don't have to pay tax.

take another look at your small ring..... you won't find any shift ramps on them....you can use any chainring that will fit your bolt pattern with no issues. Remember you shift down to and up from the little ring. That gear choice sounds like it might work- I might give it a try

tonyxcom said:

yeah I reread your post and realized you wanted 24t.

anyway, you shouldn't have any problem with mixing chainrings. I currently have a 24/36 combo on my M970 cranks and don't have any shifting problems. I think some of the fancier chainrings (like XTR) have different shift ramps for 22 or 24t inners.

And Universal is great. Prices aren't always the best, but they are ultra reliable, only 2 days to San Fran and I don't have to pay tax.

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Thanks Tony,

What brand 24 and 36t ring are you running on your Shimano cranks. I know XTR makes a 24t inner, but aluminum, not what I want, looking for 24t steel only that would work well with the 36t SLX middle ring. Universal price matched a 26t SLX inner ring for $9.22 only, so may just go with that, but I hate to lose gears for the climb, especially while on a +35lb bike.

I liked 36/26t more than 36/24t- steep rolling terrain worked better with the 26, it shifted a bit better, and the gear range gap when i shifted the front end wasn't as big. Those deore 26t rings are cheap too. That's what i'd do.

scottzg said:

I liked 36/26t more than 36/24t- steep rolling terrain worked better with the 26, it shifted a bit better, and the gear range gap when i shifted the front end wasn't as big. Those deore 26t rings are cheap too. That's what i'd do.

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Thanks Scott, that's what I will probably do. I don't like the jump between the 36t and 22t ring right now, doesn't shift so great up front especially with the traditional, non-compact SLX front der.

Did you happen to notice the loss of gear going to the the 26t from the the 24t? I love my 22 granny for long, steepish climbs (>2k'), but don't like the pedal kickback with the 22t, so will take the gear loss.

Did i notice? Yeah, i could tell. Wasn't an issue, and i would be hard pressed to tell at all after 3 rides. How much time are you in your lowest gear that you NEED to be there?

It's been a few years, but i remember having to cut a little bit of the chainring off with a grinder to get it to clear the outboard BB cups.

jgusta said:

Thanks Tony,

What brand 24 and 36t ring are you running on your Shimano cranks. I know XTR makes a 24t inner, but aluminum, not what I want, looking for 24t steel only that would work well with the 36t SLX middle ring. Universal price matched a 26t SLX inner ring for $9.22 only, so may just go with that, but I hate to lose gears for the climb, especially while on a +35lb bike.

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I am using the XTR inner and what Universal says is an XT 36T. The XTR M970 inner has a different gear offset so you can't use a normal steal gear as it would be too close to the middle gear. You would need to add roughly 3mm of spacer between the gear and spider.

Modern rings are phased, that is their teeth are oriented with respect to the mounting and each other so shifting is smoother. That's why most have orientation marks to line up when mounting. I'm not sure whether all brands are also phased for the inner to middle shift, but there's a possibility that mixing will lose that feature.

It's no great shakes, considering that FDs worked fine before phasing came into practice some 10 years ago. In the event that you do experience sluggish, less than perfect shifts, you can try phasing the inner ring to the middle by rotating it one bolt position trial and error until you get the best action. This is how better mechanics optimized FD performance back in the Bronze Age.

rsullivan said:

take another look at your small ring..... you won't find any shift ramps on them....you can use any chainring that will fit your bolt pattern with no issues. Remember you shift down to and up from the little ring. That gear choice sounds like it might work- I might give it a try

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Correct,the small rings don't have shift ramps.However you can NOT use any small chainring even if its the same bolt pattern -104/64 in OP case.XTR & matching small chain rings have offset gear teeth, meaning you have use other bigger XTR chain rings with the small ring & vise versa.When I tried running an Extralite 22T with my XTR 32T I had to use spacers to get it to work.

xc71 said:

Correct,the small rings don't have shift ramps.However you can NOT use any small chainring even if its the same bolt pattern -104/64 in OP case.XTR & matching small chain rings have offset gear teeth, meaning you have use other bigger XTR chain rings with the small ring & vise versa.When I tried running an Extralite 22T with my XTR 32T I had to use spacers to get it to work.

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The fact that inner rings don't have shift ramps is irrelevant to the question. The ramps and gates are only cut into the larger ring to lift it from the smaller, so any ring intended to be the smallest wouldn't have them.

That doesn't mean it doesn't need to be phased so that the teeth are properly lined up for smooth shifting where the gates are.

The point about tooth offset is well taken though. The distance from the point of the teeth to the plane of the mounting determines the effective gap to the next ring. To narrow and the chain will rub when coming from the outside, too wide and might drop into the gap.