Cross-chaining

[Kalidurga]

Ok, I know I shouldn't do it, but sometimes I just can't help it. Since switching from a triple chainring hybrid to a double ring 'cross bike, I'm finding that I want more gears. I had been considering a compact chainring, but did a little research and realized that a compact might not give me anything easier than my TriCross's 48x34.

So, the next option would be a new cassette. The TriCross comes with 8 gears, 12-25 (bike specs). I find that I need one or two easier gears for hills, and I really need some more "in-between" gears to keep me from going too high in the small ring and too low in the big ring.

Or is cross-chaining ok on this bike? The tech where I bought it said that it probably would be ok. The tech at another shop said that it definitely would not be ok. And today, when I was in the big ring and the granny gear of the cassette, the chain dropped when I rotated the crank backwards to line up the pedal for clipping in at a stop.

I'm hoping some of the more technically advanced ladies here can give me some recommendations. Word of warning, though: I may sound like I know what I'm talking about, but gearing is a muddy area for me. I know intuitively how to shift into the right gear as I ride, but the mathematics of gearing go right over my head. Be prepared for me to respond to any responses with more questions.

[SadieKate]

Your smallest chainring is a 48?


Editing: I just looked at the specs and you already have a compact crank. The smallest chainring is a 34. Got it now.

[SadieKate]

Kalidurga, I know you hate math but this isn't too bad. Go to http://sheldonbrown.com/gears/ and enter your chain rings (48 and 34) and then enter each cog for your cassette (he may have it in the drop down list). Look at the results. If you put each gear combo in order highest to lowest, you'll see where you overlap. Some combos may be duplicates; others may just be a hair different. You'll suddenly see that it doesn't make sense to cross gear beyond a certain combo.

Also, to get lower/easier gears, you'll need a larger cassette (and a new derailleur and chain). But larger cassettes have larger jumps from one cog to the next. Some you'll have to decide which you want more.

[Kalidurga]

Thank you for the link, SadieKate, I hadn't found that at Sheldon's site. It clarifies some things, yet still begs some questions.

On an intellectual level, the chart confirms what I've read and was told about gearing by one of the bike techs I talked to. But...

Today I was riding in the 48/25 which put me in a cross-chained position, but it felt fairly good. It gave me the perfect cadence and ok speed. When I realized I was crossed and switched down to the small ring, I went through both the 34/17 and 34/19 combos searching for something that felt right. According to Sheldon's chart, both of those combos should have felt similar to the 48/25, but I didn't feel anything in the small ring that seemed at all the same. Maintaining the same cadence in the small ring was more difficult (which I know doesn't make sense), and I could not maintain the same speed I had in the big ring.

So the question then is: Do I go with what I "know" is right, or with what I "feel" is right? And if I go with what feels right, how much am I going to mess up my drive train?

Which was answered by Deb, and I experienced exactly what she described. One of my bike techs had advised me to stay off the last two gears opposing each chain ring, which I've tried to do until today. With all the dust on the trail, the drive train ended up getting very noisy, especially so when I moved into those "forbidden" combos. When I dropped the chain, I stopped to fiddle a bit and could see exactly what Deb mentioned about the chain angle. The chain veered very obviously from the pulley.

So, the answer is: I definitely can't cross-chain because it will over-stress my drive train.

Which brings me back to: Any recommendations for a larger cassette? Or am I just crazy? (I think there was another thread with a cassette conversation recently. I need to find that...)

[DebW]

Today I was riding in the 48/25 which put me in a cross-chained position, but it felt fairly good. It gave me the perfect cadence and ok speed. When I realized I was crossed and switched down to the small ring, I went through both the 34/17 and 34/19 combos searching for something that felt right. According to Sheldon's chart, both of those combos should have felt similar to the 48/25, but I didn't feel anything in the small ring that seemed at all the same. Maintaining the same cadence in the small ring was more difficult (which I know doesn't make sense), and I could not maintain the same speed I had in the big ring.

So the question then is: Do I go with what I "know" is right, or with what I "feel" is right? And if I go with what feels right, how much am I going to mess up my drive train?

I can't explain why the small ring and big ring felt so different to you. The 34/17 should have felt harder and the 34/19 easier than the 48/25. When you spend more time on this bike and get used to it's gears, always avoiding the cross-overs, you should get more comfortable with knowing what gear will give you what cadence when.

Which brings me back to: Any recommendations for a larger cassette? Or am I just crazy? (I think there was another thread with a cassette conversation recently. I need to find that...)

Give it more time to get used to these gears. If you really need a lower gear for hills you ride frequently, then you should go for it rather than risking damage to your knees. But the compromise is wider-spaced gears which you are already having trouble with. So maybe avoid the biggest hills for awhile and ride the bike like this until you are really used to the bike and the gears. Then gradually start to ride bigger hills and see where you'd prefer to compromise. You can probably switch your 12-25 cluster for a 12-27 without too much hassle and without losing your close spacing on the smaller cogs. Your preference and your compromise point may change with your fitness level.

[Kalidurga]

Give it more time to get used to these gears. If you really need a lower gear for hills you ride frequently, then you should go for it rather than risking damage to your knees. But the compromise is wider-spaced gears which you are already having trouble with. So maybe avoid the biggest hills for awhile and ride the bike like this until you are really used to the bike and the gears. Then gradually start to ride bigger hills and see where you'd prefer to compromise. You can probably switch your 12-25 cluster for a 12-27 without too much hassle and without losing your close spacing on the smaller cogs. Your preference and your compromise point may change with your fitness level.

As of yesterday, I have just over 600 miles on the bike. Most of my riding is on level rail-trails. When I do get out on hills, it's usually pretty small ones. I don't have too much trouble with a short, steep hill, but those long, lower gradient ones really get to me. Yesterday, though, when I was heading uphill on a 2-3% gradient for 15 miles and ended up pedaling 95rpm/10mph, I was totally disgusted.

Just what happens when you switch to cogs with larger spacing? Is it harder to shift? Does it not fit as well on the bike frame?

There's been kind of a flurry of threads on this subject lately, so I'm apparently not the only person wanting to tweak her gearing. It's been a great learning experience to read all of the comments and it's really appreciated!

[DebW]

I'll give it a stab, but others may know more specifics about some of these things than I do. Your absolute worst cross-over is big ring front, big cog rear. That's because your big chainring tends to line up with the outer (smallest) rear cog and the inner chainring to line up with the center of your rear cluster. Eyeball your setup and see what the lines look like. Put the chain in each possible gear and look at the chain angle. You can also ride each gear (on the flat at an easy spin) and listen for how noisy each of the crossed gears is. If the chain is too angled, it can't flow smoothly onto the cogs because it would need to bend from the crossed angle between chainring and cog to the flat angle (w.r.t. bike centerline) of the cog or chainring. The rules aren't hard and fast, but you can get an idea of which gear combinations work easily and and which are a strain on the drivetrain. Obviously a chain that derails as you pedal backwards is an indication of very bad chain angle and should be avoided. On my 6-speed cluster, I avoid the 3 inner cogs with the outer chainring. On your inner chainring, you should get use of more gears than you get with the outer chainring. The main problem there will that the chain may scrape the outer chainring when you use an outer rear cog. This problem will be worse the larger the gap between chainrings. Put the bike in the inner front/outer rear combinations to check chain angle and chainring scrape. Avoid the chainring scrape combinations as much as possible, though hitting such a gear briefly isn't a big deal. You'll probably find 1, or at most 2 outer cogs that shouldn't be used with the inner chainring. If you had a narrow jump between chainrings, you might get all 8. Cross-over gearing will be worse with a short wheelbase bike, less of a problem with a longer wheelbase. The cog and chainring sizes you have make a difference, so you basically have to experiment and analyze to see what combinations are not optimal. The gears that you decide are cross-overs should be avoided 95% of the time, but occasionally using one for a short time won't do any real damage. You will just wear your components faster if you use them a lot. Hope that made sense.

[mimitabby]

I'll give it a stab, but others may know more specifics about some of these things than I do. Your absolute worst cross-over is big ring front, big cog rear. That's because your big chainring tends to line up with the outer (smallest) rear cog and the inner chainring to line up with the center of your rear cluster. Eyeball your setup and see what the lines look like. Put the chain in each possible gear and look at the chain angle. You can also ride each gear (on the flat at an easy spin) and listen for how noisy each of the crossed gears is. If the chain is too angled, it can't flow smoothly onto the cogs because it would need to bend from the crossed angle between chainring and cog to the flat angle (w.r.t. bike centerline) of the cog or chainring. The rules aren't hard and fast, but you can get an idea of which gear combinations work easily and and which are a strain on the drivetrain. Obviously a chain that derails as you pedal backwards is an indication of very bad chain angle and should be avoided. On my 6-speed cluster, I avoid the 3 inner cogs with the outer chainring. On your inner chainring, you should get use of more gears than you get with the outer chainring. The main problem there will that the chain may scrape the outer chainring when you use an outer rear cog. This problem will be worse the larger the gap between chainrings. Put the bike in the inner front/outer rear combinations to check chain angle and chainring scrape. Avoid the chainring scrape combinations as much as possible, though hitting such a gear briefly isn't a big deal. You'll probably find 1, or at most 2 outer cogs that shouldn't be used with the inner chainring. If you had a narrow jump between chainrings, you might get all 8. Cross-over gearing will be worse with a short wheelbase bike, less of a problem with a longer wheelbase. The cog and chainring sizes you have make a difference, so you basically have to experiment and analyze to see what combinations are not optimal. The gears that you decide are cross-overs should be avoided 95% of the time, but occasionally using one for a short time won't do any real damage. You will just wear your components faster if you use them a lot. Hope that made sense.

So Deb, what you are saying that even though your bike has 27 gears on it,
there aren't really that many that you can/should use?
I notice my Bianchi prefers to stay in the lower gears when i am in the lowest
chain ring.. is this what you are talking about?

can you define inner / outer chain ring?

[DebW]

So Deb, what you are saying that even though your bike has 27 gears on it,
there aren't really that many that you can/should use?

Exactly

I notice my Bianchi prefers to stay in the lower gears when i am in the lowest
chain ring.. is this what you are talking about?

Yup, you figured that out without any theoretical nonsense or chain angle measurements. Or the bike told you in it's own firm but subtle way.

can you define inner / outer chain ring?

Inner and outer are relative to the centerline of the bike frame.

inner = smaller chainring, closer to frame
outer = larger chainring, further from frame