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.

[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.

[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!

[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]

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?

Switching to a cogset with an overall wider range means that the steps between gears are larger. The shifting will be not quite as quick, though not really any harder. More importantly, those wider steps between gears just make it harder to find the gear that gives you the perfect cadence. That's the trade-off: fine gradations to find the perfect gear, or a wide range (with a low low) but always wishing there was another gear between two of your gears.

With your 48-34 front and 12-25 rear cogs, you get the following gears (I'm using Sheldon Brown's chart assuming you have 700x28 wheels and listing results in gear inches):

48 front: 107, 99, 86, 76, 68, 61, 56, 51
34 front: 76, 70, 61, 54, 48, 43, 40, 36

But if you eliminate the cross-over gears (2 on each end nominally, but you may decide that more or less need to be eliminated):

48 front: 107, 99, 86, 76, 68, 61
34 front: 61, 54, 48, 43, 40, 36

you have almost no overlap (only a 61 on both chainrings, but the 48-61 may be somewhat of a cross-over so you may want to eliminate it too). The reason you're getting no overlap is because the chainrings are spaced far apart. This gives you a wide range of gears without putting on a widely-spaced cassette (i.e. you get nice quick shifts in the rear). This setup had advantages. If you want a gear between 61 and 107, you stay in the big chainring and shift the rear. If you want a gear between 36 and 61, you stay in the small chainring and shift the rear. But from 61 to 68, you have to shift the front derailleur up one (harder) and the rear derailleur down two (easier). That's a pain-in-the-butt shift, but it's an 11% jump compared to the 9-11% jumps between your other gears, so everything is nicely spaced and not overlapped. On paper, this is a very nice gearing setup, unless you find yourself making that 61-68 shift all the time, i.e. if that gear ratio is something you use a lot on flat to gently sloping ground. Though if you find that the 61 work fine on either chainring, you have a choice of making the double shift between 61-68 or 54-61. If you decide you hate this setup, there are certainly other combinations you could try, with closer spacing in the chainrings and wider spacing on the rear cogs. But that would have its compromises too.

[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

[roadfix]

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?

If you are seaching for lower gears the most practical solution would be to swap your 8 speed cassette with a mountain cassette, 12-28, 12-30, or even 12-32. The only catch is your rear short cage derailleur most likely will not be able to handle the larger cog, thus requiring you to swap the derailleur with a long cage.

[Kano]

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.

Okay, I understand about newbies and not-so-newbies and I understand about speed, I covet speed, but, you went up a 15 mile long hill at ten miles per hour????

I WANNA GROW UP TO BE YOU!!!!!

Someday, maybe I too will be able to be disgusted by ten miles per hour going up hill. For now I'll settle for being disgusted by four miles per hour up hill. And I'll continue to hope for getting to the point where I can be disgusted by five miles per hour up hill....



And now back to our regularly scheduled cross-chaining thread, which has been very interesting!

Karen in Boise

[Kalidurga]

Someday, maybe I too will be able to be disgusted by ten miles per hour going up hill. For now I'll settle for being disgusted by four miles per hour up hill. And I'll continue to hope for getting to the point where I can be disgusted by five miles per hour up hill....

Oops, I didn't realize what I said could sound obnoxious... But you have to understand the hill in question. Let me digress a bit to clarify what I was dealing with:

We're talking a gradient of 2-3%. A grade of that small degree looks perfectly flat to the eye. During the first half of my ride, I flew along, pedaling the most comfortable stroke ever at my fastest speed ever maintained beyond a .25 mile. Then, when I turned around to head back on what looked like a flat trail, I was immediately struggling. In higher gears, my legs began to feel like lead. In lower gears, I quickly fatigued myself with spinning. To be working that hard on a hill that just plain doesn't look like a hill is what got me disgusted. As much effort as I was putting in on a seemingly flat surface, it felt like I should have been flying. The only gears in which I could turn a comfortable, smooth stroke at any speed were the ones in which I was cross-chained: the inner cogs with the big ring, or the outer cogs with the small ring. I spent that 15 miles thinking that either I need to do some serious cardiovascular work, or I need a greater range of gears-- which led to my original post in this thread.

What I still can't figure out is why I was more comfortable cross-chained when, according to the gear ratio charts discussed, I should have had similar gearing in a non-crossed combo. I think I need to take the chart from Sheldon's site and DebW's explanations, get on my bike, and run through the gears. Looking at the chart and paying attention to the different feel of each combination is probably what I need to make all of this "click" in my head.

It's funny... I've been biking for years, but it's only in the last year or two that I've begun thinking about what it is that I'm doing. Time to admit that, in that respect, I'm just a newbie