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Re: School me on Cassettes [Fleck] [ In reply to ]
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Fleck wrote:
to mitigate chainline friction loss.


Always surprised to find when I go riding with triathletes, how many DON'T seem to understand this and ride on completely crossed up chain-lines!!

I kindly try and help out explaining that forget gears, power and all the stuff and think about running as straight a chain-line as you can in every situation when riding!

Do you (or someone else) mind explaining this to me now? On my tri bike, I have a 50/34 and 11/28. I ride in the big ring about 98% of the time. Is the idea that I should adjust my cadence to increase speed/power instead of shifting rear gears in order to keep the chain straight? Also, I guess I would assume keeping the chain straight would mean keeping the rear gear towards the middle? Or am I totally misunderstanding this?
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Re: School me on Cassettes [MRid] [ In reply to ]
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If you are in the big chainring, you want to stay out of the two largest gears on the cassette.

If you are in the small chainring, you want to stay out of the two smallest gears on the cassette.
Last edited by: jimatbeyond: Dec 10, 18 11:57
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Re: School me on Cassettes [jimatbeyond] [ In reply to ]
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Can a 11-30 ultegra 8000/dura ace cassette work with a short cage 6800 Rear Der. Would I need to change the chain or derailleur at all. Currently have a 11-28 but would like another lower gear because live near mountains
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Re: School me on Cassettes [transgress4] [ In reply to ]
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transgress4 wrote:
Can a 11-30 ultegra 8000/dura ace cassette work with a short cage 6800 Rear Der. Would I need to change the chain or derailleur at all. Currently have a 11-28 but would like another lower gear because live near mountains

My best guess is that it will work with no changes to chain or derailleur (except adjusting the b screw a little).

It's not so much the max cog size as the ability of the short cage to manage all the chain. Assuming you have a 16 tooth cog difference up front (50/34 or 52/36 crank) then 11-28 is the limit of the published chain wrap capacity. Those numbers are conservative by a couple teeth so an 11-30 will likely work. 11-32 is well beyond the chain wrap capacity and I just couldn't get it where I was happy when I went to a 50/34 and 11/32 for a climbing event. I swapped in a GS cage from another bike and everything was fine.

Another thing to consider is that the 30 tooth is only ~4% lower than the 28 tooth. Most people wouldn't be able to tell the difference. Going to the 11-32 or 11-34 will definitely give you a lower bailout gear, but most likely necessitate a longer cage (GS) rear derailleur and slightly longer chain.
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Re: School me on Cassettes [dangle] [ In reply to ]
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^ This.
http://productinfo.shimano.com/...C-453&acid=C-454 - the RD-6800-SS is rated to max 28T.
However Shimano are notoriously conservative, so you most likely can fit a 30T without issue; just avoid the big-big combo.

Google says people have tried a 32T cassette and it'll work except for the big-big combo.
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Re: School me on Cassettes [MRid] [ In reply to ]
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MRid wrote:
Fleck wrote:
to mitigate chainline friction loss.


Always surprised to find when I go riding with triathletes, how many DON'T seem to understand this and ride on completely crossed up chain-lines!!

I kindly try and help out explaining that forget gears, power and all the stuff and think about running as straight a chain-line as you can in every situation when riding!


Do you (or someone else) mind explaining this to me now? On my tri bike, I have a 50/34 and 11/28. I ride in the big ring about 98% of the time. Is the idea that I should adjust my cadence to increase speed/power instead of shifting rear gears in order to keep the chain straight? Also, I guess I would assume keeping the chain straight would mean keeping the rear gear towards the middle? Or am I totally misunderstanding this?
The idea is that you should select your gearing so that you can spend as much time as possible with a straight chainline, ie closer to the middle of the cassette, at your preferred cadence and power output.
This is why world class cyclists run massive front rings in time trials. Not because they need the 58-11 gearing, but so they can push 58-15 on the flat (assuming the course is flat).
But yes in general, stick to the middle of the cassette if you can. If you're nearing the big-big combo, you'd be more efficient in a small-mid combo.
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Re: School me on Cassettes [MattyK] [ In reply to ]
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That makes sense. Thank you
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Re: School me on Cassettes [TheStroBro] [ In reply to ]
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My personal preference is a 50/34 upfront and a 11/25 in the back on a tri bike and a 53/39 - 11/28 on a road bike. Plenty of gear to spin out of for my rides around the Los Angeles area, and I am from an uber cyclist.

Next races on the schedule: IM Boulder 2019, IMAZ 2019
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Re: School me on Cassettes [MattyK] [ In reply to ]
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MattyK wrote:
MRid wrote:
Fleck wrote:
to mitigate chainline friction loss.


Always surprised to find when I go riding with triathletes, how many DON'T seem to understand this and ride on completely crossed up chain-lines!!

I kindly try and help out explaining that forget gears, power and all the stuff and think about running as straight a chain-line as you can in every situation when riding!


Do you (or someone else) mind explaining this to me now? On my tri bike, I have a 50/34 and 11/28. I ride in the big ring about 98% of the time. Is the idea that I should adjust my cadence to increase speed/power instead of shifting rear gears in order to keep the chain straight? Also, I guess I would assume keeping the chain straight would mean keeping the rear gear towards the middle? Or am I totally misunderstanding this?

The idea is that you should select your gearing so that you can spend as much time as possible with a straight chainline, ie closer to the middle of the cassette, at your preferred cadence and power output.
This is why world class cyclists run massive front rings in time trials. Not because they need the 58-11 gearing, but so they can push 58-15 on the flat (assuming the course is flat).
But yes in general, stick to the middle of the cassette if you can. If you're nearing the big-big combo, you'd be more efficient in a small-mid combo.

We seem to spend a lot of time worried about cross chaining and its corresponding friction losses here. While the concept makes sense, I wonder if it's a holdover from back in the day. Chains were wider, stiffer (laterally), and there was more space between cogs when we only had 5 cogs in the back on a 126mm hub vs. having 11 on a 130mm (rim brake) hub. I would love to see a test that shows what the wattage loss is for cross changing.

There was a test a few years ago (posted on slowtwitch, iirc) showing that for an equivalent gear-inch and cadence, it was more efficient to be on the big ring. I believe the theory was that it reduced friction in the chain because the links didn't bend as acutely, similar to running larger pulleys. So, small ring and smaller cog was not more efficient.

I'd be at least mildly surprised to find that world-class time trialists spend much time in a 58x15 on a flat course. A look at a gear, cadence and speed chart shows when using a 58 big ring with a 23 tire, that for 34mph with a 15 cog, a cadence of 112 is necessary. For a 14 cog, the cadence is 105. For a 13, its 97-98 . For a 12, it's 90. For an 11, it's 82-83. Changing to a 25mm tire changes the required cadence to 111-112, 104, 97, 88-89, and 82. I don't believe we see cadence over 100 very often anymore, with the exception of descents. In his heyday, he-who-shall-not-be-named was in the 102-105 range. Tony Martin looks more like low 90s to me. Using 34mph and a cadence of 95, the rider is spending a lot of time in the 13. Not a big/small, but not likely to be a big/15, either.
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Re: School me on Cassettes [FatandSlow] [ In reply to ]
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FatandSlow wrote:
We seem to spend a lot of time worried about cross chaining and its corresponding friction losses here. While the concept makes sense, I wonder if it's a holdover from back in the day. Chains were wider, stiffer (laterally), and there was more space between cogs when we only had 5 cogs in the back on a 126mm hub vs. having 11 on a 130mm (rim brake) hub.

There was more space between cogs, but due to the smaller cog count, the freewheels were still considerably narrower than modern 11-speed cassettes. The width of modern cassettes is the main reason that rear hub OLD switched from 126mm to 130mm, and despite the extra real estate provided by 130mm, modern rear wheels also need much steeper drive-side spokes at very high tension. The wider cassette actually results in cross-chaining experiencing far more extreme angles on current-gen drivetrains than on drivetrains circa 1980.

But yes, concerns regarding cross-chaining go way back. Many racers used to be extremely concerned about chain behavior in general... in retrospect it's hard to know how much of it was ever justified, and if so, when it was justified. Some of it definitely got pretty silly, like the efforts in the 30s and 40s to use derailleurs on racing bikes while keeping the amount of bends in the chain to a minimum (resulting in a variety of strange mechanisms that provided less than 10 teeth of chain wrap and didn't shift particularly well).

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I'd be at least mildly surprised to find that world-class time trialists spend much time in a 58x15 on a flat course. A look at a gear, cadence and speed chart shows when using a 58 big ring with a 23 tire, that for 34mph with a 15 cog, a cadence of 112 is necessary. For a 14 cog, the cadence is 105. For a 13, its 97-98 . For a 12, it's 90. For an 11, it's 82-83. Changing to a 25mm tire changes the required cadence to 111-112, 104, 97, 88-89, and 82. I don't believe we see cadence over 100 very often anymore, with the exception of descents. In his heyday, he-who-shall-not-be-named was in the 102-105 range. Tony Martin looks more like low 90s to me. Using 34mph and a cadence of 95, the rider is spending a lot of time in the 13. Not a big/small, but not likely to be a big/15, either.

I think you'd have to accumulate some data to answer the question, because cadence choice varies a lot from cyclist to cyclist. Anyone could tell any narrative if they just picked a couple cyclists from any given era. Eddy Merckx and Bradley Wiggins set their hour records on very similar cadences to each other, for instance, both a bit over 100rpm.
Last edited by: HTupolev: Dec 10, 18 18:40
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Re: School me on Cassettes [KG6] [ In reply to ]
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Dura-Ace is lighter. Also noisier- I prefer an Ultegra cassette.
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Re: School me on Cassettes [FatandSlow] [ In reply to ]
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FatandSlow wrote:

We seem to spend a lot of time worried about cross chaining and its corresponding friction losses here. While the concept makes sense, I wonder if it's a holdover from back in the day. Chains were wider, stiffer (laterally), and there was more space between cogs when we only had 5 cogs in the back on a 126mm hub vs. having 11 on a 130mm (rim brake) hub. I would love to see a test that shows what the wattage loss is for cross changing.
Reference to testing that is now ceramicspeed proprietary:
https://www.bikeradar.com/...oper-shifting-44016/

Quote:
There was a test a few years ago (posted on slowtwitch, iirc) showing that for an equivalent gear-inch and cadence, it was more efficient to be on the big ring. I believe the theory was that it reduced friction in the chain because the links didn't bend as acutely, similar to running larger pulleys. So, small ring and smaller cog was not more efficient.
Depends how far across the cassette you are. See link above.
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I'd be at least mildly surprised to find that world-class time trialists spend much time in a 58x15 on a flat course. A look at a gear, cadence and speed chart shows when using a 58 big ring with a 23 tire, that for 34mph with a 15 cog, a cadence of 112 is necessary. For a 14 cog, the cadence is 105. For a 13, its 97-98 . For a 12, it's 90. For an 11, it's 82-83. Changing to a 25mm tire changes the required cadence to 111-112, 104, 97, 88-89, and 82. I don't believe we see cadence over 100 very often anymore, with the exception of descents. In his heyday, he-who-shall-not-be-named was in the 102-105 range. Tony Martin looks more like low 90s to me. Using 34mph and a cadence of 95, the rider is spending a lot of time in the 13. Not a big/small, but not likely to be a big/15, either.

Numbers were for example only.
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Re: School me on Cassettes [FatandSlow] [ In reply to ]
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Put your bike on the work stand, put it in the big ring, big cog cross over gear and slowly spin the cranks. Now put it in a gear with a straighter chainline. When I do this I can feel the difference in resistance. As a road racer I will use this gear when it makes sense for a period of time, like a short hill where I or someone else is attacking and I don't want to shift out of and then shortly thereafter back into the big ring. But I wouldn't say do a whole climb crossed over like that. Nor would I want to time trial for 20 minutes into a head wind in that gear.

Another reason for the super large chainrings besides chainline is to avoid the added drivetrain drag from small cogs. This is the same reason that everybody is spending $500-$600 on those ceramic speed large jockey wheel derailleur cages. There is a lot more drag wrapping that chain around an 11 tooth cog than a bigger cog. If for example a 58x15 gives you the best chainline, riding in the 58x13 would still be better than an equivalent gear on the 11 cog.

Kevin

http://kevinmetcalfe.dreamhosters.com
My Strava
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Re: School me on Cassettes [nslckevin] [ In reply to ]
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Thank you for weighing in. I appreciate your expertise. Tried your suggestion and I can feel the difference, too. Between a 52x15 and a 52x11, but not for a 52x15 and a 52x14. But that's just me.

I get the concept. And I had read the article referenced above when it came out, but had forgotten it. In addition to being fat and slow, I'm old too.The 2 takeaways were that leaving chainline losses out, bigger rings and cogs were always more efficient than smaller ones and that in most cases, the big/big combination should be avoided.

What I was trying to say is that I don't think a 58x15 is going to work for world-class time trialists on the flats because I don't believe they're turning a cadence above 110 to go 34mph - on average. In my pea brain, it was a bad example that didn't support the argument. My suspicion is that the main reason the pointy end of the field uses 56 and 58 rings is for speed, but I have no data.
Last edited by: FatandSlow: Dec 11, 18 10:34
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Re: School me on Cassettes [FatandSlow] [ In reply to ]
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FatandSlow wrote:
Thank you for weighing in. I appreciate your expertise. Tried your suggestion and I can feel the difference, too. Between a 52x15 and a 52x11, but not for a 52x15 and a 52x14. But that's just me.

I get the concept. And I had read the article referenced above when it came out, but had forgotten it. In addition to being fat and slow, I'm old too.The 2 takeaways were that leaving chainline losses out, bigger rings and cogs were always more efficient than smaller ones and that in most cases, the big/big combination should be avoided.

What I was trying to say is that I don't think a 58x15 is going to work for world-class time trialists on the flats because I don't believe they're turning a cadence above 110 to go 34mph - on average. In my pea brain, it was a bad example that didn't support the argument. My suspicion is that the main reason the pointy end of the field uses 56 and 58 rings is for speed, but I have no data.

On the other hand, a 58x13 at 100 rpm is good for 34.9 mph. Maybe not a perfect chain line or friction due to small cogs, but it's better than being in the 12 tooth cog. Every little bit adds up.

Kevin

http://kevinmetcalfe.dreamhosters.com
My Strava
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Re: School me on Cassettes [MRid] [ In reply to ]
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MRid wrote:
I guess I would assume keeping the chain straight would mean keeping the rear gear towards the middle?



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