Can I have an even more compact crankset?

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simonn
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Re: Can I have an even more compact crankset?

Postby simonn » Tue Sep 02, 2014 10:22 am

Xplora wrote:I did my first ever 53/39 with a 11-23 on the weekend, including 3kms at 6-11%. 45rpm sucks but I had enough juice at the top to change up and attack (because I'm that guy). I had 40kms to warm up... and I've done more weights than I care to remember recently. I like to spin 90rpm no matter how flat or rolling the hills are, and 15 minutes of climbing vs 5 hours of bliss, I know what my knees preferred.

Audax is a different story - they can't make a low enough gear once you've passed 250kms, even 2-3% feels like 30% that far in.
Bobbo clockwise at around 01:30 in the morning with ~390km on the legs (including Dog Trap Rd). I think my average speed was was ~6km/h for the climb and if it had been warmer than ~6oC I'd have had a hobo nap. I don't think that was the most physically and mentally challenging thing I have done. Just the last 30-40km from the top of Brooklyn to Gordon Station via Bobbo.

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Xplora
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Re: Can I have an even more compact crankset?

Postby Xplora » Tue Sep 02, 2014 10:26 am

LUXURY! You didn't even have to get up before you went to bed to clean the lake! :mrgreen:

michael.chaseling
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Re: Can I have an even more compact crankset?

Postby michael.chaseling » Tue Sep 02, 2014 3:57 pm

Derny Driver wrote:What size are your chainrings? 34 and 50?
And what is your cassette, in teeth numbers?

I would think that 34 -46 chainrings with an 11-28 would be good for you.
Thanks for your help mate.

Mine is 50 / 34T with the 5 screw 110BCD (Did I say that right?). I have 10 gears on the back.

So, would it work if I was to buy a small outer ring like this one? http://www.this link is broken.au/ta-110-pcd-zep" onclick="window.open(this.href);return false; ... chainring/

How small is too small? Would I lose too much if I went for the 40T?

Would the derailleur still work ok? Does 110 PCD mean the same thing as 110BCD?
Last edited by michael.chaseling on Tue Sep 02, 2014 4:14 pm, edited 1 time in total.

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Re: Can I have an even more compact crankset?

Postby michael.chaseling » Tue Sep 02, 2014 4:04 pm

Derny Driver wrote:
RonK wrote:
michael.chaseling wrote:when I shift to the bigger chain ring, I find I then lose cadence and feel like I need to ride harder and faster. I only change up to avoid the rubbing and cross chaining, not get a dramatic increase in speed...
Makes no sense at. If the small ring is so low you have to change to the big ring, smaller will just make it worse.

Sounds like you need a bigger small ring.
Ron I think what he means is that once he gets to the 34-11 and is crosschaining he wants to change up to avoid that. When he changes chainrings he ends up in the 50-11 and the cadence is too low. Even if he knocks it back a couple of cogs the gear is still too big and cadence too low so he feels he has to speed up. He would need to change back 5 cogs to the 50-16 to find an equivalent gear to the 34-11 he was comfortable on. By replacing the 50 with something smaller he can minimise the difference or even just ride everywhere in the big ring.
Yeah Derny, thats exactly the thing. A few posts here also suggested I "learn to shift properly" or some such. That might be true if I wanted to constantly think about shifting up and down. But frankly I want to just jump on, ride it, get the maximum efficiency and most enjoyable ride without engaging my brain too much.

Also, the lowest gear is just about right. Maybe a little too high for some of the hills I ride, but not so much to cause trouble.

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singlespeedscott
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Re: Can I have an even more compact crankset?

Postby singlespeedscott » Tue Sep 02, 2014 7:44 pm

As already stated, the OP really needs to learn to shift up before cross chaining. Sitting on a 34t chainring whilst cruising really isn't ideal for chainring life. A 46 tooth would be ideal for most commuter and endurance riders. Combined with a 12 tooth rear sprocket will give them more then enough speed for that style of riding.

Another combo I like is using is the trusty 52/42 crankset combined with a 13/34 cassette. A huge range of gears for fast and slow rides. The 42 tooth is very useful for longer rides. The 42x34 is as low as a 34x28 and max of 42x15 will give you a 75" gear without cross chaining.
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Xplora
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Re: Can I have an even more compact crankset?

Postby Xplora » Tue Sep 02, 2014 8:30 pm

michael wrote:A few posts here also suggested I "learn to shift properly" or some such. That might be true if I wanted to constantly think about shifting up and down. But frankly I want to just jump on, ride it, get the maximum efficiency and most enjoyable ride without engaging my brain too much.
This is a massive contradiction, Mike. You cannot ignore your gears if you want maximum efficiency. You can't switch your brain off unless you just don't use a front derailleur at all. The rear gear changes are quicker, so you are responsible for planning the front changes to make the rear changes more useful - the simple fact that gears require you to use your head or your legs.

I've complained about gears plenty of times. A pub bike should not cost you any money. You don't need big gears for downhills, as long as you can climb!

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Derny Driver
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Re: Can I have an even more compact crankset?

Postby Derny Driver » Tue Sep 02, 2014 11:25 pm

michael.chaseling wrote:
Derny Driver wrote:What size are your chainrings? 34 and 50?
And what is your cassette, in teeth numbers?

I would think that 34 -46 chainrings with an 11-28 would be good for you.
Thanks for your help mate.

Mine is 50 / 34T with the 5 screw 110BCD (Did I say that right?). I have 10 gears on the back.

So, would it work if I was to buy a small outer ring like this one? http://www.this link is broken.au/ta-110-pcd-zep" onclick="window.open(this.href);return false; ... chainring/

How small is too small? Would I lose too much if I went for the 40T?

Would the derailleur still work ok? Does 110 PCD mean the same thing as 110BCD?
The link didn't work. But yeah 110 BCD =PCD.
I would look for a Shimano 44 or 46 tooth outer chainring, 10 speed. Changing a 50 tooth for a 44 or 46 tooth will mean you have to slide the front derailleur down lower. The cage needs to be quite close to the teeth of the chainring. With a 40 I am not sure if there is enough movement in the derailleur slot to slide it down that far. Someone in the BNA Workshop section might know. I think a 10 or 12 tooth difference between large and small chainrings is good. 34-40 is only 6 teeth difference ...may be okay but Id go the 44 or 46. I think that would be what you are looking for.

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singlespeedscott
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Can I have an even more compact crankset?

Postby singlespeedscott » Wed Sep 03, 2014 6:21 am

Going to a 46 tooth or lower chainring may require a change of front derailleur. The end tip may hit the chain stay as you lower it to get a close enough gap between the cage and the teeth. As said before the Shimano CX70 cyclocross front derailleur will do the job perfectly

Another option is to completely toss one of the front chainrings, the derailleur and shifter and install a single narrow wide cyclocross chainring. These are available from a number of companies online in a wide range of tooth choices.
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Blakeylonger
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Re: Can I have an even more compact crankset?

Postby Blakeylonger » Wed Sep 03, 2014 9:48 am

I'll echo the others, learn to shift. Change front ring, shift a few sprockets on the rear. done. If the 50T is too big for any riding, get a 46. 40 is a ridiculously small big ring unless it's an MTB / cargo bike / etc. A friend stripped a triple down to make a 42/30 double for gravel use and frequently spins out the 42/11, before the road turns downhill.

If this is too hard, then by all means, get a ~42/44T narrow-wide ring, a suitable rear mech to match with an 11-36 (and perhaps even a OneUp 40/42T rear replacement sprocket) cassette and never have to think about your front shifts again. Of course this is a significant investment in a pub bike, and steps between gears will be much larger.

==========================

I have two bikes setup with 'medium' big rings, one 46/30 for touring etc and one 48/34 for road/commute/etc. Both shift fine and neither have special mechs. 46/30 is shifted with a chorus 11sp lever to a 6400 mech, which was better than an 8sp XT mech, which was better than a 9sp Campy CT mech. 48/34 is shifted by athena 11sp lever to a 6700 mech.

cx70 mech is curved slightly closer to the smaller ring radii, but in practice it's not a big deal.

If you have to drop the mech significantly for smaller big rings, the tail of the mech might hit the chainstay or the clamp might interfere with the bottle cage brazeon. slotted brazeon mech clamps and judicious use of a file/pliers can address this. I used a 6500 mech with a 42/34 chainring setup for CX and it shifted incredibly well due to the small difference in teeth, but was still a little too high as the tail was right on the stay, and I had to file the bottle boss down for the clamp to close.

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simonn
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Re: Can I have an even more compact crankset?

Postby simonn » Wed Sep 03, 2014 12:33 pm

Blakeylonger wrote:If you have to drop the mech significantly for smaller big rings ... the clamp might interfere with the bottle cage brazeon. slotted brazeon mech clamps ... can address this.
I had to do this. Like one of these:

Image

Somewhere on the internet, I found out that an accurate enough way of determining the radius of a chainring based on the number of teeth is:

((12.75mm * t)/Pi)/2

Roughly:

53t ~= 107.5mm
52t ~= 105.5mm
50t ~= 101.5mm
48t ~= 97.5mm
46t ~= 93mm

So going from 50t to 46t I needed to drop my derailleur 101.5 - 93 = ~8.5mm - exactly where the bottle cage brazon was. On the plus side, it is how I ended up with a CX70 as my existing derailleur was band on and I can fit a 1L bottle on my seat tube which I cannot do on my other two roadies where the brazons are well out of the way of where the derailleur needs to be - just what you need on an audax bike.

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Re: Can I have an even more compact crankset?

Postby find_bruce » Wed Sep 03, 2014 3:07 pm

I have always found this gear calculator to be useful in visualising the effect of changes to your gears. It also allows you to adjust the permitted chain angle to avoid rubbing

The theory behind a compact is that you use the small ring to climb & the big ring on the flat and descents

The difficulty for many people is that the changeover point is around the 30 km/h mark

Have a play around with various size rings and see what the effect is.

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Xplora
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Re: Can I have an even more compact crankset?

Postby Xplora » Wed Sep 03, 2014 3:29 pm

find_bruce wrote: The difficulty for many people is that the changeover point is around the 30 km/h mark
This is pretty much why I dislike the compact, it seems to offer the worst of all worlds - except a super low climbing gear. Too big to spin 25-30kmh, too small to spin 30-35kmh, big jumps in the shifting, and it creates a big incentive to spin ugly in the big ring most of the time. I'd rather spin pretty and learn to muscle the climbs more - but I don't do any serious climbing. I'll pick up a 12-29 for those days, but it's really hard to find anyone actually interested in such heavy duty climbing to go with you :lol:

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Re: Can I have an even more compact crankset?

Postby brendan c » Wed Sep 03, 2014 7:30 pm

I agree with the 25-30kph compact cross chaining thing X. Almost every ride I do at the moment includes an 8km false flat to the bottom of a climb, there's a few little flat bits and few kicks too, so it's crap in either ring. 34 is too small for a recovery ride on gently rolling terrain where a 39 is perfect. Chuck something like 12-23 on a compact and ride a rolling course, heaps of fun ;)
Whatever you pick is going to be a compromise on either range of gears or gaps between gears.

Lots of people could do with this 'more compact compact' how many recreational riders spin out 50/11?? Every cassette needs an 11 for some reason according to the guys making them. In Adelaide 34/28 is probably a minimum if you like exploring, but there are tons of bigger guys who ride the 5% climbs in that gear and are forced to grind anything steeper.

Regarding the loving hills and hating compacts, I had a play with that gear calculator and 39/28 is near identical to 34/24 and there's only the 1 extra gear with the compact anyway. 39/32 is nearly identical to 34/28 and should be easy enough to set up with the new 11speed stuff.

There's been a bit of evolution since I was first looking at bikes 6 years ago and most of the entry level bikes seemed to have 39/25 as the lowest gear.

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Re: Can I have an even more compact crankset?

Postby Xplora » Wed Sep 03, 2014 8:15 pm

I think it's the Treks and Giants finally submitting to the market demand for fat climbers. No crime in that, just reality. A Shimano 28 doesn't have the worst steps down, combining it with the compact should solve the dramas. Heroes can use the midcompact 52/36, in the marketeer's minds. The Propel comes with the midcompact.

Which is all a bit of a shame really, because once you develop the horsepower to push 40kmh for an hour (flat crit) the compact is utterly useless. Have they abandoned the racing rider? I request further conjecture and speculation :lol:

I'm not sure I'm sacrificing anything except rest time at the top if I can drag 39/23 up the Gorges or Hawkesbury as everyone waits for me. There was something quite nice about dumping it to the bottom gear and saying "nope, no heroics today, just get up there" on the weekend. Sadly, we don't race up climbs in Sydney except once a year. We aren't blessed with Adelaide's natural excellence ;)

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Re: Can I have an even more compact crankset?

Postby durianrider » Tue Sep 09, 2014 10:12 pm

Xplora wrote:I think it's the Treks and Giants finally submitting to the market demand for fat climbers. No crime in that, just reality. A Shimano 28 doesn't have the worst steps down, combining it with the compact should solve the dramas. Heroes can use the midcompact 52/36, in the marketeer's minds. The Propel comes with the midcompact.

Which is all a bit of a shame really, because once you develop the horsepower to push 40kmh for an hour (flat crit) the compact is utterly useless. Have they abandoned the racing rider? I request further conjecture and speculation :lol:

I'm not sure I'm sacrificing anything except rest time at the top if I can drag 39/23 up the Gorges or Hawkesbury as everyone waits for me. There was something quite nice about dumping it to the bottom gear and saying "nope, no heroics today, just get up there" on the weekend. Sadly, we don't race up climbs in Sydney except once a year. We aren't blessed with Adelaide's natural excellence ;)
Ha ha. How come Contador runs a 34x32 set up then? David Millar had a 36 cassette in the Vuelta with a sram mountain bike RD.

I run a 34x32 as well and pretty surprised if anyone on this forum could beat me up Woodlands Way. http://app.strava.com/segments/628886" onclick="window.open(this.href);return false;
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