Help choosing a new crankset

37 replies · 801 views

Jimbop
89 posts
#1Dec 9, 2018, 3:13 AMedited
I bought my 2016 CAADX 105 when i knew even less about bikes than I do now. It came with this crankset FSA Gossamer Cross, BB30, 46/36, and a mate helped me swap the 36 to a 34 to make climbing a bit easier. I find 46 on the front is fine for me - if I'm going faster than I can pedal then honestly i'm fully focussed on making sure i don't stack it because i feel pretty exposed doing those types of speeds.

When i get into seriously muddy conditions even with 1:1 gearing I start to struggle without any weight on the bike, and i'm hoping to get out bikepacking in 2019 so my bike will be loaded up and i know that's going to make me struggle on steep climbs. I've only been riding seriously for six months and I don't have easy access to hills so i don't get a lot of time training on hills (although a friend dropped off his spare turbo trainer yesterday so that should help). I'm pretty happy with the 46 big ring but if I could get a smaller small ring for steep climbs does appeal quite a bit - i reckon i'd be able to get up most climbs happily with a 30 small ring.

I've done some googling and the option that looks the one I like the look of most is the AbsoluteBlack oval crankset, partly because it's compatible with shimano cranks (not that i have them) and partly because the oval chainring idea seems sensible although I understand from googling that there are mixed views on whether it works and power meter readings. Not too worried about the power meter readings because if they consistently over read by 3-4% then I have nothing to compare it to as have never had a power meter (and i'm not planning on getting one in the immediate future). I like the look of Ultegra crank arms and i'm impressed with the RS685 levers and RX800 ultegra rear mech i've put on so i am thinking of going with them.

Questions:
1) Given that i am pretty happy with 46 tooth big ring then is there any disadvantage to moving from a 34 to a 30 small ring?
2) I understand that if I want to put Ultegra on my bike then i need a BB30 adapter. Googling suggests that the Wheels Manufacturing BB30 to 24mm crank spindle shims might be a good option. Any advice on this would be helpful.
3) Is there much difference between the Ultegra 6800 and 8000 crank arms? The 6800's chainset can be had for £119 and the cheapest I can find the 8000 for is £175. The weight seems to be like 2g different and as for aesthetics - if I get the AbsoluteBlacks - they aren't the most beautiful so that's not a big worry.
4) I can't seem to find Ultegra 6800 nor 8000 crank arms as stand alone components - you have to buy the whole chainset, which seems like a waste if i'm just going to put the rings in my growing spare parts bin. Have I missed something?
5) Are there any 46/30 chainsets that stand out and might be a better option than the AbsoluteBlack with Ultegra crank arms combo that i'm thinking about?
6) I did some googling on crank arm length - any advice on how to size this would be helpful as it doesn't seem that straightforward.
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bnystrom
459 posts
#2Dec 11, 2018, 7:35 AMedited
First off, I'd forget about the oval chainrings for one primary reason - chain retention. The huge gap between the front derailleur cage and the rings at their minor circumference is just an invitation to a dropped chain when you're riding on rough surfaces. Considering that there's no real evidence that they're actually beneficial, why compromise chain retention?

I suspect that the only place you may find Ultregra crank arms would be on the used market. However, they won't accept anything smaller than a 34 tooth chainring, so if you want lower gearing, you don't want a Shimano road crank.

FSA makes both carbon (K-Force Light) and aluminum (Energy) cranks with 46/30 gearing. I installed the K-Force Light on both of our gravel rigs and they work well. However, there's a caveat if you're installing them on a BB30 of PF30 frame. If the chain falls off to the inside, it can get caught by the chainring bolts and jam. This cannot occur with threaded bottom brackets with external cups; it's only an issue with the narrow BB30/PF30 BBs. It can be fixed with a simple spacer and I sent FSA details of the problem, but never heard back from them. I'm pretty sure that I covered this in detail in a previous thread here.

There are some other 46/30 cranks out there, but the FSAs seem to be the most readily available.

As for crank length, you didn't provide any details about your height or leg length, so it's difficult to make a recommendation unless you just want to do like MTBs and go with 175mm.
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GHC
169 posts
#3Dec 11, 2018, 11:25 AMedited
If you are looking for round 46/30 cranksets ... In addition to those already mentioned, Rotor makes them, as well as BB30 compatible bottom brackets to support them if your current BB30 bike doesn't have the correct applicable inside diameter. Can "easily" change ring sizes with the Rotors.

https://rotorbike.com/      Really nice 46/30 cranksets, with relatively light weight cranks to boot.   Not inexpensive.

My advise....spend some time on this thread http://ridinggravel.com/forum/?p=post%2Fgravel-gearing-7306120

and more particularly, use this gearing calculator
http://www.gear-calculator.com/?GR=DERS&KB=34,46&RZ=11,13,15,17,19,21,23,25,27,30,34&UF=2200&TF=90&SL=2.6&UN=MPH&DV=development&GR2=DERS&KB2=30,46&RZ2=11,13,15,17,19,21,23,25,27,30,34&UF2=2200

With the calculator, you can adjust front rings, back cassettes, tire size, cadence, etc ....and compare to what you have now........what you might gain with a swap, and what you might give up.

If you are riding a 46/34 now, but think you might really want 46/30 .... you will have to decide if the $ you will be spending to make the upgrade is worth it for the lower slow gear ....sometimes it is.   Again, spend some time working through the calculator to help you decide.   If the dollars to change the front gearing are too much, larger rear cassettes are always an additional (albeit heavier) option.

Keep in mind changing spreads also affects chain length and may affect your front derailleur.

Q) What am I trying to say?
Answer) If you decide on 46/30 and don't already own the Shimano Ultegra cranks, and are simply buying the Ultegra to mate with absolute black rings.....I would consider the Rotors, consider the FSA previously mentioned, and decide how much you want to spend.

(I share the view that most 2x gravel bikes ship over geared, meaning 46/30 subcompacts would better serve the average gravel riding consumer than 50/34 or 46/36, my O, ymmv)
bnystrom
459 posts
#4Dec 11, 2018, 11:45 AMedited
Agreed.

I picked up a couple of Rotor 3D+ cranks when The Pro's closet had them for $300, 1 for a road bike and 1 as a spare (I've learned the value of having a spare crank on-hand). I bought a 46/30 Spidering in case I ever want to go that route on a road bike or if I need to use the crank on a gravel bike. They're not making either of these products anymore and I didn't see any 46/30 options on their site, but I may have missed it.

I installed one of the cranks on a road bike (50/34 gearing) and I like it. It should be rugged enough for gravel use.

On my gravel bike with the FSA crank, I'm currently running an 11-32 cassette and that does the job for me on the low end. I had been using a cobbled-together 12-32, but it just didn't shift well enough so I went back to 11-32. I really have no need for the 11 at all, but 12-32 cassettes are hard to come by. IRD allegedly makes one, but finding one is another issue entirely.
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GHC
169 posts
#5Dec 11, 2018, 1:01 PMedited
bnystrom and OP,

Gosh, I was assuming Rotor still offered the 46-30 option .... I didn't confirm. Will be a shame if they don't offer it any more.

I stand corrected and thank you for the correction if that's the case, darn it.
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bnystrom
459 posts
#6Dec 11, 2018, 1:10 PM
I agree that it's a shame, but perhaps it's not a permanent situation. Their new cranks are even more modular than their old ones, so they certainly could offer sub-compact gearing options if they choose to. I spoke to folks there pretty extensively after I bought my cranks (they sent me spiders and lockrings to switch the cranks from BBRight to BB30/PF30 at no charge). I got the impression that they have a lot of things in the works.
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drwelby
531 posts
#7Dec 11, 2018, 1:22 PM
Instead of going from a 34 to a 30 in the front, can you switch to a cassette that has a largest cog that is about 4 teeth bigger? There's a lot more options for going larger on the rear at the moment.
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bnystrom
459 posts
#8Dec 11, 2018, 1:27 PM
That's true, but it's likely to require a different rear derailleur or an adapter that could compromise shifting performance. It also increases the gaps between gears, which is one of the things that many of us who prefer 2x setups are trying to avoid.
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Jimbop
89 posts
#9Dec 11, 2018, 5:27 PMedited
Much food for thought - thanks for everyone's input. I have had a play around with gear-calculator.com and it shows on the surface of things what i expected - less overlap (vs my current 34/46) and more range. However, two things concern me:
1) Right now if I change big rings in most situations I just double shift the rear at the same time and i end up with the right ratio. With the overlap being smaller then I'm guessing that shifting rings would require three shifts to get to the right ratio?
2) What would be really helpful is to ride a bike setup with 46/30 11-32 so i could compare.

The 11-36 PG1170 cassette option by the looks of things would work with my RX800 and that would be a much cheaper option.

Easton make some nice looking cranks, rings and even a spindle power meter (actually it's left side only and if i got one i'd want a dual). if I wanted to spend a fortune I could get their setup in either 46/30 or 47/32 and if necessary add the 11-36.

The FSA SL-K Adventure 46/30 looks really nice but I don't know how it relates to the FSA K-Force Light.

Try before you buy i think is the key here. Just need to try to figure out where near London (UK) I can find a bike shop that happens to have a 30/46 setup demo bike...

EDIT Another advantage of not going the Absolute Black oval route is that they only sell pairs of 30/46 and 32/48 - i don't think you can mix and match if i remember well. However, if i got the FSA (or similar) I think I could just swap the small ring whenever I wanted to and I imagine it's not toooooo terribly tricky; remove cranks, swap ring, done, install cranks done? If I do end up changing crankset then LBS will be doing the installation and I'll watch. I've learned a lot about bike maintenance but i don't have those tools and I suspect it's probably one i should let a pro do properly rather than botch it myself. They were really nice to me when I went in there with my incorrectly mounted new RX800 RD and poorly adjusted new R8000 FD :-)
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bnystrom
459 posts
#10Dec 11, 2018, 5:56 PMedited
I'd like to clarify a mistake I made above. I have the SL-K cranks, not the K-Force Light. Looking at the specs, the only obvious difference is that the K-Force is 20 grams lighter for $221 more. I guess it's prettier, so maybe that makes it worth the extra money.

I don't quite follow your comments about the overlap. A 46/30 crank has less overlap/duplication than a 46/36, due to the larger tooth difference between the rings, 16 vs. 10.

By all means, if you can find a bike near you with a 46/30 on it, take it for a test ride. The FSA cranks are currently spec'd on a few new gravel bike models, though I don't recall which brands offhand.
1
Jimbop
89 posts
#11Dec 11, 2018, 6:04 PM
Ah OK that makes more sense. I think the SL-K's are really good looking - particularly when compared to the Absolute Blacks, which kinda my eyes bleed when I look at them if i'm honest.

I've edited my post to clarify - as you rightly say the 46/30 has less overlap than my current 46/34.

WRT crank length - i'm 182cm (5'11-6' ish in old money) and i wear 32" inseam trousers but i don't know what my legs actually measure as i've not yet taken the trouble to measure (figured i'd work out if new crankset is the right answer first)
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bnystrom
459 posts
#12Dec 11, 2018, 6:21 PMedited
I would suggest 175mm cranks.
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Volsung
878 posts
#13Dec 11, 2018, 7:46 PM
Unless you have knee problems crank length doesnt matter much. I'm taller than you and use 170s but I have the knees of a 120 year old.

I have heard of long distance riders using short cranks to reduce knee strains, but most people dont race across Kazakhstan.
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romany8806
21 posts
#14Dec 12, 2018, 3:54 AM
I'm a big fan of 46/30 chainrings. I run a 46/30 Sugino crankset and 11-36 cassette on my AWOL and it's ideal. I can scale pretty decent off road climbs with a load and 29x2.1" tyres. I find it basically operates as a 1x setup for most road riding - 46x36 is low enough even for steepish climbs. That bike weighs about 12kg in road mode and about 13.5kg in off road touring mode.

I'm waiting for my Enigma Escape frameset to arrive - I've got a Rotor 3D+ 46/30 and 11-34 to go on that. It'll be a touch over 8kg so I think the gearing should be plenty.

Crank length: I'm 179cm with loooong legs. I've tended to use 172.5mm cranks but I find I get pain above and behind my kneecaps because the pedals are too high at the top of the stroke. I'm going to a 170mm crank because of that. The Enigma also has a low BB so my centre of gravity won't suffer compared with my other bikes.
1
bnystrom
459 posts
#15Dec 12, 2018, 8:25 AM
Crank length is largely a personal preference and you can find recommendations from sources that are all over the map. There are people claiming that the cranks on bikes are all too long and others claiming that riders my size should be riding 200mm cranks. It's no wonder people get confused and it's probably why the industry has pretty much standardized on cranks in the 165-175mm range; they're not likely to cause problems for the vast majority of riders. It's interesting that the standard crank length for MTBs has always been 175mm, pretty much regardless of frame size. However, bouncing around off-road is very different than grinding out road miles.

I've been riding 175mm cranks since the mid-'70s and they've never caused me any problems. I guess I'm used to them by now.
1
GHC
169 posts
#16Dec 12, 2018, 8:53 AMedited
Sorry to hear about the pain around the knees guys. Not for nothing, one thing that might help there (if they are "helpable") is less lugging/higher cadence and/or a professional bike fitting (tell the professional fitter what is ailing you!!!).

Speed being equal .... Lugging in the saddle is much much harder on the knees than dropping a gear or two and spinning fwiw. (power meters will confirm some other advantages of maintaining cadence)

Which ironically, gets us back to lower gearing for climbing :-]

2
RobF
35 posts
#17Dec 12, 2018, 10:09 AM
Good discussion. I'm convinced 46/30 with 11-32 to 11-36 is perfect for 90% of us out there. That chainring spacing is far more appropriate for you than the close 46/36 cyclocross setup.
The Sugino 46/30 is a good choice, although not cheap. I put a lot of miles on one.

I actually recommend the Easton crankset for a few reasons.
1) It sounds like you like to experiment with things yourself. The modular setup on direct mount rings is great for that. I ran 1x for a long time, and am switching back to 2x. It's a quick, easy, & elegant. You could easily experiment with the 47/32 they make as well, which could be a good happy medium for you. Try it & let us know!
2) You can buy the power meter spindle and pop it in without having to replace the whole system. Yes, it is left-side only, measured in the spindle. I've been running it a year without issue, including through water crossings and mud. Are you really likely to be tuning your left-vs-right pedal stroke for smoothness anytime soon?
1
Jimbop
89 posts
#18Dec 12, 2018, 4:09 PM
RobF wrote:
Good discussion. I'm convinced 46/30 with 11-32 to 11-36 is perfect for 90% of us out there. That chainring spacing is far more appropriate for you than the close 46/36 cyclocross setup.
The Sugino 46/30 is a good choice, although not cheap. I put a lot of miles on one.

I actually recommend the Easton crankset for a few reasons.
1) It sounds like you like to experiment with things yourself. The modular setup on direct mount rings is great for that. I ran 1x for a long time, and am switching back to 2x. It's a quick, easy, & elegant. You could easily experiment with the 47/32 they make as well, which could be a good happy medium for you. Try it & let us know!
2) You can buy the power meter spindle and pop it in without having to replace the whole system. Yes, it is left-side only, measured in the spindle. I've been running it a year without issue, including through water crossings and mud. Are you really likely to be tuning your left-vs-right pedal stroke for smoothness anytime soon?

The Easton crankset looks really good but some plusses and minuses...
i) Super light at 538g for the 32/47 and i guess a smidge lighter for 30/46. The FSA seems to weight in at 617g.
ii) Direct mount on the Easton as you say but the FSA SK-L adventure is too so they are even on that score. Actually - looks the inner ring on the FSA mounts to the outer - not sure how the Easton inner ring mounts.
iii) Seemingly nigh on impossible to actually buy the EC90 SL cranks and the rings, at least in the UK. I've found a couple of places that sell the cranks but can't find the rings at all. Am i missing something? I'll pop them a line. I wrote to FSA about something this morning and they wrote back within hours - i'm impressed.
iv) Power meter - i know the square root of nothing but a friend who has done a few iron mans says that everyone has an imbalance and not only that but the imbalance can shift substantially during a ride. I broke my left femur several years ago and the bike fitter/physio in the summer measured my leg strength (prior to getting into cycling really) and my left was about 20% weaker. That may have evened out - or not but i know i have a problem there and historically i've always had a slight problem with my left knee, so the combo is probably going to make a left only read funky. If it were a constant imbalance then it wouldn't matter but if it's dynamic then surely it makes a difference?

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bnystrom
459 posts
#19Dec 12, 2018, 4:17 PM
The question about power meters is really how important is the data to you? Although it may not be absolutely accurate, it should be consistent, which is what you need to know if you're trying to gauge improvement over time. There are pedal-based dual-side systems out there, so if they're available in the type of pedal you prefer, that might be a good alternative that would allow you to use whatever crank you want.
1
Jimbop
89 posts
#20Dec 12, 2018, 4:21 PM
bnystrom wrote:The question about power meters is really how important is the data to you? Although it may not be absolutely accurate, it should be consistent, which is what you need to know if you're trying to gauge improvement over time. There are pedal-based dual-side systems out there, so if they're available in the type of pedal you prefer, that might be a good alternative that would allow you to use whatever crank you want.

And that's the problem my bud said to be careful of, i.e. the data might not be consistent if the imbalance can change depending on terrain, fatigue, injury, etc. I haven't heard of any SPD (MTB type) pedal power meters. There are spider and crank options but the spider ones I guess wouldn't work with either of the cranksets i'm looking at now.
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