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COMFORT + EFFICIENCY = PERFORMANCE

COMPACT CRANKS vs STANDARD CRANKS: gearing implications

Last Updated on July 7, 2014 by stevehoggbikefitting.com

Lately I’ve been getting a lot of email from readers of the site asking in one way or another: “Should I be using compact cranks or standard cranks?” It is going to be much easier to give enquirers the URL address for this post than it is to  recap multiple times. This post borrows heavily on an article I wrote for  BA magazine some time ago. So my apologies to Australian readers who may have already seen much of this.

COMPACT VS STANDARD CRANKS:  GEARING IMPLICATIONS

What is the difference between ‘standard’ cranks and ‘compact cranks?

The difference is in the chain ring sizes which is a product of different PCDs. PCD stands for “pin circle diameter” and is occasionally referred to as BCD or “bolt circle diameter” and is the size of a the circle formed if the centre of the circle is the axis of the bottom bracket axle with the circle passing through the centre of each chain wheel pin.  By far the most common chain ring size option for ‘compact’ cranks is large ring of 50 teeth and a small ring of 34 teeth, though other options exist with 50 / 36 , 52 / 36 and 48 / 34 also being available, but less common. These all require a PCD of 110mm and this PCD is common to all compact cranks other than Campagnolo who use a 113mm PCD

In contrast, standard cranks use a PCD of 135mm for Campagnolo or 130mm for Shimano, SRAM, FSA and the rest. a PCD of 135mm allows small chain ring options down to 39 teeth and while a 130mm PCD  will allow an inner chain ring size of 38 teeth, in practice 39 teeth is the default option and is usually paired with a 53 tooth or occasionally, 52 tooth outer chain ring.

2014 Update  An exception to above is that the latest model Shimano road cranks are all 110 mm pcd. They can be sourced with 50/34 or 53/39 chain rings.

What difference does this make to gearing?

The answer is dependent on what rear cogs are chosen. If the same rear cassette is chosen, say 12 /25 comprising 12/13/14/15/16/17/19/21/23/25 tooth cogs, then the compact crank will have a lowest gear ratio that is 13% lower than a standard crank. However, top gear will also be lower by 6%. So in simple terms, if using the same rear ratios, the standard crank will always have a higher top gear and the compact crank will always have a lower low gear.

What effect will these differences have on speed?

With the 12 / 25 cassette example above and while pedaling at 100 rpm, a compact crank with 34 tooth inner ring would give a bottom gear speed of 17.3 km/h. Meanwhile a standard crank with 39 tooth inner ring would give a speed of 19.8 km/h at 100 rpm. The 2.5 km/h difference in speed in low gear doesn’t sound like much but in fact it is a substantial difference. The key to understanding just how large a difference is to calculate what size rear cog a 39 tooth inner ring on a standard crank would need to be paired with to give a similar speed for cadence in low gear. The answer 39 x 29, yes, 4 teeth larger would be needed to give a low gear speed of 17.1 km/h as compared to 17.3 km/ h from a 34 x 25 combination.

At the other end of the spectrum, top gear; 53 x 12 gives a speed of 56.1 km/h at 100 rpm when compared to the speed achieved in a gear of 50 x 12 at the same cadence which would be 52.9 km/h. The only option open to a compact crank user who wanted to gear up in high gear would be to use an 11 tooth cog which would give a 50 x 11 gear speed of 57.7 km/ h at 100 rpm.

What effect will this have on pedaling speed?

Using the examples above: let’s assume that the 39 x 25 user is struggling a bit on a long steep hill at 75 rpm at 14.9 km/h. Using a compact crank, the same rider using the same 25 tooth lowest rear gear paired with a compact 34 tooth inner ring would be able to pedal at a much more sustainable 86 rpm for the same road speed. This means that the compact crank rider would be noticeably fresher. Alternately, the compact crank rider could pedal at the same 75 rpm in a 23 cog at 14.1 km/h keeping the 25 cog in reserve or push a bit harder at 15.4 km/h in the 21 cog keeping both the 23 and 25 cogs in reserve.

In top gear, the difference is that the compact crank user would have to pedal the 50 x 12 combination at 106 rpm to achieve the same road speed as the 53 x 12 user at 100 rpm.

What if the rear cogs are not same ratios?

It is possible to have roughly similar ranges of speed for cadence with compact and standard cranks depending on what rear ratios are chosen. For example, the table below gives speed at 100 rpm for a compact crank paired with rear ratios of 11 / 23 versus standard crank with 12 / 25. I have deleted the more extreme combinations; i.e. large chain ring / large rear sprocket and small chain ring / small rear sprocket.

 

11 12 13 14 15 16 17 19 21 23
50 61.2 56.1 51.8 48.1 44.9 42.1 39.6 35.4 32.1
34 38.2 35.2 32.7 30.5 28.6 26.9 24.1 21.8 19.9
12 13 14 15 16 17 19 21 23 25
53 59.5 54.9 51.0 47.6 44.6 42.0 37.6 34.0 31.0
39 40.4 37.5 35.0 32.8 29.5 27.6 25.0 22.8 21.0

 

What is the better option; compact or standard?

Which is best depends on what you want to do with your bike and what your strengths are. If you are riding flat to undulating terrain either option will work when paired with the appropriate rear cassette. If you are really strong rider then you will always be able to have a higher high gear with a standard crank because of the larger chain ring sizes.  Conversely, a compact crank will always have a lower low gear option for the same reason.

Is either more efficient than the other?

Yes. At some level the standard crank is more efficient at the same speed for cadence. This is because a standard crank uses a larger chain ring and larger rear cog than a compact crank does at the same speed for cadence.  In turn this means that the chain takes a less tight turn around both the chain ring and rear cog resulting in lower frictional losses. Equally, the chain is engaged over more teeth for the same road speed for cadence with standard cranks, meaning a longer wearing drive train.

This being the case, why do compact cranks exist?

The bottom line is that a rider will be able to climb a steeper hill on a compact crank than they will be able to on a standard crank.

How long have compact cranks been available?

The name and popularisation of the concept is relatively recent but Ritchey and Sugino ( and probably others) have been making 110 mm BCD road cranks for many years. In Sugino’s case, at least 30 years; so the option has been available for some time.

If I want low gears, wouldn’t I be better off with a triple chain ring crank?

Maybe. It depends on what you want to do with your bike and how strong you are. Triples for loaded touring have traditionally had a 1:1 low gear. That is a low gear where the chain ring and rear cog are the same size. In practice, a lower gear than this is achievable with the various gearing options out there but a triple has a wider Q factor than a double chain ring crank, which doesn’t suit everybody. Also the additional complication of changing between 3 chain rings rather than 2 may be a problem for some. Assuming the same low and high gears, a triple doesn’t really offer a lot more as most of the extra chain ring / rear cog combinations are duplicates or near duplicates of other combinations. What a compact crank does is offer a decent gear range with simplicity and ease of use when compared to a triple.

If you must have a really low, low gear or you are going to consider expedition touring, then a triple is still the way to go. If your bike usage profile is more varied and you do a bit of everything, including plenty of climbing, then a compact crank is a better bet.

So why would I choose a standard crank?

Because you don’t climb alpine climbs and maybe you do a bit of racing or fast riding where seriously low gears aren’t necessary. At normal solo training speeds on flat to undulating terrain a standard crank is probably a better bet in the sense that at typical flat road solo training speeds of 32 – 35 km/h, a standard crank can be ridden on the small ring with margin for speed increase without changing chain rings. On a compact crank, if the speed rises much above that example, it is necessary to do a ‘double shuffle’ from the higher gears (smaller cogs) combined with inner chain ring to the lower gears (larger cogs) on the outer chain ring. In practice, this can be worked around, but there is a difference.

Can I go racing with a compact crank?

Of course. Plenty already are. Just make sure that your high gear is high enough for the type or racing that you’re planning on.

Are there any new developments in gearing?

Not with standard cranks. 53 x 11 is a realistically high high gear for a strong rider and in percentage terms, not many need that gear in reality. It’s kind of like owning a car that will do 250 km/h in an area of 110 km/h speed limits. Nice, but not necessary.  SRAM’s new Apex group offers a compact crank potentially paired with the option of a 11 / 32 wide range 10 speed cassette. Conceivably, this low gear could be used for loaded touring but in practice a triple is better because the jump between low gear and second gear is quite large. I suspect the target market is riders who want to occasionally ride Alpine style 20+ km climbs with moderate fitness levels.  IRD also make aftermarket 10 speed cassettes with 32 and 34 tooth lower gears than can, in some cases, be finessed to work with Sram and Shimano rear derailleurs even though they have smaller maximum cog sizes recommended by their manufacturer.

Another option if using Sram is that all Sram road and mtb rear derailleurs and 10 speed cassettes are interchangeable. That means you can potentially pair a pair of road Sram shifters with an mtb rear derailleur and use a compact crank for a low gear combination of 34 tooth chain ring and 36 tooth rear cog.

Will my life change if I buy a compact crank?

No. But you may be able to get up the hill that defeated you last time.

Will I be undergeared for racing or riding in fast bunches with a compact crank?

Put a cassette on that has an 11 cog and you should be fine.

Will there be any effect on my position if I switch from a standard crank to a compact crank or vice versa?

Providing crank length is the same, there are no implications for your position on your bike.

Note: Often, more specific answers to your questions can be found in the Comments below or in the eBooks section and FAQ page.

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Comments (42)

  1. Just to let other readers how I chose my gearing: getting the straightest chain line for the most used gears.

    I originally had a triple 50/42/30 x 12-25 bike. I rode it for a couple of months and figured out my favorite gears for the climbs and for the flats.

    So when it was time to get a new bike, I made sure to have my favorite gear ratios have the straightest chain line. The result is I now use a 50/34 x 12-27. My favorite gears for flats are 50 x 14/15/16 and 34 x 19/21/24.

    I also have a standard 53/39, which offers most of the ratios I need but the chain line wouldn’t be as straight.

    The result hopefully is a quieter drive train and less chain wear. And while I can spin out of descents, it does not bother me as I would rather get aero and coast.

  2. I recently changed my rear cassette from 11-25 to 11-27. that gave me the little bit of extra gearing i needed on the hills, without losing the 53+11 max speed i had before (not that i can use it often!). not sure if i missed any import considerations by just going ahead and making the change. I checked that the rear derailleur could handle it (said up to 32). my front chain rings are standard 53/38T

    1. G’day Daniel,
      You’ve done fine. The only thing you may not have considered is this. Realistically, very few people other than elite riders can genuinely push a 53 x 11 other than downhill. By changing from a 11 / 25 to an 11 / 27, you’ve gained a lower low and maintained the same rarely used high gear at the cost of losing a gear in the middle of your range. If you have your time over again, a 12 / 27 might be a better bet in that it would give you more useable gears than a 11 / 27. You don’t mention brand and what I’ve said assumes that a 12 / 27 is available.

      1. Ah cool. No matter how much you learn, there’s always more 🙂

        I had a SRAM 11-25 cassette, then got new wheels which had a Shimano specific freehub. So i decided to get a new cassette instead of another freehub (only finding out later that Easton has a freehub exchange program. doh!)

        I bought a DuraAce 10 speed 11-27. good point about the 12-27. makes perfect sense now that i think about it. ah well. my wife got my old wheels and cassette. she’d outgrown her gearing (in the big chain ring of her compact crankset always, even up hills)

        Thanks for the awesome blog. its an amazing resource. I’m learning so much. stuff I’ve read here has prompted me to try moving my seat back a bit. i can feel the difference in my hands and arms already. and this is after a $300 3 hour fitting session last year that really didn’t make much difference at all. The standout thing was how little i learned from the session. lots of little changes were made, but i was no wiser or more enlightened afterwards

        reading this blog however, i understand what’s going on on the bike SO much more now.

        Once I’m a bit fitter and can ride a decent distance (120km is the goal) I’ll book myself in for a fitting with you.

      2. You’re welcome Daniel and I’m glad that you are getting positive results.
        Funny your comments about the bike fit you had. I think one of the major considerations during a fit is for the fitter to explain everything. What they changing, why they are making a change and the expected outcome. I would rather be guilty of giving a fit client too much info than too little. It sounds like I might see you in the future. Best of luck.

  3. I noticed that 110mm Compact Chainrings usually come branded as being a combination set of 50/34 or 52/36. Is there any reason for this? I can imagine 52-34 being really wide with shift accuracy/time suffering, but shouldn’t 50/36 work fine, if not better?

    1. G’day Guedavid,
      I can’t help you. In my part of the world Compacts usually come as a 50/34, 48/34 or uncommonly as a 50/36. In practice 50/34 is by far the most common option.

      1. SRAM now offers 110 bcd compact rings in 34/36/38 and 48/50/52 now. Available separately of course. A lot more flexibility in gearing than the standard setup, which is why I prefer compact in my hilly region. I’m not doing any time trials though.

  4. Being a little slow, I finally figured out yesterday, (after feeling like a poor climber for the last 3 years) that my buddies were all running 20-30 RPM’s faster than me on the hills. Turns out they all have compact cranks while I’m riding Ultegra 12-27 and 52-39. It appears that simply by going to a 50-34 I will get that approximately 20 RPM increase? Or would there be more benefit to going with a 50-30 (Shimano 105). I ride around the SF Bay Area, always climbing, which I enjoy, but will enjoy more if I get dropped a little less :-() Thanks

    1. G’day Dan,
      Going from a 39 inner ring to a 34 inner ring will give a cadence increase of 13% for a given road speed and rear cog choice. I’m not aware of a Shimano 105 50 / 30 chainring option crank. Unless you are talking of the triple with 50/39/30?

      If so, you will have to change your STI levers and front and rear derailleurs to make it work. If you choose to do so, your cadence will increase by 23% for same road speed and rear cog selection.

  5. I just purchased a 2011 Specialized Tarmac Expert and have had many opinions and readings and as a 47 year old avid cyclist and no one person or article better explained it then you….Thx!

  6. Hiya Steve,
    I’ve had my Felt AR5 for about a month. Came with FSA Gossamer Pro 52/36 compact, and 11/25 cogs. I tried my first hill climb last weekend and found it pretty tough. I’ve ordered a 50/34 Super set from FSA to use with the existing cranks. I’ll try it with the existing cogs; if I still want a lower gear I can go to 12/27. Derailleurs are Shimano 105. This should work without complications, no?

    1. G’day Alcalira,
      You are correct. If you need even lower, use a Shimano
      or even a Sram 11/28 10 speed cassette. Sram cassettes will work fine with your Shimano equipment

  7. Hi Steve,
    first thanks a lot for your highly informative website. Having been a cyclist and triathlete in my youth and an all time commuter, I got back into sportive cycling last year at 41, having loads of fun and trying out a few things to work on my position. E.g., I already and successfully used some sort of shim before, and your articles prompted me to use some wedges – all very minor corrections, which allow me to really feel “free” when sitting on my bike.
    On standard and compact cranks, you’re wrinting on efficiency. I found using cyclocross cranks (46/36) much more efficient than anything else, because now I use the big chainring excusively here in the complete flats and low hills (46-19/17/16 mostly), whereas at 53/39 I would often have used 39-15/14, or 53-21/19, all at quite bad chainlines, and with that silly cross-switch right in the middle. And, as it comes to max speed, 46-11 is faster than the 52-13 I used to do in the old days, for now I am comfortable with 46-12. Next time in the Alps, I will mount a 34, though.
    So, for someone like me who does up to 260 km a day @ 30-33 av. speed and never goes further than an occasional everybody’s race, a cross crank really is an option to consider…
    Btw, ritzelrechner.de really helps checking these things out graphically…

    So, just my 2 c on that, and again many thanks for your incredible work!
    Greetz, sven.

    1. G’day Sven,
      thanks for the information. Cyclocross is almost unknown in
      Australia and I know this will seem strange to a northern hemisphere rider but I have only ever had one client on a ‘cross bike! It was the only ‘cross bike I’ve seen in 20 years. I have no doubt that what your saying is correct and hope your information helps other readers.

  8. I’ve just purchased a Super Record groupset 50/34 with 12-25.
    I am planning to buy TA chainrings for 11 speed specifically 52/36.

    How would a 52/36 running a 12-25 would suit me. I’m thinking about this size so I can use for racing here in the UK and also for the Dolomites, Alps etc. Is this suitable? Do you think this would be a good choice?

    1. G’day Steve,
      My crystal ball doesn’t work on Thursdays. I know nothing
      about you, how strong you are, how heavy you are, what sort of terrain you ride ove and have no idea whether it would be advantageous or not. If you are really asking ‘will the 36/25 low gear will get me up the grades in the Dolomites?’ you will have to work that out yourself. You are a lot closer to both the Dolomites and yourself than I am. All I can say is that if in doubt, better to have a low gear that doesn’t get used than to need one that you don’t have.

  9. G’day Steve,

    I am currently running a standard 53/39 (Ultegra) on my road bike, however I find that I rarely use the higher gearing on the 53. I also do quite a lot of climbing and the 39 is too big. I am looking to change to a compact 50/34. What considerations do I need to make when changing over? (ie do I need to change the whole crankset or can I just change the rings?, chain length? derailleurs?)

    Buying parts is so much cheaper online but I want to make sure I buy compatible parts.

    Regards,

    Matt

    1. G’day Matt,
      Assuming you are currently running Ultegra 6600 or 6700, all
      you need to do is to replace your crank set with a 6700 compact crank with 50 /34 rings. Additionally, and assuming your chain is currently cut to the correct length, you will need to remove 4 links.

  10. Hi Steve,

    I am looking at changing over to a 50/34 (Ultegra) compact. I want to buy the parts online as they are so much cheaper. What things do I need to consider when purchasing? (eg. chain length?, derailleurs?, bottom bracket sizes? do I need to change the whole crankset or can I just change the rings?)

    1. G’day Matt,
      Assuming your current cranks are Ultegra 6600 or 6700, you will need to change your cranks as the bolt circles for compact and conventional cranks differ. Your levers, derailleurs and bottom bracket cups will work fine but you will need to remove either 2 or 4 links from your chain.

  11. Hi Steve,

    Great article. Really enjoy it. I currently use Dura Ace 53/39 with 11/28 cassette. When climbing steep hill with 39 and 28 I can only produce around 60-67 RPM at the maximum. I am wondering if I should switch to compact Ultegra 50/34 and if I do so will that help me to spin at a faster RMP and in turn going up the hill faster?

    Thanks
    Jim

    1. G’day Jim,
      I’m a believer that if a rider has to drop below 75 rpm for any
      length of time then they need a lower gear. The 34 / 28 combination would allow you to ascend at the same speed as your current 39 / 28 but your cadence would rise from 60 – 67 rpm you mention to 69 – 77 rpm which should be easier on the legs. Basically a 34 tooth ring is 14.7% lower gear than a 39 tooth ring. Call it 15%. So you are lowering your bottom gear by 15% which is substantial.

  12. Hello Steve,
    I had been riding and racing using a 53/39 chain ring with a 23-12 or 25-12 cassette in the past.
    This year I had to do a race which involved a 7 mile climb and borrowed a compact crank 50/34 which allowed me to tackle that climb quite easily compared to in the past when I had the 53/39 and 25/12 option.
    I decided to experiment with a compact crank after that and the combination I have now is 52/38 on a 23/12 cassette. I also purchased 50 and 34 teeth chain rings that I can swap out if I go to a race that has losts of climbing.
    Most of the road racing and riding is on relatively flat or rolling terrain and crits which are flat.
    I did notice that I was missing the high gear when I needed it especially when going downhill or in tailwind sections. A 53/12 is a bigger gear than a 52/12 and 53/11 is considerably bigger. Most people here run a 11 tooth cog in the rear cassette. That put me at a considerable disadvantage especially in long road races where I would have to pedal around 100 to 105 rpm to keep up whereas previously I used to keep me cadence around 95 rpm. Over a 70 to 95 mile road race it takes it toll.
    I am not sure I made a wise decision for a few races that have sustianed climbs which I may or may not travel to every year.
    The other option is to go with a 23-11 cassette but I like the way a 23-12 cassette has the gears laid out which does not have a big jump in the gear lengths at the low end (23-21-19-18… versus 23-21-19-17…). There is always the 21-11 option but those cassettes are upwards of $200 here in the US. I use Shimano components.
    What are your thoughts? (Sorry for the long winded question)

    1. G’day Frank,
      I’m surprised that someone who is racing can’t sustain a
      cadence of 100 – 105 rpm. That is not a high cadence; it’s pretty normal. So I’d suggest you initially focus on improving your pedaling speed. It will cost you nothing and by the sound of it, solve your problem.

      An easy way to improve your cadence is to put your bike in your 38×15 gear and leave it there for a couple of long flat to undulating rides per week for 6 weeks. Make sure you pedal down the the hills with as little coasting as possible. if you do this for 6 weeks you will have no problem pedaling at 100 to 105 rpm. As a bonus, riding all the hills (not mountains) in 38 x 15 won’t harm your strength either.

      1. Thank you Steve for the response.
        I surely will make this part of my workout. In the winter I do a lot of cadence work where I keep my cadence between 100 to 110 rpm but over the years going over my race files I have noticed that my cadence averages around 95 rpm.
        Mid season this year I changed from Shimano DuraAce 7800 cranks to SRAM S975 cranks, I noticed the Q factor is a different between the two. Do you know how much the difference is and do you think it is a good idea to add washers between the crank arm and the pedal to make the Q factor the same?

      2. Sorry Frank,
        In your original mail you said you tried to keep your cadence to 95 rpm. Averaging 95 rpm in a race is a different story. If your average cadence is 95 then I’m sure there are periods when you are pedalling at 100rpm plus so you don’t have a problem with leg speed.

        As that’s the case, I’d go for the 11/23 cassette and just live with the absence of an 18 cog. It sounds like a lot of your opposition must be in the same boat.

  13. Hello Steve,
    I am writing to ask about a chain ring possibility. On my previous go-to road bike, I had a compact 50/34 Ultegra 10 speed set up with an 11/27 cog set. I liked this set up a ton, with the ability to climb several of the 20% grades in my area while staying seated. I am setting up a new (used) bike now. It has a 11/28 cog set on it now, and while I want to keep the small chain ring at 34 for the perfect low climbing gears, I would love some more high end if possible. Someone recommended a mid compact 52 chain ring that they said would be the largest possibility for a compact 110 mm Ultegra set up. Is this possible? Can I have the best of both worlds??

    1. G’day Jordan,
      yes it is possible. The only negative is that on some front derailleurs the shifting needs to be more deliberate so as not to throw the chain on the down shift from big to small ring. There are devices that will prevent that though. The question to ask yourself is whether you actually need a 52×11. 50×11 is a bigger gear than 53×12 and is good for 58km/h @ 100 rpm. How often are you riding at that speed or above with real pressure on the pedals?
      52×11 @ 100 rpm is 60km/h which is a negligible difference with potential complications for shift quality.

      1. Thank you kindly for the specific information Steve. This is exactly why I asked you the question. While I do enjoy aggressively bombing down the longer smooth descents around here…..being a bit of a masher at heart, the possible complications of shift quality do not make this idea worth it for me. I think you just saved me some cash.
        Thanks again!

  14. Hi,

    Ive recently replaced my SRAM chainrings 52/38 with 53/39 (old ones were damaged intransit) Will this work? Is there anything else i need to replace (eg chain?)

    thanks in advance

    1. G’day Ben,
      there is no reason that it won’t work, though you may have
      to raise your front derailleur a touch. If only the chain rings have been replaced you will not need a new chain.

  15. Brilliant article Steve. I would like to mention 11 speed. With a compact 50-34 coupled to a 25-11 gives you all the advantages of a compact and the top end gearing of a standard without any jumps in the rear cassette.

    1. G’day Thomas,
      With hindsight I should have covered 11 speed. I didn’t
      because I was lazy. That post was based on an article I wrote some years ago for a local mag and I’m not sure whether 11 speed was around at the time. Thanks for bringing it up though.

  16. Steve,

    I’ve tried to get a definitive answer to this question but I reckon you could be the man.
    I am currently using a 52/39 with a 13/26 rear cassette with a pretty basic Sora groupset.I want to upgrade my bike to one with a 105 compact groupset.
    My cycling will include a lot of long climbs(including Alpine type climbs).Will the compact make these climbs easier to mange.What would the best set up in the rear cassette be just to spin at a higher cadence,12/27 or 12/28 maybe.
    At the moment even in the 39/26 my cadence is awful.

    John

    1. G’day John,
      If your cadence drops below 75 rpm while climbing for any
      length of time, you won’t recover well. What you need to do is note your cadence in lowest gear on climbs similar to those you will be doing. Lets say you are down to 60 rpm. 60 rpm is 80% of 75 rpm which means you need a 25% lower gear than you do currently to get up the bare minimum cadence you need to be able to do.

      Your 39 x 26 x a wheel circumference of 2.1 metres gives you a gear development of 3.15 metres per pedal crank revolution. That is 39 divided by 26 x 2.1.

      To have a gear 25% lower with a compact crank you would need a gear development of 2.36 metres. Using a 34 tooth chainring you would need to use a 30 tooth rear cog continuing this example. That is 34 tooth ring divided by 30 tooth rear cog x 2.1 metres.

      That maths are simple if you know what to do.

      So, work out your current rpm when riding steep climbs. Work out what percentage lower you need to get to to maintain at least 75 rpm (lower gears and higher rpm is fine!) and then you will know what to specify.

  17. Thanks Steve,

    I suppose what I am really asking is would it be easier to turn a 34/27or 28 on long climbs as opposed to a 39/26 even though each turn of the crank won’t eat up as much ground(something I am not really worried about.)

    1. G’day John,
      39×26 is 3.15 metres per pedal stroke with a 700c wheel with
      23mm tyre. 34×28 is a 2.55 metres per pedal stroke. So yes, a lot easier. About 19% easier.

  18. Steve
    I currently have TruVativ Roulier 39x52T ISIS (1st Production Triple) and SRAM PG950 9 speed 12-26T with Ultegra and would like to ride up hills a bit easier. Do I (as per the answer to previous question by Matt)need to change the whole crankset to say compact 50/34 and remove chain links or can I change only the small ring on the existing crankset? Which crankset would you recommend? Or what about just adding a larger rear cog -is this cheaper/effective?
    Thanks

    1. G’day Craig,
      If you have a 39 tooth inner chain ring on a TruVativ
      crank, you will have a 130 mm bcd. That means that the smallest chain ring that will fit is a 38 tooth if you can find one. That will lower your gearing by 2.5% which is negligible. You can fit a Shimano cassette with a 28 tooth low gear which will give you another 7% reduction from the 26 tooth low gear you currently have. Those measures will be enough of they won’t.

      If they are not, then yes, a new compact crank is the way to go. A crank with 34 tooth inner ring will give a 13% reduction in bottom gear using your 26 tooth cog and a further 7% if you use a new cassette with 28 tooth cog.

      There is also another way to lower your low gear that doesn’t work all of the time. If you use a Shimano road long cage rear derailleur and screw the B tension bolt all of the way in, then if the rear derailleur hanger shape and placement is okay, they will work with a Shimano mtb 10 speed 11 – 32 cassette for a further substantial reduction in low gear. The only problem with doing this is that it is out side of the design parameters of a Shimano road long cage rear derailleur and it won’t work on every frame and you have to try it to find out.

      We’ve set a number of customer bikes up like this but failed on just as
      many.

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