gear ratios and hill climbs

[Cranky]

I checked out a Sram cassette. I ride a 12 - 23. Sram have a 12 - 26 listed, ChainReaction £24.
Going to LBS to count the intermediate sprocket sizes to see if it lies in a smooth gear progression with my 52 - 42 - 30 tripple.

For MTB use, they have a 11 - 32 and 11 - 34
The upper jockey wheel will be pressing the chain onto this size sprocket on a road derailleur.
I've been there. I fitted a 13 - 28 on an old road bike. Its a bit noisey, but worth the lower gearing on the North Devon coast road. Not the thing for everyday, just for when demand dictates.

Hi jimboalee, I use the Sram 12-26 with a 52-42-30 triple myself. It's an excellent combination IME and the Sram cassettes give a very smooth change, too. I also use Sram 11-32 on my MTB.

 

[butki55]

The first figure is the number of teeth on the smallest chainring (The gears at the front.)
The second is the number of teeth on the largest sprocket of the cassette (The gears at the back)

You then divide one by the other to get the gear ratio

A gear ratio of 1 means that everytime you turn the pedals one revolution the wheel will rotate once. A gear ratio of 2 means that for every half turn of the pedals the wheel will rotate once. Obviously the lower the gear ratio the easier it will be to climb a hill.

I know that I am on a MTB as im just getting into this cycling....and may I say the time I have been out its great. I have counted me teeth on the above sprockets as you said and my front small was 24 and the rear large was 34. Is this then a 0.7 or a 1.4. What does this mean for me riding this setup? What are the pros and cons for me.

 

[gbs]

To butki55; as a novice maybe I should not offer advice but since I started the thread I should show the kind contributors that I have learnt something.

I would say F/R 24/34 gives 0.71 ratio a v low gear ratio designed for difficult terrain (gradient and mud)

 

[RedBike]

I know that I am on a MTB as im just getting into this cycling....and may I say the time I have been out its great. I have counted me teeth on the above sprockets as you said and my front small was 24 and the rear large was 34. Is this then a 0.7 or a 1.4. What does this mean for me riding this setup? What are the pros and cons for me.

It is a ratio of 0.7. It means that it is a very low gear compared to the bottom gear of most road bikes. Although, irronically it's not as low as most MTBs. Most MTBs have a 22 sprocket at the front! Im guessing the bike is acutally more of a hybrid?

It means that using this gear you'll have to pedal MUCH quicker than someone on a road bike in order to keep up (Probably almost twice as quick). However, you should be still going long after the road bike rider is pushing. It is also low enough to enable you to cope with a bit of off-road riding.

 

[butki55]

Thanks to you both for that I thought it would be the lower number as it is a MTB and therefore making it easier on trails or off road terrain.

Well I have to put up with it for at least this month as I am not intending to invest in anything untill February (My date). This gives me time on the bike, to see if one I will still enjoy it then.

The problem of course will be when I want to invest in new/second hand road bike and getting used to the new ratios.

butki55.

 

[jimboalee]

A 0.7 ratio on an MTB ( 18" gear length ) is for climbing stairs.

 

[rickangus]

GBS, your cranks are fine. crank lengths is one of them often debated cycling red herrings. 175 is fine for most cyclists
simply put:
shorter cranks are easier to spin
longer cranks can give more leverage

any more words will just confuse the issue

As for gearing. You would benefit from 12/28 cassette.

I find this comment a little dismissive.

Crank length is often debated and for cyclists who fall within average dimensions then, yes, 175 will be fine and for those people the topic may, indeed, be a red herring.

However, for those riders who fall outside the normal boundaries, whether tall or short, it is an issue. And the further you fall outside of it the more of an issue it becomes. Of course you can use 175s and live with it, being none the wiser. But why do people spend time and a lot of money perfecting their bike 'fit' or having custom frames built? Because they want to get the greatest possible efficiencies and not taking into account crank length just does not make sense.

For years I used 170 cranks - I never gave it another thought until I tried 175 and found they offered me a noticeable improvement. And now I have much longer ones that even better match my physiology.

I can only repeat my experience of 'fitted' cranks which has been that the benefits are twofold;

First and foremost, comfort. This is a big one (for me, anyway). Long legs simply don't spin as well as shorter legs. I rode a friend's bike recently with 175s and for me that felt like having to walk with a shorter step than normal, if you see what I mean. Not disastrous, obviously, but certainly a lot less comfortable.

Secondly, I believe there to be an efficiency improvement - although this is difficult to measure. I got my long cranks while recovering from illness so any improvement in performance could be attributed to increasing strength, fitness or mechanical efficiency. However, I did find my cassette ratio was then a bit on the 'low' side and changed it for a taller set.

Perhaps I should say that I am a touring cyclist, not a racer.

GBS, you do appear to have longish legs and it is for you to decide whether this is an area that requires further investigation. My opinion is that you would be better served by those with experience of being outside the 'average' rather than accepting a 'one size fits all' mantra.

I've attached a couple of links on this matter that make for interesting reading but there are loads of others if you do a google.com search.

I would say, though, that obtaining non std length cranks won't be cheap so you'll need to be sure it's right for you.

http://www.polaris.net/palmk/Crankset.html

http://www.peterwhitecycles.com/fitting.htm

 

[Steve Austin]

You are right my comment is dismissive. dismissive of the confusion your post causes.

I gave a personal recommendation on the length he needs based on the height he said he is.
Its not rocket science, and crank length is one of these oft mystified measures on bikes. Its not worth debating the point, but the majority of people would be happy with 170 on roadbikes, and 175 on commuters/tourers/mtbs. it really is as simple as that.

 

[rickangus]

You’re right and I agree it’s not rocket science. It’s really very simple - so why you don’t get it I just don’t understand.

Actually, I think I can see where your confusion arises. Crank length is a function of leg length not height.

Happy on std length? I'm sure the majority of people are happy on std length but we're talking about people who are outside of the majority.

I was happy on std length, too, for a while. But I am much happier now on the correct length cranks.

What's confusing about that?

 

[gbs]

to Rick; thank you for passing on yr sources. I will probably look at these tomorrow - heavy work day today. I still have the intuitive view that longer cranks means more leverage and that must help on the steeps. Having said that I think my first priority is to degear ie fit the largest cog possible and reduce the lowest gear ration to something around 1.5x

 

[rickangus]

gbs, I think you're right. You do experience an increased leverage with longer cranks - it's a law of physics after all. But there are other implications also that you should be aware of and take into consideration.

In the first instance changing the cassette will be a cheaper and quicker change. Changing cranks for non std length is a much greater financial commitment.

 

[Chris James]

For years I used 170 cranks - I never gave it another thought until I tried 175 and found they offered me a noticeable improvement.

I have ridden 165mm and 175mm and didn't notice any difference in the crank length, so i find myself agreeing with Steve Austin, albeit that I am 5 foot 11and so presumably within normal design parameters.

 

[jack the lad]

to Rick; thank you for passing on yr sources. I will probably look at these tomorrow - heavy work day today. I still have the intuitive view that longer cranks means more leverage and that must help on the steeps. Having said that I think my first priority is to degear ie fit the largest cog possible and reduce the lowest gear ration to something around 1.5x

Wrong length cranks is probably more of a problem for short people with standard cranks being too long than it is for tall people with them too short.

Even if longer cranks were a benefit uphill they would be a nuisance elsewhere. Bear in mind also that longer cranks mean that at any given speed the pedals describe a bigger circle. Your feet will need to move further for the distance travelled and your legs have to be moved faster to keep up. Your knees will also need to bend through a greater angle at the top of the stroke, putting more strain on your muscles and joints. As you are an old fella, like me, you probably move a bit slower than you used to and appreciate less strain on the knees, not more. I think, on balance, it is better to keep standard cranks but lower your gearing for hills. This is also the implication of the advice given in the second of the two links given. You will, I guess, have 18 or 20 gears to choose from, so you can have low ones for uphills and high ones for down.

Even at 16 stone and 50 yrs old I could manage White Horse Bank which is 25% on 36/24, 1.5:1. To get up Mt Ventoux I fitted a 34T 'megarange' at the back. That was a mistake as it was too low, but the 24T next lowest was too high. 28T would have been about right. So from my experience I would suggest that on a road bike a compact chainset with a 34 or 36 T front sprocket and a low of 27 or 28 at the back should get you up almost anything the UK can throw at you once you are fit . If you can outpedal 50/11 at the top end you are probably going quite fast enough, thank you. If you can manage with 39/28 that's the cheapest option and the one to try first.

Hope this helps.

 

[rickangus]

Completely agree that cranks that are too long can cause discomfort and possible knee problems. Cranks that are too short simply lose comfort and efficiency. Far better to go too short than too long.

Regarding your point, Jack, about spinning the pedals faster because of the greater pedalling diameter. In my experience (which is what my comments are based on) I don't think I do spin faster, rather I turn more slowly but in a higher gear. I say this because when I am cycling with others at the same speed, I have a lower cadence.

I know my legs don't spin fast - I have a b/c with a cadence counter and I seriously doubt I could get anywhere near 80 rpm (I have other background health issues which don't help).

An analogy in one of the links I posted compares two track athletes running at the same speed, one of them tall, the other short. Although running at the same speed Lanky's legs are turning more slowly compared with Shorty's but with a longer stride, whereas Shorty's legs are spinning faster. We're all built differently and that is how we adjust to meet at a common point.

 

[Randochap]

One other disadvantage (perhaps the worst) of longer cranks is the increased danger of pedal strike in corners.

I have short legs, so have recently tried 165s. Don't feel much different to the 170s I've always used.

I've always been a "spinner" and this is probably why knee problems are relatively rare, despite the distances (audax) and climbing I do.

Get longer cranks if leg length dictates, but don't worry about "leverage" on hills; make sure you have the gears you need to spin up them.

Your knees will thank you.