Life of chain - which cog do you ride?

[Opendro]

I have read many posts in the past concerning about frequent replacement of chain. While I know for sure that some people change it very early before it is actually worn out (I have even reused them for thousands of kms), I'm also wondering if the choice of rear cog they ride makes a difference.

As a rule of thumb, the wisest choice of the cog should be the largest cog as it will considerably reduce the chain tension while producing the same power/torque on the wheel. Of course, it is not feasible all the time as it would mean selecting the front bigger ring all the time and chain main cross too much.

However, for all flats, there is no doubt that riding in big chain ring with a larger cog in the rear is the best for your chain's life and the life of the cog too.

[Ashok Kumar S]

Why biggest ring in the front?

Thanks and regards,

Ashok

Sent from my iPhone

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[Opendro]

Aim is to ride the biggest cog feasible in the rear as the chain tension depend only on this.

Now, assume you are going at a certain speed and certain cadence. Lets say, you are riding at smaller front ring and 7th cog in the rear. For us to maintain the same speed (power on the wheel) and cadence while being at a larger rear cog, say, 3rd cog, you would need to shift to a larger chain ring in the front.

[Ashok Kumar S]

I thought lower gear and spinning helped in chain life. For that, ideally front should be in smaller rings and rear should be in larger ones. I'm not understanding something here. 🤔🤔🤔

Thanks and regards,

Ashok

Sent from my iPhone

[Opendro]

If you chose smaller front ring with larger rear cog, you will spin out too early in the speed. That is why I said "for a given speed/power/torque on the wheel". Let me repeat, the tension on the chain at a given speed (riding at constant speed) depends only on the rear cog choice, not on the front. You select the front just so to maintain your cadence.

Anyway, irrespective of the the choice of the front ring, you still have to maintain the same ratio between the front and rear. I'm saying that we should maintain the same ratio using bigger ring/cog to increase the life of chain/cassette. The effort on leg and power on wheel will remain same.

[Ashok Kumar S]

At given speed and given rear cog, won't the tension reduce with a smaller ring (higher cadence) in the front? At least it feels easier to pedal. So I assumed that the tension on the chain also reduced. 

Thanks and regards,

Ashok

Sent from my iPhone

[Opendro]

No no. We should always keep our cadence at whatever is efficient or optimum of the individual, say 60 to 80 rpm for a typical commute and 80 to 120 for a typical racing. If we reduce the cadence, power drops due to reduced rpm. If we increase cadence, then also power drops due to reduced torque or our energy efficiency drops (just like automobiles). So, that scenario is ruled out.

Suppose, I'm going at 25 kmph with 80 rpm cadence, what should be the choices of the cogs? That is what I tried to answer - choose bigger front chain ring and the appropriate rear cog.

In other words, in a typical 8 speed cassette, one should sparingly use the 6, 7 and 8. They should use those smaller cogs only when one is spinning out in the bigger front chain ring itself, say, speeds above 30 kmph. If one is going at 25 kmph with smaller front ring and 7th rear cog, consider going to larger front ring so as to bring down the gear in the rear.

[udayak...@gmail.com]

What is an acceptable average kms for a chain for an average rider ?

I find it lasts me some 2000-2500kms on city roads. Have ruined a few cassettes because I did not change the chain in time. I am most often riding in the middle front and 5 or 6 in the rear on a 8 speed, cadence is usually around 60.

Also curious to know what would be the life on a single speed .

Thanks

Uday

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[Prashanth Chengi]

Cross chaining is something I try and avoid. I have a triple crank and a 10 speed cassette, and I try not to get onto the big ring, if I'm going to be in gears 1-3. This means that I spend more time in the middle ring. I only switch to the big ring when I feel the need to go to gear nine or ten, which is typically when I'm going flat out on a flat, or when I'

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[Prashanth Chengi]

or when I'm going downhill or have a significant tail wind assist. I try to keep my power up, even when I have tail-wind, to both ensure that I train better, as well as to make better time.

/Prashanth

[Ashok Kumar S]

Do you mean, for a fixed cadence as well, bigger front with bigger rear has less tension than a smaller front with a smaller rear (assume same ratio) ?

Thanks and regards,

Ashok

Sent from my iPhone

[Opendro]

Yeah, you got it right. Apologies for the lack of the right word on my part. Maintain same gear ratio and try to be in larger cog, except when chain is too crossed.

I too have 3 in front and 8 in the rear. I typically start at 3x4 and go up to 3x6. In slight climbs, 3x3 if I have decent momentum, else 2x3. I never ride 3x1 or 3x2 as Prashanth mentioned.

[Opendro]

I rode roughly about 20,000 km on my hybrid stock ones as well as road bike stock ones. When I changed chain, I changed cassette as well - both the cassettes were used ones and got new chains. I also had to change the middle front ring in the road bike. 8th speed cog was as good as new. So was the 1st. It is usually the 3, 4, 5 cogs that got worn out.

To give you an idea, I rode BITH 2015 on a used cassette which I got when I bought a used wheel and a new chain. The same were used for the Tran Am Bike Race which is about 7000 km with about 60,000m of climbs. People often change tires, chain, etc. mid way. I didn't even change the tires. I just swapped the front and rear tires midway. With that kind of climbing, the life would have been at least 30% less. But never in the range of 2500 km. That is way too less.

If you are using 5 or 6 in the rear, try considering 3 in front and 3,4,5 in the rear. That will increase the life considerably.

[Opendro]

2x8 is a "NO" according to me even on a 10 speed. 2x6 would be the last I would suggest. Then go to 3x4 or 3x5 whichever appropriate. 7th onward should go only with big ring only for speeds.

[udayak...@gmail.com]

WOW ! That's vastly different from my experience.

 I changed to a new chain just a few days back, let me switch to your technique  see what I get. Apparently, lubricant on the chain is a big factor influencingchain life as well ?  

Thanks

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[Opendro]

Oh yeah. Lubricating is very important. I fact, my chain always look dirty and with muck because I always put lubes. I hate the sound of dry chain grinding. It is very bad for the life of both chain and cassette.

[Prashanth Chengi]

Lube on chain is indeed a big factor, but also remember that lube on a dirty chain is a bad idea. Do the degrease-clean-dry-lubricate cycle, and repeat it as often as your riding merits it. 

/Prashanth

[udayak...@gmail.com]

ON the topic of gear combination that will be best for chain life, here's a simplified attempt at deducing a technique.

1) Chain wear I would think is a direct function of the speed of travel of the chain  ( actually the rotational velocity at the link) 

2)  So for any given cycle speed,  the gear combination that causes the slowest speed of travel for the chain is the optimal one .

3) That will be the largest gear in the front and the largest possible gear in the rear.

But cross chaining will introduce an increase in the rate of wear, how much ? I cant imagine, maybe someone somewhere has experimentally studied it.

Thanks

Uday

 

[Opendro]

That is the opposite :-)

The chain should move as fast as it can. In fact, if the rear cog could be as large as the wheel, it will never wear off :-)

Don't think too complicated. The simple principle is that to move a given resistance, least amount of force is required if you increase the lever arm. So, here, we are increasing the lever arm by increasing the diameter of the rear cog by keeping the rest of the parameters same.