20 Speed Bike..

skooter

I have a Giant TCR 1 with 36/50 front and 10 gears at the back.
Now if you have lets say a 50/40/30 on the front you shouldn't ride with big cog to big cog and small cog to small cog..
But with just the 36/50 fronts on mv bike I should be able to use all the gears Yes...

night_porter

Yes, crosschaining only really occurs with triple chainsets but I find that there is less rub on the front mech if you stay away from big/big & small/small. So just a smoothness/quietness thing really!

skooter

Thanks NP...
That was my thinking.. I asked as I have lets say an oddness on my bike and I wanted to elimate things..

Cheers..

lc1981

night_porter wrote:

Yes, crosschaining only really occurs with triple chainsets but I find that there is less rub on the front mech if you stay away from big/big & small/small. So just a smoothness/quietness thing really!

Surely if it's rubbing then that's a sign of the chain being crossed? I've always been told to avoid using the big/big and small/small combinations on a double chainset.

karlth

Cross-chaining isn't just about whether the derailleur rubs; in the old days of friction shifters, and even with cheaper non-indexed front shifters that can pretty much always be avoided. It's about chainline. Big/big and Small/small combinations require each link in the chain to flex as it leaves the chainwheel to reach the cassette, flex again to go straight around the cog, then flex again to get back to the chainwheel and so on. This wears the chain and will cause a certain amount of friction and therefore inefficiency.

Sprool

^+1 I understood it increases wear and tear on your components and is generally considered poor practice.

Mikey23

@ skooter ... An oddness on your bike? Don't be so hard on yourself;-)

skooter

Mikey23 wrote:

@ skooter ... An oddness on your bike? Don't be so hard on yourself;-)

Ok.. I'm going alone a undulating road not steep enough to use the 36 front but lets say steep enough to use all ten rear cogs...
Now cogs 1 to 5 run very sweet but 6 to 10 cogs sound as if the chain wants oiling.. or even finer cog 5 is good and cog 6 squeaks like lack of oil.
Hope that makes sense, its a bit of a noise from the dashboard so of thing... irritating.
The bike runs perfect and the gears change alright.

night_porter

Have you tried "trimming" the left hand lever?

In other words you give it a half press to move the front mech slightly but not enough to get it to change to the smaller chainring.

I think I am right in saying this is only needed for Shimano groupsets as I only get this on bikes with Shimano, my Sram Red bike never needs this doing and it works fine.

skooter

night_porter wrote:

Have you tried "trimming" the left hand lever?

In other words you give it a half press to move the front mech slightly but not enough to get it to change to the smaller chainring.

I think I am right in saying this is only needed for Shimano groupsets as I only get this on bikes with Shimano, my Sram Red bike never needs this doing and it works fine.

Thats worth a try I will give it a go at the weekend..

Cheers

CiB

skooter wrote:

But with just the 36/50 fronts on mv bike I should be able to use all the gears Yes...

The same gears are available in different combinations though so you don't have to stick on one ring or the other. Jump about the rings & cogs at both ends to get the gear you need rather than hanging onto one for whatever reason.

ETA Have a look at Sheldon's Gear Calculator at http://sheldonbrown.com/gears/ - plug your rings & cassette sizes in and hit Calculate and see how many pairs of gear sizes are close enough or identical.

Or buy some Di2 which is self trimming across the cogs and means you don't give a stuff about the cost of a chain when the gears cost you so much anyway that another chain every few months doesn't even register.

skooter

CiB wrote:

skooter wrote:

But with just the 36/50 fronts on mv bike I should be able to use all the gears Yes...

The same gears are available in different combinations though so you don't have to stick on one ring or the other. Jump about the rings & cogs at both ends to get the gear you need rather than hanging onto one for whatever reason.

ETA Have a look at Sheldon's Gear Calculator at http://sheldonbrown.com/gears/ - plug your rings & cassette sizes in and hit Calculate and see how many pairs of gear sizes are close enough or identical.

Or buy some Di2 which is self trimming across the cogs and means you don't give a stuff about the cost of a chain when the gears cost you so much anyway that another chain every few months doesn't even register.

Thanks for the link that looks interesting and I have to say I have never tried the 36 cog as you suggested so I will try that as well..
All a bit learning curve.

Mark Alexander

the old addage of not big to big or small to small is a good one. On a double chainset it is less of an issue than a tripple but a good one to go by. I am happy spinning on a club run 53 on the front 25. so idealy at the rear just use the smallest and largest ring if you are in the chain ring that put's the chain 'in line'. This is all assuming your deraileur is set correctly.

A good rule of thumb is for the same cadence one tooth on the back is the same change as 3 teeth on the front.

Never use the granny ring. It is not the done thing!

Mark Alexander

BTW Sheldon Brown was the font of all cycling knowledge.

keef66

"Now cogs 1 to 5 run very sweet but 6 to 10 cogs sound as if the chain wants oiling.. or even finer cog 5 is good and cog 6 squeaks like lack of oil."

You have oiled the chain, haven't you?

CiB

Only in 5th gear.

skooter

night_porter wrote:

Have you tried "trimming" the left hand lever?

In other words you give it a half press to move the front mech slightly but not enough to get it to change to the smaller chainring.

I think I am right in saying this is only needed for Shimano groupsets as I only get this on bikes with Shimano, my Sram Red bike never needs this doing and it works fine.

Well Trimming was the answer so good call.
I went out for a quick dash and fiddled with the gears and when it became noisey trimmed as you said .. now running loverly.. though a drop of oil might not go a miss..

nolight

Shimano recommends not to have small chainring go with the 2 smallest cogs, and big chainring go with the 2 biggest cogs or something like that. There is no need to anyway since there are other combinations that give similar gear ratio.

I have a 20 speed bike. I use small chainring with cog 1-5, small chainring half-shift (between small and big) allows me to get to 6-7 so I like to keep it at half-shift as soon as possible when starting.

I use big chainring normally with cog 4-10. I guess if it needs to go to smaller cog, I might as well shift to small chainring.

skooter

nolight wrote:

Shimano recommends not to have small chainring go with the 2 smallest cogs, and big chainring go with the 2 biggest cogs or something like that. There is no need to anyway since there are other combinations that give similar gear ratio.

I have a 20 speed bike. I use small chainring with cog 1-5, small chainring half-shift (between small and big) allows me to get to 6-7 so I like to keep it at half-shift as soon as possible when starting.

I use big chainring normally with cog 4-10. I guess if it needs to go to smaller cog, I might as well shift to small chainring.

So it seems then that if you are on the 50 front and you start to climb you would come down the cassette from lets say cog 9 to 8, 7, 6 ,5 ,4, 3, then change to the front 36 but go up 2 gears to number 5 at the same time?
Does sound right..

CiB

skooter wrote:

So it seems then that if you are on the 50 front and you start to climb you would come down the cassette from lets say cog 9 to 8, 7, 6 ,5 ,4, 3, then change to the front 36 but go up 2 gears to number 5 at the same time?
Does sound right..

Not really. We all do it differently but with my 53/39 11-28 setup, I'd be in a middling gear on the 53 or a higher gear on the 39 and maybe drop onto the 39 if not already on it then drop down to whatever gear (21, 23, 25, 28) gives me a decent cadence to attack the climb. It might be 53/19 - who knows?

Bikes aren't like cars where you work your way sequentially down the gears. Grab whatever ratio suits at any given time, even if it means jumping from one ring to another and jumping a few cogs at the back in either direction. There's no rules.

skooter

This is interesting as I've learned a lot from you guys...

Now changing gears.. Do you change the chainring first then the cassette or the other way round and does this alter to if you are going up hill or down..

Wobblehead

So it seems then that if you are on the 50 front and you start to climb you would come down the cassette from lets say cog 9 to 8, 7, 6 ,5 ,4, 3, then change to the front 36 but go up 2 gears to number 5 at the same time?
Does sound right..

That is about what i do, generally drop to 34 and up 2 at the back at the same time

CiB

skooter wrote:

This is interesting as I've learned a lot from you guys...

Now changing gears.. Do you change the chainring first then the cassette or the other way round and does this alter to if you are going up hill or down..

Either. No rules. Whatever lights your candle. I like to do both at the same time; up or down one ring & one cog is effectively half a gear on the middle ratios.

karlth

CiB wrote:

skooter wrote:

This is interesting as I've learned a lot from you guys...

Now changing gears.. Do you change the chainring first then the cassette or the other way round and does this alter to if you are going up hill or down..

Either. No rules. Whatever lights your candle. I like to do both at the same time; up or down one ring & one cog is effectively half a gear on the middle ratios.

I have a couple of regular double-shifts. Ignoring the granny which I only use on 20% hills or if a knee gives out, I double-shift from 39x17 to 50x21 or 50x19, and also vice-versa. Double shifts are made pretty simple these days compared with the old days of friction shifters when you could easily ride into the back of a bus concentrating on trying to do it.

nolight

skooter wrote:

nolight wrote:

Shimano recommends not to have small chainring go with the 2 smallest cogs, and big chainring go with the 2 biggest cogs or something like that. There is no need to anyway since there are other combinations that give similar gear ratio.

I have a 20 speed bike. I use small chainring with cog 1-5, small chainring half-shift (between small and big) allows me to get to 6-7 so I like to keep it at half-shift as soon as possible when starting.

I use big chainring normally with cog 4-10. I guess if it needs to go to smaller cog, I might as well shift to small chainring.

So it seems then that if you are on the 50 front and you start to climb you would come down the cassette from lets say cog 9 to 8, 7, 6 ,5 ,4, 3, then change to the front 36 but go up 2 gears to number 5 at the same time?
Does sound right..

Ya but mostly I won't even know what gear I am on so it is all done by feeling. Most of the time I won't be on cog 9 I will be on 5-7, so I try to go lower rear gears only around 3 times to see if it is enough to climb. If not enough I change to front 39 from 53 (my crankset is 53/39).

If I know the climb is going abruptly tougher, I might even go directly to front 39 from cog 6 and quickly do a half-shift so front derailleur doesn't rub.

skooter

nolight wrote:

skooter wrote:

nolight wrote:

Shimano recommends not to have small chainring go with the 2 smallest cogs, and big chainring go with the 2 biggest cogs or something like that. There is no need to anyway since there are other combinations that give similar gear ratio.

I have a 20 speed bike. I use small chainring with cog 1-5, small chainring half-shift (between small and big) allows me to get to 6-7 so I like to keep it at half-shift as soon as possible when starting.

I use big chainring normally with cog 4-10. I guess if it needs to go to smaller cog, I might as well shift to small chainring.

So it seems then that if you are on the 50 front and you start to climb you would come down the cassette from lets say cog 9 to 8, 7, 6 ,5 ,4, 3, then change to the front 36 but go up 2 gears to number 5 at the same time?
Does sound right..

Ya but mostly I won't even know what gear I am on so it is all done by feeling. Most of the time I won't be on cog 9 I will be on 5-7, so I try to go lower rear gears only around 3 times to see if it is enough to climb. If not enough I change to front 39 from 53 (my crankset is 53/39).

If I know the climb is going abruptly tougher, I might even go directly to front 39 from cog 6 and quickly do a half-shift so front derailleur doesn't rub.

My cogs are 50/36 and like you dont use 9 or 10 cogs at the rear but I will pratice what you have said on Tuesday and I'm sure I will get it in the end..
As I live on a moutain its all hills one way or another so I will have to learn, but there are some hills that are just too steep for me at the moment almost to the extent of changing my front 36 to a 34... plus build up more strenth in my legs..

skooter

OK..
I planned a ride out to test the gears and after a few hills I think I'm getting the idea.. I didn't use the 2 big cogs when on the front 50 but I did changed to the 36 front then upped two cogs which I worked out was about the same, I did find it an odd feeling at first but as the hill got steeper I found it easier to peddle.
So I reckon 50F and cog 3 is about the same as 36F and cog 5..(cog 1 being the biggest)
Anyway guys a lot learnt..

CiB

A quick faff on Sheldon's site to get the numbers, + a quicker faff in Excel to sort them out & make it clear...

Gear   Gain Ratio
36-27	2.6
36-24	2.9
36-21	3.4
50-27	3.6
36-19	3.7
50-24	4.1
36-17	4.2
36-16	4.4
36-15	4.7
50-21	4.7
36-14	5.1
50-19	5.2
36-13	5.4
50-17	5.8
36-12	5.9
50-16	6.1
50-15	6.5
50-14	7.0
50-13	7.6
50-12	8.2

Assuming a 36/50 & 12-27 cassette.

What this shows is that there's no definite "big ring = smaller ring + 2 cogs" or whatever to get the same gear. It's also clear seeing it this way that some of the middle gears have duplicates (or near dupes) using different gear permutations.

There's no need for all this though. Swap your gears about as you see fit to keep the cadence in your zone. That's ultimately what gears are all about. Numbers make it easier but your knees are a pretty good guide.

skooter

CiB wrote:

A quick faff on Sheldon's site to get the numbers, + a quicker faff in Excel to sort them out & make it clear...

Gear   Gain Ratio
36-27	2.6
36-24	2.9
36-21	3.4
50-27	3.6
36-19	3.7
50-24	4.1
36-17	4.2
36-16	4.4
36-15	4.7
50-21	4.7
36-14	5.1
50-19	5.2
36-13	5.4
50-17	5.8
36-12	5.9
50-16	6.1
50-15	6.5
50-14	7.0
50-13	7.6
50-12	8.2

Assuming a 36/50 & 12-27 cassette.

What this shows is that there's no definite "big ring = smaller ring + 2 cogs" or whatever to get the same gear. It's also clear seeing it this way that some of the middle gears have duplicates (or near dupes) using different gear permutations.

There's no need for all this though. Swap your gears about as you see fit to keep the cadence in your zone. That's ultimately what gears are all about. Numbers make it easier but your knees are a pretty good guide.

Yes I think I'm thinking about it too much.. as to just doing it. Good bit of info though..