Gear combinations not to go in?

[Road_Runner]

Hi,

I know that i've seen the answer for my question somewhere on the internet at some point in time but i just can't seem to do the correct Google search term to get the answer.

I'm starting to think about crankset wear more and the reduction of pedaling resistance due to the chain being stretched side-wards too much.

I know the general thought of gear combinations shouldn't be at extremes, Eg. easiest crank ring and hardest cassette gear and vise versa but i'm looking for more specific gear combos than 'just the extremes'. If you know what i mean?

So for both 2 and 3 crankring setups, what gears combinations are generally considered that you shouldn't go in to with cassettes of 8, 9, 10, and 11 speeds?


Thanks

 

[yello]

I know it as 'cross chaining' and for me it's just avoiding the big/little combo you refer to. Note I say avoid, doesn't mean I never do it. And that's on my triple, the double and compact I'm even less concerned about. I think of it in terms of chain line.

 

[yello]

and another tip; little/little when removing the rear wheel makes life easier.

 

[Cuchilo]

My legs and whats ahead decide for me .

 

[sreten]

Hi,

Just use common sense to avoid cross chaining, you nearly
always have the same gears available without cross chaining.

Pointless to go into all the possibilities of the number of front
rings and rear gears and the possible teeth number on them.

Also depends on the chain line of the bike, how the front
rings line up with the back. FWIW my 2 front rings line
up almost perfectly with the rear 7 gears, at 2.5 for
the small and 5.5 for the large front ring.

Hence 2 and 3 rear small front and 5 and 6 large front
have the straightest chain line. 4th on either is the same
as 1 small and 7 large. I use 1 to 5 with small and 3 to 7
with large usually, but I don't have a compact front.

rgds, sreten.

 

[Road_Runner]

@Cuchilo - I think you've read my post wrong. It's not about gear selection in general. It's more to do with wear on the groupset and prolonging it for as long as possible - getting more value per mile with the addition of getting from a to b quicker/easier by reducing chain resistance.

@yello - Cheers for the buzz word. Googling 'cross chainring' immediately returns the type of information i'm looking for - although i haven't checked out the results properly to see if it's got the actual answer i'm looking for. And the small/small thing is what i always do whilst removing the rear wheel.

@User30090 - I've never really understood why people do gear inches. I personally just do ratios and MPH/KMH tables. Ratios table to tell me which gear combinations i need when switching chain rings to have the same or similar torque as before the shift. So i don't end up spinning up in a gear too low and so i don't select a gear that is too hard with a shockingly low cadence. MPH/KMH tables to predict achievable speeds in particular gear combinations at achievable cadences with the intentions of never dropping below 80 RPM or higher than 110 RPM. I know that gear inches states the advancement of the bike with one revolution of the pedals but to me it's an over complicated ratios table. As turning the pedals just once will never happen in real life where it actually matters about how much the bike has advanced.

I've done such tables for my mountain bike and hybrid. Since they both have triple ring cranks and a standard spread on the cassette, it means that the torque at the pedals is the same or very similar if i shift the crank ring up one and cassette down one, and vice versa. I've perfected shifting, where i shift the crank ring a split second before the cassette. For me, this seems to minimise the gear shifting period and i loose very little speed before i apply power again. This works across the entire selection of gear combinations but i always avoided the extremes of cross chainring.

I'm finding that adjusting to the compact cranks on my road bike is harder; maybe it's because of the number of gears i have to jump through and the time it takes/coordinating my fingers to do how ever many shifts i need to do. I'm finding that i have to jump between 3-5 cassette gears depending on when i choose to shift crank rings and whether i'm going up hill, flat-ish, or down hill (and the steepness). When i bought the bike, i just jumped on thinking that i'd figure out the shifting within no time at all. Since i'm still struggling and getting annoyed that i'm constantly slowing down too much, I've obviously made the ratios and MPH/KMH tables for the compact cranks. So now i've made the table i realise that there are only 5 overlaps, which two of them should definitely not be used because of extreme cross chainring, which results in only 3 overlaps. So now because of cross chainrings, i'm wondering if that shrivels to only 1 usable overlap or whether it remains at 3. Hence my question in the original post. I asked about so many different variations because of A) Just out of interest to compare with how i've previously/currently treat my mountain bike and hybrid bike. B) Because when my current groupset wears out, i plan to upgrade to a system with a higher number of gears and it would seem silly to ask such a question again in such a small period. C) So i can advise friends that are just getting in to cycling because of the hype around the TDF.


I think that parking a bike in low/low is a placebo effect because one would associate that leaving the cable in constant steady state tension would cause the cable to fail/have a shorter lifespan. If this was the case, i don't think they would have designed suspension bridges. An educated guess is that cables fail due to repeated tensile loading and unloading especially throughout a curvature. Not to mention throughout their life span they attract dirt because of the lubrication and the lubrication fades towards the end of their life. Both of these factors causes the cable to wear because of the abrasiveness between the cable and the housing and dirt.

 

[andrew_s]

I generally avoid the smallest 3 cassette sprockets when I'm in the small chainring, the largest 2 or 3 when I'm in the big chainring, and the largest (usually) and smallest when I'm in the middle chainring (from 3x8 or 3x9, depending on which bike).

Small/small crosschaining generally givers more wear than large/large. I pretty much killed my transmission in one ride - a very wet and very hilly 200k (Exmoor), when my front gear cable snapped and I'd not got a spare. I needed the granny to get up the hills so I didn't want to jam it in the middle ring with the limit screw, and used 24x11 a lot to keep within the time limits.

 

[sreten]

Hi,

FWIW with my 42/52 front I've got a lot of overlap and change the front every half hour or so,
and use both of them about the same amount of time on average round one of my loops.
Because I know my loops, with the prevailing wind that day, I leisurely change the front
well before I need to, noting I'm quite happy to cross chain for short distances if the
overall conditions indicate I really don't want to change the front rings at that time.

With a compact front the big ring is your main ring and changing the front rings
requires big jumps on the rear to just swap the rings when you don't need to.
However that is much better than waiting until you have to swap rings and
assuming you will get the hang of gear changing intuitively at that point.

I use gear inches to compare gears because they are easy to understand.
My folder is 30" to 60" and my road bike 40" to 100" (but goes up hills better).
My basic bike computers tell me how fast I'm going, and to go at any decent
speed on the folder I have to spin, pedal cadence is very easy to compare.

With a compact front on my bike I'd expect the two front rings to be little
more inboard lining up with the rear, say on on 2 and 5 of 7 gears,
and use 1-4(5) with the small front and 2-7 with the big front.

There really wouldn't be much overlap at all not allowing the (X) gears.
2 with the big front -> (5) with the small front (or 4 to drop a gear),
(5) with the small front -> 2 with the big front (or 3 to go up a gear).
(So 4 with the small front -> 2 with the big front to go up a gear.)

(I'm assuming the front is 2 rear on my bike and 3 rear with a compact,
my 7 speed is like a 8 speed with 2 missing, 14,16,18,20,22,24,28,)

rgds, sreten.

 

[double_dd]

My general rule for my compact is:

Changing to large cog at front = two downshifts to easier gears

Changing to small cog at front = two up shifts to harder gears

This keeps me going along the same speed having to only adjust cadence slightly to match the previous speed

 

[Dogtrousers]

I know that gear inches states the advancement of the bike with one revolution of the pedals but to me it's an over complicated ratios table. As turning the pedals just once will never happen in real life where it actually matters about how much the bike has advanced.

Hold your horses! It's not that simple! Gear inches states the advancement of the bike with one revolution of the pedals divided by pi.

A 1:1 ratio (say 28T front and rear) is ~27" (with the appropriate wheel/tyre size). Turn the pedals once and you advance by the circumference of the 27" wheel, about 86"

The advantage is that, unlike simple ratios, a value in gear inches is independent of wheel size. A 50" gear is a 50" gear on a Brompton, a road bike and a penny-farthing (which is why the measure was invented). Whereas gears with the same ratios as a Brompton would break your knees on a road bike.

However, it doesn't take into account crank length. Sheldon waxes philosophical on the subject here

 

[glasgowcyclist]

Cardigan with Bermuda shorts.

GC

 

[ScotiaLass]

Cardigan with Bermuda shorts.

GC

You forgot the sandals and socks combo...

 

[glasgowcyclist]

You forgot the sandals and socks combo...

Let's take it one fashion disaster at a time.


GC

 

[NorvernRob]

I've left mine so I get a bit of chain rub in small front - small back and big front - biggest two back. I know straight away I'm cross chaining and adjust to a better line.

 

[Road_Runner]

Hold your horses! It's not that simple! Gear inches states the advancement of the bike with one revolution of the pedals divided by pi.

I stand corrected that it's just the diameter multiplied by the ratio of the gears. Although technically it doesn't particularly matter since pi is just a coefficient and all results will be relatively different with pi included.

I admit that i was ignorant about the measurement but now I understand that it's for comparing torque/effort between different bikes and their gear combinations.