Hole in my 2X9 Gearing!!

[Skylark]

I started running 36/26 with a 32 cassette.....changed to a 34 cassette and have now just ordered a 24 for the front. Mainly cross country and I think that's as close as i'm going to get to my perfect setup on 2x9. Next stop 2x10 with a 36.

How did 36/26 feel?

Thats a 1.384 ratio which means you will not have a big hole rather a very small hole so you would also probably need a shift on the back cogs to maintain cadence?

So on every front chainring shift I make where I need to compensate by going to a bigger back cog , you will compensate by going to a smaller back cog

Edited January 18, 2012 by SkyLark

[BushGoblin]

Pretty much AM trail riding single track stuff , no Blazing XC racing

 

so if you not doing a massive amount of XC stuff why not look at your type 2X10 configuration of 26/39. With this syou shouldn't have the "hole" if you go according the 1 to 1.5 rule. You should be able to climb fairly comfortably with the 26 and gets some better top end on the flat/down with the 39. I must admit i did suffer a bit at first with the 27/40 but loving it now.

[NINER_boy]

Hey guys

 

Me again

 

I have a XX setup with 26 / 39 chainring sizes.

Before I had 27 / 40, that ended up to be too much on my 29" bike (bigger wheels needs a smaller ratio to turn them over).

 

Now the 26 /39 is PERFECT.

 

At the rear I run a 11-32 cassette, and have never ran out of revs (fast down OR slow up).

 

For me, the smaller ratio defenitely works.

[NINER_boy]

Sorry to sound really ignorant here, but is it possible to explain in lay-mens terms what going on here with Gear ratios and the teeth on your cogs that you so expertly explained, cause that went way over my head.

 

Hi Cearus

 

Front chainring ratios you get by dividing the bigger chainring's tooth count by the smaller chainrings tooth count;

EG

Ex1; 27 / 40 tooth chainring: Calculation 40/27=1.54

That is a ratio of 1:1.54

 

Ex 2; 26 / 39 tooth chainring: Calculation 39/26=1.5

That is a ratio of 1:1.5

 

What that means is that you will get 1.5 times more out of the exact same gear (on the cassette) on the bigger chainring (39tooth) than the small chainring (26tooth).

 

Then, have a look at the posted gear ratio table, and do the following excercise:

1. Same chainring size, compare the distance covered on a 17tooth sprocket (17t on your cassette) vs the distance covered on a 18tooth sprocket. Note the jump in distance covered.

2. Now, use a 18tooth sprocket configuration, and compare the distance covered on a 32tooth chainring vs a 33tooth chainring.

Note the "smaller" difference.

NB, in both excercises there was JUST a 1tooth jump or difference...

 

That is the point I wanted to get across, that increasing or decreasing FRONT chainring sizes will keep your gears "closer" to each other, than to try and compensate with your cassette.

 

IMO, the 2x10 guys (in my case SRAM) got the calculations spot on with Front chainring ratios, in order to get the most out of your drivetrain.

 

I hope this clarifies some...

[NINER_boy]

In SlyLark's initial question his chainring sizes were mentioned as 36/22

 

That gives a ratio of 1.64

That made his "jumps" between gears (when changing on his rear mech) too big, and made him heel that there was a hole with some gears missing.

IE the difference in pedal cadence (or distance covered per pedal stroke) was just too big.

[Caerus]

Hi Cearus

 

Front chainring ratios you get by dividing the bigger chainring's tooth count by the smaller chainrings tooth count;

EG

Ex1; 27 / 40 tooth chainring: Calculation 40/27=1.54

That is a ratio of 1:1.54

 

Ex 2; 26 / 39 tooth chainring: Calculation 39/26=1.5

That is a ratio of 1:1.5

 

What that means is that you will get 1.5 times more out of the exact same gear (on the cassette) on the bigger chainring (39tooth) than the small chainring (26tooth).

 

Then, have a look at the posted gear ratio table, and do the following excercise:

1. Same chainring size, compare the distance covered on a 17tooth sprocket (17t on your cassette) vs the distance covered on a 18tooth sprocket. Note the jump in distance covered.

2. Now, use a 18tooth sprocket configuration, and compare the distance covered on a 32tooth chainring vs a 33tooth chainring.

Note the "smaller" difference.

NB, in both excercises there was JUST a 1tooth jump or difference...

 

That is the point I wanted to get across, that increasing or decreasing FRONT chainring sizes will keep your gears "closer" to each other, than to try and compensate with your cassette.

 

IMO, the 2x10 guys (in my case SRAM) got the calculations spot on with Front chainring ratios, in order to get the most out of your drivetrain.

 

I hope this clarifies some...

 

Thanks for that further explanation, much appreciated. I must say I did a lot of reading about this last night via the interweb. I now have a much better understanding of whats going on with gears and ratios

[Seadog]

Where'd you get a 24t from?

I just found out now standard shimano 9 speed chainrings are 22t or 26t & 32t or 36t

24t & 34t doesn't seem to be easily avail

I use 104mm pcd 4 bolt middle rings

http://www.starbike.com/p/Specialites-TA-chainring-Chinook-64-mm-2800-en

[koukie]

Your front chainrings are the wrong size, i did the same thing also went 2X9 but you cant just take your big blade off, what is the use in that. You loose a lot of speed.

 

I bought myself a (i think) 38 or 39 "middle blade" and a 26 small blade from starbike chainrings (brand Specialites TA)google it, its very nice rings!

Edited January 19, 2012 by koukie

[Seadog]

How did 36/26 feel?

Thats a 1.384 ratio which means you will not have a big hole rather a very small hole so you would also probably need a shift on the back cogs to maintain cadence?

So on every front chainring shift I make where I need to compensate by going to a bigger back cog , you will compensate by going to a smaller back cog

Sorry Skylark...wrong info! I have a 38/26 which means a ratio of 1.46.....and just discovered that the 24t i ordered from Germany was incorrectly ordered! I ordered the compact 58mm (5 bolt) instead of the 64mm 4 bolt. On the Sram/truvativ cranks, the rings fit on the middle and inner, and I think Shimanos fit outer and middle. Will now have to re-order the correct 24t. Damn shipping costs more than the ring itself, so my mistake is going to cost me!

[Skylark]

http://www.starbike....k-64-mm-2800-en

 

Eeish those things are kinda pricey!!

How would a 22/32t feel - thats a 1.45 ratio pretty much the same as your 38/26t?

I'm more interested in mid range - although I will have pretty much limited top end I suppose

[Seadog]

Eeish those things are kinda pricey!!

How would a 22/32t feel - thats a 1.45 ratio pretty much the same as your 38/26t?

I'm more interested in mid range - although I will have pretty much limited top end I suppose

My feeling was that it was a good and cheaper way to try two rings than go with a full 2x10 groupset. I would say that for what you are doing, 22/32 sounds perfect. Ivé gone 38/26 and soon 38/24 because i do mainly cross country and stage racing, so i need the right mix of climbing and top end.

I'm going to re-order, so if you need to order a 22 and save on the freight, let me know.

[Skylark]

My feeling was that it was a good and cheaper way to try two rings than go with a full 2x10 groupset. I would say that for what you are doing, 22/32 sounds perfect. Ivé gone 38/26 and soon 38/24 because i do mainly cross country and stage racing, so i need the right mix of climbing and top end.

I'm going to re-order, so if you need to order a 22 and save on the freight, let me know.

 

Thanks man!

I already have a 22t , I just need a 32t (or 34t)(or 24t to match the current 36t) ..... if anyone has a useable 104mm pcd 4 bolt ring or 24t to flog or donate let me know!!

 

I'm probably gona get a Deore M510 metal 32t ring - works perfectly only 80g heavier than aluminium and last 3 x as long - whats not to love!!!

Also they only R140 on Chainreaction , anyone know of local online or LBS with Deore M510 metal chainrings in stock - CWC said they dont have

[Climate]

There will always be a "hole" in your range, when changing from small to big blade, unless the step up is so small that it isn't worthwhile shifting between blades anyway. I'm not sure what the actual tooth count is on your 9-speed cluster, but have highlighted what is most probably the configuration for 11-34 with a 22 and 36 tooth chainring combination, in the attached spreadsheet. This is of course calculated for a 26 inch wheel, but the argument remains valid for a 29er as well. You'll notice that from almost any cog on your cassette, if you change gear to the other ring, you'll need to gear down or up by 2 cogs on the cassette (depending on which ring you're changing to), to simulate a single cog change on the cassette without a ring gear change. This does not hold for the extreme combinations of 11-22 or 34-36 of course (when you'd need to shift across by 3 cogs on the cluster for the same simulation), which you know you shouldn't do anyway, since "cross-chaining" is a swear-word!

Gear Ratios 2x9.pdf

[Skylark]

There will always be a "hole" in your range, when changing from small to big blade, unless the step up is so small that it isn't worthwhile shifting between blades anyway. I'm not sure what the actual tooth count is on your 9-speed cluster, but have highlighted what is most probably the configuration for 11-34 with a 22 and 36 tooth chainring combination, in the attached spreadsheet. This is of course calculated for a 26 inch wheel, but the argument remains valid for a 29er as well. You'll notice that from almost any cog on your cassette, if you change gear to the other ring, you'll need to gear down or up by 2 cogs on the cassette (depending on which ring you're changing to), to simulate a single cog change on the cassette without a ring gear change. This does not hold for the extreme combinations of 11-22 or 34-36 of course (when you'd need to shift across by 3 cogs on the cluster for the same simulation), which you know you shouldn't do anyway, since "cross-chaining" is a swear-word!

 

Mmm as many replies have pointed out the ratio between my 2 chainring is a little to far out of the 1.5 range , so although there will always be a small hole between any 2 rings , mine is quite big so I will lose cadence no matter what I do unless I counter shift on the back cogs , the 1.5 ratio is implemented to avoid this.

 

"You'll notice that from almost any cog on your cassette, if you change gear to the other ring, you'll need to gear down or up by 2 cogs on the cassette"

If you have the 1.5 ratio and you are only dropping 1 ring at a time and you are not at either of the extreme ends of the cassette (ie first or last 3 cogs) you need to check out your technique - cause its not supposed to be like that.

From my understanding thats the whole point of the 1.5 ratio - it allows smooth transitions between rings without needing an immediate cog change

Edited January 19, 2012 by SkyLark

[Climate]

Even with a 1:1.5 chainring ratio, you're gonna have to shift 2 cogs at the back (if you shift to a different chainring), to simulate a single shift on the cluster. I've highllighted the gears for a 26/39 chainring combination, which is a 1:1.5 ratio. Now suppose you're in the 3rd smallest cog on your cluster, but still small ring (14~26 = 48.3) and you need a slightly bigger gear. In order to keep the most efficient path for your chain, you change to the big ring and your cadence will drop dramatically (14~39 = 72.4). Changing up 2 cogs on your cluster will get you to the 5th smallest cog on your cluster (19~39 = 53.4), which is still a bigger gear than you were in before changing to the big blade. Had you just dropped to the 2nd smallest cog and stayed in the small chainring, your gear would have been 56.3, which would have impacted your cadence more, than the single-click in front and double-click at the back.

Gear Ratios 26x39.pdf

[Skylark]

Even with a 1:1.5 chainring ratio, you're gonna have to shift 2 cogs at the back (if you shift to a different chainring), to simulate a single shift on the cluster. I've highllighted the gears for a 26/39 chainring combination, which is a 1:1.5 ratio. Now suppose you're in the 3rd smallest cog on your cluster, but still small ring (14~26 = 48.3) and you need a slightly bigger gear. In order to keep the most efficient path for your chain, you change to the big ring and your cadence will drop dramatically (14~39 = 72.4). Changing up 2 cogs on your cluster will get you to the 5th smallest cog on your cluster (19~39 = 53.4), which is still a bigger gear than you were in before changing to the big blade. Had you just dropped to the 2nd smallest cog and stayed in the small chainring, your gear would have been 56.3, which would have impacted your cadence more, than the single-click in front and double-click at the back.

 

Check your technique because the way you riding is giving you the problem. You should have changed up to the bigger chainring before you reach the 3rd smallest cog.

 

Did you bother to read what I wrote : "If you have the 1.5 ratio and you are only dropping 1 ring at a time and you are not at either of the extreme ends of the cassette (ie first or last 3 cogs) you need to check out your technique - cause its not supposed to be like that.

From my understanding thats the whole point of the 1.5 ratio - it allows smooth transitions between rings without needing an immediate cog change"

 

Anyways you going off the plot here , we talking about the front chain ring ratios - All I know is that I have a hole when changing front chainrings thats 2 big to power through and its been pointed out that its due to the ratio between the 2 front chainrings, once my ratio is closer to 1.5 I'm confident I will be able to power through the hole.

 

Simple