Dual Drive

[cjwally]

So...Yesterday, dropped by the Path to pick-up my warranty Niner Sir9 frame. I meticulously put the bike together myself...Which was a first for me.

Prior to leaving, I had to make a few upgrades. Ended up leaving with some CB Shoe Shields, a gold seat clamp, a 38T chainring, 16T Cog, Sunline carbon bars, and a Thompson stem. More money than I expected to spend, but then again it is for my bike...so whatever.

Put it all together...Everything is working great until I start messing with the drivetrain. I decided to run a dual drive on my SS Sir9. For climbing, I run a 32 x 22 for a total of 54 teeth. For getting to the trailhead, I run a 38 x 16 for a total of 54 teeth. Problem is...I tensioned the chain on 38 x 16 gearing. After that I decided to move it over to the 32 x 22 to see if the tension would be the same....You think it would be. It is wierd because when it is tight on the 38 x 16, it is really loose on the 32 x 22... How could that be? Same number of teeth....

Anyone?

[slowSSer]

Originally Posted by cjwally

Prior to leaving, I had to make a few upgrades. Ended up leaving with some CB Shoe Shields, a gold seat clamp, a 38T chainring, 16T Cog, Sunline carbon bars, and a Thompson stem. More money than I expected to spend, but then again it is for my bike...so whatever.

the path has a strange way of making you spend money.

Originally Posted by cjwally

Put it all together...Everything is working great until I start messing with the drivetrain. I decided to run a dual drive on my SS Sir9. For climbing, I run a 32 x 22 for a total of 54 teeth. For getting to the trailhead, I run a 38 x 16 for a total of 54 teeth. Problem is...I tensioned the chain on 38 x 16 gearing. After that I decided to move it over to the 32 x 22 to see if the tension would be the same....You think it would be. It is wierd because when it is tight on the 38 x 16, it is really loose on the 32 x 22... How could that be? Same number of teeth....

Anyone?

as for the slack/tight chain question, i think it has to do with wrap of the chain around chain ring/cog....or it might be gear inches....or something else.

[mtnbikerfred]

Geometry lessons are not included with your subscription to STR

The angles are different even if the number of teeth is the same, thus you will alway have more "free chain" on one combo than the other.

[destroyer]

Pythagoras Theorem could solve your problem.

[autoduel]

You have to take the angle of the chain in relation to the chainstay into account. Remember Pythagoras? The greater the angle, the longer the chain needs to be. The bigger the chainring the tighter the chain. I run 38x18 with 36x21 and the chain is looser in the 36x21 combo. Check out this site to get exact ideal chainstay length measurements for each gear combo: http://eehouse.org/fixin/formfmu.php

[jcampbell]

I run a 32:21 and a 36:17. Chain is always tighter with the largest ring because you have to take into account for the additional diameter.

[mtnbikerfred]

Math geeks. Everyone one of us....

[HUGH]

38x16 + 32x22 = 32 x 19

No problems getting to the trailhead and no problems climbing.

Simple math
or just put gears on it.

HUGH

[cjwally]

Originally Posted by autoduel

You have to take the angle of the chain in relation to the chainstay into account. Remember Pythagoras? The greater the angle, the longer the chain needs to be. The bigger the chainring the tighter the chain. I run 38x18 with 36x21 and the chain is looser in the 36x21 combo. Check out this site to get exact ideal chainstay length measurements for each gear combo: http://eehouse.org/fixin/formfmu.php

I plugged in the info... still a little confused. Help?

http://eehouse.org/fixin/formfmu.php...ey=Stay_length

[Abui]

BTW does the loose chain dip about 1.125"?

[slowSSer]

Originally Posted by HUGH

38x16 + 32x22 = 32 x 19

Simple math
HUGH

what?

no, your equation equals 1312.

[cjwally]

Originally Posted by HUGH

No problems getting to the trailhead and no problems climbing.

Simple math
or just put gears on it.

HUGH

38x16 + 32x22 = 32 x 19

1 + 1 = 4

[slowSSer]

Originally Posted by cjwally

38x16 + 32x22 = 32 x 19

1 + 1 = 4

no, per my math, 1 + 1 = 11

[cjwally]

Originally Posted by Abui

BTW does the loose chain dip about 1.125"?

That sounds about right... It was quite a bit.

Do you think that it would solve the problem by putting a 17T cog instead of a 16T? 32 x 22 and 38 x 17

[G-Ride]

Get a chain tensioner. Problem solved. Next question.

[HUGH]

just put a rear gear changer thingie on it

HUGH

[cjwally]

Originally Posted by G-Ride

Get a chain tensioner. Problem solved.

That is definately not an option.... No tensioners...

Originally Posted by HUGH

just put a rear gear changer thingie on it

HUGH

What do those do?

[Abui]

Originally Posted by cjwally

That sounds about right... It was quite a bit.

Do you think that it would solve the problem by putting a 17T cog instead of a 16T? 32 x 22 and 38 x 17

38x15!!

[0gravity]

Forgive me for not knowing, but what is dual drive? Two cogs in the back and two cranks up front and then you get off the bike and manually move the chain from one to the other?

[HUGH]

Originally Posted by cjwally

What do those do?

Just what you are trying to do, You just wont have to get off the bike to do it(or take off the rear wheel).

HUGH