Shifting Theory with a Wide/Low Double

[Ben Mihovk]

Hello!

I did try a few searches for some discussion or an answer to this question and came up empty...but I'm sure someone will provide a link with everything I'm looking for!

But here's my question...if I have the Clipper wide/low double (42/26) with a 9 speed cassette, am I "cross-chaining" and putting premature stress on my chain by staying on the 42t at all times unless climbing? The way I understand it, in a double crankset with a guard, the big ring is where the middle ring would be in a triple and can use all the rear cogs. Am I wrong?

If I'm out riding for fun, I'm usually on the big ring and the smaller half of the cassette and I'll shift the FD to the small ring if I have a climb (there's a really fun short cut through one end of a switchback that I like dropping down and climbing). On my work commute, I'm riding uphill for about a mile before things level off, then theres a series of descents and climbs that keep the ride interesting. But that first mile is boring and I stick with the big ring in the first three cogs most of the time. Would it be easier on my chain to use the 26t ring with the middle of the cassette for that section instead?

Thanks for your thoughts!

-Ben

[John Hawrylak]

Ben

I think calculating:

The front chainline for the outer and inner rings of the double    and comparing them to

The rear chainline for the #5 sprocket (mid point of a 9s)

AND THEN calculating which sprocket lines up with the 2 rings will give the minimal wear combination.

 

Then assuming Outer to #1 sprocket is acceptable   and   Inner to #9 sprocket is acceptable,

determine how far you can go down on the Outer ring

& likewise how far UP you can go on the Inner ring)      so chain wear is no greater than Outer to #1 or Inner to #9.

 

Shimano spec for Road front Chain Line (CL) is 43.5mm.  I can’t find a crank spec for the Outer to Inner ring spacing, but my best measurement on a XD2 triple is 7mm from Outer to Middle ring.  

Outer Ring CL = 43.5 + 3.5 = 47mm

Inner Ring CL = 43.5 – 3.5 = 40mm

 

Can’t find a Shimano spec for a rear CL with a 130mm OLD hub, but I calculated 42.5mm (for #5 Sprocket)   using

130mm OLD

4mmm from DO to face of #1 sprocket

4.3mm sprocket spacing.

                      

So Outer Ring is 4.5mm out from the #5 sprocket,  or just about even with the #4 Sprocket.  This places the # 1 Sprocket 12.9mm out from the Outer Ring (3 x 4.3mm), which is acceptable wear.

Outer to Sprocket #7 has the same 12.9mm distance, so Outer Ring & #7 has same wear as to #1 sprocket.  Outer Ring to #8 or #9 sprockets has increased wear.

 

Inner Ring

Front CL is 40mm    (43.4-3.5) which lines up about

REAR CL (#5) is 42.5mm so the Inner Ring is about in the middle of #5 and #6 Sprocket.

Rear CL on #9 Sprocket is 25.3mm  (42.5 – 4x4.3,   the 4 is spacing for5 to 6, 6 to 7, 7 to 8, 8 to 9).

So Inner to #9 distance is 14.7mm   or about 4/10 ths of sprocket more than   Outer to #1.

SO the Inner to #2 sprocket has the same 14.7mm distance, indicating Small to #2 has about same wear as Small to #9.

 

Hopes this helps,  the math probably needs checked.

 

John Hawrylak

Woodstown NJ

[dougP]

"The way I understand it, in a double crankset with a guard, the big ring is where the middle ring would be in a triple and can use all the rear cogs."

Your perfectly sane.  The middle ring position on a triple should allow access to all the cogs.

" Would it be easier on my chain to use the 26t ring with the middle of the cassette for that section instead?"

Don't see how.  The smaller ring requires the chain to wrap tighter & engages fewer teeth & links.  Probably harder on things than using the big ring.

Those are just my opinions.  You may get responses to the contrary. 

dougP

[John Hawrylak]

Ben 

I missed the fact you are actually using a triple with only the middle and inner rings.  Same math except Front triple CL = 46.0 mm for the Middle Ring.   I dont know the Middle to Inner ring spacing, but on my XD2 is is about 8 to 9mm.

A front CL of 46 and a rear CL of 42.5 (130mmOLD) places the Middle Ring at the #4 Sprocket, so Middle to #8 and #9 has increased wear.

Your ACTAUL Front CL and Rear CL may be different from assumptions.  You can measured both and use the same method.

John Hawrylak

Woodstown NJ

[Joe Bernard]

My entirely unscientific opinion is it's basically a 1x system with a granny bailout. You're supposed to use the 42 most of the time and across the full range. 

[tuolumne bikes]

Ben, there are lots of different points of view about riding. Nobody's right or wrong. I would only worry about cross chaining if it was noisy and bothering me. I would cruise up hills that are unlikely to need the small ring by just shifting the back. If I thought I would need the small ring, I would think about whether I should shift that big gap on the front sooner than later so I'm not stuck with the big shift when the going is harder. Doubly so on dirt.

In general, cutting switchbacks undermines trails that people work hard to maintain. It's not a good look. Clearly I don't know the specifics of your trail, so I don't want to be too judgemental.

Carl

On Sunday, October 11, 2020 at 5:08:37 PM UTC-7 bjmi...@gmail.com wrote:

[Ben Mihovk]

I would only worry about cross chaining if it was noisy and bothering me.

The only noise I've had was a brutally bad/poorly timed shift in the small ring while climbing and was in too small of a cog in the rear...I've never had noise going in big ring/cog, so I think I'm okay. 

In general, cutting switchbacks undermines trails that people work hard to maintain. It's not a good look. Clearly I don't know the specifics of your trail, so I don't want to be too judgemental.

Yeah, that's something to think about for sure. It's a paved pedestrian/bike trail maintained by the city, and I mainly like cutting it because it helps me avoid really tight/slow turns when there are pedestrians around (and I never could go up it on my 1x7 setup on my last bike!). But I see your point. 

[Ben Mihovk]

I missed the fact you are actually using a triple with only the middle and inner rings.  Same math except Front triple CL = 46.0 mm for the Middle Ring.   I dont know the Middle to Inner ring spacing, but on my XD2 is is about 8 to 9mm.

A front CL of 46 and a rear CL of 42.5 (130mmOLD) places the Middle Ring at the #4 Sprocket, so Middle to #8 and #9 has increased wear.

Your ACTAUL Front CL and Rear CL may be different from assumptions.  You can measured both and use the same method.

John, 
I appreciate both your thoughtful and detailed responses. I'll definitely give it a look and do some measurements...there's nothing I'd love more than to put numbers to the situation so I can know exactly how much more wear 8 and 9 would be getting in the big ring. 

[Ben Mihovk]

My entirely unscientific opinion is it's basically a 1x system with a granny bailout. You're supposed to use the 42 most of the time and across the full range. 

That's what thought.

The only reason I'm asking is because I had a bad shift incident last week (really noisy/rough while climbing in small ring...) and so I started digging around the ever-so-helpful internet and found a lot of dogmatic writing about NEVER cross chaining big ring to big cogs/small ring to small cogs. In retrospect, my bad shift incident was almost certainly waiting too long to drop down to the small ring, probably combined with spastic movement of the shifter.

[brendonoid]

Everyone with a 1x drivetrain is cross chaining worse than you. 

Seriously however I found that forcing myself to use the granny ring on my wide/lows as often as possible saves a lot of premature wear and tear on my drive train. The stainless/steel granny ring is a lot more durable and spreading the load means you replace the alloy chainring less and wear out the chain slower.

Just my two cents.

[Ben Mihovk]

So...after waking up to some replies and feeling okay about how I've been riding, I decided to do the opposite and utilize the granny ring more on my ride to school today. Long story short, I think I have the hang of it and can see spending more time on it. I did, however, have more slipping/lack of engagement while in the granny ring that was a little befuddling, but I'm pretty sure it's technique (I've got one of Grant's bluhgs about shifting pinned to read when I get some time during lunch today). I also read some shifting theory from Sheldon Brown this morning before I left and am feeling pretty good about it!

Thanks again for everyone's thoughts/feedback!

Ben

[Rick Thompson]

This is how I use my 2 bikes with wide/low. The commuter has the big ring on a triple center with bashguard on outer, the rando is 9 x 2 but the granny gets used only with the low 4 and only really for steep loaded hills.