davei1980

I am planning to use the black SRAM crank on my Bianchi as a 1x. I just assumed the ring would be in the "outboard" position, but looking at my Specialized single speed bike with the Shimano 105 crank, it's clearly mounted in the inboard position (it looks like this crank can handle doubles, like the SRAM unit). Before posting a new thread without thinking, I went over to my single speed Nishiki with a Sugino crank and it's ALSO mounted in the "inboard" position (this crank is a dedicated, 1x crank, unlike the SRAM and the 105 but the ring is still on the interior).

NOTE: the Bianchi, which is getting the black SRAM crank will be a 1x7, not a SS like the others in my stable, so chainline is maybe not as important but you guys are the experts!

Thanks in advance!

cny-bikeman

You are confused because you are approaching the problem incorrectly. The question is not whether inboard or outboard is correct, but rather what chainline you need. The chainwheel is positioned, whether by inboard/outboard, spindle length, BB spacers, or a combination, according to the chainline of the rear cogset. https://www.sheldonbrown.com/chainline-multi.html. Chainline is important, period.

davei1980

i like it. Thanks. I will set it up in such a way that my 1 ring lines up with my 4th cog.

I know to check other sources before posting but I didn’t think of chainline being an issue in this case

CliffordK

With single speed, chainline would be the most important factor, and can be adjusted on both the front and rear of the bike. Although it may also impact your wheel dishing.

With 1x multi-speed, perhaps a different issue, although I would think chainline shouldn't be ignored. Which gears are you using most?

davei1980

Most likely the 2nd highest ratio and 3rd highest (2nd and 3rd smallest cogs)

I am guessing that a single speed freewheel cog is farther inboard than the middle of a 7speed freewheel, even on a dished wheel, hence why my SS chainrings are set up that way.

xenologer

Mount up the crankset
then measure which position puts the sprocket at 50mm from the centerline of the bike.
+-3mm is OK

and go with that.

davei1980

i like it!!!!

I am decent at wrenching and problem solving but I am also the same guy who very recently had the red bike apart because I installed the bb spindle backwards 😅😂😅

Racing Dan

Imo you should place the ring such that you have the straightest possible chainline in the gear combinations you use the most.

fietsbob

best chain line, is in line with the middle of the rear gear cluster .. 4 of 7 , etc..

same as middle of a triple ..

DannoXYZ 

Which gear will you be using on the 7-spd freewheel?

1. Pick that first.
2. Then measure chainline distance.
3. Then select chain-ring position that gives you straightest chainline.

HerrKaLeun

Pick the middle cog as the chainline.

I don't think the advice to analyze which gear you use most is solid. Subconsciously you may be in gears you don't think you are often. And a well chosen drivetrain probably has you ride in the few center cogs most of the time and the most-outer ones only occasionally. If you happen to ride most of the time in the largest cog, yoru chainring probably is too large. Same if you use the smallest most often, too small chainring... if that is the case, the mismatched chainring shudl be resolved. Even if you could use a datalogger to find your most often ridden gear, what if you ride elsewhere tomorrow or you get lighter or more fit?

The center as the chainline also has the advantage that the outer cogs don't have to be too extreme. If you for example set your chainline to the small cog (if even possible), any gears towards the large cog will be very extreme.

DannoXYZ 

Middle cog can vary from 14t to 24t depending upon cassette. He hasn't even told what tooth-count or overall gearing he wants to use. Terrain is major factor in choosing gearing. What's suitable for flat Kansas flat-lands will be completely inappropriate for hills of San Francisco. There's a lot of data that the OP hasn't considered or told us about yet and all that needs to be hammered out before even touching the bike.

davei1980

Looking at a freewheel with 13-15-17-19-22-25-28.

Front ring is 39t - to quote Baymax from Big Hero 6- I am not fast

based on the gearing of my old 1x8 commuter, I should be using 15 and 17 most often.

Terrain is mostly flat but I want the ability to ride up to my moms on a steep (not long) hill from time to time. I can’t reasonably do this on my single speed (42 ring/17t cog)

Note- 700c wheels

DannoXYZ 

Heh, heh... I was using 40x17 on track-bike, good for 38-39mph at CSUD.

Ok, so you'll need lower gearing than 42x17 = 2.47

That rules out the 39x15 as it's taller at 2.60, leaving you with 39x17, one out from middle.

Measure offset from centre for chainline, don't just eye-ball it. Easy way is to measure from drop-out inner-face to centre of cog, call this X

Then divide OLD by 2 and subtract X. For example (130/2) - X = 65 - 20 = 45mm

Take ruler and start at centre of seat-tube and measure actual number you calculated out over crankset. Which chainring is closest to number you calculated?

davei1980

Excellent!

Also, my single speed with the 42/17 gearing is a track bike too!! (well, track-inspired since it has mounting holes for water bottle cages and
It’s drilled for brakes)

davei1980

Excellent!

Also, my single speed with the 42/17 gearing is a track bike too!! (well, track-inspired since it has mounting holes for water bottle cages and
It’s drilled for brakes)

Zaskar

I just finished a 1x11 setup. The advice to use the middle cog as the centerline is spot on. I have full range of the 11-28 11-speed cassette and can backpedal in the 11t and 28t without dropping the chain - not running any chain guide, but am running a narrow-wide 52t chainring.

DannoXYZ 

Why would you backpedal?

DrIsotope

Say for instance you're clipped in and have to take off from an intersection. Sometimes, it's a lot easier to rotate the clipped foot to your "starting position." Particularly if you forgot to shift to an appropriate gear. Not that I'm speaking from experience or anything.

Bandrada

+1 on what everyone else has said about the chainline being the priority, especially with the narrower chains/cog spacing of the 11 and 12 cluster setups...

I posted this in another thread. I found it very useful in my research. It pretty much confirmed what I suspected through my own experience dealing with proprietary spacing such as the 142+ rear spacing on my Specialized Enduro.


https://www.oneupcomponents.com/page...-and-non-boost

davei1980

thats a wide OLD.

Guessing it’s got a big casette + disc

Bandrada

Sorry, here is a better link. This is actually the one I was looking for.

https://www.wolftoothcomponents.com/...and-chainrings

RoadLight

Hi davei1980,

I converted my SRAM 2x road drivetrain to a 1x and I was very careful with the driveline before I started. All of the information that I acquired along the way is for 10 and 11-speed cassettes. The fact that you are using a 7-speed cassette may change things because the total width from outer to inner cog will be less, reducing cross-chaining issues. And that's why the driveline is so important for the 10-11 speed systems: cross-chaining. Your 7-speed system may be a little more "forgiving".

Generally, what SRAM recommended was that you should locate the chainring about 1-2 mm outside of the cassette centerline. I believe the reason for this is to favor the smaller cogs a little since they have fewer teeth to hold the chain in place.

My crank is a compact SRAM Red 22 and I used it instead of a Force 1x crank. I removed both 2x chainrings and installed a single 50t SRAM X-Sync 1x chainring. It has a BCD of 110 mm so there was no choice as to where it went---it had to be mounted on the spider in the outer position. But the X-Sync 1x chainring is made differently than a standard 2x outer chainring because the centerline of its teeth are a little farther inside. This produced the driveline that I needed that was just 1-2 mm outside of the centerline of the cassette.

If you plan to use a 1x-specific chainring with the wide/narrow teeth to better hold the chain and increase contact, then it will probably dictate the mounting position on your crank. There's no way that I could have achieved a good driveline on my bike without a proper 1x chainring made for the purpose. And the 1x-specific chainring reduces the likelihood of chain drop so dramatically that a chain guard is not needed for road applications---even with a standard road rear derailleur (because you won't get the kind of chain slap that cyclo-cross, gravel and mountain bikes get).

Therefore, measure the distance of the centerline of your cassette from centerline of your frame and look for a 1x chainring that will give you a similar position at the front. If you have to settle for being a little off-center with the chainring, favor the outside rather than the inside. But I wouldn't recommend an offset greater than 2 mm if you can avoid it. However, I think having a chainring that is perfectly centered to your cassette would be ideal for a 7-speed system.

By the way, converting to a 1x drivetrain was just step one of my drivetrain upgrade. Step two will be to switch to a SRAM Red eTap system. My purpose for an eTap rear derailleur is so I can shift from my aerobars as well as my handlebar. Tony Martin did this with his TT bike in the 2017 Tour de France. I had the idea about a year earlier but, as far as I'm aware, he was the first person to convert a SRAM Red eTap to 1x for road use.

Kind regards, RoadLight

fietsbob

Of your proposed .. 13-15-17-19-22-25-28. .. the 19 is physically in the middle..

davei1980

Wow! Your project sounds a lot more intense than mine! This is the bike I am building; I got it on trade for some work on my little brother's bike and I am putting it together with stuff I have lying around