Bottom bracket for Soma Saga build
 

I am building a Soma Saga and using a Sugino triple crankset that I already own which takes a square taper BB. From those of you who have built a Saga, what length spindle have you used? I have read on these forums preferences toward 113mm and others choosing 118. Obviously, I would like to get optimal chainline while clearing the chainstays with the inside ring. Thanks in advance

113mm works great for me with the Sugino XD600 cranks.

Thanks. Any idea how far is your small ring is from your chainstay? Would 110mm work? I ask because on my current bike which has 130mm drop outs, I have found for the chainline to be good, I have had to move my crank in. I currently have a 107mm BB and it works fine.

I'm using a 110 with a Sugino triple crank on a Sam Hillborne. I don't use the large chainring, I've put a chaingaurd there.

Marc

I'm not the expert, but I think that there are two key pieces of information that are relevant. The first piece is that the frame you are looking at is spaced for a 135mm rear axle. That is important, so when someone says "I have 11x and it works fine" and doesn't say what rear hub spacing they are using, it is not as meaningful as it could be.

The second piece of important information is how you plan to use the gears. If you favor small gears, get a shorter spindle - this will put the middle and granny rings in the largest part of the cassette. If you are a powerful rider, get a longer spindle - this puts the granny closer to the middle of the cassette but gives a good chainline on the middle and large rings.. Choose the spindle length that will give you the least amount of cross-chaining for the type of riding that you do.

aggiegrad, you have it just the opposite, if you're a powerful rider, you will be spending your time in your largest chainring most of the time and therefore to obtain the best chainline for your biggest chainring, you'll want a shorter spindle length. If you're not as strong and will be spending significant time in your middle ring, you'll want the suggested or longer spindle. Either way, don't go too extreme unless you want to take your calipers out and test your math skills.

At Sheldon's suggestion, I use a 110 bottom bracket with my Sugino crankset because I tend to spend most of my time in my big 46 ring and by using this vs. the 113 suggested length, I can achieve a slightly better chainline for the majority of my prefered chainring/cogs.

Copied from Sheldon:

The spindle length mainly depends on what kind of crankset you'll be using, and doesn't have much to do with the frame. New cranks come with a spec sheet that lists what length spindle they are intended to be used with. Sometimes two lengths are listed. When this is the case, the longer size is for use on frames with fat seat tubes, because such frames put the front derailleur mechanism farther to the right than on a frame with a standard seat tube.

The folks at Phil Wood can often help with these types of cases. Give 'em a call.

I ended up ordering a 113mm BB. I believe this is the one recommended for my Sugino crankset. I too spend the majority of my time on the big ring but I don't want to take a chance that a narrower spindle will cause the inner ring to scrape the seat stays. It was only $20 so it won't be the end of the world if I end up ordering a 110mm later.

The 113 will be fine. Please display some pics when you're done.

Thanks. Okay wll do.

and It's something that you can shift the Axle offset in the BB, in your shop.


best chain line: center of the rear cluster.. lines up parallel with the centerline of the bike,

and the gap between a double crank, or the middle ring on a triple..

I realize you've already ordered the 113mm, but I was just able to measure the gap (small ring to chain-stay) as 10mm.

My setup stats:

• Sugino XD600 triple crankset
• 113mm bottom bracket
• my dropouts are 135mm
• chainline is optimal for the middle ring

Thanks for taking the time to measure. I think 113 will be just fine.

I'm intrigued by your reply. My common sense tells me that you want the best alignment when you are in your most common gear combinations. Your reply states that you want the most rear cogs available in the most common chainring. I don't see the point in getting a shorter spindle so that you can use the big chainring in larger cogs. If I am a strong rider, I want the best alignment between the middle and large rings to the smallest cogs, which means a longer spindle.

If I was building with a single crank, I would agree with your assessment.

Your common sense is correct. If I spend 95% of my time in my largest chainring, why would I want my optimal chainline in relation with the middle ring? If you sit in your middle ring all day, then that is where you want it to be. We're not talking large differences here if we stay close to the manufacturer's recommended spindle. Of course this assuming that my smallest chainring isn't hitting the the chainstay by going smaller.