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Eccentric BB?

Old 07-04-20, 05:35 AM
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Tandem Tom
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Eccentric BB?

Yesterday while working at the shop I had a bike in the stand with the above. So it got me thinking. If you were wanting to build up a bike with an IGH would you use an eccentric BB or sliding rear dropouts? And why?
Thanks!
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Old 07-04-20, 07:25 AM
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Doug Fattic 
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Originally Posted by Tandem Tom View Post
Yesterday while working at the shop I had a bike in the stand with the above. So it got me thinking. If you were wanting to build up a bike with an IGH would you use an eccentric BB or sliding rear dropouts? And why?
Thanks!
Tom it is much easier for an amateur builder to make a frame with horizontal long slot dropouts. This is because it is not necessary to nail exactly the chain stay length. You can get it approximately right by sliding the chain stays in and out of the BB shell’s sockets. With an eccentric shell it is necessary to get the miters and chain stay length just right. That is made much easier with machine mitering and an expensive fixture.
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Old 07-04-20, 07:51 AM
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Back when people were building more single speed bikes, this was a big decision people had to go through. I think a lot of builders did a couple of eccentrics and then got tired of the creaking complaints and switched to sliders. It's a pain to get an eccentric bb now, unless Nova has one and I've forgotten.
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Old 07-04-20, 05:04 PM
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Good timing as the frame I am waiting time to finish will have an IGH. No horizontal slotted drops, no BB eccentric. I will use a spring loaded chain tensioner. Or is that wrong? Why? because I have experienced sliders and hingers that slip and creak and still want a disk set up. Andy
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Old 07-05-20, 05:09 AM
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So to further my education a follow-up question. Doug you mentionef long horizontal dropouts. What about the sliding dropouts that are a seperate "piece"? My wife's touri g bike has these.
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Old 07-05-20, 05:42 AM
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Sliding or Rocker dropouts would be my preference over an eccentric BB. Sliders and rockers have their issues too, but the Paragon sliders are the best in terms of preventing slipping of the insert. Between the double bolt washer and the adjustment bolt at the front, they don't move after you set them. The cheap cast sliding dropouts are not so great in terms of preventing the insert from slipping in use.

Paragon rockers are good, if you get the Titanium 12pt bolts with them. The steel bolts that come with the dropouts do not hold up to the torque necessary to prevent the drive side from slipping forward under heavy pedaling loads, such as climbing while standing. The hex in the bolt will strip out before you can get them tight enough.
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Old 09-16-20, 08:23 AM
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good day dear all,

well good thoughts - i am glad to be here in this great forum. It is fantastic.

Originally Posted by dsaul View Post
Sliding or Rocker dropouts would be my preference over an eccentric BB. Sliders and rockers have their issues too, but the Paragon sliders are the best in terms of preventing slipping of the insert. Between the double bolt washer and the adjustment bolt at the front, they don't move after you set them. The cheap cast sliding dropouts are not so great in terms of preventing the insert from slipping in use.

Paragon rockers are good, if you get the Titanium 12pt bolts with them. The steel bolts that come with the dropouts do not hold up to the torque necessary to prevent the drive side from slipping forward under heavy pedaling loads, such as climbing while standing. The hex in the bolt will strip out before you can get them tight enough.
well to have some photos would be great. Can any body illustrate this a bit!? I would be more than glad
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Old 09-25-20, 10:24 AM
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Originally Posted by unterhausen View Post
Back when people were building more single speed bikes, this was a big decision people had to go through. I think a lot of builders did a couple of eccentrics and then got tired of the creaking complaints and switched to sliders. It's a pain to get an eccentric bb now, unless Nova has one and I've forgotten.
I have been saving for a pair of frames to be made and was hoping to go eccentric especially since a friend recently got a Nature Boy ace with what I think is a Bushnell style eccentric and has yet to make it move despite it being exclusively a fast, high abuse, off-roader.

Were the creakers just the set-bolt types or all types?
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Old 09-25-20, 10:45 AM
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Originally Posted by Doug Fattic View Post
Tom it is much easier for an amateur builder to make a frame with horizontal long slot dropouts. This is because it is not necessary to nail exactly the chain stay length. You can get it approximately right by sliding the chain stays in and out of the BB shell’s sockets. With an eccentric shell it is necessary to get the miters and chain stay length just right. That is made much easier with machine mitering and an expensive fixture.
But why is it necessary to get the chain-stay length exactly right? Obviously if it's way off you will alter the whole geometry but a mm or so won't make any difference.
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Old 09-25-20, 02:06 PM
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Originally Posted by guy153 View Post
But why is it necessary to get the chain-stay length exactly right? Obviously if it's way off you will alter the whole geometry but a mm or so won't make any difference.
No 1 mm makes a noticeable difference. A bit off in chain or seat stay length is more important that other places. That is because of the ratio of length difference between the hub width and the distance to the rim/tire. That means 1 mm of stay length difference will move the tire/rim over almost 3mm. The tire won't just be 1mm closer to one side. That amount of tire offset is easily visible looking at where it is between the chain stays. If you off by 2 mm it is horribly off. I attached a picture with a 700C wheel in an old unpainted frame with Henry James horizontal dropouts. In one dropout I put a 1mm drill bit between the wheel axle and the back of the dropout. Notice how far over the rim is from being centered! In my opinion if I saw a frame with a wheel that far out of center, I would assume the builder is either lazy/careless or doesn't know what he is doing. If it was someone that sells frames, that is bad enough to give them an F grade. He is not yet good enough to hang out his shingle.

Getting the chain stay lengths exactly right is one of the biggest challenges in building a frame. That is why it is wise for someone starting out to choose horizontal dropouts so any length discrepancy can be compensated for by dropout screw adjustors. The problem can also take care of itself if using an IGH or a single speed in long slot dropouts.

I think every custom frame builder needs to hold at least a mm tolerance for wheels being centered. We should all take an oath that says we will hold to that standard. The problem is that a lazy/ignorant custom builder's work can tarnish the reputation of all builders. Even when they finally get to be acceptably good, their reputation (and by extension every builder's reputation) can be damaged by their 1st builds if they weren't up to standard.

By the way Guy153, this post isn't directed to you personally but rather is a general statement to all builders and potential builders of the tolerances we should all accept. We are one of the few trades that has no standards of knowledge or ability to enter. Except what we can do to encourage and complement solid workmanship online and call out poor workmanship as unacceptable.

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Old 09-25-20, 02:25 PM
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Originally Posted by Doug Fattic View Post
No 1 mm makes a noticeable difference. A bit off in chain or seat stay length is more important that other places. That is because of the ratio of length difference between the hub width and the distance to the rim/tire. That means 1 mm of stay length difference will move the tire/rim over almost 3mm. The tire won't just be 1mm closer to one side. [...]
Getting the chain stay lengths exactly right is one of the biggest challenges in building a frame.
Agree 100% and I found this out the hard way for myself I thought you meant the chainstay length in terms of the length they both are. It doesn't matter if they are both 1mm too long or short. But if one is 1mm longer than the other I agree that's a disaster. I am super stoked that on my last two frames (out of 5) the rear wheel is absolutely bang-on in the right place with no filing of the dropouts. But it took me a lot of head-scratching and modification of my crude jigging facilities and procedures to get there.

​​​​​​I do wonder if this is why bikes always used to have sort of diagonal horizontal dropouts. There's a bit of adjustment there for both CS and SS alignment just when fitting the wheel.

If the OP uses an eccentric BB with vertical dropouts there's wiggle room in one axis and potential to file a bit in the other as a last resort. Similar with horizontal dropouts unless he goes with the diagonal ones. The least forgiving dropouts are of course thru-axles.
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Old 09-25-20, 02:48 PM
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I'm about to receive a bike with a PF30 shell and a Wheels Mfg. EBB adapter for a singlespeed setup. I will report back on how well it works. I see quit a few singlespeed bikes with PF30 these days.
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