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Why are some cable guides underneath BB plastic and some integrated?

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Why are some cable guides underneath BB plastic and some integrated?

Old 09-11-18, 11:09 PM
  #1  
shuru421
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Why are some cable guides underneath BB plastic and some integrated?

I have seen many bikes with ''plastic cable guides'' bolted onto the frame (both high/low end bike frames), why is that they used plastic instead of all being integrated into the steel frame? Aren't the integrated ones superior vs the plastic cable guides? Id assume so..
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Old 09-12-18, 12:13 AM
  #2  
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As far as I can tell, the plastic cable guides wear very well for a long time. And, are replaceable if they are ever damaged.

The metal ones should last essentially forever, but risk wearing through the paint, and perhaps higher friction. Cable Liner fit in them helps.

Also, with vintage galvanized cable, the metal on metal runs greater risk of either cable or cable guides getting rust damage.

It is hard to say one or the other is better, but with good and bad aspects of both.
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Old 09-12-18, 01:24 AM
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Cost, more than anything else. If we’re talking strictly mass manufactured bikes, it’s just cost. A small bit of plastic screwed into the bottom bracket shell is a lot cheaper than manufacturing shells with integrated guides. More expensive bikes are typically going to have integrated guides, just like they are more likely to have internal cable routing and various other niceties. If we’re talking older, more hand built frames, then it depends mostly on when the frame was made. older frames either had no guides (usually used clamp on guides at the base of the down tube) or more likely had braze on guides on the top of the shell, which was much more common on 1970s and some older frames. Though a lot of older frames without brazed on or integrated guides can be found modified with a plastic guide, as a plastic one is a cheap easy way to upgrade an older frame. The most commonly found guide is manufactured by shimano and came as an accessory with shimano shifters for a long time, since the 80s maybe? And was meant specifically to be used to modify a frame that didnt have guides to be able to use the shiny new shimano parts you just bought. A lot of 80s and 90s steel frames have these shimano pieces. A craftsman of course, likely wouldnt use plastic guides unless requested for some reason by a customer. A plastic guide can be removed though, so it can offer a bit of customisation and versatility for the frame. Mostly though, it’s just cost.

Last edited by seamuis; 09-12-18 at 01:51 AM.
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Old 09-12-18, 01:36 AM
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BB Cable Guides

$$$$$$

Most of the bottom bracket shells with integrated cable guides are investment cast and more expensive than standard shells which are much cheaper to produce.

Some shells are made with the "spigots" drawn out of piece of tubing, others are stamped, formed and welded across the bottom like this BB shell:



Tubing brazed under the BB




2 styles of Cinelli investment cast BB shells with integral cable guides.


I suspect that running the derailleur cables under the BB was originally intended to save the time and labor used to braze cable guides on to the top of the BB shell.



Plastic and metal cable guides are even cheaper. They are pressed, screwed or riveted into the BB shell.






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Old 09-12-18, 05:56 AM
  #5  
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Corrosion is a very real problem down there. I have the integrated metal loops on the Schwinn and the plastic/Teflon plate on the Bianchi, and I would vote for the latter any day.
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Old 09-12-18, 06:04 AM
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+1. It's economics. After paying off the tooling investment, plastic BB cable guides are extremely inexpensive. They can also be manufactured using self-lubricating material that provides far less friction. Being a homogeneous material, they maintain a consistent appearance, unlike metal, which corrodes after the cables wear through the paint. However, the big saving is that they can be quickly installed by inexpensive, unskilled labour. Brazing takes much longer and brazers are classified as skilled labour with much higher pay rates.

When you're a mass volume manufacturer, even a small savings per bicycle quickly adds up to large amounts. Mass volume manufacturers operate in a much more competitive market segment, where profit margins are smaller and careful cost management is necessary. The smaller, prestige builders have larger profit margins to absorb the extra cost of metal cable guides, either brazed-on or investment cast into the BB shells.

Plastic guides mounted under he BB shell started became prominent in the 1980s on entry and mid-range models from mass volume manufacturers. However, there were precedents. Simplex had their hybrid material cable guides that clamped to the down tube, just ahead of the bottom bracket shell. A Delrin cable guide housing was riveted to a metal clamp. These were ubiquitous during the early 1970s bicycle boom.
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Old 09-12-18, 07:53 AM
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from a current prospective, I like plastic guides better. The old Campagnolo guides are classy, but when they forced 11 tooth cassettes on us, routing the rear derailleur cable above the chainstay became problematic. I have pretty much given up on sourcing cassettes that have more teeth on the small cog. I think I might have some metal under-bb guides in my parts bin somewhere, but they had teflon lining. I figure the plastic guides are out of sight and you can avoid any issues with holding the teflon in place.

I finally got around to overhauling the bb on my '85 rockhopper recently (30 years, what's the rush?). After struggling for quite some time to put a cartridge bb in it, I eventually realized the under bb guide mounting screw was too long, pushing the cartridge out of line.
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Old 09-12-18, 10:47 AM
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As T-Mar mentioned, the plastic is much better in terms of friction, i.e. being self-lubricating. This became more critical when indexed shifting required there to be as little friction as possible along the length of the cable in order to maintain accurate transmission of shifting movements from the shifter to the derailer.

A worst-case scenario of cable guide material selection occurred around 20+ years ago, when Trek (for several years apparently) was using a piece of formed stainless-steel sheet under the bottom bracket of their OCLV carbon frames. With the cable wires on such higher-end bikes also being made of stainless steel by this time, the friction level was quite problematic unless the cable's external path was kept well lubricated. Stainless steel on stainless-steel is of course prone to the sort of cold-welding that can multiply friction levels to well beyond that produced along the entire balance of the cable's path, so Trek's stainless guides created a need for a lot of otherwise-unnecessary maintenance visits.
I got in the habit of using the "hoops" of the stainless guides to secure short sections of thick-walled plastic tubing, isolating the cable from the guide. Luckily the guide hoops were flexible enough to be made to grip the tubing reliably using the closest size of tubing one could readily source.
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Old 09-12-18, 03:35 PM
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Translucent plastic liner inside metal guides for cantilever brake cable

As other folks noted, metal on plastic is self lubricating. The plastic is a sacrificial piece that can be replaced.

However a more elegant solution would be brass, bronze or other softer metal guide for the steel cables. The guides would need to be fairly thick to withstand years of abrasion from steel cables.

My Univega Via Carisma has a peculiar pair of metal ferrule guides for the rear cantilever brake cable. One is a curved noodle attached to the frame -- the metal is almost as thin is a straw. It looks like an elegant solution to centering the brake cable between the seat post and seat stays. But it's not a great idea to run bare steel cable through a thin softer metal guide.

So it needs a plastic liner. The guides are too small in diameter for any conventional brake or shifter cable. The old plastic liner was cracked and I couldn't find what I needed online because I didn't know what it was called. I visited the LBS, showed them the old piece and they gave me a new plastic liner from their bin. I still don't know what it's called!

Last edited by canklecat; 09-12-18 at 03:42 PM.
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Old 09-12-18, 03:51 PM
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Originally Posted by canklecat View Post


Translucent plastic liner inside metal guides for cantilever brake cable

As other folks noted, metal on plastic is self lubricating. The plastic is a sacrificial piece that can be replaced.

However a more elegant solution would be brass, bronze or other softer metal guide for the steel cables. The guides would need to be fairly thick to withstand years of abrasion from steel cables.

My Univega Via Carisma has a peculiar pair of metal ferrule guides for the rear cantilever brake cable. One is a curved noodle attached to the frame -- the metal is almost as thin is a straw. It looks like an elegant solution to centering the brake cable between the seat post and seat stays. But it's not a great idea to run bare steel cable through a thin softer metal guide.

So it needs a plastic liner. The guides are too small in diameter for any conventional brake or shifter cable. The old plastic liner was cracked and I couldn't find what I needed online because I didn't know what it was called. I visited the LBS, showed them the old piece and they gave me a new plastic liner from their bin. I still don't know what it's called!
AHHH!
From my days in the motorcycle repair industry I can tell you with some reliability that those would be classified as a “gawzintah”. Because it goes in ta that part a’ the frame. This may be a Massachusetts colloquialism.
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Old 09-12-18, 03:58 PM
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Originally Posted by Chr0m0ly View Post


AHHH!
From my days in the motorcycle repair industry I can tell you with some reliability that those would be classified as a “gawzintah”. Because it goes in ta that part a’ the frame. This may be a Massachusetts colloquialism.
Heh! And all this time I thought Ben Lawee was from Iraq. Maybe he spent some time in Massachusetts en route to California and making Univegas!
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Old 09-12-18, 04:01 PM
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All the above - except maybe for the - "More expensive bikes are typically going to have integrated guides". Typically might have been true for some time but looking at later top of the line production frames like for instance the Merckx MXL shows that even the expensive frames had plastic pieces.

Here is my Merckx Corsa Extra in MAX tubing - a short run top of the line model - with metal guides and the following top model Merckx MXL with plastic.



Same with very limited numbers Bianchi Proto and Caurus in MAX tubing. First metal and later plastic. These - both Merckx MAX/MXL and Bianchi MAX were really expensive frames.
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Old 09-12-18, 04:02 PM
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I prefer the plastic guides as well, for the same reasons others have said..
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Old 09-13-18, 01:40 AM
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Originally Posted by styggno1 View Post
All the above - except maybe for the - "More expensive bikes are typically going to have integrated guides". Typically might have been true for some time but looking at later top of the line production frames like for instance the Merckx MXL shows that even the expensive frames had plastic pieces.

Here is my Merckx Corsa Extra in MAX tubing - a short run top of the line model - with metal guides and the following top model Merckx MXL with plastic.



Same with very limited numbers Bianchi Proto and Caurus in MAX tubing. First metal and later plastic. These - both Merckx MAX/MXL and Bianchi MAX were really expensive frames.
Its funny you mentioned you're Eddy Merckx Max and MX Leader frames. I saw 2 MX leaders, A red one with integrated like the red one above and the other purple one with plastic like your blue one above..HOWEVERR, if I had to choose...Id go with the Red Mx Leader with the integrated. I guess its personal preference at this point as consumers, while it was all business for the companies.
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Old 09-13-18, 01:41 AM
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ALSO I didn't know that some MX leaders came with Ergo shifter adapters while some didn't. Nice little details I find to be very swaying when it comes to making decisions.
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Old 09-13-18, 03:45 AM
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The plastic bottom bracket cable guide on my Dawes Atlantis is glued on with what looks like cheap insulation or gap filler or something it's also technically a cable housing guide, which seems unnecessary, but since it's there I ran the cables without housing.
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Old 09-13-18, 04:23 AM
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Originally Posted by canklecat View Post


Translucent plastic liner inside metal guides for cantilever brake cable

As other folks noted, metal on plastic is self lubricating. The plastic is a sacrificial piece that can be replaced.

However a more elegant solution would be brass, bronze or other softer metal guide for the steel cables. The guides would need to be fairly thick to withstand years of abrasion from steel cables.

My Univega Via Carisma has a peculiar pair of metal ferrule guides for the rear cantilever brake cable. One is a curved noodle attached to the frame -- the metal is almost as thin is a straw. It looks like an elegant solution to centering the brake cable between the seat post and seat stays. But it's not a great idea to run bare steel cable through a thin softer metal guide.

So it needs a plastic liner. The guides are too small in diameter for any conventional brake or shifter cable. The old plastic liner was cracked and I couldn't find what I needed online because I didn't know what it was called. I visited the LBS, showed them the old piece and they gave me a new plastic liner from their bin. I still don't know what it's called!
I use housing liner (a lifetime supply for this application is about ten bucks from Jagwire).

A good fix on the spot is to use the housing liner from inside the steel guide on an available v-brake.
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Old 09-13-18, 08:20 AM
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When I'm brazing on a lot of bits on a bike with none, I use the plastic one. All I need to do is tap and drill an M5 hole in the bottom. I buy 'em 10 at a time, they're cheap and they work. The only time I'll braze on the top of the BB types is when there's a cable stop on the top of the chainstay and the frame has good chrome, otherwise it's easier to hack, file, and sand off the top cable stop and braze on underneath than to brazeon the top of the BB type.

Like others have written, it's an outta site, outta mind part.
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