[atrokz]

When designing a bike, an engineer (or team of engineers in some cases) has to decide how the swing arm's pivot points will... er... pivot.

A lot goes into engineering the bushings and bearings that are available in industry (and by industry I mean ALL manufacturing. Real industry) . We've got literally hundreds of ways to allow something to rotate on an axel, and yet every day, an engineer at your favorite bike company sits at his desk designing the latest useless manipulation for a hydroformed tube while the roller bearing on that bike takes a 20deg beating. There really is only a handfull of frame builders that use anything else.

headsets have evolved. Where there once were loose balls packed in a sleeve, there's needles and angular contact. BB's have even been treated to outward thought. So why is it then, that 99% of bikes use crap roller ball bearings to perform a task that they were never designed to do in the first place ('roller' mean anything to you?) ?

I guess what I'm asking (and ranting about), is if cost was no object what's the IDEAL pivot system for a frame? Can an Iglidur Z poly bushing suit the task at hand? Anyone here have any ideas on something not just different but better than Nicolai's needle/Axle/Polymer bush combo ? There's got to be some people on here that have some ideas.

 

[Kanye West]

My only input for that is that I wish the bike industry would make an effort to convert to using moto style angular contact needle roller bearings for headsets.

The argument behind using a bushing for pivots is that the pivots do not undergo full rotations, and they do not see the angular velocity to realize any sort of benefit from the smoothness of a roller bearing. The bushing design is inherently a stiffer interface as all ball bearings have a few degrees of axial float. This is usually compensated for by preloading the inner race from both sides, but that simply keeps that still while the outer races are allowed to float a small amount axially (in conjunction with each other from each side).

With the aggressive sideloads a rider can put on a main pivot in a single pivot interface from trying to track through a flat chopped up corner full of braking bumps and ruts, it's pretty easy to bring out the performance shortcomings of a bearing setup vs a bushing setup.

 

[EB-Mitchell]

http://bansheebikes.blogspot.com/search/label/Bushings

 

[davep]

I think if you look at all the silly-obsessive weight whiny threads, you will have some idea of why some more durable and better suited systems are not used. Tapered or roller element (needle) bearings definately fall into this catagory (the synchros HS is a tank for example). They are by also much harder/more complicated/more expensive to seal properly for this type of application.

Of course, bushings were very poorly applied by many mfg a handfull of years ago and left a bad taste for many as they design/quality/execution was so bad that they all failed.

OTOH, Turner has been using a well designed bushing system for years on their non-DH bikes. Their newest system is a significant improvement to a proven system/materials. No word if the new DHR will use this system (would be great if they did IMO).

http://www.turnerbikes.com/09pdf/turnertech_journal.pdf

 

[toodles]

RAILS!

Wait no, somebody tried that... For me, I like the bushing system on my DHR. A few squirts of grease every now and then and there has been no play or slop after months of runs. Within the same time and conditions I had replaced several bearings in my Sunday, however the differences in rotation, sealing, angles etc probably account for this as much as anything

 

[P.T.W]

RAILS!

Wait no, somebody tried that... For me, I like the bushing system on my DHR. A few squirts of grease every now and then and there has been no play or slop after months of runs. Within the same time and conditions I had replaced several bearings in my Sunday, however the differences in rotation, sealing, angles etc probably account for this as much as anything

I think youl find that your DHR has needle bearing pivotsoster_oops:

 

[buckoW]

cost is a main reason and ease of the end user finding spare parts is another reason. I have used 3 Syncros needle bearing headsets and like Davep said they don't seal well and the needle bearings have a big surface area to roll on so when they start to get contaminated you feel it instantly. They are also way too heavy.

I think the main problem is that frames are not designed stiff enough in the rear. A DHR for example feels great when it is new but ride it hard for a month and it gets a fair amount of slop in the rear end. I think that has more to do with the design of the pivot having the rear end sit inside the front triangle's pivot housing. A wider attachment of the rear end to the front end would help the bearing life, IMO.

 

[toodles]

I think youl find that your DHR has needle bearing pivotsoster_oops:

In one pivot yes. In the pivots that actually rotate the most, no.

 

[MrPlow]

I like the bushing system on my DHR. I had replaced several bearings in my Sunday, however the differences in rotation, sealing, angles etc probably account for this as much as anything

Agreed. I pulled the rear end of (yours, was mine, now sold again) Sunday and you can feel where the bottom link sits in the travel! Major ball bruising there.

Plain bearings would surely be the ultimate, but they cost more generally, and have a bad rep. Pitty.

 

[Udi]

Any bike with conventional cartridge ball bearings will fall victim to that, if anything the sunday is reasonably good because it uses fairly large bearings that don't rotate on excessively large axles (meaning the balls themselves are still a reasonable size) and they are full complement like a lot of DH bikes these days.

On paper the needle bearing is superior in low rotation applications, but in practise I think they are harder to implement well, harder to seal, and harder to find/replace. I'm also not sure how well they'd handle sideloading.

The humble bushing (Iglidur and the like) works great when coupled with those helical slotted axles + greaseports; and a good implementation is much easier to come by vs. needle bearings... but with these I wonder, is there a stiction increase? Minimal I'm sure, but in an age of BOS shocks and the like, it's probably a fair concern.

 

[wood booger]

Back in the SLO days of Mtn Cycle we used Igus bearings (polymer bushing) in the frame and the pivot was hard ano Al w/ grease grooves cut into it. This was very durable and easy to service. BUT the tolerances had to be very tight all around for the pivot not be too tight or loose. Very little wiggle room for that buttery feeling.

Normal ball bearings like most bikes have are garbage for suspension pivots. They are designed to go round and round, not turn just 1/4 rotation at most. They get pitted and die very quickly. Can you say "feel like poo"?

Needle bearings (ala dirt bike linkage) would be great, but many bike applications are too small. They don't make them small enough.

I'm not sure what Nicolai uses, but I am sure it is very cool and very expensive.

Design the bike w/ large pivots so you can get needle bearings in there. They handle load much better and w/ a grease port will last for days w/ no disassembly required.

 

[Jason4]

The new Evil bikes are using Ferrari bushings FTW!

No, seriously...

 

[buildyourown]

In one pivot yes. In the pivots that actually rotate the most, no.

Is this something you did yourself?

On my '07 DHR, I replaced the roller bearings in the main pivot with a bushing made of glass filled teflon. Not only is it lighter, but it has been maintenance free for 2+ years. Well engineered bushings really are better than bearings in this app.

 

[atrokz]

Some really helpful responses so far. I'm now debating on a Igus polymer bushing setup similar to the banshee, or a 1512 needle on a hardened roller with a modified grease port (I could edm drill out a few holes for this).

Hmmmm...

 

[Kanye West]

Is this something you did yourself?

On my '07 DHR, I replaced the roller bearings in the main pivot with a bushing made of glass filled teflon. Not only is it lighter, but it has been maintenance free for 2+ years. Well engineered bushings really are better than bearings in this app.

Interesting. Could you provide some more details on this please? Did it make the back end any stiffer? What was your hardware spec for it?

 

[P.T.W]

In one pivot yes. In the pivots that actually rotate the most, no.

Major ball bruising there.Now that sounds painfull

Is this something you did yourself?

On my '07 DHR, I replaced the roller bearings in the main pivot with a bushing made of glass filled teflon. Not only is it lighter, but it has been maintenance free for 2+ years. Well engineered bushings really are better than bearings in this app.

Sorry Toodles every DHR that ive ever seen has needle rollers every where......an iv also worked on a mates linkage pivots on his DHR (06 vintage i think) an they where definantly needles.An as Buildyourown says above his had needles in the main pivot

Im not having a go....just wondering how your came to have bushings??????

look here....http://www.enduroforkseals.com/id243.html

 

[toodles]

Well i'm stumped... i thought my 08 DHR came with bushings in the shock linkages. I'm not pulling it apart to double check so I'll guess I was mistaken. Nevertheless, my original opinion on roller bearings is valid. I've never flogged out any other system than that.

 

[P.T.W]

Well i'm stumped... i thought my 08 DHR came with bushings in the shock linkages. I'm not pulling it apart to double check so I'll guess I was mistaken. Nevertheless, my original opinion on roller bearings is valid. I've never flogged out any other system than that.

No prob toodles...im guessing you never had to pull your linkage apart......thats allways a good thing
My mates one got a lil sloppy after a year of constant abuse,no complaints there either

 

[Pslide]

Agreed with wood booger - tolerances on bushings are critical. From experience, 0.05 mm can be the difference between loose bushings (play) and tight bushings (stiction). This is OK if all your components can be machined to high tolerances, but if you are sticking bushings into a welded assembly, then you could have problems.

And I'm not just talking about radial tolerances either...you have lateral tolerances as well.

I think some bike companies go with bearings for this reason. Tight tolerances are expensive.

 

[buckoW]

Sometimes the consumer doesn't want to pay for that increase in quality either.

 

[Spokompton]

Versus makes quality frames with needle bearings and don't cost any more than your run of the mill craptastic skateboard bearing frame.


Frames are a lot like HP printers. Sure you can get one that works well for the first month and only cost $40, BUT once your ink runs out, you've got to spend $30 on more ink. On top of that, the printer starts smudging ink in some spots, BUT you stick with it because it gets 99% of the job done. Nothing worse than having to print your report for race day and having your printer give out.

Guy who buys the nicer Turner laser printer for $200 goes for months on end before needing a refill. Sure he paid more up front, but the operating costs and print quality don't kill him in the long run.

 

[rayhaan]

Interesting. Could you provide some more details on this please? Did it make the back end any stiffer? What was your hardware spec for it?

Is this something you did yourself?

On my '07 DHR, I replaced the roller bearings in the main pivot with a bushing made of glass filled teflon. Not only is it lighter, but it has been maintenance free for 2+ years. Well engineered bushings really are better than bearings in this app.

yes I too would be very interested if you provided details for this change you have performed. what the bushings cost you etc....
performance improvments....
please and thanks

 

[buildyourown]

Interesting. Could you provide some more details on this please? Did it make the back end any stiffer? What was your hardware spec for it?

The bushings are homemade. Mine needed replacing and I was in a time crunch so I grabbed a piece of material and made 2 bushings, 3/4" long.
It still uses the outer needle bearings in thrust, but the radial load is all bushing.
This really is the ultimate bicycle bushing material IMO. Teflon has enough natural lubricity to not really need any grease and the glass additive means the bearing won't deform under high pressure.
You can buy the stuff in bar form from McMaster.

 

[Terrorfirma]

Agreed with wood booger - tolerances on bushings are critical. From experience, 0.05 mm can be the difference between loose bushings (play) and tight bushings (stiction). This is OK if all your components can be machined to high tolerances, but if you are sticking bushings into a welded assembly, then you could have problems.

And I'm not just talking about radial tolerances either...you have lateral tolerances as well.

I think some bike companies go with bearings for this reason. Tight tolerances are expensive.

Pslide your are absolutely correct. We've been working with bushings for a couple years now and when you weld you pull materials in different directions. My experience is .02mm can be the difference between play and no play.
I would figure most mfg.s just don't want to deal with the hassle... and yeah its a bitch trust me.
Bearings = easier for machinests, because the tolerances are more forgiving.

 

[Kanye West]

McMaster part # 85275K48 - is this what you're referring to? What was your ID/OD/length exactly? Any shoulder?

 

[MrPlow]

build your own.
Have you noticed any difference in performance after a ride in the rain or mud?
A lot of Oil ipregnated nylons etc can swell with moisture.

 

[Jason4]

build your own.
Have you noticed any difference in performance after a ride in the rain or mud?
A lot of Oil ipregnated nylons etc can swell with moisture.

Delrin is more suitable for most bushings used in vehicles as it absorbs substantially less water than nylon but otherwise has very similar properties. That is why it is used in so many auto applications. It makes a big difference in cars if you grease it with a sticky silicon grease, it keeps the noise down and also helps the wear rate.

 

[buildyourown]

McMaster part # 85275K48 - is this what you're referring to? What was your ID/OD/length exactly? Any shoulder?

That's the stuff. I made 2 of them, 3/4" long. .500 ID and .6875 OD. Just like the bearings they replaced. I did leave the ID slightly undersized and reamed them to fit with an adjustable hand reamer after installation.

I have not noticed any issues with water. I've had these in since. July 4th, 2007. 20+ Whistler days, ~10 race weekends, 1 PNW winter. PTFE is not Nylon and it is not oil impregnated.

 

[Kanye West]

Interesting. Any increase/decrease in smoothness of rotation or lateral stiffness? Are you using the updated thru-bolt pivot from Turner?

 

[MrPlow]

I was thinking of usding UHMWPE that you can get in teflon impregnated form thought it would do the job.
Soryry BYO I thought you were using nylon and should have paid more attention.

 

[Jason4]

From what I remember of plastics UHMW is harder to machine than Delrin or nylon. I'm not sure how teflon fits into that. buildyourown, can you give some insight on how it is to work with?

 

[toodles]

PTFE is very soft and easy to machine on it's own. The Glass-filled version is significantly more rigid, but fairly easy to machine IMO. Much easier than UHMWPE or PEEK.

 

[Kanye West]

Treat it like steel basically. Slow revs/feed.

Is there any cutting fluid that would be better than the normal stuff for it?

 

[MobileChernobyl]

From what I remember of plastics UHMW is harder to machine than Delrin or nylon. I'm not sure how teflon fits into that. buildyourown, can you give some insight on how it is to work with?

UHMW(PE?) is extremely easy to turn and comes off in perfect ribbons, PFTE gets kinda waxy, never turned delrin but I hear it's fun to work with like UHMW. I got a few samples of IGUS's bushings last year and they are pretty nice.

 

[DirtMcGirk]

I myself like a bare bush.

 

[buildyourown]

It is very easy to machine. The glass filling indeed makes it more rigid, which means it deflects less under tool pressure.

Treat it like steel basically. Slow revs/feed.

Not really. Machine it dry, with high shear aluminum inserts.

 

[Kanye West]

Interesting. I'd have to check it out in person to make that call for sure. For any kind of super soft stuff that's usually my rule of thumb. Better slow than sorry.

 

[buildyourown]

Interesting. I'd have to check it out in person to make that call for sure. For any kind of super soft stuff that's usually my rule of thumb. Better slow than sorry.

Speed (RPM) is determined by the material's and tool's ability to resist the affects of heat. You run steel slow so you don't burn the tool. Switch to a solid carbide tool, and you can go faster. Run thru the tool coolant, and you can run faster still.
You can run plastic as fast as you want as long as it doesn't start to melt. Using a high shear tool keeps the heat in the chip. With thru tool coolant there really is no top end for speed.
On a lathe, speed is really dictated by the operators ability to manage the massive, stringy chip.

 

[ohio]

Funny reading all this... I designed a bike in 2000/01 to use PTFE bushings for the headset. Even more appropriate application since steer tubes don't turn enough to refresh the oil film on any kind of headset bearing especially under vibrations in a straight line.

edit: oh, and yes I recommend very slow speeds with PTFE... very easy to melt or burn. AND with the slow speeds, don't cut too much or it will deform and you'll lose precision (depending on the cuts you're making). Probably much easier with the glass-filled stuff BYO mentions above. Hard to screw up with a sharp tool though.

 

[MrPlow]

Ohio,
Did your PTFE headset work? Be a little heavy in the steering??