A few members on BikeGuide have started discussing how to improve axial coasters. The idea is to come up with a design that can be easily made and will at least improve the issues faced with axial freecoasters. Here are some requirements (see the thread for more details):
Low cost (i.e. using as many existing components as possible)
Low(er) weight; sub 20 oz
Suitable for peg use, not necessarily abuse.
Better bearing system, especially in the driver
Easy, and safe maintenance (i.e. no little pieces to damage)
If you have suggestions, or would just like to participate in the process, please post your comments in the BG thread, or here and I will forward to the thread. Once we come up with something suitable, I will post the dimensions, CAD files, and any other info on BMX-U.
Over the past 5 years, KHE’s freecoaster system has taken over the niche market. This was not because their product is the best we can do, but it is better than other options that were available (see my post on radial vs. axial freecoaster systems). In this post we will look at how the KHE system has evolved in its lifespan.
In the beginning was the Geisha. It offered a stud system (EAS) that allowed easy changing between 3/8” and 14mm in three different materials. That’s right, when it first came out, there were aluminum, steel, and titanium studs. They even went so far as to have a hybrid aluminum/steel clutch in their flatland version. The major advantage of the KHE was it’s ball-spring resistor, and low weight (Poverty coasters had the same resistor with a roller thrust bearing behind the clutch. But the resistor was eventually welded into place and the hub was pretty heavy in comparison)
Quickly after their initial run, the aluminum and ti studs, as well as the hybrid clutch were discontinued. To most people, this didn’t matter as the studs would unscrew with the axle regardless of material. Many would have preferred to use a bolt-on system (female axle), but KHE used a 3/8-26 thread in the aluminum spindle, which is very difficult to find bolts for. Blue6 now sells a bolt-on conversion kit for the KHE EAS system with titanium bolts and aluminum collars.
Now I am not sure if this next change came before the 1-piece axle or after, but it was an improvement none the less. KHE replaced the brass ball retainers with steel. Again, most people were unaffected, but to KHE’s defense, it was an attempt to fix the issue of customers tapping their axles out the wrong way (to remove any KHE axle, tap the drive side). Unfortunately, some people, when they encounter resistance, just hit the axle harder. Thus, customers still damage the retainers, and must purchase a new axle to replace them. I was always a bit annoyed that they didn’t make the retainers themselves available for the customers who damage them.
The next change marks the inflection point; when all of a sudden KHE took over the market, expanding horizontally to prevent competition. They finally came out with a 1-piece steel axle just before releasing the Federal and Reverse freecoasters. Both hubs were the same, but with different hubshells, and marketed under different brands. They both featured steel-one piece axle, but at a 4 ozweight penalty.
At this point, the Odyssey Reloader was out of the market, and the Poverty was rumored to be on it’s last run. KHE looked to fill the niche. They introduced LHD versions of both the Federal and Reverse. In order to do so, they would have to replace the threaded engagement ring with a splined one (if you run a threaded hubshell with LHD driver and clutch, the engagement ring will unscrew).There have been some issues with the splined ring coming loose, either by initial fit or compression of the aluminum splines. If you have this issue, retaining compound or JB Weld on the splines will fix it.
Some customers had issues blowing out the drive-side hubshell bearing. KHE attempted to fix this by switching the 6905 deep groove bearing with a 7905 angular contact bearing. Although not yet confirmed, it is believed the 7905 they are using is a 15 degree contact angle. Even this modest change can make a difference to someone who persistently blows out their drive side bearing. Unfortunately, the bearing seat is too thin to allow it to be bored out to accept an angular contact roller bearing, which would eliminate the issue all together (see Rob Ridge’s modified Reloader).
The drive side hubshell bearing was small potatoes compared to the driver bearing issues inherent in axial coaster systems (especially those with smaller drivers, unsealed bearings, and 14mm axles). KHE’s first attempt to resolve this issue was in the switch to steel in their 1-piece axle. The hope was that steel would better resist deformation of the measly 0.5mm bearing shoulder on the axle. It didn’t work. Their next attempt was to install a thrust bushing behind the 6902 bearings in the driver. I do not know how this has affected the number of driver bearing issues, but can’t help see it as an attempt to again fix the symptom (blown bearings) rather than the problem (axial wheel loads on the driver bearings).
Their most recent attempt to fix the driver issue was to have a custom bearing made by reducing the inner diameter from 15mm to 14mm. This gives a 1.5mm shoulder as opposed to a 0.5mm one. Although I like that they are addressing the issue, custom bearings always create headaches (such as buying a new axle that won’t work with your existing bearings). And again, it is not a proper solution to the underlying problem.
And finally, the one I skipped: somewhere along the line, KHE made a modification to the 1-piece axle to allow external slack adjustment. This was the first coaster to do so. It uses a simple screw attached to the internal stop-washer. A nice improvement indeed, but I have felt no inclination to change my slack, once set to my preference, in any of the coasters I have ridden.
So what can you take out of all of this?
KHE has made incremental improvements in their design over the years. This extends the lifespan of the product line.
KHE has committed to their system by expanding horizontally, now having 5 production models as nearly 50% of coasters currently available (Astern, Geisha lt, Reverse, Federal, Alienation).
Pushing KHE to make specific improvements may actually manifest them. Though look for incremental change, as they will likely milk this system for as long as they can before releasing something new (I hope they are working on a radial system, since they are still the only company to have released one, even if it was a failure).
Ok, this should apply to all KHE Clone coasters, as well as Odyssey and other "butterfly spring" coasters (though they may have different room in the hubshell. However, if you have an externally adjustable hub, you will just have to measure by backpedalling 1 revolution to 0* (or 90, whatever works for you), then pedaling forward and guestimating. Note: You cannot get 90* slack on these hubs, even with a relatively low 2.5 gearing and min spacers!
Driver/clutch thread pitch: 15mm per rotation (23mm/1.53 total)
KHE Spacer thickness: 1mm
Tophat Spacer: 5/7.5mm depending on orientation.
X= Total spacer stack (i.e. tophat set regular 7.5mm + 1mm spacer = 8.5)
G= Gear Ratio or Chainwheel (sprocket) size / Driver size (i.e. 25/9= 2.78)
( 12.7 - X ) / 15 * 360 / G = Degrees slack at pedals*
Essentially, there are two styles of clutches: Axial Clutches and Radial Clutches. The differing characteristic being The direction the clutch moves, along the axle, or radially out.
The majority of clutches are axial because of the system offers. For the purposes of this analysis, axial clutches can further be broken down into sub catagories:
Push type clutches push the clutch from driver to hubshell (only stock ones I know of are the Sym Hub and the Stolen/Chosen.
Pull type clutches pull the clutch toward the hubshell and driver (Geisha, reloader, etc)
An inherent characteristic of the axial mechanism is side load on the bearings. Push systems side load both the driver bearing(s) and one of the hubshell bearings. Which bearing is loaded is dependent on whether the push mechanism is located between the hubshell bearings, or outside the bearings.
Axial-outside-push system (sym-hub)
Welding two clutches together work to convert to a LHD-axial-inside-push system (modified taska)
In Contrast, pull type systems only load the drive-side-hubshell bearing. In all unsealed and some sealed hubs (such as the KHE Reverse ACB), the balls contact the races at an angle, which supports side loads much better.
Axial-inside-pull system (KHE Geisha)
In hubs where the drive-side-hubshell bearing rests on the driver, not the axel, the driver bearings must withstand sideloads from axial wheel loads (i.e. when whipping and the wheel lands at a funny angle). Repeated impacts can cause damage to the drive bearings. Interestingly, unsealed hubs are much less likely to have damage to the bearings. This is due to the angular contact that the cup and cone system provides.
Radial Clutches
Radial clutches are much less comon. The only two I can think of are the KHE Rollex, and the yet to be produced, G-sport Coaster*. The former uses roller bearings and ramps, while the G-coaster uses a cam mechanism and, what can be compared to brake shoes.
The major advantage of radial clutches are they do not interfere with the hubsell bearings, and no sideload is on the driver bearing (unless you are pedaling really hard while landing a tailwhip at a funny angle). These systems avoid the major durrability issues that are all too common in coasters.
We must, of course, note a potential issue of radial clutches: contamination of the freecoaster mechanism. Any hubs that come out with a radial system will have to make sure a good sealing system is in place.
KHE Rollex Explosion
* George from G-sport confirmed that he is still working on the coaster. Seeing how the rollex never quite succeeded, it's probably a good thing he is taking his time.
