SRAM A2 Automatix; introduction to the internals

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Brucey
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Re: SRAM A2 Automatix; introduction to the internals

Postby Brucey » 3 Nov 2012, 7:23pm

skankingbiker wrote:Newbie here. Joined this forum because this is the only place I could find where this hub is discussed. I am trying to find the build dimensions for the hub. None of the SRAM literature has the necessary information to calculate spoke length.

Does anyone have the build dimensions handy or know where I can obtain them?

Much thanks.


flange diameter 70mm, flange spacing 53mm, dish variable (but small, so the same length each side is usually OK)

cheers
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AW_hub
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Re: SRAM A2 Automatix; introduction to the internals

Postby AW_hub » 30 Dec 2012, 7:09am

Brucey, excellent description and photographs of the SRAM Automatix.
I have a few comments:

Sealing against winter weather was never one of SRAM (nee Sachs) strong points for hub gears. You'd think it never rained in Schweinfurt.

I have dismantled several Sachs T3 3 speeds ruined by water ingress (balls rusted, cage corroded and broken up.
Never seen that extent in the many Sturmey Archer AW's I have dismantled - so I have to disagree that the Automatix sealing is no worse than the AW. The AW uses a very ingenious double labyrinth seal on all 3 ball bearings, they knew about rain in 1936..

Sachs/SRAM on the other hand always leave the bearing cone exposed - you can even see the balls if you look closely from the outside. I dismantled an Automatix on the weekend after reading your review, it was the freewheel version. I was impressed with the overall design, and having your review helped me understand its operation. But it was very disappointing on the weather sealing - people buy a hub gear over a derailleur for weather-proof operation, amongst other things.

I agree the lube inside was sparse. There is little doubt it would benefit from having an oiler tapped into the hub shell, say a nylon Sturmey Archer AW one (readily available). This would have the added benefit of flushing metal swarf and dirt out from the hub over time, and keeping water out despite the poor sealing. Thin SAE 20 oil of course.

The question is - where along the hub? I have an old Sachs Duomatic from 1968 with its OEM hub oiler that should give some clues.

Dyno studies done near Seattle in 2001 by Frank Berto showed oil lubed Sturmey Archer AW's and Sachs T3's were the most efficient epicyclics, comparable to deraileurs. The grease-lubed Shimano 4 speed hub tested was terrible.

Brucey
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Re: SRAM A2 Automatix; introduction to the internals

Postby Brucey » 30 Dec 2012, 10:27am

AW_hub wrote:Brucey, excellent description and photographs of the SRAM Automatix.
I have a few comments:

Sealing against winter weather was never one of SRAM (nee Sachs) strong points for hub gears. You'd think it never rained in Schweinfurt.

I have dismantled several Sachs T3 3 speeds ruined by water ingress (balls rusted, cage corroded and broken up.
Never seen that extent in the many Sturmey Archer AW's I have dismantled - so I have to disagree that the Automatix sealing is no worse than the AW. The AW uses a very ingenious double labyrinth seal on all 3 ball bearings, they knew about rain in 1936..

Sachs/SRAM on the other hand always leave the bearing cone exposed - you can even see the balls if you look closely from the outside. I dismantled an Automatix on the weekend after reading your review, it was the freewheel version. I was impressed with the overall design, and having your review helped me understand its operation. But it was very disappointing on the weather sealing - people buy a hub gear over a derailleur for weather-proof operation, amongst other things.


Older AWs have two shields for the ball-ring, and as you say labyrinths on the cones. This arrangement is not 100% waterproof! It functions OK with oil lubrication in part because the oil film heals itself as soon as the hub is used, older type oils also decompose over time to give a 'varnish' that helps to protect the surfaces, and any water that gets into the bearings is expelled as the oil (inevitably) comes out in use. If such hubs are not used regularly and still see rain, water usually penetrates the ball-ring and causes corrosion. I am experimenting with an upgraded seal for this part, which includes a contact seal. Modern AWs have a plastic retainer in the ball-ring, a single shield, and one of the lips on the ball-ring has been deleted. All of this significantly degrades the sealing vs the older design. Despite often not having a labyrinth on the main cones (just a close-fitting dustcap) SRAM hubs are also most vulnerable at the ball-ring, as you say; modern ones should be fitted with a shield at this point, behind the sprocket, similar to SA hubs, although it is often missing, presumably either overlooked or removed following damage in service. The net result is that a modern (greased) AW has ball-ring sealing that is comparable to modern SRAM hubs. Even the SA labyrinth seals don't work as well as they used to; the use of grease rather than oil means that the seal surfaces can lose their coating of oil/grease and it doesn't heal itself (although chain lube overspill might help). Once the surfaces in the labyrinth are no longer hydrophobic (as they usually are because of the oil coating), water gets in more easily.

I agree that the sealing on many modern IGHs leaves plenty to be desired, and that the mess and routine topping up required with a total loss hub might well be a more acceptable compromise in the long term.

I am experimenting with the use of a generous fill of a thixotropic semi-fluid grease in some SA hubs at present. This requires that the ball-ring seal is upgraded to retain the lubricant in use, and on brake hubs, the left side seal should be upgraded to a full contact seal also to prevent brake contamination. On non-brake hubs it isn't necessary to revise the labyrinth seals on the main comes because there is some 'total loss' of the SF grease. Contamination of the SF grease is less of a worry than with standard grease; for a start there is more of it (the way I'm doing it) so there is more dilution of any crud and in addition there is still some total loss to remove it. So far the mess from the total loss is comparable with that from the chain lube anyway, so it is looking good to date.

I agree the lube inside was sparse. There is little doubt it would benefit from having an oiler tapped into the hub shell, say a nylon Sturmey Archer AW one (readily available). This would have the added benefit of flushing metal swarf and dirt out from the hub over time, and keeping water out despite the poor sealing. Thin SAE 20 oil of course.

The question is - where along the hub? I have an old Sachs Duomatic from 1968 with its OEM hub oiler that should give some clues.
Possibly nowhere; you may find that in hubshells that are hardened locally for ballraces -and I think the SRAM may be one such- the hubshell is hardened all over, and cannot be drilled easily. Do let us know how you get on if you try this.

Dyno studies done near Seattle in 2001 by Frank Berto showed oil lubed Sturmey Archer AW's and Sachs T3's were the most efficient epicyclics, comparable to deraileurs. The grease-lubed Shimano 4 speed hub tested was terrible.


IIRC others have questioned the methodology of these tests, although I thought -with a few caveats- that it looked OK for what it was. The three-speed gears were, unlike all the other gears tested, very well-used. I think the doubters suspect that in these tests the average torque was much lower than the peak torque seen in real-world use; this tends to favour gears with low LIL (load independent losses) rather than gears with appreciable LIL even if the LDL (load dependent losses) are possibly not as good in the low LIL gears. Grease-lubricated hubs, and hubs with contact seals, drag springs etc have higher LIL, and a four-speed shimano hub also has a double gear train for poor LDL in some gears. If it wasn't run in either, the net result was predictable. Note that Rohloff tests gear efficiency at a high torque, comparable to peak torque when pedalling. (Although this aspect of their testing is more representative, I can cheerfully pick holes in their test data in other ways).

As torque increases, at some point the use of low viscosity oil will allow metal-to-metal contact in bushings and the LDL figures will probably creep up. That there is some contact is obvious; the parts wear and continue to wear for the life of the hub. I believe that the use of slightly thicker lubricants with solid lubricant and extreme pressure additives (proven to reduce wear in highly loaded gear trains) may also reduce LDL at high torque values, although I have no means of demonstrating this.

BTW one obvious point is that IGH's with a 'normal' direct drive gear are intrinsically efficient overall, even if the other gears are not efficient per se; this is because most people ride mostly in the 'normal' gear. In extremis, a (say) ridiculous 25% loss in a gear you only use 5% of the time would only contribute a 1.25% loss overall, for example. The SA three-speed became popular in the first place in part because of this simple fact, and I still set my gearing on my SA-five speeds to exploit this, even though arguably there is a very high top gear and another lower gear might be more useful. Both current SA and SRAM two-speed gears, as well as Shimano 4-speed etc are 'gear-up' hubs and ignore this possibility; they leave gear trains in operation to sap more power than is necessary in 'normal' gears (assuming that the gear range is set to favour climbing gears over 'higher than normal' gears).

The Rohloff at least has the direct drive gear set where it will do most good for most people.

cheers
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hamish
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Re: SRAM A2 Automatix; introduction to the internals

Postby hamish » 30 Dec 2012, 1:48pm

The interesting thing about the Rohloff is that I know there is a direct drive gear there somewhere but I can't tell where it is in normal use. This is because I forget which gear I am in, can't see the numbers on the shifter and can't remember which is direct drive anyway. It also suggests that I don't notice the efficiency drop either side of The direct drive gear.

Brucey
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Re: SRAM A2 Automatix; introduction to the internals

Postby Brucey » 30 Dec 2012, 6:04pm

the Rohloff is configured as a conventional seven speed gear (i.e. middle normal) fitted with an additional gear train to give a further set of seven lower ratios which do not overlap the first set. Thus ratios 1-7 duplicate 8-14 but at a fixed fraction of those ratios. Gear 11 is the direct drive gear; gear 10 and gear 12 both use two planetary gear trains so lose a couple of percent (they say) whereas gears 8,9, 13,14 use one gear train each and are slightly more efficient.

Image

Other gear trains may well be a lot less efficient than this; also note that when others test Rohloff gears, they usually get lower efficiency figures than this.

cheers
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hamish
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Re: SRAM A2 Automatix; introduction to the internals

Postby hamish » 30 Dec 2012, 6:46pm

That is interesting then. If the gears either side of direct drive are less efficient than the ones two steps away, me not noticing much difference is a sign that I am not troubled by lack of efficiency. If you see what I mean!

The lower gears can make a noise. But if I ride with headphones in then I hardly notice those either.

I must admit though, that when I ride a derailleur bike I do enjoy the quietness of the very low gears. When I ride my rohloff I enjoy the quietness of the higher gears.

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NATURAL ANKLING
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Re: SRAM A2 Automatix; introduction to the internals

Postby NATURAL ANKLING » 30 Dec 2012, 8:22pm

hamish wrote:That is interesting then. If the gears either side of direct drive are less efficient than the ones two steps away, me not noticing much difference is a sign that I am not troubled by lack of efficiency. If you see what I mean!

Hi,
I think that NOBODY is going to notice a drop in effeciency of 1.5 % on either side of the direct drive gear :?:
When you consider that Individual effeciency wich would include also your individual cadence and heart rate at that time play a larger part :?:
So these fiqures are for interest only and mere academic :?:
All interesting for the enthusiast and the budding engineer, I am interested too.
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hamish
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Re: SRAM A2 Automatix; introduction to the internals

Postby hamish » 30 Dec 2012, 9:15pm

I think that NOBODY is going to notice a drop in effeciency of 1.5 % on either side of the direct drive gear


:) yes of course, but you often hear it said that the hub is less efficient than claimed and some people say they can really feel the drag. If we accept that the losses in direct drive are minimal, in my experience the losses on the other higher gears seem to be fairly low too.

Just got me thinking that's all. But I guess we could do without another Rohloff hub debate :wink:

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NATURAL ANKLING
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Re: SRAM A2 Automatix; introduction to the internals

Postby NATURAL ANKLING » 30 Dec 2012, 10:24pm

hamish wrote:
I think that NOBODY is going to notice a drop in effeciency of 1.5 % on either side of the direct drive gear

:) yes of course, but you often hear it said that the hub is less efficient than claimed and some people say they can really feel the drag. If we accept that the losses in direct drive are minimal, in my experience the losses on the other higher gears seem to be fairly low too.
Just got me thinking that's all. But I guess we could do without another Rohloff hub debate :wink:

Hi,
Interesting to see the hub geared superimposed on the derallier. ( Dark shading is derralier, light is hub geared, width of bands are optimum (clean lubed) and 1000 km real dirty conditions) Figure 4 is actually Brucey's already posted diagram hub geared.
http://www.rohloff.de/en/technology/spe ... index.html
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Brucey
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Re: SRAM A2 Automatix; introduction to the internals

Postby Brucey » 30 Dec 2012, 11:05pm

we are going OT here but this highlights some of the issues I have with the Rohloff data. In gear 11 the Rohloff is 'more efficient' than the derailleur geared setup.

Ah, but is it?

Uh... sort of.... the data point for the derailleur gear at this point is a middle-small (i.e. cross-chained in this case 36/12) gear. As are some adjacent ones. Rohloff 'assumed' (I suppose... :roll: ) that a rider using triple would use all the sprockets on the middle chainring before bothering to double-shift. So the Rohloff uses a 46 x 16 gear; however even though an identical gear (46/16) is available in the derailleur gear set-up, there is no data point for it....

As a long-time user of hub gears and an advocate of them (over derailleurs, which I also use...) for some purposes I know they have advantages that outweigh one or two percent here and there. It therefore pains me to say that here, Rohloff's data looks like a bit like a 'dodgy dossier' to me; concocted to support a hypothesis.

cheers
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NATURAL ANKLING
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Re: SRAM A2 Automatix; introduction to the internals

Postby NATURAL ANKLING » 30 Dec 2012, 11:57pm

Brucey wrote:we are going OT here but this highlights some of the issues I have with the Rohloff data. In gear 11 the Rohloff is 'more efficient' than the derailleur geared setup.
Ah, but is it?
Uh... sort of.... the data point for the derailleur gear at this point is a middle-small (i.e. cross-chained in this case 36/12) gear. As are some adjacent ones. Rohloff 'assumed' (I suppose... :roll: ) that a rider using triple would use all the sprockets on the middle chainring before bothering to double-shift. So the Rohloff uses a 46 x 16 gear; however even though an identical gear (46/16) is available in the derailleur gear set-up, there is no data point for it....cheers

Hi,
Nicely spotted :wink: Yes a bit OT, in suport they do mention in conclusion same page that it is very indepth and relies on much inputs.
I get your point on the selection of far small cog , cross chained, I have not studied info that long, my only experience so far was my 3 speed sturmey archer in the seventies :!: They also mention chain wear about same subject in their chain section :!:
Marketing I suppose. If we were to ignore the marketing jiggery pokery, then interestingly the sharp peaks and troughs in the hub geared, almost represent an effect of chainging from a new chain to a worn chain every time you change gear, As you have said adding extra gears in the train accounts for the drop in effeciency. Seems that a crude chain still is impresive :!: If you then studied the actual area on ineffeceincy and summed up on the power lost here that would be more considerable :?: I think you covered that earlier.
If I could afford the hub stuff I would like a try. Round world cyclist after wrecking a derralier on route went then for multi position bars and Hub Geared on later trips, Maintenance cutting winning here.
Cheers.
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michael432000
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Re: SRAM A2 Automatix; introduction to the internals

Postby michael432000 » 15 Jan 2013, 9:24pm

Hi there!

Complete hub gear novice here. I’ve never used a hub gear and probably won’t in the future unless they can really lighten them up.

However, I recently purchased a second hand bike, it was the frame I was interested in, and it came with one of these SRAM 2 speed auto hubs with a coaster brake. I can see the appeal for a certain style riding and I intend to keep it running for a while until the warmer weather comes.

It runs ok but with the wheel off the bike it doesn’t spin too brilliantly so I will take it apart at the weekend thanks to the information that people here have provided. I have a tube of Exus blue lube system grease, will that do or I should I use some ordinary stuff from my workplace?

Also, the sprocket and dust cover is loose. Can’t see how to tighten it. Looks like a C spanner wrench and maybe a clip of some sort behind it.

Thought I would ask in advance just in case there was anything I should know.

Thank you.

Brucey
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Re: SRAM A2 Automatix; introduction to the internals

Postby Brucey » 15 Jan 2013, 9:35pm

there are drag springs inside the hub so don't expect campagnolo-levels of smoothness even at best. Don't expect to be able to strip the hub down without the right spanners, either (see the original post; you need at least one thin 22mm spanner).

Re the sprocket; it is retained by a spring clip, along with the dust shield. These are never super tight, but if they are so loose they rattle, chances are that the clip isn't fitted correctly.

[edit; I thought there were spacers as well as a sprocket fitted to this hub; there are not. The dust shield, the sprocket, and the spring clip are all that are fitted to the sprocket carrier. If it rattles (e.g. because a thinner than normal sprocket is fitted, add a spacer.

Note also that the drag spring drags more going backwards than forwards. Typically the difference drag forwards vs backwards is about half the total drag spring force.

The SRAM hub feels heavy in your hand but it is replacing a lot of kit; potentially a hub, a freewheel, a derailleur, a longer chain, a gear control system, a brake caliper, a brake cable plus fittings, and a brake lever. All that lot adds up. If two gears and no cables is your bag, I don't think you will necessarily be a lot worse off, weight wise. The rim can be lighter in weight if needs be, since it won't ever wear out through the workings of a rim brake.]

Any grease is better than none BTW! The only place you don't want thick grease is on the gear control mechansim; here a thinner lube is better.

cheers
Last edited by Brucey on 15 Jan 2013, 9:52pm, edited 2 times in total.
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michael432000
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Re: SRAM A2 Automatix; introduction to the internals

Postby michael432000 » 15 Jan 2013, 9:48pm

Thank you so much for your quick response. I will make myself a 22mm flat wrench spanner and take a good look at the weekend.

Updated information noted and appreciated, thank you again.

michael432000
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Re: SRAM A2 Automatix; introduction to the internals

Postby michael432000 » 19 Jan 2013, 2:15pm

Considering I purchased the bike second hand, the innards are quite clean with more grease than I expected.

I’m pretty sure that the spring shift point has already been adjusted because on 20” wheels and with a 52/16 gear I am able to reach a sensible speed (if I accelerate slowly and smoothly) before the gear changes up, more than 15mph I think.

However, because my commute is flat and I like to spin a small gear really fast before going to a higher gear, the change is still way too early. I am also going to change to an 18T sprocket that will make the current change point even sooner.

So the question is: will I be able to make a big enough adjustment to the spring to get more like 25mph?

That spring and circlip sure are small. The spring appears to go through the pawl control plate but I can’t see where the end of the spring rests to retain tension, which is deterring me from making the adjustment.

If I mess it up then maybe it could be temporarily bodged by somehow binding/taping around the outside of the weights to keep them from opening thus leaving at least the lower gear operational. Please don’t laugh. I even thought of putting a rubber type band around the outside of the weights to control the opening with the band tension but it would probably interfere with the casing. Please, stop laughing.