Wednesday, July 30, 2014

Downhills

A short post.  Niholas, with a confident rider and in the right situations, are surprisingly easy to drive very quickly downhill.  Well in this case "very" means perhaps 35-40km/hr, to speeds where the wind roars in the ears, and guys in stretch pants riding racing bikes can't pass a coasting trike without pedaling.  It basically gets easier the more weight is in the box, and the lower and more behind-the-front-axle that weight is.  A loaded Nihola goes down a hill like a cannon ball.  A 20kg kid or two really stabilizes things, and the trike runs smoothly through the corners and pavement imperfections, but an empty Nihola with well-pumped tires is a bit jittery.  I've pedaled (sprinted) to about 35km/hr (based on a GPS track) but generally at those speeds its best to concentrate on smooth driving, and plan well ahead in case it might be necessary to stop.  Definitely a good idea to remember that stopping takes a while.

Gravel downhills work great too, so long as the bumps are not large enough to start throwing people and trikes around.  The tires and frame can smooth out a half-decent gravel road very well with a kid or two in the box, and it just seems to get smoother with speed... just avoid washboard and holes.

Niholas are also great fun on downhills when there are slippery corners.  In this past winter I was doing three-wheel slides in the snow, and in the summer I have a time or two had the chance to push it to the limit on dirty pavement.  I can't recall going nuts on gravel but I think it could be fun too.  I've noticed that in the summer, when riding fast and using the back brake hard, it tends to have abrupt consequences on directional stability.  Its perhaps more fun to squeeze 100% out of the front brakes and corner until the inside tire starts sliding.

Oh, and my kids love speedbumps.

Sunday, July 20, 2014

Brakes

An unusual Nihola that was pictured on the French Nihola site.
The picture above shows a special Nihola.  It has disc brakes in front.  And it also is designed to carry pallets, which is a bit unusual.  But about those disc brakes.  Disc brakes are unfortunately not an option that be ordered on a Nihola by anyone who isn't willing to pay for custom fabrication.  Its easy to see why the Nihola company selected mild-mannered and inexpensive drum brakes up front when virtually all Niholas are sold in Copenhagen, where such brakes are sufficient, even optimal.  Notably the big competitor Christania Cycles does offer disc brakes, as does Bullitt.  There is certainly no need for the strength of disc brakes in Copenhagen, but they look good and who knows, maybe the maintenance isn't too bad.  Its a bit unfortunate, in my opinion, that the Nihola company doesn't offer to take people's money in trade for a disc brake option, because what is decorative in Copenhagen could be practical in Oslo.
Its hard to photograph a hill, but this was a good one.
Climbing out of a valley on route from H√łnefoss to Oslo.

So I should talk about how braking works on a Nihola.  The rear is either a coaster brake (foot brake) or a v-brake, but could in theory also be a different type of hub-mounted drum such as a roller brake (grease-filled drum from Shimano).  I estimate that there is zero possibility of a disc in the rear, the lack of mounts being a prominent problem, but also the shape of the frame appears incompatible, which is a shame because all the most interesting gear hubs are available with disc mounts.  Discs aren't perfect, but I'd take a disc over a rim brake on the rear wheel of a cargo bike.

Now, the rear brake doesn't necessarily need to be strong.  Ideally it is easy to modulate, to use whatever traction is available.  Foot brakes are not known for being strong, but are more than strong enough to skid the back tire on clean pavement (presuming no weight on the rear rack).  The reason that strength is not a problem is because of the significant forward weight transfer under hard braking, especially when weight is concentrated in the box, and also especially on downhill slopes.  This all is to say, the rear brake is generally of little use for quick stops.  This effect is more significant on a Nihola than a regular bike.

Regrettably, the brakes in front are also of little use for quick stops.  They are always 7cm Sturmey-Archer drums, a type of non-greased drum with a replaceable brake shoe.  One single-pull 4-finger lever pulls to a splitter which seeks to distribute force evenly between the left and right, or perhaps it just seeks to keep the cables to each side the same length.  There is, anyway, a splitter which has the potential to allow more cable to be pulled on one side than the other (this pulling is not smooth in my experience) and which has the potential to keep the cables to the front brakes roughly the same length.  It seems to me that the observable strength of the front brakes is usually mismatched if any particular strength can be observed at all, so the splitter is not an effective way to balance braking power.

The brakes, freshly adjusted, are strong enough that on flat ground, with an empty Nihola, I need to brace myself against the handlebar when doing a 100% stop.  Some exertion is required, but certainly no danger of going over the bars unless I could somehow brake without having my hands on them, and certainly no possibility of lifting the back tire off the ground.  Gradual and smooth is the idea.  This is mostly fine at reasonable speeds and on flat ground, but hills are more problematic.  By about 10% slope, I get the impression that the brakes are mostly there to prevent speed from increasing.  Stopping requires planning ahead.  The steeper the slope, the more planning ahead is required.  The brakes are sufficient to hold the trike in place to over 25%, which I suppose is evidence that stopping is possible at such a slope, but this will require the rear brake to be used without much skidding.  A skidding rear tire is not being very helpful.

Skidding the front tires is not easy to do.  The easiest way is to brake hard when turning sharp corners at speed.  Often, because the strength of the front brakes is likely imbalanced, this is possible turning one way and not the other.  About the only other time I've managed is when one brake arm is seized up, apparently causing the other brake to gain strength, which can skid a tire on gravel.  Load in the box makes skidding a lot harder.

The view on a day tour. 
Lots of people will say drums are a low-maintenance cycle brake, but I've spent plenty of time screwing around with the drums on my two Niholas since moving to Oslo.  Understandably, stopping 150kg of trike, cargo and rider on some of these hills can be demanding.  The brakes can easily get too hot to touch.  It rains, it snows, salt and/or other chemicals are sprayed around, there is sand and gravel, mud... sometimes I get plants caught up around the brakes, and often enough they stand outside in the weather.  Its true that little cleaning is required.  There is no particular seal on the brakes, just a design which makes it somewhat non-obvious for water to flow in.  Mostly that appears to get the job done, but if moisture enters, the brakes can be weaker while wet, and can rust a bit on the braking surface.  The rust wears off but appears to contribute to lumpy and/or squeaky braking.

Squeaking from the front brakes can be a major irritant, but can also be entirely nonexistant.  Its difficult for me to figure out what causes the squeaking or how it can be fixed.  Simply using the brakes more will only silence the squeaks until the brakes cool down again, and cleaning seems to have only a short-term effect, but sometimes the passage of time (or the change of weather) seems to change the squeaking situation.  I got though months of snow and melting this winter with perfectly quiet and predictable brake behavior for no reason I can see, although there was some squeaking a week or two after I tightened up front brake cables in the summer.  Squeaking is often associated with strong braking performance, but not always.  There is a possibility that getting the brakes very hot encourages squeaking the next time (next day) they are used.  Mysterious.

The center adjuster with its rubber cover pulled up.
So, maintenance.  The brake arms need to be lubed (drip or spray some oil at the base) or they will start to seize up, which can have interesting effects because it may start causing all cable movement to be "routed" to the easier-to-operate brake, in a crude way.  Definitely oil those arms.  Brake dust might need to be cleaned out from time to time.  Cable stretch and/or brake wear require the brake cable to be tightened, and this is the most interesting bit of service to perform.  For small adjustments, there is an adjuster in the center, above the splitter.  For big adjustments, I have found that the center adjuster should be slackened, the cable fastening bolts on each brake arm should be loosened, both brake arms should be fully engaged (full brake), and the fastening bolts should be tightened again.  So the brake arms are held some distance towards engagement permanently.  Surprisingly, this does not result in dragging brakes, merely a firm brake handle and optimized brake strength.  A brake handle which pulls up close to the handlebars indicates that braking strength could be improved.  In other words, it seems that more strength is delivered when the brakes engage early in the travel of the brake lever, even in the case of a brake lever that pulls a long way but does not touch the hand grip.  I don't know why that is, but the difference can be very noticeable.

The splitter, just a round thing that the brake cable is looped over.  Note center cable at the top.

An exposed brake, with the brake arm visible to the right.
A wrench being used to hold the brake arm fully engaged while the cable on the other side is fastened.
The drums behave strangely when asked to deliver 100%.  The strength seems to reach a certain level fairly easily, and then does not improve further, regardless of the force applied to the brake lever.  I expect that the cable liner running between the lever and the spitter has started to compress at that point.  Fitting a more compression-resistant section of cable liner could improve braking strength.  I've also been tempted to set up the left and right brakes with separate levers, using a foot brake for the rear.  This would have the potential to be a lot of fun on downhill corners.

I've noticed that Sturmey Archer makes a 9cm drum that almost fits on a Nihola, as far as I can tell from photos.  Certainly the Nihola company could make it fit with a small alteration to the piece of metal that is tasked with anchoring the top of the brake's back plate and the fender.  I imagine the 9cm drum would be stronger for the same cable tension, longer lasting, slower to heat, and make for a stiffer wheel (the front wheels have a hard life).

Anyway the brakes on a Nihola are probably the weakest link for 'ambitious' owners.

Gear hub madness

Today I came across a good description of how the new SRAM G8 hub works, and I worked through the ratios in a spreadsheet. Its a strange hub and it took me a while to figure out what was going on, even when someone had already attempted to explain it. This got me thinking about another difficult nut to crack, the Alfine 11.

As far as I can determine, no one has done a teardown of an Alfine 11, counted the teeth, or posted any particular information about how its ratios are created.  In the past, I've thought it was quite similar in design to a Nexus 7, but now I've changed my mind.  However before that, lets go on a tour of gear ratios in hubs.

Gear hubs are made up of planetary gear sets: http://en.wikipedia.org/wiki/Epicyclic_gearing

Generic three speed:

The most basic hubs have one gear set, giving three speeds.  In the middle there is direct drive, then one ratio increased and one ratio decreased (the inverse of the increased ratio).

gear 1 2 3
ratio 0,750 1,000 1,333
ratio change 33 % 33 %
name 1/A - A
calculated ratio 0,750 1,000 1,333

SRAM P5:

This was extended to make 5 speeds such as the SRAM P5 by placing two gear sets into one module, so that one of two ratios could be used at a time, either up or down.

gear 1 2 3 4 5
ratio 0,633 0,781 1,000 1,281 1,579
ratio change 23 % 28 % 28 % 23 %
name 1/A 1/B - B A
calculated ratio 0,633 0,781 1,000 1,281 1,579

SRAM S7:

This also worked for 7 speeds, such as the SRAM S7.

gear 1 2 3 4 5 6 7
ratio 0,574 0,677 0,809 1,000 1,236 1,476 1,742
ratio change 18 % 19 % 24 % 24 % 19 % 18 %
name 1/A 1/B 1/C - C B A
calculated ratio 0,574 0,678 0,809 1,000 1,236 1,476 1,742

SRAM i-Motion 9:

It even worked for a 9 speed, the i-Motion 9.  This hub was basically a failure on the market, apparently because it was too heavy, rough running, expensive, and poorly sealed against weather.  However it was apparently well constructed, and it did achieve 9 tight and evenly-spaced ratios while using only one planetary gear at a time, potentially giving high efficiency.  I think its a shame it didn't make it.

gear 1 2 3 4 5 6 7 8 9
ratio 0,542 0,621 0,727 0,853 1,000 1,172 1,375 1,611 1,844
ratio change 15 % 17 % 17 % 17 % 17 % 17 % 17 % 14 %
name 1/A 1/B 1/C 1/D - D C B A
calculated ratio 0,542 0,621 0,727 0,853 1,000 1,172 1,375 1,611 1,844

Shimano Nexus 4:

But there are other fun things that might be done.  Consider a Nexus 4, which made four ratios from a set of three planetary gears, by only increasing ratios.  Leaving out the ability to decrease ratios simplified the hub.  This simplification, where each planetary gear is only used to either increase or decrease ratio but not both, is a major theme of all recent hubs.  There i-Motion 9 above might well have needed only 4 planetary gears to get 9 beautiful-looking ratios, but those 4 gears were too complicated.

gear 1 2 3 4
ratio 1,000 1,244 1,500 1,843
ratio change 24 % 21 % 23 %
name - A B C
calculated ratio 1,000 1,244 1,500 1,843

Shimano Nexus 5:

But all these hubs have fairly large steps between the gears.  Especially the gap between direct drive and the first ratio up or down was problematic.  While i-Motion 9 got this down to 17%, it was apparently unpleasant.  Even the 22% gap on Nexus 8 leads to some gear whine.  So Shimano got busy with dual-stage compounding its planetary gear sets.  Below is the Nexus 5, which used three planetary gears in two sets, and has no direct drive ratio at all, but is very smooth in my experience.

gear 1 2 3 4 5
ratio 0,750 1,001 1,159 1,335 1,545
ratio change 33 % 16 % 15 % 16 %
name 1/A B/A C/A B C
calculated ratio 0,750 1,001 1,159 1,335 1,545

Shimano Nexus 7:

The Nexus 7 is similar, but with four planetary gears arranged in two sets.  I've used two of these extensively and never been satisfied with either their smoothness or efficiency, but they seem to sell in vast quantities in Denmark.

gear 1 2 3 4 5 6 7
ratio 0,632 0,741 0,843 0,989 1,145 1,335 1,545
ratio change 17 % 14 % 17 % 16 % 17 % 16 %
name 1/A 1/B C/A C/B D/B C D
calculated ratio 0,632 0,741 0,844 0,989 1,145 1,335 1,545

Shimano Nexus 8 / Shimano Alfine 8:

But thats not the only way to do multi-stage compounding.  The Nexus/Alfine 8 is a lot like the old Nexus 4 with a new planetary gear enabling the four original ratios to be used twice.  This leaves a direct drive gear in place which is good, but creates an odd situation where the least efficient gear (4) is right next to the most efficient (5), and switching between the "high" and "low" gears can be problematic.  Still, this seems to be a robust design.

gear 1 2 3 4 5 6 7 8
ratio 0,527 0,644 0,748 0,851 1,000 1,223 1,419 1,615
ratio change 22 % 16 % 14 % 18 % 22 % 16 % 14 %
name 1/A B/A C/A D/A - B C D
calculated ratio 0,527 0,645 0,748 0,851 1,000 1,223 1,419 1,615

Rohloff:

And then there is the monsterous 14 speed Rohloff, that uses 5 planetary gears in three sets.  Gears 3 and 5 actually use triple-stage compounding, which is hard to notice in my experience.  In some ways this combines concepts which are found on both Nexus 7 and Nexus 8, sort of a combination of those designs.

gear 1 2 3 4 5 6 7 8 9 10 11 12 13 14
ratio 0,279 0,316 0,360 0,409 0,464 0,528 0,600 0,682 0,774 0,881 1,000 1,135 1,292 1,467
ratio change 13 % 14 % 14 % 13 % 14 % 14 % 14 % 13 % 14 % 14 % 14 % 14 % 14 %
name 1/B * 1/A 1/C * 1/A D/B * 1/A 1/A E/C * 1/A D/A E/A 1/B 1/C D/B - E/C D E
calculated ratio 0,279 0,317 0,360 0,409 0,464 0,528 0,600 0,682 0,774 0,881 1,000 1,135 1,292 1,467

SRAM G8:

Here is the SRAM G8 in all its confusing glory.  Five planetary gears in two sets, sort of arranged like a backwards Nexus/Alfine 8.  No direct drive, and 6 of the 8 ratios are two-stage compounded.  http://sheldonbrown.com/sram-g8.html

gear 1 2 3 4 5 6 7 8
ratio 0,609 0,710 0,803 0,903 1,054 1,204 1,355 1,581
ratio change 17 % 13 % 12 % 17 % 14 % 13 % 17 %
name 1/B 1/C E/A E/B E/C D/A D/B D/C 1/A D E
calculated ratio 0,609 0,710 0,803 0,904 1,054 1,204 1,356 1,580 0,5411 2,2258 1,4839

Shimano Alfine 11:

Then finally we get to the Alfine 11.  I spent some time on this.  There are lots of ways to make a good approximation of the published ratios, but the way I am most satisfied with uses four planetary gears arranged in three sets.  The main difference between this and Nexus/Alfine 8 is that one gear (number 7) is able to combine with gears 8 and 9 to create ratios 10 and 11.  Then all those resulting 5 ratios are re-used in positions 2-6.  This very nicely explains the 29.2% gap between gears 1 and 2... its same ratio as gear 7 has.  This also has no planetary gears which are used to both increase and decrease ratios, which appears to be very much out of style, it explains the alternating 13% and 14% ratio changes, and it explains how the 11 speed is able to match the weight of the 8 speed.  Essentially, the same number and strength of gears needed to be used.

There is no direct drive ratio, which is instead replaced by a triple-compound approximation, I imagine to achieve mechanical simplicity.  The only difference between 2-6 and 7-11 is whether or not the "low range gear" is active.

gear 1 2 3 4 5 6 7 8 9 10 11
ratio 0,527 0,681 0,770 0,878 0,995 1,134 1,292 1,462 1,667 1,888 2,153
ratio change 29,2 % 13,1 % 14,0 % 13,3 % 14,0 % 13,9 % 13,2 % 14,0 % 13,3 % 14,0 %
name 1/A B/A C/A D/A (B*C)/A (B*D)/A B C D B*C B*D
calculated ratio 0,527 0,681 0,770 0,879 0,995 1,135 1,292 1,462 1,667 1,889 2,154

Further reading, here is the grand daddy of complicated bike gear hubs: http://sheldonbrown.com/elanratios.html