Is an 8 speed hub less efficient?

[mulleady]

Hub gears are generally a superior solution for a folding bike: the gears are protected inside the hub housing, making them easy to maintain and avoiding the problems caused to derailleur systems by dirt, rain and the odd knock. Our gearing options mainly revolve around the reliable, compact and efficient 3-speed hubs perfected over many decades by Sturmey Archer and SRAM. Other hub gears on the market offer more gears but do so at the expense of efficiency; without getting too technical, the three gears in our hubs are achieved through one set of planetary pinions [rotors], whereas, for example, the leading 8-speed hub on the market channels the cyclist's energy through three sets of pinions, inevitably resulting in greater energy loss (Source: Brompton website FAQ)

Is the above true? Would this mean I'm wasting £200 on an 8 speed hub mod for the Brompton that I plan to order from Kinetics in the UK and would the 3 speed option be a better choice? I don't fancy the 6 speed gear controls on the Brompton handlebars.

[folder fanatic]

(Source: Brompton website FAQ)

Is the above true? Would this mean I'm wasting £200 on an 8 speed hub mod for the Brompton that I plan to order from Kinetics in the UK and would the 3 speed option be a better choice? I don't fancy the 6 speed gear controls on the Brompton handlebars.

Compared to whom or to what? I do agree the 6 speed gear controls on the more geared ranged Bromptons are a bit overcrowded on the handlebars. I tried one demostrator when I actually purchased my own Brompton. While I was impressed by the wider choice of gears, I did prefer the simplicity of the AW 3 speeds to a multi-shifting one. I am planning to buy one when I have the opportunity in the future. The only modification I would do is add grip shifters on both handlebars. And practice to relearn to using a dual shifting bike again. I have owned some in the past with my road bikes, so it is not much of a stretch for me. In the end, what components/accessories one chooses for your own individual bike(s). I would think that there would be little if any loss of power noticed by the rider him/herself. I never heard of anyone with a 5, 7, 8 or more internal hubs complain of it. They seem to be happy with their's.

Just remember that it is a matter of personal preferance and subjective opinion when it comes to the "feel" of the bike's handling and gearing. I would recommend to try out both types and compare before you pluck down some serious cash.

[stevegor]

The simplicity of the SA 3 spd hub is great for generally flattish areas, however 1st gear is low enough for climbing, 2nd for spinning and 3rd for moderate speed, and of course you can easily change the rear sprocket for different ratios. I rode my 3spd 20" bike on a 100km ride loaded with panniers and it was fine, but I also have an 8 spd SA hub in my R20, I find the wider range of gears better for overall riding.

[wahoonc]

There is a lot of varied information on just how efficient/inefficient the different hubs and drive trains are. I am no mechanical engineer nor a top shelf racer, so even with an efficiency difference in the low 10% range I doubt I would notice it or worry about it. Also from what I have read, it depends on which gear you are in and it varies from system to system. I have ridden 3 speeds (mostly Sturmey Archer AW hubs) for thousands of miles. When touring I carry spare cogs and swap them out to suit the day's terrain. I don't have experience with the Brompton's (yet) but I do have a sort of folder; Raleigh Compact RSW. It came with the S-A AW hub on it.

Aaron:)

[mulleady]

Thanks guys. I have the 8 speed SA hub on my Downtube VIII H but was wondering about the Brompton claim that there is a loss of efficiency moving from the 3 speed to 8 speed SA hub. I presume this loss is so insignificant that it wouldn't be noticeable. I guess it only applies to performance riders on road bikes forthese kind of small differentials. Thanks for your input. Whatever the case, I'm going for the Brompton!
Link to my favourite colour: http://www.greenspeed.com.au/brompton/raw.html
Desired 8 speed hub mod: http://www.kinetics-online.co.uk/blog/?p=54
and finally a front Son hub dynamo to power front and rear lights.............

[LittlePixel]

Chill. It's all relative. 8 Speed hubs are fine - I wish I could understand why they rubbish and then try to explain away hubs that contain more than 3 gears when they could embrace them and lose their strange 3x2 hub/derailleur setup. It's like they'd rather just be contrary than accept that a SRAM, Sturmey or Shimano 5/6/7/8/9 speed all-in-one-hub might actually be a lot less fuss than their own classically quirky hub/derailleur hybrid... "what gear am I in again?"
Huw "no gears on his Brompton" Fellamilad.

[LittlePixel]

PS.. Just looking at the Kinetics' link for the 8-speed mod. Why on earth is that chainwheel so small? I calculate it at 32 or 34 at most... Climb Everest up the backroads much? Sheesh.

[Edd]

Yes, on BromtonTalk forum there is a discussion about this and the importance of not only the number of gears but which gears you actually have and the usefulness for a particular terrain and an individuals own characteristics e.g. fitness. For my own commute I only use the middle two gears, on my 6 speed Brompton, or middle gear on a three speed. So for this ride a two speed would be fine, but the gearing of each is the critical factor. This middle gear is also the 'direct drive gear' of the hub, this direct gear and efficiency would then vary between hubs. Mulleady it would be worth noting which gears and gearing you use on the Downtube and see how this compares to Kinetics set up.


Edd

[MnHPVA Guy]

PS.. Just looking at the Kinetics' link for the 8-speed mod. Why on earth is that chainwheel so small? I calculate it at 32 or 34 at most... Climb Everest up the backroads much? Sheesh.On the SA 8 speed, low is one to one all other gears are overdrive. It's hard to get low enough gears unless you have small wheels.

[jur]

Well, that Brommie DOES have a tiny chainwheel... gearing depends very much on a person's strength.

On efficiency, the SA 8sp hub has 3 sets of planetary gears used in a power ratio kind of way... I have looked at these and realised that the gears choice, ie large step-smaller steps-large step is the only feasible one for that type of design:

Think of it as multiplying powers.
1st gear is direct, so not involved.
2nd gear is a^2, a single planetary system
3rd gear is a^3, another single system.
4th gear is a^4, the 3rd system.
5th gear is 2nd and 3rd together, a^2*a^3=a^5
6th is 2nd and 4th together, a^2*a^4=a^6
7th is 3rd and 4th together, a^38a^4=a^7
8th is all together, a^2*a^3*a^4=a^9

So you see there is a double step (a^2) step between 1st and 2nd, and between 7th and 8th. All the others are a single step.

So for efficiency, 1st is best (no planet system), followed by 2, 3 and 4 about equal (all having a single planet system), followed by 5, 6 and 7 (all having 2 planet systems in cascade) last is 8th, having all 3 planet systems in cascade.

Going by the 3sp efficiency, I would guess the efficiency as
1st: 96%
2nd, 3rd and 4th: 92%, each one slightly less than the previous
5th, 6th and 7th: 88%, again less for each higher ratio one
8th: 84%

[somnatash]

PS.. Just looking at the Kinetics' link for the 8-speed mod. Why on earth is that chainwheel so small? I calculate it at 32 or 34 at most... Climb Everest up the backroads much? Sheesh.

I think with the SA 8sp a small chainwheel comes because the first gear is direct and all others overdrive. But this is REALLY tiny, actually it was on customers wish a 30t chainwheel. Ben normally puts 33t but that's a thing you can choose, so really compare to the gearing of your downtube is a good idea. Ben speaks about the hub and chainwheel here:
http://www.flickr.com/photos/cycleologist/2272585286/

On efficiency...probably brompton is right, technically speaking a 3gears hub is more efficient than a 8gears hub. Single speed is most efficient. Only that I human with a given strength (ok. that's modifiable) feel that my actual efficiency depends a lot on the fact if my legmuscles are strong to move the bike uphill in a given gear and if my cardiovascular system is trained to spin fast enough when downhill.

[somnatash]

...Going by the 3sp efficiency, I would guess the efficiency as
1st: 96%
2nd, 3rd and 4th: 92%, each one slightly less than the previous
5th, 6th and 7th: 88%, again less for each higher ratio one
8th: 84%

Jur, why is it that you guess the 1st direct drive is 96% compared to the 3sp? How can a direct drive (in theory) be worse than the - 0.75 (-25.0%) drive in the first gear of the Sturmey Archer SRF3? Or did I get you wrong and you mean 96% in total?

[jur]

The 3sp is about 94% in 2nd gear (direct drive) IIRC. In that gear the 3 planet gears are still rotating even though not working, thus causing some drag.

In the 8sp, the 3 sun gears are rotating wrt to axle, I'm guessing slightly less drag, so 96%.

[mulleady]

Chill. It's all relative. 8 Speed hubs are fine - I wish I could understand why they rubbish and then try to explain away hubs that contain more than 3 gears when they could embrace them and lose their strange 3x2 hub/derailleur setup. It's like they'd rather just be contrary than accept that a SRAM, Sturmey or Shimano 5/6/7/8/9 speed all-in-one-hub might actually be a lot less fuss than their own classically quirky hub/derailleur hybrid... "what gear am I in again?"
Huw "no gears on his Brompton" Fellamilad.

I am chilled LP :p Especailly in the current weather we're having in April in the UK. :D

It's just a big decisions I guess to expend an extra £200. I want this purchase to be a decision that stays with me for quite a few years and to get it right. I love the 8 speed hub on my Downtube VIIIH. In fact that bike is a great commuter full stop. The only problem I've had is in the rear wheel tension and some spokes keep breaking despite s service from Velorution in London. Only disadvantage of the 20" wheel fold is the FGW train service into London Paddignton station gets totally overcrowded at the most unpredictable times and I commute peak and off-peak into London depending. Sometimes I also drop into a crowded pub too! That's when you really need the compact fold of a Brompton or Merc.

There is some debate on another thread about whether the raw lacquer finish is more susceptible to corrosion once the coating was ever chipped. But thanks LP for confirming it's a powder coated finish that helps.

With the cycle to work scheme and a 41% discount in my case, I can afford the luxury of a few extras. I was so tempted with a cash deal on the Merc and the distributor Anita is so helpful and responds to all queries. Her GT6 is a lovely looking bike in bottle green but still comes out at £480 on a cash deal whereas the Brompton with extras won't come to more than £200 extra after tax relief. I had also tinkered with the idea of the Merc GT3 but one of EvilV's friends snatched that just before Christmas lol. Yes EvilV you are partly to blame for my dilemma :p.

The temptation of a fully loaded Brompton, paid in 12 instalments from my salary and with the 41% discount tends to sway me...

Decisions decisions! :D

[BB49]

I suppose a single speed would be the most efficient.
However, your trip might be more efficient if you have a wide enough gear range for the terrain.
An 8 speed might be better for you than a 3 speed.

I wonder if Brompton claimed that 3 speeds were best, back when they also sold a 5 speed option.

[kraftwerk]

Can't answer or comment directly. Tho I have seen older bikes with three speed freewheel. That looks pretty cool. I would like one of those!

[Sammyboy]

Mulleady, have you considered a Downtube Mini? Gets you the 8 speed, and the small fold (slightly larger than a Brommie, but comparable) at a much lower price......