tcs

Note: Moulton, Birdy and Dahon (Jetstream/Jet) use front and rear suspension. Brompton has only rear suspension.

BTW, 60+ years of motorcycle design/use history and 30+ years of mountain bike design/use would indicate that if there's only suspension on one end, front suspension is favored.

reppans

I'm no racer, but the Brompton is my preferred touring bike and efficiency does matter to me... and aerodynamics is the most important efficiency component - by far. However, I think tire width aerodynamics is going to be really immaterial, especially in this context (i.e. folding bike) - handlebar aero, weight, componentry, gear ratios, and flex will likely more important.

This is an good aerodynamic analysis, also by Jan, and it also found tire width to be pretty insignificant.

https://janheine.wordpress.com/2012/...orld-bicycles/

Long story short, when I first toured on the Brompton, in my mind I was convinced I was losing 10-20% speed/efficiency to my gravel bike. So I ran a few mini time trials and was surprised to find the difference to be closer to 7% or 1 mph. I started researching it with the articles above, and also others on weight, IGH efficiency, and got a pretty good sense of the break down.

Best fix was the aero drop position on my M bars... that cut my efficiency loss in half (to ~3.5% or 0.5 mph) in my time trials, not to mention greatly adding to my riding comfort - I love having varied back angles and grip positions, just like my gravel bike's drop bars. Of the remain 3.5% difference, I calculate 1% to be weight (5lbs on 200lbs combined weight = 3% but that only applies on uphills or 1/3 of the time). And the remaining 2.5%, I figure is the IGH (drivetrain is a double hit as both IGH and derailleur), suspension block, frame/stem flex, mini clips vs Clipless, and fewer gear ratio options.

IMHO, air pressure comes behind all that, and have also chosen this path:

Anyways 3% less efficiency represents <10 mins on a 50 mile touring day - for me, well worth the added security and travel options of this folder. Comfort is now a wash between the two bikes for me.

reppans

No arguments from me, but the suspension on the B, like so many other of its multi-tasking components, just integrates so well combining effectiveness, yet still maintaining compactness, in its design. A worthy compromise IMHO.

When I first bought my B, I got the firm suspension (cause everyone seemed to recommend it), and believed in high tire pressure. I started having buyer's remorse very quickly. Went back and used the standard block (I'm 155lbs) and.... "ahhh that's so much nicer." Then started playing around with tire pressure.... "wow, that's nicer than my gravel bike"..... so now dropped the gravel bike's tire pressure to the same (50-60 psi, FWIW). Added the drop bar position on the B and the two bikes feel pretty even in comfort to me.

berlinonaut

You are really running the Brompton on 50 to 60 PSI (3,5 -4,1 bar) and are happy with that? Wow! I pump the Marathons as well as the Brompton Kevelar usually to 6.2 - 6.6 bar (90-94 PSI) and the Kojaks to 7,7 to 8 bar (107-117 PSI). Whenever I feel dragged and slow on my Brommi I check the pressure and if I missed to do so for a couple of weeks the pressure may have gone down to what you are using as a standard. I refill to my standard level and immediately riding feels much easier - like Popey after having eaten his spinach. It is really a huge and noticable difference for me which I can clearly recognize on my speedometer.

Regarding aerodynamics I am with you. First I think I am too slow to notice the effect of different tires in that aspect and second: Whoever puts a Brompton bag on the carrier block should not be afraid of the negative aerodynamics-effect that may be caused by a tire that is 3mm wider.

reppans

hehe... I did one of my usual 15 mile exercise loops yesterday, and although I know I hadn't pumped up my Marathon tires in quite a while, a finger pinch told me it was safe to ride. I just put a gauge to them now and got 38F/41R - it was a comfy ride .

On one hand, I think I should do some time trial runs to see how much air pressure really does impact my pace (and maybe Jan's article is wrong, IDK), but on the other hand, as more of a tourer than a racer, I realize comfort will always out weigh speed/efficiency for me, so I really don't care if lower pressure is a bit slower. I need my minimum level comfort for a given average road surface, and that will define what air pressure I use.

What I DO care about, is how much comfort and efficiency am I willing to sacrifice (vs my gravel bike) for the versatility of a compact folder. I think I've now matched the ergos and aero pretty well, so if my comfort between these two bikes can be tipped by just air pressure, then I think it is fair to assume that any changes in air pressure should equally impact speed/efficiency performance of both bikes, thereby maintaining my same ~3.5% differential. That's good enough for me.

jazzmanjm8

Hard to believe my first post would yield such a vivid response! Riding a bike always has an element of danger! I rode flat land for many years and twisting/turning is part of the game. I have fallen many times and know the risks! Try hitting 15 foot dirt jumps at at 20mph!... on 20inch wheels!

Yeah St. Louis has some rough spots but I'm not that concerned and really dodging traffic/people/potholes/bullets feels kinda natural here.

The real issue I think is longevity and quality control. Dahon seems to be the Hyundai of the folding bike world while brompton seems to be in the family of Porsche! Both need services and both need care... but resell is always gonna be drastically different! The same for handling can be said for both as well... I do t see many dahon bike races on social media versus the thousand or so things associated with the brompton!

People don't really like watching Hyundais race around a track!

Of course I'm not racing... I'm enjoying a great bike on my way to class or to the park or on an adventure! The brompton fits the bill for me as a top of the line whip! And will probably be my only bike for the rest of my life!

Just my two cents!
Oh I got a grey M6L!

berlinonaut

Congrats! If the order is still outstanding in regards to the "hilly area" you should think about the 44t chainwheel instead of the stock 50t one. It is one of the choices that Brompton offers and for many people a good one.

Other than that think about the front carrier block and a bag fitting to it to get the full lot of pleasure.

jonc123

Not to change the subject, does anyone know the gear inches range for the 6 speed with the -12 sprocket? I'm so used to GI! Interested in the low end, as I have hills also and live where the op lives.

edelay

Welcome to the fold.

HighValleyRanch

I was taught to use the formula:
front teeth divided by the rear teeth x the wheel size to determine the gear inches:
i.e. 50 tooth chainring with a 12 rear for 16" wheels equals. 50 divided by 12 x 16" (as hypothetical as I am not sure of actual Brompton wheel size and depends on tire selection as well)
this gives me 66.66 inch gear.

With the sturmey archer AW 3 speed hub I was using the fixed 2nd gearing plus 33 percent for high and fixed gear minus 25 percent for low. On my 20" 406 wheels I measured actual diameter and came out with 19 inch actual diameter.
I'm sure that there are gear charts for various variables, but this method seemed easier for me.

Open to corrections if my method is in error.

typical old school 27 inch ten speed high gear was usually 52 divided by 14 times 27" giving 100.2 inch gearing

smallwheeler

a few years ago i made this graphic to help me memorize that.

jazzmanjm8

lol

berlinonaut

Brompton traditionally publishes this data, just look in the support-section of their website:

https://brompton.zendesk.com/hc/en-u...es-and-ratios-



From experience: The standard setup with the 50t chainwheel is not really adequate for hilly areas and you are better off with the 44t. For really steep hills this is still too long. Fitting a bigger sprocket to the rear wheel is very limited - with some love you might be able to use a 17t instead of the stock 16t.
In this case you could mount an even smaller chainwheel than 44t, either as a single (loosing on the upper end) or as an additional one ("granny-gear", light, cheap and pragmatic), go for a Schlumpf Mountain-Drive (good, but expensive and heavy) or you could buy a single-speed Brommi and convert it to an 8-speed using i.e. the S/A XRF-8-w with 39/25 (again heavy): Bicycle Gear Calculator

desastar

+1