Aerodynamics, total rolling weight, watt and components price for upgrades
 

I just completed aproximately 20 hours studying what to do to make my Brompton a better ride, and I believe some of my findings might be relevant for other folder enthusiasts that don't browse around road bike forums and other places where performance is way more important than here.

As some of you know, I live in the USA but due to career (and lifestyle) I do travel a lot. Spending time (ANY TIME) assemblying a bike to make it ride-ready is not a good fit for my needs and personal preference, so the Brompton is the only option for me, even though I would prefer something faster, with bigger wheel, etc...the Brompton is what I have to work with for now.

Since Last March (when I purchased this red Brompton that I currently have) I have been complaining about speed. I can maintain a 14mph pace without struggling, but to keep up with 18mph for more than 60 minutes becomes demanding. Since then, my desire to make the bike faster focused predominantly on weight, and that was a mistake. Wind, poor riding geometry and friction (bearing, chain, BB, hubs) are my real enemies.

After some basic applied math (well, maybe not so basic if you take a look at my notebook), If I had the super power of unlimited budget and could invest all the money in the world to make my Brompton the lightest Brompton in the world, I still would perform "poorly" due to aerodynamics, poor riding geometry and friction.

Weight is still something important (specially if you plan on carrying the bike a lot like I do), but the price of upgrades (incluing rear triangle, front fork and bids of Titanium) and the overall performance results are just silly. If I were losing medals after severe climbs by seconds, that would make good sense. But not under the current circumstances.

With that in mind, my Brompton is now featuring some of the heaviest stuff that I had around, and my focus on improving performance will be on the following (in order of importance):

-Reduce wind resistance by changing cockpit and riding geometry;

-increase comfort. you ride more often if you enjoy riding. :)

-increase fitness conditioning specific for biking (interval training and spinning);

-Reduce friction (including rotational mass and hub quality);

-reduce total rolling mass by losing weight. Instead of struggling to lose 4 pounds on my bike, I am going to lose 15 pounds on myself.

Let the fun begin. Freds, weight nazis and zen comments all very welcome.

14R.

PS: Don't forget to read one of the first and most relevant articles of my studies:
http://www.smartcycles.com/bike_weight.htm

Fortunately low weight is easy to sell and its benefits are obvious to most riders because the calculations often thrown around do not reflect it's true importance (due to their flawed assumptions). If we listened to the exercise and sport scientists we would all be riding around on 42 pound Schwinn Varsitys. You can't just say "I'm limiting the discussion to good bikes" and then employ logic which indicates that "good" bikes aren't really "good" as they do at smartcycles.com

That being said, weight is not the only thing that affects bicycle performance and, even without considering any numbers at all, that fact alone is enough to conclude that there comes a point where one is far better off to focus on other factors. If I were you a new set of handlebars to reduce wind resistance would be the next on my list. Not sure what you could do about the hubs on your Brompton since they're nonstandard sizes and the other things such as riding more, training, etc don't really solve the problem because they require more time than what's lost by going 4mph slower.

Here are some ideas for improving aerodynamics/geometry:
Drop bar ends to tie to your saddle: leave off for quick folding, clamp on for fast rides.
http://www.origin-8.com/images/new_400/33617.jpg
http://www.origin-8.com/?page_id=91&...EBAR+ACCESSORY



Bullhorn bars with quick folding Dahon Andros stem
http://farm3.static.flickr.com/2500/...2c2c9564e1.jpg
http://www.cykelportalen.dk/UserFile...0IOX/iox02.jpg

I think your priorities are in the correct order.

Is your first priority achievable on a Brompton? My main gripe about Bromptons is the difficulty in getting a good riding position. Can you put aero bars on a Brompton?

Reducing total mass by losing weight is probably the most underrated way to improve performance. I lost 40 pounds last year. The improvement in biking performance was dramatic. I suddenly loved to ride up hills. Messing around with a pound here and an ounce there is nothing compared to losing the 15 you want to lose. I've put five of my 40 pounds back on over the winter, but spring's coming soon!!

I wouldn't get fussy about rotational mass vs. mass in general. If you are racing, or riding in a group were quick acceleration is important it makes a difference, otherwise, not so much.

Speedo

Flip the front fork around. Will radically improve the stability of the bike. I make no promises as to durability or foldability in that configuration. :-) Or warranty voiding.

Wow you guys must be fit. Even with my EBrompton I can only maintain an average of 14-15mph.

Regards

Jerry

Acceleration is also very important when riding with traffic controls, traffic, stops, turns, etc. It's hard to imagine a style of riding which doesn't overlap with either this or racing or group rides.

Sometimes I wonder if the people who advocate not getting fussy about weight have ever ridden a bike. Everyone knows how shocking the difference is when hopping on a bike which is lighter than usual. It's amazing how some people try explain it away.

Riders quoting high averages often ride on the best groomed roads without turns or traffic controls (or need for them due to lack of traffic) and in only the best weather. They also usually measure their speeds with bicycle computers which count left/right wobble and are often miscalibrated as opposed to actual clocks which can't be cheated. They also usually don't count the bad days, so their "averages" aren't really averages at all, but rather best cases (which is terribly ironic when you consider that the purpose of averaging).

When I quote my true average speeds it probably seems quite slow to most people, but I still seem to smoke most of the roadies on the rare occasion I've gone on group rides and the only thing that seems to stop me from smoking them all is that I need to either stop to read the cue sheet or follow someone to prevent getting lost.

Good point about average speed Chucky. My REAL average speed considering traffic and everything else might be 8 or 9 mph. When I say 14ish, I mean when I am riding on a respecful pace and I look to my speed, it is typically around 14mph.

smooth airflow at the front and you gain a % of speed .
See http://www.zzipper.com/Products/prod_upright.php

The ATB version works with S bars , most likely..

FIETSBOB: I've tried a zzipper fairing and it works for my Dahon, but I find it noisy. More comfortable for sure, but noisy.

JERRYSIMON: Normally when people cite their avg. speed, it means the speed they see on they bicycle computer when they are riding on a straight road with a good surface without a headwind. It does not take into account stopping at traffic lights, climbing hills and so forth. In such conditions, I can ride at 28-32 km/h (17-20 mph) on my singlespeed but that is by no means the true average speed for a ride.

14R: Static and dynamic weight play a part in the equation of bike performance. But I would say that any bike that is 20 lbs. or under is "light enough" so that the weight of the bike is no longer the primary determinant of performance. I went from 170 lbs. to 140 lbs. which is a drop of 30 lbs. Or the weight of an entire bicycle. Pretty big difference in performance right there.

Before going into lacing new wheels and hubs, experiment with tires and tubes. I have had good experiences going from Schwalbe Marathons on my 406mm to Kojaks. Much lighter tire, thereby lowering the rotational mass, decreasing momentum and improving acceleration.

I also ended up ditching the rear derailleur and going with a 66 gear inch singlespeed with a chain tensioner. The bicycle rides more silently, and is easier to clean. There is also far less to adjust and maintain without gears thereby reducing complexity.

I have to say that Chucky's point here represents a dilemma for me also.

I have 10 bikes. They range in weight between 17 lbs to 27 lbs. I ride regularly for sport (3,500 miles and 290K ft of climbing last year) and around town (maybe 800 miles a year), plus spinning class about twice a week. I know how a bike feels when I ride it.

Further, my personal performance benchmark is a 13 mile 2000+ ft climb, very similar to the benchmark route referenced in 14R's link. On my 17 lb bike, I can fly up the hill. It just feels incredible. On my 27lb TSR, it's not. People pass me up all the time when I'm on the TSR. I would guess that my time difference is closer to 5 minutes, not the 30 or 60 seconds that a theoretical calculation would suggest. BTW, on this route, wind is not a big factor as my best speed up the hill is under 12mph.

I don't dismiss the scientific calculations, they are based on physics and sound logic. But what explains the difference in my real-life experience? Is it purely psychological???

SESAMECRUNCH:
Are the riding positions similar between your fastest and slowest bike? What about gearing?

If the bikes are similar enough so that the main difference is bike weight, then it suggests that weight plays more of a role than we thought.

Does the mind ride "easier" when we are on the "heavy" bike as opposed to the light bike? Many times, the difference between human intention can account for time variances on identical routes.

Ride position and gearing are similar. I could have picked my 23 lb, vintage steel roadie, or the 27lb Bridgestone Moulton as examples also. None goes up as fast as the lightweight carbon roadie. The roadie does have pretty good wheels (Dura Ace), maybe that's a factor.

Do you LIKE riding these heavy bikes the same way you enjoy your 17lb bike? I believe there is an emotional aspect of it right there (yes, I am splitting the psychological effect into something more than "oh my god, this bike is heavy, this is so difficult" kind of thing)

Can't use that due to volume (unless I want to show up at an airport and pretend I am Captain America, having it as a carry on shield) :)

Ah that makes me feel better :p

Riding across the center of Cambridge my speed is probably down to 8-10mph between lights and junctions/crossings. Once I get to the outskirts of the city with longer flat stretches, my bike computer starts to show higher values of 14/15 mph maybe even 16/17mph if I put some effort into it ;)

Usually I find the effort is most expended getting up to speed on the flat, but once there its easier to maintain it for a bit until some obstruction forces me to slow down again and the cycle then repeats itself lol

Regards

Jerry

There are Ride time averaging computer features on some products..

It's a flexible vacuum formed Thermo-plastic .. they ship rolled up in a tube shape

you can line a duffel bag with one and fill the inside of the cylinder with clothing , or something.


Otoh, should the front bag on the frame clip, happen to add a smooth aerodynamic entry into the air stream ,
it could benefit some, as well as hold stuff.


captain america's carry on luggage. skin suit only add to the image.. :lol:

I have similar experiences with the Swift - it just wants to fly uphill and I have to hang on for dear life!

My personal guess as to the reason lies in the bike's quality of ride - this is a combination of comfort, weight and stiffness. With a good bike, all your effort goes into forward motion. A flexy bike or one with suspension will never be as good.

Wheel weight is pretty important too. When riding uphill, especially steep ones, the bike will slow down with every pedal stroke at TDC. This means with every pedal revolution there is momentum lost and re-applied - very very lossy. The heavier the bike and especially the wheels, the more severe this effect becomes. On level roads, my heavy bikes just feel like they are heavy clunkers and seem to sap my strength just keeping up speed.

Riding 30km/h on dead flat roads is pretty easy on my Birdy, but it does require constant effort. I think the Swift requires slightly less effort, but wind resistance dominates. Any wind or slope and that figure quickly drops.

Aero position: I did some roll-down tests on my bikes a long time ago, and to my surprise the only time I found a significant difference was when I went into an impractical aero tuck which would not be sustainable beyond a few minutes. But there was essentially no difference between my Swift (which I thought to be quite low) and my Raleigh 20 which was just normal for me.

So my take is,
* don't worry too much about aero position unless you are building speed downhill
* weight, while apparently not important on level roads, does make quite a difference to bike 'feel' which in the end makes a respectable difference to speed
* Friction in the drive train is very important. I take the ease of pedaling backwards as my benchmark and constantly test this to make sure as little as possible power is lost. A clean, well lubed chain works best for me (and no, Chucky, I am not interested in debating this :) ) Don't forget to test the jockey wheel on your Brommie - roll it while pushing hard, it must have almost no friction. If necessary, replace with one with a sealed ball bearing.
* use narrow 28mm tyres and pump them to 100psi or whatever your mass requires - it will make you feel faster and this all contributes to the psychological effect and I believe it makes a difference over long distances.

Sounds like a lot of it must be in your head :eek:.. actually, your difference really doesn't seem that awful..going by your figures...ultra trick carbon bike gets you up the 13 mile hill in about 66 minutes .. 71 minutes for the heavier TSR .. that's 11.8mph vs 11.0mph or about 7% difference .. and coming back down, you should be faster on the Moulton :thumb: ... and what about the Moulton speed record..:fight:

Yes, the difference is 7%, but most power/speed calculators would calculate the difference as much smaller, which is 14R's original premise.

And, the Moulton speed record is on flat land, where weight doesn't come into play as much.

I do agree with the original premise that some people obsess too much on weight of bike components. Quality of wheels, components, aero, frame stiffness, etc. all come into play as well.

At the end of the day, it doesn't matter that much, I'm not riding for a medal or for glory (I'm already a legend in my own mind :) ). It's all good fun.

What about the fact that the bike's centre of mass oscillates from side to side to counteract the force on alternating pedals? When climbing a hill, the bike's mass is following a wavy path which must use up a significant amount of power.

But then there is the argument that the heavier the bike, the smaller the amplitude...

For what little my opinions are worth: IMO upgrading a Brompton with the intention of improving performance doesn't make much sense to me. It's like turbo-charging a Ford Taurus. ;)

Increasing comfort makes sense. I'd also say that this is a rare instance where weight may matter -- not for performance, but for ease of carrying. However, most of the time the improvement in weight isn't worth the cost of the upgrade.



Guess? ;)

Actually, if we presume you are accurate, I'm seeing a theoretical difference of more like 2.5 to 3 minutes. I'd say that 5 minutes isn't too outlandish, especially since the climb is probably not a consistent 3% grade.

Lots of factors may contribute to the remaining difference as well. For example, I presume your 17 lb bike is a 700c racing bike, which means it probably has a stiff frame, larger wheels and narrow tires. The TSR, meanwhile, a suspension frame, and you're almost certainly going too slow for the aerodynamic advantages of the smaller wheels. It probably also has more rolling resistance.

A better experiment will be to put 5 or 10 pounds of weight somewhere on the frame of the 17 pound bike and do multiple test runs with a stop watch.

And the real test would be to stick power meters on both bikes (or on one bike with different weights added) and figure out your speed, while climbing, at the same wattage. I'm gonna guess that's a tad too cost-prohibitive for most of us here, though.

Remember the Taurus SHO? {-;