Can a Brompton Climb? - GCN Challenge Explained

[@2Bikes4Adventure]

Many questions were raised concerning the Rolling Resistance graph at 02:46 It represents the total Rolling Resistance experienced in each of Andrew’s race (not only one tire but both tires) So, 2x Schwalbe Marathon Racer at 90psi rolling at 26km/h will absorb approximately 60 watts. 2x Schwalbe One Pro TT at 120psi rolling at 32km/h will absorb approximately 13 watts total.

[@readyplayer2]

Fascinating breakdown! I really enjoy these videos, your explanations of physics and mechanics of cycling are top notch. Thanks!

[@eddiesaysrelax]

Wow! This video looks like a lot of work - thank you! This is the most concise run down I've ever seen of where all our pedalling power ends up on different bikes. Plus.... I have a Brompton, so extra interested. Cheers.

[@CuriousCyclist]

I love all the geekiness and science. And the visuals. Thanks for taking the time to make these videos.

[@adrianlw2750]

Another great analysis of why the Brompton is not as quick as a road bike!🙂 So one thing to ponder perhaps… is it more efficient to carry weight on the bike, or on the person instead, like, is it best to carry water on the bike or drink it all before the ride haha! One standard feature that comes with the Brompton is need for changed mindset… or at least, in my experience, simple acceptance that slower pace/more effort is a given. But I was cheered on one ride when I was keeping up a steady 17 mph on the flat as some road bikes came by “Not a bad pace for a small-wheeled bike mate!” I play mind games sometimes as I puff along, deciding which gear gives me best efficiency for the conditions. So on my 6-speed with 44T chainring… gear No.3 should be the most mechanically efficient as it uses the direct drive on the 3-speed hub coupled with the larger 16T rear sprocket. But that limits forward speed to a comfortable 10 mph which doesn’t get you anywhere very fast. More time to enjoy the scenery though. But Brompton does charm and is very useful, things which science cannot measure I suspect. And I forgive it for being less than perfect. It remains my any-time, all-time, go-to favourite bike🙂

[@2Bikes4Adventure]

This summarized perfectly our view as well!

[@FirstLast-jm4dx]

I used to think my Brompton S3E was super flexy when sprinting or climbing out of the saddle. I thought most of the flex was from the long stem, but it turned out that most of the flex is actually from the not-so-stiff "stiff" suspension block. I changed it to a really stiff suspension block (essentially a solid block relative to my weight)...and the Brompton feels like a normal bike.

[@arthursiwandavid4794]

Hi, i have been searching for answer about why my folding bike with good tire and dropbar is slower than my road bike, especially during climb .. thanks your explanation has answered all my curiousities

[@MiataBRG]

Interesting analysis! You truly are the Bellingcat of cycling videos!

[@bradk7462]

This is the the kind of stuff the internet was made for!

[@Cassiomm67]

The graphics in the video are impressive. So glad the channel took off! 😁

[@2Bikes4Adventure]

Thanks! It keeps us busy while we are grounded.

[@UncleAT]

All your analysis are legendary!

[@brianradwanski6544]

Pam dropping that Engineer mic. Love it.

[@rgfrobotics]

the technical analyses on this channel is superb!

[@2Bikes4Adventure]

It has some superb subscriber’s comments as well 😊

[@iko3]

Amazing presentation with so much effort and passion! This is what I love about KZbin. What a time to be alive!

[@NoZenith]

Haven't even watched yet but I'm saying thank you for more amazing content to help us understand.

[@nkhairil]

Great analysis! I did climbing route with my 6-speed Brompton C-line every afternoon after work. The timing is almost similar comparing with my RB!

[@MartininitraM]

I am always deeply impressed of your videos! You really dive into the nitty, gritty and I love it.

[@guywithsocks]

Your animations are next level. Still using Keynote? If so, my mind is 🤯

[@2Bikes4Adventure]

Yes, still using Keynote. Pretty much reaching its limit however. Would be faster with a Titanium Keynote 😀

[@guywithsocks]

Ah yes, the T-line Keynote 😂

[@effyleven]

@guywith socks I hear the T-line Keynote is a "missed opportunity"... (just a revamp of the colour range.)

[@karlgw]

I've done that route on a Brompton, and while I wasn't timing, I'm certain I beat those numbers. Does it matter that I did it in reverse?

[@pengy44]

Love that explanation. You all really know your math and physics on cycling. I've always been curious of performance of the bromption to a more conventional bike from a mathematical point of view.

[@2Bikes4Adventure]

Stay tuned, there are more to come

[@petekadenz9465]

A really interesting, educational and enjoyable video, as always. Thank you.

[@Ty-er5ok]

Very interesting, thanks! I'm a big fan of Jan Heine and his magazine Bicycle Quarterly and always found his "planing" theory fascinating so nice to see you reference him. Curious as to your thoughts on that? I have an H6L that I have modified with a Titanium extended seatpost as well as a scrowave suspension block. I noticed a very big difference in climbing with those two modifications and feel my Brompton does "plane" for me now as I think both help return energy in the upstroke thus propelling me along. The Brompton suspension block deadens more than springs in comparison to the Brompton rubber block. It also helps that the scrowave (coiled spring) doesn't flex as much as the Brompton block even with my 200 lb weight. However, the titanium seat post flexes more, but again I feel energy coming back rather than dissipating. Long story short, my Brompton is far more comfortable to ride compared to my 2011 Salsa Casseroll that I used for randonneuring (long-distance cycling) at least around town. I've not tried it over Randonneur distances This is all anecdotal, I know. But do you think this makes any sense?

[@2Bikes4Adventure]

Hi Ty, The merit of frame stiffness (or lack thereof) is indeed an interesting subject. GCN did a good video recently on the subject. Few studies actually quantify how much energy is lost due to frame flexing. On the other hand, subjective tests indicate that compliant frames are more comfortable and likely less tiring for long distance cyclists (thus indirectly improving performance). The titanium seatpost, being more flexible than the standard Brompton one, would likely better absorb road vibrations, thus reducing rider vertical movement (and discomfort). And bonus, it’s lighter too! As for the Screwave, it would be interesting to see the displacement vs force graph compared to the regular Brompton suspension block. It would not be surprising to find out it better filters road irregularities while being less affected by the crank torque fluctuation due to the cycling cadence (thus reducing suspension bobbing power losses). BTW, did you select the firm or soft version?

[@Ty-er5ok]

@@2Bikes4Adventure Yes, it is fascinating. I did choose the "firm" scrowave out of personal preference mainly, but also due to Scrowave's recommendation based upon my 200-215 lb weight. I am virtually certain that the tests you mention would provide results as you describe purely based upon my experience of a year with Brompton hard rubber block vs. Scrowave. Just the other night I rode to the store to pick up some food along a fairly rough trail with significant bumps. I looked down (carefully) as I hit the bumps and even with my current 212 lbs :(, there was very little spring compression. Conversely, I remember doing the same thing with the hard rubber block and noticed much more flexing, thus loss of power, etc. I also have a cargo bike. it's a mountain bike that I converted with an Xtracycle kit into what is referred to as a long-tail cargo bike. One of the things I did was change out the rockshock suspension fork to a Surly rigid fork. I immediately noticed a difference in climbing. Even with the extra 13 lbs of the xtracycle conversion kit, climbing was much easier, particularly out of the saddle. Not my brilliant idea, mind you. Xtracycle enthusiasts have long known this, which is why I did that straight away. But I do remember being quite shocked by how significant the difference was. Thanks again for another great video by the way. As a failed engineering student, I really appreciate your technical, yet approachable, take.

[@jonathanleach3914]

Very good. Thanks. I suppose the question still remains if the performance and weight difference is worth the price. The T line does look nice though!

[@2Bikes4Adventure]

For many of us, it could be better for our health, performance (and wallet) to lose 2Kg in weight and buy a C-Line instead of buying a T-Line. But yes, it does look good.

[@JasonL527]

Are you a former physics teacher? I would have LOVED your class if you taught engineering, on drag and air resistance.

[@2Bikes4Adventure]

Not a physics teacher, but Flight Simulation Engineering background

[@stevepagden9115]

Very enjoyable and insightful analysis. Thanks! I would maybe suggest that the Brompton frame geometry is laterally stiffer than a conventional frame as the vertical distance between pedal to steerer and steerer to ground is less ie smaller stiffer wheels and shorter forks. I don’t see the frame hinge design adding to flexural losses, its big and beefy compared to the tubing, and we would see signs of movement on the mating faces…just done a crude comparison against my Aluminium Giant TCR…. Pushing a pedal against a braking resistance…Visible lateral flex below the bb on the TCR… any on the Brompton disguised (and possibly eliminated) by the compression of the rubber spring…

[@2Bikes4Adventure]

Steve, folding bike frame flexing is an interesting subject. It would be nice to have some BB, Headset, Fork and Seatpost N/mm stiffness data for the Brompton. For now, in our video, we focused on suspension bobbing as the primary source of frame flexing power loss.

[@backdoorslam]

absolutely amazing analysis!

[@2Bikes4Adventure]

Hi Tarasch1, You added a comment a few hours ago, but somehow it is not there anymore, it was about Rolling Resistance. Here’s some additional info. We indeed used BicycleRollingResistance (BRR) site as the starting point. Although performed in a controlled (lab) environment, those measurements still give a good idea of the ratio between different tires (all full size unfortunately). The 25-622 Schwalbe Pro One TT (used on Andrew’s Cannondale) have a Coefficient of Rolling Resistance (Crr) of .00225 at 120PSI The 35-622 Schwalbe Marathon Racer Crr are .00626 at 90psi. So, for similar sized tire (622mm), the Racer is 3x slower than the TT. Now, we have to extrapolate what would be the Crr for a 35-349 Racer. We took two approaches: 1. AtoB Magazine No 119 Feb 2017 provides data for some Brompton tires (included the Racer). They measured 29W losses for a 30Kg load at 30km/h. If we correct for GCN Brompton race (26Km/h 73.7Kg), we get 61W 2. Using equation found in Bicycling Science 4th Edition (MIT Press 2020) (similar analysis available here (www.forschungsbuero.de/PV32_S15_19.pdf) and applying it to BRR, we get 57.9W. We decided to average out at 60W in the video. Note that Schwalbe Pro ONE TT (tubeless) will be quite superior to regular (clincher) Schwalbe ONE (as found on T-Line). This Brompton tire was measured at 13W (30Kg/30Km/h/100psi) in AtoB No123 Feb 2019 (about 1/2 the rolling resistance of a Racer in similar conditions). Hope this help.

[@davidhunternyc1]

That was brilliant. Thank you!

[@OneEclecticStyle]

Fantastic Breakdown!

[@714SNF]

Awesome video, thanks!

[@mickhurley7305]

Fantastic video, you got a sub.

[@mauricesvay]

Great video as usual and thanks for the research!

[@Swalkervf1s]

Supercool analysis

[@rob-c.]

On Strava Andrew’s power for that climb is 434W

[@sheilastallard]

First "Happy New Year to both of you!". I'll put my penny's worth in, you missed out the FUN factor you get when riding a Brompton!!. Stay Safe!! xx

[@2Bikes4Adventure]

Hi Sheila, …and even more FUN going downhill!

[@ChrisbyBike]

Love the video!!!!! Great comparison. The new Brompton T Line is my newest Dream Bike!!! Interesting to know how important tires are.

[@2Bikes4Adventure]

No more P-Line?

[@langsuan123]

In Hong Kong, various maniacs ride their Brompton up Tai Mo Shan (10km at 10% all the way - much tougher climb than Victoria Peak) and back down. Less painful on a Birdie. Yet better on a road bike of course 8:45. Due to nature of terrain here I think descending safely on a Brompton is more of an issue than doing the climbs.

[@2Bikes4Adventure]

We would appreciate the Birdy’s disk brakes during the descent

[@raeesmohammed3072]

Always surprise us with R&D

[@SubTroppo]

I live in a hilly part of Brisbane, Australia, and recently had the option to buy a cheap but almost mint 2016 basic Brompton with accessories from a friend at a very good price. My response is, yes, it can but...

[@vincentdelporte]

Two simple things you could try: 1. If it came with a 50T chainring, get a smaller one (eg. 44T; BCD130 can go down to 38T) 2. If you need, replace the single chainring with a double + derailleur, eg. 50/34

[@SubTroppo]

@@vincentdelporte Thanks for the reply. I hope the bloke who bought it reads it. I thought long and hard about it and then looked at all the bikes I've got already...

[@huangteng]

Hi, I enjoyed the depth of technical analysis! Well done! I will like to know how you got or calculated the rolling resistance of both the Schwalbe tyres. I checked on the rolling resistance website but could not find it. Is it possible to post the rolling resistance of the Schwalbe One (at 10 PSI intervals) or even better point me to where and how you got the information? Thank you so much.

[@2Bikes4Adventure]

Hi kHermiT, Thanks for reposting your comment, somehow, KZbin auto-deleted two of your previous comments before keeping this one. Readily available rolling resistance data for Brompton tires are difficult to find Some references I used can be found in the video description of our Brompton Tire video (kzbin.info/www/bejne/pmLMYopsrd5rnq8 ). They include (www.atob.org.uk/): A-to-B Magazine No109 Aug 2015 p34 (Tannus) A-to-B Magazine No119 Feb 2017 p10 (Including Schwalbe Marathon, Marathon Racer, Kojak and older Brompton Yellow and Green) A-to-B Magazine No123 Feb 2019 p24 (Schwalbe One, Strozzapreti, Greenspeed Scorcher) A-to-B Magazine No128 May 2020 p28 (Continental Contact) A-to-B No119 is particularly good for its “power loses vs tire pressure” graph. Other editions usually only give 1 measurement (for 1 pressure), ex.: Schwalbe One was 13.0W at 100psi (A-to-B No123). One useful way to approximate to rolling resistance is to find a same tire (same manufacturer, model and width but larger diameter) on www.bicyclerollingresistance.com/ and convert the value to a 349mm wheel. Studies have shown that power loses is inversely proportional to the tire radius, so multiply the power by 622mm/349mm for example, or 1.78 or so, and you will have a good approximation. Comparing those results to A-to-B Magazine actual measurements confirmed this “rule of thumb” is a good work around.

[@huangteng]

@@2Bikes4Adventure Thank you for your response. Much appreciated on the detailed explanation and links. The AtoB magazine looks like a great source of information, but needs a subscription. =( The approximation reasoning is sound and very useful! Will keep that in mind in the future. One more comment, will it be useful to include rolling resistance of inner tube? I reckon Ollie is running either latex or tubeless (which is around 9W loss per tyre) whereas Andrew should be on butyl (which is around 20W loss based on your approximation). Or are they already factored in?

[@2Bikes4Adventure]

Hi kHermiT, Most of the latest issues of A-to-B Magazine can be downloaded as PDF for about $1.50 each (that’s what we did). The Bicycle Rolling Resistance measurements identifies the inner tube used (for example, the Marathon Racer analysis was done with a Conti Tour 28 170gr butyl), so it’s factored in the results. Andrew’s Cannondale Schwalbe Pro One TT are tubeless (partially explaining the superior performance we presume).

[@leonardotovarcurieux]

Great analysis. ❤

[@seductive_Octopus]

🤔 I wonder what the Time of the new Titanium Bromton with a 4 Speed Gear would be.

[@2Bikes4Adventure]

About 9 min 32 sec

[@Mick_Holland]

Watching that hurt my brane. Thanks? 😉👍🏼

[@TribusMontibus]

I never considered a Brompton as the basis for my riding. I have taken my Tern folding bike to four continents. It even holds a few top 10 performances on some African climbs. Not bad for a folding bike with a rider well into his fifties. The Tern is much easier to modify into a sturdy all-terrain race bike. Its frame is much stiffer and the 20 inch wheels do a lot better on horrendously bad roads.

[@2Bikes4Adventure]

What Tern model are you using?

[@TribusMontibus]

@@2Bikes4Adventure I use a D8, with the mudguards removed. It will take any Shimano 8 speed cassette so it gives me a lot of flexibility wherever I go. I have fitted a Campagnolo 42-52 crankset, although I don't have a front derailleur. When roads get steep (I have climbed gradients over 20% with it) I just get off and shift it to my 42 with my fingers before continuing the climb. I've fitted drop bars and brake shifters, so I sit in approximately the same position which I have on my regular road bike.

[@2Bikes4Adventure]

Dual chainring (even without front derailleur) is a great idea, something we are thinking to implement on our Brompton.

[@TribusMontibus]

@@2Bikes4Adventure Yes, in the modern era, some consider it 'primitive' to have to dismount, in order to change gears. But I figure that I am many steps ahead there of the first Tour de France riders, who had to disassemble and reassemble their gears before climbs. Oh yes, another thing I forgot to mention, which is a huge bonus to my D8; the quick release wheels. I fit very different tires when I am going to ride mountain roads in Rwanda (where even 4x4 terrain vehicles take it slowly) as opposed to smooth North American roads. The quick release is also a big bonus when changing a flat and in disassembling the bike for transportation. Having 20 inch wheels even enables me to use a widely available range of sturdy BMX tires. Last, but not least, my D8 cost me approximately € 150,-, which was before modifications. Most of the parts I fitted were road bike parts I had lying around anyway and I fitted a new Bickerton stem, because the Tern stem couldn't be lowered far enough and didn't allow for fitting drop bars.

[@TribusMontibus]

@@2Bikes4Adventure This is a short video, showing the D8 in action: Climbing Mt Greylock on the Tern D8 kzbin.info/www/bejne/f5XRoYafjLSer5Y

[@ergergzbhzefer]

In the record run, the athlete might have been better prepared, feeling better etc. It's not certain he'd be able to do that well each time. Anyway, the brompton being 6km/h slower than a top performance bike is not that bad.

[@2Bikes4Adventure]

We completely agree that it’s difficult to quantify the difference between Andrew’s level of effort between the two races (on the Cannondale (record run) and on the Brompton). If he put less effort during the Brompton race, for example, generating 10% less, or 340W, it would mean that the performance difference between the bikes is even less! So the 6 km/h speed gap actually represents the worst case scenario for the Brompton.

[@Alex-kr7zr]

Shouldn't the Titanium frame increase flexing? I compensated this on my Brompton by replacing the suspension block with a stiff 3d printed one.

[@2Bikes4Adventure]

Titanium frames are often considered to offer a good compromise between stiffness and compliance. In our analysis however, we particularly focused on the suspension power loss (and the improvement provided by the new T-Line suspension block).

[@paulketchupwitheverything767]

Interesting analysis of the results of the entertaining GCN video. Weird pronunciation of "schwalbe".

[@dgenerationx5855]

pronunciation is completely correct ( with english accent though) I guess you are on Team „shwolb“ which is terrible wrong…

[@chinno321]

How does this thing handle hills?

[@2Bikes4Adventure]

The small wheels and relatively narrow (35mm) tires are more suited to paved roads. With proper gearing (6 speed 44T), an average cyclist can climb a 10% slope for 45 minutes. (Ref our Gearing video for details kzbin.info/www/bejne/baa5qICubrSNb5Y )

[@american-professor]

I live in Seattle and there's not a single hill in the city I cannot climb on my 6-speed brompton

[@2Bikes4Adventure]

Did you go for the 44T chainring or kept the default 50T?

[@american-professor]

@@2Bikes4Adventure The default

[@hasheemmakupa5289]

N¡ce

[@johnlong9862]

👍👍👍👍

[@HDsharp]

For climbing you need a mountain bike!

[@sssxxxttt]

Exactly, use the right tool for the job. On the other hand, a known saying from the photographic world: "The best camera is the one you carry". And speaking of carrying, I much rather commute with a Brompton. Wouldn't mind it being lighter though :)

[@AlexBayes]

That Cannondale cannot weigh 5.4kg. Google suggests 8.5kg+?

[@2Bikes4Adventure]

@AlexBayes, not your typical Cannondale indeed. References used for 5.4Kg data point: www.bikeradar.com/features/pro-bike/andrew-feathers-cannondale-supersix-evo-hill-climb-bike/ pezcyclingnews.com/interviews/hill-climb-specialist-andrew-feather-gets-pezd/

[@hikingout2988]

The science is good but the use of this example of a pro cyclist using bikes with such high gear inches for climbing, is not realistic to say the least.