How fast is a Brompton?

[@Quetzacoatl85]

Wow, what have I stumbled upon here? Expecting a cozy Brompton bike channel made by a friendly elderly couple, proceeds to be an absolutely STELLAR explanation of advanced bicycle riding physics. The friendly and clear narration, the positive yet calm music, the consistent and considerate use of standard units (and their translation), the absolutely mindblowing animation (so clear, so detailed!), all of that in one great package. Rarely have I been this impressed by content on KZbin; thank you so much.

[@2Bikes4Adventure]

If you like this video, feel free to watch our Technical Video Playlist kzbin.info/aero/PLY2cxn6D6SpviTXWZVZiIOiDCgHwEOFgU&si=XBsBd0xS6Hben8X4 PS We are indeed a friendly elderly couple.

[@esesoysho]

super +1 on this, I was incredibly surprised by the quality of this content!

[@Chris-xz2il]

As a rider of both, I found this very informative. Thanks! You forgot scenario 3 where the Brompton rider decides they don't feel up to the 60km ride, spends a very efficient 30 seconds folding up their bike and hopping on a train to the destination, and having several celebratory beers and a full course meal before the road cyclist reaches the destination. This is one reason why, although loving my road bike, I'll never get tired of my Brompton!

[@Boub65]

Hahahaha excellent!

[@handsonbrompton7875]

I love this 3rd scenario… 😂🍻

[@whazzat8015]

True appreciation of the speed they are capable of.

[@geraldshields9035]

@クリス Yeah Chris: The thing with a Brompton is it's foldability.

[@MartijnVos]

Yeah, comparing a folding bike to any road or even racing bike, is never going to make the folding bike look good. The big advantage of a folding bike is that you can fold it and take it with you on a train. Bike to the station, hop on a train, and then bike the last mile to your destination. I bet that's going to be a lot faster than any road bike.

[@JBBell]

Wow, this is a Sheldon Brown level of both very detailed physics information and a presentation that makes it very accessible. Great job!

[@alxie]

^ so much this. Sheldon Brown must be smiling from the unknown place in the universe he inhabits nowadays. Cycle heaven?

[@bmp12]

Wow made me miss Sheldon Brown all of a sudden. He would have had a flourishing KZbin channel transferring all the written articles he wrote to videos.

[@jimmymacdad8194]

I am so absolutely stunned at how amazingly marvelous, informative and just absolutely brilliant your videos are... Someone should be nominating you for an award 🏆🏆 Many many thanks ❤️

[@whazzat8015]

It's the sound track.

[@zaharyaacob]

.

[@user-ot1dv6ri4f]

me too!

[@reptoJane]

I am so going to use this in my Physics class this year! I teach about rolling resistance and aerodynamics, but always in relation to cars. The info graphics and info here are absolutely fantastic. Thank you!

[@2Bikes4Adventure]

Stay tuned, a new “physics lesson” video coming up shortly.

[@TheAnimejosh]

This was totally not what I expected when I clicked on this video. This was a very well made and very informative video. Hope to see more these kind of videos fro his channel. 👍

[@bisiklettin]

I'm pleaseantly disappointed as well 😊

[@redstwok1123]

Holy cow, this is the best explanation of bikes on youtube

[@alb.2021]

This is how math teachers make learning come alive and relatable to real life.

[@dawnjohnson8739]

No kidding :-). I iNSTANTLY fell asleep :-)

[@sepg5084]

Doesn't matter, some people hate math regardless. And liking math is regarded as being a nerd: pop culture hates needs and celebrates anti-intellectualism

[@terryc8164]

What a brilliant piece of work. There has long been the "Bromptons are dead slow " type comments, but your calculations stack up with what I have found in practice. My P6R and old 1980s 5 speed "racer" show differences in average speed in the 1.5 to 2.0 mph range. Pretty close to your calculations. I must add though it depends greatly on the rider, when commuting on my Brompton I used to enjoy passing the lycra clad fancy road bike riders and wishing them good morning etc 😁 Can't do that anymore sadly!!!

[@2Bikes4Adventure]

Hi Terry. Older roadies are probably slower too by now.

[@paulfaulkner6299]

What an educational video. I don't ride a Brompton or any other fold away bike but I do ride a flat handle-barred so called hy-brid. I have 3 cranks and 7 speeds at the back being 28, 38 & 48 over 34, 24, 21, 18, 15, 13 & 11. I know intuitively that I will always lose out to "racers" because of their aerodynamics - but i just wanted to say that even though I don't have either of the 2 bike types mentioned in the video, I learned something. The most important thing is to get a bike you like and enjoy riding it. My friends keep bugging me to buy a racer - but I just prefer "sit up and beg" over bending forwards for hours looking through my eyebrows! The main thing is that cycling is healthy and good for the environment. Happy safe cycling everyone. Have a great Xmas & 2022!

[@2Bikes4Adventure]

Hi Paul. The important is to enjoy the freedom it provides, what ever shape or form it has.

[@keaixiaomeinv]

I did not expect this when clicking on the video thumbnail. Needless to say, the video completely blew me away, too!

[@guycharron11]

I've seen dozens of videos explaining all of this in one form or another, but this was the best and clearest explanation I have ever seen. Thank you for putting this together. Your teaching and illustrating skills are amazing.

[@EverydayCycling]

How can anyone condense so much information in such a pleasant and engaging video, with a perfectly written script and beautiful animations... I am stunned! There's no one else on the face of this planet even attempting to make such informative videos on YT, I'm glad we have the two of you!

[@2Bikes4Adventure]

Funny, my mother was saying the same thing 😀

[@tim2015]

The videos produced by Brilliantbikes are also very informative, with a slightly different but very helpful perspective.

[@JurisKankalis]

What a great piece of graphical explanation! THanks! Been riding MTBs for decades - and in the recent years advocating against the recently popular 1x12 systems, mainly because shifting upwards under heavy load (when experiencing sudden steep uphill) is nearly impossible, while dropping a cog or two by the front derailluer is almost instant and effortless... Another point being - if I have the biggest sprocket in front at 44 and smallest at rear at 11 (golden standard in MTB for decades up to recently), I'm still limited at max speed slightly - while in my 29 inch MTB I have 3x10 with 48 and 11, which means I can overtake almost anyone on the road... Which is perfect, but bikes (especially frames) like that are being phased out, esp. in higher end stuff. The problem is new bikes don't even allow to have several sprockets in front, relying solely on smth. like a 36 or 39 max at front and going down to 10 in the back... Which kinda seems all kinds of messed up. IN addition to that, as I see now in the video, there's more friction, also, in smaller sprockets, which proves my point - don't change what's been working since Gary Fisher. So they better watch out, those big manufacturers - I got the facts now! Nah but seriously - not being able to buy the sprocket combination I want for my own money bums me out. Greetings from Latvia - you've got yourself a new subscriber.

[@jacek5894]

I can nothing but agree with you. I have 2 bikes - a Specialized hardtail with a 3x9 and a full sus Scott with 1x12. On the hardtail, I can pedal untill around 60 kph, on the full sus I can barely pedal above 40. I know, full sus bikes aren't made for going fast on a road, but my point about the drivetrain still stands. 1x systems are useful for riding the trails as they are simpler, however they make no sense on bikes made for easier terrain. To add on top of that, they are much more costly, both to buy and to maintain. By the way, could you recommend an affordable 29" tire to put on my hardtail? I have a Schwalbe Thunder Burt on my rear - it works great, I gained a couple extra kph just by upgrading the tire. Now my front tire is pretty worn so I'm going to need to get a new one but would like something cheaper (the Thunder Burt was like 45€) - do you have any ideas?

[@pokie0622]

This was the most detailed video on this subject i have seen. Well done

[@AethericEchoes]

I've pondered this question for years. Incredibly informative. Thank you. But there's one variable you overlooked. Since the Brompton folds, you will sometimes be able to ride when you would otherwise have to walk. In such a case, the Brompton will be much faster!

[@ABDLLHSDDQI]

Exceptionally informative. One of my favorite videos on KZbin ever, saying that as an engineer who's been watching a lot of informative engineering videos since years.

[@2Bikes4Adventure]

Stay tuned, more technical videos to come.

[@kkaupapa5469]

Great, very professional information! I appreciate it! 👍👍👍 I own a Bromton and now I am taking a break while riding a road bike. Though it is slower, I find Bromton has its own merits and unique fun that road bikes cannot give. Speed is not the only purpose of riding, is it?

[@peterforde9513]

Wow, love this video. Now I know why I prefer to tour on my Brompton; more time to smell the roses.

[@maievshinoda9442]

The best tire review for 16 349 . Thanks !

[@r.d.7094]

I never comment videos, but this such a good video. As an mechanical engineer it was pure fun to watch. Thanks for this high quality, superb video which is so on point. Never boring, no bla bla and perfectly reseachered and explained.

[@2Bikes4Adventure]

The following two videos may appeal to your MechEng background: Brompton Acceleration - Myth or Reality? kzbin.info/www/bejne/qaWkY518q5p6oc0 Downhill with a Brompton [safely] kzbin.info/www/bejne/gne9hWyElt1_rqM

[@neverzleep212]

Good analysis, on the top of it, the small wheels of Brompton also slows down more by bumpy road than the road bike. But after all, a road bike cyclist will need to find a safe place to park the bike before entering a pub for beer, while Bromptoner can fold it and take it into the pub 😏.

[@2Bikes4Adventure]

Hi Calvin, Yes, road obstacles would seriously impact the smaller wheels, something we may want to expand upon in a future video.

[@ClanMacqueen]

Very educational - beautifully explained physics! I rode my Brompton in the 100 mile RideLondon sportive last month with 20,000 other cyclists. The ability to draft other riders mostly negated the wind resistance penalty of the Brompton and I managed to keep pace with the road bikes, much to their surprise! Great little bikes.

[@2Bikes4Adventure]

The Brompton lower profile helps when drafting full size road bikes. With proper gearing, you can indeed surprise them, but stay in the middle of the pack (i.e, resist the urge to take the lead :-)

[@donaldoconnor7689]

Nifty, I am a die hard roadie but i respect the small bike world even if I choose something more suited to my strength.

[@stevethecat9194]

Brilliantly explained. Both the bicycle enthusiast and physics teacher were completely engaged. Thanks.

[@winngh]

Presentation is beyond words. I owned a Brompton years ago (i loved hiw u was abe to get on and off easily), I currently own a mountain and roadbike ...this is really informative.

[@2Bikes4Adventure]

Time for a Brompton ride once again?

[@NoZenith]

I love how informative and yet accessible you make your videos with the visuals and the thorough explanations. Are you an engineer? Thank you Pam, you're amazing!

[@2Bikes4Adventure]

Pam is a technical writer and Gilbert is an engineer, a great team since 1993.

[@NoZenith]

@@2Bikes4Adventure amazing, phenomenal, Immaculate team! Thank you both very much for your efforts in making this information accessible to others.

[@rasmus9311]

Wow this is the most detailed and well explained video I have seen on bicycle power efficiency, very impressed and unexpected. Honestly speechless.

[@2Bikes4Adventure]

Stay tuned for more (and/or watch some of our previous Brompton-related technical videos)

[@2musiclover534]

Thanks. Very informative. The difference is less than I anticipated. There are other high performance folders such as the Canadian made Helix. It has 24" tires but folds remarkably compact and is much closer to a full sized bike in performance.

[@joshb7415]

People like you are why we have come so far as humanity, thanks

[@cmchenth]

Even a road bike rider could be benefitted by this video,awesome job!

[@cwartcam]

Marvellous work, thank you! In practice I find my Brompton pretty similar to my road bike in terms of speed, maybe because I normally have the aerodynamic load of panniers on the latter, as opposed to a rucksack in my slipstream on the Brompton. I proudly remember one occasion when riding my Brompton, I found myself with a couple of club road bike riders slipstreaming me :-). I was fortunate enough to compete in the Brompton World Championship once, too -- and that felt like pretty scary full-on bike racing, with welcome straw bales on the corner obstacles. Thank goodness the tarmac was dry at least, as cornering traction is not a Brompton forte...

[@gam1471]

A very interesting presentation, thank you. I've been cycling for over 60 years, and have never got on with straight handlebars, particularly on hills. I've noticed that casual cyclists are unwilling to embrace the idea of drop-type handlebars - I've never made a convert!

[@ThisTimeTheWorld]

I like dutch style bars. Like drops but higher up. They look great and make cornering at speed a lot more fun

[@yujiin9850]

My friend owns a 6 Speed Brompton & we usually do group rides. I used to always bring my 7.5kg road bike (it isn't some overpriced Bianchi, but has Carbon wheels and a very hollow aluminium frame) & the difference in speed is massive. Bromptons are definitely quick but past 40kph, they'd struggle to keep pace. Though, for city use, they're zippy and fast!

[@SingaporeUntold]

True. Over 40 is hard to maintain even with drafting. Over 40 is possible just can’t hold for long lol

[@mpg1fam]

Which one is easiest to maintain? The Brompton or regular road bike?

[@sravan1842]

@@mpg1fam obviously a regular road bike.

[@Gregorydyesmith]

Excellent work. Thanks for a great explanation of why I prefer my road bike with panniers over my Brompton in even short commutes to work- except for the cool factor in riding the Brompton, which is worth several km per hour!

[@fender1000100]

The most informative and enjoyable bike channel I've ever found on youtube. This upload is simply amazing. Subbed...

[@make.and.believe]

Wow this was wonderfully informative. Way beyond what I expected when clicking on the vid. I ride a Mountain Bike primarily for cardio calorie burn, it's better for my purposes than a road bike because about 1/4 of my daily circuit is off of the paved roads. I have a salvaged BMX that I use for my backup bike (when the primary bike is down with a flat, etc. and I don't have time to fix it before my riding window) - and I'm planning to replace my BMX with a Brompton style folding ebike, so was doing some research on how they ride. This was a great vid, thanks for diving deep in your analysis. Have an awesome weekend!

[@itsame1277]

Very comprehensive explanation of which I only understood a small amount of the mechanics and maths!

[@2Bikes4Adventure]

Luckily, there are no exam at the end.

[@voilier3000]

I compared my speed when going to work and back with my Brompton and I had an average of around 2 km/h slower with my Brompton compared to my road bike. I would suspect it would be greater with a great wind since my position is more aerodynamic on my road bike. I will certainly follow your advice, and use the second gear of my internal hub more often. Nice technical analysis, well illustrated with excellent comments. Keep up the good work !

[@sophocles1198]

I do not understand your first sentence.

[@2Bikes4Adventure]

@sophocles1198: 2 km/h difference between both bike types we would assume?

[@fuwafuwadance]

this is the most educational video about bicycle that i found on the internet, thanks for producing this kind of content

[@888SpinR]

Incredibly well done video, even my half-asleep brain can understand it! I've noticed barely any difference to my commute time or tiredness so I'm glad to know why! Of course what my hybrid lacks in foldability, it more than makes up for it in comfort and stopping power (not to mention it costs less than a third of the price!).

[@stf0146]

The best video on the topic I've seen so far. Thank you!

[@grahamatsea3575]

What an excellent and very understandable explanation on the different efficiencies of both bikes. Well presented, thank you.

[@sven_ftw]

What a delightful instruction and diagram set. Kudos!

[@danhoang6335]

Very informative and fairly accurate in real life. I thought that I could ride much faster on my road bike than my Brompton but on average I was gaining only 10-15% while riding a road bike compare to Brompton on the same courses.

[@whazzat8015]

Wind, tires, position. I use the big bikes more if distance is an issue, as gears , weight and tires make a big difference in fatigue. And of course if road conditions are harsh

[@harrisonswyter4601]

This is everything I want in a bicycle video.

[@Ontheroadtourism]

My son who rides a SL6 S works goes out for a cycle and comes back looking like he needs to go to The ICU. I go out on my Brompton and do the same miles all be it slower, but when I get home I carry on cooking dinner feeling energised and most importantly with a smile on my face. As he gets older he will understand the pleasure of the journey and and sometimes slower is better.

[@JeanPierre-980]

Wouahhhh !!!! Superbe vidéo très enrichissante et impécablement présentée. un grand MERCI !!!

[@2Bikes4Adventure]

Nous vous invitons à jeter un coup d’oeil à nos autres vidéos (ex.: kzbin.info/www/bejne/jKi1g2aLl9Vjercsi=8VsZYBMPUBztC4uN )

[@Ozz527]

Fantastic video packed full of great information. Thank you!

[@ClownAl3n]

I love these detailed and informative videos. I wish school was taught like this in ALL Subjects and than maybe I would have gotten a "B" in some of my classes 🙄. Man school blows.

[@2Bikes4Adventure]

Stay tuned for more like it (no need to stay up until 3am however)

[@MartinSchwarzmann]

Fantastic vid: I can contribute that SQ lab inner 411 R bar ends fit very well with brompton (fold well) and should give you around the same resistance as the brake hood position, i'm feeling a lot faster with them!

[@mingng3482]

I've got these too, so good! I had the Ergon GP5s which were also nice but the weight difference is substantial. When using the SQLabs it's like having another gear!

[@gclh22]

This some of the best analysis I have seen of cycling on KZbin regardless of the "expert" making the video or type of cycling. One other factor of a Brompton ride is the suspension system/ hinge, lots and lots of flex in that area of the bike meaning lots of effort lost also. But they are still unchallenged in the folding/ storing of a bicycle. There are other folding bikes availble that should not be dismissed by consumers. Dahon are very good, lighter and quicker but no where near as well marketed and not London made and don't fold as well. But would be nice to see their ride quality analysed like this

[@2Bikes4Adventure]

You are right about the frame flex (and the suspension in particular). Additional energy lost would be noticeable when high torque is applied to the bottom bracket (high speed in our video). We own a Dahon Mariner D8, it would be interesting to do some comparison against the Brompton. A subject for a future video.

[@batlin]

Excellent and unexpectedly detailed but comprehensible explanation!

[@linusloo]

Learned so much from this video. Thanks for putting this together.

[@Alex-kr7zr]

Great content! I did a sprint triathlon a few days ago with my 3-gear Brompton and got 33kph average speed on the 20km. Which means I could be 4-5kph faster with a road bike, that means 2-3min difference. I'd assume a tri-bike would load to an even greater difference due to improvements in aerodynamics and gear setup.

[@2Bikes4Adventure]

In the context of a race, we would have to take drafting into consideration. A Brompton drafting behind conventional bicycles would likely be able to keep up with riders of a similar fitness level (if gearing permits). A recumbent (even more than a trike) would have an aerodynamic advantage over conventional bikes.

[@Alex-kr7zr]

@@2Bikes4Adventure in the special case of triathlon bike races, drafting is not allowed. This is also the reason why there special bikes for this particular purpose, aerodynamics is more important than in a conventional bike race. A recumbent is unfortunately not allowed.

[@jamma246]

What an amazing video. No opinions, no conjecture. Just solid fact-based discussion, methods carefully explained and presented in a totally clear way with extremely helpful graphics. Just awesome. I love my Brompton and currently don't have a roadbike. This almost makes me feel like I don't need one. Between a 10-15% gain in speed isn't too relevant to me, I'm not competing in races (and it's so fun to overtake MAMILs on a Brompton, you sometimes get funny looks!).

[@BELLAPHONTOO]

Oh my good god! Learn something new everyday...thank you Mme Pam!

[@Swalkervf1s]

wow, this is a master degree essay, thanks a lot

[@fabiopunk1661]

excellent analysis - even if the actual numbers depend on the modeling/ simulation tools of which we have no insight and just have to trust. they question however is ill posed. If I use a foldable bike it is because I need to fold it - at some point during the trip. So, the comment made by Chris below where he suggests the foldable bike rider stops, takes a train, has a meal before the road bike rider arrives, is very realistic. If I do not need to fold my bike during the trip, there is no question I would hop on my road bike - which, thanks to its larger wheels and different geometry, offers better stability and smoother rides.

[@2Bikes4Adventure]

Hi Fabio, This is the model we used: www.researchgate.net/publication/279937184_Validation_of_a_Mathematical_Model_for_Road_Cycling_Power If you have experience with a better one, we will be happy to experiment with it.

[@bikebudha01]

Unexpected level of science and graphics on a channel like this..

[@2Bikes4Adventure]

Some of our other technical videos may be of interest as well: kzbin.info/aero/PLY2cxn6D6SpviTXWZVZiIOiDCgHwEOFgU

[@barrydonaldson]

Fantastic graphics. Brilliantly researched and presented. Well done!

[@hanwellfoxfoxy5008]

Can't wait to watch your calculations on recumbent vs upright velocipede transport

[@tommyrq180]

I am a long-time bike racer who commuted for years on a Brompton in Washington, DC. I can put out the watts and rode fairly hard during my 15 mile commute to/from the train. I measured my speed differences using a Wahoo ELEMNT Bolt computer and also used very accurate Favero Assioma pedals that measured my power. I have a six-speed Brompton and I found my road bike to be approximately 15-20% faster than the Brompton at normal solo wattage outputs and speeds ranging from 16-22 mph. This generally agrees with the analysis outlined here. I set several Strava KOMs on the Brompton along the commute, but if someone eclipsed me, I could come back with the road bike and get back on top. Other riders didn’t appreciate my Strava KOMs using a Brompton and often had KOMs protested. Strava backed me every time due to my Assioma wattage numbers which were recorded by the Wahoo computer. In one case (a sprint section) Strava actually locked my KOM from any protest as it had become annoying to them and they had already checked out my data. Loved my Brompton! I’m retired now so no more fast commuting to/from the train, but it was definitely the best part of my work day. 😅

[@2Bikes4Adventure]

Thanks for the “real life” input. Pleased to see to its generally agrees with our mathematical model. Hope you enjoy your retirement as much as we do 😊

[@tommyrq180]

@@2Bikes4Adventure I will add that I bought a Brompton because it allowed me to get closer to my road bike racing position than any other premium folder. I tweaked a lot of items on my bike so it was fairly tricked out because I’m an obsessive bike guy. I waxed my Wipperman chain, ran a flat bar with bar extensions to get a more flat back, ran bigger front chainring (made by Wolf Tooth) that dramatically helped chain retention. I would often drop my chain when jumping city curbs and obstacles and the Wolf Tooth completely eliminated that due to its design. But I was commuting so I never ditched the Marathons (ran Plus on back) or the fenders or flaps because I rode all winter and in the rain. I was pretty hard core but hardly get to ride my Brompton (a beautiful 2017 Black Edition S6L in Lagoon Blue) anymore, which is a shame. Love your channel!

[@farikkun1841]

this is comprehensive and technical analysis videos. Could you do wiht other type of bikes as well like MTB with road tires aero bar, MTB with knobby tires, gravel bike, road bike, etc?

[@Shindinru]

This very well done and a clear explanation. Having said that the numbers used are under "lab" conditions. The chain line efficiency discussed is the maximum efficiency that you could expect. Actual efficiency drops quickly under real world conditions. The largest influence on drive line efficiency is chain tension followed by cog size. As the chain stretches, gets dirty and the cogs wear those numbers steadily drop usually ending in the low to mid 80's or even high 70's at the time of scheduled replacement. The tire rolling resistance is the same in that the numbers used are lab conditions and are only true for professional level indoor velodrome tracks where tire deformation is a non-issue. For real world surfaces, like asphalt, a wider tire (more air volume) with a lower pressure is more efficient.

[@2Bikes4Adventure]

Hi Shindinru, Yes, we assumed both bikes’ chaindrive were clean and in good condition. Would be unfair to have one bike with a dirty and stretched chain while the other had a new and clean one (The effect of dirt/stretch could make an interesting video). Lower pressure/wider tire can indeed provide improved rolling resistance in many situations (ref Frank Berto’s 15% deflection rule). This rule obviously applies to both bikes. Both being equipped with the same tire/pressure (35mm Schwalbe Racer) in this study, the main differentiator will be tire diameter. The relationship mentioned in the video was taken here: Bicycling Science, Chap 6 Rolling: Tires and bearings, MIT Press 2020, Figure 6-2. For more details, the book refers to this (German) study www.forschungsbuero.de/PV32_S15_19.pdf .The analysis was done at various pressure (3 to 7 bars/44 to 100 PSI) with various tire sizes and, no, not in a velodrome.

[@allismg5691]

Amazingly in depth video

[@johnwight6041]

This is the most awesome video I’ve seen on this

[@LucaMatteis]

The animated charts on these videos are outstanding. What tool did you use to make them? Everything should be thought this way.

[@2Bikes4Adventure]

Hi Luca. Apple Keynote (+ a few hours) did the trick. Needed Javascript and HTML5 for the internal hub animation.

[@ONEly-uc4et]

Nice diagrams. Keep making the great content.

[@andymonis5368]

Very informative and well put together

[@RabidMortal1]

Wonderful video. You have a real give for delivering a lot of analysis succinctly and clearly. One small error I caught: "As the speed doubles the power required is multiplied by eight" should say "...is multiplied by four" The drag increases by the square (not the cube) of the speed. The drag force equation is Fd = 1/2 * ρ * u² * A * Cd (where u is the speed )

[@2Bikes4Adventure]

Pd = Fd * u, so Power is the cube of the speed

[@austinswallow]

I had no idea gear position 2 on the internal hub was the most effective in either High/Low external positions, I had always felt it best to get to the highest gear as quickly as possible, will experiment with my ride! Thank you, love my Brompton!

[@jackt1400]

Most roadbikes uses double chainrings. When the chain is on the large chainring, they're usually matched to the smaller sprockets, resulting in almost straight line. you've also missed out one of the most important point: Frame rigidity(hence the pedaling efficiency). And the suspension block on a brompton doesn't help in this aspect. i rides both Bromp and a roadbike, the differences are clear. Great effort on the presentation though.

[@2Bikes4Adventure]

Hi Jack. For simplicity reason, and after some deliberation, we decided to illustrate 1X geartrain and only 3 efficiency points (low, medium, high). The 2X slope would be slightly less steep, but the mid-point would be roughly identical, which would give the same efficiency conclusion for the 20km riders (i.e. 10% or 2.3km difference). At high speed, the aerodynamic drag would quickly eat-up any 2X efficiency advantage and would not significantly affect the results. For example, a 1X at 95% efficiency and .320 CdA would need 240W to go at 35km/h. A 2X, assuming 97% efficiency, would be only 0.2km/h faster at this power setting. If your calculations are different, we welcome your correction. Frame flexing is likely not a major contributor at medium speed (20km/h, the most likely used by a Brompton rider). As for high speed, we agree, frame flexing will become more significant. We could not easily quantify the effect however so we welcome your input if you have any. Factors we also didn’t take into consideration are clipless pedals and lycra vs business jacket :-)

[@viktor.tsonev]

wow, amazing presentation and analysis

[@JohnUyArts]

i know nothing aboutthe channel, just watched first time, SOOO VERY INFROMATIVE AND VERY GEEKY NERDY I DUNNO!!! SUBSCRIBED INSTANTLY :D

[@vjs1991]

Thank you for a very informative and well made video! Absolutely loved it!

[@happyswissjoe]

You are so amazing with your videos and physics lessons! Bravo!

[@garyphilip3382]

Thank you for another great and informative video! Your video on handle bars helped me solve a problem I had with Brompton S6XL which now has the shorter M stem . I converted this bike to a single speed 58t x12t and it is very fast indeed !

[@2Bikes4Adventure]

Single speed S6XL with 58/12, doesn’t come a lot faster than that!

[@veins101]

wow this level of analysis.

[@remote3652]

wow VERY well done! I'm picking up my first Brompton in few days and I'm very excited!

[@2Bikes4Adventure]

Congratulations and enjoy your first Brompton (you can even have a celebratory beer).

[@remote3652]

@@2Bikes4Adventure thanks will do!

[@xuchenglin6256]

wow as a side effect what amaze me most is the explanation of the angle and drivetrain loss, I don't know if this holds true scientifically or in an serious engineering aspect of view, but that explains my feeling that going with big chainring on the front and big sprocket on the rear on a road bike feels "faster" and more "efficient". I don't ride a Brompton, but I do ride folding bikes a lot. My folding bike is a Tern X30h, which has an internal 3 speed rear hub combined with a 10 speed cassette, which provides almost the same gear inch range as a road bike. In my experience, my folding bike and my fancy road bike with deep carbon wheels are almost identical speed wise. The tyre is a big factor, the identical feeling is after I changed the tyre on my Tern to 20'' Schwalbe Pro One and go tubeless, while my road bike run GP5000TL tubeless. The limiting factor be the rider, especially when you travel fast, you are the most cause of aero drag, if your position is similar, which in my case it is (my bike is more of a foldable road bike, a little big aggressive position), the difference between bike's is trivial.

[@2Bikes4Adventure]

Hi, The Tern X30 is a very nice (fast) bike. If you want to learn more about chain drives efficiency, you can look at the references we added at the end of the video description (including this one.: www.ihpva.org/HParchive/PDF/hp50-2000.pdf).

[@xuchenglin6256]

@@2Bikes4Adventure Thanks for your reply! Definitely will check these, so curious about that for a long time but cannot find an explanation to accord with my own feeling that big front + big rear feels faster, which contradicts the common belief that it's bad. Finally it seems I could justify that. Please continue to do great videos, ride safe and fast!

[@AlexRusAlex]

Thank you for the amazing explanation!

[@s.bruyere8496]

Stunning vid. Thanks for this accurate analysis.

[@IbraHimself]

I stumbled upon this video after viewing GCN's Brompton vs road bike video. Thank you very much for this well montaged explanatory video.

[@2Bikes4Adventure]

Too bad GCN’s video wasn’t on a flat road (could have been used to confirm (or disprove) our calculation).

[@SingaporeUntold]

@@2Bikes4Adventure I think no challenge as the road bike will obtain a faster top speed

[@MrGabirahellim]

Perfect explained! Thank you.

[@grouchy88]

this was unexpectedly informative, thanks!

[@2Bikes4Adventure]

Stay tuned for more videos

[@rogberube6422]

Really informative. Thanks for sharing.

[@dhpdaedalusStudio]

Blew my mind. Thanks!

[@2Bikes4Adventure]

If you like this video, feel free to watch our Technical Video Playlist kzbin.info/aero/PLY2cxn6D6SpviTXWZVZiIOiDCgHwEOFgU&si=XBsBd0xS6Hben8X4

[@ChrisbyBike]

Fantastic comparison! I'm a Road rider as a Brompton rider. Great bikes for diferent goals.

[@2Bikes4Adventure]

Hi Chris, if we were to evaluate the folding speed, the Brompton would beat all road bikes :-)

[@ChrisbyBike]

@@2Bikes4Adventure That's for sure! Love my bikes😍🚴‍♀️

[@icehei11]

that's true. I take my Road bike for ride 27km/h and Brompton around 22-23km/h

[@normawingo5116]

It would be so wonderful if you gave this lovely detailed information about a gates belt system and an internally geared hub. I wish Brompton offered this, I’d buy one so fast.

[@2Bikes4Adventure]

@normawingo5116, unless Brompton widens the rear triangle, we would likely be limited to a 3-speed hub if a belt drive is used.

[@rockyf0611]

Am well agreed on your well detailed and scientific comparison. But, I don’t have budget for Brompton and just riding Bianchi Oregami folding 20 and my RB is Cinelli Willin SL. Thanks

[@goku445]

Wow, I didn't expect such scientific and detailed review, nice one!

[@Eroamagorath]

I never had the opportunity to ride a brompton, but as a physical education student I'm almost sure the most critical piece of this comparison should actually be the riding position biomech efficiency.

[@2Bikes4Adventure]

You raise an interesting point. While both bikes can adjust seat height and setback, the Brompton only offers 3 stack/reach configurations (S, M and H). The comparatively priced road bIke selected for this simulation (a Specialized Allez Sport) is available in 6 sizes and could certainly be further fined tuned for a better fit. We assumed the rider was comfortable using both bikes and was generating the same amount of power (as measured at the crank) during the test. For a casual ride (defined as 15-20km/h in our video), do you think the difference in biomechanic efficiency would be significant considering the relatively low workload and associated small joint moment at the hip, knees and ankles? As for a faster ride (defined as 25-30 km/h), would the Brompton’s poor aerodynamic drag be considerably more debilitating than any difference in biomechanic efficiency assuming the same power setting? In any case, this could be an interesting follow-up video. Any reference(s) you suggest we should look into?

[@yunnamed]

I love the boy racing you at the beginning of the video without front or rear brakes hahaahahhah

[@2Bikes4Adventure]

Indeed, both calipers seem to be disconnected from their respective brake cable! PS This was filmed on a backroad in Serbia btw.

[@jonathanb3255]

Amazingly well done video. Thank you!

[@ChrisTheLaCat]

Really impressed by the thoroughness and quality of your videos and the fact that you maintain the focus on Bromptons 🙂. One thing that I have never seen addressed in regard to the smaller wheels is the impact on the aerodynamics. In my own experience from participating in many road races on my S6E, I have noticed that I often roll downhill faster than similarly sized riders on "real" race bikes. I have attributed this to the fact that the top part of the wheel moves at twice the speed of the rider and therefore has 8 times the drag. This is the case for both types of bikes, but the frontal area of the Bromton wheel is much smaller and therefore I have assumed this effect to explain my advantage. Do you have any thoughts on this effect?

[@2Bikes4Adventure]

You raise a very interesting point. While the Brompton wheel wasn’t especially designed to be aerodynamic, its small frontal area (and associated smaller spokes) will provide some advantage over its bigger cousin. The longer stem however will negate some of the gain. Wheel aerodynamics come into play at speeds greater than 30km/h (20 mph), so particularly noticeable during descent. It would be an interesting subject to investigate in a future video.

[@jpchiles]

AWESOME VIDEO 👏🏻👌🏻!!

[@hawkenfox]

Wow the information on this video is impressive! Well done!

[@adrianlw2750]

On a Brompton, if you can, always cycle with a following wind. That front bag-carrying system then acts like a spinnaker sail! Great video, interesting and informative. Regardless of efficiency, my Brompton remains my favourite bike 🙂

[@gordonlbelyea4409]

Yes, and in a head wind, you might as well have a snowplough on the front! (I still love my S-bag.)

[@2Bikes4Adventure]

Needless to say, we assumed nothing on the B’s front luggage mounting block 😀