CLARIFICATION: While the Terminal Velocity of a Touring Brompton (T-Bag/Large Borough+20Kg luggage) is similar to having no luggage, the braking force required to slowdown (and the associated rim heat generated) will obviously be higher with a Touring Brompton. Brake force and rim temperature shown in the video were computed for a Touring setup.
This channel is a gold mine. These are not Brompton videos, but general science and physics that everyone riding a bike should pay attention to. The Brompton part just adds for a good exemple of physics variables changing and how the models follow.
I've reached 56 km/h terminal speed, on a long slope I travel very often last year and know very well in northern part of China(Jinan city, Shandong Province). Mine is a six-speed s-bar Brompton.
To prevent overheating my rims on long descents from Alpine mountain passes I do fully stop the bike and apply a wet cloth/rag to the rim (be careful not to burn your fingers!) to help them cool down quicker. I do that after every half a dozen to a dozen hairpin bends (every two to three hundred meters of elevation loss) (depending on the gradient of course) If there's a fairly flat section I ride that with wet rims without breaking so that the evaporating water cools down the rims quicker. Spritzing them with my water bottle has the same effect as wiping them with a moist rag but uses a lot more water, hence the wet rag. I noticed that the rear wheel heats up much quicker than the front wheel, probably because there are more obstructions to the airflow (frame, my legs, rear fender). (May be a funnel could help with directing more air onto the rim to help with cooling) I blew my tube once because I raced a motorbike down a mountain... the rim was unbelievably hot afterwards and it's scary but I could stop alright. On Großglockner I saw full sized bikes with rim brakes blow their tubes too. (Dipping the wheels in ice meltwater besides the road helps too if the brook can be accessed easily/safely but I'm always worried about abrasive stuff in glacial meltwater) (Usually the maximum speed is determined by the road, i.e. I could go faster if there wasn't a bend in the road. But there is so I need to brake...)
Indeed, as much as we would like to ride our bike at terminal velocity, roads twists, turns and switchbacks may dictate otherwise. From your experience, you never had issue with degraded brake performance due to a wet rim (i.e., it would dry fast enough even if spraying it with a water bottle?)
Would caution that depending on the rim material and how the metal was treated during manufacturing, rapidly cooling the rim could cause warping. LIkewise, depending on the tire compound, going from hot to cold could weaken the rubber over time. Let things cool down for a few minutes. Temperatures will drop fairly quick esp. with aluminum alloy rims. They're great thermal conductors, also also great heat dissipators.
@@2Bikes4Adventure Of course wet rim brakes brake terribly - but that's mostly an actual problem in wet weather conditions. (Which is one of the reason I wish the Brompton had disk brakes) If only the rims are wet (on purpose, as in my example) but the conditions are dry (dry road/no rain) braking (the brake pads touching the rim) wipes most of the water off the rim on the first few rotations of the wheel. Yes, you do need to anticipate that but very quickly braking performance is back to normal. Thanks for pointing that out! (Yes, purposely wet rims do negatively affect braking performance but I never had any issues) If you often "do" mountains on your Brompton do often check how much of your rim material your brake pads already shaved off. In seven years of ownership I had to replace the front rim once and the rear rim at least twice because I didn't like its shape anymore (too concave). You can get a css treated rim which lasts longer (because it's coated with ceramic material and therefore harder than the stock rim) (That is the other reason I'd love disk brakes on my Brompton)
@@AlbertCLee True. This would especially apply to dipping the wheels in an ice cold creek. However, wiping the rims with a wet rag is only evaporative cooling and has the benefit of wiping off crud/brake pad material off the rims. The cleaner the rims the less damaging the braking is to the rims (I've had to replace them because after some time the rims become more and more concave from braking with rim brakes)
I'm always learning with your videos. I have two Bromptons, one for commuting and general traveling, another one for long distance tours. I've done 215k on a single day on my Brompton. Many of the strategies I apply using my Brompton were adopted after watching your vids. Awesome work, I appreciate it a lot 👍🏼🤜🏽💥🤛🏽
@@2Bikes4Adventure It was from Berlín to a town outside of Magdeburg (only about 200 meters ascent). That's my longest single day personal record. But I'm fine with 100k+ routes on the Brompton. Luckily I have a P6 and without that bar I'd go nuts.
@@ChrisShawarma have you ever ridden an H? I understand you're probably saying the multiple grip points help you for Speed and then chilling relaxation but I'm curious what your take on the H bar is in comparison. I'm looking at the ergon GP5 as a touring option with additional hand positions with the GP2 or GP3 as daily foldable option. I'm not ready to invest in hardcore modifications (p stem and bar) but I'm gathering information for future Brompton stuff. Thank you very much
@@NoZenith @NoZenith Hey there, I wrote an answer and somehow deleted it :P Yes, I know the ergons, they'll be a great addition to your bike, for sure. I have a second brompton with an M-Bar and 3 speeds. I have done a couple of 100k+ rides on that one. But I only have the normal handlebar grips. The only thing I don't like about the ergons is the way the horns bulge out when folding the bike. The P-Bar is simply amazing because you can change the body position and not only the hand placement. That's a major relief when going for longer rides.
Purely anecdotally, I recall descending from the Cat and Fiddle towards Macclesfield some years ago on a Brompton equipped with old-style single pivot brakes; I shall never forget the look on the face of the driver of the oncoming car I met near the bottom! It would seem from your helpful comments that black aero rims would be an advantage.
Amazing piece of content! I have never thought about the rim temperature. However Downhilling the brompton at top speed is not my thing. The bike feels comfortable to 30km/h to me. Airbreaking is good advice as it is effective at top speeds
Wonderful. I am always leary of too much speed downhill when touring fully loaded on my Brompton. On my latest tour on Isle of Skye I reached 34.6 mph (55.6 km/h) with 10 kg front and 10 kg rear of extra weight. The bike was solid with absolutely no wobble. I pulsed my brakes (equally front and rear) and just enjoyed the ride. The ambient temp was approximately 19 C and the road was smooth tarmac. Thanks for the excellent analysis.
Common maximum gradient for major roads are often in the 6 to 7% range, thus a 50-55km/h terminal velocity is likely the maximum most of us will (safely) experience (assuming a normal riding position and no tail wind).
Masterpiece again. What you're doing is so great, thanks. My personal feedback : 62 km/h descending on the long slope arriving on the airport in the Shetlands islands, Scotland. M6L with my 78 kgs on it. I think I had no luggage then, as far as I can remember.
We are always impressed by the Brompton’s stability at high terminal velocity. Obviously, we always hope the pavement will be without cracks and potholes as we reach those speeds.
Loved this. I love digging into the science of things and also recently bought a Brompton. I doubt I'll be pushing the limits of braking in the streets of Chicago, but it was really interesting to understand the math of it.
So impressed with your videos!! Science and Bromptons…a wonderful combination! You’re providing fantastic knowledge to someone like me that wants/needs to learn! Thanks again 😊
Hi Miriam. Thank YOU for taking the time to bring us along on your travels around Ireland. Filming while traveling can be a lot of work. Set up the camera, cycle away, come back to take the camera, store the camera, cycle away. Rinse, repeat. Hope our paths cross one day.
@@2Bikes4Adventure rinse and repeat 🤩 Crossing paths would be great! Lovely to hear you’ve seen some of Ireland! Looking to change my standard 3 gear setup and sussing out my options - leaning towards a 40T chainring and maybe just see how that works out before changing to a 6 gear..or maybe I’ll just splurge with the cost of changing to a 6 gear setup and 40T chainring 🤭
A smaller chainring would certainly help climb those steep hills. It’s an inexpensive upgrade that can be swapped back depending on the intended destination.
As a Dane in a flat country (hardly 200 m above the water at our highest point!) we do have a rocky island in the Baltic, Bornholm! And on this we have a few serpentine roads which are very steep! I couldn't ride up even with 6 gears, but had to walk much of the way up. And besides that, we have "cattle prevention bars" crossing the road at several places on the one and have to walk over or around them, with a self closing gate! Going down again I had my serious doubts, but even braking down from extreme speeds to pass the bars, my Brompton brakes never let me down!!! Finn. Denmark
I have thought about changing my similar - titanium fork to a hydraulic disc brake version in front (Which is possible from non Brompton producers), but as the braking power is enough for really most of my use, I decided to save my money! Finn. Denmark.
Denmark may have a flat profile, but from what we remember from doing the Berlin to Copenhagen trail, it can be quite windy. Not to the point where we needed better brakes, but we could certainly have used an additional low gear.
Trading the lightness of a titanium fork (and conventional brakes) for a more robust, wider (and heavier) steel fork with disk brakes would make sense if the bike is used for (heavy) touring in hilly terrain. On the other hand, if occasional travels (or frequent local trips with minimum load) is the intended use, a lighter configuration is probably more appropriate. The money saved can be used on other bike accessories.
Day 1 Alpe DHuez I met someone who saw someone go over a hairpin having suffered brake fade at high temperature. They were very lucky to survive. Advice was the same. Release brakes to increase air cooling, brake evenly and hard when you need to. Don’t just trail them! I was on a full size roadie. Checking periodically by hand probably a smart move on a Brompton - if too hot to touch, stop and enjoy the view.
Great video. I have had a quite bad experience that I think is worth sharing. I once did a descent from Chiang Dao to Ching Mei in northern Thailand. I was riding my titanium Brompton, that is equipped with one of the best v-brakes you can get. The bike was only lightly loaded, with a Brompton bag mounted in the front carrier bracket. My guess is that I was doing 60 km/hour, the road conditions was perfect, but suddenly the bike started shaking. I couldn't do anything to stop the shaking because the front bag that caused the shaking is mounted directly on the frame. If it had been mounted on front rack I would have been able to counteract the vibrations with the handlebar. The brakes was useless, If I had applied them I would be send flying. This is probably the most scary thing I ever experience bicycling for 40+ years.
Frightening story indeed. Wobble/shimmy need speed (more than 50km/h) and particular mass/frame stiffness conditions to occur. In your experience, do you feel the particular front luggage setup contributed to the situation? Do you think the presence of titanium fork and/or seatpost (?) were contributing factors in the system instability? And most importantly, how did you eventually stop the bike from vibrating (or it just stop by itself)? PS This would make a great video subject.
@@2Bikes4AdventureI'm quite sure it was from the luggage on the front carrier block, but there could be other factors at play of cause. I only have good experience with the titanium frame parts, and they still look like new, even though the front and rear frame on my bike is from 2006 :o I tried stabilise the frame with my legs, not easy on a Brompton, applied very low force on the brakes, and rode it out for a kilometer or so before I could stop the bike and take a deep breath.
@@petergriebel7321 😬wow. I'm going to have to do more research on this because I love going fast and I don't intend to keep anything on the rear rack and I do not want to have to carry backpack so I've been focusing on shopping for a highly functional front bag. I had not heard about this being an issue before. Thank you for sharing
Rim wear is also of concern when using a Brompton. I killed at least 2 rims in my 10 years using it so far. The first one within a year using a downhill path to work.
Chris from Chris by bike made a video that relates to this. She actually reduces the pressure especially in her front tire for extremely steep descents. She blew a tire out coming down from Christ the Redeemer in Rio
Reducing tire pressure prior to decent is a valid strategy, but it has to be used judiciously as it will increase rolling resistance (and heat up the tires) even if no brake are applied.
@@2Bikes4Adventure thank you very much for for the information and qualification on that method. I haven't had to exercise any of this but I intend to do more traveling and I know I'll experience such Hills one day 😊
I have had inner tubes pop a few times on descents, two at pretty much the same point on different years on a charity ride on a 1:6 hill using Kojak tyres. Never happened when using Brompton Green tyres. I did note that it happened where the tube was touching the rim where the yellow Brompton rim tape was not centrally position. I have replaced the B tape with normal bike adhesive rim tape since. Not sure if this has helped. This year I had a failed in a similar manner but using Brompton green tyres and again the yellow rim tape was slightly off centre where it failed so now have adhesive rim tape on both wheels. This happened as I came to a holt after a similar hill but on the flatter part.
Tire failures after stopping can indeed occur as the absence of convection airflow leaves the rim suddenly without cooling. I suppose it’s preferable to a failure at terminal velocity. Thanks for the feedback.
What is a Brompton Green tire. I Googled it and went on the Bronson website and I don't find them. I've been shopping for my next tire as I'm still on the stock Racer and I think my next tire is going to be the Continental that just got released recently but I have never heard of the Brompton Green before so now I want to look that one up. Thank you
@@NoZenith Brompton Green are no longer available. Ref our video about tire (it does mention the "Green" and "Yellow" tires) ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-p1i1W6xy8hM.html
@@2Bikes4Adventure I do remember you mentioning Brompton tires that used to be Brompton branded that came stock and I'm sure I've seen that video :-) I thought maybe they came out with something new and I hadn't heard about it yet. Thank you very much
Yes I still have a couple of pairs of older tyres. The yellows which were the least puncture resistant and the other Bromptons that are actually not green banded but were the ones that replaced them but the same I think. I do need to replace them maybe with the continental.
I've gone up to nearly 60mph on my road bikes, but 37mph is the fastest I've descended on my Brompton (S3E upgraded to S5E), for fear of overheating (and not that stable to start out with).
Shortly after a longish descent on a steep and slightly bumpy route, I did have the spokes on a Brompton front wheel unravel - it was very alarming. It may have been a badly built wheel, and I may have been unlucky, but it makes me somewhat cautious in the speed I go and the kinds of shocks or vibrations that I may be creating on these little rims.
This strategy could work as well, but since only one wheel will be used at one time, there would be a risk of larger temperature excursion (min to max) when transitioning from one wheel to the other (thus increased risk of failure if not careful). Note that in turn, you reduce the risk of skidding if both wheels are used for braking.
While Canada has adopted the metric system back in the 70’s, most people here are still using PSI to discuss tire pressure (somehow bars and kpa never caught). Note we added conversion to alternate system in our video subtitles.
I live in South Korea where the metric system has been used since the 1960s. However, when it comes to tire pressure (especially on bikes) everybody I know still uses PSI, myself included. I think it's due to the unit's "granularity". It's easier to think in whole numbers rather than fractions when talking about pressure. For example, I find it easier to grasp when it's said that the tire pressure increased from 85 to 90 PSI, instead of saying 5.8 to 6.2 bar. Fractional numbers somehow just feels awkward...
They are slightly heavier. The front fork and wheel spokes need to be stronger. But the resulting braking performance would certainly be superior (less susceptible to overheat and contamination). Would be a nice option to have indeed.
Does applying small pressure in the brakes constantly to prevent acceleration cause less heat than full braking at top speed? I feel you could just use the brakes for a slow descent and there would be little to no heat generated, this problem would be completely avoided. Can someone explain?
Interesting question. The answer would vary depending on the slope angle and speed at which the test is performed. As shown at 03:55, for a 10% slope, the maximum heat generated occurs at about 35km/h, the “red” zone being between 20 and 50km/h. If your light braking keeps you above that speed, you should be fine.
Through the years, we tried various mirror types (handlebar, helmet and eyeglasses mounted). For the last few years, Gilbert has been using the “Take a Look” from Bike Peddler [ amzn.to/3Rt2KEc ]. It is inexpensive, light, robust and easy to attach and removed from eyeglasses.
So if I go do that Montana downslope, I might be able to finally hit 100kph. Fastest speed I've gone on flat ground here is 76.6kph. Downslope is supposedly 96.6 but I think Strava was glitching out, since that was on my MTB, which shouldn't be able to go even near that considering the gear ratio means I top out at 50. There's no way I could have done that. Singapore by the way, your example of high air pressure. The 76.6 is on my road bike, I've done it with 2 different bikes, downslope on my old one and on flat ground with my new one because some illegally tuned e bike overtook me, he was probably going 60 and I don't believe they deserve the speed when they didn't train for it or even pay for it, therefore I must show them the error of their ways. Unless they're going 80 on those things that are more like electric motorbikes, then they paid enough for it . I heard that there are now disc brake compatible parts for Bromptons, probably safer to switch to those if anyone plans on going down a large slope. Even comparing road bikes, my old one with rim brakes really cannot compare to my new one with disc brakes. Then again my old road bike had pretty low end components. It was really terrifying going downslope on the old one. I believe Bromptons come with better brakes. But speaking of the luggage to add extra weight, what if the luggage came with an aerodynamic fairing of sorts, detachable so you can fold and reattaches around the folded form when you want to push the bike around. Maybe with air ducts for the disc brakes. I think the limiting point for that would be the wheel size. Those small wheels aren't the most stable when they hit bumps.
Brompton rim brakes upgrades are available, but quite costly. They would add some weight to the bike as well (many people preferring to pay a premium to have a lighter bike (ref T-Line/P-Line)). However, if fast descent is the goal, rim brake would be a welcome upgrade. Fairing around the front luggage would indeed improve terminal velocity (increasing further the need for good brakes).
Lower psi? I've ridden in the 20's w/ cheap BMX tires Since my bikes doesn't have suspension Zero snake bites too Learned that would make regen braking useless
@@2Bikes4Adventure true, Interestingly On a park hill with mowed grass, W/ maxed rated rear tire (50psi) & about hand deflectable, to take off the bite of the road, In the front I was stopped in my tracks Down hill Granted I was inching down With no real momentum & The slope was maybe 2' x 4' Also I've been too lazy to put my brakes back on After testing something & I've learned how to brake without brakes 1/5 ways if there's grass on the side It can help :)
I was thinking of the electric Brompton, I think it has regen braking If you used the motor up hill I think you won't over charge the battery, but I wonder if there's so much it can take.
@@kentwydell9322 dang: ( @Teun Jansens if you want disc brakes You'll have to take it to bike Smith Specializes in Bromptons, Buy a used custom one , Came across one during the pandemic On a local e-commerce site , Or get a knock off I can't find it in my notes anymore But they're 5 different brands (2021) & 1 of them has disc brakes
@gdwlaw5549, Indeed. We alluded to it in our recent video about the K3 Plus (which has disk brakes) ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-4W0bZHCytR0.html
how bad would this be on 20 inch rims? i hit 40mph on average on my ride to the train station and gone almost 50 on some other hills on 26 inch rims and was thinking of getting a dahon mu to get up the hill easily and then take it on the train or bus its hilly everywhere round here too should i convert to disks maybe?
20” wheels with rim brakes are also susceptible to overheating but to a lesser degree than 16”. A comparison graph is shown at 05:36. Disk brakes would mostly solve the issue.
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