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Why is a road bike faster than a city bike with the same effort? And how much faster it is? (if someone have measured it)

Motive of the question:

My current bike is a city bike with front fork shock absorber and seatpost shock absorber under the saddle.

It is very heavy & I feel maintaining 20 km/hr for 30 minutes is very hard on flat city roads. I am thinking of switching to a road bike but I want to understand if it is really worth it as my bike is very sturdy, with hub dynamo, fenders & rear rack (all of these are not on the entry level road bikes.)

I know this sound a bit controversial but I hope someone will help me from our community.

From OP's link

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    If it has shock absorbers on the front and back, it sounds more like a mountain bike than a city bike. – HAEM Sep 21 at 15:14
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    Your question is related to this SE.bike question: "How can one estimate drag for a bicycle?". In your case, you would want to compare drag for a road bike with a commuter bike. The short answer is that your bike has higher drag due to weight, rolling resistance, and probably aerodynamic drag -- but, in addition to those, you also have losses in your power production due to your bike's suspension. – R. Chung Sep 21 at 15:48
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    There are other opinions about saddle height, too. A common one is that knees should be not fully extended while riding, and usually the height is correct when you can reach the pedals with your heels with knees extended but without rocking your hips. – ojs Sep 22 at 7:41
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    @HAEM I think the asker is describing a hybrid with front shocks and a suspension seat post ("back shock absorber under the saddle"), not a dual-suspension bike. – David Richerby Sep 22 at 11:49
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    @DavidRicherby Well, that is the point of a high-enough saddle: That you pedal with your forefoot, being able to almost fully stretch leg and foot. And trust me, it's perfectly doable without cleats, I'm always riding that way. – cmaster - reinstate monica Sep 22 at 14:25

11 Answers 11

38

Having made the change myself, I can confirm that shock absorbers are actually detrimental to city riding. You lose a lot of power, especially when trying to stand on the pedals for acceleration.

Road bikes are also typically much lighter, which in my experience not only helps you go uphill faster, but also makes it a lot easier to carry the bike when necessary. For instance when I am leaving my place, with my old bike I would've had to clumsily roll it out, but with the road bike I can just carry it out to the street. It's not something you typically think about, but it saves time.

As a final note, while you can't turn a mountain bike into a road bike, you can make some changes that would improve it's road performance a bit. One thing you can do is swap out your normal nubby tires for slicks. Slick tires, pumped to the appropriate pressure, will reduce your rolling resistance. Also if your shocks are the adjustable kind, then increase the firmness, or even lock them entirely, so that they won't waste as much of your energy.

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    Welcome to Stackexchange. I normally suggest people read the tour but this is a great first answer. Keep it up. – Criggie Sep 21 at 22:56
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    Unfortunately I don’t have exact numbers. What I can say is that, if your concern is the price of a new road bike, one alternative would be to look for an antique through Craigslist/a flea market/etc. There’s plenty of them around that are still in good working order. Going this route means you can get the general experience of a road bike... with perhaps a few quirks like down-tube shifters... without having to pay top dollar. – Dylan Luttrell Sep 22 at 1:25
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    The difference was night and day to me, even after making my MTB more of a hybrid commuter, I've gone from an average of 10mph to 13mph on the road bike and that's not even pushing the road bike that hard. Weight makes a huge difference along with no suspension. I'm yet to try the clip in SPDs as yet but I expect to gain another increase when using them – Dan K Sep 22 at 10:40
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    Good answer, I would add that it is certainly true that shock absorbers also absorb the force we want to commit to the surface via the drivechain - but it is equally true that riding a bike on through the city on rough cobbles without at least hybrid tires and shock absorbers is detrimental to not only the bike and it's tires but eventually also the desire to bike. There are shock absorbers that can be locked with a handlebar switch - which is tremenduously useful for when you need the best of both worlds. – Stian Yttervik Sep 22 at 11:14
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    I don't agree that shock absorbers are always detrimental. I converted my old city bike with shock absorbers to a drop bar bike, installing a drop bar and high-performance road tires. It was about as fast as my subsequent drop bar touring bike. – juhist Sep 24 at 3:47
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Some representative values from http://bikecalculator.com/veloUS.html. It's a road-bike calculator, so it's not quite accurate. I simulated a hybrid/city bike by having the rider on a 30-lb road bike with MTB tires, and riding that "road bike" in the least aerodynamic position possible. Note that the difference between a road bike and an actual hybrid or city bike will likely be larger than this example indicates:

enter image description here

Putting 100W into the pedals in this simulation, on level ground, results in a 16 mph/25 kph speed on a road bike. The simulated "city bike" only gets 12 mph/19 kph from the same power input.

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    Dang - I was just about to do the same with bikecalculator.com I got 103 W required for a flat 20 km/h, 10 km in 30 minutes on a 15 kg MTB (but that didn't account for suspension) and a 70 kg rider. Simply changing from MTB tyres to Clinchers gives a time saving of 4 1/2 minutes for the same power, or a speed boost to 23.7 km/h. Any other single change is smaller difference. – Criggie Sep 22 at 23:49
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    Importantly, this doesn't even account for suspension losses. – Kylos Sep 23 at 14:17
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    30 lb for a hybrid bike seems quite optimistic to me even. With the thick frame, suspension in both fork and seatpost, and hub gears, I'd think 18 kg (40 lb) is more likely. – BrtH Sep 24 at 9:44
  • Racks, fenders, kickstand. I really can't imagine this thing being under 40 lbs. – Eric G Oct 4 at 18:16
  • @EricG Well, I didn't want any hybrid/city bike rider responding with, "But MY hybrid is only 17 kg! This is sooo biased!" So I picked parameters as favorable to a hybrid as I reasonably could. Besides, weight doesn't affect speed all that much on level ground. How fast you ride on level ground for any reasonable power input (~100W or more) is dominated by aerodynamic drag. You could easily set up a road bike so you have a very upright posture and wind up with, IMO, a much better "upright" bike than any hybrid with its "one hand position, all of them uncomfortable" straight bar. – Andrew Henle Oct 4 at 18:28
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Let's assume you are talking about speed on a non-inclined surface for a given level of effort. (When we talk about how 'fast' a bicycle is we can also mean how well it accelerates from a standstill or low speed, or how well it handles around turns or on a bumpy surface.)

Constant speed is achieved when power applied to the pedals is equal to the power lost to overcoming aerodynamic drag, rolling resistance of the wheels and all other losses in the bearings, drivetrain, frame and wheels flexing etc.

Power needed to overcome aerodynamic drag increases with the third power of velocity so at higher speeds it dominates. One of the biggest difference between a 'city' or 'hybrid' bike and a drop bar 'road' bike is a more upright riding position which results in a larger frontal area and a much higher drag.

City or hybrid bikes also typically have wider tires run a lower pressures which have higher rolling resistance than narrower, higher pressure tires typically seen in road bikes.

On bikes with suspension cyclic compression and uncompression of the springs and dampers due to unevenness of pedalling force and movement of the rider also soaks up energy.

Your hub dynamo will also be adding some resistance.

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    Thanks for the nice explanation, so actually all these nice gadgets make you slower in the end ? (for the same effort) but would a switch to a road bike make you much faster? I mean do you have any numbers for reference (something like I had a city bike & my average was 20 km/hr then with a road bike it is 30 km/hr) – Ahmed Elkoussy Sep 21 at 22:54
  • @AhmedElkoussy too many variables to know how much faster you’d be on s road bike. Test ride a few and find out. – Argenti Apparatus Sep 21 at 23:26
  • true I should do that, the problem is that it is not easy to take a bike for a 10 km test drive so that is why I asked if someone had this switching experience before replacing my bike, thank you for the help – Ahmed Elkoussy Sep 21 at 23:49
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    The hub dynamo has very small resistance. It provides 3 watts and resists at around 6 watts. That's 6% of 100 watts or 3% of 200 watts. Since power is speed cubed, it subtracts between 1% and 2% from speed. – juhist Sep 22 at 12:43
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    Drag increases with the square of velocity. Power increases with the cube. /pedant – Holloway Sep 24 at 9:31
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Why is a road bike faster than a city bike with the same effort?

Three reasons:

  • Smaller air resistance due to (primarily) smaller frontal area and (secondarily) thinner tires.
  • Smaller rolling resistance due to slick tread pattern, less puncture protection and smaller tread depth, narrow tires and higher tire pressures.
  • (If going or accelerating very fast) a riding position that's optimized for hard pedaling, so what might feel like same effort may actually be a higher effort on road bike!

Two very small, almost insignificant reasons:

  • Weight. It is a non-issue: main resistance is air resistance, weight plays no role in it. Second resistance is rolling resistance, weight plays a small role in it but you're seeing around 6% difference in the total system weight, i.e. around 2% difference in speed if all resistance is rolling resistance (and if 25% is rolling resistance, 0.5% difference in speed). Light weight is nice when going up hills, but then high weight is nice when going down hills.
  • Hub dynamo. It generates 3W, resists at 6W, so it's 6% of 100 watts or 3% of 200 watts. Around 1% - 2% difference in speed.

A non-reason:

  • Positive attachment between pedal and shoe. The reason this is a non-reason is that you don't push up with the back pedal when not accelerating, you just support some (but not all) of the weight of your leg.
and how much faster it is?

Not by much. Power is proportional to speed cubed, thus speed is proportional to cube root of power. If the main resistance is air resistance, you can reduce it by perhaps 35%. It means 54% more speed cubed is possible (as 1/(1-0.35) = 1.5385), i.e. 15% more speed is possible. (If you take into account rolling resistance, perhaps you gain 2-3% more, if weight, perhaps 0.5% more, if hub dynamo, perhaps 1-2% more, so you're not gaining more than 20.5% more speed, that's around 5 km/h more only at typical city bike speeds)

Note that you can buy 28mm high performance tires and install them on city bike rims. So part of the reason road bike goes faster is actually a non-reason, as those 28mm high performance tires are compatible with city bikes. (Don't buy 23mm tires, though: they require thinner rims.)

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    +1 for a sober, pragmatic answer. However, 1. “High weight is nice when going down hills” – if you refer to it being faster due to gravity pull, this doesn't really do much. More mass can make for a smoother ride, but only with good full-sus on rough terrain. 2. The upright position on city bikes really does make pedalling a lot less powerful, and I think this isn't just that you put in less effort but also that it's actually inefficient because body parts keep sloshing back and forth in useless, yet muscle-demanding ways. — Therefore, I think 15% is a very low estimate. – leftaroundabout Sep 23 at 15:32
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    Also on the weight issue. While it doesn't make much difference when at speed it IS a big issue when accelerating. In a city environment you are likely to spend a significant amount of time slowing down or stopping due to traffic and then accelerating again. I use both a road bike and a hybrid and I get back up to my usual cruising speed far faster on the road bike. – Eric Nolan Sep 23 at 18:38
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    but then high weight is nice when going down hills What goes down had to go up. And the slight gain going down doesn't make up for the extra effort needed to go up. Adding 10% to your overall weight adds 10% to a 10-minute climb, and takes off 2% of a 2 minute descent. As a 200 lb/90 kg+ ex-road racer (maybe again someday...) I know all about hills and weight... – Andrew Henle Sep 23 at 20:03
  • @EricNolan concur on speed/weight/acceleration comment - my `bent weighs 22.7 kilograms and cannot accelerate like a 7 kilo road bike. But due to aerodynamics I can catch a road bike at 30~45 seconds of tail chase, with +5~8 km/h of speed difference. – Criggie Sep 24 at 1:08
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    Weight doesn't play a part on downhill speed. A 1kg hammer falls at the same speed as a 30kg anvil, remember physics? – Carel Oct 24 at 10:43
6

Besides the other answers, the sitting position on a city bike encourages you to look around and pedal at a leisurely pace. The sitting position on a road bike encourages you to ride more energetically. You can do the opposite on either kind of bike, but there will be a tendency to work harder on a road bike. You may view that as a good thing or a bad thing.

5

I made the change earlier this year and I can highly recommend it.

The difference between a city bike and a road bike is like the difference between walking and running. On a city bike you have a comfortable upright position that encourages more relaxed cycling, whereas a road bike encourages much more intense cycling.

On a city bike you might cruise at 15-20 km/h with effort comparable to walking and on a road bike you would cruise at 30-45 km/h with effort comparable to running. My point being that the real world difference is much bigger than the theoretical difference, because the way you ride your bike will change. Pushing a bit extra on a road bike is much more rewarding.

If you are commuting to work, pushing your bike as hard as you can, to make it on time, the difference between a city bike and a road bike will be much closer to the theoretical difference. I normally use http://www.kreuzotter.de/english/espeed.htm to make these calculations. Not knowing your weight, height, fitness level, etc. I can't give you a very accurate estimate, but you will probably go 5-10 km/h faster on a road bike, than on a city bike, with the same effort.

You also asked why road bikes are faster, so here are the reasons:

  • Better aerodynamics (mainly due to seating position)
  • Lower weight (mostly important uphill)
  • Lower rolling resistance (slick tyres with high pressure)
  • Stiff frame (no suspension)
  • Higher gears (you can go faster with the same cadence)
  • Unless you're a pro rider, with other pros to draft with, you're not going to manage anything like "cruising" at 45km/h on a road bike. That's about my flat-out sprint pace on a flat road without a tailwind or drafting, and I'm rarely overtaken by other cyclists. – David Richerby Sep 24 at 10:16
  • @DavidRicherby I'm not going to argue with you on that. I only ever reach 45 km/h on long descents without traffic lights. Most of the time there's not enough time to reach 45 km/h before the next red light. I did give a range of 30-45 km/h and while 45 km/h is pro level speeds, I think most road cyclists will not have a problem cruising at 30 km/h or more. – Erik B Sep 24 at 11:44
4

It's Faster

With high confidence, I can say that virtually any road bike you test ride will feel like a sports car compared to the bike you have described. I can't say you will go 10% or 20% faster, but there is no question whatsoever that you will feel a qualitative change in your biking performance that is unmistakable and undeniable. If you can afford a road bike, and you intend to do a reasonable amount of biking, then you should really head down to your local bike shop and ask for some test rides. A pretty good starter bike can be had for about $1000 in the US, but I can't speak for Berlin, sorry.

The Differences

I can attest that putting slicks on your mountain bike and making sure you have tubes that can go up to 100 psi or so will also make a huge difference on your road performance. You could be running anywhere from 25-50 psi right now, which will easily double your contact patch, resulting in huge rolling resistance. As others have noted, the posture of road bikes is also more conducive to reduced air resistance, which becomes the dominant force above 10-12 mph (and also why mountain bikes are not designed for a hunched-over posture: not only is that dangerous when clearing obstacles, but it's nearly impossible to maintain 20-25 mph over rough dirt dodging tree branches, unless you're going downhill, and that's especially dangerous).

But one of the biggest differences is clipless pedals. This is like going from a 4-stroke engine to a 2-stroke. Normal pedals only allow you to transfer power about 1/3 - 1/2 stroke per foot. You actually need to apply negative power with the other foot just to maintain pedal contact. Clipless pedals "lock in" your shoes to the pedals, which allows you to apply power over 100% of the stroke, with both feet. You can literally pull up with the opposite foot while the primary is pushing down. While some mountain bikes have toe cages on the pedals to give you 2/3 - 3/4 stroke coverage, this is less common than road bikes (with a toe cage, you obviously cannot apply power while your foot is moving backwards, unless you rotate it in an awkward an unnatural way).

Conclusion

Each of the differences above would be noticeable all by itself, if you just compared bikes that differed in a single feature. But when you put them all together, you will likely be overwhelmed by the difference in agility and performance. Mountain bikes do indeed feel like tanks. On the other hand, road bikes can sometimes feel a bit flimsy if you are cranking hard and not in perfect balance.

Now, most road bikes will not come with fenders or gear rack or panniers. Nor will these be transferable from your mountain bike, for the most part. But obviously, they are all available for the road bike form factor. If you are trying to save money, you can get a used bike and try to find used fenders, etc., or see if you can get a used commuter bike that already has the accessories you want. Road bikes will usually have traditional gearsets with a 2-gear front sprocket and 7-10 gear rear with external derailleur. Hub gears would be very unusual. This does entail a bit more maintenance and care, but nothing overly dramatic.

If you can afford it, you should definitely get a road bike! You will not be sorry.

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    Toe cages are just fine on a road bike, especially one that's going to be used around town: needing special, awkward shoes for your bike makes shopping and errands much less convenient. While, in principal, you can pull up on the pedals with clipless, most people don't (and even pros don't do it much). You can certainly exert backward pressure with toe cages without needing to dip your toes very much. – David Richerby Sep 22 at 12:03
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    Fenders and a rack probably won't be transferrable from a mountain bike (actually, I think the asker is describing a hybrid with front suspension and a suspension seat post, but that doesn't really make any difference). Most road bikes don't have mounting points for racks, and the fenders on a hybrid or mountain bike will be designed for wider tyres and probably won't fit a road bike even if it does have mount points. The asker might want to consider a touring bike, which will have rack and fender mounts. – David Richerby Sep 22 at 12:05
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    tubes that can go up to 100 psi Be careful. No bicycle tube can hold 100 psi on its own. Bicycle tubes are prevented from expanding and bursting by being held in place by the tire and rim. Exceeding maximum pressure ratings on a large bicycle tire can be dangerous. A 2.5-inch 29er tire probably has a surface area over 500 sq in (a perfect "29er-sized" torus with a 1.25" radius has over 750 sq in of surface). If you pump a 2.5" 29er tire up to 100 psi, that tire is holding in a total of 50,000 lbs of pressure. There's a reason bike tires can be LOUD when they burst . – Andrew Henle Sep 22 at 12:56
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    You can effectively apply power without clipless pedals on the back stroke. It's done by supporting the weight of your rear leg. – juhist Sep 22 at 13:04
  • The times of high pressures is over. businessinsider.com/… 100 PSI is OKish for a 25 mm tyre, 28 mm are becoming popular and even smaller pressures too bikeradar.com/features/… 25mm is probably too slim for a mountain bike and its rims. Anyway, I became considerably faster by getting a wider tubeless tyre with lower pressures. Just a bit less knobby (G-One). – Vladimir F Sep 22 at 14:05
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In my opinion, it's all about aerodynamics. You are more upright on a hybrid/MTB/Town Bike. Which is a good thing while commuting as you are more heads up and aware of the busy space around you. But your frontal area robs you of a LOT of watts.

On a drop bar road bike, you can make an effort to keep as aero as possible by staying on the drops. You will save a lot of energy or be able to go faster for the same energy expenditure. But you will be head down so will be able to see less.

In a sort of exception that proves the rule kind of way, I have a hybrid bike that I can push pretty much as fast as my touring/endurance/comfort oriented road bike. I believe this is because, even with flat bars, I can get into an aero position by resting my forearms/elbows on the bars. (Not recommended unless you have a clear, smooth road!)

2

This is the question that you did not ask, but I feel that the answer would not be complete without considering this one as well:

Why is a city bike faster than a city bike with the same effort?
If so, what would be the difference between the two?
And how much faster would it be?

(1) and (2) obviously is a matter of quality and maintenance, and (3) the difference may be tremendous: To my experience a good city bike can easily compete with a shabby road runner (in terms of speed, not theft-proofness).

Your bicycle is clearly not a mountain bike. This is what is sold on the German market under the name "Trekking-Bike": 37mm to 47mm (1.5 to 1.75 in) tires; mudguards, racks and lighting are common. City-proof and conforming to the German law (as long as the lamps do their work). Ironically the low-budget ones use to come with suspension (and heavy stiff aluminium frames), the more expensive models (800€+) often don't need one since delicate steel forks can provide the same comfort (and don't absorb your energy).

The bike that you own has been assembled by a manufacturer located in Sangerhausen, (former East) Germany, which has a long tradition, and is known to have produced mainly for the budget mass market (discount stores...) in the past 20 years. Yet that don't mean your bicycle won't run (even if there's a German proverb claiming the opposite - check Wikipedia).

A few hints may help:

  • Pump tires to the admissible pressure (~3 bars, "hard" to the rule of thumb)
  • Adjust the brakes carefully to make sure the brake shoes do not touch the rim in idle position.
  • Chain lubrication matters - Not clear from your photo, but I guess your chain has done a few years work and is worth replacing (10€ + service). If so, at least the rear sprocket should be replaced as well (which is kind of easy, 5€ + know-how). You will be surprised.
  • Looks like the common 7-gear or 8-gear hub, these may last a life. The hub dynamo may call for replacement if it makes some uncommon noise (not so cheap, unfortunately).
  • Thanks Jan for the fantastic answer, I bought it as a trekking bike from a used bikes shop but with the high handle bar I think it's a city bike, tires are too thick and it's too heavy i think all these make it harder to go fast as per all your answers – Ahmed Elkoussy Sep 24 at 23:01
1

Anecdotal and non-quantitative, but I've got two bikes: a road frame built up as a hybrid, and another road frame set up with racier geometry (see attached photo). Both are of 1980s vintage and maintained equally well so I think they offer a useful comparison. Even after owning them both for 5+ years now, I'm still surprised by the striking increase in speed and simultaneous decrease in effort when I hop on the racer after riding the upright monster for a while. I don't quantify speed or effort at all on any bike I ride, but the difference is unmistakable even for someone as unobservant as I am (as well as for my young son, who routinely accompanies me on/behind both bikes).

Bikes

0

I'd say there are 2 quite simple differences - tyres (size & pressure) and rider position.

If you have better tyres (lightweight and high pressure ones), you can decrease rolling resistance significantly and if you adjust or change the handlebars, you can decrease air resistance, which is a significant factor even at the 20km/h you mentioned.

There is more info and comparisons in this other question: How much resistance comes from each part of a bicycle.

That said, all these changes may reduce comfort and are also most effective on a good road surface. If you want to ride comfortable, slow and get sweaty soon, keep you current bike, while you want to ride faster with less effort, upgrade the tyres and body position.

I used to commute daily on similar trekking bike, starting on OEM 37x622 tyres but have changed to 23x622 tyres at 8 bar and handlebars from an old RMX set down & front to get more horizontal pose (in city it is way more comfortable to have them up, but on longer track I prefer to have them far down). Riding a 20km track on an old MTB took me 1.5 hrs and I was extremely exhausted, now I ride it in 50-65 minutes and feel fresh and way better than spending the same time (staying) in a bus.

After approx. 30 years and riding a lot of different bikes, I can tell - if you change the wheels (tyre size, model), you can feel almost same difference as changing the bike. You can compare tyres here: https://www.bicyclerollingresistance.com/

And also load or power makes big difference, so enough to change back tyre often to get lower resistance + significant uphill bonus too. But crappy cheap tyre is like riding against bungee jump fixing @ any size/with and do not suppose one can buy old bike with excellent tyre type when even lot of new has terrible resistance one's like Schwalbe Lugano (perfect puncture proof and long life, but worst resistance).

  • And also interesting link from different SO site physics.stackexchange.com/questions/445132/… cyclist do not like physics often ;-) Also from my experiments with an old still punctured e-Scooter if you increase mass of tyre or improve puncture resistance layers, you lose power on rolling resistance. – Tom Sep 24 at 9:53
  • Thanks a lot Tom, Yes, based on all your answers I think I better get even a basic road bike – Ahmed Elkoussy Sep 24 at 23:03
  • Btw I have narrower rims (13) from previous street bike, but left original trekking's of 18mm inner width - no problem even with 8-9bars, but not riding that long (<1000 km). Never got any problem even when tyre outer with is similar to rim outer and on one old had 20mm tyres on 25mm inner steel rims and only problem was a tick on rim sometimes (no problem for that steel) when pressure was too low or met unexpected edge. – Tom Sep 25 at 17:55

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