What impact does weight have on flats

This is a really intriguing question. I know that the current trend is to claim that “aero is everything” and that weight doesn’t really matter on flat terrain.

But I feel like weight matters somewhat more on “flat” terrain than most of us understand. I sometimes commute with a backpack with 20-25 lbs in it and I feel like the toll of constant small-ish accelerations is pretty significant, compared to when I have no backpack on. And I also question the impacts of continuously slightly rolling terrain that we describe as flat, because it mostly is, but that in reality is constantly undulating.

I realize that I am less aero with my backpack. And I understand that a heavier rider will decelerate less than lighter riders, generally. My comment regards the toll of constant small accelerations that are typical on a flat-ish road. Aero is the most critical factor on flat-ish (do most of us ever ride truly flat terrain? Isn’t it almost always somewhat rolling?) terrain, but I believe that weight matters more than the most current thinking accounts for.

Does the difference between a 16-pound bike and a 17-pound bike make a big difference on flat-ish terrain? No, probably not in a way that matters to most race outcomes. But I’m also thinking, wattage held at a constant, that the difference between a 200-pound rider + bike + kit is a big disadvantage compared to a 175-pound rider + bike + kit once all the different real-world factors of flat-ish terrain are accounted for.

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Wouldn’t a bigger rider have more mass and thus more drag though? Hard to quantify adding a layer of fat/muscle under a jersey vs. a weighted vest…but the added weight does mean more bulk on a frame and generally pushing a bigger hole through the wind.

Unless I suppose it’s added exclusively in the form a beer belly, which is well sheltered from the wind. Ha

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The one advantage is the potential max velocity on steep downhills a heavy rider can obtain compared to an ultra light rider.

Otherwise you’re right, being light touches on many more valuable aspects. It is not often that a +50-80mph descent plays a defining role in a race, but hey, the advantage is there for the heavier rider should it come up. :slight_smile:

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This was my 110 km ride today: Follow Pedro on Strava to see this activity. Join for free.

I started at 5 m below see level and it took 65 km to get down to 15 m below see level…

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No. On perfectly flat ground, gravity is orthagonal to motion and thus has no direct impact.

What you have to overcome is resistance, mostly from the air, but also from the tyre rolling (gravity plays a roll there), and from friction within the moving parts of your bike.

Gravity comes only into it when you increase your distance from the centre of the earth, aka, climbing.

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Yes. Exactly, at least for cyclist. Gravity has more impact on runners on flat ground where my legs need to both prevent me from collapsing to the ground, and propel me forward. On the bike, the bike itself is doing most of resisting gravity (and is quite efficient at it).

If gravity was resisting going forward, its force vector would have to be something other than straight down. If that was true, even at a stop, gravity would be pushing me backwards, but it does not.

The vast majority of resistance on level ground is wind resistance, as others have pointed out, there’s some in the drivetrain and tires, but not a lot. Wind resistance scales with speed, so there’s not force when you’re stop, and more and more as you go faster (and its non-linear).

There is no such thing as a perfectly flat road, but even if their was, more weight means more rolling resistance. This goes double with roads that aren’t perfectly smooth.

In real world conditions, 20 kg is a massive disadvantage even on “flattish” roads.

Yes, more bodyweight would mean larger frontal area. This calculator also takes that into account: Bicycle Speed (Velocity) And Power Calculator

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You haven’t ridden around where I live. :rofl:

Based on the thread title I thought this thread was going to be about the effect of weight on flat tires, not riding on flat terrain. :grinning:

This is not true. Rolling resistance is not proportional to rider weight, it is constant given proper tire inflation.

As for the terrain… Given the same watts, the lighter rider will usually be faster. Given the same W/kg, the heavier rider will always be faster.

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Heavier riders typically have greater drag, yes, but given similar proportions and riding positions the percentage difference drag is smaller than the percentage difference in weight. So given the same W/kg, the larger rider will have an a air resistance advantage. This is partly why larger, higher raw power riders excel more of flatter roads.

This is incorrect. Rolling resistance increases more or less linearly with rider weight.
There is more to RR than just hysteresis losses!

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Several things here: as others have pointed out, course profile matters a lot, as does strategy and who you are comparing to whom.

On a perfectly flat course with few accelerations, weight matters very little, aero is much more important. So if the two riders have a comparable drag coefficient, then putting out the same power they can ride at the same speed. Of course, you could think of complicating factors, e. g. you are comparing a 2.00 m tall person to a small 1.60 m rider. In all likelihood, the smaller rider will have less drag.

However, typically, bigger riders tend to put out more absolute power. If the two riders have comparable fitness, the 2.00 m tall rider will have a higher FTP, whereas the smaller rider might have more W/kg. If you pitch them against one another, any number of things can happen. The course plays a huge role, but also tactics and skills.

On a flat course, the heavier rider will have an advantage, plain and simple.

On a rolling course, it is trickier. If I were the heavier rider (which I usually am — I am not a heavy guy, 73–74 kg, but I live in Japan and I have male team mates who are in the <= 55 kg Strava bucket) should invest into honing their cornering skills and invest their energy wisely. On the downhill heavier riders do have an advantage, if you are a heavier ride, roll near a lighter rider on a descent, you will see that you are accelerating more quickly.

Finally, on a hill climb TT, it is all about W/kg. Don’t expect to excel here as a heavy guy, unless your W/kg merits optimism.

Ok. I’m curious to learn something here. I did a bit of reading and most sources mention only hysterisis as the primary/main source of RR. Contact patch size and shape? This is mitigated by pressure as well. Bouncing? A lighter rider should bounce more given the same pressure. Some studies show an increase of RR with weight, but it looks like those are done with constant pressure. I love to know the details of these things, though, and am genuinely interested.

Either way, since at least a large part of RR is
constant, given the same W/kg, RR is definitely in favor of the heavier rider.

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My understanding is that tire deformation is the dominant contribution here as well. And while you could make comparisons at constant pressure, I don’t think this is relevant to real world scenarios where two riders have significantly different weights.

Agreed, although I’d say on flat terrain, pure watts is what counts. Even additional rolling resistance gives athletes that put out more watts in absolute terms an advantage since the extra rolling resistance (e. g. going from tarmac to single track or from single track to sand) is a smaller relative to their absolute power. That holds true on inclines as well, further muddying the waters our discussion happens in.

Just to double check and see if I am wrong here, but do you have a link or so? Just to be clear, of course there is also static friction between the surface and the tire, and that is certainly proportional to system weight (= bike + rider). But I thought the dominant contribution was hystereses losses, which is why tire compound is as important as it is.

As for the heavier rider “always” being faster, this is true in theory, in a time trial.
But in races, the name of the game is separation. A lighter guy may be able to accelerate out of tight criterium corners or up small hills better, allowing them to create separation, or save their legs for the finish.

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Here is current record for Germany south to north end to end record, set starting on August 27th 2022, . Note speed and power numbers. He spent 2 hours 52 min stopped total.

Aero counts for a hell of a lot if you do it properly. This was in a velomobile weighing about 24kg.

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I like how it’s titled ‘morning ride’ like it’s nbd.

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The title of this thread is not specific enough.

Speed at a steady velocity = Rider weight has a very negligible effect on velocity.

Accelerating and decelerating = Rider weight has a larger effect.

This has been explained by someone who better understands physics than I, on this very forum. I’ll attempt to summarize it.

Speed on flat land = power vs CDA/rolling resistance/mechanical loss.

Two riders. Assuming they both have a perfectly equal rider position. One is just scaled up to a larger size. Exact same equipment etc. (obviously the larger rider will have a larger CDA, this is mitigated by the extra power and other benefits listed below)

1. 100kg 400w FTP 4w/kg
-20w rolling resistance
-5w mechanical friction
-40w bike drag
= 335w remaining watts to battle air

2. 60kg 240w FTP 4w/kg
-18w rolling resistance
-4w mechanical friction
-38w bike drag
= 180w remaining watts to battle air

Answer = heavier rider is significantly faster on flat ground.
Even more so on poor surfaces. Hence why heavier riders usually win Paris Roubaix.

CDA is one dimension, frontal area. Human mass is cubic, meaning a larger human has more muscle mass advantage at a greater rate then their frontal area cost. Their larger power is also less taxed by the non rider aero losses. The bike aero drag, rolling resistance and mechanical loss are march larger percentages of a smaller riders total power.

If you’d like to see this easily demonstrated, simply ride with a young child. 40kg 160w FTP 4w/kg. The 100kg 400w FTP riders will be dramatically faster on any flat road at the same w/kg output. Provided they have equal riding positions etc.

Heavy = advantage on flats and downhills.

The only time weight matters, is when climbing. Unfortunately, that’s where a majority of amateur cyclists measure themselves against other riders. It gives many a very distorted perspective on rider advantages.

Vingegard could not win the Tour de France without a team of large powerful riders to move his tiny body from climb to climb around France :joy:

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