Mountainking7

Ok I've read many threads and posts about how getting a lighter bike is insignificant w.r.t. getting fitter etc and that even if you were fitter, the gains would be very negligeable and would mostly be visible on steep hills on accelerations and the gains would be lost by rolling momentum or something like that of the heavier wheels.

So, if one person uses 2 bikes, say one weighing 15 likos and one weighing 9 kilos and climbing a steep CAT1 hill, he will essentially get no gains in speed? Is this correct? assuming a seated constant climbing effort...

Now, if the same person rides a 30kg bike instead of a 10kg one, will it be the same speed once the initial acceleration/motion is established?

Homebrew01

Lighter bikes will go faster for the same effort. How much faster, and at what price are the questions most debated.

WestPablo

+1

Yes, what @Homebrew01 said, plus the fact that when you are climbing uphill, you're expending more energy and losing more time as a result, thus slowing you down. Even on the "flats", in addition to the frictional road resistance, most times, the "flats" aren't really perfectly flat. There are little tiny bumps and rises in the road. Each bump or miniscule elevation, counts as a "hill" that you must climb, it requires a tiny bit more energy to expend to overcome it. Climbing those "hills" with a heavier bike, requires even more energy than a lighter bike.

Therefore, whenever you just stop pedaling to coast on a more evenly flat surface, you'll coast a further distance, than coasting on a somewhat uneven "flat" surface. Of course, we must remain aware of the fact that a heavier bike will have greater momentum, thus more kinetic energy, but need that same energy to lift itself over the uneven surface. The energy gained from momentum, is lessened by the energy used in lifting the bike while climbing "hills".

slorollin

It is the same conversation for any vehicle be they cars, boats, planes, skateboards or rickshaws. You can't avoid your power to weight ratio. Either decreasing weight or increasing power generally improves speed performance in MOST situations.

VegasTriker

There are other factors that come in to play. Cheap bikes with crappy components are almost always among the heaviest bikes sold. They often have useless ad-ons such as exotic looking suspensions that work poorly. Lighter bikes almost always come with higher quality components that simply work better. It's a real pleasure to ride a good bike. Since it takes less effort you are likely to ride faster and go farther on it. If you do so you will achieve the same level of fitness.

BTW, you can get a much better bike at a reasonable price if you search hard among the many bikes sold second hand. Let somebody else take the hit on depreciation as you ride the bike out of the bike store.

fietsbob

Well designed load carrying bikes like touring bikes, will be heavier to better deal with the loads on them .

the frame made more rigid, by increasing the tube wall thickness/diameter, in higher strength steel or aluminum alloys.


A frame made with low cost steel will use more steel to make it strong enough , a high tensile strength alloy steel
will be sufficiently strong with Less .

if not in a hurry , like in Racing, by lowering the gear ratio, heavy, eg Touring loads, get up hill in a reasonable time period..


Overcoming air resistance .. the guy on the saddle is most of the air resistance ..
bike parts weight and aero stuff is about the last 2%

like to ride all day bent over, as low as you can? is that comfortable? not to me..

Garfield Cat

That Category climb is not the end of the story. One would take the entire ride into consideration when discussing the difference the weight of a bike makes on the ride.

By isolating the discussion of weight just to a Category climb would be riding a bike without a rider just to measure the wattage expended on the dummy rider.

cplager

Weight matters (mostly) in three aspects and in all three, it's total weight (bike + rider + crap) that counts. So how much is the 6 kilos extra weight compared to the total weight answers most of your question.

1) Climbing. 10% more weight takes (at most) 10% more energy.
2) Rolling resistance: 10% more weight means 10% more rolling resistance
3) Accelerating: 10% more weight means (up to) 10% more energy.

(1) only matters when you climb. Even then, you'll only get the full effect if you're climbing so slowly there's no aerodynamic drag.

(2) you pay all the time. But at around 15 mph, rolling resistance is only half of your drag and it falls quickly after that.

(3) is the same as (2). Once your in a regime where aerodynamic drag is important, weight becomes less important.

Find one of the several bike calculators online. They can answer these questions quite nicely.

And, for the record, this is only in dispute by those who don't (want to) know basic physics.

WestPablo

+1

Excellent!

@cplager is right on the money, here!

elcruxio

When considering steel the amount of material also comes into play as well as the actual material composition.

A heavier bike most likely will use a cheaper lower tensile strength steel (not to worry, still plenty durable for bicycle application). This means the wall thickness needs to be greater. This can then lead to lessened "suspension" in the tubes as they are thicker hence creating a harsher ride than a premium steel frame would. With better steel thinner tube walls can be used making a more compliant and road buzz damping frame.

I'm pointing out here that rarely is weight the only issue at work in premium bicycles. Of course a lighter bike will cost more, but you also get other things than just the weight. With carbon you get aero benefits and all that. As mentioned earlier higher end models usually sport higher end components which to a certain point are more durable, function better and especially with wheels give again, some aero benefit.

Weight is just one part in the sum of incremental performance improvements. One just needs to decide what performance index is sufficient. I'm not going for over 9 kilo road racing bikes again. It's pretty easy actually to get under 9kg with a road bike. And my lower limit is at the 6.8kg which is the UCI mandate (not going there any time soon). With a touring bike things are of course different if they are going to incorporate disc brakes and rohloff hubs.

Little Darwin

While I think this explanation is close, I would highlight one thing, and add something to the mix...

First, the weight to be considered is a combined weight of rider + bicycle + anything else being carried. This puts the weight of the bike in proper perspective, it is only part of the weight related issues. I have heard that there are more benefits for reducing rotating weight, etc, but I think that would be minimal for most riders.

Climbing hills is basically a form of acceleration (fighting the acceleration of gravity) so 1 and 3 are closely linked in my mind.

However, is rolling resistance actually linear? If so, it is not intuitive to me. Not disputing, just curious.

The one element to add to the mix is the impact of weight on wind resistance. For flat roads, riding at your cruising speed (assuming a speed over a couple of miles per hour), the wind resistance is the main thing that is consuming the rider's energy. I wonder if cruising speed on flat ground may actually benefit from extra weight, for the same reason that heavy riders can coast down hill faster, and I think can even coast further on flat ground due to the momentum... I know this is true on hills, since I can coast on my hybrid, and pass smaller riders on their road bikes... at least until I start braking because 35 mph descents are about all I am willing to do because I don't trust those wimpy bicycle brakes to stop over 350 pounds very quickly. Give me a long straight hill, and a little bravery, and I would beat most cyclists down a hill.

cplager

First, the weight to be considered is a combined weight of rider + bicycle + anything else
being carried.

But... But...

From the first line of my reply:

Actually, I don't mind you pointing this out again as this really is the important point (and seems to be the point that gets ignored most in these discussions).

I've got a heavy bike and I've got 15 lbs I could lose. It's cheaper and just as effective to lose the 15 lbs.


For bicycles, rolling resistance is usually quantified as Crr and the force due to this is proportional to Crr * total mass. Does this mean it's really linear? Close enough.

So...

If you want to cruise at a constant (high) speed on flat ground, then the energy you need to provide is determined only by the aerodynamic drag (I'm ignoring rolling resistance here). So being heavy doesn't help.

But...

If you're going a high rate of speed and then stop pedalling, the higher mass cyclist will slow down more slowly.

cplager

But... But...

From the first line of my reply:

Actually, I don't mind you pointing this out again as this really is the important point. I've got a heavy bike and I've got 15 lbs I could lose. It's cheaper and just as effective to lose the 15 lbs.


For bicycles, rolling resistance is usually quantified as Crr and the force due to this is proportional to Crr * total mass. Does this mean it's really linear? Close enough.

So...

If you want to cruise at a constant (high) speed on flat ground, then the energy you need to provide is determined only by the aerodynamic drag (I'm ignoring rolling resistance here). So being heavy doesn't help.

But...

If you're going a high rate of speed and then stop pedalling, the higher mass cyclist will slow down more slowly.

ColnagoC40

Put in the numbers and see the difference.

Bike Calculator

Little Darwin

I bolded that, and worded it differently than yours in case a little difference helps someone remember it the next time they start agonizing about weight of a component... It is definitely the thing people seem to forget in bicycle weight discussions. And here we are increasing the repetition for those who learn by rote.

Unless they start building anti-gravity bikes, there will never be a bike light enough for me to be a great climber or accelerator unless I lose a lot of my body weight.

Thanks for the clarification on weight related to rolling resistance and air resistance... Maybe I can use the (nearly) linear nature of rolling resistance to motivate myself to lose weight to make my flat rides easier (or faster). Especially since most of my riding is on crushed stone, I think I can make pretty good improvement by cutting my weight by 30 or 40 percent. plus a narrower body will reduce wind resistance a bit as well.

Little Darwin

Thanks for that... I will be running some numbers to motivate myself to lose weight.

cplager

This (or one of the other calculators) is really the way to do this. Even if they calculator isn't perfect, they're close enough and work very well at giving you an idea of how big different effects are.

dynaryder

Four,actually. You forgot lifting the bike. Folding bikes get picked up and carried often,so a couple pounds can make a big difference. My old Novara FlyBy was a nice bike,but it weighed a little over 27lbs. My old Mu SL weighed a little over 20lbs,def easier to deal with. There's also folks who have to carry their bikes up stairs,and there's the inevitable having to put the bike in a workstand or flip it over to work on it. I run a free bike clinic,and whimper whenever I see a Euro-bike or old English 3spd come in.

cplager

Agreed. ( Although this doesn't affect speed. )

Little Darwin

Although it could make the pit stop longer for a flat repair etc. Races can be won or lost in the pits.

Mountainking7

I used the numbers on the bike calculator....

Compared a 14kg bike to a 10kg bike on a 10km 6.7 gradient. Well, it says 3 minutes less....There goes the theory of weight not affecting climb speed....

stephtu

No one advocated that theory, of course it affects climbing speed. It's just that the magnitude of difference isn't that much in normal cases. 3 minutes over a 70 minute climb isn't that huge in the big scheme of things, unless you are racing. Also, the gap is usually more negligible because:

- comparing bikes, one is normally comparing ones of the same type. Weight differences are usually more like 2 kilos or less, entry level race vs. near top of the line, not 4 kilos. Usually one isn't comparing between a racing bike and a heavy touring bike.
- makes less difference on less steep climbs, and the time gaps are smaller on shorter climbs since the time to finish is less. Usually long 10km climbs have lower average gradient. Category 1 steep/long climbs are exceptional, not the norm, that's why they are cat 1.
- time gap smaller at higher power level than the bike calculator default of 150 watts
- less difference with heavier rider

On more normal climbs at faster pace, typical bikes, more typically one gets results like say 30 seconds faster on a 25 minute climb.

Mountainking7

@stephu: I made this thread because while deciding if I needed to get a race/road bike to ride on roads vs my current mountainbike (with large road tyres) It weights 14kgs and has lockable front suspension. I reasoned myself with the many posts I've read here and elsewhere that the kgs won't matter as long as there is no acceleration on the bike and the climb speed would be virtually the same given a constant effort. Other common responses was to incite a person to loser weight.

I am in a situation where my weight is irrelevant. Im 1m80 (5ft11?) and my weight dropped from 65kgs to 62kgs in a year. The only benefit (drawback)I have seen is that I am now more comfortable out of the saddle (maybe losing weight or muscle mass I don't know)

This is why I was comparing a 14kg (MTB) to a 10kg or less road bike.

stephtu

I think you probably misread the posts. I don't think anyone would ever dispute that weight hurts you when climbing, and dropping 4 kgs would definitely help. Where weight doesn't much matter is on the flat. You perhaps were confused by posts clarifying that *rotating* weight, e.g. extra weight on wheel rims, doesn't hurt you any more than *non-rotating* weight, once you get up to steady speed. Total weight, whether rotating or not, certainly matters when climbing at constant speeds.

In any case a road bike also gives you a more aero position with narrower bars, & multiple lower position options with the hoods and drops, and somewhat lower rolling resistance with higher pressure thin tires, so definitely a good idea for extended road riding.

fietsbob

Phinney claimed that because he was heavier, he descended faster and at the bottom of the hill opened up a gap .

and time-trialed the rest of the way into Santa Barbara FTW.

of couse he had to be at/near the front of the group, at the summit.