prj71

No. That is not the case on flat roads.

As a bike gets rolling it gets resisted mainly by three forces...Aerodynamics, gravity and tire rolling resistance.

Gravity will only come into play climbing which takes into account the total weight of both bike and rider.

seypat

A lot. If going uphill, you want the bike to be light as a feather. If going downhill, you want it to be a boat anchor.You really need the team/support car following you so you can switch bikes as needed.

RChung

My friend Damon Rinard says when comparing bikes you can usually think about substituting the word "easier" for "faster." Human beings aren't good as measuring "faster" but our senses are pretty good at measuring "easier."

If you know about Damon, you know he can do the actual science. Lighter, more aero, lower rolling resistance, bikes can be shown to be "faster" with science, but it doesn't usually require science to determine that they're easier at the same speed.

Koyote

Yes, but the physical laws which determine the relationship between a bike's weight and it's speed do not vary from rider to rider.

People often "feel" faster on newer and lighter bikes because they have that new bike fever -- the adrenaline and excitement. Hell, I've seen it: the guy who shows up on a new bike and is, for the first time, pulling the group and contesting town line sprints. And there's also the subconscious need to confirm the big expenditure by believing that the bike is making the rider faster, rather than vice-versa. And, of course, a lighter bike is generally a little bit faster, ceteris paribus -- but none of us, out on the road, is capable of performing anything close to a real experiment that would quantify the difference.

Yes, hence the poster (post #8) who jumbles together the two concepts of speed and "easy."

livedarklions

Understood, but these effects may be so marginal that they really aren't noticeable to the individual rider. If they're only "spinning" up to a speed of 11 mph, say, I'm not sure they'd even notice that it took a split second longer to do that on the heavier bike. Also, keep in mind that people vary in weight a lot more than bicycles do. A 150 pound rider may be getting the same 4 pound reduction in weight from bike to bike, but notice it a LOT more than the 250 pound rider.

Honestly, I take the subjective approach primarily because it's literally the only thing I care about since I'm not racing or doing anything where I need truly objective data.

Finally, I'm not sure that individual body geometry doesn't have some weird effects that are hard to quantify. I felt I was a much better climber on my FX3 than I have been on several much lighter bikes. I didn't try to quantify that, but there was something about the geometry that just lended it to stomping on the pedals like a madman.

As always, I will defer to RChung if he says I'm spouting nonsense.

greatbasin

I have a 32 pound steel touring bike similar to your Sutra, and I have a 20-pound Bianchi road bike -- not as light or high-tech as the carbon Roubaix, but close compared to the touring bike. At low speeds, the difference in power needed is negligible. I mean, due to rolling resistance, one bike might actually take more than TWICE as much power as the other bike to go 7mph, but if one bike is taking 4 watts and the other 9 watts, who cares? Either bike should seem effortless as this speed. I would not describe the road bike as any "easier." Is there 6 watts there due to lower rolling resistance and lower drag? Maybe, but I can't feel that difference. At low speeds, the road bike will not feel any easier and may actually feel harder simply because it's uncomfortable.

Only at the higher speeds is the difference remarkable. At higher speeds like 30 mph, aerodynamic drag resulting from the effect of riding position on frontal area, and the overall coefficient of drag is by far the biggest difference in terms of the power needed to maintain a certain speed. If you can reduce your frontal area by just one square foot, the needed effort could drop as much as 70 watts. Similarly, an improvement in the Cd by 0.1 could save 70 watts. So get your Lycra on and get in the drops if you want to go fast.

If you enjoy going fast or riding with others who do and are willing to adopt the riding position, the road bike will no doubt be much better suited than the touring bike. If you'd rather sit upright and see what you're riding past and you're not in a hurry, don't sell the Kona.

VegasJen

I don't know about that. For one, you're making a perfect scenario assumption. Even on flat ground, you're assuming a rider is producing constant effect on the bike. Unless you're a trained, competitive athlete, this is highly unlikely. I'm not going to pretend to be a competitive athlete, but I know I'm certainly not the only one who goes in "bursts". That is to say, even on flat ground, I might average a 17mph pace, but at any given moment, I might be doing 15, or 19, or something else entirely. Then, even in flat Florida, I'm sure there are the occasional stops, for whatever reason, which I don't think anybody here is arguing gives the advantage to the CF bike.

So there's a lot of Perfect Scenario science going on here. And in a lab, you guys may be right. I wouldn't know because I've never ridden in a lab environment. But out in the real world where even in "flat" Florida, there are the occasional dip or rise, bad pavement, headwinds, tailwinds, traffic lights, etc., the CF bike will be faster.

My two primary bikes are an all CF Specialized Roubiax and an aluminum Trek Lexa. And in a snapshot moment, on flat ground, they're probably so close as to not be able to tell them apart. But after 30 miles, I can tell you which one is faster.

icemilkcoffee 

That is true as far as steady speed is concerned. But first you need to accelerate up to that steady speed. The lighter bike will accelerate up to that steady speed quicker. Unless you ride in a velodrome, this will happen multiple times on your ride with stop lights, dodging people etc.

VegasJen

Exactly the point I made above.

RChung

Well, if you have a power meter you can calculate the energy used for all those accelerations and decelerations. Yes, you need to accelerate each additional kilo of mass, but your momentum is thereby a little bit higher so you don't decelerate as quickly. The place where you lose energy is when you have to use your brakes.

As it happens, I went on a 25 mile flat, mostly leisurely, ride (unusual for the SF Bay Area) a few weeks ago. We had lots of turns but not many actual stops where we had to use our brakes. I just calculated how much extra energy would have been saved for a 1 kg decrease in mass: for me, it would have been a bit less than 100 Joules. The total ride was ~700 kJ, over just a bit more than 2 hours. So, on a flat ride, mass does have cost but on this ride 1 kg would have been roughly equivalent to a difference in energy expended of about 1 part in 7000. So not much.

rsbob 

How much difference does a bike make on speed? Well I have never taken speed and ridden my bike and as far as I know my bike doesn’t take it either, so am not much use to you.

As the others have said, you will be able to accelerate and climb faster.

beng1

A light bike will only help with speed when going up a decent grade, otherwise it will do zero for you except empty your wallet. Biking is for exercise and getting in shape, which you will get less of with a light bicycle. Look at the routes you usually ride, if they are not full of any challenging hills, then a light bicycle is a waste of money. Where I live it is flat east to west, and from north to south it is an incline, so on some rides if I am going east and west I can have no net elevation change, if I ride north or south I will only have to ride uphill for about half the ride, big deal, I am on the bike to get in shape right? Also look at your weight, if you are big like I am, a bit over 200 pounds, then any bicycle is a very small percentage of the total bike/rider weight, if you are a small person though, and any bike is going to be heavy for you, then dumping cash into a lighter bike might be more worth it. I would stay away from carbon or aluminum though, aluminum maybe if it is used and very cheap, but carbon never, it is garbage. Steel bicycles are the best and always will be. Titanium is garbage too.

terrymorse 

Nice try, troll.

Maelochs

Bikes make a Huge difference in speed.

I am so much slower when I don't ride my bike.

BlazingPedals

If you change nothing but the bike's weight, then you will only see a minor improvement in overall speed. Most of the resistance you see at 16+ mph will be from aerodynamics. Changing your frontal area and airflow will make more difference than a few pounds one way or the other.

terrymorse 

[QUOTE=BlazingPedals;22573552Most of the resistance you see at 16+ mph will be from aerodynamics.[/QUOTE]

That depends on the grade of the road. Power estimate for 16 mph on a road bike:

Flat road: 98 Watts
1% grade: 156 Watts
3% grade: 272 Watts
5% grade: 388 Watts

Chinghis

My personal test is commuting. Real-world conditions, same route repeatedly on a "hybrid" (90s MTB) with 26" wheels, panniers, and flat bars/bar ends) and a road bike (80's Ironman, slightly better gearing for old legs).

I realize that average speed is affected by city driving, but over time I think it tends to even out. A faster bike should allow you to make more of those lights that are about to turn yellow, etc.

My best speed home, with 560 feet of climbing, has been 14.41 mph, at 41:53, on the hybrid. (My notes say "Good hydration and calories this day.")

My next best speed home, same route, same elevation gain, is on the road bike: 14.19 mph, at 42:39.

Now, most of the other top times belong to the road bike, but there's a time or two hybrid in there as well. My conclusion is that in real-world conditions, for me and my gearing/legs/condition, there's little difference in the 43-45 minute rides that I do.

That being said, I've also ridden the hybrid up GMR/GRR (a long, 22-mile climb up a mountain here in Southern California) twice, and used the road bike this year. Over the first ten miles of the climb, the road bike bested the hybrid by a couple of minutes. So, five pounds of difference between the hybrid and the road bike certainly helps on the climbs. But I couldn't do what I did last year on the hybrid, which was climb 12 miles on the pavement, and take a dirt trail back down. That was a hoot, and it's why I like the hybrid for just going out and riding. Dirt? not much I can't do, so long as it's not highly technical. I can find a lot of nice hardpack and "groomed" trails out here, since we get so little rain. Pavement? A few mph slower, but I don't care as much about road conditions. Need a good fast workout with not so much time? Take the road bike and do 14-15 miles for an hour, depending on the elevation gain.

Herzlos

My 15kg 29er mountain bike feels a lot slower than my 10kg road bike, but I haven't done any direct comparisons to prove it. I suspect the difference is slight.
I did an experiment before with a hybrid bike and road bike and found the speeds were pretty much the same over a 4 mile loop.

VegasJen

So I have a China-Mart aluminum full suspension MTB bike I weighed at one time and it came in at nearly 40 pounds. My Lexa comes in right around 22-23 pounds, so very nearly half the weight of the China-bomb. I did the same ride not that long ago between the two bikes and was surprised at how close my overall time was. The route was basically an 8 mile loop in my neighborhood. I was less than three minutes faster on the Lexa than on the China-bomb. However, as close as that was, I made the ride back-to-back with only about 5-6 minutes between, and I started on the China-bomb, so by the time I got on the Lexa, fatigue was already a factor. I'm sure that if I were to take a snapshot look at that ride, the max speeds were probably pretty similar, but there is simply no doubt in my mind that in the real world, the racier, the lighter, the faster the bike, the faster overall the ride will be.

Camilo

You should tell us what happens rather than asking a bunch of unknowledgeable strangers for an opinion of dubious (dare I say worthless?) value.

terrymorse 

Rather presumptuous, there.

Some of the strangers here are quite knowledgeable.

Camilo

You're absolutely right, I was wrong to word it that way. There's a lot of general knowledge here - and even more opinions masquerading as knowledge.

What I meant by my poorly written statement is that we are unknowledgeable about your personal fitness, motivation, the terrain you ride in, the bike's fit, any changes in air resistance on the new bike vs. the old (frame, wheels, tires, position) and other factors that will affect the speed you go. You could just go faster or slower because one bike and your position on it is more aerodynamic regardless of the weight. You might go faster or slower because of better or more properly inflated tires, regardless of the bike weight.

My point, though, was that the best answer to your question is what you experience yourself. Did the lighter bike make you faster, and under what circumstances. if not faster, was it more fun in any way? I was saying that your experience is the only truth in this situation.

Maelochs

... and quite strange ....


which I see as a good thing .....

BlazingPedals

Tailwinds never get the credit, do they??? It's either a headwind day, or "good hydration".

Chinghis

Haha, except that the prevailing winds on my current commute are literally almost always headwinds, in each direction. There's frequently an offshore flow in the mornings as the landscape warms up, but the earlier I go, the better. But in the late afternoon, there's an onshore flow that often ends up giving us haze or fog the next morning. When I worked in the opposite direction, yeah, I had tailwinds. That little 2% grade or whatever up Venice was no match for me! At least in the afternoons.

I'll take better notes in the future