contango 

This might seem like a stupid question, and I posted it in here rather than Road Cycling because being a lot heavier than most of the folks in there I'm not interested in replies that only apply to people who look like beanpoles.

My normal bike is a Specialised Tricross. I run 700x32 Schwalbe Marathon Plus tyres on it, leave a rear rack permanently mounted (for convenience, it's a bit of a faff taking it off and on). For the most part I can cruise reasonably comfortably at speeds between 15-20mph on the flats, usually closer to the low end but on a good day can cruise in the high teens for a while. The gearing is 50-39-30 at the front and a 9-speed 11-32 at the back.

The owner of my LBS lent me a bike built for speed. It weighs a good bit less than the Tricross, has 700x23 tyres, and I think the gearing is 53-39 at the front and it's got a tight 9-speed cassette at the back (I haven't counted but I'd hazard a guess it's 11-25 or similar). On a test ride today cruising at 15mph felt like it was no effort at all, and holding speeds in the low 20s didn't feel overly difficult. Local hills that are quite hard with my 30-32 gear on the Tricross were comparably difficult in terms of perceived effort in the 39-25 (give or take) on the lightweight bike.

So here's the bit that's confusing me. Obviously the speedy bike is lighter than the Tricross but by the time you put 250lb of me on the top the difference in bike+rider weight is going to be small. The speedy bike has something like 20 bladed spokes rather than 32 round spokes but it's hard to see that making such a difference. I can see going from 700x32 to 700x23 tyres would make a difference, as would tyres lighter than the Marathon Plus I normally run.

I've got two bikes already and would seriously struggle to justify a third one to my wife, who is very gracious about bikes living in the kitchen. If I can get a good performance boost by putting lighter wheels and thinner tyres on the Tricross that's certainly something I'd look at doing, even if I kept a spare wheel with a fatter tyre (my existing 700x32 in all likelihood) for the times I want to take it on more rugged terrain or load up the panniers.

Given the state of my local roads I'd want tyres tougher than the Continental 4-season tyres that were on this particular bike. I ran over something that went straight through the sidewall, trashing the tyre (almost brand new) and the inner tube. So whatever the performance benefits of going uber-lightweight I'd rather lose some performance and not have to carry a spare tyre around with me.

InTheRain

For me:

1. losing a significant amount of body weight
2. lightweight, stiff wheels
3. stiff lightweight frame (mine is a mid level carbon fiber already... not changing it.)
4. money (lots of it if you really want to reduce the total weight of your bike... or replace it altogether)

I know where the most appropriate place for me to start would be (#1)

furballi

Make sure the speedometer of both bikes are properly calibrated. The LBS could tweak the calibration curve of the lighter bike to report a faster cruising speed. Make sure the tire pressures of both bikes are properly inflated to support your weight. If you didn't have to put out much effort to hold speeds in the low 20s, then I'm quite sure that the odometer is set to fake a higher riding speed!

I would recommend that you have another person ride your old bike while you ride the lighter bike. Both should pace at 20 mph and compare speed.

I doubt that a lighter bike will give you an extra 2 mph on top of an 18 mph cruising speed unless there is a big difference in crank rpm.

jsigone

to me a fast bike is race geometry, fit, nice wheels and frame stiffness where it needs to be. Stiff front end w/ taper head tube and fork for better handling and off the saddle work. Stiff bottom bracket where flex isn't felt and everything my legs churn gets to the rear wheel.

contango 

#1 is a priority for me although seeing difference in the way these two bikes handled caused me enough interest to wonder just what it was about the lighter bike that made such a difference.

I know what you mean about #4 - in theory I could throw lots of money at a bike but for as long as I've got some 40-50lb of surplus fat around my middle it seems an expensive exercise in futility. #2 might be worth a look, it seems cheaper and easier than a new frame.

No chance for the LBS to tweak any measurements, I used my own GPS to measure speeds on both bikes. Despite the higher gearing of the lighter bike I was surprised I found it easier to spin the pedals faster in a higher gear. Hence I got to wondering which aspects of the lighter bike made it easier to go faster, and whether copying those elements onto the Tricross would give me the kind of gain that would warrant spending the money.

cplager

The Marathon Plus tires are good for puncture resistance, but known to have relatively high rolling resistance. That may be the biggest effect.

Clearly the engine is the same in both cases. Are you in a more aero position on the faster bike? (Are you in a position that lets you generate more power)?

After aero considerations and rolling resistance, losses in the power train would be next to check out. The differences here are probably quite small, but...

Cheers,
Charles

p.s. For flats, total weight is all but completely irrelevant for top/average cruising speed.

IBOHUNT

If you have a chance swap out the wheels/tyres of the fast bike with those of the slow bike. I think you'll find much of the difference.
The weight difference of the bikes doesn't make that much of a difference except when climbing and if you're like me the bike isn't the real issue in that department. It's the extra 2 stone I carry round (pun intended) that's the issue

nymtber

a 160hp, 1000cc 4cyl japanese motor....OH you mean bicycles

Rider. Frame stiffness (which can lead to a terrible ride, as well). Tires, bearings, wheels, position on bike, etc etc.

TrojanHorse

I for one do NOT subscribe to the view that there's no value in a lighter bike if you're over weight. I'm certainly not a weight weenie but a nice, light, stiff & responsive frame makes a big difference in my book. Stiffness is especially important for us larger fellas - I used to get chain rub all the time on my old Ti bike and never get it at all on my carbon bike. If I'm putting an erg into the pedals, it feels like I'm getting the whole erg out the back end. So yes, I think the bike makes a difference.

The second thing that may be more important in light of this discussion is your position on the bike. I can get an extra .5-1 MPH easy out of my bike if I"m going 18 and go from the flats to the drops, with no particular increase in perceived effort. SO the riding position of the bike you tried out may have been more efficient for you.

The tighter gear ratios probably help too... to get you into that exact right gear so you're not pushing too hard. You should be able to replicate that on your tricross since you have a triple - put a narrow cassette in the back and don't be afraid of the granny gear up front.

Last, I go faster when I'm feeling good and what's a gooder feeling than being on some superfly racing machine, eh?

TrojanHorse

Oh, the other thing that makes a bike fast is a mean dog chasing it.

CACycling

Don't underestimate the placebo effect. You were psyched to be on a go fast bike so you probably had a bit of extra adrenaline pumping through your veins.

CommuteCommando

For a given rider at whatever weight and physical strength, skinny, high pressure tires and good technique (i.e. cadence) are the biggest factors. Weight is a huge factor on hills. I have had experienced bikers tell me weight makes no difference on hills. These guys A. have never been heavy, and B. slept through high school physics.

I have been told, and it makes sense (that high school physics again) that lightweight wheels help you accelerate faster (angular momentum).

abbynemmy

+1 This most likely made the biggest difference.

bigfred 

Ruling out the obvious, "the engine" answer.

Assuming the same rider and condition and some reasonable speed (20mph or better):

1. Rider position is going to contribute to the majority of resistance. A more aggressive position will result in greater speed for a given RPE.
2. Tires and wheels.
3. Close gearing and the resultant ability to be at close to optimum cadence within a narrower performance spectrum.

And then all the rest. It can be a cummulative effect of many small things.

IBOHUNT

Had one of those encounters last night.
My reaction time and sprint, paltry wattage that it may be, was better than the guy ridding next to me.

johnnyboy1

I had the same question about going to a road bike. I am on a commuter with flat bars and an 8-speed internal hub. I noticed a 10% drop in my commute time when I changed my tires from deep tread 32s to minimal tread 28s. Putting different 32s on for winter added the 10% back.

I figured I would ask the guy who sold me the bike, because he rides road bikes. I thought he would say something along the lines of "you'll see some improvement, not a lot". He said going to a road bike will be like night and day: the skinnier tires, the better gearing, the lower riding position, and lower total weight combine to make a big difference.

So, now it's time for my second bike.

chasm54

Tyres. I love marathon pluses on my singlespeed, which is my "urban" bike, because they are pretty much indestructible. But they are heavy and don't roll as well as a performance tyre.

Rider position, probably.

Placebo, almost certainly. Aggressive geometry and position tends to encourage more aggressive riding, and you'll have been struck by how light the bike felt.

Really, frame weight is of little significance on the flat. Go to one of the many bike calculators on the web and mess about with a couple of pounds here or there on bike weight. The difference in power to maintain similar speeds on flat terrain is tiny. It makes more difference on the climbs.

Your tricross isn't a heavy bike, it's stiff, it is very unlikely that you'll significantly improve your performance by replacing it.

bigfred 

On the subject of frames and speed. I was always entertained by a co-worker who used to commute on a fat chance mtb with suspension fork. But, for commuting's sake he had a set of reasonably light wheels with 26" X 25mm high pressure road tires, an oversized outer chainring, a lower stem that he would swap onto the bars and a set of aero clip ons. It was always entertaining to see the faces of roadies as he tt'ed past them on a "mountain bike" wearing a backpack:-)

Homeyba

For all the nay-sayers out there the bike does make a difference. The difference may be small but it is there. The issue is that there are so many factors involved. Most of them are small but when you add all the small advantages up they become big. To emphasize what Bigfred said, the biggest factor here is aerodynamics. The faster you go the more it matters. A race bike puts you in a much more aero position than your bike. Add in the more aerodynamic wheels etc and the difference gets big. Many people say that aero benifits are for speeds above 20mph but the benifits don't just "turn on" at 20mph they start much lower and the faster you go the more you benifit from them.

Homeyba

How much faster would be pass them on a proper road bike?

IBOHUNT

Woo Hoo! Back to physics class with the cubed bits to go twice as fast.

melvinator

[h=2]What makes a bike fast?[/h]
the rider.

BaseGuy

80% tires;
10% more aero riding position;
20% less weight.

I spent 2012 riding a 26 pound, steel, rigid mountain bike and a 22 pound, 1987 aluminum road bike. Once I fitted skinny, 100 PSI slicks to the mountain bike and lowered the handlebar, my bike computer said it was just as fast as the road bike.

I've now got a proper, new, 2013 CAAD10 5. It feels great, but I'm only vary marginally quicker on it vs. the old bikes (like 0.5 to 1.0 mph average speed across a 20 mile ride).

Skinny, slick tires, aired way up, just roll faster. Getting your upper body leaned forward, into the wind, via lower bars/stem, helps, too.

I weigh 216, and last year, started at 290. Even at those weights, I could feel a big difference going up a hill on my 22 pound road bike vs. my very quick 26 pound steel hybrid. Now that I'm used to an 18 pound bike, the hybrid really feels link an anchor going up steep hills.

cafzali

I know this sounds counterintuitive and at first glance makes no sense, but rolling resistance on tires actually decreases with lower pressure, not higher pressure. Now, you reach a point where if your pressure drops too low for your weight and road conditions, you risk pinch flatting and even potentially damaging a rim if you run a pressure that's too low. But the "pressure law" is actually the reverse of what many think.

CenturionIM

It is the color of the frame man.