body weight & bike performance correlation (Page 2)

150lbs, 0% incline = 22.3 mph

160lbs, 0% incline = 22.1 mph

170lbs,  0% incline = 20.9 mph

I'm a lot heavier (read: fatter) than I'd like to be over these past three years but am luckily trending back to optimal now. I'm 5'9" and 170 lbs. My best racing weight is (was?) 140 lbs.

I notice a difference in performance on the bike, most significantly in acceleration and climbing. I can't climb right now, partially due to weight, partially due to fitness. Obviously both play a role.

As I drop weight my run speed at the same heart rate improves. 9:00 per mile at 150 BPM, 8:30 at 150BPM... 8:00 per mile at 150 BPM... It keeps coming down. Also, my top end goes up. I can hold a much higher (170 BPM + average) heart rate longer (20:00 during a 50:00 run) at a very high rate (for me) of about 7:45, even 7:30-7:45. For a 50 year old stroke survivor with a cardiac implant, that is OK.

Bottom line: lighter is faster. It is. Any time you open the can of worms of body weight and composition people are... very sensitive. Feelings can get hurt pretty easily and people are pretty defensive, often on each others' behalf. I understand. I also understand I was faster then I was 20-25 pounds lighter. Fact. I also understand that the fastest triathletes, cyclists and distance runners are a lot, a lot, leaner than most of us. And while that may not be a practical benchmark it is true.

You are correct. I get a "C"in cut-and-paste

Yeah I was thinking...anyone out there sitting at 170 could become a whole different beast on the flats if they cut 10 pounds!

I try to look at this from a practical standpoint that's easier to visualize.  Maybe this is too extreme of an example, but let's say you put a human on a bicycle and didn't have them pedal.  They just sit there dead weight and you push them along a flat surface.  Now put a hippopotomus on that same bike and push it along the same flat surface.  Will it be easier to push the human or the hippo? 

That's likely a valid observation aboput your personal experience, although it has more to do with your fitness in each state than your weight.   Obviously, there may be some correlation to your being fitter at the same time you weigh less.  Weight loss will likely lead to gains for a triathlete, but mostly on the run, nominally on the bike and negligibly in the water.  Weight loss in conjunction with fitness gains, would be the combo most hope to achieve.

You should do some tests.

ETA: regarding cycling races

Furthermore, even if the net elevation change is zero, weight still plays a factor when one tries to win a hilly stage.  What will happen is that during the first few climbs, the ligher riders will take it easy, and stay with the pack while the heavy riders are working harder to go the same speed.  Then on the downhills, where the heavy riders have the advantage, the lighter riders will let the heavy riders lead out, but the lighter riders will be able to keep up because of the draft.  Heavy riders don't get nearly as much draft benefit when climbing.

This will go on for several climbs throughout the stage...all the while, the lighter riders are either working less, or equal to the heavier riders...and are thus fresher for the finish.  That's why you see the peloton usually stays together until the last climb when the lighter riders take off.  Not only do they have a weight advantage when climbing...but they are fresher.

Heavier riders don't really have a way to play this game against the ligher riders, except for maybe the TTs because they can generate more power.  But in most tours, there is far more time to be made on the climbs than ther is to be made during the TTs...therefore it's better to be lighter.

ETA: in triathlon, because you can't draft, lighter riders don't get the drafting benefit on the flats and downhills that road racers get.

And you hold wattage steady. In reality what I find it really means is that being light means you can power up the hills at a lower wattage than a big guy.

Let's look at it a different way, and hope I don't typo again:

Hold speed to 20mph.

Watts required @150 lbs, 0% incline: 149

Watts required @160 lbs, 0% incline: 153

Watts required @170 lbs, 0% incline: 157

Watts required @150 lbs, 2% incline: 289

Watts required @160 lbs, 2% incline: 301

Watts required @170 lbs, 2% incline: 313

Watts required @150 lbs, 4% incline: 428

Watts required @160 lbs, 4% incline: 448

Watts required @170 lbs, 4% incline: 468

So the wattage difference is trivial on the flats, but to hold speed going up a 2% grade takes an extra 24 watts, and jumps to 40 watts up a 4% grade.

This is why w/kg is important for the TdF, on a hilly course the differences are very significant.

Those are really the key points, IMO.

As a practical matter, though, as opposed to a matter of physics (and another poster already alluded to this), I think the extent to which gains on descents by heavier cyclists balance out gains on the climbs by lighter riders is probably being overstated (in this thread and elsewhere).  Technical elements obviously affect speed on a climb less than they can on descents (esp. for inexperienced riders).

Personally, I don't see heavier riders blowing by me on descents, ever.  What I DO see is heavier riders who are also better/more powerful riders on better bikes blowing past me in the flats, a lot (which speaks to the point made here that power and aerodynamics trumps weight on the bike).

It will help you significantly more on the run. On the bike a few lbs won't make a huge difference unless you are climbing large hills. I was 175-80 after the off season and I'm down to 165-170 now and I climb better but my TT times are fairly similar. I've taken a fair amount of time off my run though.

And people spend TONS of money on lighter bike parts simply because they can. Buying things is easier than working hard and there are a lot of people that like to find an easy way out. Those 6oz of savings might save 2sec over 40k!

The other piece of the puzzle your missing is the decline's.  Your speed goes up in a similar fashion with your weight on the declines.  Gravity/physics at work.  I personally don't feel it equals out in my experience because with an equal climb/decent distance I'm going to climb at 10mph for 5 minutes, but go 40mph for only 30 seconds or a minute on the other end.  Without getting my toes out to count I don't think the math works out to even it out, but I could be wrong.    Sounds like a good high school math problem for one of my kids.

If bikecalculator.com is to be trusted, then the weight loss is definitely worthwhile on a hilly course. For a 200w rider, at 150 lbs or at 170 lbs:

On 5% uphill: 38 seconds per mile benefit of being lighter
On flat: 1.5 seconds per mile benefit of being lighter
On 5% downhill: 3.5 seconds per mile benefit of being heavier

Moral of this: if you're light: seek out hilly courses with long runs. If you're not light, then a nice flat Tristar event is best for you (100k bike, 10k run). 

http://www.everymantri.com/everyman_triathlon/2010/12/one-of-the-oldest-cycling-dilemmas-resolved-weight-vs-speed.html  

This article says on average a rider will gain .1 mph for every 1 pound lost.

http://www.coolbiking.com/blog/cycling/cycling-tips/how-to-achieve-your-ideal-cycling-weight/ 

That article is used as support for the previous article.

I've noticed that since I've lost 20 pounds I don't get nearly as winded going up a climb and can spin a faster tempo on the flats in a bigger gear. 

 IMHO there is no question that losing 10 pounds will make you a faster cyclist.  If you could somehow have a clone of yourself in a race and the only thing different about one clone is that they are 10 pounds heavier, that 10 pound heavier clone is going to get beat by your lighter self.

... if you don't lose power at the same time.

The only thing that does not make sense is how increased body weight makes you faster on the downhills.

Remembering vividly from my College Physics classes that All objects (with air resistance aside) fall at a rate of 9.8 m/sec...therefore if you drop a bowling ball or a marble at the same height at the exact same time (I did this in college physics lab to prove this law) they will reach the ground at the exact same time.....we forget air resistance because if you do it with a piece of paper the "sailing effect" will slow it down....so if you try it with most objects you will get the same result....i didn't believe it till I tried.

Therefore, with that law of physics(forget the name of the law but maybe an engineer can help me out) both riders with the same stature, same bike, effort everything the same etc  except for body weight should descend at the same rate......I could see that a heavier rider would create more friction on the road causing them to slow down fster but not speed up

So if it is really true that a heavier rider goes faster on the downhills, something else must attribute for it than weight alone.

But just my 2 cents...carry on...great thread

I think this is the key point. It's the combination of the body mass and the air resistance that yields the *small* benefit of weight on the downhills. But that benefit is nothing compared to the benefit of being light on uphills and on the run. 

F=MA, basically.

Simply, force equals mass times acceleration.  When descending on bike, skis, whatever, you generate more force if you have an "enhanced" relationship with gravity, which allows you to more easily overcome frictional forces between you and the ground (with bike or skis as intermediary), and have more left over to overcome air resistance.  Thus, better acceleration, and higher velocities achieved quicker, assuming the bigger person's aerodynamics are not so much worse that they compensate.  Usually they're not.

I could throw in some stuff with vectors, but I don't think that'd really help clarify.

Just wanted to quote these articles and recommend them for everyone...good stuff, thanks for posting.

A full MPH for 10 lousy pounds that I should probably lose anyway, plus whatever that gets me on the run...seems damn worth it.  Although, there is another thread going on on this board right now about competing in order to 'eat whatever you want' which is a theory I generally hold near and dear to my heart...so that will have to be compromised in order to get to where I should be, which is something I knew anyway.