Hi,

We all know that every serious rider weights their bike & themselves separately. But what about the distribution of the weight? After all, Formula 1 & MotoGP teams spend a lot of their time on the "balance" of their machines.

I'm looking to collect information on the distribution of weight of your bike and of your weight on the bike. I think it will be interesting to see how "balanced" we are on our racing bikes.

I will be grateful for the following information about you & your race-bike : type of rider : elite, 1st cat, 2nd cat, 3rd cat, casual-rider. male or female. age group 16 to 20; 21 to 25; 26 to 30; 31 to 35; 36 to 40; 41 to 50; 51 to 60; 61 & above.

You will need a set of scales [any bathroom type scale will do as long as you know that it is accurate] and your race bike. You do not need to be in your race gear but wearing your race-shoes will help to collect more accurate data.

1. put the front wheel on a scale, with the back wheel on some books/magazines to make the bike level on the ground, holding the bike steady by the stem with minimum effort & note the weight; [e.g. my Soloist Team race bike showed 4.0kg].

2. take the front wheel off the scale and now put the back wheel on the scale with the front wheel now level on the books/magazines on the ground, holding the bike steady by the saddle with minimum effort & note the weight [e.g. my race bike showed 4.4kg].

Please do be very careful with the next part when you are getting on & off your bike. [please note this is a voluntary exercise and I will not be liable for any accidents you may cause before, during or after your attempts in collecting the data]

3. take the bike & the scales close to a wall. place the bike parallel to the wall. again put the front wheel on the scales. this time, get on the bike, hands on the drops of your bars, feet on the pedals in a comfortable position & note the weight on the scale, keeping your balance by leaning gently against the wall. You may need a helper to read the scales for you depending on your type of scales [e.g. in my case, it showed 31.2kg].

4. carefully dismount from the bike. take the front wheel off the scales. place the rear wheel on the scale, get on the bike, hands on the drops of the bars, feet on the pedals in a comfortable racing position & note the weight on the scale, keeping your balance by leaning gently against the wall. You may need a helper to read the scales depending on the type of scales. [e.g. in my case, it showed 44.2kg].

Many thanks in advance for your help. Please post your data on this forum or directly to me. I will collect as much data as I can, depending on how many people responds to this request, and I will publish the information/results on this forum.

it would be best if the wheels were at the same height as this will have an effect on your weight distribution trial.  If you recall your physics the center of gravity will shift slightly, which means the lower wheel will see more weight than the wheel on the scale.  This effect will be exagerated by the wheel base distance.  Though for this test it may not be enough to measure, I would be interested in your data if you repeat it with a block/ or something to raise the wheel not on the scale to the same height as the other. 

Another option might be to put your bike in a trainer since the bike is free to swing, now put the scale under the free wheel and let's assume it is close to the same height as the other wheel, zero the scale before you get on, then you can see how much weight is on that wheel, assume the rest of your weight is on the other, I don't see the need to weigh the other wheel.  Of course weigh yourself as well.  I have yet to try this but if you can clamp the front wheel in the trainer you can verify if the weight on the back is as you suspect it should be (I think it should be the other portion of your weight ie front weight plus back weight should be your weight) and if yes then you know things are working right, if they do not add up to y-our weight then there is an error in the method.

In the wheel clamped into the trainer idea it would be interestig (remember zero out the bike if you can, if not record it and subtract it out)to see how it changes when you are 1- in the drops, 2- on the hoods, 3 if you have them in aero bars, then 4- no hands on the bars sitting up straight.  In this method relatively little chance of accidents.  If others are into this idea, I will post my data, when I get my bike set up with the scales, it is an interesting question.

Post personal weight then position 1,2,3,4 bike size and stem length would be neat to see if it has impact on 2 people with the same weight.  Again it will depend upon your weight distribution upper body to lower body as you bend at the waist.  This is a very complicated exercise the more I think of it so I wil stop now.

here is your data, bike my trainer bike a Trek 1200, my Cervelo is not used for this type of abuse, and right now is undergoing annual mainteance wishing for the snow to go.

the wheel on the scale was almost exactly the same height as the one clamped into the trainer, bike was nearly perfectly level.

when I got off the bike the scale returned to zero indicating it was moving freely.

peislc:

my wt	152	lbs
	lbs front	lbs back	kg front	kg back	ratio front	ratio back
bike front wheel before zeroing out	12
sitting upright	36	116	16.4	52.7	24	76
on hoods	65	87	29.5	39.5	43	57
in drops	68	84	30.9	38.2	45	55
aero	75	77	34.1	35.0	49	51
standing looking down at front axle	90	62	40.9	28.2	59	41

Great data peislc, thanks.

Looking at your rightmost column, "ratio back", that's like percent weight on the back wheel, right? So your 76 is like 76% rear wheel weight distribution? If so, you've documented a pretty large variation: 35% change in weight distribution among the various (not-unusual) riding positions (76 - 41 = 35). That's cool - we ride (more or less) happily in these different positions, so I wouldn't be surprised if your 35% might give a rough idea of "safe" ranges of weight distribution.

All this talk about weight distribution has me thinking about the Cervelo RS. Time for a thread hijack, sorry...

Cervelo explains on the RS web page (http://www.cervelo.com/bikes.aspx?bike=RS2010#G ) about the weight distribution: "Because a higher handlebar position rotates the rider’s torso and therefore his center of gravity backwards. Longer chainstays ensure the weight distribution between the two wheels remains balanced for optimal handling characteristics."

So the RS has (1) a higher handlebar positon, and (2) longer chainstays. Cervelo says the second compensates for the first. Did Cervelo get it right?

Your data might help us guess. One interesting pair or rows is "on hoods" and "in drops".  You measured a difference there of 2% between hoods and drops (57 - 55 = 2)

This is sort of like the RS's taller head tube: the torso changes angle. But the RS head tube is only 2 cm taller than the R3, while typical bar drop is more than that. For example the 3T Rotundo is abour 14 cm, 7 times more: http://www.thenew3t.com/details.aspx?i=road&t=Dropbars&p=rotundo&d=TEAM .  For several reasons, the RS's adjusted geometry might not be 7 times less than yours. First, maybe the RS rider also has his stem pointed up - as a guess, that might be worth maybe 3cm higher, so total difference is now 5cm (2cm head tube + 3cm flipped up stem). (Obviously there are lots of what ifs.) Second, brake hoods aren't usually right at the top of the handlebar, so let's say your effective drop is less than 14cm, maybe 10cm.

Just for simple calculation, let's assume the RS rider has hands 5 cm higher, and your drops are 10cm lower than your hoods, so the RS rider gets about half your change in torso height (5 is half of 10). In this case I'd expect the RS rider's weight distribution to change about half as much as yours did: 1%. (Just typing that small a number makes it seem obvious it can't matter, especially compared to your range of 35%, but let's do the math to see.) 

So the question is: How did lengthening the RS chain stays by 11mm affect weight distribution? Anyone know how that can be calculated?

If it's around 1%, then Cervelo's about right.  (Though I can't belive even a 2 or 5% change could matter "for optimal handling characteristics" in real llife.)

yup % front back= ratio as they do add to 100.  I did not try the position on the top of the bars but....

What I found interesting is this probably has more info for a mtb.  When you are rolling along and hit a rock or log this ratio front back really comes into play.  So it affects cses where you hit something I think a great deal and why you should sit back.  

The more I look at the data the less I see what it can tell me about riding my road bike except how we might consider the way the bike handles under these different positions? How much weight for traction?  how much weight for turning? I posted it mostly to get a few reactions, maybe some interesting thoughts on it like yours.  So it does say the more racy/ aggressive the position the more likely the weight goes to the front wheel.  So of course the higher the position the more it goes to the back wheel and balances the weight distribution. 

The only one that really was interesting was that the aero position leads to about 50/50 within my experimental error so this was kind of enlightening as when you race like this you stay in this position most of the time. 

Now the big kicker, the bike was level, how often during a ride is this the fact?   If I was so inclined I might set up a spread sheet to look at how angle effects this ditribution but I will let the engineers and physics types do this.  It is time to see if others find anything in this interesting and can make some interesting comments, the reason for a forum, exchange of ideas.

peislc:

Now the big kicker, the bike was level, how often during a ride is this the fact?   If I was so inclined [snip]

peislc, you're a pretty punny guy! ;-)

So two questons for the engineer types:

1. How much did Cervelo change weight distribution (in percent) with the RS's 11mm longer chain stays, and

2. How does road gradient affect weight distribution?

the geek got the better of me so I was inclined to find out and here is the gory details:

so we can see what happens to weight when the angle is changed.  I did this with the scale, bike in the trainer, and a riser I could vary. Of course I only read front wheel weight the rear wheel is the difference to my total wt.

oh yeah it is snowing here and I got bored, I think I will go xc skiing now. :-)

Nice!

A few random thoughts, in no particular order:

 - Comparing "% back" between the top and bottom rows on level ground, you show a max of (76 - 51 =) 25% change among your various riding positions. Gives an idea of how critical one or two percent change in weight distribution might (not) be.

 - Comparing "% back" across the three cases in the bottom row, you show about (70 - 51 =) 19% change from level ground up to a 22% grade. I assume this is uphill, and there might be another -19% on the down hill, which gives a theoretical total change of about 38% for up-hill-and-down-hill riding. Gives another reference for how critical one or two percent change in weight distribution might (not) be.

 - Comparing "% back" among all positions and gradients, you show at leat 51%, and up to 88%, of the weight is on the rear wheel. No wonder back wheels get damaged more than fronts!

So now all we need is someone to do the math about Cervelo's 11mm change in chain stay length... How can that be calculated?

It's gotta be pretty stright forward:

 - Your bike's wheelbase is 99cm;

 - your total weight is 152 pounds, and

 - on level ground in the aero position, weight is distributed 49% front, 51% rear.

If nothing else changed (your riding poition, etc.), but the chain stays were 11mm longer, then:

 - The new wheelbase would be ~100.1cm;

 - your total weight might be 152.001 pounds (estimated increase due to extra carbon fiber in the frame and one more chain link :) and

 - on level ground in the aero position, weight is distributed ??% front, ??% rear.

What are the new numbers??

(Enjoy your skiing.)

the wheel base has an effect, but the bike wt was zeroed at the start, no rider.  The bike used for this data is the Trek 1200, the Cervelo SLC has a 1 cm longer wheel base both are 56cm bikes.  I doubt the 1 cm makes any real difference within the experimental error, this is not a gold standard experiment, I used our cheap bathroom scales.

it was a great ski thanks

peislc,

I agree the change in weight distribution due to a ~1cm change in wheel base would not be easy to measure; didn't mean to imply another "homework assignment" for ya!

I'm still hoping someone knows how to *calculate* the effect though.

You guys just gave me A.D.D. Thanks a lot.