Front/rear weight distribution - does it matter?

[Mark McM]

Cyclists sometimes talk about front/rear weight distribution on a bike, and how it affects characteristics like stability, handling, and traction. But do we know that it really matters as much as some have said it does?

The reason I wonder this, is because if it matters so much, then you'd think that it would be something that was actually measured and quantified, so that we could at least have points of comparison. We do this with steering trail (values for "neutral" trail are often stated to be in the 55 - 75 mm range). We do this with chainstay length (400 mm stays are often called "short and responsive", while 430 mm stays are called "slow and stable"). We put numbers on saddle setback and stem length, and pontificate on their affects on performance and handling. Why do we never discuss numbers for front/rear weight distribution, if it actually makes a difference?

Every once in a while you hear someon quote "ideal" weight distribution, sometimes said to be 40% front/60% rear, or even 45% front/55% rear, or there abouts. Were did these numbers come from, and do they really reflect reality? In an internet search on this subject, I found a few references to how to measure weight distribution, using simple means such as weighing the bike and rider with the wheels on two bathroom scales. And usually the references cite that actual measured values show the bias is more rearward than the 40%/60% or 45%/55% values, and more closer to a 30%/70% value.

Since I'm interested in this, I've actually measured my own weight distribution, using the 2 scale method. While my attempt was probably not the most precise, I have come up with some numbers, and seem to be about 43% front/ 57% rear. Compared to the small number of measured values I've seen, I appears to be a bit more forward biased than average.

This got me to wondering what the implications of this was. For example, I typically like road bikes with shorter than standard steering trails. The stabilitizing affect of steering trail is affected by weight on the front wheel, so maybe a forward weight bias requires less trail for stability. What other affects could a forward (or rearward) weight balance have on bike stability and handling? Or maybe it doesn't really matter much?

[MattTuck]

Damn, time to post such a quandry is on a rainy Monday at lunch time. Not Friday right before, or after, a bunch of us have left for the week.

I don't pretend to know the answers you seek, but I do wonder how well the bathroom scale technique translates to distribution while actually out riding. More pedal down force probably means less weight on the handle bars... so I could see that method skewing toward 50/50 equal weight distribution.

Not sure what the right way to do it would be. Perhaps rollers, with the front part supported on a scale, and the rear part supported on a scale?

[Mark McM]

I don't pretend to know the answers you seek, but I do wonder how well the bathroom scale technique translates to distribution while actually out riding. More pedal down force probably means less weight on the handle bars... so I could see that method skewing toward 50/50 equal weight distribution.?

This is a common misconception. The weight distribution on the wheels only depends on the location of the center of mass. It doesn't matter how (or where) that mass is attached to the bike.

Consider this bucket truck:

http://www.rentittoday.com/cmsAdmin/uploads/thumb/bucket-truck-non-insulated.jpg

The bucket is hanging over the front wheels, but the bucket arm is attached directly over the rear wheels. If I load a bunch of weight into the bucket in this position, does the extra weight load up the front wheels or the rear wheels?

[Bob Ross]

More pedal down force probably means less weight on the handle bars...

But it also means less weight on the saddle!

[David Tollefson]

Consider this bucket truck:

http://www.rentittoday.com/cmsAdmin/uploads/thumb/bucket-truck-non-insulated.jpg

The bucket is hanging over the front wheels, but the bucket arm is attached directly over the rear wheels. If I load a bunch of weight into the bucket in this position, does the extra weight load up the front wheels or the rear wheels?

It loads the front wheels. Even though the attach point is in the rear, it imposes a bending moment at the base which moves the load forward. Similar to the torque bars on a travel trailer.

[ultraman6970]

So... whats the answer??? :)

This is a common misconception. The weight distribution on the wheels only depends on the location of the center of mass. It doesn't matter how (or where) that mass is attached to the bike.

Consider this bucket truck:

http://www.rentittoday.com/cmsAdmin/uploads/thumb/bucket-truck-non-insulated.jpg

The bucket is hanging over the front wheels, but the bucket arm is attached directly over the rear wheels. If I load a bunch of weight into the bucket in this position, does the extra weight load up the front wheels or the rear wheels?

[David Tollefson]

Weight distribution is one of my primary design considerations in my builds. But the number changes depending on the use intent. Road racer will be more front-wheel biased, gravel rider will be more rear-wheel biased.

[Mark McM]

Weight distribution is one of my primary design considerations in my builds. But the number changes depending on the use intent. Road racer will be more front-wheel biased, gravel rider will be more rear-wheel biased.

What would be a typical front/rear weight distribution for a road bike? And what would it be for a typical gravel bike?

[Peter P.]

What would be a typical front/rear weight distribution for a road bike? And what would it be for a typical gravel bike?

I think the numbers you listed above are the generally accepted numbers, and nowhere have I read that it varies based on the bike's use.

The problem with the numbers is they are so heavily influenced by the body composition of the rider. A rider with a heavy, muscular lower body will certainly bias differently than one whose upper body carries more mass than average.

Next, it should be obvious that riding uphill will shift the weight bias vs. flats and downhills, and the specific grades of each. That alone is enough to illustrate there's practically no way of getting it perfect or even near perfect for all conditions.

It would be interesting to get a bunch of rider say, at the beginning of a group ride, and measure all of them for their weight distribution, just to see the variations and through casual observation if it corresponds to performance.

So, does it matter? In my opinion, probably not that much that I'd being weighing myself on bikes before a purchase, or even discussing it with a framebuilder before placing an order. Experience and history has shown me they've pretty much got weight bias ironed out.

[jumphigher]

Experience and history has shown me they've pretty much got weight bias ironed out.

Kinda how I feel, too. :)

[Buzz Killington]

I'm all about the bass, 'bout the bass. No treble.

[93KgBike]

It loads the front wheels. Even though the attach point is in the rear, it imposes a bending moment at the base which moves the load forward. Similar to the torque bars on a travel trailer.

I agree with you, but I feel like he was implying the opposite? And I was thinking, Softride TT bikes. ������

[cachagua]

The stabilitizing affect of steering trail is affected by weight on the front wheel, so maybe a forward weight bias requires less trail for stability. What other affects could a forward (or rearward) weight balance have on bike stability and handling? Or maybe it doesn't really matter much?

The stabilizing effect of trail is affected by variations in weight on the front wheel?

Not sure I'm quite clear on that. Can you say more? Does it have to do with the way aiming the wheel straight lifts the front end slightly, and turning allows it to fall?

[martl]

in my experience, it does matter and influences the way the bike handles. Only, also in my experience, it is not really down to the bike, but how you sit on it.
A bit like skiing: more weight forward gives you better control in the turns.

[Peter P.]

in my experience, it does matter and influences the way the bike handles. Only, also in my experience, it is not really down to the bike, but how you sit on it.
A bit like skiing: more weight forward gives you better control in the turns.

I have to agree with you on this.

My friend and I ride the same size bike. Shortly after he took delivery of his Trek Domane and I picked up a new Soulcraft Royale, I asked if he be interested in swapping bikes for a ride. So he rode over to my house, we switched pedals and adjusted seats, and off we went the 17 miles back to his house.

While he had the maximum number of spacers under the stem (3cm, maybe?), I ride with lower bars. I couldn't weight the front end enough of his Domane to get in the same position. Consequently, the front end steering characteristics didn't feel right and I'm sure it wasn't the bike.

[justaute]

Riding position and torso length/build also matter, I assume.

[ColonelJLloyd]

We do this with steering trail (values for "neutral" trail are often stated to be in the 55 - 57 mm range).

fify

[MadRocketSci]

here's how i see it....

the best handling, at least in my experience, is when your butt is not sitting on the seat, and your weight is all (or mostly) on the "outside" pedal. It's easy to figure out in that case what your weight distribution is....

For a typical road race bike:

Chainstay length is around 405 mm
Front center is dunno, 585 mm

when you have your weight on the extended leg, that is at a crank aligned with seat tube position

typical STA: 73 degrees

using easy numbers, assume total wheelbase = 1000 mm
rounding,
CS length = 400 m
FC = 600

weight at pedal position, 170mm*cos(73) ~ 50mm

Because the rider is being held up at one point (the outside pedal), assuming little (ie no) weight on the hands, inside foot, or butt, that's where the rider CG is.

Moment balance on bike:

rear wheel force*450 = front wheel force*550

front wheel force = rear wheel force*450/550

rear wheel force + front wheel force = total force

rear wheel force/total force + front wheel force/total force = 1

rear wheel force/total force + (rear wheel force*450/550)/total force = 1

(rear wheel force/total force)(1 + 450/550) = 1

rear wheel force/total force = 1/(1+45/55))

rear wheel force/total force = 55/(55+45) = 0.55 or 55%

front wheel force/total force = 1 - RWF/TF = 0.45 or 45%

so, bob's your uncle, no butt weight on the seat, little on the hands, all on the outside food, your bike will pretty much take care of the 55/45 split weight distribution for you. This of course assumes no brakes. Some braking will add weight to the front wheel.

You can probably verify with the bathroom scales, but the simple physics should produce the right answer (if you use more exact numbers).

Sitting on the seat will bias the weight towards the back, as now the rider's CG is somewhere between the seat and the pedal. That will bias the distribution towards the rear and give the more 70/30 splits that are reported.

[Highpowernut]

here's how i see it....

the best handling, at least in my experience, is when your butt is not sitting on the seat, and your weight is all (or mostly) on the "outside" pedal. It's easy to figure out in that case what your weight distribution is....

For a typical road race bike:

Chainstay length is around 405 mm
Front center is dunno, 585 mm

when you have your weight on the extended leg, that is at a crank aligned with seat tube position

typical STA: 73 degrees

using easy numbers, assume total wheelbase = 1000 mm
rounding,
CS length = 400 m
FC = 600

weight at pedal position, 170mm*cos(73) ~ 50mm

Because the rider is being held up at one point (the outside pedal), assuming little (ie no) weight on the hands, inside foot, or butt, that's where the rider CG is.

Moment balance on bike:

rear wheel force*450 = front wheel force*550

front wheel force = rear wheel force*450/550

rear wheel force + front wheel force = total force

rear wheel force/total force + front wheel force/total force = 1

rear wheel force/total force + (rear wheel force*450/550)/total force = 1

(rear wheel force/total force)(1 + 450/550) = 1

rear wheel force/total force = 1/(1+45/55))

rear wheel force/total force = 55/(55+45) = 0.55 or 55%

front wheel force/total force = 1 - RWF/TF = 0.45 or 45%

so, bob's your uncle, no butt weight on the seat, little on the hands, all on the outside food, your bike will pretty much take care of the 55/45 split weight distribution for you. This of course assumes no brakes. Some braking will add weight to the front wheel.

You can probably verify with the bathroom scales, but the simple physics should produce the right answer (if you use more exact numbers).

Sitting on the seat will bias the weight towards the back, as now the rider's CG is somewhere between the seat and the pedal. That will bias the distribution towards the rear and give the more 70/30 splits that are reported.



I am humbled with this answer. I know nothing.
I was trying to concoct a front and rear fork stand with scales.
Guess there's an easier way.

[carpediemracing]

I always have weight on my hands, or so it seems. If not on my hands then my core is tensed.

I have access to two digital scales and my bike happens to be in the living room....

47/53 front/rear

Reversing the bike direction on the two scales, same ratio (slightly different numbers).

Chainstay 39 cm (about 38.3 if measured horizontally). I have a 75.5 deg seat tube angle. Wheelbase 101.4 cm, very long due to 56.5 cm top tube.

I'd consider my bike to be a pretty weight-forward kind of bike. No way I'm anywhere near "neutral" in terms of weight distribution. During a fit session we tried to get me to a position where I could lift my hands off the bars and not fall forward. I had to lower my saddle maybe 20 cm, move it back maybe 20 cm, and raise my bars who knows what. It was a ridiculous, seated-on-a-BMX-bike-with-saddle-slammed position.

[Mark McM]

The problem with the numbers is they are so heavily influenced by the body composition of the rider. A rider with a heavy, muscular lower body will certainly bias differently than one whose upper body carries more mass than average.

This is all true. But that doesn't mean that weight distribution can't be measured. It also implies that riders of the same segment sizes (arms, legs, torso) and same bike fit, but of different body composition, might benefit from different frame geometries for weight distribution purposes. So if weight distribution matters, it should be measured to find the best bike geometry.


Next, it should be obvious that riding uphill will shift the weight bias vs. flats and downhills, and the specific grades of each. That alone is enough to illustrate there's practically no way of getting it perfect or even near perfect for all conditions.

This is not a strong argument. Riding on different grades will change many other fit/geometry parameters, such as saddle setback, saddle/handlebar height differential, etc. And yet, we find it necessary to adust these parameters with fine resolution (often to millimeters) to find the best fit. So why not weight distribution?


So, does it matter? In my opinion, probably not that much that I'd being weighing myself on bikes before a purchase, or even discussing it with a framebuilder before placing an order. Experience and history has shown me they've pretty much got weight bias ironed out.

Well, it either shows that frame designers have gotten weight bias ironed, out or it shows that it doesn't matter much.

[Mark McM]

The stabilizing effect of trail is affected by variations in weight on the front wheel?

Not sure I'm quite clear on that. Can you say more? Does it have to do with the way aiming the wheel straight lifts the front end slightly, and turning allows it to fall?

What you are describing is one of the main causes of what is called wheel flop, and it is certainly one way weight on the front wheel interacts with steering geometry to affect handling. But there are other ways, too.

As we know, trail is the distance between the wheel ground contact point and the where the steering axis intersects the ground. When a bike is leaned out of alignment with gravity, it creates component of the gravity force that is lateral to the bike But the steering trail acts as a moment arm (i.e. torque arm), so when that lateral force component is transferred to the ground, it imparts a torque around the steering axis, and this torque acts to turn the front wheel in the direction of lean. This is actually good for stability, because it helps to steeri the bike back under the center of gravity, and back into vertical balance.

Obviously, the greater the weight on the front wheel, the greater the lateral force and the greater the steering torque, so weight distribution will affect the action of the steering geometry on stability and handling.

[Mark McM]

here's how i see it....

the best handling, at least in my experience, is when your butt is not sitting on the seat, and your weight is all (or mostly) on the "outside" pedal. It's easy to figure out in that case what your weight distribution is....

Only, the situation is not as easy as you say. When I corner, I do lift my butt off the saddle - but I don't slide my butt forward, and I doubt others do either. Typically, when weighting the outside pedal, one stabilizes the bike by pressing the thigh of the extended leg against side of the saddle, which means the butt is in the same fore-aft position as when in the saddle. And if you don't move your butt/body fore or aft, your weight distribution won't change

In another case, to be be in a position to be able to do some hard braking, I will stand on both pedals with the cranks horizontal, lift my butt off the saddle, and then straighten my arms and shift my butt and body backward. This has the affect of shifting my center of mass backwards - further back than if I was sitting on the saddle with no weight on the pedals. And thus with a more rearward weight bias than when my butt is in the saddle.

[Mark McM]

So why did I start this thread? I've heard many people say (or at least imply) that weight distibution matters on a bike. But how do we know this? It is very rarely actually measured. But if it isn't quantified, how can we be sure that it has the affect we think it does?

History has shown that there are many things about bicycles that everybody just knows. That is, until it is actually measured, and then we find out that what we knew wasn't true:

Everybody knew that narrower, higher pressure tires had lower rolling resistance - until it was measured, and we found out they didn't.

Everybody knew that we can we can power the pedals all the way around the circle, and that pedaling circles is the most efficient and powerful way to pedal - until pedal forces were measured, and we found out we don't.

Everybody knew that the reason that women generally prefer shorter saddle-to-handlebar reach then men was because women have longer leg-to-torso length ratios - until men and women were actually measured, and it was found that there is no statistical difference in leg-to-torso ratios between men and women.

Everybody knew that wheels with deep carbon rims are vertically stiffer than wheels with shallow aluminum rims - until we actually measured the stiffnesses of these wheels, and found that they didn't.

Unless we can actually measure some bicycle front/rear weight distributions, how do we even know what they really are, let alone if it has the affect that many claim it does?

[MattTuck]

Thought more about the bucket truck analogy, and I think it adds to my point. if you can get on your scale and replicate the position of a big effort, you'd capture what I was talking about. The thing I was referring to was the idea that if you are stationary, you have a tendency to bring c.o.g. rearward. just by being on the tops vs. the hoods.

Also, if you are riding and doing the Lemond rocking motion, you would be moving slightly forward with each downstroke. Not sure by how much, 1-3 inches, at the head, movement only of the torso, still, it would repeatedly load and unload the front wheel, just like if you kept moving the bucket forward and then backward.

Other question for you. Let's say you get a bike and find two people that it fits, because they are the same height/leg length, etc. One is a 160 pound racer, other is a 210 pound guy that rides once or twice a week. How different would the weight distribution be?

[weisan]

When I sneeze, I change my weight distribution almost instantaneously.

[cachagua]

Unless we can actually measure some bicycle front/rear weight distributions, how do we even know what they really are, let alone if it has the [e]ffect that many claim it does?


I agree, we'll know fairly little until we can measure better. We have to measure weight distribution, and measure it dynamically since it's always changing, and when we've done that, then comes the hard part: we have to define and measure what "good handling" is.

With unlimited budget and an open-ended schedule, this could be feasible. A lot of strain gauges and sensors. A lot of subtly different bikes, to calibrate the ranges of the various parameters... a lot of hypothesizing over adult beverages. But we must balance all that with plenty of empiricism, checking our assumptions against actual experience. Maybe some place like the Swiss Alps might be the best site for our research center? No, let's not forget: this is a dynamic thing we're trying to get a grip on. Chimeric, protean, evanescent, the way a bike feels to ride is a phenomenon inextricably linked to the surroundings. We'll need to load our, uh, instruments into a few trailers, and travel to a range of environments, repeating our experiments under varying conditions. The whole process could take decades.

Isn't this exactly what Kickstarter was invented for?

[martl]

So why did I start this thread? I've heard many people say (or at least imply) that weight distibution matters on a bike. But how do we know this? It is very rarely actually measured. But if it isn't quantified, how can we be sure that it has the affect we think it does?

History has shown that there are many things about bicycles that everybody just knows. That is, until it is actually measured, and then we find out that what we knew wasn't true:

Everybody knew that narrower, higher pressure tires had lower rolling resistance - until it was measured, and we found out they didn't.

Everybody knew that we can we can power the pedals all the way around the circle, and that pedaling circles is the most efficient and powerful way to pedal - until pedal forces were measured, and we found out we don't.

Everybody knew that the reason that women generally prefer shorter saddle-to-handlebar reach then men was because women have longer leg-to-torso length ratios - until men and women were actually measured, and it was found that there is no statistical difference in leg-to-torso ratios between men and women.

Everybody knew that wheels with deep carbon rims are vertically stiffer than wheels with shallow aluminum rims - until we actually measured the stiffnesses of these wheels, and found that they didn't.

Unless we can actually measure some bicycle front/rear weight distributions, how do we even know what they really are, let alone if it has the affect that many claim it does?

some of the things you mention have merit, others are merely academic. About the weight distribution: the bike weighs 10kg, the rider 80. By just changing the grip position, the weight balance is altered in a way that has a noticeable effect on the handling.
So i personally wouldn't lose too much sleep about it. I would put it in the same category as tinkering with aerodynamically optimized forkcrowns when my drag is ifluenced more by holding my nose an inch lower, or optimizing "frame dampening" when a difference of 0.1bar tire pressure has a bigger effect on riding comfort.

[oldpotatoe]

Cyclists sometimes talk about front/rear weight distribution on a bike, and how it affects characteristics like stability, handling, and traction. But do we know that it really matters as much as some have said it does?

The reason I wonder this, is because if it matters so much, then you'd think that it would be something that was actually measured and quantified, so that we could at least have points of comparison. We do this with steering trail (values for "neutral" trail are often stated to be in the 55 - 75 mm range). We do this with chainstay length (400 mm stays are often called "short and responsive", while 430 mm stays are called "slow and stable"). We put numbers on saddle setback and stem length, and pontificate on their affects on performance and handling. Why do we never discuss numbers for front/rear weight distribution, if it actually makes a difference?

Every once in a while you hear someon quote "ideal" weight distribution, sometimes said to be 40% front/60% rear, or even 45% front/55% rear, or there abouts. Were did these numbers come from, and do they really reflect reality? In an internet search on this subject, I found a few references to how to measure weight distribution, using simple means such as weighing the bike and rider with the wheels on two bathroom scales. And usually the references cite that actual measured values show the bias is more rearward than the 40%/60% or 45%/55% values, and more closer to a 30%/70% value.

Since I'm interested in this, I've actually measured my own weight distribution, using the 2 scale method. While my attempt was probably not the most precise, I have come up with some numbers, and seem to be about 43% front/ 57% rear. Compared to the small number of measured values I've seen, I appears to be a bit more forward biased than average.

This got me to wondering what the implications of this was. For example, I typically like road bikes with shorter than standard steering trails. The stabilitizing affect of steering trail is affected by weight on the front wheel, so maybe a forward weight bias requires less trail for stability. What other affects could a forward (or rearward) weight balance have on bike stability and handling? Or maybe it doesn't really matter much?

I slide forward and back, move my hands around, hoods, drops, top of bars..all in combo so my weight distro changes some too. So, if the bike 'fits', feels good, no injuries including stuff like saddle sores and such..don't think it means a whole bunch..whether it's 45/55, 47/53, 42/58, etc.

Ahh, said right above..

[fuzzalow]

Well, this is something to talk about as something to talk about. But I am at a loss as to the relevance as to why this has any bearing on why anyone needs to know this and, more importantly, what anyone would do with this information once they've built a thesis.

Weight balance in a bicycle means very little because

Variability in how a human rider can fit into the available adjustment envelope of a frame influences front-rear weight bias. And even then only to a very limited degree because the main weight bearing structure is the bottom bracket and saddle. Weight bias has long ago been solved by how weight is carried and distributed in the geometry imposed by the double diamond bicycle frame.
Cycling is a forward propulsion activity, not a racetrack circuit activity. Nobody wins because their weight bias is dialed in which allows them a higher corner entry speed (tuning out understeering on a bike? Laughable.) I'd guess nobody has done research on weight bias because it's immaterial to cycling.

The kind of precision to achieve a fit & position is not the same as any degree of precision that would translate into a handling difference on a bicycle. Any bicycle, or racing motorcycle for that matter, is not that sensitive to weight bias inherent to the vehicle itself exclusive of the rider. A car on a racing circuit is a little more sensitive to weight bias but that is still outweighed by things like roll stiffness bias between the front or rear axle of the car.

Basically, on a bike, front to rear weight bias doesn't matter.

[Rusty Luggs]

Weight distribution matters on every other wheeled vehicle, so why wouldn't it on a bicycle?

Anyone who has shifted their weight fore and aft on a bike has likely noticed the impact on handling, hence that is why people conclude it matters.

Why isn't it measured? Probably because it may be easy to do statically, and difficult to do dynamically while actually riding. Sure, maybe it is an overlooked parameter. But, even doing measurements, folks aren't all looking for they same thing when it comes to bike handling characteristics, so if you went around measuring, I think you would come up with a fair bit of variability

Why should it be assumed that there is one universal front/rear weight distribution ratio applicable to every bicycle design and every intended usage, and that there would actually be universal agreement on that ratio - as if there is such a thing re: crank length, saddle height, etc. etc.?

Motorcycle road racers often talk about front end feel being extremely important - so what set of numbers/measurements do you think you could add up to create the desired feel? If it was easy, none of those guys would be complaining about lack of front end feel on their race bikes, yet you hear that constantly. Can't be easily measured so doesn't exist, I guess.

[unterhausen]

I was thinking about this recently, because a rando front bag is a lot more useful with a shorter stem. Some rando bikes have a longer top tube to make this happen. I think I might try it. Of course, an inch longer top tube probably doesn't change the relative position of the cg that much, and the chainstays can be a little longer too.

I'm a little skeptical that weight distribution is all that noticeable. I was looking at the geometry for 2 frames that were nominally for the same size person. There was a 3 inch difference in wheelbase! It would be really interesting to try those two bikes back to back.

[Mark McM]

I agree, we'll know fairly little until we can measure better. We have to measure weight distribution, and measure it dynamically since it's always changing, and when we've done that, then comes the hard part: we have to define and measure what "good handling" is.

With unlimited budget and an open-ended schedule, this could be feasible. A lot of strain gauges and sensors. A lot of subtly different bikes, to calibrate the ranges of the various parameters... a lot of hypothesizing over adult beverages. But we must balance all that with plenty of empiricism, checking our assumptions against actual experience. Maybe some place like the Swiss Alps might be the best site for our research center? No, let's not forget: this is a dynamic thing we're trying to get a grip on. Chimeric, protean, evanescent, the way a bike feels to ride is a phenomenon inextricably linked to the surroundings. We'll need to load our, uh, instruments into a few trailers, and travel to a range of environments, repeating our experiments under varying conditions. The whole process could take decades.

Isn't this exactly what Kickstarter was invented for?

I suppose you are just joking a bit, but I don't see why we have to start looking at weight distribution dynamically. A baseline of static weight distribution would be a good start, plus some quantification of how it changes as a rider shifts position on the bike.

To this end, I pulled out my bathroom scales, and took a few other weight distributins measurements with my body in a range of different positions I might use during a ride:

Neutral position (hands on hoods, butt in normal position on saddle): 43% front / 57% rear.

In the drops (hand in drops, butt in normal position on saddle): 43% front / 57% rear.

"On the rivet" (hands in drops, butt perched on the forward tip of saddle): 46% front/ 57% rear.

Sitting up (hands on bar tops, butt in normal position on saddle): 40% front / 60% rear.

Weight back for hard braking (hands in drops, arms straight, butt off the back of the saddle): 31% front / 69% rear.

I didn't try to measure pedaling out of the saddle (as in a sprint), as this a far more dynamic situation and therefore more difficult to measure. I would imagine that it would weight the front wheel a bit more than riding on the rivet. I think it is also recognized that this position is less stable than most other positions.

So, there is only a variation of +/-3% (of total weight) between casually sitting up, and the forward "on the rivet" positions. Out the saddle, either weight forward an on tip of the pedals or with body as far rearward as possible, might shift the weight balance by up to +/- 10% (of total weight) from the neutral position.

[Mark McM]

Well, this is something to talk about as something to talk about. But I am at a loss as to the relevance as to why this has any bearing on why anyone needs to know this and, more importantly, what anyone would do with this information once they've built a thesis.

Well, there may be other considerations than simply "handling" (more below).


Weight balance in a bicycle means very little because

Variability in how a human rider can fit into the available adjustment envelope of a frame influences front-rear weight bias. And even then only to a very limited degree because the main weight bearing structure is the bottom bracket and saddle. Weight bias has long ago been solved by how weight is carried and distributed in the geometry imposed by the double diamond bicycle frame.

The main geometry constraint isn't so much the diamond frame, but the wheel size(s). For example, switching to 29" MTB wheels generally resulted in a longer front centers, and therefore more of a rear bias, than 26" MTB wheels did. In contrast, Terry bikes use small front wheels to shorten the front center, which has the opposite effect.



Cycling is a forward propulsion activity, not a racetrack circuit activity. Nobody wins because their weight bias is dialed in which allows them a higher corner entry speed (tuning out understeering on a bike? Laughable.) I'd guess nobody has done research on weight bias because it's immaterial to cycling.


I'd argue that weight bias actually does become very important in certain forms of racing - specifically downhill MTB racing. But perhaps it doesn't make as much difference for road races, where the surfaces are far more uniform (and usually less steep).


The kind of precision to achieve a fit & position is not the same as any degree of precision that would translate into a handling difference on a bicycle. Any bicycle, or racing motorcycle for that matter, is not that sensitive to weight bias inherent to the vehicle itself exclusive of the rider. A car on a racing circuit is a little more sensitive to weight bias but that is still outweighed by things like roll stiffness bias between the front or rear axle of the car.

Basically, on a bike, front to rear weight bias doesn't matter.

There may be some other considerations where weight distribution has practical meaning. Here are two of them:

Tire pressure: As we know, tire pressure can be very important because it affects rolling resistance, shock/vibration absorption, and pinch flat resistance. The best tire pressure is largely affected by the load (weight on the wheel). Since there is roughly 25 - 100% more weight on the rear wheel than the front wheel, if we use the same (or nearly the same) pressure in both front and rear wheels, we are probably over-inflating the front, and/or underinflating the rear.

Braking effectiveness: Braking causes a shift in weight distribution from the rear tire to the front tire, which has two effects on braking affectiveness: Since traction is proportional to tire load, the forward weight shift decreases the braking traction available at the rear wheel; At the extreme, the weight on the rear wheel can be zero, at which point the rear wheel can leave the ground. So, we can either accept the braking limitations imposed on however the weight distribution falls out, or we can make adjusments to weight distribution to improve braking (which is pretty much what Downhill MTBs do).

[weisan]

Mark pal, good discussion.

[martl]

Weight distribution matters on every other wheeled vehicle, so why wouldn't it on a bicycle?

Well, i think it does. Only, as you've measured yourself, it is a function for rider+bike+position, not for bike alone. So you can measure yourself for a given bike, as you did. One could also measure several bikes with the same rider to find out differences, but that is about it as far as usefulness goes.
It is not a result that would make much sense to put in a bike comparison test.

Agree about the front end feel wholeheartedly. Like i wrote, i register very different cornering when, on a downhill bend, i shift weight forward, compared to when i sit more back. Even if, as your measurements show, this causes only little weight balance shift.