_ForceD_

I've often wondered about weight distribution on a bicycle. Obviously it's apparent that most of the weight is on the rear wheel (as tire wear shows). But that's with the rider in the saddle. If you're up out of the saddle does that distribution change? There's a couple of reasons I've wondered about this: 1) I think that it affects your steering/handling of the bicycle. And 2) If the rider is out of the saddle does the distribution change? Does standing on the peddles even out the distribution...on bumps or extremely rough surfaces for example...so that the rear wheel doesn't take a harder impact while the front wheel gets a lighter impact (I know that can be avoided with a bunny hop).

What I've read is that the distribution is somewhere around 60% rear to 40% front. Can that be altered by steerer length, and/or fore-aft seat adjustment?

Dan

Bike Gremlin

When you stand up from the saddle and keep your knees and elbows bent, you work as a shock-absorber when hitting a bump - relieving both front and rear wheel.

Weight distribution when standing up from the saddle changes with your body position - if you lean forward and put more weight on the bars, the rear wheel is unloaded, front loaded. If you lean backwards, or pull on the bars - the opposite.

Fore-aft seat adjustment and steerer length are important for comfort. Don't change them to alter weight distribution. The only way to really alter it, while staying comfortable is getting a frame with a longer chainstay.

79pmooney

Yes seat fore and aft and stem lengths will change where you plave your body which is the big part of the weight distribution over the wheels.

But - if you are looking at performance, and I mean just enjoying the ride as much as speed or racing, you should be setting up your bike(s) to best suit you and let the weight distribution fall where it may. For me, that means placing my weight further forward than yields best results on most stock frames. I have gotten around this over the years by acquiring bikes with geometry that does work and having three custom made for me. Best for me are bikes with steep seat tubes that allow a forward rear wheel and longish front centers (BB to front hub distance).

For many of us, weight distribution changes a lot out of the saddle and that location is not in one fixed place. I like to come way forward on hard climbs but I push my weight back when needed to keep the rear tire from slipping.

My weight distribution is much closer to 45-55. You can check yours with a bathroom scale. Put the rear wheel on it and the front on a same thickness phone book. Sit in your usual position, steadying yourself against a wall. Have someone else note the weight. Turn the bike around and repeat. The percentages are:

Front % = Front wheel weight / (total weight) X 100

Rear % = Rear wheel weight / (total weight) X 100

Ben

_ForceD_

I'm not sure that's completely accurate. When you stand on the pedals that weight is concentrated at the bottom bracket. When you're in the you're in the saddle where is that weight concentrated? And, the distribution can be altered by steer length and fore/aft seat adjustment. In other words...I can adjust my seat forward ## distance, and increase steerer length by the same distance and keep that measurement constant. It's in effect changing the geometry. Depending on the terrain it can be more advantageous to move the weight distro/center of gravity fore or aft.

What I want to know specifically is the weight distro, and can it be altered permanently by adjustment, or temporarily by standing/sitting/etc?

Dan

Bike Gremlin

If you move saddle forward and use a longer stem - your distance to the bars might be the same. Weight distribution will change. But onot directly because you moved the saddle forward and used the longer stem. It will change because when you move saddle forward, more weight is distributed to the hands - making the ride less comfortable. Moving the saddle backwards, relieves weight put on the hands.

In short: moving saddle fore-aft, or up-down in order to change anything but the distance to the cranks is wrong (i.e. moving forward because the bars are too far away, or lowering because the bars are too low) - the saddle height and fore-aft position are set up relative to the crankset (bottom bracket) and there is only one optimal position for one rider (and type of riding that is done).

Puting more weight to the hands in order to alter weight distribution can make you tire more quickly, shoulders, arms, palms taking more weight. That can be compensated with harder pedaling - but then there's more weight at the rear again.

Best way to alter weight distribution is to change the frame - longer chainstay, longer wheelbase.

Wrote about basic riding position fiting here:
bike fitting

A few words on frame geometry:
Bicycle frame geometry - Cycle Gremlin

JonathanGennick 

My favorite bikes are the ones in which weight distribution front and rear is fairly even. When I lift by the bike by grabbing the saddle and the bars, I want the weight to feel fairly even in either hand. Doesn't need to be precise, but I like it close. I notice the issue more when mountain-biking than when on pavement.

cyccommute 

Your force is concentrated at the bottom bracket but the weight distribution is a function of the center of gravity of the bicycle/rider system. Since the rider has more mass than the bicycle, the position of the rider will have more influence on what the weight distribution on the wheels.

You can easily test this by moving around on the bike as you pedal. It's easiest to see the influence of body position by riding either on a slick surface (rain soaked paint is best) or loose surface (gravel or sand). If you pedal from a seated position, it's difficult to cause the rear wheel to break loose on either surface. You simply have too much weight and not enough power to spin the wheel above the friction limit.

But if you stand and shift your weight way up towards the handlebars, you can easily spin the rear wheel. You learn this very, very quickly if you mountain bike. Standing on a loose climb is usually a tricky proposition. If you shift too far forward the rear wheel spins and you stop climbing...you may even fall over.

It would be difficult to make adjustments to the bike to get this kind of distribution permanently, however. The saddle doesn't move far enough forward to significantly impact the weight distribution on the rear wheel. Back to mountain bikes: There have been lots of changes to mountain bike geometry over the years to solve this problem. Modern mountain bikes have moved the entire rider forward significantly to try and center the rider so that the bike doesn't spin out as much nor does the front wheel lift off the ground as much. The very earliest mountain bikes were difficult to climb on because the rider was too far back and there was very little load on the front wheel. The wheel tended to pop off the ground with frightening regularity. There was a significant amount of skill required to climb on a 1980s mountain bike.

curbtender

Mountain bikers get to experience this more than roadies. Hence the popularity of dropper posts.

Leisesturm

The weight dist. of a Porsche, Lamborghini or Dodge Viper are vastly different, but all can be found doing their thing on American roads. 100 years of automobile R&D and no one has been able to decide, once and for all, which is best and should be the only configuration allowed on roads around the world. The weight dist. of a tandem with a 250lb. Captain and a 90lb. stoker is vastly different from vice versa, and that of a single bike with a 150lb rider will be somewhere in the middle. It really matters very little as to the minor effect of tiny shifts of weight dist. So, riding in the saddle, out of it, or somewhere between the two is ... ... what it is. The SINGLE exception for both cars and bikes, is when the vehicle is crashing. There is nothing that can be done with tube angles and lengths to influence this. The only parameter that affects how resistant a bicycle (or car) might be to changes in weight distribution is wheelbase. Increase the wheelbase (enough) and you get a bike that can have a 60F/40R weight dist. and still be rideable. That is impractical for a single bike, but tandems, even racing tandems, can accomplish it pretty easily.

fietsbob

Rear tire wear is also a Product of Torque application to Move forward.

Touring on cargo bikes is done . both front Load Bak fiets And long tail like the Extracycle/big Dummy.

Standing on the pedals your weight , of Course, Shifts to the cranks , and some to the handlebars , How could it Not?

Your BB is closer to the rear wheel Than The Front.. a measurement you can Make ..

TimothyH

It isn't just body position. Braking and slowing shifts weight to the front wheel. The opposite is true of acceleration, seated climbing, etc. Turning, road imperfections and irregularities, etc., all contribute to changes in weight distribution.

This is why tire pressure is a moving target. Low pressure in the front might be great for riding along but it might be too low for braking hard into a corner where most or almost all of the weight is on the front wheel.


-Tim-

Shimagnolo

There is no need to wonder about weight distribution, just measure it!
Put bathroom scales under front tire,
equal thickness block of wood under rear tire,
hold brakes and mount bike in riding position,
note scales reading for front wheel weight.

Now stand on scales and pick up bike, note total weight.

Subtract front weight from total to get rear wheel weight.

Worst I've seen was a 67:33 distribution on a 64cm frame (myself).
Best was a 50:50 on a 42cm frame (short exGF).

TimothyH

Weight distribution changes as you ride. Braking puts more weight on the front wheel, acceleration or seated climbing transfers weight to the rear, etc.

Under hard braking almost all weight is on the front wheel. I did a bunny hop last Saturday - no weight on either wheel.

It is not static. I wonder what the practical application of the OP's question is or if it is just curiosity.


-Tim-

Shimagnolo

For crying out loud, quit overthinking it.
Of course it changes based on acceleration/deceleration/climbing/descending.
The only practical approach to to use the data for a level surface at a constant speed (or stationary) for the calculation.

JanMM

About 30/70 F/R on my long wheelbase recumbent. Doesn't change with standing because it's not humanly possible to do that.......

TimothyH

Some of the charts and calculators out there told me to go with 70psi front and 110psi rear based on static weight distribution.

Braking hard into a turn is the example I used previously. Nearly 100% of the weight can be on the front wheel in this case and using the charts would have left my front tire dangerously underinflated.

In many cases and certainly for aggressive road riders, using static weight distribution to determine tire pressure is dangerous. The practical approach is to use static weight distribution as a starting point to determine the minimum, give the topic some thought based on your individual riding style and then adjust (up) from there. Static weight distribution calculation should only be a starting point for those who ride aggressively.


-Tim-

Leisesturm

If you pressurize your tires... both of them, so that you cannot perform any meaningful deflection of the surface with the flat of your thumb, you will be in good shape. Works on any size tire.

TimothyH

Please define "meaningful deflection" and "good shape."

This is exactly the kind of ambiguity which causes bad things to happen.


-Tim-

ThermionicScott 

That would be too much for some of my bikes.

Doug5150

I would bet that 40%/60% is WAY out of line with reality.

Most upright road and MTB bikes that are properly sized are somewhere between about 50%/50% F/R and maybe ranging as far as 45%/55% depending on how they're set up. When you stand on the pedals you lean on the handlebars, which shifts the weight a little bit forward. With a bathroom scale you can figure it out yourself.

A typical long-wheelbase recumbent is about 33% front and 66% rear, but it depends on the rider's height. For a small person it shifts towards being more even, maybe 40%/60%. Even so it's way more uneven than any upright bike is.

The worst weight distribution of any bike I recall is probably the old BikeE recumbents. The bike "frame" was a rectangular beam that the seat clamped onto--so for a tall person, the seat ended up way back almost over the rear wheel.

Google pictures: https://www.google.com/search?q=bike...w=1920&bih=971

For a tall person, the weight distribution could be as much as 25% front and 75% rear. For these people it was common to see the wheel lift a bit under hard pedaling in lower gears. I've not heard of any other production bike (recumbent or otherwise) that would normally do that.

Leisesturm

Interesting. A 40%/60% weight distribution is WAY out of line with reality but 45%/55% isn't. Hmmmm. And the "worst" weight distribution of any bike..."? It must be said, again, that the BikeE is a recumbent! That matters more than has been acknowledged. The main concern of a front biased weight distribution for standard bicycles, is endoing over the front wheel in a panic stop. That will not happen to a recumbent or tandem. So that "worst" needs to be qualified.

Leisesturm

Not at all. There is tremendous float in the system. For the average 2?mm tire, the range of acceptable pressure runs from ~80psi to the pressure rating on the sidewall. For larger tires the range is even wider. 50mm tires are quite firm and stable at 25psi!! If you overinflate a tire 50psi (and more) past its sidewall rating it will remain safe to use, just not as comfortable. The underwriters that insure tire companies insist on that kind of overconstruction. If you badly underinflate the tire it will scare you with the poor handling, but it will not come off the rim. Millions of cyclists do not own a pressure gauge. Let that sink in for a few pump strokes. I'll help, millions of cyclists do not own a pressure gauge. It isn't rocket science performed with digital scales accurate to 0.10lb, and carpenters levels, and shimming blocks. If all that preparation was necessary to be safe on a bicycle we would all drive cars instead. That or be forced into Mass Transit purgatory.

Doug5150

Really, 45F/55R is kinda pretty extreme for a normal upright bike with just a rider.

Let's consider a 30 lb bike and a 150 lb rider: to have 50/50 F/R distribution, there would be 90 lbs on each tire.

To change the weight distribution to 45F/55R, that would require an additional 20 lbs on the rear wheel.

To change the weight distribution to 40F/60R, that would require an additional 45 lbs on the rear wheel....

--------

I don't have any info on the differences between fat and thin riders, but that would be interesting to see.
Such as:
1. get two people who both weigh 180 lbs. One is tall and slim, and the other is short and fat.
2. Have them sit on a bicycle that is properly sized for their (different) heights, and see what the weight distribution of each is... ?

Since most people gain weight mostly on their torsos I would suppose that as the rider gets fatter, the weight distribution moves somewhat rearward on the bicycle,,, but I can't even guess as to how much.

Leisesturm

I wouldn't know anything about it. But without even trying. Just on the constant background repetition of having read dozens of informative sources over decades. Rightly or wrongly, it has seeped into my general awareness NOT THAT IT MATTERS A WHIT IN DAY TO DAY RIDING, that a weight distribution of 45F/55R is more or less considered "normal" for the average bike and rider. However, as has been pointed out in this thread, that is a static measurement which is a dynamic that is very rarely present when one is actually riding a bicycle. Still, it informs (loads) the prevailing weight bias that will result from dynamic maneuvers. And? I don't know. I really don't know why we are talking about this. I sure hope it isn't in order to decide how much air to put into a tire. That's easy. You put in enough that you can't deform it with finger pressure.

Doug5150

Somebody else asked about weight distribution.

As far as air pressure, the technical answer is "it depends on how much load the tire is carrying"....
The Bicycle Quarterly "15% drop" figure takes the individual tire load into account, although you may need a second person's help with doing that correctly.

I generally always inflate my tires always enough, but not too much. Most of the time.