Weight distribution when freewheeling on quick/downhill corners

Heltor Chasca

Out-Riding the Black Dog
Loosen up. Disengage yourself from the bike and you become two independent entities. Flow. Fluidity. Be free. Man.

(Stiffen up and your teeth will end up being part of the landscape)

Peace out brothers and sisters✌
 
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Twilkes

Twilkes

Veteran
I don't agree with the first paragraph. The weight should be on the saddle as it is the power one's leg generates which is transferred through the pedals to create motion.

If weight were a factor then heavier riders, on a flat route, would be faster. Weight is only a factor in descending because it increases impetus but it doesn't increase power, often the reverse in fact.
If you sat on a pair of scales on top of your saddle, and it said 70kg or whatever when you were stationary, as soon as you started pedalling it would show less than 70kg because some of that weight is now being supported by your legs - because there is resistance when pedalling, some of the power generated is used to push the pedal down and some of the power is used to push your body up (or slightly backward sometimes). If you pedal really hard you'll find it only takes a little more power to lift off the saddle completely.

It's the weight distribution between the pedals, saddle and bars that I was asking about.

https://www.sheldonbrown.com/saddles.html
 
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Ajax Bay

Veteran
Location
East Devon
when pedalling normally there will always be weight taken through the legs, reducing the load on the saddle, unless you're pedalling at a super-high cadence? Any resistance from the pedal to being moved will result in the leg bearing weight and reducing the weight through the saddle.
I don't agree with the first paragraph. The weight should be on the saddle as it is the power one's leg generates which is transferred through the pedals to create motion.
As @Twilkes has said and then restated, if the rider applies a force downwards on a pedal and that's more than the force (if any - none on downhill) they apply upwards with hands on the bars, then the net weight supported by the saddle is reduced. I am disregarding any upwards force on the pedal moving upwards as it's negligible (and poor technique). Fisyks, init?
 
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PaulSB

Legendary Member
I'm afraid I don't follow either of these arguments. The point of a saddle and it's position is to support the rider's weight. Using one's legs to support body weight on a bike is both unecessary and inefficient.

The sitting bones support the body and the legs do the work. Putting most of one's weight on the pedals suggests the riding position is wrong. The only time the legs support the body weight should be when standing on the pedals.
 
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Twilkes

Twilkes

Veteran
You support 100% of your body weight on your legs when you climb stairs, as you straighten your legs to make yourself go upwards. It's similar on a bike, only the saddle takes some of the load - the link to the study doesn't work any more, but post #10 in this thread suggests that the saddle supports around 50% of your body weight, the rest is legs and some on the hands. https://www.bikeforums.net/road-cycling/747649-body-weight-distribution.html
 

PaulSB

Legendary Member
When cycling normally most of my weight is on my feet, some on the saddle and a little on the handlebars.
Your own figures support the point I was making. I can't define what you mean by "most" but imagine it is more than one-third. By definition "most" must be more than 50% and I suggest it means much more than this figure. The link shows 45-50% of body weight supported by the saddle, 20% hands and 16% each leg. From your own figures +/- 70% of body weight is not supported by the legs. If "most" of one's weight is supported by the legs when freewheeling I feel the position is incorrect.

When pro cyclists descend their position is pushed back on the bike over the saddle and the body lowered thus reducing the amount of weight through the legs.

I don't feel climbing stairs is relevant, our legs support 100% of our body during any type of movement which does not involve a machine.

On a bike the only time the legs should be bearing "most" of one's weight, I guess this would be around 80%, is when standing on the pedals. My own experience is this position while clearly using more body weight to help push the pedals is far from efficient and is difficult to maintain.

The pedals are centrally positioned on a cycle, the saddle is further back. If "most" of a rider's weight is on the pedals the position being used is not the one intended by the bicycle designer.
 
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I find it helps if I push down the leg on the raised side of the bike as well. So if cornering right, push down the left leg, and vice versa
 
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Twilkes

Twilkes

Veteran
So 'most' was probably an over-estimate, but I tend to pedal hard and the saddle is increasingly unweighted the more force you put onto the pedals. When you push on the pedal not all of that force makes the pedal turn, due to resistance - the rest of the force acts on your body, pushing it upwards and backwards. You can see the effect if you set off in too big a gear, as you push hard it's difficult to stay in the saddle because there's nothing keeping you there. If the pedal didn't move at all, all of the force would be acting on your body, hence the comparison with pushing against static stairs.

Anyway, I've started relaxing more on downhills so the thread served its purpose. :smile:
 

Sharky

Veteran
Location
Kent
Another thought/theory ...
With fresh legs, the body weight is shared between the contact points and a % taken up by the legs.
On longer rides, the legs begin to tire and the % weight share transfers more to the saddle, thus increasing saddle soreness on the longer rides.
 
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Twilkes

Twilkes

Veteran
Another thought/theory ...
With fresh legs, the body weight is shared between the contact points and a % taken up by the legs.
On longer rides, the legs begin to tire and the % weight share transfers more to the saddle, thus increasing saddle soreness on the longer rides.
Yeah the Sheldon Brown link essentially says that. I've found that on slow doddery rides my saddle hurts way more than on a long fast ride because there's far less power going through the pedals, so more weight on the saddle.
 

Ajax Bay

Veteran
Location
East Devon
I'm afraid I don't follow either of these arguments. The point of a saddle and it's position is to support the rider's weight. Using one's legs to support body weight on a bike is both unecessary and inefficient.
The sitting bones support the body and the legs do the work. Putting most of one's weight on the pedals suggests the riding position is wrong. The only time the legs support the body weight should be when standing on the pedals.
Don't think I have suggested that "using one's legs to support body weight on a bike is" either necessary or efficient when riding along normally, nor that a road cyclist puts "most of [their] weight on the pedals" (and @Twilkes has resiled from "most" now). So I can see why you don't follow those arguments (as you have rephrased them) - I wouldn't agree with them either. But if a rider pedals (puts force on the pedal) then the 'equal and opposite' force on the body is upwards and that reduces the upwards force of the saddle on the rider's backside (NB bit more complex because of hands/bars interaction - see my earlier post). Riders aren't deliberately supporting their body weight with their feet when riding along normally, they are just pedaling: physics does the rest. No 'work' or 'power' without 'force'.
 

PaulSB

Legendary Member
@Ajax Bay yep I get that but I didn't think I'd rephrased things. It certainly wasn't deliberate.

I don't subscribe to the Sheldon Brown theory tiredness through increasing weight on the saddle makes the saddle hurt more. That's surely s function of having the wrong saddle? Yes I get tired on long rides but this tends to be legs, naturally, and arms. I am guilty of putting too much weight through my arms on ocassions.
 
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