weight and braking (descending)

[moock]

OK, we know that we can climb faster with less weight.
But how does weight effect the overall stopping power of the system? Asking especially when descending.

eg. I weight 83kg + 1,5kg helmet, shoes etc. Bike is 8kg + 2,5kg bottles, pump, tubes etc. = 95kg system weight. (I have not measured all of this; just an example)

Could i feel a noticable difference in stopping power when I reduce the overall weight to 90kg? For example when having red lights at an end of a faster decend.

[TobinHatesYou]

Yes you would likely notice a 5kg difference under braking, but just barely.

[mikemelbrooks]

OK, we know that we can climb faster with less weight.
But how does weight effect the overall stopping power of the system? Asking especially when descending.

eg. I weight 83kg + 1,5kg helmet, shoes etc. Bike is 8kg + 2,5kg bottles, pump, tubes etc. = 95kg system weight. (I have not measured all of this; just an example)

Could i feel a noticable difference in stopping power when I reduce the overall weight to 90kg? For example when having red lights at an end of a faster decend.

Also, the heavier your set up the faster you will be going downhill,
https://www.theactivetimes.com/tour-de-france-facts

The winner of the 1947 tour, Jean Robic, was known for being a good climber but not heavy enough for a good descent. His manager arranged for water bottles full of lead to be given to Robic at the top of climbs to help speed his descent.

[tjvirden]

OK, we know that we can climb faster with less weight.
But how does weight effect the overall stopping power of the system? Asking especially when descending.

eg. I weight 83kg + 1,5kg helmet, shoes etc. Bike is 8kg + 2,5kg bottles, pump, tubes etc. = 95kg system weight. (I have not measured all of this; just an example)

Could i feel a noticable difference in stopping power when I reduce the overall weight to 90kg? For example when having red lights at an end of a faster decend.

It depends almost entirely on your braking system, compared to the mass it has to slow down. If the braking system currently has spare capability at a given system mass, then reducing that mass won't change your ability to slow down ("stopping power") in specific circumstances. However, if the system mass is currently such that braking system is already used to its limit (basically the maximum rate at which it can convert kinetic energy to heat and then dissipate that heat is reached), then less mass may well mean a noticeable improvement in stopping. So; it depends.

[alanyu]

F = ma

[Karvalo]

F = ma

f=µN

[skymasternl]

The drag experienced during descent is predominantly drag, which is only a function of velocity, density, shape and cross-sectional area. With everything else being the same (bike, body height and shape, position on bike, tyre, wind, gradient, etc), a HEAVIER rider+bike would have a HIGHER terminal velocity (Highest speed you'll reach without pedalling) .

However, if the descent gets technical and there are a lot of corners, a HEAVIER rider would have to brake HARDER and EARLIER and have to corner at a LOWER speed.

So yeah, a heavier rider+bike will likely reach higher speed, but the average speed of the descent will be dependent on the nature of the course.

[Mr.Gib]

However, if the descent gets technical and there are a lot of corners, a HEAVIER rider would have to brake HARDER and EARLIER and have to corner at a LOWER speed.

why does a heavier rider have to corner at a lower speed?

[dudemanppl]

Tires have a finite amount of grip

[Karvalo]

Tires have a finite amount of grip

For a given rider. Again, f=µN

Heavy riders' tyres grip more.

[Mr.Gib]

However, if the descent gets technical and there are a lot of corners, a HEAVIER rider would have to brake HARDER and EARLIER and have to corner at a LOWER speed.

why does a heavier rider have to corner at a lower speed?

Tires have a finite amount of grip

Tires have a finite amount of grip

For a given rider. Again, f=µN
Heavy riders' tyres grip more.

This is what I was thinking. Doesn't the heavier mass increase the traction to the point that it overcomes or at least balances out increaseed lateral force while cornering?

[skymasternl]

However, if the descent gets technical and there are a lot of corners, a HEAVIER rider would have to brake HARDER and EARLIER and have to corner at a LOWER speed.

why does a heavier rider have to corner at a lower speed?

Tires have a finite amount of grip

Tires have a finite amount of grip

For a given rider. Again, f=µN
Heavy riders' tyres grip more.

This is what I was thinking. Doesn't the heavier mass increase the traction to the point that it overcomes or at least balances out increaseed lateral force while cornering?

Only in the ideal world where your tire doesn't deform and your center of mass is always perfectly above the contact patch of the tyre, which itself stays exactly the same no matter where you are going.

Think why for race cars with the same power-to-weight ratio, the lighter ones are always faster, and there is your answer.

[blaugrana]

Think why for race cars with the same power-to-weight ratio, the lighter ones are always faster, and there is your answer.

For race cars it's a bit more complicated, because the heavier car will have a bit of extra grip due to its weight, but the same from aerodynamic downforce (assuming both the heavy and light cars have the same external shape, wings and everything, of course). But even without taking that into account what you say would still be true, of course (and it was back when cars had very little downforce).

[nikospeed]

I used to race cars (youngtimer) on track. Had about the lightest car AND smallest engine. Still in corners I snatched the V8 big boys .
And they had wider tires.
So getting back to bikes I thoroughly believe that all other things equal (esp tire width) the lighter rider corners faster due to less inertia which has a lot more impact than effective pressure/gravity of a heavier rider.
Happy downhilling
Niko

[dudemanppl]

As I said, tires have a finite amount of grip. You're saying it yourself, a heavier rider will put more force in to the tires. So what? There comes a point where the forces from being thicc will overload the amount of grip a tire has.