Never mind Ascending, what about Descending ability

[Steve A]

I read an online cycling article recently about e-bikes and their climbing ability, and that they should have their own category on strava for obvious reasons, which of course they do. Funny enough, it also said they hold no advantage downhill and people had also agreed saying they would be happy if an e-bike held the best time for a downhill segment.

Sad, but i tested this theory over the last few days with a private strata account. Bearing in mind i have a Haibike xduro allmtn 27.5, with speed dongle. I broke every (straight) downhill time by some margin for my local hills, 7 in all. Yes, if i had a road bike and there were longer stretches with BENDS, i would not have finished first as i get scared and i'm not a cat rider

Reason, the assist propels you so quickly, then the bike weight and mid drive motor is just well balanced making the bike planted giving you confidence. Yes, the bike is not as agile on the twisty stuff, and small jumps need a little more planning, but i have to say these e-bike are a treat to ride.

 

[brightonebikes]

I read an online cycling article recently about e-bikes and their climbing ability, and that they should have their own category on strava for obvious reasons, which of course they do. Funny enough, it also said they hold no advantage downhill and people had also agreed saying they would be happy if an e-bike held the best time for a downhill segment.

Sad, but i tested this theory over the last few days with a private strata account. Bearing in mind i have a Haibike xduro allmtn 27.5, with speed dongle. I broke every (straight) downhill time by some margin for my local hills, 7 in all. Yes, if i had a road bike and there were longer stretches with BENDS, i would not have finished first as i get scared and i'm not a cat rider

Reason, the assist propels you so quickly, then the bike weight and mid drive motor is just well balanced making the bike planted giving you confidence. Yes, the bike is not as agile on the twisty stuff, and small jumps need a little more planning, but i have to say these e-bike are a treat to ride.

Agree. I rip it over the other times locally on the downs as well as ups.
At sections where tight bends necessitate scrubbing speed right off, I'm straight back up to speed in no time. Short sections where only a few pedal strokes are possible, I full throttle straight out of the corner before they can even get a pedal stroke in. Corners where they have to stop pedaling otherwise the pedal would hit the floor, I keep that side pedal up and power through the bend with throttle.
It's an absolute dream once a few new techniques are developed and delivers a very fluid ride style, impossible to achieve on a non leccy bike.
Loves it I does!

 

[Interloper]

I've personally found the extra weight also makes the bike roll really well. When following friends on normal bikes on slight declines I catch them up freewheeling when they are pedalling.

 

[Steve A]

agree, bike feels well planted down hill.

 

[Deleted member 4366]

I've personally found the extra weight also makes the bike roll really well. When following friends on normal bikes on slight declines I catch them up freewheeling when they are pedalling.

Your acceleration down a hill depends on your total mass. the heavier you are, the faster you accelerate. More weight also increases your top speed.

Air resistance has the most effect on top speed, so a low drag bike will reach a much higher top speed than than something like a MTB unless you carry enough bricks in a rucksack.

 

[D8ve]

Your acceleration down a hill depends on your total mass. the heavier you are, the faster you accelerate. More weight also increases your top speed.

Air resistance has the most effect on top speed, so a low drag bike will reach a much higher top speed than than something like a MTB unless you carry enough bricks in a rucksack.

As your weight increases so it requires more force to accelerate you so in this ONE instance D8veh is wrong but as your weight increases is not directly linked to wind resistance your top speed may increase.
And low drag really counts as you can check on my strava records. I am putting up 17 mph averages now with a very streamlined bike and no electric assistance.

 

[soundwave]

there is no way you could beat a down hill bike on a 20kg plus ebike, its not going to happen as the extra waight means you cant flick and hop around at speed round the tight corners and get it back on line fast enough.

if extra waight means more speed and a faster time dont you think they would have 20kg bikes for DH 15kg is about the limit for jumping off cliffs.

 

[Deleted member 4366]

As your weight increases so it requires more force to accelerate you so in this ONE instance D8veh is wrong but as your weight increases is not directly linked to wind resistance your top speed may increase.

Unfortunately, you're wrong in this case. It requires more force to accelerate a bigger mass, but when it comes to gravity, your extra mass gives you the extra force proportion to the extra mass. That would mean that you get the same acceleration, but it's not as simple as that. It works like this in air: As soon as you start moving, the air resistance reduces the net force down the hill. The air resistance would be the same for each rider at the same speed, but the net force down the hill will be higher in proportion to the mass for the heavier rider because he started with more force. The heavier rider will still be accelerating when the lighter rider has maxed out because at that point he still has a net force down the hill. That's why he will reach a higher speed too.

This is why it takes a lot longer for a feather to reach the ground than a block of steel. The acceleration downwards and the top speed depend on the ratio of air resistance to mass. At every point downwards, the steel will be travelling faster than the feather except at the instant they started, before air resistance could have any effect.

 

[Steve A]

As your weight increases so it requires more force to accelerate you so in this ONE instance D8veh is wrong but as your weight increases is not directly linked to wind resistance your top speed may increase.
And low drag really counts as you can check on my strava records. I am putting up 17 mph averages now with a very streamlined bike and no electric assistance.

D8ve, don't forget the whisky in other hand when doing the 17mph average

 

[Steve A]

I agree with the physics, but in practice SW may have a point. It would be interesting to see a pro downhill rider test both bikes.

 

[Monoblock]

Erm, just to throw a curve ball at you all
In a vacuum a feather and a bowling ball will accelerate at the same speed, gravity does no have a higher impact on a heavier object.
Now to clarify that, gravity has a bigger pull on the heavier object BUT, that extra pull is needed to accelerate the heavier object at exactly the same rate.
The objects in a vacumn is an old piece of science and actually, technically, the heavier (more mass) object would hit first, but because both objects are pulled to the earth and both objects pull the earth to them, it reality the size of the object compared to the earth makes no difference to the impact point as, as a percentage difference compared to the earth most objects are hugely smaller than the earth and more similar to each other.

So in bike terms, a light bike and a heavy bike will have a force exerted on them to get them close to a 10m a second acceleration curve (it's 9.7 in reality I think) but anyway, both object will be pulled equally BUT.
The lighter bike will set off quicker, both bikes are subject to the downward pull of gravity keeping their tyres planted as well as the force they are seeing down the hill, once you break stiction they both have equal force applied BUT, as the heavier bike has more mass and force is equal to mass times acceleration the the heavier bike has more force meaning it is not slowed as much by bumps and key air resistance which increases exponentially the faster you go.
The balance is to find a weight that gives you the ability to overcome air resistance without creating untold friction through the tyres, to still accelerate from a standstill and low speed corners but to maintain speed once it's generated.

There will be math and it will be different for each course but if downhill bikes tend to fall away around 15kg, the law of averages means that through trial and error the pros have likely found the ideal weight range.






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[Steve A]

Erm, just to throw a curve ball at you all
In a vacuum a feather and a bowling ball will accelerate at the same speed, gravity does no have a higher impact on a heavier object.
Now to clarify that, gravity has a bigger pull on the heavier object BUT, that extra pull is needed to accelerate the heavier object at exactly the same rate.
The objects in a vacumn is an old piece of science and actually, technically, the heavier (more mass) object would hit first, but because both objects are pulled to the earth and both objects pull the earth to them, it reality the size of the object compared to the earth makes no difference to the impact point as, as a percentage difference compared to the earth most objects are hugely smaller than the earth and more similar to each other.

So in bike terms, a light bike and a heavy bike will have a force exerted on them to get them close to a 10m a second acceleration curve (it's 9.7 in reality I think) but anyway, both object will be pulled equally BUT.
The lighter bike will set off quicker, both bikes are subject to the downward pull of gravity keeping their tyres planted as well as the force they are seeing down the hill, once you break stiction they both have equal force applied BUT, as the heavier bike has more mass and force is equal to mass times acceleration the the heavier bike has more force meaning it is not slowed as much by bumps and key air resistance which increases exponentially the faster you go.
The balance is to find a weight that gives you the ability to overcome air resistance without creating untold friction through the tyres, to still accelerate from a standstill and low speed corners but to maintain speed once it's generated.

There will be math and it will be different for each course but if downhill bikes tend to fall away around 15kg, the law of averages means that through trial and error the pros have likely found the ideal weight range.






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Totally agree. I saw Brian Cox on stage in Kent last year from the Monkey cage radio program. He talked about this and proved that point. There is a huge container that can create a vacuum and he dropped a feather and a lead weight at same time and both hit ground at same time. I think it's on youtube

Sad to say that most went over my head, but intrigued that gravity is actually pushing us up, go figure!

 

[Deleted member 4366]

gravity does no have a higher impact on a heavier object.
Now to clarify that, gravity has a bigger pull on the heavier object BUT, that extra pull is needed to accelerate the heavier object at exactly the same rate.

Well, that's right apart from the first bit, Gravity is a field. It creates a force on objects in proportion to their mass. The bigger the mass the more the force, so a bigger mass is forced downwards harder, but it has inertia as well, which is also in proportion to it's mass. The inertia prevents a heavy object from accelerating as much as a lighter object thàt has the same force applied.

In other words, the heavier object gets more force from gravity, but its inertia reduces the acceleration, with the result that heavy and light objects accelerate downwards at the same speed in a vacuum, which is basically what you said.

 

[D8ve]

D8veh
that would also be what I said. Just in nicer words.
Fine points of detail get mixed up like when I ask is light a wave or particle.