Well I never...the hipsters steed!

General cycling advice ( NOT technical ! )
pwa
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Re: Well I never...the hipsters steed!

Postby pwa » 28 Jun 2019, 8:15am

Mick F wrote:Ok, the forks are tapered.
Which direction is the force bending the forks and where are they bending?
Vertically?
I don't see that it would.
I notice that it has big tyres.sutra_ltd.jpg

The Kona is basically a touring bike with disc brakes so the forks ain't gonna be bending much whether they have a curve or not. But imagine a light road race bike with caliper brakes and straight fork blades, like the Kona's but a tad more slender and thinner walled. The downward pressure of the mass of bike + rider applies vertically, so the straight blade bends over bumps in the road. At a guess I'd say the bulk of the bending will be just over half way down the blade. I have ridden such fork blades and they do bend. Think of all the debating of how to stop straight frame tubes bending, and imagine if, say, seat stays were not connected to chain stays by dropouts. They would bend a lot.

Bmblbzzz
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Re: Well I never...the hipsters steed!

Postby Bmblbzzz » 28 Jun 2019, 8:25am

The "Bicycle of the Week" series was new to me. It turns out to be an eclectic selection.

mattheus
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Re: Well I never...the hipsters steed!

Postby mattheus » 28 Jun 2019, 10:11am

Mick F wrote:Ok, the forks are tapered.
Which direction is the force bending the forks and where are they bending?
Vertically?
I don't see that it would.
I notice that it has big tyres.sutra_ltd.jpg


Mick,
It's probably a huge waste of time to discuss forces without paper-n-pencil on a desk between us, but if you want to pursue this:

take that picture, and draw an arrow showing the direction of forces exerted on the front wheel (from the ground, as it were).

(Ideally, repost it here)

This should make things a lot clearer. :)

Matt

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Mick F
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Re: Well I never...the hipsters steed!

Postby Mick F » 28 Jun 2019, 2:11pm

It's me being a little obtuse as usual. :oops:
I see the dynamic forces bearing down on the front wheel at the head angle, and not vertically.
When static, the load would be vertically down.
Mick F. Cornwall

mattheus
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Re: Well I never...the hipsters steed!

Postby mattheus » 28 Jun 2019, 3:23pm

I don't know what a "dynamic force" is. It wasn't in any physics book I read - and I've read quite a few. (I tried one in latin once, I don't recommend it!).

Magnetic force, frictional force, irresistible force ... :P

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Mick F
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Re: Well I never...the hipsters steed!

Postby Mick F » 28 Jun 2019, 3:39pm

The weight of the rider is mainly over the back.
This makes a pivot, and the front goes down with the spring forces as you ride over the bumps, but at the head angle, not vertically.

When static and still, the weight is vertical.
Mick F. Cornwall

mattheus
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Re: Well I never...the hipsters steed!

Postby mattheus » 28 Jun 2019, 4:10pm

I don't think I can move this on without paper-and-pencil (or a whiteboard these days.)

(bike dynamics are really interesting ... but text-based web chatter does tend to be a really poor way to debate them beyond the simplest ideas, sadly.)

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Mick F
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Re: Well I never...the hipsters steed!

Postby Mick F » 28 Jun 2019, 4:16pm

:lol: :lol: :lol: :lol:

I'll give it some thought, try and draw a diag, and then post it.
Mick F. Cornwall

mattheus
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Re: Well I never...the hipsters steed!

Postby mattheus » 28 Jun 2019, 4:25pm

:) It might be worth noting that 90% of any movement is in tyre-flex on most rigid-frame bikes.

Looking back over these posts, you might be thinking of all forks acting like suspension forks - I don't think that's the case. Mainly.

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RickH
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Re: Well I never...the hipsters steed!

Postby RickH » 28 Jun 2019, 5:00pm

FWIW my Kona has a 71 degree head angle. Fork length is given as 410mm & offset 50mm. By my reckoning that puts the fork legs at about a 10 degree angle to the steerer so the forks are at about 29 degree from vertical.