Well I never...the hipsters steed!

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

Postby Mick F » 25 Jun 2019, 1:29pm

Oops! :oops:
A picture is worth a thousand words!

Thanks for putting me "straight".
Mick F. Cornwall

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

Postby Mick F » 25 Jun 2019, 1:31pm

Still not explained why straight forks can be compliant though.
What bends?
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Re: Well I never...the hipsters steed!

Postby pwa » 25 Jun 2019, 1:40pm

Mick F wrote:Still not explained why straight forks can be compliant though.
What bends?

If you look at "straight" forks from the side you will see, of course, that they are not vertical. So if you go over a bump in the road the "straight" tube will bend, just a little, upwards at the dropout. How could it not? If it were overbuilt, with thick walls and excessive diameter, it would bend very little. So it has to be configured just right. But as I say, I have ridden a bike with an upmarket straight fork and it did flex enough to give a lovely smooth ride. At least as good as some 531c forks I had on another bike, and better than curved 531st forks on a third bike.

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

Postby Mick F » 25 Jun 2019, 1:48pm

Yes, I see what you mean, but the ones I've seen are basically parallel tubes - ie not tapered.

When I ride along on 531c, I can see the forks twitching and bending at the ends where the tubes are narrow to a point at the dropouts. I'm also aware that with a 531c steerer, that also flexes inside the head tube. This leads to premature headset wearing of course.

Do straight forks have a "flexible" steerer like 531c does?
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Re: Well I never...the hipsters steed!

Postby Spinners » 25 Jun 2019, 2:09pm

In the 1990's all my frames were custom made by our local frame-builder and I had two frames in Columbus Neuron both otherwise identical but one with curved forks and one with straight forks (I think they were called 'power' forks at the time). No discernible difference could be detected by me. At various times, I've preferred the aesthetics of both but today my only steel framed road bike has curved and if i was going custom I'd also go curved.

Perhaps this bike (which I quite like) would look more retro with curved forks? For me, I don't like the short head tube (about 2.5cm shorter than my custom-builds) and I don't like the HTA (73.5) being greater than the STA (73).
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Re: Well I never...the hipsters steed!

Postby pwa » 25 Jun 2019, 4:24pm

Mick F wrote:Yes, I see what you mean, but the ones I've seen are basically parallel tubes - ie not tapered.

When I ride along on 531c, I can see the forks twitching and bending at the ends where the tubes are narrow to a point at the dropouts. I'm also aware that with a 531c steerer, that also flexes inside the head tube. This leads to premature headset wearing of course.

Do straight forks have a "flexible" steerer like 531c does?

It is a while since I had them, but mine were 1" threaded so presumably the steerer behaved as you would expect with 531c. The blades narrowed considerably and were quite elegant, so a world away from those wide tubes you see on MTBs.

Look at this site. There is an image which, of you hover over it flicks from straight to curved fork, but the blades of both are very similar in taper.
http://www.llewellynbikes.com/LlewellynCustodian.html

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

Postby al_yrpal » 25 Jun 2019, 6:02pm

I suggest the non believers look up 'bending moment' and try to imagine what the offset does especially on a gently tapering steel tube. My old Giant with its straight fork was an uncomfortable dog in comparison to the Mercian

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

Postby pwa » 25 Jun 2019, 6:14pm

al_yrpal wrote:I suggest the non believers look up 'bending moment' and try to imagine what the offset does especially on a gently tapering steel tube. My old Giant with its straight fork was an uncomfortable dog in comparison to the Mercian

Al

But was the Giant's fork made of the same stuff, with the same wall thickness and taper? My old straight blade forks were made from the top end Columbus steel of that era, thin walled and tapering to make a flexy tube. And they really did soak up vibration. Maybe this contradicts preconceptions but it is true. I rode that bike on some long rides and it was as close to a magic carpet ride as you will get on a road bike. If the forks had been harsh I would have noticed.

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

Postby Spinners » 26 Jun 2019, 7:35pm

Straight forks didn't hold these lads back...

https://www.youtube.com/watch?v=mNabjYdJjJU

C40 carbon frames with steel forks

(I remember this as if it was yesterday)
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Re: Well I never...the hipsters steed!

Postby RickH » 26 Jun 2019, 9:16pm

Mick F wrote:Yes, I see what you mean, but the ones I've seen are basically parallel tubes - ie not tapered.

When I ride along on 531c, I can see the forks twitching and bending at the ends where the tubes are narrow to a point at the dropouts. I'm also aware that with a 531c steerer, that also flexes inside the head tube. This leads to premature headset wearing of course.

Do straight forks have a "flexible" steerer like 531c does?

My Kona Sutra has tapered straight forks.
Image
Incidentally they have a 50mm offset created by not having the fork leg parallel to the steerer (for those who haven't quite got how straight forks can have a "proper" offset).

The ends of your forks may be seen to be moving but I'm not sure (I don't really know - has it been measured/ modelled?) how much is actually bending in the tapered ends rather than other parts of the fork legs (& steerer).

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

Postby pwa » 27 Jun 2019, 8:28am

If you look at those Kona forks and imagine what the curved alternative would be like, if it started, as it would, in line with the steerer, and saved all the curving for the lower end of the fork blades, the length of blade that would get much closer to the horizontal would be very short. And the shorter it is the less effective. The straight fork is not in line with the steerer right from the fork crown, so whatever extra flex that buys you is there for the full length of the blade.

In practice the Kona forks will probably be a bit like the curved 531 forks on my tourer, strong (esp. with the discs) and not very flexy, so reliant on the cushioning of the tyres. My own (now gone) straight forks were for caliper brakes and had very slender blades, so gave a supple ride even with narrow high pressure tyres.

(I like the look of the Kona, by the way. Does that chain stay on even over bumpy ground?)

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

Postby RickH » 27 Jun 2019, 10:03am

pwa wrote:If you look at those Kona forks and imagine what the curved alternative would be like, if it started, as it would, in line with the steerer, and saved all the curving for the lower end of the fork blades, the length of blade that would get much closer to the horizontal would be very short. And the shorter it is the less effective. The straight fork is not in line with the steerer right from the fork crown, so whatever extra flex that buys you is there for the full length of the blade.

In practice the Kona forks will probably be a bit like the curved 531 forks on my tourer, strong (esp. with the discs) and not very flexy, so reliant on the cushioning of the tyres. My own (now gone) straight forks were for caliper brakes and had very slender blades, so gave a supple ride even with narrow high pressure tyres.

(I like the look of the Kona, by the way. Does that chain stay on even over bumpy ground?)

The Kona was always going to have beefy forks - designed for mixed terrain, disc brakes & multiple luggage bosses for carrying stuff up front.

The chain has never come off in 2 1/2 years. The chainring has tall narrow-wide teeth & the derailleur has a clutch mechanism that stops it bouncing slack. I've barely even had any chain slap - it came with a thin clear plastic chainstay protector fitted. That has 3 or for slight marks on it but is otherwise in pristine condition (when it isn't covered in a layer of dirt).

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

Postby mattheus » 27 Jun 2019, 12:33pm

Mick F wrote:Yes, I see what you mean, but the ones I've seen are basically parallel tubes - ie not tapered.


It doesn't matter what shape or profile they are - impact forces thru the wheel still cause them to bend. Because your head-tube isn't vertical!

(You cannot make a perfectly rigid rod, tube or girder out of any metal known to man.)

If you fit the same fork to a slacker head-tube, there will be a bit more bending force - all things being equal - and thus the fork will bend a bit more on that bike (over the same bumps, anyway :) )

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

Postby Mick F » 27 Jun 2019, 7:24pm

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

Postby londonbikerider » 28 Jun 2019, 7:58am

As a rule of thumb, I stay away from what's on the frontpage of a magazine.
Does anyone else have the feeling that several of those "single-speed" bikes are actually overpriced? I remember that with the same money you could buy a less fashionable, but well-woreking and frankly honest, Ridgeback/Dawes/Genesis/the likes that would have a full set of gears and better finishing kit.