Bicycle Mechanics - Fork on backwards...

The other day, while locking my bike up, I realised the bike locked to the other side of the rack had the fork on backwards! It was what I'd describe as a BSO, but it had clearly been ridden there. Just how dangerous would it be to ride a bike like that? And how the heck does that get past inspection?

Might be a little twitchy.......

opposite..
In a video demonstration, MIT Professor, Author of bicycle science,
set a handle bar less
bicycle in motion down a hill, it went dead straight, with no one on it.
because the trail was large.. it more stable, but harder to change direction.
so great if no hands butt steering is the plan..
teacup and saucer in hands while on the way.

in the carton the fork is backwards,.. BSO are assembled by min. wage clerks
in the big box stores, not skilled bike mechanics..

Of the three bikes currently being built up in my workshop, none of them would allow a backwards fork. The front wheel would be impeded by the downtube. Must have been a MTB.

Think of casters. Casters trail behind and are much more stable when trailing behind the pivot point. Turn the casters so they are facing forward (leading) on a shopping cart and then push the cart, the cart wants to shift around while the casters try to twist so they are trailing as you initially push the cart.

Cars are the same way. If you adjust the caster angle on a cart so that you have positive caster, you will make the car feel more twitchy and responsive however it won't track as straight easily and when you let go of the steering wheel while making a turn, it won't return back to center. You adjust the caster so you have negative caster, the car won't be as responsive or twitchy when you are steering but it will feel much more stable. You will be able to let go of your steering wheel and the car should tract straight for a while.

So yeah, a backwards fork will make the bike feel much more stable but when you turn the handlebars, it won't respond as quickly as a normal positive angle fork.

Guess you've never shopped at Tesco when they have bikes in. Pretty common to see incorrectly assembled bikes, and the people who buy them don't seem to mind / care about it.

See here for a photo of one on an instore display http://singletrackworld.com/forum/topic/how-many-people-out-there-with-forks-facing-wrong-way

See here for a photo of one on an instore display http://singletrackworld.com/forum/topic/how-many-people-out-there-with-forks-facing-wrong-way

I don't want to live on this planet anymore......

Stayer bike? :)

http://2.bp.blogspot.com/_oIsCw57t7LQ/TUISQsQFlJI/AAAAAAAAAZE/PF-Cg6008QY/s1600/1971---moser-stayers-1.jpg

http://farm5.staticflickr.com/4147/5060013403_0589ce5840.jpg
That's soooo wrong.

Stayer bike? :)

http://2.bp.blogspot.com/_oIsCw57t7LQ/TUISQsQFlJI/AAAAAAAAAZE/PF-Cg6008QY/s1600/1971---moser-stayers-1.jpg

Interesting pic! I guess the fork "reversal" changes the front wheel "trail" and that would certainly affect handling.

On my first trip with my folding Bike Friday I was a bit rushed and accidentally assembled it with the fork reversed. Handling was fine but a little bit too stable. But when I had to brake hard in traffic I felt the rear wheel lift much more easily than usual. Fortunately it didn't cause me to fall and at that point I checked over the bike and discovered my assembly error.

Bike in #8 is for motorbike paced track racing.., racers sheltered
Air resistance reduced , behind the 'Clyde' on a Derny.

At my own workplace:

http://farm7.staticflickr.com/6041/6390208057_fa0fd0b8c3_b.jpg

Think of casters. Casters trail behind and are much more stable when trailing behind the pivot point. But a shopping cart caster pivots around a vertical axle. If you lean a caster wheel until its pivot axle has the approximate angle of a bike head tube, the wheel will happily stay on the forward side, just like on a bike.


Cars are the same way. Are they? I think not. Bike forks have rake, or offset. Never seen that discussed for cars.


So yeah, a backwards fork will make the bike feel much more stable .

No. A backwards fork will make the bike less stable.
Look at a bike with a standard oriented fork. Notice the exact height of, say the top tube/head tube junction when the wheel is pointing straight forward.
Now turn the bar, as in a sharp turn. You'll notice your chosen reference point rising a little. Let it back into a straight forward position, see how the reference point drops again.
Gravity alone will make the bike strive to continue straight forward. This is (part of) what allows us to ride no handed.

If you flip the fork around, the reference point will be at its highest point with the wheel straight forward. Turning the wheel will lower the front of the bike. A flipped fork bike will be (near) impossible to ride no handed.
But hands-on riding isn't really much affected, as long as there's no toe strike or down tube strike.

A flipped fork bike will be (near) impossible to ride no handed.
But hands-on riding isn't really much affected, as long as there's no toe strike or down tube strike.
Nope, my Bike Friday (mentioned above) is the only bike I have where the fork can be reversed without striking the down tube. It is much easier to ride straight no-handed with the fork reversed - but harder to turn.

Are they? I think not. Bike forks have rake, or offset. Never seen that discussed for cars.

For cars, generally referred to as "caster", but the same principal. A car or truck's wheel spindle is angled back, similar the how a bike's head tube is angled back. My '32 Ford has 7 degrees caster built into the solid front axle. This allows me to remove my hands from the steering wheel while the car runs straight down the road.
With bicycles the term "rake" is somewhat misused. With motorcycles and most other vehicles rake is the angle of the axis of rotation expressed in degrees. This is equivalent to what we call HTA, head tube angle. What we call rake is actually the offset that the wheel axle has to the axis of fork rotation. On a bicycle increasing rake offset reduces steering trail, causing the bike to change directions more quickly. Reducing rake offset increases steering trail, causing the bike to feel more stable (at least at most riding speeds).
http://en.wikipedia.org/wiki/Bicycle_and_motorcycle_geometry

At my own workplace:

http://farm7.staticflickr.com/6041/6390208057_fa0fd0b8c3_b.jpg
Are we sure that seat isn't also backwards? :)