The Bum Steer

**GSVR** · 11th February 2008, 11:47

Originally Posted by Badjelly

Many years ago I made a skateboard with a castor wheel, the sort they use on furniture. (I'd already worn out the one I made earlier with my sister's roller skates.) I put it at the top of the hill with the castor wheel at the back and stood on it--it swapped ends on me. There was no way that thing would go down the hill with the castor on the back, but it was perfectly happy with the castor at the front.

So, I think the answer is that a bike with the steered wheel at the back would insist on swapping ends to bring the steered wheel to the front.

Yes but your castor wheel didn't have handlbars did it and the rake and trail were all wrong (it didn't have any)

**Badjelly** · 11th February 2008, 11:50

Originally Posted by GSVR

Yes but you castor wheel didn't have handlbars did it and the rake and trail were all wrong (it didn't have any)

No handlebars, no. It had a vertical steering axis (rake = 90 deg???) and about 3 cm trail. Not exactly analogous to a bike, but I suggest nevertheless that a bike with the steered wheel at the back would not track stably.

**Ocean1** · 11th February 2008, 11:50

Originally Posted by GSVR

Yes but your castor wheel didn't have handlbars did it and the rake and trail were all wrong (it didn't have any)

But if it did, would it respond to countersteering input the same as a cicle?

**Ocean1** · 11th February 2008, 11:53

Originally Posted by Badjelly

No handlebars, no. It had a vertical steering axis (rake = 90 deg???) and about 3 cm trail. Not exactly analogous to a bike, but I suggest nevertheless that a bike with the steered wheel at the back would not track stably.

I can attest to that, I've navigated many downhills going arsy versy, usually directly after an attempted hillclimb.

Not stable at all, at all.

**Badjelly** · 11th February 2008, 11:59

Originally Posted by Ocean1

would it respond to countersteering input the same as a cycle?

In case anyone's interested, I steered the castor-equipped skateboard by putting weight over the front wheel and leaning. It handled quite well, actually. Mind you, it was arguably a tricycle, because at the back it had a double-wheel unit from another sister's pair of skates.

With motorbikes and pushbikes at over 30 km/h, I have found that leaning has pretty close to zero effect unless accompanied by handlebar inputs. But I think that subject has been thrashed pretty hard already on this thread.

**Badjelly** · 11th February 2008, 12:28

By the way, wouldn't it be neat to look at the output from a steering position sensor on a bike? I don't really know what it would show, or what it would mean, but it would be neat. I suspect with most riders (even the determined anti-counter-steerers) there'd be a little outwards blip at the start of the corners and a little inwards blip at the end.

**Sully60** · 11th February 2008, 12:52

Originally Posted by Badjelly

By the way, wouldn't it be neat to look at the output from a steering position sensor on a bike? I don't really know what it would show, or what it would mean, but it would be neat. I suspect with most riders (even the determined anti-counter-steerers) there'd be a little outwards blip at the start of the corners and a little inwards blip at the end.

Must be a whorthwhile thing to measure....

**Mikkel** · 11th February 2008, 13:25

Originally Posted by Sully60

Must be a whorthwhile thing to measure....

You'd have to use force sensitive pads on the handlebars. Your handlebars don't actually move when you countersteer at speed. It's all about the applied force...

**Badjelly** · 11th February 2008, 13:28

Originally Posted by Mikkel

Your handlebars don't actually move when you countersteer at speed.

Not at all? I'm sure the movements are small but I doubt that they are zero, and I'd like to see the output of a sensor recording them, that's all.

**Mikkel** · 11th February 2008, 13:30

Originally Posted by Badjelly

Not at all? I'm sure the movements are small but I doubt that they are zero, and I'd like to see the output of a sensor recording them, that's all.

The movement of your handlebars are due to the steering geometry when you lean over the bike - not your input. (Except at very low speeds)

**Sully60** · 11th February 2008, 13:36

Originally Posted by Mikkel

You'd have to use force sensitive pads on the handlebars. Your handlebars don't actually move when you countersteer at speed. It's all about the applied force...

But what component/cause of the bar movements do you think they're measuring here then?

**Badjelly** · 11th February 2008, 13:55

Originally Posted by Mikkel

The movement of your handlebars are due to the steering geometry when you lean over the bike - not your input. (Except at very low speeds)

I think that when I push on the inside bar (or pull on the outside bar) to initiate a turn, the initial response is for the handlebars (and forks and wheel, of course) to rotate outwards. This causes the bike to lean inwards, at which time further adjustments take place (including, but maybe not confined to, rotation of the bars) and the bike steers around the turn. Are you suggesting that there is no initial rotation of the bars? Then how does the pushing/pulling on the bars have any effect?

Anyway, given your deep understanding of bike steering, could you please tell me what you think a steering position sensor would show as you enter and leave a turn.

**Mikkel** · 11th February 2008, 13:56

Originally Posted by Sully60

But what component/cause of the bar movements do you think they're measuring here then?

I fail to see what you mean.

But if you want to see how people countersteer you have to look at the steering input from the rider. Not the movement of handlebars.