Wheel sizes vs Handling

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pwa
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Re: Wheel sizes vs Handling

Post by pwa »

In a place where I worked about 20 years ago they got a Brompton to have available as an option for anyone who had a reasonably local errand to do. It arrived and people came out of the office to have a go on it around the car park. Half the people who tried it dismissed using it again simply on the basis of it being so twitchy at low speeds. I think that had something to do with wheel size.
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531colin
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Re: Wheel sizes vs Handling

Post by 531colin »

Mick F wrote:Hi Colin.

Marjorie - 1.75" trail and 41.5" wheelbase. Mixte with 501 main tubes and 19.5" BB to centre of seat lug.
Mercian - same trail, but 40" wheelbase. 23.5" BB to centre of seat lug.
I measured the trails rather quickly, so they could be a slight difference but it's going to be not much.

No, there's nowhere near any toe overlap with Mercian.

If you want more accuracy, I'll get back to it later today. Just in for a cuppa to check in, then I'm back out into the garden.

Is that trail or offset?http://www.yojimg.net/bike/web_tools/trailcalc.php
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Mick F
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Re: Wheel sizes vs Handling

Post by Mick F »

Trail.

Straight-edge inline with the head tube centre-line projected onto the floor.
Straight-edge vertically down from axle centre onto the floor.
Difference is trail.
As per your link .................... and as per many explanations on here. :D

I may have a chance to do it more accurately later this morning.
Mick F. Cornwall
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Mick F
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Re: Wheel sizes vs Handling

Post by Mick F »

Done it.

Mercian 46mm trail. 1010mm wheelbase. 73deg parallel. 597mm frame.
Marjorie 65mm trail. 1040mm wheelbase. 73deg parallel. 495mm frame.
I measured Marjorie's angles with a clinometer.

The trail on Marj is 20mm more than Merc. Is that significant enough?
Yes, it would make the difference, but at slow speed not so much ............ or am I wrong?

BTW, it's problematical to measure trail on a Moulton due to the suspension etc, but it seems to come out at 35mm.
Front Forks.jpeg
Sample photograph.

The main fork is bent rearwards, and the suspension fork is forward of it. I used a straight-edge down the centre-line of the head tube and project to the floor and marked the position. Vertically down from the axle is 35mm behind that mark. However, the trail varies as the suspension goes up and down of course, and that will change the figure.
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531colin
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Re: Wheel sizes vs Handling

Post by 531colin »

Mick F wrote:…...
Mercian 46mm trail. ......
Marjorie 65mm trail. ......

So it looks like trail might affect handling. And after only 4 pages.
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Mick F
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Re: Wheel sizes vs Handling

Post by Mick F »

Mick F wrote: .......First thing I noticed, was how the bike handled. I have two regular bikes - as many of you no doubt know - a Mercian with 700c (622) wheels, and a Moulton with 20" (406) wheels. They both handle and feel very different to each other of course.

I would have expected that the Dawes would have felt the same as the Mercian.
The wheel diameters aren't very different numerically, but the size to look at and to steer, felt very different indeed. ........
Excerpt from my OP.

Note "the first thing I noticed"

I would wholeheartedly agree that the trail differences make the difference, but the first thing I noticed was how the bike handled. I was riding at walking pace, and trail wouldn't affect much at that speed.
Mick F. Cornwall
Brucey
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Re: Wheel sizes vs Handling

Post by Brucey »

trail affects steering at all speeds. Varying the trail, wheel weight etc affects the minimum speed at which the bike becomes officially stable (mathematically speaking) and even below this speed it changes the severity of the instability, if you like.

What you will notice (over and above anything else to start with, probably) is whatever differences there are between a bike that you don't use often vs your usual ride (s). It is very rare that you swing a leg over a less familiar machine and feel immediately at home.

cheers
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531colin
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Re: Wheel sizes vs Handling

Post by 531colin »

Mick F wrote:………., and trail wouldn't affect much at that speed.

Why?
My experience is the opposite, once you have got a bit of speed on, most bikes feel pretty stable, at least until you start playing about or pushing the envelope. Its at the low speeds that I feel wheel flop or twitchyness.
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Re: Wheel sizes vs Handling

Post by Samuel D »

Trail is the lever through which the rolling resistance of the tyre acts to centre the steering. Since the rolling resistance is practically constant, the bicycle’s speed shouldn’t have much effect on the centring force. Maybe it’s perceived differently at different speeds, though.

Changing the tyre’s rolling resistance changes the self-centring force.

There is also pneumatic trail to consider under substantial cornering load. This a self-aligning torque arising as a consequence of the centre of the tyre’s contact patch being in front of its lateral force, due to the tyre being progressively loaded toward the rear of the contact patch.

But bicycle stability remains an area of ongoing research by people who’ve devoted years to the question. I don’t pretend to understand the half of it.
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Mick F
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Re: Wheel sizes vs Handling

Post by Mick F »

531colin wrote:
Mick F wrote:………., and trail wouldn't affect much at that speed.

Why?
Dunno, it's just a feeling.

Try walking with a bike holding the saddle and steering it by leaning it. The slower you go, the harder it is.
Moulton is almost impossible at a slow walk and I put that down to the small wheels.
Mick F. Cornwall
Freddie
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Re: Wheel sizes vs Handling

Post by Freddie »

Just resurrecting this thread to show that even push scooter sized wheels can be stable enough to ride with only body input, providing the trail is very high. I don't see why required stability can't be achieved with any typical size bicycle wheel, save a lack of understanding and concerns about what a bicycle fork should look like (thinking it must curve away from the frame, even with small diameter wheels).

text: http://www.bodenstandig.de/strassensurfbrett/

music video (an acquired taste), demonstrating scooter being ridden with no hands:

https://youtu.be/nT0k12br38U?t=70
reohn2
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Re: Wheel sizes vs Handling

Post by reohn2 »

531colin wrote:
Mick F wrote:………., and trail wouldn't affect much at that speed.

Why?
My experience is the opposite, once you have got a bit of speed on, most bikes feel pretty stable, at least until you start playing about or pushing the envelope. Its at the low speeds that I feel wheel flop or twitchyness.

+1
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willcee
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Re: Wheel sizes vs Handling

Post by willcee »

Interesting contris, I some years ago transformed a Raleigh Twenty totally, drop bars, 406 wheels instead of 451, dual pivots, STi's and 7 sp rear gearing with double on the front, and it was as nice a ride as any of my lightweights at that time... and anyone who had a few miles on it was actually surprised, no changes to the geo, my wheel change dropped the BB, I did some research and somewhere in my ploughing through reams of old material found that Raleigh when they had a few made pre launch found complaints from riders that the steering was too quick, so they modded it to slow it down, as anyone who has delved deep in a 20 theres a plastic or delron or nylon bush as the top headset setup, now I replaced that with a ahead set top and bottom , I found it OK and maybe just hit a sweet spot..
On the 27 1/4 wheels I knew a chap who collected Hetchins Bates and BAINES bicycles and he raced back 40/50 years ago, he trained on 27's preferring them and hated racing on 700 tubs..will
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