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I know I'm not the only one here who likes this sort of thing... 🙂
Negative head angles and huge negative offset for stability? Take a look.
For further reading:
http://tilting.org.za/bok/posneg.html
And if you want to play around with hypotheticals:
http://yojimg.net/bike/web_tools/trailcalc.php
Even more radical
Fascinating that the >90 degree HA is the opposite of what we normally use and yet it still seems to work in a similar way. I am struggling to get my head around how that's possible.
Perhaps because it has negative trail as well, meaning that the contact patch is still behind the axis just as it is for a traditional bike. But it clearly allows for much lower centre of mass.
It looks like it has positive trail but negative fork offset to achieve that.
I do find this stuff v interesting!
So what I think we see here is that the negative head angle steering has stability from both trail and jacking, whilst a normal bike has stability from trail and instability from jacking.
The recent changes in MTB geometry have increased trail stability whilst also increasing jacking instability. This makes them quicker to turn in when going slower but more determined to travel in a straight line when going fast.
What I found interesting was the obvious stability of the recumbent when taking off from rest. You usually see a wobble.
Or maybe he's just a very good rider, but it looked like the bike to me.
“What I found interesting was the obvious stability of the recumbent when taking off from rest. You usually see a wobble.”
That’s the reverse jacking effect - even when static the bars want to stay straight because turning them lifts the front of the bike up. So gravity provides stability when you’re not moving, and then trail adds more once you are.
Normally bike steering wants to turn under the weight of the bike and rider when the bike is static.
The head angle does look quite close to 90 degrees - so there would be negative flop, but v little of it. Also, the long front and rearward weight would reduce the effect. I wonder if the head angle was set to get the desired trail with a backwards normal fork?
How would the push bike be going up a kerb?
Always fascinates me that I can pull my sack trolley backwards up a kerb with ease but if I push it , not a chance. Same size wheel going in the same direction.
Expect to see these bars on the trails 2021, 10% wider than 2020
“Always fascinates me that I can pull my sack trolley backwards up a kerb with ease but if I push it , not a chance. Same size wheel going in the same direction.”
Force vectors innit?! If the propulsive force was applied at the same height as the contact patch then your sack trolley would behave the same either way. Same with the centre of mass being high on a bike - and that’s why hardcore hardtails work!
The bike above looks like the front wheel would be pulled up the kerb. That would be a good thing.
Or am I not understanding the science.
Also interesting that there’s a different “leverage” (not sure if that’s the correct term) effect on the handlebars to steerer tube. There’s a larger push rod attached to the bar / stem interface than at the fork steerer junction. That would be an odd sensation after coming from very direct steering that we’re used to on “normal” bikes.
“The bike above looks like the front wheel would be pulled up the kerb. That would be a good thing.
Or am I not understanding the science.“
It’s the position of the centre of mass vs the contact patch that matters, so no, it would still have a similar problem with kerbs even though the fork would be actually pulling. The lower centre of mass and long front centre will make it less of a problem than a normal bike but not because of the steering geometry.
It does look like the forks turn more quickly than the bars. Considering how we can all rapidly adapt to different steering ratios in cars and even variable ratio racks I doubt it would cause a problem.
If there is appreciable flex in the forks, that would result in a rearward and upward wheel movement, which would help with kerbs, whereas if they were the normal way round the reverse would be the case.
Normally bike steering wants to turn under the weight of the bike and rider when the bike is static.
..unless you have very low trail which can reduce it to almost insignificance, but that'll never be any good on an MTB. Some like it for loaded road bikes but even there I think it's the tail wagging the dog and it still brings in the problems MTBers associate with low trail. I don't like it anyway. Putting a bag/load on the front masks the negatives of low trail but doesn't solve what's going on at the tyre contact patch.
On the reversed trail / head tube to axle relationship, I'm pretty sure Mike Burrow's book points out how that would work. I've wondered for some time when cargo bikes would start to use those ideas since the packaging can suit it well.
Always fascinates me that I can pull my sack trolley backwards up a kerb with ease but if I push it , not a chance. Same size wheel going in the same direction.
Yeah but as above the direction of force is different. When pushing, there is a downward component to your force or at least it's purely flat. When you pull it, because the trolley is at an angle you're partly pulling it upwards, which is why it helps it climb the kerb. If you attached a yoke to the wheels and pull it flat along the ground vs pushing it flat along the ground, there'd be no difference.
Yay! I get to share things!
@Jameso
I'm currently building a 90degree headtubed, adjustable reverse rake cargobike. I should have the frame riding this week, with the rack etc. later. I just need to add seatstays and cap tube ends now.
@bigblackshed
The different leverages between the handlebar and front steered wheel don't work particularly well. At least that was my experience. I tried it on a previous bike with an adjustable link, I kept adjusting it until honed in on the perfect setup. When I measured it I realised that I had just honed in on a 1:1 ratio.
There's some video of that setup here:
@retrodirect, interesting - I've been following you and your diagrams for jack-knifing on IG. Things that I can visualise and theorise on but don't have the smarts or the tools to model. Good work!
Was staring out of the window thinking about this over lunch. I think a cargo bike is a good case for fairly low trail and reversed steering-trail relationship. Advantages to reversing it (kerbs or similar, packaging) but mid trail with a reversed flop relationship and all that weight could be terrible to ride. An element of self-raising out of a corner via fairly low trail would be ideal, safer potentially.
PS I have a theory or basic formula on low trail and jack-knife/tuck-under, will PM.. your modelling might answer it. All purely for nerd value.
@Retrodirect When I was experimenting with fat tyres several years ago I was up to a 80º HA and the steeper I got the better it felt.
I'm looking forward to seeing your creation.
I've spent the day drawing out a reverse HA version of the Scandal(V1). 🙂
(Couldn't adjust any further than 80º or I would have.)