28" Uni and arcing of the street ?

How noticable is the arcing of a road when riding a 28" UNi. Do you get pushed to the right as you ride in the US and pushed to the left when ridng in the UK?

I notice it with my 24" MUni with a 3.0 Gazz. Would it be greater or less with a larger, but narrower wheel?

I think it has more to do with the tire you’re using than wheel size. Tires with center ridges seem to be especially sensitive to the crown in the road.

I’m pretty sure wheel size is not a factor, and it’s all in the tire.

My 26" Muni is not much fun on tarmac and definitely pulls to the road edge, the centre rigged tyre that Pashley used to supply was particularly bad.

A 28" with much narrower tyre (28*0.35c I think) is a pleasure to ride on any tarmac surface, if it does pull I have never noticed it. Since I got the 28" I rarely take the Muni on the road.

Re: 28" Uni and arcing of the street ?

In article <teachndad.gilc0@timelimit.unicyclist.com>,
teachndad <teachndad.gilc0@timelimit.unicyclist.com> wrote:
)How noticable is the arcing of a road when riding a 28" UNi. Do you get
)pushed to the right as you ride in the US and pushed to the left when
)ridng in the UK?

It’s not really more or less noticable on a bigger wheel. Eventually you
will automatically compensate for it.

There are two factors at work here, and both relate to the tyre profile.

The first is similar to what motorcyclists know as ‘white lining’. A motorcycle squirms as it crosses a white line painted on the road.

What happens is that the tyre has a contact patch which is quite wide. On a motorcycle the contact patch can be 2 or 3 inches wide.

In the centre of the tread, the wheel has a given diameter. At the edge of the tread, the diameter is slightly less. If there is a wide contact patch, then the tyre contacts the road with one part of the tyre which is maximum diameter, and one part which is a smaller diameter - and all the diameters in between.

If the tyre is running across a slope - e.g. on a cambered road surface, then the maximum diameter is at one side of the contact patch (more or less) and the minimum diameter is at the other side of the contact patch.

This means that for every revolution of the tyre, the centre of the tread tries to travel a certain distance along the road, and the edge of the tread tries to travel a shorter distance along the road. The same tyre is trying to cover two different distances per revolution (and all the intermediate distances). This causes the tyre to try to turn towards the part of the contact patch which has the smallest diameter. This is a similar effect to having a cone shaped tyre! So the tyre squirms as it tries to crawl up the camber of the road.

The other effect happens with tyres with a central ridge. These ridges exist to reduce the rolling resistance when the tyre is rolling straight ahead. In normal circumstances, the weight is distributed evenly on the part of the central ridge which is touching the road.

When you ride across a slope, the weight is not distributed evenly - the effect is to ‘smear’ the central ridge slightly as the weight of the uni pushes down the slope across the line of the central ridge. This distorts the central ridge and affects the handling of the tyre.

So, to answer the question: it’s the tyre which matters. In fact, with a bigger wheel, the first effect (‘white lining’) will be reduced because (say) a half inch difference in diameter across the contact patch is a smaller percentage difference on a large wheel.

Narrow tyres without central ridges have to be best for cambered roads.

Re: 28" Uni and arcing of the street ?

“Mikefule” <Mikefule.gkr3y@timelimit.unicyclist.com> wrote in message
>> This is a similar effect to having a cone shaped tyre!

This is the same way that trains turn smoothly.



Re: 28" Uni and arcing of the street ?

“Doug Massey” <dvm@mmcable.com> wrote in message
> This is the same way that trains turn smoothly.
> http://www.stmacnissi.com/Physics/train.htm
Doug, thanks for that. I had never even considered how a train turns, but
it is so obvious now from that explanation.

If the design is such that the flange never touches the rail, then the
wheels will have a minimum design turning circle as well I guess. (
ignoring factors like multiple wheels on the loco). Did the old steam locos,
say the eight wheels as specified in a 4-8-0 configuration (I think I
remembered that correctly), have to have some side to side play in each of
the 4 pairs of wheels to compensate for curves in the track I wonder?


Wouldn’t this cause the tire to drift to the center line instead of to the right, as mentioned by Teachndad? I assume the force of gravity reverses this at some point and causes a drift in the opposite direction. It doesn’t take much road camber to cause the unibike to drift right, and it naturally drifts left for reasons I have yet to figure out.

I have noticed on the unibike, and when one-wheeling various b*kes and motorcycles that a wider tire has less tendency to fall or lean into a turn (when compared with a narrow tire running the same pressure), whether on cambered or non-cambered roads. It may take a little more lean to compensate for the road camber, but the benefit is more steering stability (less wobble). I assumed this was due to the more gradual change in circumference from the center to the side of the tire, but it may be due to my imagination. Since you’re riding on the side of the tire while on a cambered surface, wouldn’t a smaller contact radius leave you riding on a narrower surface, and therefore be more wobbly? Knobby tires excluded of course, since the smudging of the knobs screws up the steering characteristics just as a center ridge does.

I think I sense another theory correction coming (but learning is always good, so fire away). :wink:

I had the same observation that Mikefule’s conclusion is the tire would crawl up the camber and teachndad’s observation is he was pulled to the right, which I assume is down in the US.

I don’t have any experience with a 3.0 Gazz but in my normal riding the crown and slope of the road is so nominal and the effect is so slight that I really don’t notice it. Normal subconcious adjustements are made and I just ride along.

Where I really noticed it was on a Coker ride on a country road. I was going left around the high side of a banked curve, where the entire road banked down to the left, and I felt the tire was constantly trying to turn right even though I was turning left.

This would be consistent with Mikefule’s explaination that the Coker tire was trying to crawl up the slope to the right in this situation.

This was not unlike the sensation of riding my bike at slow speed around the curve of the local velodrome. The bike was turning left but the sensation was of being pulled to the right. On a velodrome once you get up to the design speed of the curve the sensation is of going straight (no steering) as you bank around the curve. I may have to take to Coker the velodrome sometime.

Any other observations out there?

Okay, I am enjoying the responses and learning new things. Now, what might create more clarity or confusion.

The sensation I feel when I stated, “pushed to the right in the US” was of a feeling that the uni wants(I think) to be perpindicular to the road, so I feel a pull/push to the right because the top of the uNi wants to (or so I sense this) lean to the right.

I hope the push/pull to the right is the same as lean to the right in everyones understanding.

Well, if you crawl uphill on a velodrome slope, I don’t imagine that gravity overcomes this crawl problem, at least with a road tire. I’ve never had the opportunity to ride in a velodrome. Yes Rod, I think we’re talking about the same thing with the right push and right lean. But I think your downhill crawl might be due to the knobby tire. My MUni reacts similarly. Again, knobby tires don’t steer as precisely as road tires, due to the smudge factor. Mikefule stated that two factors are at work here. I may have more than that on the unibike. I think I could figure out a steering problem with only two factors to work with. As I’ve mentioned before, I’ve tried to solve my left turning tendency with wheel, seat, and handlebar adjustments. Maybe the chain applies a slight twisting force to the left? For some reason, I have to lean the frame to the right and my body to the left. Somehow, this compensates for the problem. The camber crawl theory would be an easy answer, but the unibike goes straight on a mild road camber (in the US) and drifts down rather than up as the slope increases. Maybe this thread will steer me toward an answer for a not-exactly-but-sort-of-a-unicycle problem.

I think I got it, we are probably talking about two separate phenomena or sensations.

The leaning sensation is from the shift in the center of gravity necessary to maintain balance when you are riding across a sloped surface. If I stand with my feet together, perfectly balanced, and pick up my left foot, I will fall over to the left unless I compensate by leaning to the right. When I was on the left banking velodrome it was the right side of my tire that was gripping the surface so I had to lean slightly to the right to maintain balance even though I was turning left. Am I making sense?

In teachndad’s example the high side is on his left, so without compensation, the sensation is that you want to fall to the right.

I think the tire crawl is a different effect as described so well by Mikefule.

Looks like I misread the original question. However, all of the obvious physics should make the tyre pull up the camber.

There is a third factor I didn’t mention, which is that if the tyre is vertical and the road slopes down to the left, then the relationship between the tyre and road is very similar to what it would be if the road was level and the tyre was leaning to the right. (It is not identical due to distortion of the tyre being slightly different.)

And if a wheel leans to the right, it turns to the right.

So three good principles and my experience show that a wheel should tend to pull UP the camber, unless of course the camber is so steep that the simple effect of gravity dominates proceedings.

Yet the question appears to be ‘Why does my unicycle crawl down the camber?’ I can only assume that either (a) I and my sources are wrong; or (b) the problem is one of technique.

Unless… just thinking out loud here… if the tyre is absolutely rock hard, then it would be supported by a very thin contact patch slightly up hill of the centre of the tread, and the weight of the uni would then pull it over towards the down hill side, causing it to curve that way. But for this to happen, the tyre would have to be pumped up very hard or have a strange tread pattern.

What I can say is I used to notice my Pashley squirming all over the place when it was new, but as my riding has improved, I notice it less. Sometimes we can think too deeply and practise too little.

This is very standard.

Not very likely.

This is most likely the cause of my right drift on cambered roads. I run max pressure so the steering is more dependant on my input. At lower pressures, I have difficulty coming out of a turn after the tire is in a lean and trying to continue turning (due to the forces you have described).

Another factor to further muddy the water: the way we balance is to steer the wheel under us, however subtly. Because one side is “uphill”, we have to steer a little more to that side to achieve the same correction. Our habits don’t do that well until we ride a lot on highly crowned roads. I think this might be the primary camber-climb factor. This factor is independent of tire width and pressure, because it would exist with an infinitely hard, narrrow tire.

Re: 28" Uni and arcing of the street ?

May I suggest yet another additional physics effect at work: When the
wheel rolls along a cambered road, the tyre is in left-right
equilibrium when it first touches the road surfaces but then as that
element of tyre becomes load-bearing, it deforms laterally. Therefore,
the tyre will drift down the camber.

Thinking a bit more about it, however, this drifting down is just the
initial effect. It would also mean that the tyre turns uphill (when
riding forward), as the centre load-bearing patch moves down with
respect to the location where the initial tyre-road contact is made.

Yet another thought: In a bike the cause for the downhill turning
tendency is more obvious, or so it seems. Now if the unicycle rider
(still on that cambered road) leans forward (or generally has the
centre of gravity in front of the seat post so that the uni leans
backward just like the front fork of a bike) then turning the uni
downhill will lower the centre of gravity, even in static conditions
(as opposed to riding). That favours downhill turning over uphill