Search found 157 matches

by StephenW
8 Mar 2017, 10:46pm
Forum: Bikes & Bits – Technical section
Topic: Tell me about fork trail.
Replies: 19
Views: 991

Re: Tell me about fork trail.

I'd definitely recommend adjusting the seat angle as a first step. This has quite a big effect on handling. Also, most people seem to prefer the handling with the seat mounted in the furthest forward set of holes.
by StephenW
6 Mar 2017, 10:07pm
Forum: Bikes & Bits – Technical section
Topic: IGH lubrication; a smoking gun.
Replies: 163
Views: 22328

Re: IGH lubrication; a smoking gun.

The noise varies with pedalling load.

The hub is SG-C6000-8C.
by StephenW
3 Mar 2017, 8:44pm
Forum: Bikes & Bits – Technical section
Topic: IGH lubrication; a smoking gun.
Replies: 163
Views: 22328

Re: IGH lubrication; a smoking gun.

Hello Brucey

I finally got round to doing this a month or so ago. I cleaned the innards with white spirit, and removed a satisfying amount of debris. I then added Land Rover SF grease to the main part of the hub and heat resistant grease to the coaster brake (I didn't use the recommended Shimano stuff because I thought it was a bit overpriced).

Since putting it back together, a noise has appeared in gear 5. A sort of whooshing-whirring noise, that only happens when pedaling. Gear 6 is nice and quiet. I checked the cones afterwards, and I think the adjustment is OK, although I may check this again. The hub doesn't skip or do anything else bad. I don't think the chain can be making the noise, since gear 6 is quiet. (Quieter than before I did the service).

Do you think I should be worried? I did drop the innards a couple of times when cleaning them :shock:
by StephenW
3 Mar 2017, 7:16pm
Forum: Bikes & Bits – Technical section
Topic: Tell me about fork trail.
Replies: 19
Views: 991

Re: Tell me about fork trail.

Hello Dave W

I also have a Metabike. I very much enjoy riding it, but I do find the handling a bit strange at times. I don't have lots of experience of other recumbents, but I have had a go on a couple of Nazca ones, and I don't think they had anything strange about the handling.

Mine has two 26" wheels, and the carbon disc fork. The man who sold it to me said he found it more stable with 26" wheels than 700c.

Metabike produced several different versions with different forks and wheel sizes. The fork on the rim brake 700c version is 40mm shorter than the carbon disc fork (which I have). This equates to about 2 degrees of head angle I think, which is a big difference. Unless the disk fork has more rake (which I don't think it does), then the disk brake version must have a lot more trail than the rim brake one.

I think the disc brake version may have too much trail. This would explain why the man who sold me the bike found 26" wheels an improvement. If you look on BROL, one person has fitted a 700c rear wheel and 26" front. He finds this beneficial for the handling. This would further reduce trail.

I have two other reasons to think that less trail might be better:
1. The handling feels a bit "floppy", like the steering wants to flop away from a straight line, and then correct. Riding no-handed, I find it shakes about a lot.
2. Making sudden steering movements at low speed causes my head to move suddenly in the opposite direction. I feel that what is happening is that the trail is causing the front of the bike to move sideways in response to the steering, and the bike is pivoting around an axis running diagonally upwards from the rear tyre contact point, causing my head to move in the opposite direction.

The seat angle also seems to have quite a big influence. More upright is more stable, I find.

Perhaps at some point in the future I will either try fitting a shorter 26" fork (e.g. from Surly LHT), or perhaps getting a longish steel 700c fork and asking a frame builder to increase the rake (although this would increase heel strike). In the mean time I will enjoy riding it and try to avoid spending money!
by StephenW
16 Feb 2017, 9:00pm
Forum: Bikes & Bits – Technical section
Topic: Relating eigenvalue plots to subjective handling characteristics
Replies: 5
Views: 326

Re: Relating eigenvalue plots to subjective handling characteristics

Thanks for the link to the previous thread, Colin531. It is interesting. Papadopoulos was one of the people who developed this program.

if I take a bicycle that I'm very used to riding, and move the handgrips a long way (maybe 150mm?) towards the handlebars, the bike "feels" very different ...


Yes, one of the things that the model does not include is the type of handlebar - where are the rider's hands in relation to the steering axis? In fact, it couldn't include this, since it is modelling an uncontrolled bike. Another thing it does not include is the tyre width - the wheels are assumed to be infinitely narrow.

...the self stability of a bike weighing 10Kg can't hold up a man weighing 70Kg if the man is unbalanced.


If you mean that he flails about and deliberately tries to unbalance the bike, then yes! But if he sits there like a sack of potatoes, and the bike is moving at a speed between the weave speed and the capsize speed, then it should be stable. I don't think the weight of the bike or the man comes into it.

In a similar way having a loaded bike with a light rider is unlikely to be the same as a big guy on the same bike with no luggage, even if the eigenvalues are the same.


One of the nice things about the program is that you can change the mass, inertia and position of the rider, the rear rack, and the front basket. If you wanted to simulate low-rider panniers, you could move the "basket" down towards the front axle. If you wanted to simulate a frame-mounted front rack, you could move the position of the rear rack to the front. You could simulate the same bike with a front load or a rear load or both.

The other thing is that (of course) a rider will rarely sit there like a pudding; they will shift their weight around somewhat.


Yes. In the model it is assumed that the rider is rigidly fixed to the bike. This seems quite reasonable for a recumbent, but not very realistic for an upright bike, where the rider might pivot at the hips.

I'd think it very useful if it predicted shimmy behaviour, for example, but I don't think it does that.


Indeed. The bicycle frame is assumed to be completely rigid. Shimmy is connected with flexing, isn't it, although it can also be exacerbated by geometry? If we had a good sample of eigenvalue plots of bikes that do and do not shimmy, it might be possible to see a trend. (Complex roots are associated with oscillation).

in short, i think the sort of "self-stability" of bicycles which you describe is very interesting academically (and incompletely understood, I believe) but has little relevance to how the bike "feels" to ride.


This is the question! Perhaps it does and perhaps it doesn't. If the team at TU Delft were able to create a similar-handling bike by replicating the eigenvalue plot, it must be of some relevance, at least within the confines of the same type of bike. Clearly there are some other variables that are not included in the model but have an important effect (hand position, tyre width, stiffness). Nevertheless, I do think it would be very interesting to see the plots for a range of bikes, along with what the riders say about the bikes.
by StephenW
15 Feb 2017, 6:59pm
Forum: Bikes & Bits – Technical section
Topic: Relating eigenvalue plots to subjective handling characteristics
Replies: 5
Views: 326

Relating eigenvalue plots to subjective handling characteristics

Hello

Bicycle geometry and handling seems to be something that causes a lot of confusion and excitement.

Some boffins have created a program which solves* the differential equations that describe an uncontrolled bicycle. (i.e. where the rider's hands are not touching the handlebars and the rider makes no effort to shift weight to keep the bike balanced). The solution can be displayed graphically as an eigenvalue plot. Various critical speeds can be read off from the eigenvalue plot: the weave speed, the capsize speed, and the double root. The program is freely available (see below), but you need Matlab to run it.

http://ruina.tam.cornell.edu/research/t ... eb_folder/

Being able to produce the eigenvalue plot is interesting, but what does it mean? What are "good" values? There is a small amount of information given about interpreting the plot, but not much.

This problem is touched on in the paper below. In this case the designers of a new recumbent bike (Raptobike Midracer) just tried to match as closely as possible the plot of another bike from the same manufacturer.

http://bicycle.tudelft.nl/schwab/Public ... design.pdf

I was thinking that it would be interesting to get the eigenvalue plots for a range of bikes and riders, including bikes that are considered to handle well and those that are not. It would be interesting to see if there was a correlation between the subjective terms people use to describe bike handling and the plots. It would also be interesting to compare completely different types of bike (e.g. roadster, racing bike, recumbent).

This could also be very useful for someone who was unhappy with the handling of their bike. It could show them the effect of making certain changes, and see whether it would bring the handling closer to the area that most people find acceptable.

What do people think? Is this worth pursuing? Would you be interested in either doing the calculation for your bike (if you have access to Matlab), or supplying the relevant data so I or someone else could do it?


*Solves a linearised version of the equations
by StephenW
15 Feb 2017, 6:18pm
Forum: Bikes & Bits – Technical section
Topic: Rain cape / Poncho
Replies: 15
Views: 4201

Re: Rain cape / Poncho

This fellow has tried several capes and eventually made his own:

http://drewsminiblog.blogspot.co.uk/201 ... -cape.html

I have the yellow pro-route Carradice cape. I quite like it, although I haven't used any others. I could imagine a heavier cape being more comfortable.
by StephenW
2 Nov 2016, 9:08pm
Forum: Bikes & Bits – Technical section
Topic: Non-Dynamo crown mounted front lights..
Replies: 7
Views: 1398

Re: Non-Dynamo crown mounted front lights..

I have this one:

http://en.hollandbikeshop.com/bicycle-l ... ies-black/

I haven't had it long enough to give a full review. It is 20 lux, and I find it reasonably bright. It made a set of batteries go flat by themselves. When I opened it, one of the batteries was out of place, so I think it made a short circuit. I think I will use some selotape to stop it happening again. The light can droop if the bolt holding it is not done up very tight. I think a spiky washer would help this.

In general I find crown mounted lights look much tidier. Handlebar mounted lights look a bit temporary to me.
by StephenW
2 Nov 2016, 6:21pm
Forum: Bikes & Bits – Technical section
Topic: 26" hub brake compatible fork
Replies: 16
Views: 1713

Re: 26" hub brake compatible fork

Hello Nigel

I got a bargain deal on a complete wheel from eBay with the X-FD hub. I'm still using a B&M sidewall dynamo. Although this is less efficient than a hub dynamo when in use, I believe the Sturmey-Archer hub dynamo has almost the same drag with the lights on and off, so it could be that over the course of a year the sidewall dynamo works out as efficient as the hub dynamo. The noise is a little annoying, although it is sometimes useful so people know you are coming. Since I'm not using rim brakes, perhaps I could roughen up the rim (with a rasp?) and run the dynamo on that. It might be a bit quieter and more efficient.

There are two possible contributing factors to the "squirminess" of the steering with a heavy load which I haven't mentioned. Firstly, I reused the old bearing cups in the frame for the headset. I couldn't be bothered trying to get them out, and they seemed in fine condition to me. The steering turns very freely, without play, so I don't think that's it. Secondly, one of the dropouts got slightly bent in the process of getting the bearing race onto the fork. This meant that I couldn't fit the axle in, so I slightly bent it back and filed it a bit. This only affected getting the wheel in and out. The top part of the dropout, where the axle sits once it is in place was not affected, as far as I can tell.

[I had taken the fork and bearing race to the LBS man, and he was not able to get it on, and said he would sort it tomorrow. After a few days I was a bit impatient, and kind of needed the bike, so I suggested whacking it on with a hammer. It wasn't his idea!]

The fork feels quite stiff to me, stiffer than the original and the legs are larger in diameter. The frame is large (60 cm I think), so I suppose that could make it a little flexy. Seems fairly solid to me.

I like that the rack does not swing when the bike is stopped. This makes loading and unloading nice and easy. It also doesn't matter if the load is evenly distributed or not.
by StephenW
31 Oct 2016, 9:39pm
Forum: Bikes & Bits – Technical section
Topic: Project -utility bike-
Replies: 49
Views: 5542

Re: Project -utility bike-

This is very interesting!

My experience of front racks of this type is limited to the Steco one which turns with the steering (called "Transport"), and more recently the Steco one which mounts to the head tube. I originally bought the rack for carrying my accordion, which weighs 20 kg including the case, and is quite large when in the case (60x50x25 cm approx). I found that the bike handled badly when carrying the accordion with the "Transport" rack. The steering was very heavy, and I was especially conscious of having to pull hard on the steering to straighten the bike out after a corner. Although the rack is attached at the axle and handlebars, I could see the fork flexing over bumps, so it didn't completely remove the suspension which that provides.

I have tried carrying the accordion lying flat on the headtube-mounted rack, but I don't like this because I feel it is about to topple off the front. (It isn't, I just feel like that and don't like it). The steering also "squirms" when I do this. With moderate loads it handles well, and I like that the rack stays still as it is being loaded.

It may be that a trailer is a better way to carry an accordion, but this, and your comments, got me thinking about front racks.

It seems strange to me that Post Office bikes have a frame-mounted rack, whereas newspaper "Porteurs" in Paris used one that turned with the steering. Why would this be, since they are both delivering things? I could think of a few possible reasons:

1. The Porteurs were in more of a hurry and had a more aggressive riding position, meaning that there was not enough space between the front wheel and handlebars for a load that doesn't turn with the handlebars.
2. Newspapers are quite a homogeneous load that is easy to balance and wouldn't move about.
3. Loading and unloading is much easier with a frame-mounted rack. Perhaps the Porteurs stood over their bike while handing the person at a kiosk a stack of papers, whereas a postman had to dismount numerous times to deliver things.
4. A rack which turns with the frame could be stronger, because some (about half?) of the load is going directly to the axle, not through the fork, headset etc. Perhaps the stiffness of the frame does not matter as much. This could be useful for a bike that is to be ridden quickly as well as carrying a load.

At first I thought the headtube rack was a big improvement. But perhaps a rack that turns with the steering, combined with a fork with more rake, might be quite ok. The headtube rack doesn't flex much, vertically or laterally, although it can swivel around the head tube if the bolts are not tight enough.
by StephenW
31 Oct 2016, 8:54pm
Forum: Bikes & Bits – Technical section
Topic: 26" hub brake compatible fork
Replies: 16
Views: 1713

Re: 26" hub brake compatible fork

At the same time as replacing the fork, I switched from a front rack that turns with the steering to one that is fixed to the head tube. When I put a particularly heavy load on the rack (such as a very large number of cooking apples), the steering "squirms". I can still definitely keep the bike under control, but I can feel the steering pulling from side to side, kind of like a shimmy. I'm not sure if this is just one of these things, or perhaps it's a sign of something not being quite right.
by StephenW
19 Oct 2016, 8:42pm
Forum: Bikes & Bits – Technical section
Topic: IGH lubrication; a smoking gun.
Replies: 163
Views: 22328

Re: IGH lubrication; a smoking gun.

Thanks! This is interesting and very useful.

I've had another think, and I've realised that since getting the front drum brake, I am not using the coaster brake so much. (Although it is still very handy when I do want it). Therefore perhaps I am not generating such a large amount of wear debris that it needs to be regularly removed from the brake. I think I will use heat-resistant grease in the brake, and either oil or semi-fluid grease in the gears. I'm not sure which of these would be better. Since oil leaks out faster, perhaps it would be better for carrying away any stray debris from the brake? Do you think there is any difference between the two in terms of how readily they would mix with the brake grease and bring debris from it into the hub? I guess that one advantage of the tapered shape of the hub and centrifuge effect you described is that the oil should tend not to want to go into the brake.
by StephenW
18 Oct 2016, 8:51pm
Forum: Bikes & Bits – Technical section
Topic: Project -utility bike-
Replies: 49
Views: 5542

Re: Project -utility bike-

Hello Brucey

This sounds like an interesting project! Have you made any further progress with it?

I agree that a frame-mounted rack feels nicer with heavy loads than one that turns with the steering.

I hear people (like Jan Heine for example) talking about low trail geometry being good for front loads. However, I had only heard them talking about loads that turn with the steering. It seems from what people are saying here that low trail is also desirable for frame-mounted front loads. Is that right?

It seems to me that a front load which turns with the steering does three things:

1. Increases inertia of the steering
2. Increases weight on the front wheel
3. Increases radius of gyration about the vertical axis

Whereas a frame-mounted load does the latter two of these. Since there may be a wide range of weights going through the front wheel, depending on the position of the rider, without adding a front load, this made me wonder if radius of gyration is the main factor. I.e. a low trail is desirable for a high radius of gyration, and vice versa, since the bike with a high radius of gyration about the vertical axis is already more resistant to changing direction.

I may be talking complete rubbish. Perhaps I should go and read a textbook about it...
by StephenW
30 Sep 2016, 9:43pm
Forum: Bikes & Bits – Technical section
Topic: 26" hub brake compatible fork
Replies: 16
Views: 1713

Re: 26" hub brake compatible fork

Thanks Brucey.

The shimmy problem is now solved! The new wheel came with two washers on each side, so I thought I'd better use them. The fork had a circular, slightly recessed area, which was a little smaller in diameter than the washer. The washers had to bend a little, which I thought was OK. Anyway, I took the washers off and the shimmy stopped.

The stem was sold as being 7/8". It fitted well in the original fork. The bike is a Peugot, so I guess it could have had a 22 mm steerer. Seems a bit unlikely to me that the stem should happen to be under-sized, such that it fits perfectly in a (possibly) 22 mm steerer but not well in a 7/8" one.

I think the fork may have a little less rake than the original. It is also chunkier, giving less of a springy feel over bumps.
by StephenW
26 Sep 2016, 6:24pm
Forum: Bikes & Bits – Technical section
Topic: IGH lubrication; a smoking gun.
Replies: 163
Views: 22328

Re: IGH lubrication; a smoking gun.

I had a notion that I had read something in a Sutherland's manual on Sheldon Brown's site about oil and grease for some three-speed coaster brake hubs, and just oil for others. I went back and had another look, and you are right, it is grease for the brake and oil for the gears. But single speed coaster brakes with oil lubrication are a thing, yes?

I've had another idea. Perhaps every so often I could over-fill the hub with oil, give it a spin, then leave the bike lying on its left side overnight? That way the oil would drain out through the brake, hopefully cleaning it. The rest of the time I would just top up the oil with a small amount. What do you think?