Project -utility bike-

[Brucey]

Just a thought Brucey, if you want to "guinea pig" a 14mm belt solution on this one, I'd be happy to help out.

It is a kind offer but I'm using a chain on this one!

Haven't I just seen a load of pictures with seat stays bolted at the top?

yup but there is a brace between the seat stays (where you would normally mount a caliper brake) so the bolted top stay mount is of no use here. Some bikes have bolted stays top and bottom, but not this one!

Shoopper (Small).JPG

An unusual carrier bike

The argument for a step-through frame.

I can't think of anything worse (barring the headset on my post bike as it was to start with I suppose) than putting a large front load through the ghastly Raleigh 20 headset; they have a plastic bushing in the top that is sticky and/or rattly to start with; this won't be improved in any way by adding a load to it...

Progress thus far is that I have been riding my machine around with the original wheels. Plan is to strip it soon and fit it up with a load of different parts. I'm going to need some frame mods to run 700 x 38 tyres....

watch this space!

cheers

[StephenW]

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...

[Brucey]

well to date I've just been riding the beast around! In fact I have been so slothful that I have yet to fit mudguards to it!

The rear wheel has been out a few times, mainly so that I can full test any X-RD5(W) hub internals that people have asked me to fix. I have also donated the original (modified) shifter to another bike that needed it worse than mine. The present shifter is one that was completely worn out on the detent disc (lack of lube inside is what did it); I modified it so that I could use the unworn side of the detent disc which means that

a) it doesn't fit properly onto the splined centre shaft and
b) the index spacing isn't quite right.

This gives a slightly iffy third gear selection, which may yet trash the hub (another repair then.... ). I have also mounted the shifter under the left bar for a cleaner look. This 'clean look' also means that I can invert the bike without trashing the shifter. It also hides the fact that there is quite a lot of expensive hub and shifter on the bike which is no bad thing really; I don't leave it locked up much but the ratty look has so far not encouraged thieves to take any real interest in it.

In other news; I suppose I've done about a thousand miles on it and (to my considerable surprise) the vittoria Hypers have yet to puncture or cut up (at all...). Maybe I've jinxed it now.... .... but then again I have not used it much in the wet so maybe that has something to do with it too.

I have also had to make my own bungies for the carrier; I have destroyed at least three sets of bought ones (with white natural rubber inners); they last less than nine months outdoors. The bungy material I am now using (which cost a fortune) has a black inner and (on other machines) it has lasted five years outdoors without a murmur of complaint.

The front load carrying arrangements have me similarly wondering about the best method. I'd have to say that what I have works OK most of the time but it isn't perfect. I have occasionally carried a very heavy compressor (which weighs about 60-70lbs) and this makes the bike steer very badly indeed. The problem is that this machine has an appreciable trail to it (which is more than it was because I have increased the wheel diameter). Moving the steering suddenly makes the load move from side to side, because of the trail. You can see this easily when the bike is stationary, but something similar happens when you are riding the bike too. Between the fact that the frame isn't very stiff torsionally, the carrier can flex laterally a little and (especially) because the tyres I'm using have very low lateral stiffness, the whole thing can shake about quite alarmingly if you are not careful. I think that heavier duty tyres, mounted on wider rims, would give better lateral stability.

As it is, it is fine with 30lbs of groceries on board so it does its intended job well enough, but I think it could be better. Whether it is a better compromise than a turning front carrier I couldn't say for sure, but when there is a heavy load on the bike you can feel the forks and the carrier frame flexing over the bumps, which is either good or bad depending on how you look at it.

One of the things which I must address is the matter of the drain holes in the 'bucket'; I have lost several small but precious things through these holes; they need be only small to drain water, so I intend to fit plugs to them such that small things can't fall through but water can still drain away. I've also had things jump out when I've gone over big bumps, so I'm thinking about a cargo net of some kind (even though it raises the bungy quality issue again).

Other plans include to fit permanent lights and (of course) mudguards. The frame isn't quite straight, either, so that ought to be addressed as well. Somewhere I have the correct 'hockey stick' chainguard to go on too...

I daresay it'll never get finished... but it will get a lot of use in the meantime...

cheers

[StephenW]

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.

[Brucey]

I had a think about this and (as I commented earlier) if you have trail, you will also have a lateral movement of a frame-fixed carrier whenever the steering is perturbed.

[ BTW In relation to your bike in the other thread, if the bike shimmies with small variation in how the front wheel is bolted in, either the frame or the fork are likely not stiff enough. If so I'd advise against carrying a heavy load in a frame-mounted carrier if this is the case, because (in cheaper steels) flexible forks are usually ones that are likely to bend or break prematurely, too.]

In a fork-mounted (steering) front carrier, there is (with steering movement) also a lateral movement of the load, even if it is centred above the front axle (which is BTW how porteur racks are designed to be used, I believe). This lateral movement arises because of the trail (again) and because the headstock is inclined away from the vertical, a double-whammy if you like.... Anything not on the headstock axis must move in relation to it when the steering is turned.

In both cases the lateral movement is liable to be worse with higher trail and in the case of a steering front carrier the
effect will also be made worse when the head angle is slacker too. [There is also a 'rise and fall' issue with variations in head angle, too, but this ought not be too important when trying to ride in a straight line, with small variations in steering angle.]

I do not think it a coincidence that machines intended to carry a large steering front load tend to have steep head angles and low trail geometries; both features will tend to mitigate against such lateral movements when a steering front carrier is used. It also means that

a) if you attach a frame-fixed carrier to a bike it may not work that well if the trail is large,
b) as well as extra bending loads in the forks (from the load) there are additional lateral loads in the forks whenever the steering is moved quickly
c) strapping a steering front carrier onto a normal frame (that is not designed for it) may not work too well; both the trail and the head angle are likely to be sub-optimal
d) if you do want to use a steering front carrier, it may be advisable to select a frame with a steep head angle, and to fit forks that have a larger than usual offset, so that the trail is reduced.

It occurs to me that simply fitting a smaller front wheel than usual may address point d) in some cases.

cheers