Cycling UK Forum

Also agree the Ribble is not expecially racy - even with thin tyres.
I went with Tiagra rather than Sora just to get the gear change levers both down on the brakes.
Other than the price being right, I did a close check on frame dimensions trying to match my existing bike as close as possible.
The Ribble has quite a long top tube compared with some other bikes. Also note that it's not compact geometry so stand over hight is less.

If I'd wanted a more racy bike a smaller frame size and longer stem would probably suffice.

gilesjuk wrote:Ribble do a winter/audax frame for about £89, it has mudguard mounts so you can carry on riding through the winter.

This is it built up:

http://www.bikeradar.com/gear/category/ ... udax-11764

People argue about Shimano vs Campag but personally I run SRAM Rival :

Clearly when I bought mine I was ripped off! I like mine...

This might be interesting - Campag better than Shimano but not as good as Wipperman...

http://cozybeehive.blogspot.com/2010/04/bicycle-chain-wear-test-from-wippermann.html

mw3230 wrote:The easiest way of answering the question has to be to take her to a bike shop and try bikes for size. Trying to fit your daughter for a bike based on the views of people who've never met her is a bit iffy - like buying her shoes cos we thought she needed size 4! Good luck

+1

My daughter went straight from 12 to 20 inch wheels. She became fully adept at scooting along without pedals quite quickly but was reluctant to actually pedal...

As encouragement I took her to a bike shop where she looked at all the lovely pink bikes - All 16". When she had progressed well enough to be rewarded with a new bike, it became clear that 20" was a better fit. She is / was not tall for her age so I'm guessing that 20" may be right for your daughter, but a decent bike shop will know.

[XAP]Bob wrote:No the apple simply 'tries' to carry on in a straight line.
The "pull" you feel is a consequence of your frame of reference spinning rapidly - it's not a real force.

This is semantics - The force is real. The direction of the apple on release of the string is not outwards but tangential to the curve of rotation. There must be a tension in the string to start with or the apple would never be following a curved path...

Mick F wrote:A wheel is a circle. If you squash it, it must ovalise. Therefore in theory, if you compress the bottom, the sides must stretch outward. You cannot compress the rim and alter the circumference.

I suspect it's not quite that simple! Spoke tension is transferred to the rim as a hoop stress putting the rim into a uniform compression (assuming a perfect wheel). Pre-stressed components do not necessarily exhibit the same behaviour as un-stressed ones. When the wheel is sat on the ground and a downward force is applied to the axle the spokes immediately below the axle must reduce in tension. That reduction in tension would need to be replaced by another internal force/stress or the world would end. One obvious effect would be that the spoke tension in the spokes immediately above the axle would go up. If the increase in tension is the same as the reduction in tension then we have equilibrium, even without rim distortion.

Spokes broadly horizontal would be subjected to a very slight change in angle which would have a very slight effect on their tension - some resisting higher and some resisting lower...

The above is not true of course but it does present a theorectical model of the problem which is probably not too far from reality. Taking this model to the next stage would be to consider the hoop stress. Clearly near the top of the wheel the spokes compress the rim radially and also produce a stress in the hoop proportional to the spoke tension and the angle nbetween the spokes. As the force is higher at the top the hoop stress must also be higher. Similarly the lower tension at the bottom of the wheel must correspond to a reduced hoop stress.

Now for the counter intuitive part. A lower hoop stress would compress the rim less and vice versa. So the rim expands where it touches the ground and contracts at the top!

So far this is an intellectual problem for me and i have no experimental data to support or refute the above. I do however have the right frame analysis software to build and analyse a model of a wheel! It might take quite some time to do - would anyone be interested?

CREPELLO wrote:...Can I take it that you've mis-read what I've said, for your answer doesn't address what I said.

Yes you may! I've re-read your original statement and I confess my interpretation was totally the opposite... My appologies.

I think the posts over the weekend have provided better explanations of what i was trying to say, so there is probably no need to re-state my earlier posts.

Anyone with spare time wishing to find good reason why tensioning to the highest possible spoke stress is a bad idea should research Euler buckling of columns - That is the limiting condition on the rim prior to backing off the spoke nipples.

In my (limited) experience rim stability under high spoke tension is at least an equal problem to that of low spoke tension...

531colin wrote:...What I think is going on here is as follows;- the driveside spokes are almost vertical, and therefore do not support the rim well against lateral loads, but the slacker spokes the other side are at a better angle to brace the rim against lateral loads...

That sounds right to me.

CREPELLO wrote:...For example (and I am musical!), if I tighten the strings on my guitar, they are harder to stretch for a given amount of force exerted than when they are looser...

I am a very bad guitarist. Your experience is different to mine. I don't believe that guitar strings are harder to stretch when looser. In fact I struggle to see what would make you think so...

Now on to spokes, and some very basic structural theory (please don't hate me).

For elastic behaviour the tension in a spoke will be directly related to the strain and the strain is related to how much the spoke is stretched. Spokes are not actually stretched very much and over the range of real poke tensions the material may be considered to have a linear response. What this means is exactly what CJ said. If you push the rim sideways is flexes the same amount regardless of spoke tension. If this was not the case the spokes would not be behaving elastically and the wheel would either snap of the spokes would loosen when you stopped pushing.

I'm not conviced that lateral stiffness is that much of an issue anyway. There can be very little laeral force on a wheel anyway. If there was, you'd fall off...

CJ wrote:That's nowhere near enough to allow for the higher forces arising from a bumpy road or jumping on the pedals etc. You really want to allow for at least twice your bodyweight. In which case your sitting on the bike should not alter the pitch by more than half an octave (six keys on a piano, counting both black and white). Only one quarter of an octave (three piano keys) change in note will allow for forces of approx three times bodyweight.

We do know that impact force is proportional to the square of velocity. For a fully rigid wheel on a rough surface the vertical force associated with the suface roughness increases with the square of speed. In simple terms at 15 mph there is over twice the force as there would be at 10mph and at 20 mph there would be four times the vertical force.

It's obviously much more complex than that - pneumatic tyres, non-vertical accelerations, becoming air-borne over bumps and a whole lot of other things mess up the numbers but I'd guess the priciple is still broadly correct. You would need a higher spoke tenson on a faster travelling bike.

Of course really fast bikes have fewer spokes...

All good advice so far.

Rust is about five times the size of the steel used to make it. So a little steel loss can produce a lot of rusting.

If you are not touching this for some time oil or phosphating would be appropriate if you think it's condition is going to get worse between now and summer. In the absence of water corrosion will be effectively nil so keep it dry.

When you do scrape off the rust you will be looking for any loss of material thickness. If this is observable in any of the higher stressed areas - bottom bracket and head tube spring to mind then you need to proceed with caution - if at all.

Remember that while the tubes will be quite thin, they are likely to be thicker at the joins.

Also remember that if you build up the bike with a rusty frame you can "swap" in a new frame later but if you don't use the rusty frame you just don't have that essential second bike...

Mick F wrote:Hijacking my own thread here!

Mick - Is it not possible to lower the hitch to below the axle? That should prevent wheelies much like the PTO on a tractor...

I was thinking of a flat plate extending downwards from the axle and hooked over the chain stay to prevent rotation - blacksmith work rather than precision engineering!

reohn2 wrote:...My conclusions are that two lights in line (one above the other) have the effect of making me appear tall thin,whereas one on rackpack one on elbow(flashing facing rearward) make me out as either two bikes side by side or one fat one whatever the reason(I careth not) I get a lot more room with the latter.

The worst case may be two horizontal non-flashing lights as that would make you appear to be a car a long way off...

I have flashing tight under the seat and solid down close to the wheel. I also have reflective bands round my ankles and suspect that these make a BIG difference in overtaking.

Does anyone use a section of cycle path to hone their MTB skills?

Bill D wrote:NCN north of Newtown (Powys) has a stretch surfaced with 1cm round pebbles which are fine on wideish tyres but can cause a 'moment' or two on v narrow ones. Not ideal, but IMO it's better to have the NCN route than the alternative of a very busy main road.

If you have an accident on a road due to a damaged road surface there is a chance of compensation from the relevant authority. Does a similar option exist on a cycle path?

Bill D talks of v narrow tyres. I'm assuming that these tyres were purchased for a bicycle through a uk retail outlet and did not come with a warning saying to avoid rounded gravel paths? If so, how are you or anyone else to know that some surfaces, identified specifically for cycling on, are not appropriate for your, in every respect, legal bicycle?