Cycling UK Forum

maanderx wrote: ↑23 Apr 2024, 6:21pm
Anyone after a 74 BCD 33t inner ring? I've got three (from Spa Cycles) that I'll gladly get rid of.

Are they inners of doubles or middles of triples? Other details, e.g. condition?

Sounds like a broken axle to me. I've replaced a few of those in my time. A replacement is not expensive. Can you take the wheel + the loose bits to your local bike shop (LBS). They may sell you a new axle of the correct size and type, quote for repairing the wheel, or offer to sell you a replacement wheel if they assess your old wheel as not worth repairing. There's no substitute for having the parts in your hands when it comes to deciding on a course of action. Bearing parts (balls, cones) may be worn enough to be worth replacing while the hub is in bits.

rogerzilla wrote: ↑19 Apr 2024, 8:23pm It is, because an inch is now defined as exactly 25.4mm. Before 1959 it would have been a far less precise fraction, since the two measuring systems had evolved independently.

Can we not now, post-Brexit, revert to 1/36th of the distance from the King's nose to his outstretched fingertip?

Marc wrote: ↑19 Apr 2024, 6:46pm

rareposter wrote: ↑19 Apr 2024, 6:22pm Personally I think it's pretty irrelevant now cos literally the only place you'll ever find a drum brake these days is on a traditional touring tandem as a supplementary drag brake to the cantilevers (plus of course you get drum brakes on various utility bikes which it can safely be assumed are not putting anything like maximum force through them).

The advent of discs has pretty much killed the need for a drag brake system on a tandem and no performance bike would ever use drums.

Ahem... velomobiles? You hardly get more performance orientated "bikes" and pretty much all of them use drum brakes. Riders in mountainous areas usually use air-cooled drum brake hubs from Ginkgo, though.
https://shop.ginkgo-veloteile.de/en/Whe ... rakes.html



Just saying...

If you want to have some serious dissipation, those are the hubs to go for. (I said hubs not pubs". )

kylecycler wrote: ↑16 Apr 2024, 8:15pm ...

Also, apart from anything else, I've come to the conclusion (as I expect have a lot of the rest of you!) that a headwind is no different to an ascent.

Headwind = hill, innit?

A headwind can last all day. I've never met a hill that did.

Jdsk wrote: ↑14 Apr 2024, 2:22pm "Tandem Braking":
https://www.thorncycles.co.uk/tandem-braking

As well drag brakes it has lots on slow and fast descending, and some physics, and some data (!), much of which is also relevant to lonely bikes.

Jonathan

Thanks, Jonathan. That's a good article that I was unaware of.
Chris

Here's my summary of the physics, for what it's worth.

If you go down the hill really slowly you can neglect rolling resistance and air resistance (because the main thing by far that's holding you back is the brakes) so all the potential energy you have at the top finishes up as heat generated in and dissipated from the braking system, whether rim, disc or drum. If you go slowly enough all this heat has plenty of time to dissipate so nothing overheats.

If you go down the hill as fast as you dare then much of your initial potential energy gets lost to air resistance, so less energy goes into the brakes, but it might be over a short enough period to allow overheating.

In between these extremes there might well be a pessimum, which might explain those alpine blowouts.

Mick F wrote: ↑25 Mar 2024, 6:24pm The other one I was thinking about today, was "agenda". It was being said on R4 this afternoon with a politician chappy.

When I went to meetings ......... and chaired them many many times ............ was we discussed the agendum.

Looking it up earlier due to R4, the modern stuff is "agenda" as the singular, and "agendums" as the plural!

Even the spell-checker on my Mac doesn't like "agendums".

In Latin agendum means 'that which is to be done' and its plural is agenda.
In English agenda usually means the list of things to be done and is considered singular, the plural being agendas.
Like Jonathan, I would be curious to know who came up with agendums.

simonhill wrote: ↑24 Mar 2024, 11:32pm.....
Although a recent thread said weight on wheels no more important than weight elsewhere
......

Well, that sent this thread off on a tangent.

rareposter wrote: ↑25 Mar 2024, 1:05pm You don't really need maths to prove anything though. Put some 2.5kg wheels on a bike, go and ride up a hill.
Replace the wheels (keeping the same tyres/pressures etc) with a pair weighing 1.5kg , go and ride up the same hill at the same power.

The lighter wheels will feel better (which is a bit subjective) and will be measurably faster (which is purely objective).

There's a reason that performance wheels are lighter and it's not all marketing or snake oil!

OK, for touring I'd probably prioritise reliability and standard parts over purely lightweight but it'd still be a consideration even once a bike is loaded with touring gear.

Equally true. The inertia of rims+tyres is significant compared with inertia of rider+cycle when a second or so really matters.

531colin wrote: ↑25 Mar 2024, 12:53pm I can accelerate the wheel by brushing it with my hand.
I need to use both legs to accelerate rider plus bike.
While I am accelerating rider plus bike, the difference between a regular tyre ( accelerate the wheel with a brush of your hand) and a light tyre ( accelerate the wheel with a light brush of your hand) is insignificant.

Unless you would like to produce real numbers demonstrating that accelerating a bicycle wheel takes a significant proportion of what it takes to accelerate rider plus bike plus any luggage.

True. The inertia of rims+tyres is insignificant compared with inertia of rider+cycle+luggage.

simonhill wrote: ↑25 Mar 2024, 9:55am In English please?

Is the following true?

Apart from the weight they add to the overall weight of the bike, heavier wheels and tyres make very little difference to pulling away or rolling.

Someone has written on the touring tyre thread "So pulling away at a junction, 1kg on a tyre feels like 2kg on the frame". Is that untrue,?

roubaixtuesday has beaten me to it, and he's dead right. He has bitten the bullet and produced the equations I declined to do previously. The rotational kinetic energy of rim+tyre equals the translational kinetic energy. So yes, 1kg on a tyre feels like 2kg on the frame when accelerating.

531colin wrote: ↑11 Mar 2024, 12:00pm ....

What I think must happen is the front wheel goes over the object and flips it up, so that it is standing on end as the back tyre runs over it, and your weight drives it through the tyre.

....

I have known that to happen and cause a car tyre to deflate in a couple of seconds.

When I put my cycle computer on the desk next to my laptop it does erratic speeds of up to 100-ish mph. I blame Harald Bluetooth.

ANTONISH wrote: ↑6 Mar 2024, 9:44am

LuckyLuke wrote: ↑6 Mar 2024, 9:21am Hi, just to echo the others above, it sounds like your existing triple will take a 24T inner. Spa sell a steel one that I’ve found works well.
.....

A caveat ; I bought just such a steel inner ring and kept it for a while.
Eventually I decided to ride the C2C and realised I had a new inner ring - so fitted it to my 9sp setup.
Unfortunately I fitted it at the last moment so it wasn't used until I was actually on the ride.
I found that the chain was sucking on the small ring - very disconcerting on a climb as I had to rapidly unclip and get my foot down to avoid a fall.
When I consulted here on this problem it was pointed out that the chainring was probably 7sp and was too snug a fit on my 9sp chain.

I had a steel 24t inner ring (9sp), probably bought from Spa, which produced chain suck. On investigation I found burrs caused by pressure from the chain rollers. The tooth profiles had also changed a bit. I filed off the burrs. Some while later I found smaller burrs, but if I remember rightly these had not caused chain suck. I filed them off and that was the end of the matter. The tooth profile had obviously changed to something that was able to stand the pressure.