Cycling UK Forum

You can lose a fork blade and it's not catastrohpic, as Sean proved. The other blade will hold it together, in a rather flexy manner. Crown or steerer failures mean you're going to eat tarmac.

Some Sachs/SRAM geared or coaster hubs use FG (Fahrradgewinde) threads, a similar mixture of metric diameter and imperial pitch. Due to their obscurity, taps and dies cost a fortune.

I have used an M6 die to convert a front brake to a rear brake, a 1" x 24tpi die to shorten fork steerers, as well as M5 and 2BA taps to chase frame threads.

A thigh on the top tube and gentle rear braking are the two things that help. My old Hewitt Cheviot did it at around 30mph with a camping load on the back, but it came on sufficiently slowly, and at a low enough oscillation frequency, to slow down and take the countermeasures above. Rarely, a bike will do it so violently and suddenly that it is really dangerous.

I generally grip the top tube with my legs on fast descents anyway for aerodynamics, and this probably helps avoid shimmy too.

The only risk factor that seems to be universal is putting a heavy load solely on a rear rack. The rest of it is a complex mixture of weight magnitude and distribution, frame geometry and tube stiffness. A loose headset, often blamed, is very unlikely to have any impact.

pwa wrote: ↑9 Jul 2024, 9:06am I once had an Argos (Racing Cycles, Bristol) audax bike that, for some reason, had an occasional high speed wobble that required me to press a knee against the top tube to quell it, which I felt to be poor handling. I don't have it now and was relieved when I got rid of it. My current Spa Titanium Tourer (with sturdy steel fork) tracks beautifully at 40mph, with or without panniers, which makes for nicer rides. I point it the right way, and that's my job done. It's good at low speeds too, so I'm not sure what more you could want. Crucially, on very slow and difficult climbs it isn't difficult to keep the front wheel pointing the right way.

I had a Raleigh Olympus when I was younger, and that would go into a speed wobble at only 25mph. I think everything I have now has been up to very high speeds - unloaded - without issues. Speed wobble is hard to predict if you're designing a bike, as rider/luggage position and behaviour play a part. Many bikes are ok unloaded, but put something heavy on the rear and they will start wobbling at 30mph.

The no.1 rule in complaining to any organisation is to specify exactly what you want them to do. Compliance is easier for them than thinking about it and prolonging the correspondence, which all costs money. Admittedly this works best for larger organisations where there is probably an ex-gratia limit.

Rhothgar wrote: ↑14 Dec 2024, 10:15pm

rogerzilla wrote: ↑14 Dec 2024, 6:19pm Cannondale Force 40, anyone?

Are they seriously any good?

Er...no. They may well have increased MA by 40%, but they were a pain to set up and most people threw them away and used a normal straddle wire. They also came with rebranded Dia-Compe 986 cantilevers, which were equally awful to set up.

Cannondale Force 40, anyone?

The trend to host groups on Facebook (because it's trivially easy) is a curse. Not everyone is on Facebook. I'm not any more. I miss the Moulton groups but I don't trust Zuckerberg as far as I can throw him and some seriously creepy stuff was going on, like Facebook emails with accurate personal info arriving at an email address I know I've never given them.

I have sometimes heated small unplated steel components to dull red and dropped them in oil (alnost any oil will do). This gives them a blue/black finish which resists rust quite well.

Small frames on large wheels need less drop so the downtube still clears the front wheel. 29er MTBs are therefore a terrible idea unless you are at least average male height; 26" wheels allowed much better frame geometry for shorter riders. It's not quite as bad for 700c road wheels since the tyres are so much smaller, but frame sizes below about 20" (based on a level virtual top tube) start to get weird-looking, and getting a foot down at the lights will be tricky.

What's funny is that the Moulton series 2, unburdened by wheel size, still managed to have an uncomfortably high BB. In that case it was due to the strengthened rear forks losing the curve of the weak series 1 design, but keeping the main frame geometry the same.

Sum wrote: ↑8 Dec 2024, 6:54pm There's no need for the giblets, apparently a rumble strip is what you need: https://www.cyclinguk.org/sites/default ... pdf#page=2

"For a demonstration of this, stray onto one of those concrete rumble strip road edgings. The bike slows immediately and if you stick it long enough you will get hot." The article goes onto to give a rough indication of the losses: "For bump amplitudes of around 1mm and frequencies around 10Hz – which seem reasonable numbers for a bike with hard tyres on a rough road – they measured bump losses of about 25W". I couldn't see a date but it references the Christmas 2010 edition of the British Medical Journal.

Looks like I better put those giblets back in the fridge.

I remember Keith Bontrager did something similar in the 90s, using lengths of 2" x 4" timber attached to a treadmill, in order to measure the effect on power requirement with and without MTB suspension forks.

The most common source of Brompton squeaks is the rubber suspension block. Brompton advise taking out its bolt and slathering it in something innocuous like silicone grease. This shuts it up for a long time.

There's no real flexibility from the spokes, at least not unless they're so slack that the wheel is compromised. Forks make a very small difference and a vintage-style tight curl at the bottom of the blades works better than the more modern banana (or straight) style.

Yes, and Presta valves need back pressure to close them, as they have no spring. A Presta valve in a big tyre, with one of the problematic pumps discussed, can occasionally be difficult to get started.