Tag Archives: ciclismo

Thinking on removing your front derailleur?


Everytime I come across with this question on a bike forum my thoughts automatically go back to the 2003 Tour de France Prologue.

On that day, the scottish David Millar lost the opportunity to win the initial time-trial for less than a second due to his chain that came off the front ring.

News footage from the French TV shows how brave is Millar placing the chain back with his fingers upon arrival. A delicate operation while you’re riding over 30 mph.

This information points at the missing front derailleur as the reason of the problem.

dvcvxcv

David Millar, 2003 Tour de France Prologue, Paris

@ http://www.cyclingfans.com

Yesterday’s chain failure wasn’t the first time that David Millar has experienced a chain problem at a critical time in a Grand Tour. During the 2003 Tour de France 6.5km prologue (photo above), Millar’s chain slipped off as he approached the finish line, costing him the stage win. An angry Millar blamed his directeur sportif for the lack of a front derailleur, causing the chain to slip. Millar finished the prologue second to Bradley McGee by just 8 hundredths of a second.
-Pete Geyer

It’s hard to believe that a bike mechanic involved in such a race like the Tour de France, world class riders and equipment (not the case with Decathlon bikes though :roll:), decided to remove the front mech, because Millar was committed to use a single chainring setup, without fitting a chain stopper on its place.

I can only blame ignorance to be mother of imprudence. Front derailleurs allow to switch from chainwheels, and what is as important: stop the chain from jumping off. On bumpy stone paved roads (pavée) and a NOT enough rear mech to lock up the chain tension while it is working crossed along the cogs we can only predict the chain is going to fall off sooner than later. Even on flat surfaces it will slip off.

Whether if you want to convert your MTB to singlespeed or 1x type transmission, bear in mind you will need a device to prevent the chain from coming off. It can be a double bashguard, a chainkeeper/chainguide/chain stopper or a combination of both.

Posh Paul chain keeper

Posh Paul chain keeper

Many people that are simplifying old vintage road bikes should do the same for fixie/single speed purposes.

All these advises (and devices) are taken into account considering we are talking about pure vertical dropout frames with no other methods to take up the slack in the chain, such us: eccentric BB/hubs, sliding dropouts, and so on, representing the vast majority of frames.

There are only a couple of exceptions that freaks will proudly point out. SRAM XX1 single chainring gruppo and high chain tensioners on singlespeed bikes where the chain works straight! (Bromptons for example).

Even though, I’ve experienced chains coming off in my bike that uses a perfect aligned chain on a Rohloff hub and the extremely high tension provided by the DH tensioner. XX1 failures are even more common, and have been reported frequently despite engineers taking the piss with the deep profile teeth design of the XX1 chainring encouraging not to use a chainguide. I would like to recall that Hermida lost the podium in the last Olympics because of the bloody stupid tendency on bikers to remove the front derailleur and the “cojonazos” of his team fitting new-unproven parts they’d just received.

Hermida’s team underrated the importance of the chainguide that is mandatory on top of the XX1 crankset if you do not install a Type 2 SRAM rear mech. The SRAM XX1 provides extra tension thanks to a roller clutch

If you’re switching to single speed or whatever 1x setup is in your mind, fit a chainguard. You’re not likely to lose a gold medal or the yellow jersey but you teeth instead :mrgreen:. Remember how bad the Cofidis bicycle mechanic should have felt that night after the first stage of the Tour de France: “somebody shoot me”.

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Bromtpon Eazy Wheels


Replacing the factory wheels was the first repair that came to my mind when I got the Brompty. Although I did it long ago, I have saved it for last within this saga of Brompton repairs because the result is not satisfactory. I would say work in progress ūüôā

Factory rollers vs. Eazy Wheels

Factory rollers vs. Eazy Wheels

By installing the Eazy Wheels you have the added advantage of being able to pull the bicycle along on the ground. Stardard wheels are just simply a shame and won¬īt work.

I love the idea of the versatility of a Brompton

I love the idea of the versatility of a Brompton

Good, I have no more to carry mine everytime I go walking with it when commuting, I thought. But the reality is that your bike needs also a rear carrier, or Brompton mudguard at least, to support parked mode and wheel it along. Otherwise the Eazy wheels by themselves won¬īt make any difference. I can’t believe I didn’t figure it out until I put them on. Well, at work I never needed to pull/push the bike around :mrgreen: .

Eazy_wheels_4_close_up

Tyred rollers with industrial bearings can also be fitted to the rear rack

A rubber bung, fitted to the bottom of the seat post, can be used as a brake to prevent unwanted rolling.

Full kit

Eazy Wheels full kit with rubber thingy

My Brompton does not have a rear mudguard that will add the extra wheel for stability, or what it could be even better, a rear rack that comes equipped with two wheels improving the handling when it is half-folded.

IMG_4666

Bikes with no mudguards/rack but Eazy Wheels installed, are as stupid as mine looks in the picture

Not everybody need to enable this function. That is the reason it is offered as an option when placing your order. In that case you will have to pay on top 20 quid for the better quality wheels, and another 50 quid for the pricey mudguards or 100 quid for the Version R of the bike (mudguards & rack).

The installation of the wheels is so straightforward… nothing to say about it. What a drag!

Brompton rear frame clip for older models


One of the most frustating things in pre-2007 models is the lack of a mechanism that stops the rear triangle from folding when you lift the bike up.

IMG_4590

Got it from Brilliantbikes.co.uk that delivered overseas some Brompton parts faster than any spanish dealer

In order to update my 1999 Brompton the retro fit kit is needed as it comes with an 8 mm seat clamp bolt. If you are using already a 6mm bolt there is a much cheaper kit for sale without the clamp lever, £9 instead of £23,75

Packaging content

Complete retrofit kit

The installation process consists on two steps.

First you will have to modify the rubber damper discarding the conical buffer disc (aka suspension block bolt) for the one that have a recess to engage the latch lever.

IMG_4598

Suspension block bolt disc to be replaced

IMG_4605

Appearance of the new disc bolt. This time is inserted thru the elastomer from the other side

A plastic shim washer (SW), a stepped nylon washer (C) and a nut (N+BW) is necessary to hold the block (SB) from behind when fitting the new buffer disc bolt (BD) as shown in the picture (Fig. QR10). Grease the bolt not to have funny noises. After installing the bolt make sure the small hole is in the bottom position and thus the two tiny lines marked in the disc facing up.

Follow the steps shown int he picture

Follow the steps shown in the Fig. QR10

Secondly replace and discard the old quick release bolt. Three parts will be assembled inside the seat clamp band (SCB) of the bike in the order and orientation shown in Fig. QR05: a hollow stepped cylinder (S), the metal lever (L) and the spring (T). Assemble the parts sliding them with the quick release in angle.

New seat clamp and parts inside the frame band

New seat clamp and parts inside the frame band

Tighten the seat clamp by using a nut and the required metal tabbed washer (SCW) for M8 bolts. Fig. QR06

IMG_4607

For post-2007 bikes use the existing flat washer instead (M6W).

At this time, the installation is fully functional but not complete. The kit does comes however with an ergonomic black handle (HDL) that protrudes much longer than just the metal lever. Secure it to the lever with the self-tapping screw (STS). Fig. QR 07

IMG_4602

My bike now updated :mrgreen:

And this is it.

For further instructions you will find helpful the video from the official Brompton Channel on Youtube. Hard to find better technical advise and spoken english. Well done.

Nitrogen/helium filled tyres for bicycles?


For safety and service reasons nitrogen is used in the aircraft and car racing industries for filling tyres as well as a compression/expansion gas for hydraulic systems.

Will we get any benefit from pumping our tyres with a different type of gas rather than air?

Absolutely not!. There will be no performance improvements and no negligible maintenance difference at all.

Indeed, it’s only practical to inflate our tyres with just few gases apart from common air. Let’s see why.

Do not raise your hope so with helium stuff

Do not raise your hopes so high with helium

Hydrogen and helium are the two smallest and lightest atoms. On the other hand the smallest diatomic molecule that can be found in nature is hydrogen gas (H2 ). Other diatomic molecules are O2 (oxygen), NO (nitrogen oxide) and CO (carbon monoxide). Air contains 78% of N2 , 21% of O2, 1% of argon and little amount of other gases.

In this scenario hydrogen and helium stand out as potential candidates due to their light nature, specially hydrogen.

The reality is that in the case of hydrogen it will leak out from tyres much faster than air. Not because its reduced molecular size. Hydrogen permeability with butyl compounds is all about. Hydrogen diffuses through the inner tube wall faster than other more rubber compatable gases. It’s a fact that helium or hydrogen dissolution inside the rubber matrix will end up in continuous top-ups, if not during our rides reducing a lot the interval service.

For example, CO2 contained in re-fill bottles, despite it’s higher molecular weight and size, has proved conclusively to leak out faster than regular air due to a higher solubility in butyl rubber which allows it to diffuse through the inner tube wall faster than smaller gas molecules.

Hydrogen and helium are then discarded within the options of inflating tyres for obviuos reasons. We will only refer to them again to talk about weight savings.

But will the nitrogen alternative be suitable?

Yes it, is. But it does not provide any advantage inside bicyle tyres.

Nitrogen gas is present in aeroplanes and racing tyres. It is used in such situations because it’s drier than air. Even though air with free moisture contain is enough in certain applications.

Secondly, nitrogen is less chemically social. Although nitrogen is not formally an inert gas, it is however considered as such as it does not readily react with many elements whereas oxygen contained in air reacts violently.

Let’s evaluate several tyre parameters in extreme conditions to determinate if there is any gain of utilising nitrogen in bike tyres.

Pressure changes with temperature.

The volume of regular air will change with heat and thus pressure. Air contains water in vapor state (in both liquid and gas forms). While the temperature rises, moisture turns to gas vapor which increases the volume tremendously at certain point. And this variation is on top of the normal rate of dilatation of gases. An undesirable phenomenon where pressure stability is required.

For car racing the main problem is to keep moisture out of the inside of the tyre so that pressure is more consistent. Most of the wheel performance and safety issues in motorsports are solved by using dried-air and therefore no moisture is present. The Formula One competition has been reported to use air in compressors that only have water extractors.

Don¬īt panic!. The fire was caused by a broken fuel line

Where tyre friction is critical nitrogen is preferred. Nitrogen is popular in Nascar racing for avoiding tyre explosions due to moisture overboiling and oxygen reacting with high flammable rubber compounds. It is appealing as well where large volume of air is inside the tyre, and that means a lot of water that affects the pressure with temperature above the normal rate of gas expansion. This is the case of the aircraft industry.

Bike tyres don¬īt heat up as much as car tyres do. For a bicycle tyre, the volume of air is very small and usually inflated to high pressure. Any expanding accounted to water molecules will not be noticeable, and unlike high temperature apps, less than accounted on normal air expanding with temperature, which is already very low.

Even on pristine downhill races or road tubular tyres competitions on hot days the pressure discrepancy is negligigle.

Flammability.

This is a major problem in aeroplanes, rare in motorsports and no applicable to bicycles.

Aircraft burnout

Aircraft burnout

When taking off and landing a tyre can get high temperatures and pressure changes. Water vapor content that can boild up increasing the tyre temperature and also elements like oxygen that can react with rubber vapors or wheels metals and become explosively expansive in the presence of enough oxygen. Consider that rubber compounds are highly flammable. In that case nitrogen will be less likely to react avoiding ignition. Nitrogen actually helps to extinguish any fire.

Lifespan of the tyre.

Air if not dried contains moisture that adds to the corrosions concerns of oxygen. Nitrogen will prevent internal rust in parts because there is no oxygen to react with other elements and because we get it dry out of the compressors.

The use of an inert gas could be important in accumulators, hydraulic pre-charge systems, surge suppressors and fire extinguiser bottles but no concern on rubber rusting up.

In any case, performance tyres on cars and bicycles are frecuently replaced though. Note that corrosion is a long-term process.

There is no discussion on airless tyres

There is no discussion possible on airless tyres :mrgreen:

Pressure durability.

Here a question arises: Is nitrogen less porous than other gases and keep the right pressure longer than air?

Air, in fact, is made of 78% nitrogen itself as we said at the beginning of this article. So nobody expects big differences for just a 22% variation caused mainly by oxygen molecules.

But the reality is that nitrogen, being a smaller and lighter molecule than oxygen will last longer inside a tyre unlike the wrong premise of many car repair shops claiming nitrogen bigger size to be the reason to retain optimal pressure longer in compare with air.

How is possible that nitrogen diffuses slower than oxygen contradicting Graham’s law?

Well, nitrogen, despite its minimally smaller size versus oxygen, is more compatable with rubber compounds and less likely to trespass the atomic structure of inner tubes/tyres. Its worse solubility makes the gas to stay longer but do not forget air is still mainly nitrogen!

Nitrogen filled tyres for general consumers if not a scam, will elongate the gas refills periods in a 10%-20% at the most. I have not seen any literature proving its effectiveness in standard environments. Probably at high temperatures moisture can play a key role in the volume of air and pressure, but it sounds like science fiction that replacing oxygen molecules for fatty nitrogen ones is going to reduce the rate at which compressed gas diffuses through porous walls leading to more uniform tyre wear and better fuel consumption.

The cheap stuff. Not to worry :mrgreen:

The cheap stuff. Not to worry ūüôā

If nitrogen molecules was way less permeable than oxygen you would get this paradox:

Since oxygen leaks out faster leaving nitrogen molecules inside my tyre, in successive air refills I would increase nitrogen percentage each time. After ten or twenty top-ups my tyres would be mainly keeping nitrogen inside ūüôā

Did I say not to bother on bicycle wheels where you can come across with sealant filled tyres to ensure self-healing (and losing air in that process) or very porous latex inner tubes that do not keep the optimal pressure for more than a ride?

Weight.

On a bicycle the added weight of air per wheel is around 18 grams. Can we cut it down?

Amazingly light Eclipse MTB inner tube

Amazingly light Eclipse MTB inner tube

O2 weights 32 grams/mole and N2 weighs 28 grams/mole. Since air is about 78% N2, the average weight is taken at 28.9 grams/mole, which means you get a ridiculous 3% weight savings in compare to air. Less than a gram per wheel.

Theoretically, hydrogen is 1440% lighter than air (and so is helium – 724%) so we could end up in a almost 18 grams per wheel less. Unfortunately both gases are useless to conserve pressure as explained before.

Why normal air is so good for general purposes?

Because it is made of 78% of nitrogen and air humidity is a minor issue that only counts in high temperature applications.

¬ŅCu√°nto pesa el aire de las ruedas?


Este tema es un cl√°sico entre aficionados al ciclismo, automovilismo, etc. que alguna vez nos hemos preguntado si realmente es mucho peso el que se a√Īade una vez inflada la rueda con aire.

El objetivo de esta entrada es realizar un cálculo teórico para aproximar el peso extra. En un futuro capítulo veremos si hay opciones alternativas viables para hinchar las ruedas con algo que no sea aire.

Lo primero que debemos calcular es la densidad del aire, es decir, la masa por unidad de volumen. Depende de tres factores: la humedad, la temperatura y la más importante, la presión.

El segundo c√°lculo se centrar√° en el volumen del neum√°tico.

Finalmente, la masa la calcularemos como producto de la densidad del aire introducido en el neum√°tico y su volumen. Vamos all√°.

C√°lculo de la densidad del aire

En este enlace encontraréis la fórmula completa para el cálculo de la densidad del aire, además de unos campos con variables que podemos modificar para calcularla. Otra manera sería recurrir a tablas empíricas en libros de ciencia, etc.

rho

donde:

rho_data

Jugando con los valores nos damos cuenta que la influencia entre usar en las ruedas aire seco (humedad 0%) o el aire procedente de un lugar con alta humedad relativa es casi nula, al igual que ocurre con la temperatura. A efectos prácticos no hay diferencias apreciables incluso moviéndonos en valores extremos. De hecho, el cálculo del volumen teórico del neumático es mucho menos aproximado, por lo que motivo más que suficiente para descartar sus efectos y usar condiciones estándar para todos los cálculos.

Ya sólo nos preocupa la presión a la que inflamos nuestra rueda. En este punto podemos encontrar dificultades ya que la presión es de esas magnitudes que se pueden expresar de incontables formas. Conviene repasar equivalencias en estos dos enlaces #1 y #2.

Si por ejemplo hinch√°semos la rueda a 3 bar, ¬Ņcu√°l es la presi√≥n en hPa que debo introducir en la dichosa f√≥rmula de la web para obtener la densidad del aire?

Lo primero a considerar es que los artilugios que usamos para hinchar y medir la presión lo que nos indican es la presión manométrica, es decir, la diferencia de presión con el exterior que usamos como referencia. Así que no nos vale introducir directamente el valor del manómetro. Por lo tanto:

Presión absoluta = Presión manométrica o relativa + presión atmosférica

Aquí se explican los conceptos en un vídeo muy sencillo.

Considerando presión atmosférica estándar y que no vivimos en el Everest, esto es, usando lo que recomendó en 1985 la IUPAC como presión estándar normalizada de 1 bar llegamos a la presión absoluta a introducir en la fórmula. También podíamos haber usado la equivalencia de 1atm = 0,98 bar puesto que 1atm se considera como la presión atmosférica estándar.

Así pues, si la presión manométrica es 3 bar y la de referencia es 1 bar, la presión absoluta que lleva nuestra rueda resulta ser de 4 bar.

Usando equivalencias (1bar= 1000 hPA) se llega a una presión absoluta de 4000 hPa que nos da un valor de la densidad del aire de 4,75 kg/m3,o lo que es lo mismo 4,75 g/l.

C√°lculo del volumen del neum√°tico

Aquí simplificaremos bastante más y me tiraré menos el rollo. El volumen de un neumático se aproxima como el de la figura geométrica llamada toro.

Su volumen es V = 2¬∑ŌÄ2¬∑r2¬∑R

 Toro_radios

En la figura anterior y en rojo tenemos a r, el radio de la circunferencia, y R la distancia entre centros. Como es difícil medir la magnitud r en una cubierta haremos uso de una fórmula alternativa para el volumen del toro que usa los parámetros r1 y r2  en azul y verde respectivamente:

V = 1/4¬∑ŌÄ2¬∑(r1+r2)¬∑(r1-r2)2

donde; r1 el el radio exterior de la cubierta y r2 el interior de la misma. Lógicamente las expresiones son equivalentes usando r=r1-r2 y R=r1+r2.

En una rueda de 26×2.0 pulgadas de monta√Īa resulta un volumen muy aproximado de 3,75 l con r1=0.33m y r2=0.28m. Estos valores podemos medirlos con una regla de forma inmediata sobre una rueda, ya que trabajar con el bal√≥n de la cubierta r es complicado. E incluso de forma te√≥rica, suponiendo que r2 es la mitad del bead seat diameter de una rueda de 26 pulgadas (559 mm) y r1 el extra que supone el bal√≥n de la cubierta que son dos pulgadas √≥ 5 cm.

C√°lculo de la masa de aire

m = d · V = 4,75 g/l · 3,75 l = 17,8 g.

As√≠ pues, el aire en cada rueda en una bicicleta de monta√Īa de 26″x2.0″ a 3 bar ronda los 18 gramos.

Todas estas c√°balas son f√°ciles de hacer si partes de la base que un metro c√ļbico de aire pesa 1,2 kg y que una rueda de monta√Īa de medida habitual tiene unos 4 litros de volumen. En total nos sale que a 1atm de presi√≥n la rueda pesa 5 gramos extra por el aire en su interior, a 2 atm ese volumen es doble a√Īadiendo 5 gramos al peso (10 en total), y otros 5 gramos para seguir desplazando el volumen extra de aire hasta alcanzar tres atm√≥sferas, es decir, un total de 15 gramos en aire, muy aproximado al valor calculado.

Lógicamente esta información la saben pocos de cabeza y la idea era demostrarlo.

Y la realidad parece refutar la teoría. La discrepancia se debe a que siempre queda algo de aire en la cámara, y segundo que los cálculos son meras aproximaciones. Ya que partimos de instrumentos de medida inexactos y unas condiciones del entorno desconocidas, ni falta que hace afinar en los cálculos. Sospecho que el volumen de la rueda sea algo menos al deformarse la cámara en contacto con el aro.

IMG_4048

Peso rueda de 26×2.0″ desinflada: 1616 g

IMG_4047

Rueda de 26×2.0″ inflada a 3 bar: 1632 g

Sólo un par de gramos de diferencia entre la teoría y la realidad.

Presi√≥n ideal cubiertas bicicleta de carretera


No siempre la presión máxima indicada por el fabricante en la pared del neumático es la ideal para sacar el máximo de nuestras pedaladas.

En superficies lisas, como la de un velódromo, cuanta mayor presión mejor, pero en terrenos irregulares como una carretera llegado a un valor de compromiso se obtienen pérdidas extra por rodadura. Esa presión ideal depende del peso del conjunto ciclista/bicicleta y del tipo de neumático que usamos, su anchura y carcasa entre otros.

Esta genial entrada de otro blog lo explica con algo m√°s de detalle.

Adjunto tablas del fabricante Vittoria con presiones recomendadas para cubiertas de peque√Īo bal√≥n, es decir, las que se usan normalmente en bicis de carretera o ciudad.

Presión-peso-anchura

Presión-peso-tpi carcasa

8¬™ Ruta BTT Ciudad de Valverde 2011


Magn√≠fica marat√≥n de monta√Īa la que han redise√Īado este a√Īo los valverde√Īos, lejos de las tradicionales y largas pruebas de a√Īos anteriores.

Personalmente escog√≠ la ruta corta ya que estoy volviendo a dar pedales. Y se me hizo dura, a pesar de los 48 km que anunciaba la ruta corta vs. los 79 km de la ruta competitiva. La realidad es que los kil√≥metros primeros eran los m√°s lentos y t√©cnicos. Llenos de barro despu√©s del invierno, porque se surcaban zonas bajas en torno a riberas en lugar de tanta pista, que por cierto, tambi√©n hab√≠a. Me ha encantado la variedad y la dureza, a excepci√≥n del final, que se hac√≠a pesado y con cuestas inesperadas cuando ya las piernas no pueden dar m√°s de s√≠, ¬Ņo ser√° la forma?.

A√ļn as√≠, tengo la espinita clavada que Valverde es la prueba completa que me falta del calendario de maratones de Huelva. Tambi√©n San Bartolom√© y Santa Olalla de Cala, que se han disputado en dos ocasiones la primera mientras que la segunda repite este a√Īo (espero hacerla) habiendo tenido pocas oportunidades de participar.

Es una prueba de dureza alta y con una organización excelente. Junto con Cartaya y Paterna del Campo ocupa un puesto en el podio de los mejores maratones de Huelva. Dicen los entendidos que es la meca del BTT en la provincia. Desde luego por parajes tiene de todo, pasos cerrados que te obligan a pasar de uno en uno o tramos majestuosos en subidas en los que divisas a los que te preceden con facilidad.

Alg√ļn d√≠a recopilar√© las pruebas en las que he participado.¬† Anticipo que Valverde se lleva buena nota. Valverde, La Palma, Berrocal, Tharsis, Cartaya, Bollullos… empiezan a salir muchas batallitas ya :D.

Sunn Xircuit UN 999, 1999