SRAM HRD Brake Bleeding Guide

Dr David’s guide to bleeding SRAM hydraulic brakes. Having read and tried a variety of methods this is my refined method. SRAM HRD is a closed hydraulic system so all air needs to be expelled. Holding the lever against the bars is important as it empties the master cylinder of fluid and any trapped air.

You will need a SRAM bleed kit plus DOT 5 fluid. Workshop tissue/kitchen roll.

Read through the process fully before starting. Ensure hoses with clamps are secure on the syringe and the clamps will close.

Fill one syringe half full of fluid for the CALLIPER.

Hold with nozzle uppermost. Tap to move air bubbles to the nozzle. Expel all air.

Apply clamp. Pull back on plunger a few times to suck all air from the fluid. Tap syringe. Open clamp and expel the air. Close clamp.

Remove pads. INSERT Bleed block. Unscrew CALLIPER port screw.

Open clamp. Attach the HALF full syringe to calliper. Keep it nozzle downwards at all times.

Remove LEVER bleed port screw. Attach empty syringe to LEVER port. Open clamp.

Push HALF the fluid from CALLIPER syringe.

Discard fluid in LEVER syringe then fill ¼ full with fresh fluid. Use the process above to remove all bubbles from the syringe.

Screw syringe back on LEVER port and push a small amount of fluid from the CALLIPER syringe to the LEVER syringe. Close the LEVER syringe clamp.

Pull in brake lever and hold with strap.

Gently pull CALLIPER syringe (holding syringe with nozzle downwards) to remove air. Then gently apply pressure on CALLIPER syringe to “pressurise” system.

Repeat until no more bubbles.

Remove strap from lever but (VERY IMPORTANTLY) hold lever against bars.

Gently push fluid from CALLIPER syringe while slowly releasing leaver.  Do not force syringe. You should feel the pressure from the calliper syringe pushing the lever out.

Remove CALLIPER syringe and quickly screw in bleed screw.

Open LEVER syringe clamp. Gently pull back on syringe to remove air.

Gently apply pressure to plunger to “pressurise” system.

Pull in and let go brake lever 10 times or more. Gently pull back on syringe until no more bubbles. Repeat the above until no more bubbles.

Gently “pressurise” the system again.

Remove syringe (don’t apply clamp) and screw the bleed screw into the pool of fluid.

Clean up immediately before fitting brake pads.

CAUTION.

DOT 5 brake fluid is corrosive. It is neutralised with water. Have plenty of towels to hand to mop up spillage. Wash with plenty water when the job is complete.

Observe the SRAM recommended torque for the bleed screws and calliper pad screw.   

Test braking efficiency before going for a ride.

Download as pdf: SRAM HRD Bleed Guide

Dr David’s pre-ride checklist

Dr David’s pre-ride checklist

Pre-ride – a quick safety check.

  • Brakes – pads – check wear and central on rim/rotor, adjust cable if required
  • Wheels – check for trueness, bearings not worn or loose, quick release is tight
  • Tyres – check for damage, objects in tyre and pump to correct pressure
  • Chain – check wear, damage and clean it then lubricate
  • Cables – check wear, fraying and function

Less often – identify issues early before expensive repairs!

  • Headset – smoothness, play
  • Pedals – tightness, clean, adjust
  • Cleats – wear, tightness
  • Wheels – check spoke tension
  • Bolts – steerer, handlebars, seat post, saddle, brakes, bottle cages, mud guards, gear mechs , jockey wheels, chain rings
  • Gears- check indexing, cassette and chain ring wear, hangar for alignment. Jockey wheel wear
  • Lube – brake pivots and adjusters, quick release, gear mechs, gear cable adjusters
  • Saddle bag – check contents are not absent, damaged or rusty!

Tools required

  • Hex /Torx keys
  • Chain wear tool
  • Rags – especially old socks!
  • Lubricants
  • WD40 or GT85 to clean with

Dr David’s how to’s

Check brake pad wear – pads usually have grooves moulded into them. When they have worn away to a flat surface it is time to replace, especially if less that 2mm of pad left. Visually check the whole length of the pad on both upper and lower surfaces. Remove the wheel to get a better look if required.

Check Rim brake pad alignment – Look from the side and ensure all of the pad contacts the rim braking surface when the brake is applied. Adjust by slightly loosening fixing bolt and twisting to correct angle. Warning – brake pad overlapping the rim can rub the tyre and cause a blow out!

Periodically remove the pads and check for metal and grit embedded into the brake pad. Remove fragments with something pointed like a penknife tip. 

Use the cable adjuster to ensure you can apply full pressure to the brake lever without it touching the handlebars. Before you reach the limit of the threaded adjuster use the cable clamp to pull through some cable.

Check Disc brake pad wear – Remove the wheel and inspect the pads using a torch. There should be 1mm of pad viewed from all angles.  DO NOT USE THE BRAKE LEVER WITH THE WHEEL OUT!  Check  pad wear against manufacturers guidelines. (Shimano“…if the brake pads are worn down to a thickness of 0.5 mm, or if the brake pad presser springs are interfering with the disc brake rotor, replace the pads”.  SRAM – “Inspect your brake pads regularly to ensure that the overall thickness of the individual brake pads measures at least 2.5mm thick including the pad’s backing plate. When a rotor measures less than 1.55mm thick it needs to be replaced.)

Check disc brake lever travel and feel – As disc brake pads wear, cable operated brakes need adjustment. Hydraulic brakes are self-adjusting.  I you need to pull the leaver all the way to the handlebars to stop, you will either need to adjust the cable or for hydraulic brakes they need bleeding (and fluid change).  The feel should be firm not spongy!

Check wheels for true by simply spinning and looking for any side to side movement. Easiest seen between rim and brake pads. If there is a more than a few millimetres of sideways deflection the rim may rub on the brake pads. For disc brake wheels hold a plastic tyre lever against the forks 1-2mm away from the wheel rim and check.  If the rim is bent it will need truing at a LBS (Local Bike Shop).

The wheel should spin freely without any roughness or grinding noises. This could indicate bearings in need of service.  Also lift bike and try to move wheel in a side to side movement to check for play in the bearings. Most wheel bearings are easy to adjust with the correct tools. Or visit LBS.

Ensure the wheel quick release is tight and also not seized.  Typically you finger tighten the quick release screw side while the handle is in line with the axle. You should then be able to push the lever through 90 degrees to clamp closed. Lubricate the QR with winter chain oil and apply a smear of grease to the axle and threads and springs. Periodically remove through axles and lubricate according to the manufacturer’s guidance.

Check tyres for damage and wear. Damage may be obvious like cuts and woven carcase showing or may be a subtle deformity that is only obvious by spinning the wheel. Visually check the tyre. Remove any stones or glass from the tread. This is best done when both inflated and deflated – when you can pinch the tyre to expose the flint/glass. Deep cuts will require a new tyre. Check for wear. If you see any tyre carcase change the tyre!

Tyre pressure.  Most people have their preferred pressure.  Tyres are marked with a min and max pressure. Stay within the manufacturers recommended range. Typical 25mm tyre pressures would be around 85lbs/psi (5.8Bar) to 100lbs/psi (6.8Bar) depending on rider weight. See this Schwable chart.

tyre pressure chart
Schwable tyre pressure chart

Chain wear creeps up on us! Invest in a chain wear tool (less than £5) and use it. By changing your chain at 0.75% wear it is possible to get 2-3 chains per cassette. Let your chain wear get beyond 1% and you will automatically be changing both chain and cassette at the same time (expensive!).

By regularly cleaning your chain (using an old sock and toothbrush) it will last longer as will the front chain rings and cassette. While cleaning, check for any broken or stiff chain links.

Lubricate with proper chain oil with wet lube in winter and dry lube in summer. The part of a chain link that needs the oil is between the rollers. Apply oil to the edge of each roller so that capillary action pulls it where it is required. See Dr David’s chain faq.

Jockey wheels – these should rotate freely and not wobble about. They tend to get a build-up of caked-on oil and dirt. Clean them!  If they are stiff they can be taken apart, cleaned and lubricated. Wobbly bearings need replacing!

rear mech
Rear Mech

Cables wear over time. Visually inspect. Check for smooth function. Replace if worn/frayed. Keep them clean especially around rear dérailleur. A light coating of oil or grease helps prevent rust. Damaged cable outers let in water.

David’s BIG TIP!  For bikes with external cabling it is easy to clean and lubricate the rear gear cable.… Change into largest rear sprocket.  With rear wheel stationary push gear lever as if changing to small sprocket. This will slacken off the gear cable. Now release the cable from the guide on the chain stay. Clean the gear cable all the way up towards the cranks. Now slide the cable outer up the cable and clean the exposed cable. Slide the outer up and down a few times and keep cleaning. Lubricate with DRY chain lube. Replace the cable in the guide and finally turn the pedals. Smooth gear changes restored!

Headset play may manifest as juddering when the front brake is applied or a rattle over rough road surface. On modern bikes the steerer tube is held in place by bearings top and bottom that are held under mild compression. As you can imagine the bottom bearing gets a hammering over rough roads and spray. The top bearing gets wet from sweat and rain! Check for smoothness when turning the handlebars, any grinding or uneven rotation suggests worn bearings. Check for play by applying the front brake and gently rocking the bike forwards and back while looking and feeling for any movement or clicking. Adjustment or bearing replacement entails using a torque wrench. Ask a friend or visit LBS.

Pedals do actually wear out! The bearings may wear or become stiff, the spring-loaded mechanism wears, so does the platform and also under the hoop at the front. If your new cleats are wobbly it’s probably time for new pedals!  Routinely check the tightness of the pedal axles (remember that pedal threads are different from left side and right side. The right side pedal (as you look at it from the outside) has a right-hand thread (removes ant-clockwise, installs clockwise). The left side pedal has a left-hand thread (removes clockwise, installs anti-clockwise). Clean and lubricate your pedals.

Cleats. A not uncommon sight on our roads is cleat bolts and washers! Check the cleat bolts for tightness. Check your cleats for wear. Some brands do have wear indicators. If the cleat feels sloppy in the pedal or looks visibly tatty then replace it.

Wheels – check spoke tension especially if the wheel creaks or twangs while cycling. Also, if the wheel is not true (see above). Pluck every spoke to check they all make a similar note. Loose spokes will rattle or play a lower note. If you have a spoke key, try tightened by ear while making sure the wheel is not buckling. If in doubt see your LBS.

Bolts – steerer, handlebars, seat post, saddle rails, bottle cages, brakes, brake pads, chain rings, mud guards and dérailleurs. Steerer and stem bolts usually have the correct torque setting engraved on the stem. Similarly, the seat post bolt. It is worth investing in a low range torque wrench. You can buy reasonably priced tools pre-set at 5Nm/6Nm. Work your way along the bike checking tightness of all bolts. See pic.

Torque wrench

Gears– If your gears are working well and the cable is not damaged or worn then leave the gears alone!  Visually check the cassette teeth and chain ring for wear. Symptoms of wear are chain jumping and problems changing gear. Visible signs of wear are elongation of the valley between the teeth (B) and, typically on chainrings, sharpening of the teeth (A). By this stage you will require new chainrings and chain and probably cassette – Ouch! See images (X= relatively normal tooth – note relatively long flat top).

cassette teeth
chainset tooth profile

Poor gear changing may indicate a bent rear dérailleur hanger. To correct this, you need an alignment tool or see me!

Lubricate check-list. Brake pivots and adjusters, quick release mechanism, front and gear mechs (parallelogram and cage pivots see diagram), gear cable barrel adjusters, clean and lubricate cable guide under the bottom bracket.

Saddle bag – check contents are not absent, damaged or rusty! Friction between contents can wear holes in inner tubes (from my own experience!). Inner tubes perish. Tools get rusty. Pop some nitrile gloves in there and have clean hands after the next “mechanical”!!

Prevent seized components – every 6 months or so.

Seat post and clamp. Take out your seat post (having wrapped some tape just above the clamp to mark the position) and lubricate with carbon paste for carbon post or frame, grease for aluminium. Don’t forget to lubricate the clamp and bolt.

Handlebar and steerer bolts. These are subject to sweat and rain so remove one at a time, clean, lubricate and replace to correct torque.

Don’t ignore cable adjusters (inline and down-tube), skewers, bottle cage bolts. 

Pedal off – Pedal on!

Pedals take a lot of abuse (weather and crud from the road) and are designed to last for many miles. They are rarely removed before they wear out unless removing for transportation. When it comes to removal many get confused as the left pedal has a “left handed” thread i.e. it tightens anti-clockwise.

Alway use plenty of grease when fitting pedals.

Don’t leave it until the last moment if you need to remove pedals e.g. fitting in a bike box. You may require a lot of force and a large spanner/hex wrench. The weeny multi-tool may not be be up to it.

Don’t forget to pack the tool in the bike box to re-fit the pedals!

Shimano pedals typically use a a 15mm spanner or/and 6 or 8mm hex. Look pedals use 8mm hex.

The image and download below should help.

How to install detailed maps on an older Garmin – for (almost) free!

Maximise the functionality of your Garmin for navigation

This applies to the Garmin Edge 520/705/800/810 GPS devices

I recently helped out one Dittons Velo rider to install a map on her Garmin 810 before a trip to Mallorca. Whilst there, she intended to explore unknown countryside and hills. On her return she loaded a UK map. In three years of Garmin ownership, she admitted that she had never seen a decent map with road names on her Garmin!

If you’re a Garmin user (see list above), it’s likely you’re using the device with it’s very basic map. If all you ever want to do is record an activity – where you have been,  speed and other statistics – then it’s absolutely fine and you can stop reading now!

However, if you want to use your Garmin to navigate a route (there are plenty to download from the DV web site!) you’re going to need a better map; one with road names and more details!

Basemap

openstreetmapbasemapAs shipped, the above Garmin units come with a “basemap” installed. If you zoom in to the map you see very few details apart from some main A-roads and rivers (compare the images)! On those devices apart from the 520 you can add a detailed map via a micro SD card (see image below).  Newer devices including the 820, 1000 and 1030 have a navigable Europe map factory installed. For 520 instructions see below.

The good news is that maps are easily available: options include purchasing maps on an SD card or via download, from Garmin for £35 (as of November 2018) or Ordinance Survey  1:50k Full Country SD Card for £109.99!

The Free map option…

Alternatively, if you have a microSD card with a capacity of 1GB or larger (I found one in an old phone), you can install the incredible and free OpenStreetMap map https://www.openstreetmap.org/about https://en.wikipedia.org/wiki/OpenStreetMap
You can buy an 8GB SD card for under £4 online – it doesn’t need to be a digital video, high speed SD etc card.

To install the map you simply need to download the map as a gmapsupp.img file and copy it to the microSD card in a folder named Garmin (there is not enough free space in the main memory). Make sure your computer is set to show file extensions.

sd slot

There are detailed instructions available to follow on the internet e.g. https://www.dcrainmaker.com/2013/05/download-garmin-705800810.html

You can even create custom maps at http://garmin.openstreetmap.nl/ or download a range of ready-made maps for free at http://alternativaslibres.org/en/downloads.php#Europe

The Edge 520 has no Micro SD slot and not enough internal memory to add a gmapsupp.img file. A hack is to replace the gmapbmap.img (Garmin base map) file found in the Garmin folder with a gmapsupp.img file that you then rename to gmapbmap.img after saving a backup of the original Garmin gmapbmap.img file.

If you are lucky enough to travel abroad to cycle, simply download and install a gmapsupp.img file for the destination country before you travel (remember to change it back on return to the UK!).file structure

With a 16GB microSD card I keep a number of gmapsupp.img files on the card and simply rename them when required (see screenshot). Note the current gmapsupp.img file in use is a custom area of South of England only.

Happy navigating!

David Matthews

November 2018

SRAM Front Derailleur with YAW setup guide: by David

After struggling while setting up my gears on two bikes with SRAM Force 22, I had to resort to searching the web for guides. Having realised it’s easy when you know how I’ve put together this guide on how to set up the SRAM front derailleur…Success guaranteed!

You will need 4mm and 2.5mm hex (allen) keys. Familiarise yourself with the various bolts (see below) before starting.

Step 1: Height of the front derailleur: Ensure cable anchor bolt is loosened. With chain on the small ring adjust the height of front derailleur so that the outer plate of the derailleur cage clears the tallest tooth of the large chain ring by 1-2mm (loosen front anchor bolt and use a coin or the guide line – as indicated in the illustration to the right).  Use the inner limit screw to position the outer derailleur plate.

Step 2: Turn the inner limit screw (the one nearest the bike frame) while pedalling until the chain shifts up into the large chain ring. If necessary undo the outer limit screw a few turns.

Step 3: Alignment – To properly align Front Derailleur, line up the hash marks at the front and rear of the derailleur cage  (see illustration to the left) with the centre of the large chain ring teeth (even easier if done before fitting the chain).

Use the inner limit screw to make lateral adjustments and the front anchor bolt to make rotational and height adjustments.

Step 4: Set outer limit. Shift into smallest rear cog. Adjust the outer limit of the front derailleur by turning inner limit so there is a 1mm clearance between outer plate and chain. Now turn outer limit screw clockwise until you just feel resistance.

Step 5: Anchor the front derailleur cable. Screw in the the barrel adjuster (often in the cable at the handlebars) to slacken the cable. Make sure the the changer is in the large chain ring position before pulling cable tight and anchoring the cable with the anchor bolt. Take up any slack in the cable using the barrel adjuster.

Step 6: Set inner limit. Use the shifter to release the cable tension by downshifting, as you would for a shift into the small chain ring. Shift the rear derailleur into the largest cog. Back off the inner limit screw while pedalling, to shift the chain down. Continue to back off the inner limit screw until chain noise disappears then turn screw another 45 degrees.

Step 7: Check to see that the derailleur is shifting properly and make small adjustments as necessary to dial in the shifting. Use barrel adjuster as necessary.

Step 8: Install chain watcher so that it is as close to the chain as possible when the chain is in the small chain ring up front and the large cog in the back without the chain watcher actually touching the chain. Slacken the fixing screw slightly and tweak the adjuster screw while applying inward pressure on the watcher then tighten fixing screw. Caution – it may move a little while tightening the fixing screw.


Front derailleur bolts and chain watcher fixing

chain watcher fixing
front mech screws

 

Having seen a number of methods online, the above is a distillation of a few of them. If seeing a video helps, this GCN video is the closest to the method I describe above.

If you wish to print off a set of these instructions to make it easier in the workshop, you can download this PDF: SRAM FD setup Version 4

Updated May 2020

Roll on: Part 2 of EVERYTHING about Tyres

This is the second part of the two part FAQ feature on bike tyres from Dr David
If you haven’t read the first one, I recommend you see it here before reading this second installing episode…
By the way, some people have responded to ask: so which tyres do I buy? As before, we’re not telling you the right brand, but if you want to know a selection of what we use, contact us and we will drop you a list

road-tire-rolling-resistance
Click to see a larger version of this graph

Rolling resistance Some tyres roll faster than others and sometimes you can feel the difference. As stated in the previous blog, the faster you go the more wind resistance is the overriding factor slowing you down. As the drag due to wind resistance increases with the square of the velocity, the frictional losses of bearings, chain and tyres pale into insignificance. But why waste 40 watts on inefficient tyres? Tyre construction and pressure play an important part. Fine flexible tyres that deform easily are more efficient than thicker walled tyres. Extra puncture protection layers may also increase rolling resistance.

The Coefficient of rolling resistance (Crr) has been studied and quoted by numerous web sites and manufacturers. The study methods are never the same but there are some group tests. Looking at this chart you could lose 20 watts per wheel by using a GP3000 rather than an Open Corsa Evo CX!

Compound
Softer rubber compounds generally grip better than hard. But who wants a tyre that is super grippy and only lasts 500miles? One solution is to have a harder compound in the centre of the tyre and soft compound on the sides of the contact area to give grip in the bends e.g.Vredestein Fortezza TriComp. There are dual and tri compound tyres available especially as winter tyres. Continental promote their “Black Chilee” compound which seems to come out well in tests but there are others.

Weight
Lightweight tyres will accelerate better but generally are less robust and wear out faster. Not all lightweight construction will have a lower Crr though.
Winter tyres. The rain and wind spread all sorts of rubbish onto the roads so puncture resistance is essential. Various manufacturers have their own solutions including Kevlar, Duraskin, V Guard etc. When the rain comes we want grip so a good compromise is dual or triple compounds.

Butyl vs. latex inner tubes
As the tyre rolls it deforms which affects its rolling resistance. The inner tube has to be deformed as well and there is friction between the tube and the tyre. More flexible and lighter latex tubes are more efficient and produce a lower Crr by 10% but this is dependent on weight. Latex tubes are more porous so go down faster. They are also more prone to failure due to contamination with oil etc and they have been known to explode!  Read about the myths of punctures.
Some say they are more comfortable.

Wrapping up
It is all a matter of compromises. A few points stand out though:
opencorsaevo

  • 25mm is the way to go unless you are time trialling
  • Use the spreadsheet to work out ideal pressures
  • Do not over-inflate tyres
  • If your ride is uncomfortable and you are vibrating then they are overinflated
  • Some tyres roll faster than others
  • If you keep getting punctures it is time to try another tyre
  • Use tyres that you are comfortable with and have confidence in.

References/ further reading:
http://rouesartisanales.over-blog.com/article-1503651.html
http://www.terrymorse.com/bike/imgs/rolres.gif
http://janheine.wordpress.com/2012/06/13/bicycle-quarterly-performance-of-tires/
http://www.slowtwitch.com/Products/Things_that_Roll/Tires/Fast_Tires_2013_3787.html
http://roadcyclinguk.com/gear/buyers-guide-winter-tyres.html
http://hubpages.com/hub/The-Best-Road-Cycling-Tyres-For-This-Winter
http://www.bikeradar.com/gear/article/bicycle-tires-puncturing-the-myths-29245/

2014: will it be a Goodyear? EVERYTHING about bike tyres

Dr. David continues his series of useful tips on keeping your bike in tip-top shape. This article covers everything you need to know about bicycle tyres and is being published in two installments. Here is the first:

Welcome to my cycle tyre FAQ Part 1

First thing to say is, I’m not going to recommend any specific tyres. We all have our favourites!

Tyre pressure – is higher better?
Yes and no!

On a smooth surface in a lab, higher  pressure can mean faster but the benefits get smaller the higher you go, especially over 130psi (pounds per square inch). Lower pressures are more comfortable and by allowing the tyre to squash more provide a larger surface area in contact with the road and hence more grip. As the rolling resistance of a tyre is mostly produced by the friction in deforming the sidewall then underinflated tyres waste energy. Some people have studied the ideal pressure for performance and grip and came up with the 15 percent rule.

Download the Bike Tyre Pressure Calculator – (created by Bike Tinker)

rubino_cutaway

How much pressure?
100psi means that the air in the tyre is exerting an outwards force of 100lbs per square inch. So if you load that wheel with 100lbs the tyre will deform to a contact area of 1 square inch to carry the load. A lower pressure of 50psi will require 2 square inches to support the 100lbs load. That’s why giant mining earth moving trucks have very large tyres which spread the many tonnes over a large area. Too low a pressure will mean pinch or “snake bite” punctures.

The weight of a cyclist is more over the rear wheel so that needs to be a higher pressure than the front. Time trial bikes move the rider forwards and may put more weight on the front wheel. If necessary weigh the front and back wheels with you in your riding position.

It seems that to go faster, you need high pressures. Track bikes may use in excess of 220psi on the smooth wooden velodrome but road tyres often have a maximum recommended pressure of 120-135 psi. On uneven roads, high pressures make the tyre roll up and down every little bump effectively going up and down tiny hills and shaking the bike. This uses energy and slows you down. Having some give in the tyre and smoothing out the rough road surface improves rolling resistance. Importantly, added to this is the effect on the power source (cyclist) that vibration drains power sometimes by hundreds of watts (the tank driver effect).
See this article for more on tyres and pressure.

23mm v 25mm which is faster?
For the same tyre pressure a 25mm tyre has less rolling resistance. Seems a bit odd, but true. The slimmer the tyre the longer the contact patch and the more of the sidewall is deforming and therefore wasting your energy. But the faster you go the more wind resistance becomes the dominant force you have to cycle against. So a narrower tyre gives less wind resistance especially on the front. Also, 23mm tyres can be run at higher pressures. In general 25mm is a better all-round tyre.

ultremoaqua

TPI – is higher better?
High threads per inch is often seen as a mark of a better tyre. The carcase is made up of woven material which is then impregnated with rubber. Cheap tyres will have fewer, thicker, fibres probably of nylon while lighter expensive tyres will have a very fine weave often made of cotton. Lightweight cotton is less resistant to sidewall punctures but is lighter and more flexible and hence faster. Thicker nylon is much more resistant to wear and punctures. Finer more flexible tyres roll faster due to less energy wasted in deforming the tyre.

Tread
Most racing tyres are smooth and some winter tyres have a tread. For riding on a road tread is not required for grip. Obviously off-road tyres need a knobbly style tread to grip earth and mud. Car tyres are wide and have a flat radial tread formed by steel belts. They need tread to allow water to escape from between the tyre and a wet road to prevent aquaplaning. Bicycle tyres are narrow and cut through the water so a tread is not required. As with many things, Sheldon Brown’s site has some useful information on this.
Smooth tyres roll better than coarse treaded ones.

The next part of Dr. David’s tyring blog will reveal the truth about rolling resistance, the choices of compound and weights for a tyre, and inner tube choices —

 

Dr. David’s bike chain FAQ

Having suffered a broken chain at the start of a recent ride (and dashed home to quickly replace the chain), Dr. David uses his hands-on home bike repair knowledge to share some tips on how to keep the chain in tip top condition – especially important in Winter:

David’s Chain FAQ:

The chain is an important part of the bike delivering the power from you to the back wheel. There are lots available for the different chainsets and number of gears. Ensure you purchase the correct chain for your bike and look after it.

Q. Aren’t chains getting skinny now we have 11 speed. Won’t they stretch?
A. Chains have got slightly narrower over the years from 8 speed (7.1mm) to 10 speed (6.2mm). They do not stretch but the bearing surfaces do wear over time and will need replacement.

Q. I’ve been doing a lot of weights in the gym and worried I may break my chain!
A. Chains have been around for years and are a mature technology. Quoted tensile strengths are in the regions of 8-10KN (1 tonne). You will not break it. If a chain is damaged it may fail. Are you training to take on Cav!

Q. I’ve been told that Brand X is much longer lasting than my Shimano chain. Is this true?
A. Some bands of chain do wear better than others. Connex and Campag seemed better than SRAM in a Wipperman test in 2010. Try different chains and judge for yourself.

Q. I always use a Brand X because it is faster than Brand Y. Am I kidding myself?
A. Yes! We are talking miniscule percentages. All chains are >90% efficient even without lubrication or special coatings!

Q. I was told by my mate to use Castrol GTX on my chain as his local garage said it is synthetic so must be better. Is it?
A. Don’t use car engine oil on your chain/bike. It contains additives including detergents that will harm your chain and bearings.

Q. Isn’t a good idea to clean your chain in eco-friendly detergent and then re-lube it after every ride?
A. Chains are assembled with a coating of very thick grease to all internal bearing surfaces during manufacture. This is the best possible lubrication. It will wear out. Don’t wash it away prematurely with solvents.

Q. Are sprays better than liquids for lubrication?
A. Sprays tend to have the lubricant mixed with the propellant or other carrier liquid/solvent. These can harm the internal grease. It is better to use a good quality liquid and put it where it is required and not sprayed over the tyre and braking surfaces!

Q. How do I clean my chain?
A. As above it is best not to use harsh solvents and chemicals. You can get fancy cleaning baths which work well. Also a brush and a rag work well to get off the surface grime and grit. I find an old sock works well to get of the outer layer of crud! Also using oil to clean it avoids damaging the internal lubrication.

Q. How can I tell when my chain needs replacing?
A. Chains wear as the internal bearing surfaces wear (see diagram below). They are considered worn out when there is 1% wear. Buy a chain wear gauge and use it often.

Q. My bike shop says I need to replace my cassette when I replace my chain. That is expensive! Is it necessary?
A. When a cassette and chain are new the chain sits snugly in the teeth and valleys of the sprocket. The pressure is spread evenly across all the teeth. As the chain wears it tries to ride up the teeth and exerts more force in the teeth nearest the large chain ring (pedals). This causes wear and it elongates the valley and the teeth get slimmer. Over time the chain will start to cause the teeth to become hooked. Eventually the chain will jump. If you replace a chain before it causes damage then you may not need to replace the cassette as well. Ultimately the cassette sprockets do wear and need replacing. In my experience I get 3 chains to 1 cassette.

Q. Does oiling my chain make me go faster?
A. No! Chain drive is 90-98% efficient. Different oils and greases have miniscule effects on performance. (See below). Thick, sticky winter oils tend to attract the dirt but resist the winter wet and muck. Dry lubes are probably better reserved for the summer. Tests show that the different lubricants have no significant effect on performance. A “dry” chain has the same efficiency and one soaked in snake oil!

Q. Spinning along in the small front chain ring is more efficient isn’t it?
A. You are wasting energy. Studies have shown that using larger sprockets is more efficient. There is a 3% difference between an 11 and 21 tooth in favour of the 21. There is also an increase in efficiency with increased tension of the chain (3% improvement from 100 to 175watts). So you are better off powering along using the large chain ring!

Q. My Dad said never to ride with a large chain offset. Does it waste power?
A. Being in the large front chain ring and large rear gear would appear to put a strain on the chain. It may cause more wear. Studies have shown no loss of efficiency though.

Q. How do I lubricate the internal joints of a chain?
A. The manufactures do it while it is being assembled. Oils will find their way in due to capillary action. Silicone/PTFE in dry lubes (that come out wet!) will be carried in by the volatile carrier which then evaporates. In some circles people boil their chains in wax. I can remember my mate heating his motorbike chain in a pot on the cooker. The theory is that the heat expands any air in the joints and as it cools it contracts and sucks the oil/grease/wax in. I have not tried it with my cycle chains.

Chain construction Below you can see the construction of a cycle chain. The pin(3) goes through the inner plate(1) which has “shoulders” that form a bearing surface with the pin(3) on the inside and the roller(4) outside. The force is transmitted through the roller(4) and to the pin (3) via the inner plate (1) “shoulders”. The pin(3) is fixed to the outer plate(2) . The inner plate is the one that mainly wears.

chain