Tuesday, July 31, 2012

Rear Derailleur Capacity.

     Any derailleur will work back there, right? Wrong... I have lost count how many times someone has come into the store after swapping out or, upgrading a rear mech., only to find that it now does not work properly. When I ask if the derailleur capacity matches their setup, I usually am greeted with a vacant stare.
      So, before yanking off chains and clipping cables let us take a moment to work out what you need to put back there.
      Before we do the math, (yes, there is always math), it might be helpful to clarify exactly what a rear derailleur does. I imagine most people can see how it operates to change gear, you make a gear change at the shifter and the cable that connects to the derailleur pulls it side to side and derails the chain from one cog to another, simple. The other thing it does, that is equally important but possibly not as readily understood, is to take up the slack in the chain and keep it tensioned correctly.
       Why the hell is there any slack in the chain you ask? Because each gear combination requires a specific chain length to wrap around the selected cog and chain-ring. When you select the big ring at the front and the big cog at the rear, the chain wrap is at its longest. Conversely, when on the small ring and small cog it is at its shortest. The difference between these two extremes is the amount that the rear derailleur has to be able to handle. The Chain Wrap Capacity.
The math;

(No. of teeth on big cog - no. of teeth on small cog) + (No. of teeth on big ring - no. of teeth on small ring) =

For example;
cassette 12-25 and crank-set 53-39
25 - 12 = 13
53 - 39 = 14
add them together 13 + 14 = 27.
So 27 is your chain wrap requirement that the derailleur needs to be able to handle.

      The way that the derailleurs are made to handle larger capacities is primarily by increasing the distance between the jockey wheels. This is often referred to as cage length and you will see terms like, short cage and long cage used to describe different models. However do not just assume a mid cage will handle what you have, always refer to the actual chain wrap capacity figure that is published with every model and make out there to be sure

       Happy shifting..

Sunday, July 29, 2012

Adjusting Rear Derailleurs.

It seems that the temptation is great to mess with those little screws on the back of your derailleur when the shifting has gone off the boil. While I'm not suggesting for a minute that you should not attempt this adjustment yourselves, trust me when I tell you that you will not get a satisfactory result by just screwing with the, err screws. You need to follow the steps which I shall outline for you below.

Before we get to messing with limit screw adjustment I will assume that you have checked to see if your problem lies with just a slack cable, which is easily taken care of with a 1/4 turn or two of the barrel adjuster.

The picture on the right shows you the three adjustment screws that reside on your rear mech. From the top we have the B limit screw then the High limit screw and on the bottom the Low limit screw.

The B limit screw adjusts the height of the derailleur another way to look at it is the clearance between the cogs of your cassette and the top jockey wheel. Often the clearance is good until you change into the large low gear cogs and then you start to get a rumble as the jockey and chain is bumping along the underside of the cassette cog. If this is happening on your setup just turn that screw in clockwise to increase clearance. ideally we are looking for a gap of about 4-6mm. Sram works best at around the 6mm mark. Anyone using a Campagnolo system may have to search for the B limit screw, they have a few models with the screw mounted on the pulley cage behind the body and hidden from view.

If you have clearance Clarence on the jockey wheel and your problem is more on the indexing, then you need to check the adjustment of the H and L limit screws.

Firstly loosen the pinch bolt on the cable to release it. Turn the pedal to bring the derailleur to its relaxed position which should position the jockey wheel under the small cog, the high gear on the cassette. If the derailleur shoots inward and comes to rest under the big cog, low gear, then you have a low normal derailleur. These are sometimes found on mountain bike setups. Whatever you have the principles are the same and  I will cover them both. If the derailleur has come to rest under the small cog place a screw driver on the H screw, if it rests under the big cog then the Low limit screw. Stand behind the bike and adjust the screw in and out to center the jockey wheel perfectly under the above cog. As you turn the screw you will see the mech. move from side to side, use that movement to center the jockey wheel perfectly.

Now it gets a bit tricky. You have to cycle the chain through while shifting the derailleur to its other stop. The picture to the right shows it centered under the big cog or Low gear. Again stand behind the bike and use the low limit screw, for a normal derailleur, to center the jockey wheel perfectly under the cog. All the while keeping the derailleur pushed to the stop by hand, as you turn the screw in and out you will feel the pressure in your hand and see the derailleur move from side to side. Once you are happy with the adjustment cycle the chain and let the derailleur come to rest.  Now turn your barrel adjusters in and make sure that you change gear on your shifters to let all the cable out. Pull the cable taught and attach with the pinch bolt. Now try it out. If you shift at the handlebars and nothing happens at the rear then take a\ little slack out with the barrel adjuster. Try again. Keep doing this until you get crisp shifts all the way up and down.

If you are sure of your adjustments and still the shifting is not as it should be then you may have some other problems. Most common is a bent derailleur hanger, which can be aligned, but takes a special tool to do so. Come see us and we can take care of that for you. Another possible cause is a bad cable or contamination in the housing. Easily rectified with a nice slick new cable and a couple of feet of Jagwire housing. Again we can hook you up.

It's Hot Enough To...

The other day we received a call from a couple on the trail, about 5 miles east of Jefferson City. They were suffering from a serious attack of flats and finally a split tire. Through the wonders of Google and an I Phone they came to us.
       10 minutes later I am in the pickup heading over the river. Now I don't mean to whine but, it seems the only time I get called out is when the temperature is about 30 degrees above or below my comfort zone. Today's temp of 105 put it quite handsomely in the above category.
       Luckily they were in the open and easily spotted, unluckily they were in the open and I was about to get cooked. By the second handshake my eyeballs are sweating and I'm eager to get started. Without further ado the problem bike is flipped over and I'm pulling wheels.
       Now I'm not new at this tire changing thing and, whilst I'm not professing to being the faster tire changer in the west, I ain't the slowest either and my thumbs have pushed so many errant tires onto rims they have developed callouses. So you can imagine my surprise when, after pushing the front tire on, my hands and, especially my thumbs, are not just sore but downright painful.
        The rims were so hot both thumbs had developed large blisters. By the finish of the rear tire and tube change the skin had all but gone on one.
        Anyway, the job got done and the couple was very happy, although being happy in 105 degrees did make me question their sanity somewhat, but it takes all sorts. By the time I got home I figured I'd need a skin graft and a week off, Pam settled on a small band aid and told me to get back to work.
        So, here's the thing. I brought the old tires and tubes back to dispose of them and, on closer inspection those tubes suffered in the heat. The rubber definitely felt different and the valve stem needed next to no encouragement to eject itself. In this triple digit heat of late and bikes being left inside cars we have had quite a run on tubes. So try and be careful when leaving bikes in the heat. Maybe let some pressure out of the tires and be careful when removing the pump head after inflating them.
        Now, excuse me while I go and soak my thumbs...

Friday, July 27, 2012

New Raleigh Tri Bike.

Some exciting news for budding triathletes looking for their first dedicated Tri bike. Raleigh has introduced the "Singulus". It is tough finding a Tri bike that you do not have to sell a kidney for, up to this point all of the ones that have left this shop have been custom builds. So we welcome this new offering. It will be part of the 2013 range from Raleigh, we will keep you posted, I expect the 2013 lineup to become available later this year.

Thursday, July 26, 2012

Lube Responsibly.

I spend a good portion of my days in the workshop with a thin bladed screwdriver in hand chipping away at derailleur jockey wheels  and chain plates removing great clods of greasy muck.
      It seems that riders fall into two main categories when it comes to lubing the drive-train. The "I lube every March 8th in a leap year" crowd or the " I use a whole bottle of lube per ride" bunch. While both scenario's are sad sights to behold, the latter is the toughest to clean.
      So with the hopes of prolonging some chain and cassettes lets go over correct lube procedures. Firstly let's start with a good clean, if you are a serial luber this may take a while. I use a product called "Simple Green" to good effect, available at all the usual hardware stores, if all you have is dish soap then that will work as well. Remember whatever you use as a degreaser must also be washed off as well. Just flush everything with clean water and let dry.
       Now, lube choice. So many options to choose from but here is the rule. Dry conditions use a dry or wax lube and conditions are definitely dry at present, wet conditions use a wet lube. Really though the dry lubes are so good now that I recommend using them all the time. The only time you need consider a wet lube is if you plan riding your bike up the Amazon.
       Besides the wax lubes being good at lubricating they also, being dry, attract less dust and debris. Another plus point is the ability to re-apply a second, third and probably a fourth application of lube over the top of the existing coats before having to clean the chain to start fresh. Just wipe the chain down with a clean rag and apply the lube. When using a wet lube you must clean thoroughly before a fresh application. In these dusty conditions a freshly wet lubed chain will look like a ships anchor chain after a 20 minute ride on the trail and all that dusty mess will act like sandpaper on your expensive drive-train.
        Whatever your choice of lube and, regardless of make and type, show a little restraint when it comes to applying it. Go for the delicately dripping a drop on each roller approach rather than the squirting back and forth method. There really is no need to flood the whole thing to the point of drowning it. Also, no need to squirt the cassette either, all that does is pack down between the cogs and requires digging out with the trusty flat bladed screwdriver.
        So there we have it, follow these guidelines and you will be lubed to perfection.

Tuesday, July 24, 2012

Great Hub For That Classic Look

VeloOrange "Grand Cru" Front Hub.
A company that we are becoming more impressed with each time we use their products is Velo Orange. The picture above is one of their high flange hubs. Superbly made and looks beautiful too. We have used them a few times now and they build up very well, they also come with quality bearings as standard, you would not believe how many hubs that we use needing a bearing  upgrade before sending them out, these however feel slick and have good seals on them. Velo Orange also produces some headsets, a range of handlebars and lots of other nicely machined parts, all with the same quality build and style. There are a small range of leather saddles too that look and feel every bit as good as a Brooks. I know it is sacrilege for a Brit to say such a thing... Check out their website at http://velo-orange.com/ or let us know what you are interested in.

Monday, July 23, 2012

The New Web Site. Finally...

Well after a marathon session at the keyboard and a lot of help from the good folks at Yahoo we finally managed to get all the new files for the website uploaded and in their correct directories. Honestly I was about 2 minutes from calling it quits and going back to posting notices to the front of the store, however, we got there in the end. As usual I would appreciate some help spotting errors, typos (of which I am sure there are many.) or problems with links etc.

Thank you.

Gear Inches & How To Work Them Out.

I frequently talk to people in the store who are interested in knowing the gear inch specifications for their particular setup.  With such a range of wheel diameters, chain ring and cassette choices, today’s gear calc. charts take up many pages. So it makes more sense to give you the simple formula for working out gear inches yourselves.

Make a list of all your chain ring sizes, cassette cogs and the size of your rear wheel.  Once you have all that information, set about doing the calc. below for each combination.

As an example, the calculation for a 700 road bike with a 52 tooth chain ring and an 11 tooth rear cog is as follows;

52(chain ring) X 27(drive wheel diameter in inches) =1404

1404 divided by 11(rear cog) =127.6

So the above combination gives you 127.6 gear inches, this means that with every full revolution of your pedals you travel 127.6 inches. Use the above calculation for every gear and you have your gear inch chart. Remember, the higher the number, the harder it is to pedal.

Another option is to punch in 'bicycle gear inch chart' into your search engine of choice and you will find a list of handy dandy little online calculators. These come and go and honestly by the time you fill out the forms you could have had this done.

Thursday, July 19, 2012

A New Beginning...

A catastrophe occurred during the website revamp. I seem to have deleted our blog history. Well, what's done is done, so a fresh slate. In some respects it is a good thing, old news is old news and best cleaned out once in a while anyway and it gives me a chance to update theories and findings on components and technology. Some of the posts on frame geometry and tech specs I will gradually re-post over time, as a lot of that stuff was backed up on the computer.

So here we are. Day 1, again...