Chain Stretch

My previous post referred to a replacement chain that I had to fit to my Giant Defy2 road bike. The wear on the chain crept up on me really and when I measured the chain it had stretched by 0.75% If you havent come across the phenomenon of chain stretch before, this might not seem like very much, but most experienced cyclists wouldnt let the chain go above 0.5% stretch.
You measure the length of the chain using a tool that slots in between ten or so links.of the chain. Depending on the length of those links, the tool slots further into the chain link and shows the total % of chain wear. The term "stretch" is a little misleading. What actually happens is that the chain pins wear and allow the links to be a little further apart.
This has a dramatic effect on how the chain runs around the sprockets on your bike and the most affected is the smallest sprocket on the rear of the bike.
This picture shows the 12 tooth sprocket that I have just removed from my road bike. You can clearly see that the tooth shape has changed with a distinctly different angle on one side of the tooth to the other. There also appears to be a ridge on some of the teeth where the deformed metal has literally been pushed out of the way.
This led to the chain slipping when I selected that gear. Other gears were un affected but the 12 tooth sprocket was almost impossible to use as any pressure caused the chain to ride up the worn slope and slip.
There is only one option and that is to replace the worn sprocket.
I could have simply replaced the one sprocket (most bike shops sell them for a few pounds each). I decided to use this as an excuse to enhance my gear range. The Defy 2 comes with a 9 speed cassette ranging from 25 teeth to 12 teeth. I decided to go for 28t-11t.
I ordered one from Chain Reaction Cycles but in my hurry I ordered a 10 speed cassette. Half an hour later I was checking over the order and spotted the mistake but it was too late to change the order as it was a Sunday. I rang them on Monday morning only to be told that the order had already been despatched. Chain Reaction offer a 365 returns policy (Ive since found out that all online sales have to offer this by law) but the service is fantastic! There is a return label included in the box, you fill in the form and stick it to the box then take it to a Collect+ depot - a shop half a mile from where I live. This service is free!
Anyway, the 9 speed cassette arrived on Tuesday and I am really pleased with the extended gear range.
Top tip - check your chain wear every 500 miles and dont let it get past 0.5%

Schoolboy errors

As we move towards the new cycling season, I like to give my bike a good service and check things over in a bit more detail. Unfortunately, I left this too late this year!

When I returned to the cycle sheds the other day, I was surprised to find that I had a flat tyre. I checked very carefully but couldn't find anything that would have caused it and the hole in the tube didn't look like a "snake bite" which ruled out a pinch type of problem. I should have checked things a lot more carefully!

The next morning, I had another puncture on the way to work and had to swap my tube (only took four minutes, which was a re-assuring time, its nice to know all your emergency procedures work!). This time I looked much more carefully. There were signs of wear on the tyre side-wall, and sure enough the brakes were incorrectly adjusted and had been rubbing on the tyre. The tyre had a minute hole, and a greatly reduced strength so when I later pumped 120-PSI in, the inner tube pushed through and exploded.

As I had to buy a new tyre, I bought two new ones from www.nextdaytyres.co.uk and they arrived very quickly. I bought two Schwalbe Ultremo LX tubes, in black (the coloured option was tempting but doesn't wear as well)

Whilst I was in a servicing frame of mind, I swapped the brake pads and checked the chain for wear.

Another issue! The chain was at 0.75% wear and would need swapping. I ordered a Wipperman Connex with the phosphor bronze coating. They come with a quick-link and I always found them to be very reliable. It was a doddle to fit, although I did initially run the chain incorrectly around the rear derailier! I tested it and all seemed OK and it wasn't until I noticed a problem changing gear that I checked it again carefully. It let me use nearly all 18 gears but some were a little tricky to switch to. I had threaded the chain over the derailier frame instead of under it. Once I swapped it, everything became ghostly silent. Gear changing is positive and reliable and you cant hear the chain run at all.

The 0.75% wear was a worry, and sure enough the smallest rear sprocket is too worn. The gears always skip under load when in the highest gear. I've just ordered a new rear cassette and have opted for a slightly larger size or 27 teeth rather than 25 which should make the big hills a little easier. I would have liked to go for 11 tooth small and 30 tooth large but it isn't possible with Shimano 9 speed systems.

Lesson - I need to service my bike more than once per year! As the bike is far higher mileage that the Brompton, I am scheduling a service every 1000 miles. I will make the service much more thorough than just a quick check of things. Expensive lesson learnt, its cost me sixty pounds for the tyres and forty pounds for the cassette. Both replacements are good but were done way before the old component had worn out.