Thursday, March 27, 2008

Protect the Bits

Over the past few weeks, PhattKatt has stretched her claws around the vicinity. Here too, her rider seems to be taking on the personality of the little kitty. Note also the remainder of this post... how to protect the peoples near our trikes... and the trike itself, with one simple little well worthwhile add-on.

These things are not easy to find. Whether heavy duty or even cursory duty, they come on almost all Asian built bikes and recumbents... but try to find one on a USA built production machine. You can't... not even as an option. Of course, I am talking about a Bash Guard ~or~ Trouser Guard... a BMX indispensable!

With those gnarly teeth ready to bite... or scrape... or poke anything before it, I thought it a good idea to add this protection since PhattKatt's rider, my loving wife, has learned to lift the rear wheel... or even "stunt braking" on PhattKatt. I wonder if this dare~devil behavior is being passed on through osmosis.

So with too much searching and even considering importation from Taiwan, I decided that protecting the chainring was worth the $50- investment. And it comes in very nice bling colors as well. The Purely Custom Bash Guard [apologies if the site link is poor; you can Google purely custom and go to their mountain bike area under bash guard]

And now for the important bits... the pix:

Out of the Box: Note the ~included~ chainring bolts/adapters
This is the 130BCD version. Other sizes and patterns are available... and a lot of other colors.

This bash guard is rated for a 53T chainring. PhattKatt has a 52T large ring. Pretty nice fit, don't you agree?

...and it clears the Ultegra crank just fine. The guard is a bit thicker than I was thinking too. That makes it a force to be reckoned with.

From a distance, I think its bling value alone is well worth it... $40.95 plus S/H!

Saturday, March 8, 2008

As if it was Spring, but not yet

After many wet days, we started this day as a beautiful one, sunshine but still cold.

Today, PhattKatt and big Brother ABTT had their best friend, big white beast for a ride (the dog) around the neighborhood, afterwards, we left for a little ride around the Rock Creek Trail, this time we headed west from the trail to a new neighborhood, it feels like spring, bulbs are all blossoming ... Beautiful!!!! More people outside, more bicycles around.

After all the hard technical work, replacement of the gear and all testing, today was the test drive of the new stuff, worked very well, no more struggle to climb hills, all very nice and smooth, thanks Hubby for all the hard work :)

Today another nice ride, even with some clouds it was a pleasant ride ...

Saturday, March 1, 2008

Gearing Completed

A few days ago the rear cassette was changed form the stock 11-32 SRAM PG-970 to an 11-34 SRAM PG-970. This may not seem like much but in gear ratios, it is quite a bit on the bottom end.

Remember that the last change was to replace the 30T chainring with the 24T chainring. That accounted for a 20% gear reduction. The change from 32T to 34T on the rear cassette represents another 6%. The end result is that PhattKatt now has a low end of 13.2 gear inches which is considered very low... low enough that most 2 wheel'd cycles would wobble and fall over. 3 wheels are great!

Wikipedia has a quick reference for what gear inches really means HERE

In short, gear inches shows what the virtual size of the wheel would be in terms of diameter. In PhattKatt's case, 13.2 gear inches means it is like pedaling a wheel with pedals attached to its axles and the wheel would be 13.2" in diameter. It also means that each full turn of the pedal at this ratio is 41.5" of forward motion [PI*D].

Here is PhattKatt's final gear inch chart:

Please note the crossed out ratio's. There is a limitation to the rear derailleur known as Chain Wrap Capacity as stated before. This particular rear derailleur has a chain wrap capacity of 45T [T=teeth]. This is typical for long cage derailleurs. In PhattKatt's case, we have now exceeded the chain wrap capacity by 6 teeth. To calculate this, note the difference between the cassette's smallest and largest gears and the chainrings smallest and largest gears. PhattKatt has a cassette of 11T to 34T, or a 23 tooth difference and the chainrings are 24T and 52T, or a 28 tooth difference. Add the two and you get 23+28=51 teeth... now subtract the 45T capacity and you get 6 teeth over the recommended capacity for the SRAM X-7 rear derailleur.

Take a look at what happens at the rear derailleur as we go through the gears:
[click on the image to go to the animation]

The other *mystery* to rear derailleurs appears to be chain length sizing. This is specifically important to recumbents because most recumbents allow you to adjust the placement of the pedals via the boom. Changing the boom will affect the chain length, and therefore also affects the rear derailleur significantly. Maybe the next part of this post will make it clear why this is so.

You know those fine print rice paper pages that are often included with your new bike bling? They have microscopic words on them and little caricatures that kinda look like bike stuffs... and sometimes you can recognize certain words that look like "WARNING"... "CAUTION"... and "DO NOT!"... but you are to excited to ever bother to find out what they mean? Well, this is one of those explanations.

When sizing the chain on a recumbent bike you MUST understand the ramifications of doing this wrong. Errors here could mean catastrophic failure up to and including serious injury. You don't have to take my word for it as many others have posted similar warnings which often go unheeded. You've now been warned again... so let it be said... Follow the manufacturer's instructions! ....and you can always find them online so you can enlarge the fine type to a legible level. Here we will discuss the SRAM Rear Derailleur instructions as they are applicable to PhattKatt.

SRAM states that when sizing the chain for the rear derailleur, you must size the chain by wrapping the chain around the large chainring and the large cassette gear and bypassing the rear derailleur. You want the chain to be taught when doing this. Now add 2 links to the chain. 2 links means 1"... one outer and one inner link. This will provide sufficient deflection for routing the chain through the rear derailleur and still have the full chain wrap capacity as your rear derailleur was rated for. Failure to follow these requirements, and allowing for a situation where the chain would be to short for the large/large gear combination can and will cause drive system failure which can have catastrophic effects up to and including injury! It is way to easy to brain-fart that bad combination and the drive system is all to happy to try to oblige your control command into this self destructive behaviours. Just don't do it!

Below is a picture of how the derailleur looks on PhattKatt in the 3 different chainrings while on the largest cassette gear:

In short, always make sure your chain is long enough! When adjusting the boom for a friend, resist the temptation to lengthen the boom unless you are willing to dial out the top [largest] chainring form the front derailleur. This is easy to do with the limit screw on the front derailleur.

Also note that I have exceeded the manufacturer's recommended Chain Wrap Capacity with the gearing I've chosen to accept on PhattKatt. Doing this means you have some understanding and control over the way your trike is being used. I would NEVER recommend anyone do such modifications without careful consideration and understanding the ramifications of doing so. I personally feel that on PhattKatt, this is an acceptable risk.

If lowering your gearing is needed on your trike, consider replacing your crankset to remain within the manufacturer's derailleur's chain wrap capacity. A simple solution to lowering your gearing for climbing is to purchase a crankset with 22T/34T/44T chainrings. This will provide the appropriate chain wrap capacity with your 11-34 cassette.

Until next time, keep the rubber side down.