"170mm or 175mm that is the question!"

So, before I get started. I've included a picture of "blow-out ridge" for your viewing enjoyment. For those not familiar with "blow-out ridge", read the older blogs. It's a great story. (Well, I'll include the picture tomorrow. I forgot to bring my camera linking hardware home tonight, sorry, I know everybody really wanted to see it. Until then just enjoy the Schwinn bike pics! :)

Okay, I have to admit a grave error on my part. It's rather funny AND disturbing. For the bike savvy read on, for the not so bike savvy, bare with me and I think I'll explain this in a way that most anybody with or without bike knowledge will understand.

So, let's start with some definitions. The crank set is the two levers that the pedals are connected to. The chain rings are the three front chain sprockets that the chain rides on depending upon with one your shifter is selected for. I've been a little bit frustrated with my smallest front chain ring. It has 28 teeth. For a mountain bike of the vintage age that I tend to ride, that is a lot of teeth for the inner (smallest) chain ring. So, I've been going around to the local bike shops looking for a smaller one. Nobody had one in stock but all of them were sure they could still order one. I looked on ebay, no vintage chain rings. Well, the ones I found on ebay were the middle ring, certainly too many teeth in that one.

Well, deep in the back of my mind I could remember having changed my crank set on one of my previous mountain bikes from years ago. I even remembered seeing the crank set on my back porch at some point in time not too long ago. And so started my search last night. It turned out that there were too many dark spaces on my porch with the dim light so I had to wait till today to look again with daylight.

So, I get home. Look so more with no success. Then I remember that I keep a few spare bike parts out in an old tin grainery and also some in the tool shed. So, I head out and take a look through all my parts boxes and buckets in the grainery and find nothing. As I jump out of the grainery and head for the tool shed I am headed off by Dad. He's needing help disconnecting a farm implement from one tractor and transferring it a different tractor because the first tractor wasn't starting. Seems the starter might have gone bad. So, I help Dad with his chore and then quickly head for the shop (tool shed) as it begins to rain. I'm digging through parts and dust and viola! I found half of the crank set. Oh well, at least it is the half with the chain rings on it. I count the number of teeth on the inner ring and again woohoo! It only has 24 teeth, just the size I was looking for. So, I take it to the back porch and remove the crank arm from the side that has the chain rings on it. I get out the measuring tape and compare the bolt spacing on the two chain ring sets and Dang! They are different bolt patterns. Hmmm. I consider just putting on the replacement crank arm and chain rings in place of the one I took off the bike. The only concern is that crank arms come in different lengths and I had remembered reading the stamped measurement of the crank arm that I took off of my bike to be 175mm. I look at the replacement piece and it is, YES! 175mm. I look at the one I just took off the bike and, NOOOOO! It's 170mm. That's strange, I think, I was sure I had read 175mm at some point in the recent past working on the bike. I look at the opposing crank arm still on the bike and it says 175mm. Ohhhh...I've been riding for nearly three weeks now with two different crank arm lengths. My back and shoulders have been more sore than I have ever experienced when biking before. HHHmmm. Maybe I will not ache so much after this. Well, I decided, by default of the only parts available that I would have to use the replacement crank arm anyway since it matched the opposing crank arm dimension. I'm thinking "I guess I can live with the crank arms not matching in model and appearance for a while. As I am comparing the one that will go on the bike with the mate that is still on the bike, I think, "these two match in appearance better than the one I just took off the bike.

Now, we must go back in time to about 6 weeks ago when I first started putting together a junk bike before buying the Schwinn frame that I have now. Well that junk bike I first started with was missing a crank arm, the one without the chain rings, the one on the right hand side of the bike. So, now that I dig deep into my memory banks, I can recall that the "missing" matching crank arm that I couldn't find today was already on the Schwinn because I swiped those crank arms from the first junk bike several weeks ago. Apparently, when I put the junk bike together I wasn't to privy about checking the crank arm lengths. Haha!

So, I have a matching crank set on my Schwinn now and I didn't even know I didn't have a matching set to begin with. That's funny. Oh yeah. I also have the smaller inner chain ring with only 24 teeth.

Oh, you may be wondering why I wanted a smaller inner chain ring? Because fewer teeth in front means the bike goes slower in it's lowest gear. And I have been powering out on some of the steeper inclines on the mountain bike trails. Now I have a mountain goat gear for the steep stuff! Cool beans.

Addendum to post: I just got back from my morning ride and the extra low gear proved to be most beneficial. I got up some small steep sections that were kicking my tail previously, as to the different crank arm lengths. I did some thinking about the "real" effect of that as I was riding this morning. 175mm - 170mm = 5mm. Now 5mm doesn't seem like a lot by itself, however the actual effect of that is 5mm lower on the bottom end of the crank stroke and 5mm higher than the top end of the crank stroke, which equates to 10mm difference between my right and left leg and 10mm equates to 1cm which equates to 0.4 inches, almost half an inch difference. Certainly substantial. I have no answer as to why I couldn't feel that while I was riding on it for three weeks. Haha.
J