Few videos from a weekly group ride on 2016-02-06 in Helsinki Keskuspuisto (Central park) a.k.a. HKP. The videos contain only the nicest riding, don’t worry, there was also a lot of uphill 😀
Last summer I managed to ride into a pretty severe OTB (over the bar), which resulted in a few weeks break from driving, buying knee and elbow protectors and the most severe of them all, a broken Reverb remote.
From outside I could tell that the remote had a bent piston and broken bushing. After the breakage, I could still use it a little on the rest of the ride, until it leaked too much and stopped working. The leakage resulted probably because the piston head was not perpendicular to the cylinder. Normally the bushing keeps the button level and guides the (straight) piston rod and centers it in the cylinder.
When I took the remote apart I also found that there were some scratches inside the cylinder, probably due to still using the remote after the initial breakage.
I heard/read multiple instances of people pondering if they should or shouldn’t change their tire and/or shock pressure for winter. This got me thinking how much of a change there is and should I take it into account?
Science to the rescue!
In this scenario the amount of gas ( nR ) does not change and also the change in volume is not significant. We can then derive the following equation to calculate the necessary fill pressure to achieve a desired riding pressure, based on the temperatures of filling and riding.
I have a 125mm RockShox Reverb (A1) in my Enduro bike. The bike was bought second hand and the Reverb had some sag and extended easily if bike was lifted from the saddle. So it was clearly in need for full rebuild but I was lazy and kept riding as it still mostly worked.
Then came winter weather with -10 degrees C, which was enough for the Reverb in its current condition and it didn’t stay up anymore. At home I took it from the bike and it had leaked oil (or something similar but more gooey) under it, no use trying to fix it by pumping more air.
After using the 30T oval on my 29er hardtail, I was convinced of the benefits that the oval chain ring brings to mountain biking: easier to rotate the cranks (no stalling) and the added traction from the lack of pulsating power on climbs. On other situations I didn’t even take notice that I was riding oval chain ring, that’s how natural it is to pedal!
So I naturally wanted an oval chain ring to my newly acquired 26 inch Specialized Enduro Comp (2011).
We went to a dirt track after the last mtb group ride in local forest. This was my first time in actually built jumps, but luckily I had watched some videos in the internet. Most importantly I knew to lighten the front on the edge of the jump and then steer the front back down to landing while in air.
After monitoring my current 2×10 (32-24 : 11-34) gear usage and comparing different oval chainrings I came to a conclusion, that Doval 30T 3032OCP would be good for my usage, but also ordered 32T 104bcd version.
- only oval that is available for 104bcd in 30T size with the 3032 mounting system and 99.5bcd
- “double oval” i.e. rapid transition to minor axis after power stroke on major axis (see mtbr forum for more pictures and details)
- cheap and easily available from ebay
One day my trusted shop for bicycle parts ( bike-components.de ) had a banner on their site about oval chainrings and that woke my engineering curiosity:
what is this? why? science??
I started searching for information and soon discovered that there were multiple cooks in the mix and that oval chainrings could be the next thing in mountainbiking …or maybe just another gimmic?
Continue reading “Oval Chainrings ?”