A MTB thread for info, fun, and wacky ideas

[jazclrint]

Pardon me if the title seems a bit presumptuous. There isn't a whole lot of discussion about MTB use and I thought a unifying thread might be helpful for folks like me. I also have some questions, and some crazy ideas I thought might be fun bantering about.

There a few good threads on how to get your iBike setup to work on a mountain bike that took me a while to find:

http://www.ibikeforum.com/viewtopic.php ... ike#p12053

http://www.ibikeforum.com/viewtopic.php ... ike#p10552

http://www.ibikeforum.com/viewtopic.php ... bike#p9544

http://www.ibikeforum.com/viewtopic.php ... mtb#p13789

There seem to be a few big issues with using and iBike on our Mountain bikes, that really aren't so much of an issue. The first is the friction numbers. In the threads above there are a few Crr numbers thrown about. 0.080, 0.088, 0.010, and 0.013. But, as mentioned, people start getting negative numbers in certain places, and the why doesn't seem to have been answered. A bigger issue is simply the difference in friction between hardpack, mud, and grass. The friction values change so much on a course that getting super accurate results seems near impossible. But I feel ball parking it gets you close enough to be useful, especially after reading some of the threads. I also think I read somewhere that Issac won't let you put in MTB tire sizes or high enough friction values? Since I only have an iSport I have no way of knowing. An oversight, or do things get too complex?

The second issue is the suspension. John often refers to it as flex suspension. Call me nit picky, but this doesn't seem like a very good descriptor. Suspension articulates, steel flexes. Here's where I begin to question a bit what I have read. Suspension is designed to suspend something, in this case a bike. The goal is for the fork and swingarm to move over or through bumps or ruts without affecting the frame. I would think that a rigid bike would cause the iBike more problems than a full suspension bike on the same trail. Now, the fork compressing under braking, or the bike bobbing under hard acceleration I can see throwing things off. Anther issue is sag and tilt cal. If you tilt cal your bike while you are not on it, then when you get on it'll be off. On my bike it's off by 3 degrees usually. So, you have to carefully do a tilt cal while sitting on the bike in your normal riding position. I have only managed to do this once, and it was recently. It took me a bit. I also wonder about the wisdom of doing a cal ride with the suspension locked out. You would have to be very careful about compressing your fork under braking, but if you lock your suspension out, it is supposed to be only when the shock and fork are fully extended (I think this has changed a few times over the years though) so your aero profile will be off, but how far off could it really be? Personally, my rear shock bobs more when locked out than when not. I know it means I'm not pedaling as smooth as I should be, but oh well. If you have the ability to lock your suspension out at your sag level, then you have life way easier than I.

The last issue I have been able to gleen is the tilt sensor, its ability to keep up, and that darned 5 minute re-cal based on altimeter readings. It seems to me the ability to turn that automatic recalibration off would be darn useful. At least until the sensors and processor reach a point they can keep with a mountain bike course.

Really, it does what I want it too. I don't have it dialed, but I get a general tss, if, np, etc, ft climbed, peak and average power, accurate mileage, speed (and now cadence, yeah!), temp, blah blah blah, and power on the climbs and flats. Sorry, but it seems to me if you're watching your power meter on the descents, you're either really good or slow.

Now, for the crazy thought I had. What if you had position sensors for the suspension? They have this for world level racing motorcycles. If they were ANT+ they could talk to the iBike. Really, if the suspension was dialed, they would probably do more harm than good, but suspension guys would go nuts with recorded travel data. Well, the ones that have a chance at interpreting it anyway. Kind of wondering if you get false power readings with a dfpm with some of the force and weight that gets applied throwing the bike around.

The last thing I have been wondering is if any of the new things about the Newton and Issac lend themselves to better dealing with the mountain biking.

[NorBike]

It’s winter in my country, so I use my Ibike Newton on a MTB now.
I have a rigid carbon fork and have little problem with the iBike on MTB.

I got around the MTB Crr/Cda question with the Virtual elevation method. I have a pretty aggressive bike setup and got nearly the same Cda as I have on my racing bike when riding on the hoods with my arm bent (and Isaac setup number). My handle bar is around 5-6cm below my saddle. I am 178cm and 74kg, and have a Cda around 0.34. I always am focusing using tight clothes, also when riding with my winter collection.

For Crr I have two Continetal Race King Supersonic 2.0. A german magazine have done a rolling resistance lab test for the 2.2 wheel.
http://forums.mtbr.com/wheels-tires/tir ... 19392.html

Calculating it backwards give those tires a Crr =0.00877 on the test machine. With the virtual elevation method. I get around 0.0060-0.0065 on new smooth asphalt, and up to 0.014 (!) on hardpack gravel road with some loose gravel on top with these tires. I normally ride on asphalt so I set the Crr =0.007. I also have another excel sheet made by myself for coasting uphill, and get the same results here. So I trust this result.

Also, Crr can be seen as the same as a slope. A Crr of 0.005 is the same as always riding uphill +0.5% slope. Crr of 0.006 is like riding a 0.6% slope.

I also use the 15% tire drop theory as a ballpark for my tire pressure, both on my racing bike and my MTB, setting my MTB to 32 psi front and 35psi rear, a bit higher than the 15% tire drop theory, but the tire feels a bit dangerous in corners at high speed below 30 psi. This theory works even better on racing bikes and showing the mistake too many people do over-inflating tires.

I also did some test insure myself the 26” wheel circumstance is correct.

I use 5sec smoothing interval in the iBike window.

The only thing that should be included when using it on a MTB is an option to turn off the 5min auto tilt function. Outside smooth tarmac roads this function does strange things. Please let the people have this as an on/off option.