Huh?

While I understand the difference between riding a bike on the road and riding a bike on a trainer and the effect of the flywheel's size on the perceived resistance, the only inertial frame of reference i know of refers to INS navigation (used for many planes and subs). What is this high or low "intertial frame of reference" that are you talking about? Did you just make this term up, or can you give me a link or source?

---

Advanced Aero TopTube Storage for Road, Gravel, & Tri...ZeroSlip & Direct-mount, made in the USA.
DarkSpeedWorks.com.....Reviews.....Insta.....Facebook
--

No, I didn't make it up. It's just a physics term. It's applicable to any system with kinetic energy. I believe that the first time I saw it used with respect to bicycles was in Whit & Wilson's "Bicycling Science." (But I'm not sure and don't have my copy with me.) Basically, if you consider the low kinetic energy of the system when riding on the trainer and recognize that is very different from when you ride outside, some of the perceived differences between riding inside and riding outside make a lot more sense. Or, to put it more simply, riding inside is just different than riding outside.

From wikipedia: In physics, an inertial frame of reference (also inertial reference frame or inertial frame ) is a frame of reference which describes time homogeneously and space homogeneously, isotropically, and in a time independent manner. This allows motion and interactions to be described without the presence of fictitious forces.[1][2] Special relativity states that there are actually infinitely many such frames, and the physical laws takes the same form as they do in any other inertial frame of the same handedness.[3][4] In flat spacetimes, all inertial frames are in a state of constant, uniform motion with respect to one another.

---

"Non est ad astra mollis e terris via." - Seneca | rappstar.com | FB - Rappstar Racing | IG - @jordanrapp

I know you didn't make the term up out of thin air, I was asking if you just made up the use of this term regarding bike trainers.

I looked at my copy of bicycling science and I don't see the term being used anywhere in the book, but if you do find it, let me know, I'd really like to see it being used in terms of cycling and stationary trainers. And with your wikipedia definition, while generally correct, for the life of me, I cannot see how that definition applies in any way to the perceived difference in resistance between outdoor and trainer riding.

---

Advanced Aero TopTube Storage for Road, Gravel, & Tri...ZeroSlip & Direct-mount, made in the USA.
DarkSpeedWorks.com.....Reviews.....Insta.....Facebook
--

I also currently run 172.5 on the road- don't know my inseam but my saddle height is about 72.5. I am currently on 167.5 on the tt bike and contemplating the move to 165.
Should I consider 170 for the road bike?

I don't think there's a reason not to. But it's more dependent on how you like to ride your bike (as well as power). In other words, some people who sit quite slack (say 72 or 71) may not have the same clearance issues. I would say with a saddle height of 72.5, that seems to me like a pretty low saddle for 172.5. But it doesn't seem to be as much of a limiter on roadbikes as on tribikes.

It's really nice if you have access to a fitbike with some varicranks. That makes it easy to try without spending the money.

---

"Non est ad astra mollis e terris via." - Seneca | rappstar.com | FB - Rappstar Racing | IG - @jordanrapp

I like to sit back but I do creep forward. Feeling better on the shorter tt cranks got me thinking about the shorter road cranks. One of the things that you mentioned (may have been in another thread) got me thinking. How to tell if your cranks are too long. One of the things you said was if you are the 1st to stand up when it gets hard on a climb- that totally happens to me- I can train seated more or less all the time- get in a race, I stand when I am looking for power. I was thinking the 170 cranks might help with that.

I think so. I set a pb for my local hillclimb on my 2nd ride on 172,5s down from 175s. I'm a seated climber, and i felt like i had notably more power on the kick-ups where folks would want to stand. That was the ride where I took Tom A's tip and also moved my saddle 2.5mm back. I just felt like I was always able to "get on top of the gears."

---

"Non est ad astra mollis e terris via." - Seneca | rappstar.com | FB - Rappstar Racing | IG - @jordanrapp

Thanks- I am going to give the 170 cranks a try on the road

I'm 5'8" and ride a 172.5 mm crank. In fact I'm selling a brand new 2010 Shimano Ultegra 6700 crank for $225 if you're interested. PM me

campy only!

I too think I will give 170 a try.