Go Back  Bike Forums > Bike Forums > General Cycling Discussion
Reload this Page >

Mechanical or Di2?

Notices
General Cycling Discussion Have a cycling related question or comment that doesn't fit in one of the other specialty forums? Drop on in and post in here! When possible, please select the forum above that most fits your post!

Mechanical or Di2?

Old 08-02-16, 08:45 AM
  #26  
rm -rf
don't try this at home.
 
rm -rf's Avatar
 
Join Date: Jan 2006
Location: N. KY
Posts: 5,619
Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 854 Post(s)
Liked 275 Times in 201 Posts
I have both Di2 and mechanical bikes.

Di2
My carbon Di2 is great on fast group rides and on rolling, hilly rides. It's like clicking a mouse to shift, and I can do it with my ring fingers from the hoods. The rear shifts great under load on hills, and the front shift is quite quick and drama free. I'll sometimes shift the front for just a 30 foot high climb. I'll often shift the rear for just 2 or 3 pedal revolutions, then shift again.

To keep up with fast rides, I'm always hunting for my best cadence, so I shift a lot. And when the other riders are standing and grinding up a short hill in a too-high gear, I've already dropped to my 34 chainring and a big cog. And way back in the draft, I'll go 50-11 or 50-12 and pedal very easy at a low cadence to both save my legs, and avoid coasting. (It's easier on the following riders when the rider in front doesn't pedal & coast repeatedly.)

Mechanical
I have a gravel / all-day bike with a triple crank. It's great for really low gears on steep rides. And the 39 middle chainring is really nice with a 12-25 cassette for all-day flatter rides--I have very close shifts that just change the cadence by 5 or 6 rpm. (If Di2 had a triple, I probably would have done that.)

I'm riding at a more relaxed pace, and don't need to shift quite as much, and can afford to wait longer to do a shift. So the mechanical shifting is fine for these rides. It's interesting how quickly my fingers adapt to the very different shifting when I switch bikes.

Last edited by rm -rf; 08-02-16 at 08:58 AM.
rm -rf is offline  
Old 08-02-16, 07:53 PM
  #27  
WizardOfBoz
Generally bewildered
 
WizardOfBoz's Avatar
 
Join Date: Aug 2015
Location: Eastern PA, USA
Posts: 2,945

Bikes: 2014 Trek Domane 6.9, 1999 LeMond Zurich, 1978 Schwinn Superior

Mentioned: 20 Post(s)
Tagged: 0 Thread(s)
Quoted: 1108 Post(s)
Liked 300 Times in 225 Posts
Drew,

Sorry to dis your bike. There are two points of view. One is that "It should last indefinitely if not crashed." The other was exemplified in the extreme by the recent thread "CARBON FRAMES NOT SAFE AFTER THREE YEARS!" (or somesuch). I'm an engineer, and looking at the fatigue chart for carbon fiber composite I think that the answer is probably somewhere between the extremes. If the bike was designed such that the parts are somewhat stressed (and a good design does this, else the frame is too heavy), then it will fail after a certain period of normal use. Given your Kestral frame is competitive in the weight department, it WILL fail after a period of normal use. What is that period? That's where we don't have a lot of data. IIRC the guy posting the "NOT SAFE" post had a catastrophic failure in his older (2002? 2005? It's late forgive my laziness not looking it up). So my only failure data point is that the safe period for a CF bike is 5-20 years. But there are CF bikes that are decades old and going strong. The interval will be shorter, if you weight 240# (like me) and ride a very light bike (Trek Domane Series 6). Longer if you weigh 120# and ride a 50cm frame that is really beefy. So there is a risk in riding a CF bike for decades. It may be nil, or it may be significant. The experts here are pretty positive on longevity, but the post I mention above documents a failure after 15 years or so. Point is, the useful life of CF bikes is not established in my view. I love my current CF bike, but will probably sell it after five years of use.

But you were interested and excited about trying Di2. To tell the truth, I was thinking of it. Given that I'm an engineer AND I worked in a bike shop for many years I'm pretty persnickety, and the kit for my bike is a bit more expensive (~$1400-1700 - heavens, you wouldn't expect me to use derailleurs with a different name on them, would you?*). That's put me off so far, but I definitely can see the interest and excitement about the upgrade.

I guess if you don't like the current setup, or it doesn't do something you want/need, and you can afford it you could try it. I'm thinking if you don't like it, you probably can resell it on eBay for very little loss.

Sorry to be the fart in your elevator of excitement.

*So far, I haven't gone through the bike and replaced all the nuts and bolts with titanium, as my mechanic friend (and engineer, btw) at my LBS did.

Last edited by WizardOfBoz; 08-03-16 at 07:41 AM.
WizardOfBoz is offline  
Old 08-03-16, 06:40 PM
  #28  
RushFan2112
Senior Member
 
Join Date: Apr 2015
Location: East Bay CA
Posts: 192

Bikes: 2016 Cannondale Synapse Carbon Disc Di2, Cannondale F1000 SL

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 48 Post(s)
Likes: 0
Liked 3 Times in 2 Posts
I wouldn't bother upgrading an older bike to electronic shifting (be it Di2, eTap or EPS), but I can't imagine purchasing a new bike without it. If you have the means and it turns you on I can't see a reason not to go electronic. It really is that good.
RushFan2112 is offline  
Old 08-10-16, 12:22 PM
  #29  
Bluebatmobile
Senior Member
Thread Starter
 
Join Date: Jan 2005
Location: San Diego
Posts: 83

Bikes: Look 795, Kestrel 500EMS, Zipp 3001,Cannondale Raven, Outland VPP

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 27 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
thanks for the input guys !


B@t™
Bluebatmobile is offline  
Old 08-10-16, 06:32 PM
  #30  
rydabent
Senior Member
 
rydabent's Avatar
 
Join Date: Apr 2010
Location: Lincoln Ne
Posts: 9,716

Bikes: RANS Stratus TerraTrike Tour II

Mentioned: 43 Post(s)
Tagged: 0 Thread(s)
Quoted: 3114 Post(s)
Liked 959 Times in 575 Posts
Anything that is more complicated will have more complicated failures. Mechanical shifting has worked great right from the start and continues to do so.
rydabent is offline  
Old 08-10-16, 06:40 PM
  #31  
andr0id
Senior Member
 
andr0id's Avatar
 
Join Date: Feb 2009
Posts: 2,522
Mentioned: 11 Post(s)
Tagged: 0 Thread(s)
Quoted: 1422 Post(s)
Likes: 0
Liked 5 Times in 3 Posts
If you love your Kestrel frame, which is awesome and unique, go for it. Get a group from one of the UK online vendors and do it yourself and save a ton on money.
Seems you can just run the wire along the bottom of the down tube, tape it nicely with clear or matching tape and it will be practically invisible.

Tap test that frame while you have the parts off. Make sure there are no areas that make thunking or dull sounds.

Originally Posted by WizardOfBoz View Post
Given your Kestral frame is competitive in the weight department, it WILL fail after a period of normal use.
No, just stop it now.

CF does not typically fail unless damaged by being used in a manner for which it was NOT designed.

CF bikes that fail are because people dropped them, crashed them, banged them up on their racks or possibly in rare cases manufacturing defects.

Last edited by andr0id; 08-10-16 at 06:45 PM.
andr0id is offline  
Old 08-10-16, 08:28 PM
  #32  
Steve B.
Senior Member
 
Join Date: Jul 2007
Location: South shore, L.I., NY
Posts: 6,056

Bikes: Flyxii FR322, Cannondale Topstone, Miyata City Liner, Specialized Chisel, Specialized Epic Evo

Mentioned: 18 Post(s)
Tagged: 0 Thread(s)
Quoted: 2653 Post(s)
Liked 1,408 Times in 816 Posts
Originally Posted by rydabent View Post
Anything that is more complicated will have more complicated failures. Mechanical shifting has worked great right from the start and continues to do so.
As well, consider replacement cost. A Shimano Di2 6870 rear derailleur is about $165. A mechanical 6800 is about $55-60. A Di2 internal battery at $130 that'll probably go 5 years ?. That's a lot of shifter cables.

As much as I might desire Di2 and can see moving towards it in time, the overall cost of everything is so much higher, makes me currently stick with mechanical.
Steve B. is offline  
Old 08-10-16, 08:51 PM
  #33  
WizardOfBoz
Generally bewildered
 
WizardOfBoz's Avatar
 
Join Date: Aug 2015
Location: Eastern PA, USA
Posts: 2,945

Bikes: 2014 Trek Domane 6.9, 1999 LeMond Zurich, 1978 Schwinn Superior

Mentioned: 20 Post(s)
Tagged: 0 Thread(s)
Quoted: 1108 Post(s)
Liked 300 Times in 225 Posts
Andr0id, I disagree in theory, and in practice the situation is not as clear cut as your argument assumes.

Any material that has a fatigue failure mode will break, given high enough stress and enough cycles of flex. Any material - steel, aluminum, or CF. See here for simulated pictures of an actual event: an F-15 breaking in half in flight, due to fatigue. Recall that stress is, simply put, force per area. If we assume that the forces a bike part sees are about the same for any material (for argument's sake for right now), then the smaller the part's cross sectional area, the higher the stress. But the he smaller the area, the lower the weight. So there is a performance objective (low weight) that pushes designs to low cross sectional area in parts, which gives higher stress. So a good design will have stresses that will eventually cause fatigue failre. Your argument is that, for an undamaged bike that is not abused, carbon fiber will never break. My point is that for a properly designed bike (e.g. one with cross section low enough to be competitive in weight), there is a finite limit to the frame life due to CF composite fatigue failure. It may be 500 years, but it is finite. But that 500 year figure is based upon fresh composite with a fresh matrix resin. I'm not sure that the longevity of the resins used have been studied. The resin is almost certainly not as stable as the underlying carbon fibers. So there may be another failure mode due to resin matrix failure or delamination, which might be 5, 10, or 20 years. The bike company legal weasels are trying to limit liability with there "Hey, this here bike may fail after 3 years of use" statements. I don't think its that bad (e.g. the damned things fall apart in month 37), but CF frames will fail. Add to this that there's certainly a significant amount of variability between brand build quality and materials. So I don't think we can say a bike will not fail for 30, or even 20 years.

The practical matter is that CF frames DO fail, and catastrophically so. For some pics, see here, on the Bike Forum. We agree that most failures are probably due to local damage caused by a frame member being poked, hit, or otherwise not used as intended. But how do you tell? I have a CF frame (and I love it), but the head attached to air pump I had attached in a bracket made a little blemish on my seat tube. I noticed this before the CF itself was frayed and will rectify the issue, but will this cause my frame to fail? These small dents can be what are called stress concentrators, and can cause local stress to exceed normal stress. If the stress exceeds yield stress, in a steel bike the frame bends a bit. In a CF bike, the failure mode is brittle and you get sudden and total failure. I think that there's a lot of these small little dings and dents that folks don't even notice that may (or may not) cause CF frame failure.

But looking at what is called a fatigue chart (the stress applied, as a percent of yield strength, plotted against cycles to fail) for CF is much flatter than a lot of other materials. So undamaged CF probably does have exceptional life, as you point out. But if there's a small local bit of damage, or if the bike wasn't constructed ideally, the local stress at points may be higher than design, leading to premature and sudden failure.

Last edited by WizardOfBoz; 08-10-16 at 09:03 PM.
WizardOfBoz is offline  
Old 08-11-16, 11:42 PM
  #34  
Dreww10
Full Member
 
Join Date: May 2014
Posts: 355
Mentioned: 4 Post(s)
Tagged: 0 Thread(s)
Quoted: 195 Post(s)
Likes: 0
Liked 12 Times in 6 Posts
Originally Posted by Steve B. View Post
As well, consider replacement cost. A Shimano Di2 6870 rear derailleur is about $165. A mechanical 6800 is about $55-60. A Di2 internal battery at $130 that'll probably go 5 years ?. That's a lot of shifter cables.

As much as I might desire Di2 and can see moving towards it in time, the overall cost of everything is so much higher, makes me currently stick with mechanical.
i think this partly depends as well on how much you ride. I put in 7-8k miles a year, and so I'm generally putting on new cables 2-3x a season, new housing every winter, and a roll of $30 bar tape annually. Add in the cost of a $50 set of Park cable cutters to do this at home (or the labor cost to have your shop do it) and it adds up fast. In five years, I've already spent well beyond what Di2 would have cost in parts and labor to have mechanical, no doubt. I'm reminded of the pitfalls of mechanical each year when I rip off and throw away bar tape that still looks brand new.
Dreww10 is offline  
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
Plainsman
Road Cycling
51
04-07-21 06:34 AM
0100
Road Cycling
2
04-09-18 10:46 AM
huskie69
Road Cycling
4
05-08-17 01:59 AM
dmanthree
Road Cycling
71
03-11-17 05:42 PM
palmgreens
Road Cycling
15
05-10-16 12:17 AM

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell or Share My Personal Information -

Copyright © 2023 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.