Go Back  Bike Forums > Bike Forums > Bicycle Mechanics
Reload this Page >

DIY way to stiffen rear triangle?

Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

DIY way to stiffen rear triangle?

Old 10-26-18, 07:28 PM
  #1  
Stormy Archer
Senior Member
Thread Starter
 
Stormy Archer's Avatar
 
Join Date: Jun 2018
Posts: 164
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 73 Post(s)
Liked 0 Times in 0 Posts
DIY way to stiffen rear triangle?

Anyone heard of a DIY way to stiffen the rear triangle of a frame? I was thinking you could use steel cable like a slingshot frame (except across the rear triangle like a mixte) or carbon tow.

My related question is: what parts of a frame flex to cause reduced power transfer to the pedals? Does stiffening a rear triangle with another pair of tubes (like a mixte) have more impact on power transfer or ride quality?

I know that pretty much everything about a frame contributes to the stiffness, I'm talking more about specific cases when the bike is noodly enough to feel the rear wheel steer or see it move when pedaling hard.
Stormy Archer is offline  
Old 10-26-18, 08:39 PM
  #2  
AnkleWork
Senior Member
 
Join Date: Jan 2013
Location: Llano Estacado
Posts: 3,326

Bikes: old clunker

Mentioned: 8 Post(s)
Tagged: 0 Thread(s)
Quoted: 539 Post(s)
Likes: 0
Liked 25 Times in 15 Posts
Originally Posted by Stormy Archer View Post
My related question is: what parts of a frame flex to cause reduced power transfer to the pedals?
None. Frames are elastic enough to efficiently release the tiny energy stored during flex.
AnkleWork is offline  
Old 10-26-18, 09:07 PM
  #3  
Andrew R Stewart 
Senior Member
 
Andrew R Stewart's Avatar
 
Join Date: Feb 2012
Location: Rochester, NY
Posts: 11,654

Bikes: Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Raleigh Pro, Trek Cycle Cross, Mongoose tomac ATB, GT Bravado ATB, JCP Folder

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1730 Post(s)
Liked 45 Times in 32 Posts
Frame stiffness as an indicator of efficiency or "power transfer" (whatever that means) is highly manipulated by those who want to sell you something. Andy
__________________
AndrewRStewart
Andrew R Stewart is offline  
Old 10-27-18, 08:19 AM
  #4  
HillRider 
Senior Member
 
Join Date: Aug 2005
Location: Pittsburgh, PA
Posts: 31,489

Bikes: '''96 Litespeed Catalyst, '05 Litespeed Firenze, '06 Litespeed Tuscany, '12 Surly Pacer, All are 3x8,9 or 10. It is hilly around here!

Mentioned: 32 Post(s)
Tagged: 0 Thread(s)
Quoted: 1141 Post(s)
Likes: 0
Liked 20 Times in 19 Posts
Unless your frame is so flexible that you experience "ghost shifts" or brake rubbing under pedaling forces the stiffness is fine. The "stiffer is better" concept has been badly oversold.
HillRider is offline  
Old 10-27-18, 08:58 AM
  #5  
Crankycrank
Senior Member
 
Join Date: Jan 2009
Location: San Diego, CA
Posts: 1,341
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 184 Post(s)
Likes: 0
Liked 10 Times in 7 Posts
Sometimes you can add a bridge between the chainstays right behind where they attach to the BB shell to eliminate some flex. What is your frame, steel, CF, Aluminum? IMO though the best answer is to get another frame that feels right to you since farking around with what you have could make things worse. Might be a good idea to also post in the "Framebuilders" section.
Crankycrank is offline  
Old 10-27-18, 09:32 AM
  #6  
Andrew R Stewart 
Senior Member
 
Andrew R Stewart's Avatar
 
Join Date: Feb 2012
Location: Rochester, NY
Posts: 11,654

Bikes: Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Raleigh Pro, Trek Cycle Cross, Mongoose tomac ATB, GT Bravado ATB, JCP Folder

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1730 Post(s)
Liked 45 Times in 32 Posts
Originally Posted by Crankycrank View Post
Sometimes you can add a bridge between the chainstays right behind where they attach to the BB shell to eliminate some flex. What is your frame, steel, CF, Aluminum? IMO though the best answer is to get another frame that feels right to you since farking around with what you have could make things worse. Might be a good idea to also post in the "Framebuilders" section.
I'm not sure how much stiffness a missing bridged frame would gain if a bridge was added, at the usual location. Years ago Bicycling magazine had a series of articles involving what was then considered leading edge engineering, a finite stress analysis computer modeling, of bike frames. They used a few different arrangements of frames including with and without chainstay bridges. Their findings were that the CS bridge didn't change the results. My seat of my pants experience bears this out.

I attribute the focus on stiffness as a selling quality began about the same time. Cannondale had just begun to go to the bank on Klein's patented use of oversized tubes to increase frame stiffness. Those of us who rode small sizes already knew the truth, overly stiff frames increased rider fatigue and this led to a slower end of ride. Andy.
__________________
AndrewRStewart
Andrew R Stewart is offline  
Old 10-27-18, 09:47 AM
  #7  
Crankycrank
Senior Member
 
Join Date: Jan 2009
Location: San Diego, CA
Posts: 1,341
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 184 Post(s)
Likes: 0
Liked 10 Times in 7 Posts
^^^I have read from at least 3 frame builders that they claim a bridge can help in some situations but I am not a frame builder and you probably have more experience than me on this. Would definitely agree that overly stiff is not fun on longer rides.
Crankycrank is offline  
Old 10-27-18, 09:56 AM
  #8  
Gresp15C
Senior Member
 
Gresp15C's Avatar
 
Join Date: Sep 2014
Posts: 2,661
Mentioned: 16 Post(s)
Tagged: 0 Thread(s)
Quoted: 629 Post(s)
Liked 29 Times in 25 Posts
Unless the frame is heating up from flexing, you're not appreciably losing power.
Gresp15C is offline  
Old 10-27-18, 10:36 AM
  #9  
3alarmer
******
 
3alarmer's Avatar
 
Join Date: Nov 2010
Location: The Big Tomato
Posts: 17,274

Bikes: old ones

Mentioned: 226 Post(s)
Tagged: 0 Thread(s)
Quoted: 14533 Post(s)
Liked 71 Times in 61 Posts
...you can experiment with running a very long seat post in hopes that further increasing the stiffness of the seat tube portion will change the feel and flex.
If you have a set of bottle bosses built in on the seat post, this kind of limits how far you can go with this experiment.
3alarmer is offline  
Old 10-27-18, 08:16 PM
  #10  
Homebrew01
Super Moderator
 
Homebrew01's Avatar
 
Join Date: Jul 2004
Location: Ffld Cnty Connecticut
Posts: 21,055

Bikes: Old Steelies I made, Old Cannondales

Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 797 Post(s)
Likes: 0
Liked 30 Times in 22 Posts
Maybe your rear wheel is flexing. Loose spokes, or not enough spokes .
__________________
Bikes: Old steel race bikes, old Cannondale race bikes, less old Cannondale race bike, crappy old mtn bike.

FYI: http://www.bikeforums.net/forum-sugg...ad-please.html
Homebrew01 is offline  
Old 10-27-18, 08:38 PM
  #11  
Andrew R Stewart 
Senior Member
 
Andrew R Stewart's Avatar
 
Join Date: Feb 2012
Location: Rochester, NY
Posts: 11,654

Bikes: Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Raleigh Pro, Trek Cycle Cross, Mongoose tomac ATB, GT Bravado ATB, JCP Folder

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1730 Post(s)
Liked 45 Times in 32 Posts
Originally Posted by Gresp15C View Post
Unless the frame is heating up from flexing, you're not appreciably losing power.
Interesting, this is what Al Eisentraut told us back in 1979 during one of his building classes. Andy
__________________
AndrewRStewart
Andrew R Stewart is offline  
Old 10-27-18, 09:57 PM
  #12  
Brofessor
Senior Member
 
Brofessor's Avatar
 
Join Date: Aug 2018
Location: IL
Posts: 127

Bikes: Schwinn Circuit 89'

Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 46 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
More Stiff==>less energy absorbed in the frame==>better power transfer to the road (ceteris paribus) ==> Speed
Less Stiff==>more energy absorbed in the frame==>better dampening of road harshness (ceteris paribus) ==> Comfort ==> Speed

We have a bit of a paradox here....
Brofessor is offline  
Old 10-28-18, 06:03 AM
  #13  
zebede
Hello
 
zebede's Avatar
 
Join Date: Aug 2007
Location: Suncoast, Florida
Posts: 843

Bikes: n+1

Mentioned: 5 Post(s)
Tagged: 0 Thread(s)
Quoted: 80 Post(s)
Likes: 0
Liked 4 Times in 3 Posts
I am convinced that an experienced frame builder can change the level of flex per design. My primary example is an 1980s Trek 720 touring bike. It was an "OK" ride when unloaded, but when you put loaded panniers on it became luxurious pleasure to ride. Another example was a 80s Gitane with Super Vitus. Many people called it "flexy" , and I think for "masher" it was, but for a "spinner" like myself it was a comfortable road bike. You could stay in the saddle longer and it wouldn't beat you up as bad as the compared to the currently popular stiff bikes.

So what type of frame do you have? What kind of peddler are you? Maybe the bike is not right for you?
zebede is offline  
Old 10-28-18, 07:09 AM
  #14  
raria
Senior Member
 
Join Date: Jul 2017
Posts: 914
Mentioned: 7 Post(s)
Tagged: 0 Thread(s)
Quoted: 759 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
But it does impact speed

Im a steel guy but ended up buying a CAAD12 with almost the same geo as my steel bikes and exact same grupo including casette.

CAAD is faster on any ride longer than 20 miles. So what could it be if its not better power transfer.

Originally Posted by Andrew R Stewart View Post
Frame stiffness as an indicator of efficiency or "power transfer" (whatever that means) is highly manipulated by those who want to sell you something. Andy

Last edited by raria; 10-28-18 at 03:23 PM.
raria is offline  
Old 10-28-18, 08:30 AM
  #15  
Ferrouscious
Some Weirdo
 
Ferrouscious's Avatar
 
Join Date: Dec 2017
Location: SW OH
Posts: 145

Bikes: '82 Austro Daimler Alpina, '71 C. Itoh, '86? Maruishi Excellence

Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 46 Post(s)
Liked 1 Time in 1 Post
weight, aerodynamics, placebo effect, perceived benefits unconsciously making you work harder and therefore faster, tires...
Ferrouscious is offline  
Old 10-28-18, 08:45 AM
  #16  
JohnDThompson 
Old fart
 
JohnDThompson's Avatar
 
Join Date: Nov 2004
Location: Appleton WI
Posts: 20,417

Bikes: Several, mostly not name brands.

Mentioned: 109 Post(s)
Tagged: 0 Thread(s)
Quoted: 1689 Post(s)
Liked 60 Times in 41 Posts
Originally Posted by Andrew R Stewart View Post
Frame stiffness as an indicator of efficiency or "power transfer" (whatever that means) is highly manipulated by those who want to sell you something. Andy
+1 this. The relationship that a stiffer frame was a better frame became popular with Klein's use of oversize diameter aluminum tubing back in the 70s. But the oversize diameter was as much to provide sufficient weld joint area to ensure against failure as it was to increase stiffness.
JohnDThompson is offline  
Old 10-28-18, 08:51 AM
  #17  
JohnDThompson 
Old fart
 
JohnDThompson's Avatar
 
Join Date: Nov 2004
Location: Appleton WI
Posts: 20,417

Bikes: Several, mostly not name brands.

Mentioned: 109 Post(s)
Tagged: 0 Thread(s)
Quoted: 1689 Post(s)
Liked 60 Times in 41 Posts
Originally Posted by raria View Post
CAAD is faster on any ride longer than 20 miles. So what could it be if its not better power transfer.
A light rider may find an overly stiff frame to be uncomfortable to ride long distance, and difficult to control on rough surfaces.
JohnDThompson is offline  
Old 10-28-18, 08:57 AM
  #18  
wphamilton
Senior Member
 
wphamilton's Avatar
 
Join Date: Apr 2011
Location: Alpharetta, GA
Posts: 14,550

Bikes: Nashbar Road

Mentioned: 65 Post(s)
Tagged: 0 Thread(s)
Quoted: 2505 Post(s)
Liked 55 Times in 33 Posts
Regarding the first question, steel cables on the rear stays could increase the rigidity but you'd be adding considerable compressive stress that would likely be beyond what the frame was designed for. That's my intuition, not any specific calculations or design experience, but I'd be very reluctant to try it.

On the derivative question "why?" it's clear that energy IS lost in flex, and it is not "returned" to forward motion by the frame springing back. While most of that energy would be converted into heating the frame, it does NOT follow that you'd feel the frame getting hotter or otherwise note an obvious heating, for the same reasons that our bodies don't cook while riding. So I can't agree with responses that dismiss your concern completely, although it probably is true that differences are very minor.

I think that frame designers are the more appropriate group to ask because where and how they beef up stiffness is likely where you'd need to address in any DIY efforts. That is beyond my specific knowledge but from general reading on the subject, after the tubes are selected joints are the main areas of concern. In that case, it seems to me that adding more tubes to the rear triangle will be disappointing, having limited impact.
wphamilton is offline  
Old 10-28-18, 09:30 AM
  #19  
fietsbob 
coprolite
 
fietsbob's Avatar
 
Join Date: Jun 2010
Location: NW,Oregon Coast
Posts: 41,928

Bikes: 8

Mentioned: 188 Post(s)
Tagged: 0 Thread(s)
Quoted: 6833 Post(s)
Likes: 0
Liked 212 Times in 177 Posts
placebo effective

if you thinka tube is not stiff enough?
wrap with soggy carbon fiber sheet already wet with epoxy..
let it cook.





....

Last edited by fietsbob; 10-28-18 at 12:40 PM.
fietsbob is offline  
Old 10-28-18, 10:22 AM
  #20  
Gresp15C
Senior Member
 
Gresp15C's Avatar
 
Join Date: Sep 2014
Posts: 2,661
Mentioned: 16 Post(s)
Tagged: 0 Thread(s)
Quoted: 629 Post(s)
Liked 29 Times in 25 Posts
Originally Posted by Andrew R Stewart View Post
Interesting, this is what Al Eisentraut told us back in 1979 during one of his building classes. Andy
Right. The energy has to go somewhere. Either it comes back out as mechanical energy, or it's dissipated as heat. Granted, one other possibility is that too much frame flexing (or too little) makes your body less effective at converting your strength into forward motion of the bike.
Gresp15C is offline  
Old 10-28-18, 10:39 AM
  #21  
McBTC
Senior Member
 
McBTC's Avatar
 
Join Date: May 2015
Posts: 3,763

Bikes: 2015 22 Speed

Mentioned: 14 Post(s)
Tagged: 0 Thread(s)
Quoted: 1493 Post(s)
Likes: 0
Liked 2 Times in 2 Posts
how about filling the tubes with spray foam for added support and stiffness? ...a web search shows that spray foam is, said to expand up to 60-times its unmixed volume and is the result of combining isocyanate and polyol resin.
McBTC is offline  
Old 10-28-18, 12:33 PM
  #22  
Andrew R Stewart 
Senior Member
 
Andrew R Stewart's Avatar
 
Join Date: Feb 2012
Location: Rochester, NY
Posts: 11,654

Bikes: Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Raleigh Pro, Trek Cycle Cross, Mongoose tomac ATB, GT Bravado ATB, JCP Folder

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1730 Post(s)
Liked 45 Times in 32 Posts
Originally Posted by McBTC View Post
how about filling the tubes with spray foam for added support and stiffness? ...a web search shows that spray foam is, said to expand up to 60-times its unmixed volume and is the result of combining isocyanate and polyol resin.
How about if you do this test and report back to us? Andy
__________________
AndrewRStewart
Andrew R Stewart is offline  
Old 10-28-18, 02:02 PM
  #23  
cny-bikeman 
Mechanic/Tourist
 
Join Date: Apr 2007
Location: Syracuse, NY
Posts: 7,510

Bikes: 2008 Novara Randonee - love it. Previous bikes:Motobecane Mirage, 1972 Moto Grand Jubilee (my fave), Jackson Rake 16, 1983 C'dale ST500.

Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 477 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Your assumption seems to be that if the rear triangle does not flex the pressure you apply to the pedals will result in more efficient forward motion. But pedals are off-center to the bike, so it seems to me that some counter force would have to resist that off-center force. I believe there are only two possibilities - the frame or your muscles. Only one of those potentially has elastic properties, so that the energy can in large part be recovered. If a frame is completely stiff then either the entire bike will sway from side to side under hard pedaling force or you will use energy trying to prevent that.
__________________
There's no such thing as a routine repair.

Don't tell me what "should" be - either it is, it isn't, or do something about it.

If you think I'm being blunt take it as a compliment - if I thought you were too weak to handle the truth or a strong opinion I would not bother.

Please respect others by taking the time to post clearly so we can answer quickly. All lowercase and multiple typos makes for a hard read. Thanks!
cny-bikeman is offline  
Old 10-28-18, 03:25 PM
  #24  
raria
Senior Member
 
Join Date: Jul 2017
Posts: 914
Mentioned: 7 Post(s)
Tagged: 0 Thread(s)
Quoted: 759 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Well said

I was starting to think I was the only sane person here!

Originally Posted by wphamilton View Post
Regarding the first question, steel cables on the rear stays could increase the rigidity but you'd be adding considerable compressive stress that would likely be beyond what the frame was designed for. That's my intuition, not any specific calculations or design experience, but I'd be very reluctant to try it.

On the derivative question "why?" it's clear that energy IS lost in flex, and it is not "returned" to forward motion by the frame springing back. While most of that energy would be converted into heating the frame, it does NOT follow that you'd feel the frame getting hotter or otherwise note an obvious heating, for the same reasons that our bodies don't cook while riding. So I can't agree with responses that dismiss your concern completely, although it probably is true that differences are very minor.

I think that frame designers are the more appropriate group to ask because where and how they beef up stiffness is likely where you'd need to address in any DIY efforts. That is beyond my specific knowledge but from general reading on the subject, after the tubes are selected joints are the main areas of concern. In that case, it seems to me that adding more tubes to the rear triangle will be disappointing, having limited impact.
raria is offline  
Old 10-28-18, 03:30 PM
  #25  
AnkleWork
Senior Member
 
Join Date: Jan 2013
Location: Llano Estacado
Posts: 3,326

Bikes: old clunker

Mentioned: 8 Post(s)
Tagged: 0 Thread(s)
Quoted: 539 Post(s)
Likes: 0
Liked 25 Times in 15 Posts
Originally Posted by wphamilton View Post
On the derivative question "why?" it's clear that energy IS lost in flex, and it is not "returned" to forward motion by the frame springing back.
Really? How much energy is clearly lost? Got a source?
AnkleWork is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

Copyright 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.