trek330

I hear the term "stiffness" used alot a regarding the ride or feel of a bike.I really don't know what it means.Maybe its a basic inability to comprehend but could anyone help me understand?Steel is stiff right?But isn't the joy of the ride its flexibility?Liveliness?Stiff means inflexible.Is there different types of stiffness?Aluminum as opposed to CF?A stiffer bike is faster?More,less comfortable?Help!

jdon

It generally refers to torsional stiffness or the bikes resistance to twisting. Stiffer frames tend to provide better power transfer but a more harsh ride.

fietsbob

people put a foot against the BB and push the parked bike sideways to test this

vertical compliance is now being put back in stiff frames so the 120 psi tires
and stiff frame doesn't beat you up.

Zerts in Specialized And the new Trek Domane, CF frame are examples..


work cycles bending aluminum and it breaks, so their stiffness is also benefiting reliability.

nice springy steel frame gives a bit, some call it planing ,, since it springs back
but some of that thin wall tube light liveliness, makes the ride more comfortable.

unterhausen

the more I think about stiffness, the more I realize I don't know what it is either

You can have a torsionally stiff frame structure, but if the front end is wobbly it will not matter. The other issue is bb height. Many manufacturers are deathly afraid of pedal strike, so they build bikes with high bb. This can also lead to a bike that doesn't feel stiff. I have always been pretty happy with my '80s racing bike that is not at all stiff by today's standards. Never noticed frame flex at all.

Barrettscv 

Stiffness is a benefit when it improves power transfer from the pedal to the rear wheel rim. It also is a benefit when it improves tracking and cornering.

However, a completely rigid bike frame would be unusable. The tires would lose contact with the road often enough to be dangerous. The rider would take up a new sport, too.

AzTallRider

The stated goal these days is "lateral stiffness with vertical compliance" and a lot of engineering and manufacturing expertise is going into making that a reality. It's certainly easier to accomplish using CF than with steel or aluminum. It's hard to know what it feels like unless you've ridden a bike with lateral flex, and then one that doesn't have that flex. Ditto for the vertical compliance. Some bikes beat the hell out of you on anything but a totally smooth road (do those roads even exist?) - some do not. Other than a direct comparison riding a flexy and then a stiff bike, I've found the flex most easily detectable on wet days, which cause the rim to pick up some grit. Apply some torque when accelerating out of a slow turn, and you will hear the the grit against the brake pad - from the flex. My steel Gunnar does that. My Madone does not, and yet it is a very comfortable bike to ride. And of course, if you race or really push things a lot, you can feel the effect the stiffness has when you are accelerating. There are a lot of factors that go into handling in corners. Flex is certainly one of them, but for me, position/balance has an even greater impact.

lhbernhardt

Back in the 70's, an acquaintance had purchased one of the Speedwell Titanium frames that were then being released. He let me ride it. Even though I didn't stress it, the frame felt like a limp noodle. It was not "stiff" at all. You had to be careful accelerating because it would throw off your steering. I heard later that the frame had broken, and I'm not surprised.

You can generally tell if a frame is "stiff" when you climb with it out of the saddle. "Stiff" generally means that the bottom bracket does not move side to side as you torque it up the hill. But if you think about it, it's not just the frame that needs to be stiff for this to happen. You also need the wheels to be "rigid." If the spokes aren't tight enough, the wheel will "give." However, it is possible for a wheel to be too rigid. A good example of this is in a Tour de France technical time trial, where the rider goes around a tight, fast turn on a rear disk. Because the wheel doesn't "give" a little on the turn, the tire is pushed laterally and loses adhesion, causing the rider to either crash or have to take evasive maneuvers.

A bike's design is a fine balancing act. This is why you should never buy an aluminum frame. It's a lousy frame material. Build it like a steel frame and it's not "stiff" enough. Because the frame bends, the aluminum "work-hardens" and gets more and more brittle, eventually breaking. Build it so it doesn't flex in order to make it last longer, and it gives a very harsh ride. Steel and carbon fiber will take repeated cycles of mild flexing, so can be built to be stiff in one direction and compliant in another, so "stiffness" becomes no longer an issue. The question now is, do you prefer the frame to be "springy" (steel) or "absorbent" (cf)?

Luis

stapfam

Now I am not in agreement with Luis because I have aluminium framed bikes and I prefer them over other materials.

Any of the materials a bike is made of can be stiff or not. I have ridden Steel frames that are rock solid and C.F that flop about on acceleration. One material I have yet to find that is "Flexible" is aluminium but saying that- My Boreas is aluminium- lightweight aluminium- and at the time it was a top edge engineered frame. It gives the best ride of all my bikes so there must be some flexibility within that frame. By selecting different gauge tubing for different parts of the frame- you can get aluminium to react in a sensible manner. Stiff where needed but still compliant in others but frames like this were never cheap and I doubt that they are made any longer. I will agree that it is not a long lasting material though but still have my Bianchi 2000 MTB in one piece after the very hard life it has had and the 2002 Cannondale Tandem is still handling well. Both are Aluminium by the way and the only frame I had problems with was The Giant TCR-C (C.F.) and initially that was one stiff frame that I could not keep on the road at speed.

Then there is the "New" style of bike- Aluminium Main frame with C.F rear stays. Stiffness from the main frame and a bit of flexibility from the stays. Sounds the wrong way round but "Some" of these frames are stiff where necessary but compliant when required.

jim p

I have a couple of steel frame bikes. I am satisfied with the ride. On both bikes I have had to extend the quill stem to the point that the flex in the stem is scary. I make sure not to pull on the bars as I pedal because it looks like I could get 1/2" flex side to side.

So to me a stiff bike would be one that I could mash the pedal as hard as I wanted and pull up on the bars as hard as I could and not see any flexing.

I have heard that the ride of the bike is affected by the stiffness of the frame. I also think that an important part of ride comfort is the correct pressure in the tires. I weigh 150 and I have been riding 100 front and 100 psi in the back. A little research shows that the 100 in the rear is good but I could go down to 60 psi up front. This tire pressure change will probably reduce quite a bit of road buzz.

lhbernhardt

Hard to argue with what one is comfortable with. And I will admit that my current track bike (a British-made Dolan, in fact) is made of aluminum, but I need the stiffness, and a harsh ride is inconsequential on the track.

I thought that the Vitus and Alan frame strategies of the 80's was appropriate for aluminum - provide a cheap, throwaway racing frame that was light and had resilient in the right places. Sean Kelly winning sprints on an aluminum Vitus was certainly a major selling point! But about the only Vitus alu frames you see today are in the smaller sizes and ridden carefully by non-competitive riders.

The alu frame with carbon fork and stays are, I think, no longer made. It was a phase the manufacturers went thru before deciding that all carbon worked better. At least I haven't seen too many of these lately.

Luis

Barrettscv 

One trait of frame flex proven by mechanical tests is that larger frame sizes flex far more than smaller sizes. This is true for steel, aluminum, titanium and CF.

Ironically, larger & heavier riders need to use larger frames and smaller lighter riders need to select smaller frames.

Larger riders usually find the more flexible large frames will provide a compliant ride but larger riders might also discover some unwanted flex. Smaller riders often enjoy the performance benefits of a stiff and responsive frame, but might find the reduced compliance of smaller frames to be uncomfortable.

I have a light-weight friend who has a collection of smaller sized titanium bikes that were produced about 10 years ago. He enjoys the very compliant ride of these bikes. He also finds modern race-level CF and aluminum to be way too stiff for recreational use.

I'm a larger guy who has large frames in CF and steel. I find the CF bikes to have the right amount of flex. I have had titanium bikes that were overly flexy with bad handling characteristics. I find some steel bikes to be good riding bikes but not stiff enough for very fast rides.


The point to remember is that don't use another opinion of what might be "too stiff" or "too flexy". A large guy rarely finds a bike to be too stiff and a smaller person might dislike the ride quality of a very stiff model since a small frame size might increase frame stiffness to an unacceptable level.

stapfam

Barrett has made a point on rider weight. When I got Boreas it worked a dream for me but it was probably one of the last Aluminium frames made by this company. Next bike was C.F. and I had tried the Giant TCR3 on test and liked it but bought a TCR-C frame and built it up. Lighter weight and a race geometry with a few other changes. That bike was diabolical to ride. Rough road and it was harsh- hit a manhole cover and it bounced sideways but it climbed hills a dream. Downhill and I was worried at speed over 35mph as it stopped handling. Tried lots of things but the final solution was a set of handbuilt wheels from another bike that were compliant enough to keep the bike on the road. My lightweight of 140lbs- a very stiff frame and stiff wheels were not a combination that worked. Luckily I found a solution and it still goes up hills.

cccorlew

If teh fame flexes that's power that isn't getting to the ground. It can also feel less solid. As an extreme example, imagine a cheapo mountain bike with super bouncy suspension. All that bouncing uses enegry that would otherwise be propelling you. That's just vertical. For still, imaging riding on solid rubber tires. It isn't exactly the same, but you get the idea.

In the other direction, I once rode an older tandem with a friend just to try it. When we applied big power(OK, big for us) the bike felt like it was twisting under us. Better built stiffer tandems don't feel like that.

I had a 80s Cannondale Black Lightning that was unbelievably stiff. No flex in any direction. Perhaps a great critrium bike, but on chip seal I was beaten to death. I ride a Roubaix now, and the same roads don't hurt at all.

NOS88

Perhaps these links will contribute to the discussion:

https://www.bikethink.com/frame-comfort/

https://sheldonbrown.com/rinard/rinard_frametest.html

cccorlew

Is there some cheap joke waiting to be made about the 50s forum and the discussion of stiffness and the lack thereof? Just asking.

trek330

Thanks to everyone for the thorough and intelligent responses to my inquiry!I'm starting to understand the concept.I think.

jdon

Yeah, but I witheld it fearing the moans of the masses.

ragtoplvr

ever bend some metal over and over to break it. Notice it gets hot. That is energy dissipated from bending. When you petal the bike, and the frame flexes, which has to happen, some of your energy is going to heating the frame. Not enough to feel, but it is still gone. Bike with suspension, as the shocks give, it heats the oil in them, one of the reasons a mountain bike is harder to petal. That is why the elite bike have lock outs for the climb and then full suspension for the descents.

Of course our bodies would not like a completely stiff bike. the vibration and shock would be horrible. So we want the frame to have some give when transferring wheel shock to the bars and the seat. But when pedaling, there is a twisting force to the bottom bracket, movement here is wasted energy so we try to minimize it.

We are low powered motors, so every last bit of power we want to put into locomotion.

Rod

stapfam

Several of these about-Just bought a Pinarello FP Uno that has this set up but it looks as though Giant are stopping the TCR in this form as They are no longer listed in the UK.

That Uno was an expensive bike for a Tiagra equipped bike but you can feel where the money has gone on this bike. Into the frame and although a bit heavier than my other bikes- No downgrades on groupset to cut costs and it rides superbly.

BluesDawg

There are features in Specialized Roubaix frames, seat stay shape and carbon fiber layup profiles etc., that contribute to vertical compliance, but the function of Zertz inserts is to dampen frame vibration, not to provide vertical compliance.

StanSeven

This "new" idea just didn't work. It was a gimmick seven or eight years ago and slowly diminished to not available now except mostly on some very low end bikes for selling appeal. Instead of bringing the best features of both materials into one design, it combined the worse of both materials.

What has been more effective in getting to the same objective is altering the thickness and design of the rear. Cervelo does that with thinner stays and others use various curves.

bruce19

I have a Masi Gran Criterium S that is AL with CF fork and stays that was made around 2005. I've had steel and one LeMond TI and this bike is the one I like best. Well actually I liked my steel TSX an awful lot. I don't know if Masi still makes AL w/CF. Now I'm curious.

bruce19

That hasn't been my experience. My Masi is a great bike. I'll never part with it. It's stiff enough and comfortable for me.

bruce19

Here ya go: https://www.masibikes.com/bikes/performance/vincere-2012

big john

To me, the benefit of a stiff frame is better handling through turns, especially at my weight.
The disadvantage of a too stiff frame is loss of ride comfort.

I've heard the power loss thing debated for decades and have never believed there is power loss from a frame flexing and have never seen a shred of evidence to support that claim. I also don't buy the full suspension mtb analogy. Road bikes are not full suspension mtbs.

The most noodly bike I have ridden was a steel Landshark of standard diameter Prestige tubing. I climbed well on it (for me) but it flexed so much I knew it would break, so I sold it.
The stiffest, most harsh riding bike I have owned was also steel, a Tesch S-22. Awesome turning ability, but rattle your teeth loose on a rough road-stiff.