ht001

I'm torn between two bikes. Both are carbon fiber with roughly the same components and very close in price. The ride quality is fantastic on both, but there is a slight difference. One feels slightly softer than the other. This is especially notable when climbing.

My question is, what advantages and disadvantages are there in a frame that is stiffer vs. one that has a little more softness to it? I've read several posts, and articles about the physics behind flex and stiffness, but I'm not getting a strong sense of what I could lose/gain in performance, comfort, etc. by going one way or the other. Any thoughts?

To encourage objectivity I'm leaving out the make/model details...which will probably be frustrating for potential respondents.

If it helps to know a bit about the riding I do, I live in CO and will use this bike for road rides of various distances and 2-3 triathlons per year. I'm currently on an aluminum ride with all 105, and this new bike will be an upgrade. The current bike will become my commuter.

Thanks!

zonatandem

For climbing, sprints, tri'lons: stiffer will be better
For more casual riding (including non-competitive centuries): the bit softer ride will do the trick

Hitchy

...what frames are you looking at?

Hitchy

jthj

I would probably go with the stiffer one. I don't like frame flex.

ht001

OK. I'll fess up.

Kestrel Talon
Giant TCR 1

jslopez

On the looks I'd go with the Talon but I'm guessing the Giant is the stiffer ride.

ht001

Actually, the Giant is the 'flexier' ride. (I know that's not a word, but it seems to fit) It is just a slight difference, but I definitely notice it, and I never thought I'd be able to feel such a thing.

jthj

Was it flexier as in softer over the bumps or flexier as in pedal induced flex? It's the pedal induced flex that I don't like.

Hitchy

G'day,

You running the same set ups on each bike when you tested them?...ie tyre pressures, tyres, gruppo's seat posts etc?....the TCR has plenty of things wrong with it, but I wouldn't of said that 'Flex' is one of them. I don't know the kestrel frame at all.

hitchy

jslopez

Would have to agree with Hitchy, if it's indeed flexy I would almost think that the bike you tried was bad stock or something. How long did you ride it for? Could it be that you really want the Kestrel and your mind is biased against other bikes?

The reason I say this is when I was testing out bikes (which was your usual 1-2 block round) I really didn't feel that much difference on the ride. Component difference is usually easy to spot for that time but ultimately all bikes on the same price range felt equally good.

seely

Actually I can induce BB flex on a TCR ('04) without too much effort, so yes they do flex.

Hitchy

I doubt it...unless you are 900lbs or something!....there may be other issues with the bike you rode that 'felt' like it was BB flex. Mind you, I'm not defending the frame at all, I really don't like the TCR at all....but they don't flex thru the BB,

cheers,

Hitchy

seely

They do. When I stand and pedal hard in a big gear the chain will rub the derailleur cage when I am mashing the drive-side. Sitting or going easy it wont.

khuon

Given that the Kestrel is a monocoque frame design, I'm not at all surprised it's a stiffer structure just due to the shaping. Also, it seems that Giant uses 4 layers of various directional and cut T-700 standard modulus (235 GPa) while Kestrel uses 7 layers of M30S intermediate modulus (294 GPa) with an additional outer layer of T-700.

JavaMan

Sounds like you already know the answer to your question. Now you must choose...

I used to go for stiffness (aluminum Klein with 36 spoke wheels), but that I am older I like comfort better (Trek carbon with paired spoke wheels). Too bad you can't buy both bikes you are looking at.
Tom

jslopez

That's interesting (as the TCR was a bike recommended to me by my LBS). If you don't mind the question, how much do you weigh seely? Highly illogical but maybe the TCR has an unlisted weight requirement.

Indolent58

If one of the bikes has noticable BB flex when you are out of the saddle mashing the pedals, then you don't want it. If neither do, it's a subjective choice of what feels best to you. "Soft" can be a good or a bad thing, from the proverbial magic carpet ride to feeling like you are trying to run on beach sand. But barring major flex there will probably not be a significant difference in actual performance between the two bikes.

jthj

You're flexing the crank and not the frame I would think. I can do that with my Giant OCR Elite with a TruVativ Rouluer crank on the trainer and I can see the chainring flexing. Not an issue to me becuase I usually do high cadence low torque ridding. Try looking down when you hear that, but on a trainer not the road

2Rodies

If you want a really stiff fast Carbon frame buy a LOOK Kg481. They are not the lightest carbon frame but they are stiff and stable. I also own an Orbea Orca which is nearly as stiff and quite a bit lighter. I would say the BB stiffness between the two frames would be 10-15%.

galen_52657

buy the stiffer frame

PiratePete

Buy the one that looks cooler.

seely

Thats the crux of it all, I'm 6'1 and like 150lbs soaking wet. FWIW the bikes I've tried out were a 54cm and a 58cm (I think)... one was about average sized and one was larger in anycase.

ht001

Could flexing in the crank be more plausible if it is a carbon crank? The TCR 1 that I test rode has a carbon crank. It doesn't seem possible I could have induced major flex in the BB. But I don't think I'm crazy. I've ridden both bikes a couple of times, and I swear that Giant feels softer.

Otherwise I agree with what someone else suggested, that unless all conditions are equal (tire pressure, wheels etc.) I won't experience the same sensation on the rides. Perhaps that's what it boils down to???

I'm sure by the time I figure out what I think I want I'll have to ride the '05s....I'm reminded of a line from a Jimmy Buffett tune, "I know one thing, Indecision may or may not be my problem."

jthj

I think the carbon cranks are supposed to be stiffer than the Al alloy ones. Although I've never used them so I'm only speaking from what I've heard from others I ride with who have them. I know my cf handle bars are stiffer than the al ones I had before. I judge this based on rigity when I'm out of the saddle and putting my weight forward on the bars in a sprinting position. However they also feel smoother over the rough stuff. I could see that is being described as softer which would imply flex. But they really don't flex much. That being said at what contact point on the bike does it feel softer? Are you sure it's flex? I would describe the frame flex I experienced with steel frames as making the frame feel noodley under me when out of the saddle and climbing or sprinting. See if they will put the bikes on a trainer. Crank the resistance all the way up, put it in it's highest gear combo and mash the pedals while looking down to see what if anything is flexing.

BigFloppyLlama

I'd imagine it's something other than the bottom bracket. The TCR has a very stiff bottom bracket according to Tour Magazine's tests.. 101Nm/° for the bottom bracket and 56Nm/° for the headtube/lateral stiffness. I don't have the individual stats for the Kestral, but it has a Stiffness to Weight ratio of 58.