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Can lighter and stiffer bike make climbing significantly faster

Old 03-31-21, 03:52 AM
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Can lighter and stiffer bike make climbing significantly faster

Currently I own ~ 10.5kg aluminum xc bike. I like to train on uphill roads (average 8-9% of gradients or so)

Lets say I buy a crabon frame ~8kg bike. Will this make my times significantly faster?
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Old 03-31-21, 05:14 AM
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Define significant.
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Old 03-31-21, 05:39 AM
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I have a hard time believing carbon would be "stiffer" then the aluminum frame. Are these paved or unpaved? I'd be playing with wheel/tire/pressure choices first.
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Old 03-31-21, 10:58 AM
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Originally Posted by shelbyfv
Define significant.
I dont know, I guess if its going to justify a purchase price, the answer is definitely no. But I am just wondering about the possible difference.

I am talking about paved roads.
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Old 03-31-21, 11:00 AM
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Originally Posted by GrainBrain
I have a hard time believing carbon would be "stiffer" then the aluminum frame. Are these paved or unpaved? I'd be playing with wheel/tire/pressure choices first.
I though carbon flexes less under pedal pressure than alu frame?
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Old 03-31-21, 11:15 AM
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You're the engine, so remember that as the "first factor" regardless of what's under you. Second, weight is a bigger factor than stiffness. I'd rather climb with a 15lb aluminum bike than a 23lb carbon bike any day. Third, it's easier for me to lose 3lbs than it is to make a 23lb bike become a 20lb bike (cheaper, too). Fourth, I only hear sprinters fussing about stiffness, rarely climbers.
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Old 03-31-21, 11:17 AM
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Yes, if you religiously do intervals up those climbs.
The difference in weight is probably about 3% of the bike and rider.
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Old 03-31-21, 11:21 AM
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Originally Posted by utoner34
Currently I own ~ 10.5kg aluminum xc bike. I like to train on uphill roads (average 8-9% of gradients or so)

Lets say I buy a crabon frame ~8kg bike. Will this make my times significantly faster?
Climbing speed is inversely proportional to total weight.

Assuming you weigh 70kg, dropping that 2.5 kg of bike weight will make speed 80.5 / 78 kg = 1.032 times what it was before; or save 2.5/80.5 x 3600 = 112 seconds per hour.
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Old 03-31-21, 11:31 AM
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Originally Posted by blacknbluebikes
You're the engine, so remember that as the "first factor" regardless of what's under you. Second, weight is a bigger factor than stiffness. I'd rather climb with a 15lb aluminum bike than a 23lb carbon bike any day. Third, it's easier for me to lose 3lbs than it is to make a 23lb bike become a 20lb bike (cheaper, too). Fourth, I only hear sprinters fussing about stiffness, rarely climbers.
You could explain why would you "rather climb with a 15lb aluminum bike than a 23lb carbon bike any day" ?

Originally Posted by Drew Eckhardt
Climbing speed is inversely proportional to total weight.

Assuming you weigh 70kg, dropping that 2.5 kg of bike weight will make speed 80.5 / 78 kg = 1.032 times what it was before; or save 2.5/80.5 x 3600 = 112 seconds per hour.
But isnt bike weight different that rider weight? For example, lighter wheels means you ride faster, dont they? Or you are saying if I ride 5kg bike and weight 70kg, I will ride as fast as if I ride 10kg bike and weight 65kg?
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Old 03-31-21, 11:48 AM
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Originally Posted by utoner34
But isnt bike weight different that rider weight?
Not at steady speed.

For example, lighter wheels means you ride faster, dont they?
Wheel weight difference doubles accelerating as you move from axle center to road surface although it's not enough to matter unless you're contesting a sprint finish.

Accelerating an extra 500g at the road surface from 0 to 20 MPH only costs you the energy it takes covering 12 feet.

Or you are saying if I ride 5kg bike and weight 70kg, I will ride as fast as if I ride 10kg bike and weight 65kg?
Yes.

Last edited by Drew Eckhardt; 03-31-21 at 02:56 PM.
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Old 03-31-21, 12:13 PM
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Can lighter and stiffer bike make climbing significantly faster?

Nothing you can buy will make you significantly faster.
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Old 03-31-21, 01:43 PM
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And if you ride a mellowly gravel bike vs stiff race bike, there is still no significant difference when climbing and getting in and out of saddle constantly?
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Old 03-31-21, 01:55 PM
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Originally Posted by utoner34
And if you ride a mellowly gravel bike vs stiff race bike, there is still no significant difference when climbing and getting in and out of saddle constantly?
Correct.
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Old 03-31-21, 02:00 PM
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Originally Posted by utoner34
Can lighter and stiffer bike make climbing significantly faster
Depends on how much lighter, and what "significantly" means.
If the bike+rider system is 80kg, and you slash this by 2kg, that's a 2.5% reduction in gravitational drag. When you're moving slowly up a steep hill, this might actually give you close to a 2.5% improvement in climbing speed for the same effort.

"Stiffer" is more complex. As much as "stiffness" gets talked up, power transfer losses in rigid frames usually aren't all that significant, even with frames that by modern standards are considered very flexible. There's some evidence that differences in frame stiffness can result in tangible rider power output differences due to how their pedaling interacts with that flex, but this might not be quite as simple as stiffer=better.
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Old 03-31-21, 02:10 PM
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Originally Posted by tomato coupe
Can lighter and stiffer bike make climbing significantly faster?

Nothing you can buy will make you significantly faster.
Thats not entirely true, now, is it? Hashtag WADA
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Old 03-31-21, 02:12 PM
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Of course, we're talking watts per kilogram.





On the one hand, we have J.J. Watt. Then, there's Charlie Watts. On whom would you place your uphill bet? Discuss.
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Old 03-31-21, 03:52 PM
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How fast do you ride now?

Once you exceed about 15 MPH, aero drag surpasses all the other factors combined that are holding you back. If you want to become significantly faster, work on your aerodynamic form and, of course, the motor. Everything else is small potatoes.
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Old 03-31-21, 05:45 PM
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"Significant" defined how?

As for less weight .... How many minutes do you spend climbing on your favorite (or least favorite) climbs? How would you be willing to spend to save three seconds on a ten-minute climb? How many seconds on a ten-minute climb would you consider "significant"?

Pretty sure any losses due to frame flexibility are not significant except to the really anal nitpickers and the guys who still use slide rules. Biggest thing with stiffness with modern frames is when sprinters can actually warp the frame enough to have stuff rubbing ... but unless you are cranking out 1600 watts .....

And as far as carbon fiber .... CF is different, not better. A CF frame is not inherently better than any other. There are engineering reasons for using CF in certain applications ... but I ride an 17-lb CF wunderbike and a 27-pound Al working bike up the same hills at about the same speed. The engine is really all that matters.
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Old 03-31-21, 06:00 PM
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Originally Posted by utoner34
Currently I own ~ 10.5kg aluminum xc bike. I like to train on uphill roads (average 8-9% of gradients or so)

Lets say I buy a crabon frame ~8kg bike. Will this make my times significantly faster?
Anyone got proof that frame stiffness is faster?

Jan Heine in his new book The All Road Bike Revolution would disagree. Page 58 for those interested.
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Old 03-31-21, 06:19 PM
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If you are going to convince yourself you can buy speed, go for it. The first few times on that carbon climber, you will be faster because psychologically, you will give a bigger effort to confirm your choice. Afterwards, not so much.
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Old 03-31-21, 07:47 PM
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Originally Posted by utoner34
I dont know, I guess if its going to justify a purchase price, the answer is definitely no. But I am just wondering about the possible difference.

I am talking about paved roads.
You would probably be a bit faster, but would only really notice an observable difference by riding with other people you've ridden with before. If you could not keep up with them before, you will probably notice an improvement with a lighter bike. For example, you might not lag as far behind, might actually keep up with them, but I doubt you'll go faster than someone you couldn't keep up with on the old bike. Only fitness plus good equipment will do that.

Originally Posted by utoner34
I though carbon flexes less under pedal pressure than alu frame?
No, there's world class stiff aluminum frames. High quality aluminum racing frames are as stiff as you'd be able to use or need.

Originally Posted by utoner34
You could explain why would you "rather climb with a 15lb aluminum bike than a 23lb carbon bike any day" ?
It's more fun because it probably feels more responsive and faster. See my above comment as to whether it actually matters in practical terms.

But isnt bike weight different that rider weight? For example, lighter wheels means you ride faster, dont they? Or you are saying if I ride 5kg bike and weight 70kg, I will ride as fast as if I ride 10kg bike and weight 65kg?
Like others have said, only when accelerating. OTOH, in a normal ride, especially with others, you do accelerate a bit a lot of times. Lighter wheels will feel more responsive probably. See above whether it matters.

Originally Posted by tomato coupe
Can lighter and stiffer bike make climbing significantly faster?

Nothing you can buy will make you significantly faster.
Agree but it can "feel" faster, might actually be a little bit faster, but probably be more fun.

I have absolutely no problem with people buying whatever they can afford in quality, lightweight bike products. In my experience as an aging "enthusiast" with mediocre fitness and natural ability, I really enjoy the top tier stuff I've managed to cobble together in a way that's affordable to me. It's just fun and not a horrible way to spend money.

Last edited by Camilo; 03-31-21 at 07:54 PM.
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Old 03-31-21, 08:22 PM
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Originally Posted by Drew Eckhardt
Climbing speed is inversely proportional to total weight.

Assuming you weigh 70kg, dropping that 2.5 kg of bike weight will make speed 80.5 / 78 kg = 1.032 times what it was before; or save 2.5/80.5 x 3600 = 112 seconds per hour.
Just noting that while the gravity term will dominate, there will be rolling friction and air friction terms when climbing. If I climb a 5% grade at 12 mph, the gravity term will be about 250-260W and the other terms will be about 60W. The weight difference would make a proportional change in the gravity term but not affect the other terms.

Otto
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Old 03-31-21, 09:52 PM
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Originally Posted by Phil_gretz
Of course, we're talking watts per kilogram.





On the one hand, we have J.J. Watt. Then, there's Charlie Watts. On whom would you place your uphill bet? Discuss.
Drummers are all about endurance and controlled substances. Charlie Watts easy.
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Old 03-31-21, 10:01 PM
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You said you are training. So do you want to train less with a lighter bike?
Do you also buy light weight dumbbells?
I heard they make CF dumbbells now....
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Old 03-31-21, 10:55 PM
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Like a famous local racer once told me: until you're missing the podium by less than a minute, the bike isn't going to make a difference.
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