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PostPosted: Wed Apr 20, 2011 4:20 pm 
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This is going to seem a daft question. My winter/hack bike is an aluminium hardtail mountain bike fitted with rigid forks & 25mm slicks. The "cockpit" is set up exactly as my expensive carbon road bike. Why is it, when climbing on the bar ends of the mountain bike, that it seems/is much quicker? Is it anything to do with the much longer wheelbase of the MB (1055mm)? It also doesn't seem any slower on the flat. This all seems crazy as the road bike is 3kg lighter than the MB. Perhaps I should upgrade the MB & see if that slows it down.


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PostPosted: Wed Apr 20, 2011 5:26 pm 
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Any speed data to back up what you're 'feeling'?


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Posted: Wed Apr 20, 2011 5:26 pm 


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PostPosted: Wed Apr 20, 2011 5:31 pm 
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Location: In the Land of Cotton
The mtb wont be faster. Maybe it feels faster if you really lever the bar ends on the climbs so you feel as if you're working harder.
Will it be any faster / slower on the flats? Not really. Rolling resistance and aerodynamics are probably fairly close.
Over a 100 mile hilly route, the lighter CF rode bike would be faster but probably by seconds rather than minutes unless you run aero wheels on it. Then it might be minutes faster.
3kg out of a bike / rider total weight of, what, 85kg? That makes the road bike 3.5% lighter as a total weight. Not much, certainly on the flat when weight doesn't matter.
I wait to be proved wrong by those wiser than me!

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PostPosted: Wed Apr 20, 2011 5:36 pm 
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I'm going to say it's the gearing. With low gears, you accelerate super quick and feel like you're going super quick just because of the immediate response. If you're grinding a hard gear, regardless of how fast you're actually going, you'll feel like you're going so slow.


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PostPosted: Wed Apr 20, 2011 8:27 pm 
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It isn't the gearing as it's very similar to my road bike, ie no super low gears. As suggested I'll fit a computer to get some av. speed comparisons.


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PostPosted: Wed Apr 20, 2011 8:46 pm 
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The smaller diameter wheels will spin up quicker than larger wheels, and maybe that's what you're feeling. But other than that no idea. I'm assuming both bikes are in proper working order and no dragging brake pads or anything.

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PostPosted: Wed Apr 20, 2011 9:29 pm 
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Location: by Crystal Springs (Sawyer Creek Trail)
My old Trek 7500 FX felt very fast compared to my Trek Al road bike. Flying past one of those stationary police speed traps showed that top speed is equal for me. I get very very low on the hybrid (time trial low and narrow) and was able to manage 30 mph. I was able to get 31 with the road bike (there's not a huge run up to the trap as it's somewhat close to the stop lights) in a sprint and seated. On the long run though, I could easily follow the road ride on the road bike whereas I struggled after 10 miles with the hybrid.


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PostPosted: Wed Apr 20, 2011 10:20 pm 
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so you now know the truth,
weight and aerodynamics make very very little difference to performance.


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PostPosted: Wed Apr 20, 2011 10:39 pm 
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bikedoc wrote:
so you now know the truth,
weight and aerodynamics make very very little difference to performance.


:thumbup: The truth hurts, but it is the truth after all.

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PostPosted: Thu Apr 21, 2011 2:00 pm 
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bikedoc wrote:
so you now know the truth,
weight and aerodynamics make very very little difference to performance.

At a 25 mile TT last weekend I went faster with 286W than my clubmate went with 340W. If it's not weight and it's not aerodynamics, what is it that made over 54W difference?


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PostPosted: Thu Apr 21, 2011 2:32 pm 
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bikedoc wrote:
so you now know the truth,
weight and aerodynamics make very very little difference to performance.

There you go. We declare a winner based on some guy's "feeling"!

I have two road bikes, both expensive and fast (Storck Fenomalist and Trek Madone 5.9SL). I only use the Trek in the rain and for some reason it always "feels" faster. I think it's because I have softer tires on it and they feel smoother to ride. Anyway, now for the science -- at the same power outputs I average more than 0.5 mph faster on the Storck on the same courses. So much for "feel".

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PostPosted: Thu Apr 21, 2011 2:37 pm 
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Stevei, sometimes people say things which are a bit tongue in cheek. I thumb uped bikedocs statement because I believe many overestimate the benefits they're really getting from small aero/weight changes. But if good marketing will sell a product, then companies will do good marketing. Yes, bike weight and aero matters. No question. But I doubt those were the only things accounting forth difference between you and your clubmates performance differences. How much does he weigh versus you? Was the course hilly which would require more relative watts/kg than if it wasn't. Were your powermeters both calibrated properly and reading the same wattage for a given power. Maybe you are just a more efficient rider, using more efficient gears at a given wattage. I don't know. Just saying the weight and aerodynamics of the bike in a wind tunnel are one thing. Throw a flailing human body on the thing bobbing up and down over non ideal roads and the differences between two fairly similar bikes becomes a lot less of a factor. But yes, you are right, and I did not mean to imply that weight and aerodynamics does not matter at all. Damn, the truth really does hurt. :)

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PostPosted: Thu Apr 21, 2011 3:13 pm 
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Location: Islip, NY
stevei wrote:
bikedoc wrote:
so you now know the truth,
weight and aerodynamics make very very little difference to performance.

At a 25 mile TT last weekend I went faster with 286W than my clubmate went with 340W. If it's not weight and it's not aerodynamics, what is it that made over 54W difference?


I'll guess rider position was the biggest difference. You probably punch a smaller hole into the wind.

That's my theory without knowing more.

-Eric

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PostPosted: Thu Apr 21, 2011 3:16 pm 
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Location: Islip, NY
dieselgeezer wrote:
This is going to seem a daft question. My winter/hack bike is an aluminium hardtail mountain bike fitted with rigid forks & 25mm slicks. The "cockpit" is set up exactly as my expensive carbon road bike. Why is it, when climbing on the bar ends of the mountain bike, that it seems/is much quicker? Is it anything to do with the much longer wheelbase of the MB (1055mm)? It also doesn't seem any slower on the flat. This all seems crazy as the road bike is 3kg lighter than the MB. Perhaps I should upgrade the MB & see if that slows it down.


Bike/wheels being stiffer might make the bike feel faster. The amount of trail also effects feel. I went to a bike with faster front end geometry and "felt" faster even though speeds were about the same.

The slicks will decrease the trail compared to the larger, off-road tires the bike was designed for.

-Eric

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Posted: Thu Apr 21, 2011 3:16 pm 


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PostPosted: Thu Apr 21, 2011 4:12 pm 
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I have a very similar situation: a mtn bike set up for road riding in winter.
It feels like a speedy little sports car.....as long as I am by myself. But it is mainly just because you are sitting closer to the ground on the smaller wheels. It is easy to see the difference if you ride with other riders of known ability.


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