It Doesn't matters, It's not the bike/kit you have...

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SkipdiverJohn

Deplorable Brexiteer
I just ran the figures for a more realistic 150 watts power, for a 90kg rider on a 7kg bike and on a 16kg bike, both on clincher tyres (my MTB tyres are ancient 1.75" commuter/touring pattern), both riding up on the bar tops. For an 80km trip, the 7kg bike comes out at 181 minutes journey time, the 16kg bike comes out at 184 minutes.
So a fancy £3-4k super-light carbon bike saves a whole 3 minutes compared to my £20 secondhand old steel workhorse!
 

Gravity Aided

Legendary Member
Wider tires, same pressure and same tread, may be faster, due to the decreased friction of less tire deformation.
 

cyberknight

As long as I breathe, I attack.
2 average minute saving over 9.7 miles comparing road bike vs aforementioned MTB with 450 ish feet of climbing on my commute.
 

SkipdiverJohn

Deplorable Brexiteer
2 average minute saving over 9.7 miles comparing road bike vs aforementioned MTB with 450 ish feet of climbing on my commute.

Which rather tends to prove the point that the journey time savings of having a very light and expensive bike are pretty minimal, unless the rider of the light bike rides on drop bars and the rider of the heavy bike is in a sit up and beg position. Commuters and pleasure cyclists (as opposed to speed merchants just trying to go as fast as possible) tend to sit up for the better view rather than just go hell for leather in a low position.
 

cyberknight

As long as I breathe, I attack.
Which rather tends to prove the point that the journey time savings of having a very light and expensive bike are pretty minimal, unless the rider of the light bike rides on drop bars and the rider of the heavy bike is in a sit up and beg position. Commuters and pleasure cyclists (as opposed to speed merchants just trying to go as fast as possible) tend to sit up for the better view rather than just go hell for leather in a low position.
My mtb is drop bar conversion with same bike fit as my road bike though so same aero effect, differences are rolling resistance, time to accelerate and weight on hills, plus m more knackered to do that time so im effectively putting more watts out to get those times.By the end of the week my legs are toast on that bike.
 

delb0y

Legendary Member
I'm looking forward to trying out the new Giant Toughroad v the Tricross over the coming weeks and months. The weight is about the same, so it'll be a very un-aerodynamic position and very wide tyres versus the opposite. Be interesting to see the real world difference. I suspect those two factors will make the cycling much harder work, but I'm rather hoping the lower gearing will get me up some hills on which this year I've had to get off and walk up, and I'm hoping to tackle a lot more bridle-paths. So it might be harder, more enjoyable, slower, less enjoyable... may even be faster... although I suspect not.
 

bpsmith

Veteran
Which rather tends to prove the point that the journey time savings of having a very light and expensive bike are pretty minimal, unless the rider of the light bike rides on drop bars and the rider of the heavy bike is in a sit up and beg position. Commuters and pleasure cyclists (as opposed to speed merchants just trying to go as fast as possible) tend to sit up for the better view rather than just go hell for leather in a low position.
This thread is about the 2 example bikes being ridden to get the most speed out of them. If people choose not to use the drops and not ride for speed as their goal, then the modified MTB with road type tyres will naturally be similar over a flat route with no stops or in traffic for the commute.

My argument is that a light road bike compared to a heavy MTB, being used how they are intended and with the components they are sold with (including tyres), will be faster. It’s misinformation to suggest otherwise.

You’re argument centres around a road bike being ridden like a MTB, half heartedly whilst taking in the views, and a MTB being equipped with road tyres on a flat route without ever changing pace. I won’t argue against that type of comparison, so will end it there.

The overall fact, that we are sure to agree on, is that we should all equip our bikes and ride them how we like, ignore how much money anyone else has spent on their bikes, and enjoy ourselves. Far too much negativity in the world to let that get in between us cycling fans.
 

bozmandb9

Insert witty title here
Run all the numbers you want. When I was using my winter bike, an 11kg Whyte with touring geometry, I got dropped if I tried to ride with my sons team training ride. Now my 6.8 kg BMC is fixed, I can stay with them. I know the weight may be only one factor. Your computations aren't taking into account geometry and the effect on aerodynamics (except basics like tops or drops).
 

Smokin Joe

Legendary Member
You might have a hard slog up a hill, but once over the crest you can bomb down the other side. What you lose going up you gain going down,
No you don't, because the ascent is taking far longer than the descent so the gain on the way up on a bike that is 3kg lighter will not be made up by having the extra weight on the way down because of the much shorter time it gives you any advantage. I've ridden for long enough to know that losing 3kg off the bike makes a noticeable difference to average speed, whatever someone's lab calculations come up with.
 
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Ajax Bay

Guru
it would take an additional 36 mins for the same rider to travel 80km on a 7kg road bike compared to a 16kg MTB and that’s on the flat!
You're not comparing like with like though.
Online after a lovely, sunny 75km this morning with an excellent coffee stop and good company.
Yes, unusually @bpsmith's contribution did not add value.
Keeping all else the same, at 150w power for a 90kg rider the difference in time between riding 80km on a 7kg bike and a 16kg bike (on the flat) is less than 2 minutes (172.1 minutes < 173.7 minutes) according to calculations provided using:
http://bikecalculator.com/what.html [= 0.3kph slower]
Not off topic, dropping 10kg of bodyweight (or cycle weight) saves 2 minutes.
Each kg lost/saved suggests an increase in speed of 0.04kph. Compare that with saving rolling resistance by choosing decent tyres - 4 watts is easily available (2w each wheel) which will imply a speed increase of 0.3kph.
Changing Gatorskins to GP 4000S II suggests 7w . . . . . . per tyre (many other makes are available).
 
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bpsmith

Veteran
Online after a lovely, sunny 75km this morning with an excellent coffee stop and good company.
Yes, unusually @bpsmith's contribution did not add value.
Keeping all else the same, at 150w power for a 90kg rider the difference in time between riding 80km on a 7kg bike and a 16kg bike (on the flat) is less than 2 minutes (172.1 minutes < 173.7 minutes) according to calculations provided using:
http://bikecalculator.com/what.html [= 0.3kph slower]
I will assume that you are inferring that I generally do add value, so I appreciate that. Feel free to state otherwise though. :smile:

You’re right about the difference that solely weight makes, all else being equal. The comparison here was comparing 2 completely different bikes though, hence my comparison encompassing said differences.

More importantly, how was your ride today? Wish I had experienced a gloriously sunny morning in the saddle. #ProperJealous!
 

Ajax Bay

Guru
The 'unusually' was an edit, though quite a quick one, as I thought without it I was being harsh (for the season of good will). Please infer what you prefer. ^_^
This was the scenario I focused on (quote from the OP):
you will be just as fast on a cheap $50 Used 15kg mtb with NICE tyres . . . than someone on a 7kg $5k bike . . . - as long as you have the same Aero Drag and aren't going up-hills.
That is: on the flat, same aero drag (ie position) - just different weights of bike.
View: https://ridewithgps.com/trips/19768982
5 degrees, maybe 6, and only one 30m flood (about 8" deep; feet unclipped and at downtube changer level).
 
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