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Re: 25mm tyres

Posted: 8 Mar 2018, 12:35pm
by elPedro666
I'd need to see your methodology and peer review for that please...

Joking aside, unless you're racing and every second counts I'd have to wonder why anyone would want to go super-skinny at all, even if it is a fraction quicker; the reduced comfort and subsequent extra fatigue seem far more significant in (my version of) the real world.

I now feel compelled to immediately own up to having skinny 24mm on my silly Italian road bike, but I claim the defence of 'Pretty Summer Toy' y'r Honour

I'm a trendy consumer. Just look at my stupid phone.

Re: 25mm tyres

Posted: 8 Mar 2018, 12:50pm
by Keezx
IF you compare 2 tyre sizes, then you should use tyres with comparable construction/carcass/thread, otherwise it's useless.

Re: 25mm tyres

Posted: 8 Mar 2018, 1:39pm
by mullinsm
Keezx wrote:IF you compare 2 tyre sizes, then you should use tyres with comparable construction/carcass/thread, otherwise it's useless.


The 23,25 and 28mm were all Conti Gatorskins. The only difference apart from the size was the weight. Rolling resistance theory says the 28mm should be quicker on the roads in question, but they aren't. I suspect the difference therefore is the weight and I imagine that the extra 60g between the 25s and the 28s makes as much difference as the 60g difference between good wheels and very good wheels.

Re: 25mm tyres

Posted: 8 Mar 2018, 2:00pm
by andrew_s
What pressures did you run the 3 sizes at?
On rough roads, the increased comfort (i.e. less vibration of you) from lower pressures should be the difference, and if you run all 3 sizes at the same pressure you won't see any significant benefit from wider tyres.

In the real world, people don't ride to power meters, and the extra fatigue in elPedro's "even if it is a fraction quicker; the reduced comfort and subsequent extra fatigue seem far more significant" is likely not just down to discomfort, but to having to work harder for his preferred cadence/pace.

Re: 25mm tyres

Posted: 8 Mar 2018, 2:26pm
by Brucey
both the above posts are ignoring the fact that you are having to push fatter tyres through the air and that this may consume much more power than you might 'save' in a change in Crr.

Just to put in into context, at 10m/s (about 20mph) an extra resistance of just 0.1N (~10g) is required to increase your power requirement by 1W, and folk get very excited about tyres that might drag 1W less... :roll: .

You can generate 0.1N of extra aero drag by (literally) sticking two fingers in the air. Whacking fat tyres on is likely to have a greater effect than that.

cheers

Re: 25mm tyres

Posted: 8 Mar 2018, 2:30pm
by Keezx
mullinsm wrote:
Keezx wrote:IF you compare 2 tyre sizes, then you should use tyres with comparable construction/carcass/thread, otherwise it's useless.


The 23,25 and 28mm were all Conti Gatorskins. The only difference apart from the size was the weight. Rolling resistance theory says the 28mm should be quicker on the roads in question, but they aren't. I suspect the difference therefore is the weight and I imagine that the extra 60g between the 25s and the 28s makes as much difference as the 60g difference between good wheels and very good wheels.


Weight does matter a little bit when accelerating but nothing noticable for your average speed.
No way 60 gr./wheel would have any significanty influence, the tyre width does matter for air resistance though.
My guess is you sit also a bit more aerodynamic on the faster bike.

PS 1 thing which isn't even mentioned here is the fact that the rim inner width influences the tyre width, contact patch and riding properties significant.
Food for thought:
https://intheknowcycling.com/2016/04/03 ... eel-sizes/
I don't bother anymore about 23 mm or 25 mm , take what I can find for a good price, put them om 18C or 19C rims and pump 5-6 Bar depending on the expected road surface.

Re: 25mm tyres

Posted: 8 Mar 2018, 3:09pm
by mullinsm
Keezx wrote:
mullinsm wrote:
Keezx wrote:IF you compare 2 tyre sizes, then you should use tyres with comparable construction/carcass/thread, otherwise it's useless.


The 23,25 and 28mm were all Conti Gatorskins. The only difference apart from the size was the weight. Rolling resistance theory says the 28mm should be quicker on the roads in question, but they aren't. I suspect the difference therefore is the weight and I imagine that the extra 60g between the 25s and the 28s makes as much difference as the 60g difference between good wheels and very good wheels.


Weight does matter a little bit when accelerating but nothing noticable for your average speed.
No way 60 gr./wheel would have any significanty influence, the tyre width does matter for air resistance though.
My guess is you sit also a bit more aerodynamic on the faster bike.

PS 1 thing which isn't even mentioned here is the fact that the rim inner width influences the tyre width, contact patch and riding properties significant.
Food for thought:
https://intheknowcycling.com/2016/04/03 ... eel-sizes/
I don't bother anymore about 23 mm or 25 mm , take what I can find for a good price, put them om 18C or 19C rims and pump 5-6 Bar depending on the expected road surface.


With all due respect, that's simply incorrect.

Re: 25mm tyres

Posted: 8 Mar 2018, 3:14pm
by Keezx
Then explain to me what difference it makes....(on a flat course), (theoretical and not anecdotal)

Re: 25mm tyres

Posted: 8 Mar 2018, 3:24pm
by Mick F
Keezx wrote:Weight does matter a little bit when accelerating but nothing noticable for your average speed.

Are you saying that a heavy bike has the same average speed as a light bike when moving?
If so, you're ignoring hills. :wink:

Re: 25mm tyres

Posted: 8 Mar 2018, 3:33pm
by Keezx
I think you got my point. :wink:
On a hilly course 5 kg makes a difference , but 120 grams in the wheels, really?
All over the world people are brainwashed about wheel weights, 1400 grams are light and 1800 grams are boat anchors.
For me it's not much more than fetishism.

Re: 25mm tyres

Posted: 8 Mar 2018, 4:16pm
by mullinsm
Mick F wrote:
Keezx wrote:Weight does matter a little bit when accelerating but nothing noticable for your average speed.

Are you saying that a heavy bike has the same average speed as a light bike when moving?
If so, you're ignoring hills. :wink:


And not only hills. The idea that a heavy bike is just as fast as a light bike on the flat is just plain wrong. Certainly the difference is more noticeable on hills, but anyone who has ever toured on a heavy bike knows that, even on the flat, you know you're carrying.

Re: 25mm tyres

Posted: 8 Mar 2018, 4:16pm
by mullinsm
Keezx wrote:I think you got my point. :wink:
On a hilly course 5 kg makes a difference , but 120 grams in the wheels, really?
All over the world people are brainwashed about wheel weights, 1400 grams are light and 1800 grams are boat anchors.
For me it's not much more than fetishism.


I know which ones I'd rather do 100 miles on....

Re: 25mm tyres

Posted: 8 Mar 2018, 4:21pm
by Mick F
Yes, I agree, 120g isn't much to write home about.

I just took issue about your statement.
I actually agree that a heavy bike once up to speed, will have the same average speed as a light bike ................. until you come to an uphill.

Try climbing a steep hill on a bike and chucking out 120g on your way up. Personally, I'd chuck out as much weight as I could, and 120g, even if it is small, is quite welcome.

Re: 25mm tyres

Posted: 8 Mar 2018, 4:45pm
by amediasatex
Try climbing a steep hill on a bike and chucking out 120g on your way up. Personally, I'd chuck out as much weight as I could, and 120g, even if it is small, is quite welcome.


I 'd happily bet two choccie bars* against anyone being able to detect a 120g difference repeatably in a proper double blind test. You're welcome to choose the hill :-)

*roughly 120g as it happens...

Re: 25mm tyres

Posted: 8 Mar 2018, 5:13pm
by Mr Evil
A lot of unsubstantiated talk about the detriment to performance from the increased weight and drag. Let's put some numbers to that:

http://www.slowtwitch.com/Tech/Why_Wheel_Aerodynamics_Can_Outweigh_Wheel_Weight_and_Inertia_2106.html
http://www.biketechreview.com/index.php/reviews/wheels/63-wheel-performance

In summary, the effect of increased wheel weight is approximately nothing. Aerodynamic drag from the wheels is potentially more significant, but it's still small (and tyre width only contributes part of that). Even if you're a racer who cares about these things, the reduced rolling resistance and increased comfort of wider tyres may still be worth it. For normal folk there should be no contest - does it really make sense to use less comfortable tyres just because you're worried that your journey might be a couple of seconds slower?