25mm tyres

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Brucey
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Joined: 4 Jan 2012, 6:25pm

Re: 25mm tyres

Postby Brucey » 14 Mar 2018, 12:42am

which is fine, but ignores the fact that the rear tyre usually provides a tractive force to propel the bike down the road. The results (like many other Crr measurements) might strictly apply to front wheels, not so well to driven rears.

cheers
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reohn2
Posts: 35959
Joined: 26 Jun 2009, 8:21pm

Re: 25mm tyres

Postby reohn2 » 14 Mar 2018, 6:03pm

The single thing that sold me on larger section tyres,a jump from 28's to 38mm,was the degradation of road surfaces in recent years and a desire for more comfort as a reslt for an ageing body riddled with artritic joints.
The big surprise was,although the bike felt slower,which was definitely down to a lack of high frequency vibration,it was minimal(about 1mph or less)but the comfort factor more than made up for that minimal speed loss.
The other thing I found was I could descend roads and particularly rouh tarmac roads,about 10mph faster and with more confidence than I ever could on smaller high pressure tyres as the bike is more "planted" on the road and absorbes rougher tarmac and small potholes much better.When riding with others,on more than one occasion following riders(on smaller HP tyres) have told me they have to ride around what I ride over.

All that said,young bucks with bodies not ravaged by time and hard graft,may think I'm being a bit soft,let them think what they like,I'm happy :D
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I cycle therefore I am.

roger
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Joined: 5 Jan 2007, 2:14pm

Re: 25mm tyres

Postby roger » 14 Mar 2018, 7:45pm

Having come across this topic today, although having gone from 23 to 25mm Contis on all bikes I may have speed read too eracticaly. In any event I have not seen anyone picking up our American members data on rolling resistance measured on what seems to be an appropriate bit of kit.
What about it you physicists and non-physicists.

From a slightly different tack, I am surprised that none of us cyclo- tourists have thought about the aerodynamic effect of our mudguards as the section inside them changes. I had not.

Roger.

reohn2
Posts: 35959
Joined: 26 Jun 2009, 8:21pm

Re: 25mm tyres

Postby reohn2 » 14 Mar 2018, 8:01pm

roger wrote:Having come across this topic today, although having gone from 23 to 25mm Contis on all bikes I may have speed read too eracticaly. In any event I have not seen anyone picking up our American members data on rolling resistance measured on what seems to be an appropriate bit of kit.
What about it you physicists and non-physicists.

From a slightly different tack, I am surprised that none of us cyclo- tourists have thought about the aerodynamic effect of our mudguards as the section inside them changes. I had not
.

Roger.

Do you think it has any significance at average touring speeds Other than in a strong headwind?
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I cycle therefore I am.

Brucey
Posts: 35628
Joined: 4 Jan 2012, 6:25pm

Re: 25mm tyres

Postby Brucey » 14 Mar 2018, 8:16pm

this article has a lot of common sense in it

http://www.slowtwitch.com/Products/Things_that_Roll/Tires/Choosing_your_tire_width_4026.html and

this

https://www.bicyclerollingresistance.com/specials/conti-gp4000s-ii-23-25-28

is an oft-quoted webpage too. Note that the data is not identical for both links, even though the same tyres are measured. Note also that the tests don't allow for driving torque and use some kind of textured roller that may or may not simulate a real road surface and may or may not unfairly flatter a wider tyre.

In any event if you (not unreasonably) assume that you would run a wider tyre at a lower pressure than a narrower tyre (so as to keep a similar spring rate in the tyre), and you believe the numbers, the actual difference is stuff-all. You can usually gain much more by choosing a tyre at the same width that is faster than if you keep the same type of tyre and just make it wider.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

roger
Posts: 118
Joined: 5 Jan 2007, 2:14pm

Re: 25mm tyres

Postby roger » 14 Mar 2018, 10:00pm

Thanks, Brucey.

Can make sense of Slowtwitch. Interested to see 145mm cranks in Alloy and carbon. Will have to look at 2nd site tomorrow.

Roger.

elPedro666
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Re: 25mm tyres

Postby elPedro666 » 15 Mar 2018, 12:17am

I've often thought that the lovely smooth surface of my mudguards must aid my graceful flow through the air, only partially negated by the 8x2½" flap dangling off the end of it!

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

Brucey
Posts: 35628
Joined: 4 Jan 2012, 6:25pm

Re: 25mm tyres

Postby Brucey » 15 Mar 2018, 6:04am

BTW I feel that I should mention that the common sense on the slowtwitch site is in a racing/training context, where "speed is king"; touring, audax, commuting needs have the same things apply of course, but their relative importance is likely to be different. It is likely that your choices outside of training and racing may be more to do with practicality and comfort rather than outright speed. It is good to know what kind of things are likely to make a difference though.

FWIW mudguards that have a decent clearance are like little sails that slow you down. Narrower ones, or ones that fit closer to the tyre are likely to be more aerodynamic, but this is not without consequence; they may clog up with mud, rub, or fail to work as well as they should.

Recently the front mudguard broke on my hack bike. The broken one was big enough to accept a ~44mm tyre beneath it, which was a bit much given that the frame was designed for 32mm tyres (limited by the space between the chainstays at the rear) and I normally run a slightly narrower tyre at the front anyway. Needless to say a narrower mudguard went on to replace the broken one; not much point in dragging a wider mudguard around for no good reason.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

roger
Posts: 118
Joined: 5 Jan 2007, 2:14pm

Re: 25mm tyres

Postby roger » 15 Mar 2018, 8:46pm

I have SKS guards which have "vertical sides", had them for years. I went out today trying to see what was happening with the surface water I was picking up. Unfortunately, there was a strong wind coming off the moor and I did not get much time to look down. When I did there was nothing apparent.
It did seem as if the front was pushing water out to the sides. I had no means of judging how much went into the bottom of the guard. Just before arriving home I rode through a large pile of well compressed beech leaves. I will look tomorrow and see what has dried on.
Air and any moisture in it must go between the tyre and the guard and keep moving towards the rear of the guard. It may be forced out by the rotation of the tyre before it reaches the end of the guard.
As to why guards fill up with road debris I don't know, perhaps it accumulates at low speed. Do treadles tyres pick up less ?
Just thoughts perhaps prompted by the return of the hitch hikers guide.
Will concede it has very little to do with 25mm tyres.42mm next?

Roger.

Samuel D
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Joined: 8 Mar 2015, 11:05pm
Location: Paris

Re: 25mm tyres

Postby Samuel D » 15 Mar 2018, 9:42pm

Following a casing failure from a cut on a rear tyre that was about to show the threads anyway, I have just switched from the 25 mm Schwalbe One HS 448 to the same tyre at 23 mm and slightly higher pressure. (I got a pair of 23 mm tyres for cheap, probably because this size has gone out of fashion.) The difference in feel is barely perceptible as I remembered from going the other way.

I believe you need to jump two sizes, e.g. 23 mm to 28 mm, to get a meaningful change. Or you could go wild and try a 35 mm or 38 mm tyre. Now those give a different riding experience. With that sort of rubber on your side, you don’t need to man a permanent watch for surface blemishes. On the other hand, the front half of the front tyre, the rear half of the front tyre, and the two halves of the rear tyre – that’s four bluff bodies of tyre width – are hard work to push through the air at 40 km/h.

Scunnered
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Re: 25mm tyres

Postby Scunnered » 22 Mar 2018, 8:30pm


And here:
http://www.slowtwitch.com/Tech/What_s_in_a_tube__1034.html

Skip down to "Tyre Pressure" and the graph of actual measured rolling resistance on road and compared with rollers.
Then realise that this was written in 2009!

Samuel D
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Joined: 8 Mar 2015, 11:05pm
Location: Paris

Re: 25mm tyres

Postby Samuel D » 22 Mar 2018, 9:44pm

Scunnered wrote:Then realise that this was written in 2009!

Tom Anhalt has contributed much to our understanding with his good theoretical knowledge and careful testing. However, concepts like this were discussed long before 2009. Archibald Sharp got the main parts right in the late 1800s!

More directly relevant is this Google Groups thread from 1994 (I say thread but it was originally an email discussion … before Google existed). Jim Papadopoulos, whom I regard as an outright genius, had much to say on the topic, starting with his direct mention of suspension losses and then the remarkable claims in his second post.