spectastic

provided optimal pressure on both tires, i'm pretty sure that 25 mm will provide slightly lower rolling resistance, better comfort, better pinch flat resistance, and wider contact patch for traction, while the 23 mm tire will have slightly better aerodynamics.

however, which combination will provide better handling and why?

fietsbob

15cm? That's like 6"..

Leebo

2 mm is the thickness of a dime, no measurable difference.

fietsbob

More a question of how expensive a tire you are willing to buy..

Andrew R Stewart 

Any differences will be rather minor with only 2mm separating the tire widths. Having said that the human body is pretty good at picking up on slight differences. And the human mind is great at taking that perception and making a big deal over it. Andy.

spectastic

2 extra mm on a 23 wide tire means 18% more air volume. that's not trivial.

15c as in 15mm inner rim width.

bradtx

spectastic, I think I can give a fairly close apples to apples comparison. Real world difference is nil.

-Bike is a CAAD3 Cannondale
-Rims with Continental 23 mm tires are CXP22
-Rims with Continental 25 mm tires are CXP23

Brad

bradtx

True, which means that the 25 mm tire can run with slightly less air pressure, but whether I ran the same air pressure in my example, or 5 PSI less in the 25 mm tires I just couldn't detect a real difference in handling.

Brad

TimothyH

Please define "better handling". G-force during cornering near the limit of adhesion? Threshold braking distance in the wet? "Better handling" is a broad concept and ambiguous in and of itself. You need to be more specific. It has to be measurable.

All things being equal, a tire with a larger contact patch will provide more mechanical grip. You summarized this well when you said...


-Tim-

fietsbob

Winter is the time for Recreational Speculation..

bulldog1935

more rubber on the pavement provides better handling.
Nobody is brave enough to chase me around turns on my 38mm Barlows.

Leebo

My 60 mm geax tattoos provide scary side grip through turns, Almost to super sport cornering. ( in my mind)

Bike Gremlin

Big difference in air volume = comfort.

noglider 

'c' is not a unit of measurement. The 'c' in 700c refers to a series, where 700a, 700b, 700c, and 700d are different diameters (not widths) of wheels that are close in size.

It's unfortunate that people refer to tires with terms like 700x28c. It's really 700c by 28mm.

Bezalel

Contact patch size is a function or weight and pressure. At equal pressure a 23mm and 25mm tire will have the same size contact patch.


If your bike frame uses thicker tubes than 25mm, you're not getting much more aerodynamic with 23mm tires.


Lower rolling resistance and comfort are both based of tire deflection. You can't get better on both counts just by changing tire size.


Pinch flats shouldn't be a concern with properly inflated high pressure tires.

Leebo

Ugg, just go pedal. Sure there is a difference. Measure the difference in rolling resistance and the increase in contact patch. As well as the aero difference and get back to me. Make a chart, what ev.

JohnDThompson 

I agree, but it's a losing battle when even the tire companies mark their tires as 700 x 28C, etc.

bulldog1935

it's one of those pet peeves that's never worth arguing...(and yes, shared by me, as well)

the consolation is when it's your turn, you can do it your way

noglider 

Well put. I wasn't looking to argue, though. I was looking to tell someone who I'm sure didn't know and also was not looking for an argument.

spectastic

fwiw, tire width is not so critical in aerodynamics so much as the junction between the tire and the rim. a bigger delta between the rim width and the tire width, the less the cross section resembles a tear drop, the greater the turbulence, leading to greater drag. it has absolutely nothing to do with down tube width, but rather about the streamline

Sy Reene

I've always tried to figure out my Vittoria 37-622 tires that also labelled 700x35

Andrew R Stewart 

While I recognize air volume is a factor I'm just not sure how much it is compared to the % that is above the rim's outer edge.


I come from riding slightly wider sew ups (23/24mm usually) the common for close to 30 years. During this period the clinchers I rode were 30mm+ wide. I noticed that the sew ups had better pinch flat resistance even with their narrower spec. But the amount of air above the rim's edge is greater with the narrower sew up then with the wider clinchers. (The thinner casing and tube helped the smoothness too)


So, back to this thread's topic, I view this discussion through the amount of added air that's above the rim, not the total volume. Call me two dimensional (and making bad puns) but I think the height of the tire has a large factor to real life, everything else being the same. IIRC the 2mm of width is usually about 1mm in height, difference wise. So I see 4% of difference between a 23 and a 25mm tire on the same rim. Not too much.


Having said that I would choose the 25mm tire every time, over the 23mm one. Andy.

Sy Reene

+1.. That 4-10% spatial distance difference has meant a lot less flatting and a more comfortable ride. I have no idea whether my speed/watt impact was positively or negatively impacted, but if it was, it it was miniscule.

SquidPuppet

I would pass you on 35mm Kojaks.

The supple carcass of the Compass tire sucks up bumps like there's no tomorrow, but that tread pattern significantly reduces cornering and braking grip. I have both types of tires and there's no comparison.

bulldog1935

this isn't exactly true.
Drag is coefficient of friction times frontal area (that's why it's the coefficient of friction).
You do lower the coefficient by having a smooth teardrop-shaped transition, but the frontal area is simply the width times the height.