I was sent a pair of 700 x 25 Continental tires when I ordered 700 x 23. I am wondering the pros and cons of this situation, and whether I should exchange the 25s for the 23s. Will these make that much of a difference?
I weigh about 155 pounds.
700 x 23 vs. 700 x 25 Advice
Tue, 11/29/2005 - 10:30am
Tue, 11/29/2005 - 10:57am
#1
if they fit your frame, ride 'em.
always better to ride a wider, fatter tire in winter.
Tue, 11/29/2005 - 11:48am
#2
Continentals are undersized. 25mm Contis only measure about 23.5mm. Keep the 25s.
- Christian
Tue, 11/29/2005 - 12:41pm
#3
23 vs. 25 mm tires
"It's almost impossible to feel a difference in rolling resistance between 23 and 25 mm tires at the same pressure. But if the labels are accurate (in this case they aren't, as Christian pointed out) the 25 mm tire holds about 18% more air volume, so you can run lower pressures without risk of pinch flats. This gives a smoother, more comfortable ride with better traction.
http://sheldonbrown.com/tires.html#pressure"
Tue, 11/29/2005 - 6:21pm
#4
bigger is better for colder/wetter
It's simple--you'll mostlikely get fewer flats when with even a slightly bigger tire. I switch to 25mm tires at this time of year for my road bike because it's no fun to fix a flat in Central Park at 6:00 AM in pitch blackness at 28f. I definitely get fewer flats with the bigger tire.
Wed, 11/30/2005 - 6:28am
#5
flats
A wider tire provides greater exposure for picking up debris. So how do you explain getting fewer flats with a bigger tire?
Wed, 11/30/2005 - 7:03am
#6
Not quite
At the same inflation pressure, the contact patch size should be proportional to the rider weight. So, wider or narrower tires, the contact patch size should be the same. It's commonly believe that lighter rider has fewer flats because the contact patch size is slightly smaller. Though personally I doubt that's the only reason.
It's a common pratice for people advocating wider tires to use lower pressure. In that case, the contact patch size should be a little bigger. But equal number of riders inflat the wider tire to the same high pressure as well. In the later case, contact patch size doesn't change.
I'm no flat expert since I don't get many. (knock on keyboard...)
Wed, 11/30/2005 - 7:30am
#7
tire pressure
"The max pressure rating decreases with tire width. I'd find it odd that folks with 25s would pump their tires up to the same pressure as 23s. If so, it's basically defeating the purposeful advantage of having 25s in the first place. I'd find that hard to believe with such ""educated consumers"" (meaning most bikes and tires sold come with/default to 23s; 25s are normally expresssly sought out).
Regarding hard, as in hard tires, I find that when I inflate my tires past the max pressure, I'm more likely to trash my tire when I do get a flat. By trash I mean get a large(r) gash in the tire. I've learned not to do such at least with various flavors/models of Michelins.
As for tire pressure, I tend to ride with them underinflated (midweek) out of laziness and inflate to full pressure on the weekend. I don't flat often enough to notice a material or more likely subjective difference in flat frequency v. tire pressure.
FWIW, I agree with the many others - keep the 25s."
Wed, 11/30/2005 - 10:10pm
#8
Is it true?
"""meaning most bikes and tires sold come with/default to 23s; 25s are normally expresssly sought out""
You must have been talking about more high-end bikes then. Mine (TREK 5200, last year) came with 25's, so was the one it replaced (TREK 2300, mid-90's model).
I do notice more than half of the riders I met on group rides were riding 23's. Some were even trying to convince me that 23's are faster! So I thought those were the ""educated consumers"" who sought out 23's expressly!
I broke down and tried them and had such bad luck with them that I switched back to the 25's. Yes, the 23's were lighter and ""felt"" faster. But I lost all those ""time gain"" to having to fix flats 3 times within a month! (If I don't count those 3 flats, I probably flated only once in every 3 years!)"
Thu, 12/01/2005 - 5:29pm
#9
Eight is Enough
I just checked more than a few websites for kicks.
You are correct, lower end Treks (as in non-carbon) and lower-end Lemond bikes (which are a different brand of Trek) have 25s stocked. From what I personally see riding on club rides, non-carbon Treks are the exception and not the rule.
I'm sure you'll be more than delighted to know that the following bike companies all stock 23s from their low end road bikes on up:
cannondale
specialized
gt
jamis
bianchi
iron horse
marin
felt
I ran out of bike brands to look up from the top of my head, ones that shops normally stock on their floor. Nevermind the likes of Merlin, Colango, Orbea, etc.. I'm sure if one were interested, maybe say Dick Van Patten or Betty Buckley they could pursue and rerun this exercise further. I figured eight is enough.
Wed, 11/30/2005 - 7:08am
#10
A Wild Guess
I get less flats in winter than summer and I use 23's for both seasons. Could it be that most people ride less in the winter than in summer and therefore the probability of getting flats decreases?
Keep the 25's. You probably won't notice the difference unless you're time trialing and even then...
Wed, 11/30/2005 - 7:35am
#11
Tires with larger air volume are less susceptible to snakebite flats, which allows them to be safely run at lower pressures. The lower pressure makes the tire more able to deform over sharp objects and less likely to puncture.
- Christian
Wed, 11/30/2005 - 8:34am
#12
snakebites and pressure, tire deforming
"If tires are sufficiently inflated, snakebite flats should not be an issue. I've never snake-bited (if that's a word); if I were to it would most likely be a by-product of a bad crash something which would be of greater concern. If you are on the heavy side, weight wise, I'd think a MTB would be more suitable.
As for the comments regarding deforming over sharp objects, the engineer and gruffy-technocrat, Jobst Brandt differs, in response a usenet posting about tire pressure.
He wrote, ""...The firmer the backing, the easier penetrating a tire casing becomes. Just visualize trying to stab your tire with a jack knife with 20psi inflation
compared to 120psi. Penetrating the tread requires a certain force for a given object and what you report does not follow...""
It's not hard science and opinionated, but definitely something to consider.
Full archive of the discussion is here:
http://www.usenetsport.com/thread258318.html
News at 11....
"
Wed, 11/30/2005 - 9:04am
#13
"If you read the entire thread, it's clear that Jobst misread the original posting and agrees with the ""lower pressure gradient = lower incidence of point-punctures"" hypothesis. Carl Fogel refers to it as ""tenting.""
The issue with snakebite flats is that for a given weight and tire volume, there is a given pressure required to prevent snakebite flats. For 23mm tires, this is somewhere around 115-120psi for a 175lb rider. This pressure is 1) uncomfortable and 2) risks point-induced punctures.
25mm tires at 105psi are better all around.
- Christian
- Christian"
Wed, 11/30/2005 - 11:50am
#14
more flats flap
"Ok, true. I'm guilty of misreading hs followup comments. My bad.
That said, it's worth pointing out that the discussion there was about less flats using a lower pressure (80-90 psi) with the same 23 tire.
The max pressure of Michelin 23s are 110psi. I doubt the ""tenting"" effect of 5 psi less in tire makes much difference. For argument sake, let's say so.
+ 1 for lower tire pressure, but
-1 for a bigger tire patch exposure
Which one is of greater significance, who knows? My guess is if there is indeed a flat prevention difference between a 23 v 25, it's insignificant and immaterial much like a 150lb rider concerning himself with pinch flatting riding a 23.
"
Wed, 11/30/2005 - 9:57pm
#15
do the math
"Good question Peter! Christian, i always enjoy the insight and value that you add to these threads.
Which effect is worse? Bigger contact patch picking up more debris or higher pressure 'forcing' sharp things through the rubber? It's relatively straightforward. Let's start with the easier of the two:
EFFECT FROM LOWER PRESSURE
Let's start with Christian's numbers: 115psi to avoid a pinch flat on 23mm. 105psi to avoid pinch flat on 25mm. Since pressure is what drives a shard through the rubber, the 25mm tires have (115-105)/115 = 8.7% less pressure than 23mm tires. This means that the pressure on each sharp object (lbs / sq. in.) will 8.7% less if you roll over it with the 25mm tires than if you roll over it with the 23mm tires.
In other words, the same sharp object will exert 8.7% less force on the wider tire than on the narrower tire.
This is not much of a difference. When a sharp object punctures the tire, the pressure is much higher than the rupture-threshold of the tire. If this wasn't the case, than people would have many more sharp objects lodged in the tire that didn't puncture the innertube. Although i occasionally find pieces of glass stuck in my tire that didn't cause a flat, it is rare.
EFFECT FROM LARGER TIRE CONTACT PATCH
1) This is a little more complicated. Let's use Christian's pressure numbers and Chris's weights to calculate contact patch areas:
Chris weighs 155 lbs + 20 lbs bike = 175 lbs of force on both wheels
175 lbs total force = 87.5 lbs per wheel
23mm tire contact patch area = 87.5 lbs / 115 psi = 0.7608 square inches
25mm tire contact patch area = 87.5 lbs / 105 psi = 0.8333 square inches
Notice that the 25mm contact patch is 9.5% larger than the 23mm tire contact patch. This 9.5% increase is regardless of the chris's weight.
Does this mean the 25mm rides over 9.5% more debris? Not so fast, because you only ride over more debris if the contact patch is wider. In the next step we calculate the % increase in patch width due to a 9.5% increase in area.
2) How much wider is the contact patch if the area increases by 9.5%?
Let's assume the contact patch is in the shape of an ellipse. Let's also assume the proportions of the ellipse remain the same on both tires.
The area of the ellipse is
A = pi * C * r * r
where A is the ellipse area, r is the short radius of the ellipse (the width of the contact patch is 2*r). C is the proportionality of one radius to the other (C = r2 / r where r2 is the longer radius).
To examine the behavior of changes to these values, we take a differential:
dA = 2 pi C r dr
For relative changes, divide both sides by the area and then simplify:
dA / A = 2 pi C r dr / A
dA / A = 2 pi C r dr / (pi C r r)
dA / A = 2 dr / r
On the left, dA/A is the %change in area. on the right, dr/r is the % change in radius. Thus:
% change radius = 1/2 % change area
so a 9.5% change in area equal a 4.75% change in radius. A 4.75% increase in radius is also a 4.75% increase in width (diameter).
You will ride over 4.75% more debris with the 25mm tires than you will with the 23mm tires.
CONCLUSION
For these two tires, the wider contact patch causes more flats than the lower pressure prevents.
Of course, the occurrence of flat tires are random rare events, which the human mind has a hard time grasping. A slight % increase in flats will not be a noticeable. If we understood random events better, than people wouldn't play the lottery, believe in voodoo, or buy google stock.
"
Thu, 12/01/2005 - 5:36pm
#16
And they think I am a d0rk with the watts and kilojloues... (nm)
Thu, 12/01/2005 - 5:55pm
#17
welcome to the club
Like the rest of us, you do wear lyrca, a styrofoam hat and walk funny in those shoes.
Thu, 12/01/2005 - 5:53pm
#20
A+ post
Outstanding work, Ben. Thank you. I very much enjoyed reading your and Christians' many posts. This is quite a thorough analysis removing alot of the subjective guesswork among us, me included. I was about to submit such cold case to Mythbusters....
Allow me one potentially persnickety comment, your post mentions the front and back wheel sharing equal weight. As I'm sure you are already aware, the rear wheel borns most of the rider's weight. (Weight is a constant used in your calculations so the front/back % split is immaterial) I only point this out here since we're discussing flats and this weight differential would explain why it's more common to flat the rear tire, e.g. more weight and much faster wear of the rear tire.
Taking liberty with your numbers, to underscore further the conclusion, in very loose terms, one would have to flat roughly 22 times in a year, to experience the _one_ extra flat exposed by the more-flat prone tire width.
I certainly don't experience anything close to that number in a year and the actual amount I do, 3, 4, 5,... varies from year to year. That flat prevention savings would easily get lost in the variability and randomness of (infrequent) flats from year to year.
Even though, 25s are more prone to flatting than 23s (in the most trivial sense as you detail), there's much better reasons, like ride comfort, to consider 25s.
Now if you can come up with a mathematical Utility Function to compute the merits of a 23 over a 25 and vice versa, I'd be even more impressed. :-)
Fri, 12/02/2005 - 4:11pm
#21
Thanks Peter,
I didn't think about the rider's weight being unevenly distributed. The contact patch should still increase by the same percent.
Fri, 12/02/2005 - 6:10am
#22
> This is not much of a difference. When a sharp object
> punctures the tire, the pressure is much higher than the
> rupture-threshold of the tire. If this wasn't the case,
> than people would have many more sharp objects lodged in
> the tire that didn't puncture the innertube. Although i
> occasionally find pieces of glass stuck in my tire that
> didn't cause a flat, it is rare.
I don't follow this logic at all. It strikes me that a puncture is best thought of as a binary event. You roll over an object, and it either punctures the tire or not. If it does not puncture the tire, there doesn't seem to be any logical reason to assume it would adhere to the outside of the tire for the remainder of the ride. How are you drawing that conclusion? Given that this, and the subsequent dismissal that inflation pressure affects punctures, is the sole basis of your concluding that narrower tires puncture less than wider ones (in opposition to empirical evidence), it seems a central question to your analysis.
I think the math is correct, and I'm enjoying the serious analysis, however.
- Christian
Fri, 12/02/2005 - 8:21am
#23
Empirical?
Christian, what empirical evidence are you referring to above? The statements of some people that they get less flats in winter when using 25's than in summer when using 23's? I don't think those statements were arrived at by very rigorous testing.
Fri, 12/02/2005 - 4:09pm
#24
Hi Christian,
I was kind of refering to it as a binary event too. It either punctures or not. That's why if it's going to puncture one tire and it hits the other tire with 8% less force, then it that won't make much of a difference -- it will puncture both tires.
I didn't say it very clearly. My reference to things adhering to the tire was trying to explain that things either go through or they don't -- There isn't much in between that might puncture the 23mm high pressure tire but not the 25mm lower pressure tire. I was assumiing that if it punctured one but not the other, then we would see it lodged in the rubber close to puncturing the low pressure tire or we would find a hole that doesn't go completly through the rubber. My conclusion was that, since i rarely find things lodged in my tire that would have punctured with little more pressure, that means that things that do puncture must have a lot of pressure. It's not a complete logical thought... just a thought
Fri, 12/02/2005 - 11:11am
#25
Contact patches
"Ben wrote:
""2) How much wider is the contact patch if the area increases by 9.5%?
Let's assume the contact patch is in the shape of an ellipse. Let's also assume the proportions of the ellipse remain the same on both tires.""
I'm having trouble accepting the latter hypothesis. If we take two tires of different widths, one 20 mm, the other 40 mm (to take an extreme example), and pump them both to the same pressure, the area of the contact patch would be the same for each tire. But I don't think the shape of the contact patch would be the same. I'd say that the contact patch would be wider and shorter on the 40 mm tire, narrower and longer on the 20 mm tire. There wouldn't be a linear relationship between the length of the major and minor radii of the ellipse, or between area and width.
"
Fri, 12/02/2005 - 3:58pm
#26
Hi Mordacai,
You are right, if the tires are the same pressure. I was using 105psi for the 25mm and 115psi for the 23mm. I'm still not sure if the patch has the same long radius to short radius ratio... i'm just hoping that scaling the tire from 23 to 25 keeps all of proportions the same (or close enough to it).
Fri, 12/02/2005 - 11:33am
#27
Why fewer flats on 25 mm tire?
"Peter O'Reilly wrote:
""A wider tire provides greater exposure for picking up debris. So how do you explain getting fewer flats with a bigger tire?""
Wider tires typically have thicker tread than narrower tires. 20 mm or 23 mm tires, designed with racing performance in mind, are made with thinner tread to save weight and minimize rolling resistance. Tires 25 mm and wider, on the other hand, are designed more for general use."
Fri, 12/02/2005 - 12:25pm
#28
your argument is flawed
"The same can be said for 23s. There are plenty of 23mm tires that are not designed with racing in mind - ones with lined with kevlar, real ""treads"" and what not.
If you are going to compare a lesser-flat prone (as in considerably heavier and more rolling resistance) touring 25 tire to a 23 performance tire, then you are taking away that additional utility or benefit of the nicer, more comfortable ride of the 25 tire.
You need to make an equivalent, apples-top-apples comparison. For instance, let's look at Chris's selection, Continental Grand Prix 4-season. Per Continental's website, the weight of 23s is: 220 grams. For 25s, it's 250 grams. I doubt that extra 30 grams, which is not much to begin with, is solely on the road contact patch section of the tire. It's also worth noting that at 250 grams, that Conti 25's weight is less than or equal to many performance 23 clincher tires.
If you think that the even larger Continental Grand Prix 4-season 28mm tires have more rubber where it counts, guess again. The listed weight is surprisingly the same as the 25s.
"
Fri, 12/02/2005 - 12:38pm
#29
Yes, some 23 mm tires aren't designed for racing
"I wrote, ""Wider tires typically have thicker tread than narrower tires.""
Would a few extra grams on the tread be ""taking away that additional utility or benefit of the nicer, more comfortable ride of the 25 tire""?
Continental's sizing is deceptive, and I don't know if I'd swear by their weights either."
Fri, 12/02/2005 - 1:20pm
#30
Well, Mordecai, that is true
Sure one can introduce an external condition/variable, like wider tires with thicker treads much like another condition that performance oriented folks who ride their 23s in the summer tend to ride alot more than others do with their 25s in the winter. There's also alot more folks drinking cold beverages out on the road in glass containers in the summer v. hot beverages in the winter, etc...
Since you have been following the thread, which I know you have, since you replied to Ben, the idea was to remove personal selectivity, biases and prejudices, etc. of why people think 25s are less prone to flat than 23s and provide something more empirical as some others have already stated. For instance, how does tire thickness effect flat resistance numerically.
In light of your last response, it's the timing of prior post that is confusing.
Wed, 11/30/2005 - 8:03am
#31
other advantages to 25mm vs. 23mm
All things being equal, the wider footprint should afford better braking on dry surfaces and better overall wear characteristics.
Tue, 11/29/2005 - 7:09pm
#32
2mm is a nickel.
Ride 'em.
Wed, 11/30/2005 - 11:00am
#33
Dirksen revisited (but did he ever say it?!)
A mm here and a mm there, and pretty soon you are dealing with real width (2 mm does add almost 9% width to a 23 mm tire).
But thanks for the good advice, the tires are mounted and ready to go.
Thu, 12/01/2005 - 6:32pm
#34
It makes some sense to spec a 25mm tire on a lower end bike.
"1) The larger/lower pressure tire will better cushion an inexpensive wheeset from road damage.
2) It gives the salesperson a, perhaps artificial, way of distinguishing a base level model from its pricier brethren: ""Well for another $1000 you get carbon stays vs. aluminum; Ultegra vs. Tiagra and Mavic Ksyriums vs. CXP22s which lets you run ... faster, lighter, high pressure 23mm tires!""
-------------
FWIW, I run 2004 28mm Specialized All Condition Armadillos at 120 PSI. They are heavy but they're fairly fast, handle and brake well and -- as I often ride in bad weather -- are as flat resistant as it gets.
I had originally tried 23mm Armadillos but hated the harsh ride. The greater air volume of the 28mm offers a much softer ride at the same PSI."
Sat, 12/03/2005 - 7:48am
#35
What???
" >>It makes some sense to spec a 25mm tire on a lower end bike.
25mm tires make sense for most recreational riders. It has nothing to do with ""high-end"" or ""low-end"" bikes. It has more to do with comfort, rider weight, and type of riding. Almost everyone I know who tried 25s preferred them to 23s.
>>The larger/lower pressure tire will better cushion an inexpensive wheeset from road damage.
That implies that ""expensive"" wheels are more durable. I would argue just the opposite.
>>I run 2004 28mm Specialized All Condition Armadillos at 120 PSI.
Why on earth would you run 28s at 120 psi? The point of using wider tires is that you can run less pressure, and enjoy better traction and a smoother ride. Proper tire pressure is a function of rider weight and tire width. See:
http://sheldonbrown.com/tires.html#pressure
Unless you're well over 200 lbs, try riding those 28s at 90 to 100 psi and see how they feel.
""Chainwheel"""
Sat, 12/03/2005 - 9:25am
#36
Why on earth would you run 28s at 120 psi?
"Because I can.
Seriously, the ""recommended"" range of the 28s, as written on the sidewall, is 115-125PSI (Sheldon's comments notwithstanding).
""Unless you're well over 200 lbs, try riding those 28s at 90 to 100 psi and see how they feel.""
I don't have a problem experimenting at the lower pressures.
-----------------
FWIW, I had to hunt to find the 2004 models. The 2005s are only rated to 100 PSI and the quality of construction was visibly inferior.
Previously, I rode Panaracer T-Servs (rated to 95 PSI) and found the sweet spot at 102 PSI, but they cut too easy.
"
Fri, 12/02/2005 - 10:58am
#37
Maiden voyage
I too have enjoyed the many thoughtful posts here as well as the good advice I have received.
I took my nice new 25mm tires out for a spin through River Road yesterday. What a perfect day.
Guess what? I got a flat. Dohh.
There is a first for everything, such as the type of flat I got yesterday. As I was attempting a rolling dismount at about 4 mph, my SPD cleat got stuck and I yanked my foot. It came out, and while not by any means going into the spokes, it smacked directly against my ridiculously lengthy valve (at least 3 inches). The valve snapped at the wheel base and poof, flat in 1 second.
The tires held up well. And I felt very confident through leaves, puddles, and various debris along the way.
April, if you only get one flat every 3 years you must be doing something wrong.
Fri, 12/02/2005 - 12:27pm
#38
that should be a once-in-a-lifetime type of flat (nm)
Fri, 12/02/2005 - 1:06pm
#39
LOL
"I should eat more and gain some weight! ;o)
Or, I should charge over big cracks on the road instead of avoiding them.
More over, when I roll over obstacles I can't (or ""shouldn't) avoid, I should maintain a death grip on the handlebar with locked elbow and sit firmly on the saddle so all of my weight will transmit over the impact.
I think that should guarrantee a better chance ""improve"" my flat opportunity. What do you think?"
Fri, 12/02/2005 - 4:22pm
#40
The pinch flat
Don't forget your best bet: lower the pressure on the tires so they are very comfortable, like shock absorbers. Then jump up and down curbs at every opportunity.
When I was young or at least naive, I used to ride with soft tires for comfort, always wondering where all those snake bites came from.
Sat, 12/03/2005 - 1:12pm
#41
As if you need more input...
Continentals are excellent for flat prevention in either the 25 or 23 category. But I find Continentals to ride slower than a smooth tread tire (Michellin, Bontrager, Hutchison). So you have to decide is it speed or fewer flats/more traction/all-weather tires you're looking for.
For speed--simple--the narrower the better, as in faster. Also, the more pounds of pressure you can put into the tire, the faster you'll go. Be careful of overpumping the tires past max psi, as it can blow and destroy your wheel.
I prefer smooth tread tires in the 23 profile that I can pump to at lest 120psi (Bontrager, which come with Treks and are found at Trek dealers). These are going to be more prone to flats, but I prefer the faster ride.
That said, I'd say keep the 25's if you're keeping up with the pack. Ride fat in the winter and switch to thin in the spring and you'll be racing!
Karol
