Question About Tires
 

Hello all, this is my first post. I am looking to replace my (very) old 23mm tires base on a recommendation from the bike shop that fixed my flat.

My question is this: I have heard that 25mm tires ride noticeably smoother, but it seems not everyone agrees on this. I don't know yet whether my frame (Cilo road bike from many years ago) would have the clearance to take a 25mm tire.

Can anyone tell me their experiences with 25mm Vs 23mm tires ?

I can't, personally, tell the difference.

Same for me, I've tried both on the same bike, with the same wheels, and I didn't see this great difference a lot of people speak of. It wouldn't hurt to give them a shot and try it for yourself if your frame will allow it.

Basically it comes to lower tire pressure so you have a more comfortable ride... in theory. I don't really notice a difference but it could be the tires (Conti Gran Prix) or the roads themselves.

Inferring from your reply... You are saying that it is normal to use a lower tire pressure for a 25mm as compared with 23mm tire - is that correct ?

As a rule people run lower pressure in the bigger tires.

I'd use the same pressure with 23 and 25 mm tires.

IMO "comfort" comes more with supple sidewalls (silly autocorrect thought I meant to say "supple sidewalks") than with width on its own. So consider the tire construction when you choose.

Look at your frame to verify you have a few mm of clearance at all the tight spots.

If you put the pressure at the maximum, then you won't notice a big difference between 23mm at 110 psi and 25mm at 110psi.

If you drop the pressure somewhat (80 psi?) then, the softer tire may give slightly more cushion.

I can't really differentiate either.

Determining the correct pressure for optimum traction and rolling resistance will be a long discussion, and may vary with road conditions. Chip seal?

Yes. You can run about 10# lower. And the wider tire corners a little better as well.

Ok, that's interesting. So what would I need to look for in the tire specifications that would indicate supple sidewalls ?

There is a tire size and pressure sweetspot relative to your weight...and supple is something you need to feel with your hands. It's obvious.

Thread count, aka TPI. It's listed in the specs of a tire. A tire with a higher thread count, like 120 and above, would be a more supple tire than a 60TPI tire because there's more thread and less rubber in the carcass and makes it more flexible, it will conform to irregularities in the road better. And it will be lighter. And more threads tend to work as a form of puncture resistance.

Actually TPI makes a tire more supple or flexible because the threads are thinner. More, thinner threads are more flexible than fewer, thicker threads even when the total weight of the threads is the same in each case. As far as the ratio of rubber to fiber, I don't know whether that varies with TPI or not. My guess would be not necessarily, although these days high thread count is pretty much reserved for the tires which are "best" in many respects, so they are designed to weigh less than tires with low thread count. Since they are intended for smoother roads and special "race" days, they likely do start with less rubber.

In case anyone is interested, the reason more, thinner fibers are more flexible than fewer, thicker fibers is the same as the reason a small diameter cylinder (frame tube) is more flexible than a large diameter cylinder of the same weight. Stiffness depends upon the third power of the radius of a rod or cylinder (of a given length and material), while weight only depends upon the second power. So at equal weight, the larger radius member is stiffer.

It makes it more flexible and supple (and thinner) because there's less rubber in the carcass, which is the result of thinner threads, not because of them.



A larger thread equates to a lower tpi and a stiffer casing, notes former professional cyclist Ian Dille writing in Mountain Bike magazine. A standard downhill mountain bike tire might use a 60 tpi casing, while a performance cross-country tire or road bike tire might be 120 tpi. A smaller thread size, he notes, makes for higher tpi and less rubber packed between the threads, making the tire lighter and more supple on the road. Cross-country tires have a single sheet of casing bonded under the center of the tread, Dille writes, while all-mountain tires use a two-ply casing.

- See more at: What Is the TPI on Bicycle Tires? | LIVESTRONG.COM

I think supple sidewalks is a great idea.

I did not mean to contradict your explanation. It may indeed be that there is some effect of less rubber in between the threads. What I know for sure is what I said: more, thinner threads are more flexible than fewer, thicker threads. That is the underlying principle of using high TPI and is a well understood physical phenomenon. Other factors may indeed contribute to the effect. I don't know since I am having trouble finding anything on the subject written by a bona-fide bicycle tire designer or other engineering type.

The majority of the effect is because of less rubber in the carcass. The flexibility of the minute size difference of threads in a tiny bike tire is irrelevant. It's not even something that would need research, it's kind of a no brainer.

I ride 25mm and not a major difference. It is mostly on longer ride and down to tire pressure. If I max it out its just as harsh at a 23mm but if I back down about 15psi I can see a difference.

Despite our disagreement about why, at least now OP knows that higher TPI is better. I suppose that is all that matters.

Yes, thank you all for your input.

One thing I am not quite clear about though, is the relationship between thread count and susceptibility to punctures. Lazyass seems to indicate that greater TPI comes with better resistance to punctures, but a friend of mine contradicts this saying that greater rubber content as in the Gatorskin type products are better in this regard. Any insights ?

The reason lower TPI casing is offen more puncture resistant is likely that the structure is much thicker and heavier. I agree with Lazyass that higher TPI is inherently more puncture resistant than plower TPI, all else equal. So if you have a low TPI casing and a high TPI both with the same total amount of fiber, the higher TPI casing should be much more puncture resistant. Problem is, high TPI casings are usually found in the lightest tires and the effects offset each other.

Tire size differences will vary according to the bike too. My Cannondale SSix EVO rode very rigid with 23's and I hated the ride. Then, I put 25's on it and the ride was much more compliant to my liking.
I put the same 25's on another bike (from 28's) and couldn't tell the difference.
I think before I would make such a minute tire size change, I would play around with air pressure first.
Bikes, tires and people are all different and with some many variables to allow for, the assumed results may not be worth the expense or effort.

Right. I don't know much about the actual construction of tire carcasses, but I had a high (290?) tpi pair of Vittoria Corsa Evo clinchers that felt fantastic but flatted constantly, like every 3rd or 4th ride, and would gash with sharp rocks that would bounce off other tires. Super light, but no flat protection.

Lower TPI tires like Gatorskins (180, I think) have belts of kevlar or somesuch woven into the thicker tread. They may not have as much grip or the "supple" feel everyone's talking about, but there's no question they last longer and offer much better puncture protection against the usual things you find on roads like glass shards and metal wires.

I didn't say "better" resistance to punctures. But they do provide some measure of puncture resistance which helps when the rubber carcass is thinner.

That's how I read it.