Optimal tire size for 17.0mm internal width (21.5mm external)

[rides4beer]

On a 17mm internal rim, the Conti 23C will be 25.5ish. The 25C will be 27.5ish and the 28C will be 30.5ish. Another thing is that the Conti tires are tall for stated size. I could not run a GP4000Sii in a 25C on a rim 17mm or larger on my Colnago C60 because it would be too close to the fork crown. But, I could use a Vittoria Corsa G+ in 25mm width on a 20.5mm inner no problem. So for the OP, make sure you can get a 25C GP4000Sii to fit before buying them.

And Hexsense is on to something important, having the inner width significantly more narrow than the tire width creates a very different riding tire. I've played around putting a 28C Conti on a 15mm innner width rim, and on a 20.5mm inner width rim with all other variables kept the same. The narrow rim gives the tire much more of a lightbulb shape and the feeling under hard cornering is much more vague. And climbing steep grades out of the saddle, the front wheel always feels more flexy. This is the effect of the very round sidewall on the 15mm rim vs a much more vertical sidewall on the 20.5mm rim.

For the wheels I have that are 17C I use either 23C Conti or 25C Vittoria.

Thanks! I will def check my clearances before buying anything, as well as measure my current tires for comparison.

I should add that it's hilly here, my last ride was about 3400ft of climbing. So I want it to climb and descend well. So maybe the 23c Conti would be better for my purposes. What kind of pressure do you run with the 23c Conti?

[Bigger Gear]

And Hexsense is on to something important, having the inner width significantly more narrow than the tire width creates a very different riding tire. I've played around putting a 28C Conti on a 15mm innner width rim, and on a 20.5mm inner width rim with all other variables kept the same. The narrow rim gives the tire much more of a lightbulb shape and the feeling under hard cornering is much more vague. And climbing steep grades out of the saddle, the front wheel always feels more flexy. This is the effect of the very round sidewall on the 15mm rim vs a much more vertical sidewall on the 20.5mm rim.

I typoed this, it was a 25C Conti, specifically on a Dura-Ace C35 wheelset, and a HED Belgium+/White Ind wheelset. Now obviously those wheels have a different feeling, with the C35s being a little rougher riding. But just in terms of how the tires feel in the transition from straight up to leaning in a corner, the wider rim is so much more confident feeling at that transition moment. I live in a town with very steep streets and I have a couple of very safe but very hard/fast turns where I can really feel how different bikes/tires/wheels feel during cornering. And I love to test things.....

[rides4beer]

I typoed this, it was a 25C Conti, specifically on a Dura-Ace C35 wheelset, and a HED Belgium+/White Ind wheelset. Now obviously those wheels have a different feeling, with the C35s being a little rougher riding. But just in terms of how the tires feel in the transition from straight up to leaning in a corner, the wider rim is so much more confident feeling at that transition moment. I live in a town with very steep streets and I have a couple of very safe but very hard/fast turns where I can really feel how different bikes/tires/wheels feel during cornering. And I love to test things.....

Ideally I would get a wider rim and have the handling and aero, but I'm also working within a budget, so something has to give lol I figure if I can make these work for a while then maybe I can step up to something wider later.

[Bigger Gear]

Ideally I would get a wider rim and have the handling and aero, but I'm also working within a budget, so something has to give lol I figure if I can make these work for a while then maybe I can step up to something wider later.

Fair enough, and to be honest we are really talking about marginal differences here until we go out to the extremes. I've got some first-gen ENVE 3.4s that are 18.5/16.5 inner width and I'm not about to give up on them just because they are not the latest in terms of wheel technology. I also have wheelsets with HED Belgium C2 (17mm) and Belgium+ (20.5mm) and when I use the same tire on both wheelsets I really don't notice much difference there. I will say that going from really narrow rims like the older Mavic Ksyriums (14mm?) to HED C2 (17mm) made a much more appreciable difference than going from 17 to 20.5 so the relationship is far from linear, despite what the bike industry wants you to think. In case you're unsure of exactly what they want you to think: aero-road, hydraulic disc, super-wide rim with tubeless. Anything else is a complete fail

[Calnago]

Kind of depends on what you like. On a 17mm internal width clincher, a 23mm nominal width tire will generally get you an end result with the equivalent volume and (as close as can be) shape to that of a 25mm tubular tire, which is pretty much standard fare in pro peloton type racing these days. While a 25mm tubular is going to remain the same volume no matter what rim you put it on, with clinchers it's all over the board, so it all depends what you're looking for. Experiment. There's no one right answer. But I did like @BiggerGear's response above. The last couple of lines especially.

[rides4beer]

Fair enough, and to be honest we are really talking about marginal differences here until we go out to the extremes. I've got some first-gen ENVE 3.4s that are 18.5/16.5 inner width and I'm not about to give up on them just because they are not the latest in terms of wheel technology. I also have wheelsets with HED Belgium C2 (17mm) and Belgium+ (20.5mm) and when I use the same tire on both wheelsets I really don't notice much difference there. I will say that going from really narrow rims like the older Mavic Ksyriums (14mm?) to HED C2 (17mm) made a much more appreciable difference than going from 17 to 20.5 so the relationship is far from linear, despite what the bike industry wants you to think. In case you're unsure of exactly what they want you to think: aero-road, hydraulic disc, super-wide rim with tubeless. Anything else is a complete fail

Gotta start building the collection somewhere, right? I was thinking that too, I mean, we're talking 2mm here. I'll try the 23c Contis and play with the air pressure, if I feel like maybe I need more comfort, I'll try some 25's later.

I did go for the aero-road, but only because after test riding the aero bike and the "climbing" bike, the aero bike felt better, even if I am going to end up doing a lot of climbing lol It's lighter and feels stiffer and I have no issues climbing with it, dropping 3-400g off the wheels should only help with that.

Kind of depends on what you like. On a 17mm internal width clincher, a 23mm nominal width tire will generally get you an end result with the equivalent volume and (as close as can be) shape to that of a 25mm tubular tire, which is pretty much standard fare in pro peloton type racing these days. While a 25mm tubular is going to remain the same volume no matter what rim you put it on, with clinchers it's all over the board, so it all depends what you're looking for. Experiment. There's no one right answer. But I did like @BiggerGear's response above. The last couple of lines especially.

I've only been riding for a few months, so I don't know what I like yet, well, except that I know I like to go fast lol I think I'll try the 23's to start and see how it goes, then maybe some 25's later if I want to see the difference.



I really appreciate everyone's input, thanks for helping the new guy learn!

[alcatraz]

If you like to go fast don't pump your tires up too hard. Rookie mistake.

You need more width to avoid getting pinch flats at such pressures. It'd be annoying to spend the money and find out you can't keep optimal pressure. Might as well just stay on the 25c vittorias than to go 23c conti.

A weight reduction tip is to pick up some thinner inner tubes. It will also reduce rolling resistance.

Putting a 23 in the front and 25 in the rear is possible and would save you a few grams but you would lose the ability to swap the tires when your rear is wearing out.

[robertbb]

I've got Shamal C17's. If GP4000S2 is your tyre of choice*, then without any doubt the 23mm size is what you want for a 17c rim - assuming handling and aerodynamics are important to you.

*and for most people I think it should be, despite the bad wrap it gets from some it is simply an excellent all around tyre. At 72kg, I run ~85PSI (plus or minus a 2-3PSI depending on weather or the ride of the day) and they have been faultless, and even on my alloy bike (Canyon Ultimate AL) the ride is actually very comfortable.

[mpulsiv]

Too much information for a new rider.
For training, stick to 25mm, even though Conti GP4000 run wider. As a matter of fact, train on the widest tires your frame can clear.
If you are gunning for the podium and looking to yield every watt then 23mm is your weapon of choice.

[pdlpsher1]

If you like to go fast don't pump your tires up too hard. Rookie mistake.

I think we can all agree that too high of a pressure on very rough road will increase RR. But do we know what that break-even pressure is? I don't recall ever seeing a scientific experiment that answers that question. I have a feeling that the break-even pressure is much higher than what people are using today.

[robertbb]

Too much information for a new rider.
For training, stick to 25mm, even though Conti GP4000 run wider. As a matter of fact, train on the widest tires your frame can clear.
If you are gunning for the podium and looking to yield every watt then 23mm is your weapon of choice.

Why? A 23mm Conti GP4kS2 tyre on a 17c rim will be comfortable (because it actually measures up at 25mm and can still be run at lower pressures), will handle better than a 25 due to shape, and will be more aero. On a 19c rim or above, sure let's talk about the 25mm but at 17c I really strongly suggest 23mm for any kind of road riding - be that training or racing.

[alcatraz]

The guy weighs 84kg, including bike and gear maybe 94kg.

He is on Vittoria 25c tires now. Rims aren't very wide, roads aren't the smoothest. He wants to go faster.

Conti 23c is pretty close to his current tires. For an 80-85kg total riding weight 23C conti is probably good. For 94kg it's very likely to be closer to conti 25c~27mm being the faster tire.

Then as you go over 100kg you start looking at 28c and so on.

Stretching the use of the 23c up to 95kg is a bit extreme. Don't you think? Conti 25c in the rear and 23c in front is a fair compromise I think.

/a

[Calnago]

Real world scenario... curious what you guys think.
1 rider. 1bike. 1 climb. 2 wheelsets, essentially identical in every way except for the tire size: both tubular... one set shod with 23mm Veloflex Carbon Tubulars, the other set shod with 27mm Veloflex Vlanderen Tubulars.

Situation: Climb is 1 mile long. Average grade 7%, with short stretches up to 12%.
Rider: 95kg
Road surface: Decent tarmac.
Tire pressure specifics:
Set A (23mm): Rear/Front: 110/100psi
Set B (27mm): Rear/Front: 80/75psi

Question: Which set either gets up the hill faster at the same power or takes less power to reach the top in the same time?

[mpulsiv]

Too much information for a new rider.
For training, stick to 25mm, even though Conti GP4000 run wider. As a matter of fact, train on the widest tires your frame can clear.
If you are gunning for the podium and looking to yield every watt then 23mm is your weapon of choice.

Why? A 23mm Conti GP4kS2 tyre on a 17c rim will be comfortable (because it actually measures up at 25mm and can still be run at lower pressures), will handle better than a 25 due to shape, and will be more aero. On a 19c rim or above, sure let's talk about the 25mm but at 17c I really strongly suggest 23mm for any kind of road riding - be that training or racing.

To begin with, Conti GP4kS2 is far from comfortable, even 28mm (e.g. measure ~30mm wide). It's a German-engineering overbuilt vulcanized tire, made to last ~5000 Km. If one is looking for supple tire, then open-tubular (e.g. Veloflex, Turbo Cotton) is the weapon of choice. When it comes to aero, there's already a violation of 105% rule. In order to optimize aero for 21.5mm wheel, one must be running 19mm tire. So, going from 23mm (measure ~25mm) -> 25mm (measure ~27mm) is not going to slow down a rider.

[rides4beer]

The guy weighs 84kg, including bike and gear maybe 94kg.

He is on Vittoria 25c tires now. Rims aren't very wide, roads aren't the smoothest. He wants to go faster.

Conti 23c is pretty close to his current tires. For an 80-85kg total riding weight 23C conti is probably good. For 94kg it's very likely to be closer to conti 25c~27mm being the faster tire.

Then as you go over 100kg you start looking at 28c and so on.

Stretching the use of the 23c up to 95kg is a bit extreme. Don't you think? Conti 25c in the rear and 23c in front is a fair compromise I think.

/a

Sounds about right, bike is just under 8kg. I haven't read anything about weight limits for tire sizes, just varying pressure depending on weight, which I guess goes to comfort and pinch flat prevention?

To begin with, Conti GP4kS2 is far from comfortable, even 28mm (e.g. measure ~30mm wide). It's a German-engineering overbuilt vulcanized tire, made to last ~5000 Km. If one is looking for supple tire, then open-tubular (e.g. Veloflex, Turbo Cotton) is the weapon of choice. When it comes to aero, there's already a violation of 105% rule. In order to optimize aero for 21.5mm wheel, one must be running 19mm tire. So, going from 23mm (measure ~25mm) -> 25mm (measure ~27mm) is not going to slow down a rider.

FWIW, the 23mm Gatorskins on the bike I started with (on 15mm wheels), and the 25mm Vittorias are both comfortable enough. So maybe my idea of "comfort" is different. The 25mm Vittorias on 19mm rims are definitely more cushioned, but both have been fine for my purposes.

So if comfort and speed aren't an issue, would you give the nod for handling to the Conti 23mm or 25mm?


Maybe a little more info on my riding? So far I'm doing 20-50 mile rides (will get up to 100, just easing into it, have the endurance for it, just haven't carved out six hours to do it yet lol), 18-20mph avg on rolling terrain, 38-40mph on good descents with braking, still getting comfortable with going that fast downhill. Fair weather rider (don't mind the cold, but not interested in riding in the rain, just doing this for fun/fitness, I'll go run when the weather is bad).