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

[Hexsense]

I repeat this again, with picture.

Wide tire without big internal width supporting it, at low pressure can easily be push sideway in corner. To solve that, you'll want to over pressure it a little bit to make tire more rigid.
Going wide rim allow you to drop a lot of pressure without having such effect.

Also, yes all tire make some kind of light bulb shape. It tries to be circle if possible. But rim wall geometry and volume between rim walls effect where center of the bulb curve is. That's a big deal. Very wide rim have a lot of volume between rim side wall and bring center of the circle closer to the rim compare to narrower rim with wide tire which do the opposite, pushing center of the curvature far away from the rim.

[robertbb]

When people say that 23c "behaves" better downhill than a wider tire I wonder if we are talking about the same things. The only way a 23c tire could be better downhill than a 25 or 28 is if they are installed on very narrow rims. On a modern wide rim there is no color, wider descends better.

Simply not true. The best descending setup is a *combination* of a rim (comprising internal and external measurements) and tyre that create the most tubular-like (i.e. non lightbulb) shape.

And although the tubular-like shape can be accomplished with 23c tires and certain rim widths, and that is probably the more agile (others would call it "nervous") configuration, a wider tire will have more grip and will work better as suspension when the asfalt is not glass-smooth. Good damping of tarmac irregularities means more control of the bike. The braking is also better (they do not get locked that easily) and definitely more confident-inspiring. Again, if by "handling" we understand "agility" then maybe yes, on very good tarmac 23c could be the best option. But for grip, braking and damping, wider is better (if supported by the right rim).

I wouldn't call it "agile" or "nervous" - I'd call it balanced. The argument of more grip on a wider tyre is true but it is irrelevant, which is more misleading than false. Handling is about more than just grip. You can have all the grip in the world but if the tyre flops about underneath you then your overall handling will be compromised.

Anyway, it seems we're in violent agreement about the rim dimensions needing to match the tyre size to maximise performance. Where we disagree is in what that looks like on a 17c rim as noted by the OP. Having extensively ridden both 23mm and 25mm continental GP4kS2 tyres on Shamal Ultra C17's, I'd pick 23mm (in that particular model of tyre) any day of the week.

[mpulsiv]

As I said in my first reply" Too much information for a new rider". Train on wide tires and race on narrow tires. Simple as that.
Why many of you are so obsessed with performance on training rides? Your tire is wider, so what? Your bike is heavier, so what? You are not racing! If you feel that wider tire is slowing you down and you can't rail corners, then work your fitness to become a better rider. Stop blaming the equipment, blame your legs! I purposely train on heavy steel bike with 30mm tires and it's not slowing me down. As I matter of fact, I hit more PR's than on my race bike. Train heavy and race light, simple as that.

[spartacus]

I have two sets of campy C17 wheels, 23c seems to be a better fit but the 25c were good too.

[rides4beer]

As I said in my first reply" Too much information for a new rider". Train on wide tires and race on narrow tires. Simple as that.
Why many of you are so obsessed with performance on training rides? Your tire is wider, so what? Your bike is heavier, so what? You are not racing! If you feel that wider tire is slowing you down and you can't rail corners, then work your fitness to become a better rider. Stop blaming the equipment, blame your legs! I purposely train on heavy steel bike with 30mm tires and it's not slowing me down. As I matter of fact, I hit more PR's than on my race bike. Train heavy and race light, simple as that.

I might not ever race tho, so I want to enjoy every ride as much as I can and get the most out of my equipment. I don't think there's any magic in the equipment, I know it's the engine (which is pretty good thanks to an ultra running background, and getting better), but that doesn't mean there's any need to have a less than optimal setup. I don't see it any differently than having a good fit, keeping everything cleaned/lubed/adjusted, it all works together and makes for a more enjoyable ride.

[Marin]

There's very little equipment that makes you faster, but there is lots that improves the feel of the bike. Bike fit (and all components affecting it), gearing and tires are the most important.

[spartacus]

As I said in my first reply" Too much information for a new rider". Train on wide tires and race on narrow tires. Simple as that.
Why many of you are so obsessed with performance on training rides? Your tire is wider, so what? Your bike is heavier, so what? You are not racing! If you feel that wider tire is slowing you down and you can't rail corners, then work your fitness to become a better rider. Stop blaming the equipment, blame your legs! I purposely train on heavy steel bike with 30mm tires and it's not slowing me down. As I matter of fact, I hit more PR's than on my race bike. Train heavy and race light, simple as that.

I might not ever race tho, so I want to enjoy every ride as much as I can and get the most out of my equipment. I don't think there's any magic in the equipment, I know it's the engine (which is pretty good thanks to an ultra running background, and getting better), but that doesn't mean there's any need to have a less than optimal setup. I don't see it any differently than having a good fit, keeping everything cleaned/lubed/adjusted, it all works together and makes for a more enjoyable ride.

I agree it sounds weird to train on a slow setup, the effort level is the same you just go slower lol

[AJS914]

Not everybody trains for races. My racing days are probably over but I still enjoy training and riding with mates, fast group rides, and centuries/fondos.

I don't need a 1200 gram racing wheelset but a 1500 gram wheelset is more enjoyable to ride every day than an 1850 gram "training" wheelset with truck tires installed.

People show up to our club ride with full aero gear - aero bike, wheels, helmet, etc. I know that gives them a 40-50 watt advantage over me when the pace picks up. It makes me lust after an aero bike.

[rides4beer]

The Novatec Jetflys arrived, 1470g for the pair with rim tape and valves already installed (645g front/825g rear). Advertised weight is 1435g for the pair, not sure what the rim tape/valves weigh, but I guess that sounds about right. Freehub is a lot quieter than the stock Oval wheels, they seem to spin pretty well and look true to the naked eye (not sure if there's a better way to test that).

Tires should arrive today, went with 23mm Continental GP4kS2s and Continental Race Light tubes.

I still need to pick up a pair of calipers so I can measure everything, including the stock wheels/tires for comparison. I'll post measurements, final weights and pictures when they're ready to roll.

[rides4beer]

Went out for a 30 mile test ride yesterday, what a difference! Definitely improved the ride and handling. Did some standing sprints and didn't feel any flex. Freehub is super quiet, I like it. The stock one is crazy loud, it would scare people when they'd hear it (which I guess can be good sometimes lol).

23mm GP4KS2s measure right at 25mm on the Jetflys, and from what everyone has said, might grow a lil bit. For comparison, the 25mm Vittoria's on the stock wheels measure 26.2mm, so only lost a lil over 1mm (maybe less once the Conti's are broken in), and def improved the ride and handling.

For under $400 for everything, I have zero complaints.

Since this is WW, I dropped 400g, bike is down to 7.64kg (w/pedals, cages & Wahoo Bolt), not really noteworthy around here, but for an entry level bike with only a few upgrades on a budget, I'm happy with it.