The new 5k 28's are only ~ as big as the old 4kSII 25's. I personally wouldn't consider anything less than the 32's.

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"They're made of latex, not nitroglycerin"

What do you mean when you say "gravel?" Manicured dirt roads? Bike paths? Rails to trails? Or B roads, fire roads, and single track?

I did my first gravel race on 4000S 1's in 23c.

Depends on how hard pack it is, the type of gravel, wet, etc...

Oh let's just say someone talked me into heading out towards San Marcos, California in early May...

Go bigger. I'm finding in my road testing that there is almost no disadvantage to larger tires. A 2.0 G-One Speed is only a handful of seconds slower than a GP4000SII. I would love to try the 32mm GP5000 tl on some of my gravel roads; at least some of the roads that do not get too sandy.

If that is the case, I'll be joining you on the start line.

I decided against my CX bike as the gearing of 42x11/36 isn't quite enough low and top end. That means no wide tires for me.
My wife, who is doing the Wafer (greater % of course is not paved) and is not a strong rider will be using a CX bike with 38C Panaracer Gravel King slicks and 40x11-42.

I'll be riding my road bike with IRC Roadlite tubeless 25C as they are the widest tire that will fit.
They measure just under 28mm and have a couple mm's to spare inside my Ultegra rim brakes.
52/36x11/28 gearing.
I'm sure I'll wish for a bit more volume on the unpaved sections, but I'll take that compromise.

My CX bike still has a front derailleur (gasp! the horror!). Stock rings are 36/46, thinking of dropping to a 34 I have lying around. 11-32 cassette. Thinking a 34x32 should get me 'round?

Gravelking TLC 700x32 is also in the running.

Been through the BWR threads, mostly wondering if/how the new GP will compares with the Pro 1.

The question is how long the sidewalls will last. (that's funny to anyone whos used a GP4k)

Seriously, 28c can do hardpack smooth dirt or fine, hard crushed rock. 32c if you've got a deformable surface. Low tire pressures will protect the tire. GP5ks aren't any thinner or less protected than something like a GravelKing or Compass tire. I wouldn't do any non-smooth dirt with anything over 55psi. Tubeless helps a lot here.
I'd look at the new Vittoria Corsa Control or Specialized Roubaix Pro / Hell of the North too. The G-One Speed is a bit more flexible for dirt hills.

32C Gravelking slick would be a good choice. But yeah, if you can get 32C GP's... would be a fast tire.

34x32 is a pretty low gear, I think that will be more than enough.

The guy I ride the most with tried it with the 4000sII in 28 on Hed Jets. Measured 32 mm or so. IL/WI border, so a fair share of loose stuff. Very dry conditions. He ran really low pressures. Less than 50, but over 40. It was definitely squirrelly in the rough stuff and he smacked the rims a couple times, but came out okay (latex tubes). Those "rough" sections made up <2% of our riding those two days. The loose slowed him down a little, but not as much as I would have thought. He was a pain to keep up with on the paved sections though. He was probably not too far off of 100 miles before the sidewall went on one tire and the threads were visible on the other.

It's possible to do, but not a good idea. Something with a little more sidewall and tread is highly desirable. You might make up some time on the paved, but tip toeing through any actual gravel isn't fun either.

do you have a reference for the new 28s being same as 4000 25s? Thanks!

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36 kona qualifiers 2006-'23 - 3 Kona Podiums - 4 OA IM AG wins - 5 IM AG wins - 18 70.3 AG wins
I ka nana no a 'ike -- by observing, one learns | Kulia i ka nu'u -- strive for excellence
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Inflated measurements on 17c rim, width x height (mm)

4kGPSII 25c, 27x 25
4kGPSII 28c, 31 x 29
5000GP 25c 26.3 x 24
5000GP 28c 28.5 x 26
5000GP 32c 31.8 x 30

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"They're made of latex, not nitroglycerin"

The sidewalls of GP's with the threads showing have always alarmed me but I've never had one go on me.
As a 136lb rider I can get away with a lot when it comes to tires though.

i had two pair of GP4000's (1st gen) that i got to 5k miles on. Threaded sidewalls were present from 3.5k onward. Never was an issue. Might be different if i'd been running a tubeless set as evidenced by my Pro-One's behaving very similarly (longevity and sidewall threading) but only lasting 2.5-3k due to sealant and air leakage once the sidewalls start to go.

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36 kona qualifiers 2006-'23 - 3 Kona Podiums - 4 OA IM AG wins - 5 IM AG wins - 18 70.3 AG wins
I ka nana no a 'ike -- by observing, one learns | Kulia i ka nu'u -- strive for excellence
Garmin Glycogen Use App | Garmin Fat Use App

gracias

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36 kona qualifiers 2006-'23 - 3 Kona Podiums - 4 OA IM AG wins - 5 IM AG wins - 18 70.3 AG wins
I ka nana no a 'ike -- by observing, one learns | Kulia i ka nu'u -- strive for excellence
Garmin Glycogen Use App | Garmin Fat Use App

I ran 28c ProOne's last year.
I would think you'd want 32c GP5k's, but I say that without experience with them.

For gearing,
I'd go 50/34 on the front. There's enough pavement miles and fast descents that you'd want the 50 over the 46.

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