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Discussion Starter · #1 ·
Hi all.
I got a set of "new to me" Zipps 30, and I'd like to know what tyre would fit these wheels better, the 23mm or the 25mm.
Currently I weight about 170 pounds, but I am working to get back down to 160. I live in northeast Indiana, so no big hills here. I mostly do club rides or team rides and I do sprint more than anything.
My bike is a 2009 specialized Allez Sport with Sram Force 10 speed group,
I got the Zipps 30 about a year ago, and I have a set of continental 4000 in 23mm, I just don't know if I should get the 25mm or just put the 23s on.
This is pretty much the last upgrade I do to my bike.
Thanks!
 

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25's all day long...
but since you already have the 23's, perhaps ride em til they wear out, then go with 25mm
 

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Discussion Starter · #3 ·
Evrything I have ever had, it's been 23mm.
I have a set of Vuelta Corsa wheels and a set of older Shimano Dura Ace WH-7701. I still have a pair of used Kenda Kountach, a pair of new Specialized Turbo, and the conti 4000 that still lol new as well; all in 23mm.
I might have to sell or trade pretty much all my tires if I go to 25mm.
I am planning on keeping only the shimano and zipp wheels and sell the Vuelta.
 

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A couple of things. First, what do you hope to gain from going to 25s or keep by staying with 23s? What parameters do you want to maximize?

Aerodynamics pretty much always go to the narrower version of the same tire (it has in every instance I've seen, and I've seen a TON) while the rolling resistance favors the wider - so long as you keep the pressure the same. Neither difference is going to make more than about a tenth of a mile per hour difference, and that may be a generous estimate.

The GP4000 is wide for its size. I just measured some this week, and though your wheels are narrower than any I've measured on that I can remember, they are still going to be big. On an 18mm (inside width) wide rim, a "23" GP4000 will be ~26mm wide. A "25" will be close to 28mm - and by "close to" I don't mean almost, I mean it might be 27.8 it might be 28.2. Your rims are likely to narrow those measurements by ~1mm or so.

I also measured Specialized S-Works Turbos this week, and the 24 size equates closely to the GP4000 23, while the S 26 and the C 25 are closely matched in size. If you have Specialized tires in 23 then you have different ones than what I measured as the ones I measured come in 24 and 26 only. I'm not familiar with Kenda Kountach.

To my mind, there is no rational justification for displacing a set of perfectly good tires for new ones. The Conti at least will be great tires for almost any purpose you choose - I use their 23s often, and they're great. I weigh 160. The perceptible difference between 23 and 25 is, in my experience, small in every regard.

There's also the potential issue of Conti 25 not fitting your bike, or having almost no clearance. That's not at all unusual, especially in bikes from your bike's era.

My take is absolutely to keep the tires you have (at very least the Contis), wear them out, and then make a decision from a cleaner piece of paper.
 

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Discussion Starter · #6 ·
A couple of things. First, what do you hope to gain from going to 25s or keep by staying with 23s? What parameters do you want to maximize?

Aerodynamics pretty much always go to the narrower version of the same tire (it has in every instance I've seen, and I've seen a TON) while the rolling resistance favors the wider - so long as you keep the pressure the same. Neither difference is going to make more than about a tenth of a mile per hour difference, and that may be a generous estimate.

The GP4000 is wide for its size. I just measured some this week, and though your wheels are narrower than any I've measured on that I can remember, they are still going to be big. On an 18mm (inside width) wide rim, a "23" GP4000 will be ~26mm wide. A "25" will be close to 28mm - and by "close to" I don't mean almost, I mean it might be 27.8 it might be 28.2. Your rims are likely to narrow those measurements by ~1mm or so.

I also measured Specialized S-Works Turbos this week, and the 24 size equates closely to the GP4000 23, while the S 26 and the C 25 are closely matched in size. If you have Specialized tires in 23 then you have different ones than what I measured as the ones I measured come in 24 and 26 only. I'm not familiar with Kenda Kountach.

To my mind, there is no rational justification for displacing a set of perfectly good tires for new ones. The Conti at least will be great tires for almost any purpose you choose - I use their 23s often, and they're great. I weigh 160. The perceptible difference between 23 and 25 is, in my experience, small in every regard.

There's also the potential issue of Conti 25 not fitting your bike, or having almost no clearance. That's not at all unusual, especially in bikes from your bike's era.

My take is absolutely to keep the tires you have (at very least the Contis), wear them out, and then make a decision from a cleaner piece of paper.
Great post, thanks!

I really don't know much about it, and I have been reading about the 23mm vs 25mm debate, but I didn't see much about the wheel tire combination I have.

To be honest with you, I am not even sure what I want to get out of the 23s or 25s, I guess I just want to know what would better fit my wheel. I got the 23s because I check what I had before, and they all were 23s.

If there isn't a lot of difference, I'll just stick to the 23s conti and I might sell the turbos to replace them with continentals, just not sure if I will get 23s or 25s. I have to check the clearance in my bike as well.

Thank you very much for your response, I understand more about it now.
 

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I'm in NE Indiana too and have found the change from 23mm to 25mm to be nice. The main reason for it is improved ride quality, especially on those older rougher country roads, it may even have lower R.R. on the rougher surfaces.

I actually started out switching the rear to 25c after cutting the 23 that was on it on glass. For a while I rode it like that which I didn't quite like as the front seemed a little steeper and didn't ride as nice.

When I finally got around to switching the front to 25c which I did on a hunch that I was missing out, the change was noticeable. It was quite a bit better and I really started enjoying the bike a lot more.

Now, I switched from a Hutchinson and Specialized 23c slick to the Conti GP 4000s II. Switching from a 4000s II 23c to 25c may have been a little less different. The 4000s II 23C prob rides decent since they like to run large. I measured 26.7mm on my 25c tires mated to a narrow rim.

That was all on my alu Speedster S20 which turns out to be a pretty nice riding frame compared to the first gen Foil which is noticeably stiffer and harsher. I will definitely be rolling minimum of 25c on the Foil. I even had to drop psi a little to get a lil closer to the S20's feel.

I recently bought a Speedster CX20 that is going to replace the S20 once i get a road wheelset for it, I'll likely end up putting 28c on it.
 

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I'm not discounting what you experienced even one tiny little bit - probably most people would have experienced the profound change you did in the switch you made. But Hutchinson clinchers generally run very narrow, and there's only one tire in their clincher lineup that really compares to the ride quality of a GP4000. So it's possible you went from a tire that rides not so great to one that does, and gained perhaps 5mm in width at the same time. That's a big change.

No idea what Specialized tire you've had but Specialized did recently hire Continental's entire bike tire engineering team, so that tells you something.

Switching from GP4000s in 23 to GP4000s in 25 is almost certainly a less notable difference than your change was. I've switched back and forth a lot between them and I might be able to pick out the difference blind. I have 23mm Hutchinson Fusion 3s on my around town bike (had them on hand and they just won't die) and I could spot the difference between those and 25mm GP4000s blindfolded, drunk, and sleep deprived. It's a big difference.
 

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A couple of things. First, what do you hope to gain from going to 25s or keep by staying with 23s? What parameters do you want to maximize?

Aerodynamics pretty much always go to the narrower version of the same tire (it has in every instance I've seen, and I've seen a TON) while the rolling resistance favors the wider - so long as you keep the pressure the same. Neither difference is going to make more than about a tenth of a mile per hour difference, and that may be a generous estimate.

The GP4000 is wide for its size. I just measured some this week, and though your wheels are narrower than any I've measured on that I can remember, they are still going to be big. On an 18mm (inside width) wide rim, a "23" GP4000 will be ~26mm wide. A "25" will be close to 28mm - and by "close to" I don't mean almost, I mean it might be 27.8 it might be 28.2. Your rims are likely to narrow those measurements by ~1mm or so.
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That's not my experience. The GP4000S might be slightly oversized, but the difference you report is due to the wide rim. It's interesting how much the wide rims affect the inflated tire size.

the GP4000S 23c tires measure 26.7mm on a very wide HED rim, which has a 25.5 mm outside width, 20.6mm internal width. Yes, the tires are only about 1mm wider than the rims, but they work great, and I inflate them to the same psi as a 25c on a standard rim. This is a "tubeless ready" rim, so the beads snap into place on the rims, and I don't worry about a bead popping off the rim.

A 25c GP 4-Season measures 28.5 to 29mm on the same HED rim.

On my older 19mm outside width rim (14mm internal width), the GP4000S in 25c is 25.6mm wide, right at specs.

The Zipp 30 appears to be 20.4mm outside width, instead of 19mm.
 

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Good info - I haven't measured on a narrow rim in quite a while. Haven't even held a narrow rim quite in a while. What's the inside width of that 19mm rim? Inside width governs tire inflated width, as you likely know.

Zipp doesn't show the inside width of the 30. A Stan's Alpha at 20mm outside is 17, Zipp 30 is 20.4. So the Zipp could be 15 and it could be 17, which would make about a 1mm difference. We've historically found a reliable conversion rate of 1mm of tire inflation width gain for every 2mm of inside width gain. So if the Zipp is 17, GP4k 23 should be a bit over 25.

I'm currently using a GP4k 23 on an 18mm inside width rim (Kinlin XR31T) and it's just shy of 26. 25.85 or so, but it's got some mileage on it.

In any case, whatever it is, I'd sure recommend trying the current tires on the new rims. There's nothing to lose and $80 (if you find a good deal online - $130 at the bike shop) to save. At the VERY least, install one, blow it up, and check the clearances.
 
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