Just bought a pair of 25mm Conti GP4000IIs for my new Zondas – going on a new build. Previously running 23mm on narrower Mavic rims.

However, the mounted 25’s look mahoosive – more like a hybrid balloon tyre – not tried them yet and reluctant to as I might chop them back in for 23’s but have you switched to 25s and are the benefits worth it? The mounted 23’s actually measure just under 23mm wide, the 25’s near 26mm probably due to the slightly wider Zondas.

Can’t help wondering that staring down at these things would make me feel slower…

I sort of did (turned out I couldn’t actually fit one on the back!) and I also thought it looked ridiculous when I first put it on. Now they look the same though. Front one is staying because I think it feels a bit better.

I’ve got them on my winter wheels, although my summer wheels are stans so they make everythig look big anyway.

Use them, if you don’t like them they’ll be worn in 6 months anyway and you can pick something else.

I’ve stuck with them and think they’re great.
Feel much softer to ride but faster. Normally run tyres at 120 psi but had to drop the front one to 100 as I got some rubbing on the fork, especially when heat built up on alpine descents.

Yes. Brands vary – my 25mm Michelin Pro4s are noticeably bigger than Conti GP 4 seasons.

The main benefit for me is I can drop the pressure a bit to improve ride comfort – they don’t feel any slower.

Yes, I run Schwalbe One 25c and they look huge (and are wider than 25 mm – more like a 28c). But with latex tubes they roll so well and corner like nothing else. I also run 25c Yksion Pros and they roll much better than the 23c’s I have on another bike – both on the same rim profile (Open Pro/CXP33).

You’ll get used to the look after a while 😉

My 23’s barely fit in the frame (I used to get rub marks) so 25,s have got no chance

I’ve switched back and forth, mainly because I love Michelin Pro4 Endurance tyres and it’s been hard getting them in 25mm sometimes and I’ve reverted to 23mm.

Never notice that much of a difference going down from 25 to 23, to be honest. But just having gone back the other way, 23 to 25, and I believe it feels more stable and comfortable, which I prefer.

I actually couldn’t care what they look like, provided that tbe fit in the gap. I’m a 5’9″, nearly 13 stone bloke in Lycra. It’s not the tyre width that makes people look and laugh!

OP

Gosh you are so right ,when you see it up close that 2mm difference is huge,it must be a lot slower 😛

I’m a 5’9″, nearly 13 stone bloke in Lycra. It’s not the tyre width that makes people look and laugh!

😆 good on you mate.

I put a 25c 4 Seasons on the back of my winter bike, noticed no difference at all.

25c should be faster as less rolling resistance right?

Dunno if I’d notice it but do like using 25c in the winter and suspect I’ll use in the summer too once my current stock of 23cs have worn out.

I’m sure I read (no, I don’t have a link) that wider tyres feel slower but are faster on less than perfect surfaces, with the fastest for crappy british tarmac being 27c and narrower tyres being fastest on smoother roads.

Yes, had to go back to 23c for a bit, didn’t like it!

No noticeable difference in speed for me, but loads of confort and insurance against flats/dinged rims thanked to the extra volume.

My experience (and that of many others) is better cornering thanks to lower pressures (80psi), but cynic al will probably be along shortly to refute that with his clever science.

Thanks guys, great feedback – fasthaggis, sadly a picture of a ruler does not tell the whole story (actually over 3mm 🙂 ), when you see them fitted the difference is far more significant in width but volume and height and as many have posted has a real world effect.

Since posting I found this useful link too which seems to back up the ‘science’ bit:

http://www.competitivecyclist.com/learn/25-vs-23

I have 25c on my Equilibrium and 28c on the Flyer. If I can get 28c under the guards on the Equilibrium I will be fitting them when I need new tyres. I don’t race, I commute, so comfort is king to me.

sadly a picture of a ruler does not tell the whole story,

I know ,you couldn’t even see where I was holding the ruler. 😉

Tried 23’s, didn’t get on with them. 110psi or more to avoid pinch flats and a jarring ride was not for me.

Used 25’s for a while now, so much better. 95-100psi in the tyre instead, lots more comfort and grip, and no negatives.

Now gone tubeless with 25c Schwalbe One’s on Campag Eurus wheels (Basically a Fulcrum Racing 1) and now I’m down to 80-85psi most of the time, with increased grip, less rolling resistance and it’s so comfortable!

In fact I’m now tempted to try 28’s if they’ll fit…

I tried 25s for the first time last winter. Hated them and was very glad to switch back to 23s, which i use for everything (summer, winter and racing). Have no issues riding them in the wet/ice etc. The only time i’ve wished for wider tyres was racing up a cobbled climb 20 times 😯

I grew up racing and time trialling on 18/19’s so 23’s feel like an armchair.

25’s? i’m on 28’s now. The roads round here are terrible; the roads aren’t so much potholed, as ‘ploughed up’.

2mm more tyre, and ~15psi less pressure, makes a world of difference.

if i wanted to go faster, i reckon pedalling harder would probably make more difference than fitting harder tyres.

I tried 25s for the first time last winter. Hated them and was very glad to switch back to 23s,

Just a guess, but you might be a fair bit lighter than most STWers?

I’m on 28mm Gatorksins.
Always have been.

My bike fits me nicely, I get on with the saddle, am always comfortable and never get punctures.

I only road ride for personal fitness and just to look at the countryside, not racing.

gone from 25s to 35s, but i guess i’m an mtber at heart. 25mm is the minimum for me!

I’ve been reading a lot of articles on this lately and I have to say most things I have read are very one dimensional. For example:

a 25mm tire experiences less rolling resistance than a 23mm tire at the same air pressure

Isn’t the point of a 25mm tyre that you would run it with less pressure, increased comfort, better handling, 15% drop, etc. Plus if you run them at the same pressure surely a 25mm will be a harsher ride? So what performance effect does that have? And I read lately that tubeless have less rolling resistance than tubs or clinchers.

wider tyres are more aerodynamic when paired with the right rim

But not everyone is running wide U section carbon rims. Plus there’s the whole argument about how fast you need to be going in the first place to get any significant aero advantage. And what about when it’s windy? Wouldn’t a smaller tyre/rim side profile be better in cross winds?

May be neither is perfect, perhaps 25 are better in some circumstance and 23 better in others.

25s are great for commuting, but the ones on my posh bike have to be deflated on the rear if I want to remove the rear wheel

I tried 25s for the first time last winter. Hated them and was very glad to switch back to 23s,

Just a guess, but you might be a fair bit lighter than most STWers?
[/quote]

How very dare you! We are all racing snakes here. Albeit some have us have just had a rather large lunch.

I’m running that exact setup – went for 25mm as the Zondas are supposed to be really stiff. In terms of speed, you won’t notice it as the aero effect is negligable, there’s naff all weight difference and the rolling resistance isn’t going to be that much different either.

I’ve also run 23mm 4Seasons on the Zondas, didn’t notice the difference (other than the grip in the wet!) – only observation was that the clearances on 25mm tyres wouldn’t allow room for my mudguards in winter!

Overall those Zondas won’t disappoint you, I’m loving mine.

Interestingly a lot of the top end bikes are shod with 28mm rubber, tyre size used to make a difference but now it’s more to do with comfort than advantages.

In terms of speed, you won’t notice it as the aero effect is negligable, there’s naff all weight difference and the rolling resistance isn’t going to be that much different either.

so might aswell use the bigger tyres then?

tyre size used to make a difference

have the laws of physics changed?
🙂

25s have cured pinch flats from the combination of potholes and my fat arse. No slower really either. I’d be tempted with 28s next time I change.

I’ve ran 23’s and 25’s on Zondas. The 25’s will give you a slightly plusher ride on crap roads and because of their profile, should offer slightly more grip when it’s cranked over.

I’ve currently got Conti Race 23’s on some Campag Bullet 50’s and they fly along with 100psi in ’em. Cracking wheels!!

On my TT bike I run a 22 Sprinter tub at the front at 150psi in good weather, that really screams along on good roads. I’m tied to a 23 on the rear disc due to frame clearance.

A lot of pro’s ride 25’s, I think mainly for the rounder profile. Years ago they all thought the narrower the better but the perceived aero advantage has pretty much been rubbished these days.

Personally I buy what ever’s on sale for my training bike, half decent stuff on my summer bike (conti’s). Tubs are lovely though, just not quite as “every day” pracrical.

I’ve dabbled, normally run 23’s and have done for bloody years until the fashion police came knocking and my whippet mate pointed and laughed.
So I’ve tried 25’s, Mav’s Yksion that came with a set of M40C’s I bought back in April, nice for the bumpy part of Yorkshire I rode around before the Tour, but then I changed to Challenge Crit’s 23’s and they’re soooo much better.

I’d say it’s all about the quality of the tyre and Brand, some will like the softness of 25’s but some manufacturers had hardened up the sidewalls to compensate for the “bulging” and made them just as stiff as blown up 23’s.
I’m a fanbouy of Challenge and like the way they build tyres, so I’m sticking with 23’s which I really do believe make me look and ride like that bloke Boonan… or Gilbert 😆

D0NK – Less about the laws of physics and more about tyre technology – compounds, vectran breakers and the like, now that makes a difference.

Again, thanks all, great info all round and pretty much unanimous that I have to at least give them a fair chance. 🙂

And one last one (I could really be asking for it here…) – logos – there are two on the Zonda opposite each other and two Conti logos opposite each other on the tyres.

Valve goes through the Zonda Campag logo.

How to line them up? (I went a logo per quarter).

(Really sorry).

No.
I went from 21mm tubs straight to 25mm last year. What the things look like is irrelevant as most modern bikes look like crap anyway 😆
I have yet to see the point of dropping the pressure though. A 25 rides nicer than a 23 at the same pressure. Only bang them to 100psi though some maybe In have yet to know any different. Try wider tyres. I also use 30mm Challenge Strade Bianca’s at 80psi. Very nice and I cannot tell the difference between them and my 25mm Pro 4’s which sort of contradicts my point about keeping pressure the same. Weight isn’t far off either.

yes (training and race bikes)
never going back.

Went from 23mm GP4000s to 25mm on Ksyriums on my SuperSix. Much more comfortable as they enabled me to drop pressure to F85/R90psi. They certainly feel smoother and faster. Better at dealing with the disgraceful road conditions too. I’d go bigger but they wouldn’t fit in the frame, and I’d need new wheels.

I’m running 28s at 90psi and they feel much more stable

Conti 28c GP4 seasons.. not sure what the sacrifice in speed is but they seem like good tyres. Even been down gravel and bridle paths on them.

I’m on 28s too. Have been all summer. Was a bit reticent at first, but given the quality of many of the roads I ride on I figured they’d be an all round better choice. If anything they haven’t proved to be any worse. Riding faster than ever. You get some raised eyebrows turning up at time-trials and stuff, but what the hell.