mschwett 

i just switched from 30mm GP5K TR S to 28mm. feels faster, but isn’t really. the difference is modest but very noticeable, next time around i’ll probably go with whatever is more readily in stock, and if both, the 30s.

t2p

agree - Conti 25mm GP5K's measure around 23mm on my old school Campy Omega 19 rims (mounted tubed @ approx 100 psi)

t2p

the 30mm prob rolls faster than the 28mm - and a 32 might roll faster than both

unless you get carried away and reduce pressure too much

but of course there is a weight increase as you go up in size

( see chart above and link below )

https://www.bicyclerollingresistance...000-comparison

.

t2p

currently have 32mm GP4S on a hybrid ; they measure 32mm (mounted w/tubes @ approx 90 lbs)

they are relatively light, roll well, and have a little more puncture resistance than a GP5K ... good compromise tire

don't roll as well as a GP5K - but then again not many tires do
.

DangerousDanR

We have GP5K tubeless running right at 90 PSI on the tandem. They work just fine. Noticeably faster than the Schwalbe Marathons they replaced, but that is to be expected. The first set went over 2,000 miles with zero issues or flats. They are ready to go again when the snow is gone next spring.

veganbikes

I generally will ride the widest tires my frame can take without causing issues. If I could fit 30s on my 28c frames I would do that in a heart beat or even go to 32. I think maybe my mountain bikes I am not absolutely maxing it because I want room for mud and debris. Wide tires and lower pressures is the way of the future.

bampilot06

All of my bikes have GP5000. My race bike has 32mm. They have lasted about 6,000 miles and still going. I weight 163 wet and run them at about 80 psi. I don’t see myself switching tires anytime soon.

eduskator

Don't want to start (another) tire width debate, but tests done in labs are only good in labs. Real world usage is another thing, and there are several other factors to consider than RR.

force10

Vittoria Corsa N.EXT's in 30mm here. Measure right at 30mm on my 21mm IW rims

jackb

I ride Continental GP 4000 Four Season 32mm. Love these tires. No flats in three years. Nice, comfortable ride.

PeteHski

Yeah, in the real world the benefits of wider tyres are even more noticeable i.e. ride comfort, grip, faster rolling over rough ground etc. Potential downsides are aero (although some modern rims are optimised around wider tyres) and weight. I find the benefits of 30 or 32 mm tyres massively outweigh any disadvantages for any road conditions I experience. I think my chances of going back to traditional narrow tyres are zero at this point.

eduskator

I must agree with you, sir! I find that 28mm is the perfect balance, especially that I ride on tarmac that's in very good condition most of the time, but I may very well try 30 next year. They're cheaper as well for some reason (less popular than 28mm I guess).

I'd rather feel fast and comfy and actually go slower, than to feel slow and uncomfortable and go faster.

prj71

I went from 28mm Continental GP5000s to 32mm Continental GP5000s. Night and day difference in comfort and I can go faster over the rougher sections of pavement with the 32mm tires. Would never go back to 28 again.

PeteHski

Unfortunately my local roads are pretty rough in places, so 30 or 32 mm offer a better ride and are probably slightly faster on these surfaces. It helps that my rims are relatively wide too (22 mm internal).

mschwett 

the issue i have with BRR (which i love reading!) is that the differences are so tiny in this kind of tire (a few watts max) that they’re totally swamped by aerodynamics, which is not discussed. i know that i only see consistent/measurable differences in speeds on segments which have pretty high averages, meaning some descending. the 28mm tires i’m on now come closer to the ideal profile with my current rims, and i definitely am braking more on descents that i do multiple times a week. wouldn’t be surprised if there was another 2mph at 35+. but it’s not really useful, since i’m braking it off, and at the more typical 15-20 average i see no difference at all other than a rougher ride.

Bassmanbob

I went from Conti 5000 tubed 25 on one bike to Vittoria Corso 30 tubeless on another bike, and I'm in love. I love the 30. I know I'm comparing apples and oranges because of the two different bikes, tubed vs tubeless, but that's my limited experience.

Sy Reene

Of course looking at that chart, you should also likely be comparing the 23s at 100 or so PSI to 32s at about 60psi. In addition from aero perspective, the assumption is generally all-else-being equal. Ie. a bike that's built to take 32mm+ tires, conceivably isn't going to be as aero as a bike built that could only take max 25mm tires. Nor could said bike likely be built to the same weight as a bike that hasn't been built to take only narrower tires. IOW, there's a number of factors.

aliasfox

My Lynskey has a GP4000 25mm on the back (fills out to about 28mm), and the OEM 28mm UltraSport 2 on the front (fills out to just under 32mm).

The UltraSport 2 looks massively chunky compared to the GP4000. It seems comfy, and it does seem to have reassuring bite on curves and under braking.

That said, once the UltraSports wear out (I have two), I'll probably replace them with something smaller, or at least lighter. I've noticed that I'm fairly sensitive to how a bike feels under acceleration, and heavier wheels and tires just make a bike 'feel' slower and less fun to me. Might be some time though - nearly 3500 mi on that front tire, and I can still clearly see the wear dimple...

mschwett 

right; my recent experience has been riding on 26, 28, and 30mm tires on a bike which takes 32mm max; obviously everything else is the same in this case. i run pretty low pressures relative to the recommendations, so i was likely looking at 10.5 watts ish on the 30mm, and maybe 9.5 watts on the 28. i haven't done the math but i have to imagine the increased frontal area and the less optimum rim/tire profile is way way more than a watt, which is really splitting hairs for anyone but the most pro!

downtube42

I've run 35mm and 32mm GK Slicks, and now 32mm GP5k, on my rando bike. Prior to that bike build, I'd never run wider than 28mm on a road bike.

I'm not too lazy to ride a 1200km brevet, but I'm too lazy to try analyzing data to determine any speed difference.

If GP5k came in 35mm, I'd run those. In 40k of rando miles, I've often wished for wider tires; not once have i wished for narrower tires.

Ramshackle

30mm gp5000 clincher on a Spec SL4. Would have preferred 32's but they might be a little too wide. The 30s ride great and similar to the 28 Corsa they replaced.

crazyravr

I have GP 5000 TL on my TCR and absolutely love the 30mm. Its the perfect middle ground IMHO for comfort and speed.

ClydeClydeson

I ride 32s - currently a Conti F and Maxxis R. I could go a bit smaller for most of my riding, but there is a stone dust rail-trail near my house that I feel a bit better on wider tires for the occasions I ride there.

If you have no specific rough terrain or loose surfaces you struggle to ride with 28s, I would keep them on until they wear out, THEN consider getting slightly wider tires. As someone said above, it's not worth the effort or expense to go up 2mm, but tires are a wear item and will need replacement sooner or later, so for sure try a wider set then.