Hi all, I am planning to change tyres on my Specialized Tarmac SL6 – wheels are stock ones with DT470R rims, 21mm internal, 24mm external width, 24mm deep, so shallow rims.
At the moment I am running 25mm Victoria Rubino Pro 2.0 and thinking to switch to Conti GP 5000 25mm or 28mm. In terms of rolling resistance, it should be a faster tyre. Future plan is to buy some carbon 40mm-ish wheels with wider rims (29mm-30mm external width) – which would be your choice to have the most balanced benefits in terms of RR, aero and comfort? I think the aero gain derived from the 105% rule, with such shallow rims, it’s minimal, but it would be there with deeper rims. Some more data: I am 5.10 (179cm), 70-71kg, avg speed on flat 34km/h (21mph), I run both flat courses and hilly terrain. Thanks for your insights!

I’m not a proper road rider tbh but for me, bigger has always been better- more comfortable, more stable, and faster on average. I’m not fast over distance mind, maybe aero would be more of an issue if you’re battering out fast flats but then road roughness has the same effect regardless.

(though, my GP5000s cracked pretty prematurely which was annoying- now on Schwalbe 32s)

25mm front and either 28mm or even 32mm rear for your current wheels.

But if you intend to get the new wheels before end of this summer, maybe get a 28mm and 32mm now.

I ran 23mm front and 25mm rear on 17/19mm interal rim wheels last summer, they felt quick compared to ~32mm (big 28s) GP4000S IIs on Hunt Aero Disc Light and Fulcrum Racing Sport 77DB wheels i.e. not terribly deep.

Thanks for the suggestion!

(though, my GP5000s cracked pretty prematurely which was annoying- now on Schwalbe 32s)

Thanks – I see, I keep reading that GP5000s are somehow prone to punctures and weak in the side walls. Anyway, I will give it a try.

My bike wouldn’t take Gp4000 28s, I had to put 25s on. A few weeks ago I bought a pair of GP5000 25s and was disappointed to see they came up much smaller. I reckon 28s would have fitted.
However, I’m impressed by the smooth ride if them. But they’re a bugger to get on the rim.

28s always.

however, be prepared for the 5000TL to be awesome but fast wearing.

Don’t know about the 25s but I fitted a pair of tubeless 28s to my Creo last wee, on Roval C38 wheels and have ridden it the last 2 days. Mighty impressed with the feel of them compared to the Spesh 28 turbo pro’s that were on it previously.

If you are racing, or trying to take strava segments, or anything else that requires opimisation then 23 front and 25 or 28 back. At similar levels of tyre deformation, the RR is remarkably similar. Even with a matched width front wheel, narrower tyres are more aero.

You didn’t mention grip, which with a larger contact patch would be better in a larger tyre.

However, if you aren’t racing, then why does aero matter? Why not just ride a slightly shorter distance and be more comfortable?

I’ve just put on some 30mm challenge strada bianca open tubular (quite the name) on a 20.5 internal width rim. For absolute aero I think a 25mm would be better. But for riding around on the terrible condition roads around me. I think the 30mm will be faster.

I have the 27mm Challenge Strada on 37mm deep rims. Can’t remember the internal measurement but they’re wide.
32 for me is slower. Not by a great deal, but like a few of the guys on here as I used to race I’ve spent a lot of time working out what wheel and tyre combo works best. We have access to a Closed Road Crit circuit so have been able to spend the time working this out. It’s a fast track with a 1 minute uphill drag, so gives us a good idea of weight, aero, RR. It’s a fairly smooth surface.
My fastest combination was the 65mm wheels, 23mm front and 25mm rear. Rim brakes so 28mm was the largest this could take.
But as I like longer rides (80 miles+), my main concern is comfort with speed being important but less so. The Challenge tyres are in my opinion that bit more comfortable than the similar sized Conti 5000. In Autumn and into early winter I used Conti 5000 in size 32, these came off after about 1 month or so. Clinchers, but had a fair few flats and I found them difficult to get on/off the rim. Not ideal when your hands are cold and it’s raining! The Conti’s also nicked really quickly.
With regards to 40mm wheels, I have 3 sets of wheels in this range. I prefer the look of this depth on a non aero frame, but there is a definite aero loss. If aero gains is your main goal then I would go 50mm as a minimum. If like me you prefer the pose value over performance, then 40mm is ideal!

Thanks so much for all your inputs and sorry for late reply – very informative!

My fastest combination was the 65mm wheels, 23mm front and 25mm rear. Rim brakes so 28mm was the largest this could take

Thanks, probably 25mm would be the most efficient but I guess giving space for a bit of comfort is not a bad idea. Looks like these Conti 5000 are not that great value at the end and prone to punctures – will look into alternatives. As for rim depth I was thinking about 40mm as middle ground, it will be my only set of carbon wheels.

if you aren’t racing, then why does aero matter? Why not just ride a slightly shorter distance and be more comfortable?

I see your point, it is not a matter of life and death 🙂 but since I avg 20/21 mph – on fairly flat ground – I thought it could be taken into the equation. In fact I am quite positive about getting 28mm tyres which is a good compromise (or experimenting with 25mm front and 28mm back).

Even with a matched width front wheel, narrower tyres are more aero.

I thought the logic was Teh aero benefits comes from blended tyre/rim profile top and bottom, not just as narrow as possible outer profile. i.e. try to get the outside width of the tyre to match the outside width of the rim as closely as possible…

So a 25mm tyre on a 25mm rim should be optimal, of course some tyres can come up a bit wider if put on a wider rim, others are apparently undersized to start with…

Of course if you’re planning to do lots of miles I reckon comfort is marginally more valuable than aero and therefore maximizing volume would be better, especially in the front to try and benefit neck/shoulders (IMO of course).

https://www.conti-tyres.co.uk/latest-news/165-wider-tyres-go-faster

Cookeaa, our understanding is the same. It’s about matching the rim profiles with the tyre size. Both Enve and Zipp have been going on about this for a while. So a narrower tyre on a narrower rim is OK, but a wider tyre on a narrower rim loses aero performance gains.
Weird to see the article extolling the
Virtues of wider tyres, obviously Conti 5000s in particular….but the Schwalbe 28mm performs relatively poorly.
I’m always very sceptical of anything in Tour magazine, not sure they are the most impartial of testers. They appear to have their favourites….

@paton that ignores aerodynamic benefits.

In fact one of the main reasons the GP5000 tested faster in 25c than the old GP4000 in 25c, is because the old one came up at like 27-28 wide and the new one is true to size (actually, about the same size as the 23c GP4000).

Steps are not aero, but unless you have like a 28mm internal width a 23c tyre will probably still have the best aerodynamic efficiency. If it was on a TT bike that’s absolutely what i’d run.

But again – if you aren’t racing, I don’t see the justification for aero anything. Comfort, grip aesthetics, economy and safety should be the priorities.

Thanks again guys for the additional thoughts! I guess when we talk about “matching the rim profiles with the tyre size” (105% rule) it is about the real width of the tyre on that specific rim – not the nominal width.