Just thinking out loud here. It has been measured and verified that assuming all things constant, wider tires have lower rolling resistance. However, the benefits of going to a wider tires would be the ability to run lower tire pressures for more comfort.
According to data from Continental Grand Prix 4000S II 23 25 28 mm Comparison , 25c at 80 psi is slightly more efficient as compared to 28c at 60 psi and those pressures are in the ballpark area of what I would run typically.
So all things considered, in real world scenario, 28c tires are heavier, marginally less efficient and limited choice of aerodynamic wheels designed around 28c, is it still worth the trouble moving to 28c?
Iām considering between the Enve 3.4 and 3.4 AR wheels, hence the question. Tire clearance would not be an issue btw.
First of all, if you are deciding between the 3.4 and 3.4ARs, the choice is dead easy IMHO: just get the ARs. Even if you decide to stick to 25 mm rubber, you can still mount them on the wider ARs without a big aero penalty. And you could go far wider than 28 mm if you wished in case it is warranted (e. g. for light off roading or off season riding where safety may be more important than minimizing rolling resistance).
Before I comment on the arguments you bring forth, let me bring up a few points you havenāt mention, but that I feel are important:
Wider tires provide more grip, which translates to better braking and faster cornering ā especially in difficult weather.
Wider tires are not just more comfortable, but safer as you bounce around less. This is important when you frequently encounter less-than-perfect road surfaces, where narrower tires pumped up to higher pressures can get a bit ājumpyā.
You have way more options when it comes to adjusting pressures. I run on 28 mm Corsas when the weather is nice and 28 mm Corsa Controls in the off season. During my last race, it was raining buckets. I was really glad I could lower my pressure to 63ā65 psi. Rolling resistance <<< not crashing.
Now let us have a look at your arguments, and your conclusion rests crucially on your assumption that 60 psi on 28 mm is equivalent to 80 psi on 25 mm. Fortunately, since you are deciding between two Enve wheelsets, this one is quite easy: Envy has a list of recommended pressure as a function of rider weight. I donāt know how much you weigh, but for the sake of argument, let me assume you weigh 73 kg. Enveās recommended pressures are now as follows: for 25 mm it is 63 psi, for 28 mm tires it is 53 psi. If you scroll through the list, you see that generally, the difference in recommended pressures is 8ā12 psi, depending on your weight, with the difference increasing slowly with rider weight.
Bike rolling resistance does not go down to such low pressures, they only measure 60 psi, 80 psi, 100 psi and 120 psi. However, you could take the lowest figure, 60 psi for 28 mm and interpolate the rolling resistance for the 25 mm tire. You see that the 28 mm performs about 0.5 W better (using my eyeballs). So that suggests that also at Enveās recommended pressures youād be better off with 28 mm tires.
25mm tire will be (probably) be more aero. It is difficult to put some watts on it. But you also have to take it into consideration. Maybe put a 25mm up front for the aero part. And 28mm in the back.
Thatās a valid point in principle. But in this case: yes, maybe?
We are comparing two optimized wheel-tire combos: the AR rims are optimized for 28 mm tires and hence, compared to the outer rim width, even 28 mm tires do not baloon out on them. (This is how I have understood the OPās question: he wants to either get the regular 3.4s and use 25 mm tires or the ARs and stick 28s on them.)
The gains will probably be marginal (although I wouldnāt know how to quantify them). Moreover, the 3.4s are climbing wheels, so I donāt the OP is focussed on aerodynamics first (otherwise he or she would have opted for 4.5ARs or so instead). Nevertheless, you do bring up a valid point.
Tire width selection would depend on what rims i get eventually. From Enveās data, it looks like both the 3.4 and 3.4 AR are pretty evenly matched aerodynamically wise when paired up with the correct tire width.
One consideration for the AR is the very limited number of tires approved to be used on them, plus the GP 5000 TL is specifically called out as not safe to be used on those rims.
I was considering the 4.5 AR too, but I thought aesthetically speaking, the 3.4 would be a better match for my custom steel frame
If the data is to be trusted, it looks like the difference between the 3.4 AR and 4.5 AR is ~ 1 watt weighted average or roughly 2-3 watts diff at 48kph, 10 degree yaw? If we drag it out to 15 degree yaw, the deeper 4.5 AR starts to break clear of the 3.4AR.
The 4.5ARs are the goldy lock rims that strike a balance between aero dynamic gains, stability in cross winds, weight and accepting wide tires. In practice, I think the larger yaw angles will play a significant role, because winds rarely come head on and are rarely laminar.
Of course, aesthetics will also play a role, although personally, I really dig larger aero wheels. Tastes may vary, of course
But if you want to save every watt, then going deep is the answer ā¦ choices, oh choices In either case, if these are your choices I donāt think there is any way to go wrong here, Enve rims are top notch, light, aero, beautiful, the only downside I can think of is the price tag.
This is anecdotal and non-scientific, but I believe my 28s are faster. I have a Allez Sprint Disc with Roval CL50s and run āHell of the Northā Sagan Turbo Cottons, and also have a Scott Foil with 404ās and GP4000II 25s. The 28s are more plush, bounce around less, and can hold corners with more confidence. Those three things help make them faster in my case. I donāt think Iāll go back to 25s if I can help it.
Also ājumpy and bouncyā equals slower, not just less comfortable or less safe.
IMO its a no brainerā¦unless the main application of the wheels is going to be time trials or something at 25mph plus all the time.
The 28s will be noticeably more comfortable. That is an absolute, easily apparent advantage. Every other consideration is a āmaybe???ā It could honestly IMO go either way speed wise, and will likely depend on your roads, wind, how fast you are, how much drafting you do. In other words - too close to call.
Agreed, for me its 28s @ 60psi, wont be going back. Even if some new data comes out to tell me how much slower they are for some reason, they ride the choppy roads I ride so much better, and grip better everywhere
Absolutely. I explored new routes last weekend and ādiscoveredā a surprisingly deep and large pothole right after a turn at full speed. I thought I would have a flat for sure, but no, my (28 mm) tires and my wheels were fine. But I had to return to the scene of the crime, because I noticed a few kms down the road that I had lost one of my bottles.
Another consideration is 28s do great off road as well. Not say a downhill rocky mtb trail of course. But crushed limestone trails, tame gravel, packed dirt trails. 25s can handle most of that too if conditions are bone dryā¦but 28s are MUCH better, and Iād wager faster even on a super smooth crushed linestone rails to trails path
That would certainly be a consideration if I have such terrains over in my area. Typically I just have to deal with poorly maintained roads in certain areas and the occasional potholes.
If there were gravel riding to be had in my area, it would be a clear nod towards the AR, Now Iām just trying to figure out if it makes sense for the AR if the surfaces Iām riding on doesnāt include gravel.
WRT the non approved tires, the AR rim profile is a non-hooked bead design. Therefore the tire needs to have a built in tubeless compatible bead in order to mount safely.
The GP5k TLās are great tires. I run them on HED Ardennes+ as training wheels. 25mm measure out to 27.8mm inflated. However, they are impossible to mount on my 50mm Mavic Carbon wheels. Too tight.
Iāll be curious to see if Specialized soon to be released tubeless tires will be AR compatible.
I remember reading something about the GP5000 beads being a little too tall/thick for hookless beads (which the AR series is), which can result in the tires popping off in certain scenario.
They are not safe. The 4.5ARās are hookless rims, and GP5000ās are ONLY for use with hooked rims. As in there is a very real chance of blowing the tire off even at normal pressures
