Bob Dopolina 

Years ago Continental offered the Force/Attack tire set where the front tire was smaller than the rear tire.

I always thought this was a good idea for two reasons: 1. The weight distribution is roughly 60/40 rear/front and aero is important for the front tire but not so much for the rear. I always felt that I could get the aero benefit with a slightly smaller front tire and the comfort with a slightly larger rear tire.

I still do this. I often run 25c/28c. Anyone else still doing this?

As I went down the rabbit hole, I also started thinking about varying rim widths, as well. Maybe 19 INT for the front and 20 INT (with offset for the rear)? There hasn't been a Taichung Bike Week or TPE show for 2 years so I wonder if I have missed this? Or am I just off on a tangent here?

SoSmellyAir

Still does (Continental Grand Prix Attack-Force Road Tire Set Excel Sports | Shop Online From Boulder Colorado), but maybe less widely available?

I also read about this setup when I first looked to upgrade from the relatively crappy 25 mm wide Schwalbe Lugano stock tires on my bike, but while what you said above is theoretically true, I did not think that either the aerodynamic gain (from using a 23 mm front tire) or the additional comfort (from using a 28 mm rear tire) would be worth stocking two tire sizes for me. Also, since my road bike seems to have better rear compliance than front -- which I assume is generally true for most road bikes? -- I kept both my tires at 25 mm. But my local area has pretty decent roads and bike lanes; some MUPs are slightly bumpy (probably to slow us down for the pedestrians).

WhyFi

I did one set of Attack/Force, but then I couldn't rotate new -> front, front -> back, back -> discard, so I didn't bother getting another set. Now that I'm on tubeless, I don't really do that anymore, anyway (I buy tires in threes, leaving the front in place for two rear tires), so maybe I'll consider it again.

As far as wheels, I think that Specialized/Roval did one or two sets of wheels like that, with different depths and widths, but I could be mistaken.

Edit: yeah, the Roval Rapide CLX are mixed depth and width, there may be others. Interestingly, the front is wider, supposedly for additionally stability in gusts.

cyclezen

aero is quite complicated area of study. much of which flies well above our heads as the great unwashed..
of course, thinner is more aero, given all other factors are the same - which they never are.
I do remember (a hard thing these days as aging makes everything old, 'new' again... LOL!) reading in the early days of Y2K, in studies which were brought forth by both HED and ZIPP, that 'profile' had as much and even more to do with 'aero' than just pure width on road tires. Meaning turbulence created at the tire/rim interface and further back were overriding considerations in creating a low COF. They even present pics of profiles and their apparent COF. Narrow rims being very poor on mitigating turbulence. Hence the wider rims to smooth the tire/rim interface.
What became a search for the best Toroidal shape (donut) for smooth flow. Streamlining the rim and tire combo. Turned out 'deeper' rim depth was not the real answer, it was 'shape'.
So tire size to match the rim shape and make the best toroidal profile...
Rim brakes, flat braking surface of rims .... BAD !!!! - at which point I was convinced that Disc brakes were the future, to allow best shape to the rims without relying on braking surfaces, this was in early 2000s... now I find myself a luddite with nothing but rims brake wheels.... LOL! life has its twists...
Anyway - I did goggle for those studies, and so far with no success. But I did find this... which I've just start to fumble through (I'm not a rocket scientist...). Have at it if you wish, can be downloaded, and it doesn;t seems to be a trojan horse...

A COMPARATIVE AERODYNAMIC STUDY OF CFD

back to size...
I'm going with the manufacturer recommended tire size for their rim - since I mostly have HED and Shimano wheels (some Mavic which are never used) HED knows what they're tawkin about...
.I still have a few 23s, from some nice discounts on good tires - so they get put up front on a few wheel sets, because lower weight distributed up front means I can keep the PSI lower...
But, by prolly Spring 22, I will have put the remaining on wheels, and from now on expect to only ride 25... I haven;t experienced any advantage to going to 28 or greater, I'm 150 lbs and riding the 25s at 80ish psi...rear....
Personally, I think the 25s up front is a better idea, because of a slightly greater contact patch , especially at lower psi. I really can't 'pull' anywhere near what to I could in younger days - but I can still descend fairly rapidly, and as big a patch as I can have is a good thing...
Ride On
Yuri

EDIT: just found this:

HED's Toroidal 2.0 Patent

and this : HED FAQ - see Best Tire size for our wheels
also recommended is the History/story of HED...

woodcraft

A friend gave me a set of Force/attack tires. I rode them on a double century, & in a fast pace line I (& multiple others in the group) pinch flatted the front on some big divot in the pavement.

These days my standard deal is 23/25 Sprinters.

datlas 

I run 23F 25R. Works for me. Only downside is when rear tire is worn you can’t do the usual move front to back and new on front trick.

biker128pedal

Roll my own. On my Domane I use a 25 front and 28 rear. GP5000s. The primary reason is I wanted to take off the 32mm Bontrager tires and this is what I had left over from trying tire sizes. When they are worn out I’ll probably go 28 tubeless front and rear.

DaveSSS 

I haven't run a larger rear tire, but there's certainly nothing wrong with it. The larger rear might last longer. FWIW, the new trend is wider hookless rims, larger tires and lower tire pressures, since it's been proven that the vibration created by high tire pressure actually causes more drag. As an under 140 pound rider, I use 28mm tubeless tires with pressures in the 60's, with 19mm internal width hooked rims. If I try some new wheels, I'd get 23-25mm hookless rims, with 28 or 30mm tubeless tires. Only a few brands offer 30mm. 28 and 32 are more common.

zipp.com has a good pressure calculator. Just be sure that your pressure gauge is accurate. My old silca pump gauge was reading about 8 psi higher than actual.

Sy Reene

Since we're in a rabbit hole, doing differing rim widths can have some implications. If you were of a mind to run eg. 25F/28R tires, having a rear wheel with wider internal rim than the front width would make the inflated tire widths more disparate. So you might end up with the 25mm tire actually at 25mm, and the 28mm with a wider rear rim close to 30mm -- just an example. Another route would be to have a wheelset with the differing rim widths to create effectively wider tires in the rear than in the front, when using the same tire on both. Eg. a wheelset with a 19mm INT front/23mm INT on the rear. Running a 28mm tire on both might yield a 28mm front measured inflated with, but a 30mm inflated width on the rear, but you can use the same tire.

Bob Dopolina 

That's a good point.

If the effective widths vary while using the same sized tires (say 25c/25c), the rider can benefit from the aero/comfort I mentioned while still being able to do the front to rear swap. Win, win.

Bob Dopolina 

We used to offer 38/50mm carbon rim setups a few years ago. The fad came and went.

Bob Dopolina 

Yes, this is still the case. The transition from tire to rim has to be smooth and the shape of the tire (which is affected by the rim width) is what matters. That was kind of my point.

This primarily concerns the front wheel while the rear wheel can be more about comfort. So why not a wheelset where the rims are designed to do exactly this? That was basically my thinking.

woodcraft

An under-noted advantage of tubulars- a smoother transition from tire to rim, at least in smaller sizes.

Symox

I always thought it made more sense for non racers to have a wider tire up front for traction in corners (if you were going to mismatch them).

isn’t this why some mountain bikes have 27.5 in front 29 rear?

PeteHski

The MTB "Mullet" trend is to use a 29 front and 27.5 rear. Idea being that the bigger front wheel rolls over rough stuff better and the smaller rear sharpens the handling.

Symox

ah, thanks for the correction. Love the mullet name 😁

PeteHski

I've noticed that Canyon have recently started fitting different sized front and rear tyres on some of their road bikes e.g. Endurace SLX comes with 30 mm front and 32 mm rear Schwalbe Pro 1 tyres.
But what I find is that it's the front end that tends to feel most harsh on a road bike (with carbon seat post, thin carbon seat-stays etc.) So I just run wider tyres at both ends for added comfort.

I have run 32 front, 30 rear recently, but not deliberately. I had to swap my front tyre out in a hurry after getting a big cut and just left the rear. It rode fine like that, but I wouldn't do it deliberately.

Kapusta

I think you may be mixing up two different things: Wheel diameter vs tire width.

A mullet is a bike with a larger wheel diameter in the front. 29/27.5 is the current thing, but you use to see 27.5/26 and before that 29/26 and before that 26/24 (a DH thing). But Mullets are actually not that common and never really were. A niche thing for the most part. Every few years a new wheel size combo pops up, a few people get exited about it, and then it goes away. 26/24 probably had more success than the rest, but it was never the norm even for DH bikes. Time will tell if the current 29/27.5 flavor sticks around.

I have never seen someone run a smaller wheel in the front of an mtb, The only instance of this that I am aware of was one of Jeff Jones’ bikes that ran a 26" fat tire in front and 29er standard wheel in the back.

Tire width is a different story. Running a wider tire in the front than the rear on mountain bikes is very common and has been for a good two decades. This is regardless of the wheel sizes.

Chandne

I think it makes sense. Comfort is also key if that is a goal. Some bikes are a bit harsh so I'd prefer a cushy rear tire for sure. I do the opposite and due to my frame limitations on tire size. I use a tubeless front (mainly to reduce the likelihood of a a potential instantaneous flat coming down the bigger steeper mountain passes) that measures almost 30 but the rear only fits a true 28 (older BMC) so I run a regular tubed GP4000 that is around 27-28 mm. The 2014 BMC is a relatively comfy and compliant bike for a carbon racy bike so I have not upgraded yet. In mountain biking, I do the same and I run a very slightly wider front tire (sometimes a softer compound too) for traction. With full suspension, comfort isn't as much of an issue there.

N2deep

I run a 26/28 specialized turbos on my Domane and will go 28/30 next tire change but am limited to 30mm max due to the frame. Although the change in width is minimal I believe that it helps with weight distribution as well as ride quality. Wider rims would give a little aero advantage but they are not in the cards for this bike.

PeteHski

How does it affect weight distribution?

Sy Reene

A wider tire distributes its rider's weight across more surface/contact area.

PeteHski

Isn't that just another way of saying that it improves ride quality?

N2deep

Absolutely. Again minute changes. I believe the weight spread is 40/60 so a little wider rear tire should theoretically spread the load over a few more mm’s and provide a little more dampening. It would be interesting to statically measure the weight and distribution on each wheel to see if this makes any real difference or if were just screaming at the dead chickens in the freezer. Have a great day

PeteHski

I totally get the improved ride quality from the higher volume, wider tyre. But the front/rear static weight distribution is not going to be affected at all, if that's what you mean. To affect that distribution you need to change your position on the bike i.e. move your centre of mass forward or backward.