robertj298 

I've read 2 different theories on the subject. Lets say I want to run 1 28mm tire and 1 25mm tire. Which should
go on the front and which should go on the back to get the smoothest ride?

oneclick 

Big rear; most people have one.

cbrstar

In BMX we used to do the opposite big in the front and small in the rear. The bigger tire in the front gave you more control and softer landings. With a road bike I can see having the bigger in the rear where all the weight is but some frames I hear won't fit a 28.

dddd

OP mentioned comfort as a priority, so a bigger tire can be run safely at a much lower pressure to give a softer ride.

But the pressure aspect is more important here than one might imagine, since a bigger tire actually presents a harder surface to the road unless the pressure is reduced. That's right, as the tire width increases, the tension in the casing fibers increases, making it less resilient. So the pressure first needs to be dropped proportional to the size increase just to equal the resilience of the smaller tire, with the pressure then dropped yet further to make the bigger tire more resilient than the smaller one!

Because of the bigger tire's larger width AND larger height, the pressure can fortunately be dropped quite a bit without losing any pinch-flat protection compared to the smaller tire, making wider tires better for dealing with rougher surfaces.

The choice of increasing the front or rear tire size comes down to which end of the bike is giving the particular rider discomfort.

A further advantage of using bigger tires at much lower pressure is that the tread lasts longer, not to mention improved traction when traversing perhaps-hidden bits of gravel.
There will definitely be some increase in smooth-road rolling resistance, but which tends to pay back in both efficiency and comfort as the road surface becomes rougher.

canklecat

I've ridden mixed widths on a couple of bikes. No problems.

On my Centurion Ironman**, Ultra Sport II, 700x25 rear, 700x23 front. Made for a softer ride but retained better handling. Some 700x25 tires felt a bit splashy on fast curves when mounted on that skinny front rim, 622x13 or x14. Too much tire overhanging the rim, made for imprecise handling on fast curves on rippled pavement. My favorite 6 mile time trial route has some sketchy parts like that.

My early '90s Univega Via Carisma came with new low end but usable generic hybrid tires, 700x38 rear, 700x35 front. I never noticed the mismatch until I upgraded to Continental Speed Rides.

**(I no longer use that bike for faster rides, PRs and KOM attempts. Now it's mostly on the indoor trainer, or for leisurely outdoor rides since it's very comfy. At the time it was my only bike. Now I have a couple of lighter carbon fiber bikes for go-fast rides. Nowadays the Ironman mostly wears either 700x25 Conti GP Classic skinwalls or Some Supple Vitesse skinwalls, currently 700x23 but I plan to try 700x25 or even x28 next. The Soma 700x23 tires are a perfect match for the Mavic CXP30 sorta-aero rims I ride outdoors. But on the indoor trainer I use Conti Ultra Sport II on some functional rims that won't stay true -- good enough for the trainer, tho.)

bwilli88 

I typically have used a larger tire up front, It has worked for me but I tend to like wider tires over all.

mpetry912 

think about weight distribution; especially on larger frames, the weight bias is to the rear.

The larger tire should go on the rear. Sometimes MTB use a larger tire on the front for better flotation

but on road bikes, it's the rear. 32 / 28 is a sweet combo that I use on several bikes.

Mark Petry
Bainbridge Island, WA USA

cannonride15

I find greater comfort with lower pressured tire on front, easily 5psi lower for same size tires. Likewise if I had to go mismatched sizes I would put larger on front. Better yet put the 28 on the back and get a 32 for the front. Now you're getting comfort! Both tires must be of similar construction (suppleness) or course. Try it both ways and report back!

randyjawa 

Since most weight is carried by the rear wheel, I used to go with 25 on the back and 23 on the front. These days, if they will fit, I go with 28s back and front. That is my present comfort factor set-up.

I learned in Jamaica to fit the biggest volume tire that I could. Thanks to 700c tire unavailability in rural Jamaica, I was forced to install a set of 32s on my Bianchi (just barely cleared the chain stays). A touch harder to make it go but the comfort factor went way up. These days, bigger is better in my world.

ctak

20 yrs ago it wasn't uncommon to see 28r/25f at Flanders and Paris-Roubaix

easyupbug 

After years of experimentation, this is exactly my position. I can even tolerate Gatorskins when in AZ.

John E

I normally run equal-sized tires, with about 5psi lower pressure in front, but the big exception is my Peugeot UO-8, on which I have 27 x 1-1/4" (32mm) in back and 700C x 28 in front. When I use the panniers for grocery hauling, etc., I put a lot of weight on the rear tire.

I switched to a smaller diameter 700C x 28 up front to decrease toe-to-tire overlap, caused by the reduced rake of my aftermarket fork. This is also why I run 165mm cranks on this particular bike.

Bad Lag

I have been running 28 rear and 25 front for four decades.

PoorInRichfield

I wonder if there's any aero-advantage to running a narrower front tire than back tire? I'm assuming the width of the back tire is negligible from an aero perspective since the frame, rider, and front wheel have already disturbed the air before it gets to the back tire. Seems like a good topic for a GCN video!