less RR too

 

it's way easier to recover from a rear tire breaking loose and sliding than it is to recover from the front sliding. there's also more force on the front tire in a corner, and a narrower rear tire, as nauc said, reduces rolling resistance.

 

On the most frames there are also problems with tire clearance in the rear (rubbing on the chainstay, especially ladden with mud and dirt).

The most forks allows a wide tire without problems. Also the steering quality is with a wider tire much better (and braking).

 

The big reason is rolling resistance. When pedaling seated most of your weight is on the rear. A slow tire is way more noticeable in the rear.

 

^^^ agree w/ rotating weight savings but after some experiments, I noticed that a smaller size rear tire made the back end "slightly" lower than the front. Hard to believe how a li'l change can affect the handling. Now, I stayed w/ same size tire. I'd rather have the extra traction. The extra weight can make you a stronger rider =)

 

Weight

 

often times it's also because the large tire one can fun up front just won't fit in the back, so you size down the back. for AM, i like the fact that running a bigger front slackens things up a tiny bit.

Plus you tend to hit stuff with more force with the front, since that's the first thing to hit (like say in a rock garden). I guess for tail landings, not so much.

 

I like having a consistant and predictable amount of grip between my tires so I run both the same size. I can't see any actual benefit to a narrower rear tire, there are plenty of claims but I haven't seen any actual empirical reasons to do it.

 

Narrower tires don't reduce rolling resistance, particularly when the tire carries the majority of the weight as the rear tire does.

 

More traction is needed for cornering in the front. Narrower tires are lighter meaning they're easier on the pedaling (and its not really a minor difference, au contraire..). All the other reasons are valid too

 

Narrower tires are lighter meaning they're easier on the pedaling...

That's not an argument for a narrower tire on the rear, it's just an argument for a narrower tire (and a poor one). In order to accelerate a bicycle, both wheels have to be spun up.

Inertia stored in the wheels is of little consequence compared to rolling resistance off road. A fast rolling tire is better than a light one.

 

regardless better to use the same tire in back as front.

 

better why? They do different jobs...

 

I like a less aggressive, smaller, faster rolling tire in the rear because I like the rear to drift while the front keeps good traction. I also like how a smaller rear tire will slightly slacken the head angle. Just my preference. On my 150mm bike I'm running a 2.3 bronson front and 2.2 mutano rear with good results.

 

I always wondered why also in bmx race setups. The larger front smaller rear has been a bmx standard race set up for a long time. Yes a smaller rear reduces some rolling resistance. Heres a few reasons. Smaller tire needs slighter more air to prevent pinch flats. That included with a narrower tread = reduced contact with the ground. Whats faster a beach cruz tire or a roadie tire. On top of that choosing a center tread that typically run tighter also reduces resistance between knobs. Also a 2.1 can be 100-200 grams lighter than a 2.3 or 2.4. thats anywhere from a 1/4 to almost a 1/2 lb or rolling weight. In xc race terms thats significant.

1lb of rolling wieght (rims tubes or tires) is equivalent to 4 lbs of static weight. if you can save 1/2lb on tires thats like shaving 2lbs off your frame respectivly.

On the front, a wider tread leads tracking through turns better because of larger ground contact. Combined with pressure slightly lower, causes even more ground contact. All of which can help resist the front from pushing or plowing through turns. Its a combination that tries to get the best of both worlds, traction and speed. theres a method to the madness.

but i run a small 2.3 in the rear. the newer wtb weirwolf runs about 2.2 on my rims. it also has a nice grouping of treads in the center which rolls pretty decent for 28psi. all in all i put a premium more on traction than pedalablity. i look more forward to turns and agressive play more that pedaling.

 

Here is the simple answer.
The front tire serves a greater need for control.
The tire in the rear serves a greater need for speed.

Better??? That's the personal rider's call to make for themselves on what fits them and their riding style best. All our preferences are different.

 

It's a funny thing on rolling resistance. I run a smaller tyre on the back than the front for the "control vs speed" arguments many have put above; however it's probably psychological in terms of "sizing".

There's research to suggest a larger tyre has less rolling resistance off road. Part of that is the shape of the contact patch (I wasn't convinced).. but I think what I've found running fatter vs thinner tyres is i) that like the old >26" argument, a bigger tyre rolls over bumps better than a smaller tyre and ii) a low pressure again rolls over bumps better than a higher pressure, which deflects; these both counteract and I think outweigh the extra drag created by increased contact patch size, off road.

But other factors affecting rolling resistance are tread pattern - big tyres can have wider spaced bigger knobs which create drag; and additionally in softer ground like mud, where the tyre is sinking in, a wider profile is going to drag more.

And then there's simply the weight of the tyre.. one heavy tyre is better than two heavy tyres if you're pedalling, and that one is going to be on the front. But really, you look at the Minion DHF Exo 2.5, it's not all that heavy, and it rolls over everything.

So all in all, each to their own; there's lots of arguments in both directions and the fact is we all ride different conditions on different bikes, so there's probably not a right answer.

 

Front tire provides 2/3 of the braking power.

 

depending on the dirt/slope i will run the same size and pattern frt and back like a hans dampf and then tweak tire pressures and shock pressures. whatever combo gives me the best grip.