jwiner
I'm a mountain biker at heart, and have wondered why the mountain bike model of different tires and widths for front and rear tires hasn't really been adopted with GG. What are your thoughts?

I run WTB Nano 40's today and love them.

I'm eyeing the Panaracer Gravel King SK's and think 35's are what I need (they commonly measure 38), but why not 40 in the front (they commonly measure 43)???

Review of both widths:
http://www.gravelcyclist.com/bicycle-tech/review-panaracer-gravelking-sk-35mm-and-40mm-tires/#comment-2106
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shiggy
jwiner wrote:
I'm a mountain biker at heart, and have wondered why the mountain bike model of different tires and widths for front and rear tires hasn't really been adopted with GG. What are your thoughts?

I run WTB Nano 40's today and love them.

I'm eyeing the Panaracer Gravel King SK's and think 35's are what I need (they commonly measure 38), but why not 40 in the front (they commonly measure 43)???

Review of both widths:
http://www.gravelcyclist.com/bicycle-tech/review-panaracer-gravelking-sk-35mm-and-40mm-tires/#comment-2106

The only reason to run a narrower tire in the rear is your frame does not have enough clearance, which is also the original reason we did it on mtbs (mostly).

With good tires there is little difference in rolling resistance, and the comfort and control of wider tires is a plus.
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benmills
I actually run wider tires on the back for comfort.  It seems like there are more jarring impacts in the back.  I run a 32mm up front and a 40mm in the back (Vittoria Voyager Hypers).

Out if interest, why would you want a bigger tire up front?  More grip?  Or more comfort for your hands?
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barturtle
Since it's now basically accepted that wider tyres have lower rolling resistance than narrower tyres (all else being equal), the few remaining reasons for running narrower tyres are mostly limited to: frame fit, weight, and aerodynamics.

Mixing tread patterns could make sense in some scenarios, mostly as I would see it where you would like to run a speedier tread pattern, but you need a grippier tread to keep the front from washing out, so more aggressive tyre up front and speedier on the rear.
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Osco
Yeah these bikes benefit from wider and the widest Is not very wide compared to a true mountain bike tire.
If wider for traction was my focus I'd wan't wide as reasonable at both ends. I'd also doubt that I could fee a performance advantage with narrower on the rear.
I figure we mostly go for wide on these bikes for float In the soft stuff and comfort on these rigid bikes so, again why give up any of this with a narrower tire out back.

I'm running 2.35" on both ends of my 27.5 wheeled Mtb and when the back quits working I'll go to a 2.25" because I can drop a few hundred grams on the out side of the wheel were It counts the most.
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bobknh
My $.02: Like other discussions of bike tech details, like the discussion about frame material, you can't really isolate one feature such as tire width, without also looking at the the tire, wheel, and bike as complex system. Bike tire manufacturers spend big bucks researching materials and tire design to come up with competitive products for specific uses and customers. Tire width, is only one factor to consider. Also, since tire width is at best approximate and varies with pressure, IMHO this is something to worry about only if you have fit concerns. In short, I doubt if varying the tire width front to back will make any difference in tire selection. We are very fortunate that the manufactures are now producing a whole slew of great products, at very reasonable prices. So far, in my limited experience, every GG specific tire I've tried has worked well - some better than others - but no real clinkers. I've been more or less going by the tests done by Gravel Cyclist, and haven't been disappointed.
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Flydyl
Also to consider: a larger front tire ever so slightly shifts your weight back, your head up, etc.  I like this posture (a tad more like mountain biking) because I ride a lot of single-track on my GG.  
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shiggy
Flydyl wrote:
Also to consider: a larger front tire ever so slightly shifts your weight back, your head up, etc.  I like this posture (a tad more like mountain biking) because I ride a lot of single-track on my GG.  

A 5mm headset spacer would do more than a slight tire size difference.

When needed, I just slide my butt back a bit. Weight distribution should not be static.
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imajez

benmills wrote:
Out if interest, why would you want a bigger tire up front?  More grip?  Or more comfort for your hands?
More grip would be my reason. Front wheel losing grip tends to a lot more disastrous than if the back slides out.

Another thing would be that a bigger tyre up front, if taller than rear one it will slacken angles slightly, which may be a benefit to riding in rougher more downward terrain.

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piggybladder
shiggy wrote:
A 5mm headset spacer would do more than a slight tire size difference. When needed, I just slide my butt back a bit. Weight distribution should not be static.


Yes - but only if you have an extra 5mm of steerer tube to use!

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piggybladder
barturtle wrote:
Since it's now basically accepted that wider tyres have lower rolling resistance than narrower tyres (all else being equal), the few remaining reasons for running narrower tyres are mostly limited to: frame fit, weight, and aerodynamics.

Mixing tread patterns could make sense in some scenarios, mostly as I would see it where you would like to run a speedier tread pattern, but you need a grippier tread to keep the front from washing out, so more aggressive tyre up front and speedier on the rear.


That's it in a nutshell - big grip on the front with a knobblier tyre, speed (and a not insignificant weight loss) on the rear with a smaller semi-slick. It slackens the headset angle a tiny bit which make for less effort on the flat and downhill but is slightly disavantageous on the up (you want to get lower on the front again). I've run this way for donkey's years. It feels faster.

I'm still unclear tho whether it's the rolling resistance, wind resistance/drag, or contact patch which makes a smaller rear feel faster. After all if it was only about rollling resistance we would see road racers riding 2.4" tyres would we not?  
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Barrettscv
I'm using a 700x40 Clement MSO on the front and a 700x35 Clement USH on the back. It's a practical decision, since the front accepts a 700x42 but the rear won't accept any 700x40 and most 700x38s are unacceptably tight.

The combination does have its advantages. The front of the bike is very stable and I can brake hard on loose gravel, even while descending. The road-friendly 700x35 rolls very well on pavement and the tire helps maintain speed on the flatter sections.

The primary disadvantage is climbing traction is marginally insufficient on very steep and loose conditions. I can climb almost anything, but I need to stay seated.
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barturtle
piggybladder wrote:


That's it in a nutshell - big grip on the front with a knobblier tyre, speed (and a not insignificant weight loss) on the rear with a smaller semi-slick. It slackens the headset angle a tiny bit which make for less effort on the flat and downhill but is slightly disavantageous on the up (you want to get lower on the front again). I've run this way for donkey's years. It feels faster.

I'm still unclear tho whether it's the rolling resistance, wind resistance/drag, or contact patch which makes a smaller rear feel faster. After all if it was only about rollling resistance we would see road racers riding 2.4" tyres would we not?  


Up to a certain speed, rolling resistance is a bigger factor than air resistance, past that air resistance takes over and becomes huge as speed increases.

As far as things "feeling faster", feelings are mislead easily. A narrower tyre at a higher pressure will certainly transmit more feels into your saddle and bars, making things "feel faster". I could certainly roll some 90psi 28mm tyres down a chunky gravel path, and it would "feel fast" at pretty much any speed, while a 30psi 2.2" down the same path would feel much more calm and relaxed at double the speed I was riding on the 28s.

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RoverAl
I'm going slightly against the grain here. Schwalbe g-ones in 35 tubeless were my all around tire until the rear started wearing and I started getting puntures. So I picked up a pair of Clemment 36 mso's and put one on the rear and left the front Schwalbe 35 G-one on. Mainly because I really like the G-ones but also because I was a little lazy. 
Now my set up is a grippier semi knob tire in back with a smoother slightly narrower  tread gravel tire in front. 

I have about 200 miles like this and I am pleased with the ride, I have better grip and flat protection in back and a smoother tire in front. Handling is better over loose rough stuff at lower psi because of the MSO and the front is about the same. Now I don't ride 100% gravel or dirt so when I hit the pavement it's fast enough for now. When my course changes or I feel like switching just to see any difference, I will throw the other MSO 36 on front but for now I am good.


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chas

On a road bike, I put a larger tire in the rear (say 25mm front, 28mm rear). This is bvecause the rear carries more load, does not have as high cornering forces, and mostly becasue I want a softer ride under my butt.

On a gravel bike, I put a larger (and more aggressive) tire on the front because
- I'm not so concerned about high speed aerodynamics
- On really tough trails/roads, the front is going to loose traction first with tires around 35-40mm.
- I want more shock absorption in the front for the rougher stuff.
- I don't want tread or carcas distorition from high torque in the rear tire - on the front tire, distoriton only matters for braking and cornering.


Really, on dirt, it is mostly about traction in the front tire.

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chas
barturtle wrote:


Up to a certain speed, rolling resistance is a bigger factor than air resistance, past that air resistance takes over and becomes huge as speed increases.



It starts around 15mph, but air really takes over about 20mph.  It goes up exponentially.  

Below 15mph, aerodynamics doesn't do much of anything. That is why I encourage my wife to use large tires.
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RoverAl
@chas #15 That makes sense to me and probably why I like it since I don't really ride any real gravel for long distances. I will try throwing a 42c upfront sometime to see what thats like on my next dirt adventure.
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