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http://www.sheldonbrown.com/tires.html#mixing

Bikes that are used some of the time on loose surfaces often benefit from a wider front tire, with a fairly agressive tread, coupled with a somewhat narrower, smoother rear tire.

The wide, knobby front tire will provide the all-important front wheel traction. If your front tire skids, it almost always leads to a crash. For riding in soft conditions, such as sand or mud, a wide front tire is essential. If the front tire sinks in and gets bogged down, you're stuck. If the front tire rolls through a soft patch OK, you can generally power the rear through to follow it.


The narrower, smoother rear tire will have lower rolling resistance. Since most of the weight is carried by the rear tire, rolling resistance is more important on the rear than the front. If the rear tire slips, in most cases the worst that will happen is that you'll have to get off and walk.

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What is the speed and energy penalty of a tire 25 mm at 120 PSI vs high quality 35 mm tire at 85 PSI on a typical American 100 mile road tour?

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I will agree with that. Hitting a step in pavement or a pot hole (at 30 MPH or more) is life threatening with the Madone and 23 / 25 mm 120 PSI tires.
Not so with the CX bike.
Therefore one can use that controlability to use aerobars in lesser quality road conditions. An important advantage for CX bikes I think.
BTW, the aerobars give me at least 5% energy savings vs hands on hoods.

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The difference to hands on drops is less and requires more study.
My problem is that I can do aerobars forever but not drops.

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I do not have "a power tap". Therefore my statement regarding energy savings is conjecture based on my ability to go faster with my typical HR 130.
My statement regarding aerobars is simple. I go on flat ground and keep HR constant and go from hoods to aerobars. Look at the speed. It is about 5% faster (minimum).

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http://www.crazyguyonabike.com/revie...ested=1#162308

I have about 600 k on one Dureme tire and based on that limited experience I give the tire a 5 star rating. I obviously can't speak much to tread wear and overall longevity. I will rate several characteristics that are important to me and will try to answer any question folks might have. It goes without saying on CGOAB that others should add their comments and experiences. The Dureme certainly seems to be a likely tire consideration for many of the CGOAB riders judging from past reviews and forums about tires.
Size: It is sold as 700-40 (622-42) and it calipers out on my Mavic A319 rims at 40.5 mm. I don't know why, but it is the old French system, which is still the manufacturers' standard. 5 stars
Rolling resistance: I only have my subjective road experience to qualify (not quantify) this aspect. Comparing it to my two other wide tires the Schwalbe Extreme (40 mm) and the Continental Travel Contact (37 mm) it rolls easily. 5 stars


Tracking and cornering: I put it through some down hill corners at speed with the Dureme on the front and the Travel Contact on the rear. There was a huge different in the tracking angles with the TC trailing off at a disconcerting angle. Exchanging the Travel Contact with the Extreme on the rear the tracking difference was much less and quite acceptable. With the Dureme on the rear and a Panaracer Ribmo 32 semi-slick (an excellent cornering tire) on the front the balance between front and rear tires were good. 5 stars


Rough roads: The Dureme has that big balloon tire feel. Small and medium size potholes and cracks in the pavement give me little notice or concern. My plan is to use the Dureme as the rear tire on rough pavement and on narrow roads with soft shoulders where I may have to dive off the road for safety reasons and need predictable flotation. 5 stars


Off paved road: I was sure this would be the Dureme's weakest suit. In these conditions it will be the front tire with the Extreme on the rear. With this set up I rode an uphill gravel and dirt road in Portland, after several days of heavy rain. I could not ask for better response. Then I rode off the trail into deep oozing mud and clay mixed with ivy vines and small tree branches and roots. Up hill the Dureme tracked with assurance as it sunk into the mud and rose up over the vines and sticks. The Extreme was slipping and barely pushing the bike forward, but I never lost steering. (As a side note, for a multipurpose dirt tire the Extreme did quite well in the mud.) Both tires cleared the mud out of their treads quickly. Going back down the same trail the Dureme did great on the dirt and gravel. On the mud it was dicey and at one point it slipped out from under me with mud over the rims. That is a compromise I am willing to make for not having to carry two Extremes on tour. 4 stars


Puncture resistance and over all damage resistance: Unknown but probably very good. The core of the tire appears to be identical to the Extreme. I've not had a puncture on either the Dureme or Extreme.
Purchased from Wallingford Bicycle Parts for $66.00.


In summary I was looking for a do all tire, a folding spare for the open road, a balloon tire for back road comfort and safety, and sturdy front dirt tire for US Forest Service type roads. And all that plus being relatively light weight. It seems to do it all.

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http://www.crazyguyonabike.com/revie...age=1&nested=0

Schwalbe Marathon Extreme - 4 stars ****After putting approximately 1,000 kilometers on the SME during my most recent tour I feel I can make a few comments on their characteristics. I hadn't intended to put that much distance on them but a tire failure of my rear road tire made it necessary. I give them four stars and that rating is based on how closely they meet the advertised characteristics and how they filled my personal riding needs. I was torn between giving them four stars and three stars, but was hoping for five stars when the package arrived at my home. They earned the forth star by being the only tire on the market that met all my basic criteria. Relatively light weight, durable, folding, good off-road capabilities, the largest size my bike can handle, and at least fair performance on paved roads were the must haves.


Size accuracy - **
Despite the universal acceptance of ETRTO/ISO tire sizing I think most riders know actual size of a tire is still a guessing game. According to ISO standards a bike tire can be +/- 3 mm and still be within acceptable size limits. Nonetheless the Extreme is the flagship world touring tire of the premiere bicycle tire manufacturer in the world. The most advanced and stable materials are advertised. For a $78.00 tire I didn't expect a tire 2 mm under the stated size. It measured 40 mm wide and 39 mm high.


Tracking - ****
On both the front and rear the tires tracked well. They are not as crisp as a quality road racing tire or even a good road touring tire, but they track straight with little wandering. On rare occasions the rear tire would catch an uneven break in the road and take an unexpected short hop to one side or the other before coming back into line.
On dirt and very rough pavement they tracked very well.


Cornering - ***
The round profile and even tread pattern give the Extreme much better than expected cornering characteristics, but they are not high performance road tires. On two occasions, the rear tire broke loose while braking on a down hill corner.


Rolling resistance - ***
They are big tires with an aggressive dirt tread. I could feel the increase resistance and see it in my daily distance and max speed. I was surprised when I did a down hill coasting test, the Extreme had less resistance than the 37-622 Continental Travel Contact. The TC is actually 34 mm wide and has a smooth center section. I repeated the test three times to make sure.


Road noise - *
They are really loud on paved roads. I was past by thirty two wheel Canadian B-trains that made less tire noise. At fifty kph they literally scream. On dirt this is not a problem.

Mud - ****
They handle mud well and clear out quickly.


Tire wear - ****
I measured the wear when I got home and they lost about 20% of the center tread depth. Most of the time was on paved roads and that would equate to about 5,000 kilometers of road life. That seem pretty good to me for a knobby tire. I am sure on dirt the center tread would wear more slowly.


Flats - *****
Not even a sign of a glass nick or a cut. They seem to be about as bullet proof as you can get.

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On the road they do hum quite nicely. Personally I find over about 20mph the wind noise in my ears drowns the tyre noise but it can be fun to turn my head slightly just to hear the drone. I've taken them over 30mph a few times and wouldn't say they scream at all, the noise is louder but then so is the wind noise.

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Thank you - I was just wondering about this. I'm incredibly un-noticing of anything except road/trail and traffic when I ride. I had no idea that my Muds made road noise until someone else pointed out that on the gravel we were riding my bike sounded like a Panzer column. I don't even notice canti squeal until I start to think about tuning my brakes. I'll listen for noise on my ride tonight.

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You're on an MTB - how do you find the suspension effect of the tyres? Do you share my impression that you get a bit more of it than you'd expect from a 40mm? Although I suppose this might be hard to judge if you have a suspension fork, which you probably do.

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and if you're turning 500g it takes much less effort than turning 1000g. If the same force means more acceleration then it follows I'd go faster with the same force.

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The Extreme is on the back so no suspension there for me. I've only ever used a Plus and an Extreme on the back and the Plus was before I felt confident to do much that banged the back around too much. Even now I'm not into what you might call hardcore MTB stuff - most of my riding is on roads and trails with occasional jaunts through mud and stones and stuff. The Extreme does feel like it cushions in a way the Plus didn't but I couldn't say how much of that is due to the fact it doesn't have a half inch of plastic lining all around it. Most of the time I keep them about 60psi for reduced rolling resistance, I'd imagine (but can't say for sure) that a slightly reduced pressure would give them a lot more suspension than the Plus tyres had, again because of the lack of plastic lining.

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Actually, the best pressure for low RR depends on the surface - higher on smooth tarmac, lower on rough stuff. This is because high reduces hystereis energy (the energy needed to bed the tyre carcass) but low reduces losses to vertical travel of the bike and rider (i.e. energy lost lifting the bike over small bumps.) Schwalbe have some papers on this on their site.

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Btw - what do you have on your front wheel? You might want to put an Extreme there if you have a slick there at the moment: most of the grip for braking and turning comes from the there.

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Using F=ma was to figure that if m is cut in half then the same F would result in double the a. Ironically it was thinking terms of F=ma that left me surprised at the claim that a loss in m of well under 1% would actually make any appreciable difference (and a difference the other way when I figured that losing the near-bombproof puncture protection meant I wanted to carry a spare tube and a pump).

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A significant part of the riding I do is on hard and fairly smooth surfaces - I often think it's worth pumping the tyres for the sections of road to get me to a trailhead, then softening them for the trail and pumping them again for the ride home.

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At the moment the Marathon Plus I had put on when the bike was new. It's got a slick zigzag down the middle with nobbly bits at the side. The idea is that it offers little rolling resistance on tarmac and on softer surfaces as the zigzag sinks in the nobbly bits offer some traction. I've never really been aware of issues at the front, the main issue I've had was spinning the rear wheel. That could be down to a suboptimal tyre or lack of skill on my part - I'd willingly accept either being the cause.

When the Plus goes to meet its maker I'll most likely look at a Dureme or another Extreme. I've been happy with the Extreme on the back and read a few things about a Dureme at the front and Extreme at the back being a good combination. But then I read a few things about how important rotational mass was, so I'll need to fine tune my "believing stuff on the internet" filters :)

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