Wednesday, February 08, 2017

Some Thoughts On Tires

What gravel looks like, for reference.
Many of you that have been reading the blog here know that I have been writing reviews on things for a long time for different sites. My very first review for a site was done in 2005 for the long defunct "The Biking Hub" on a set of tires from WTB. Exiwolfs, I believe they were. Since then, I've ridden so many different tires I could not possibly remember them all.

That is to say, I've ridden my fair share of tires, and there are a few things that make a tire "good" in general. You can guess the first thing- weight. No one wants to spin up a big, heavy tire, especially up a long grade. The other thing that is apparent to many riders is the way the tire's casing "works". In other words, is the tire supple, or does it ride like a solid rubber chunk of crap? (This affects more than just ride feel, by the way.) Then there are the finer things, like traction, cornering, and braking performance. Basic stuff that if it is good, makes or breaks a tire's reputation.

That seems simple enough, right? Get those three basic areas "right" and you can't lose. However; it isn't all that simple. Obviously. That's why we have a gazillion tire choices. If "one" thing worked for road, and another for "gravel", and another "one" thing for mountain biking, well, there would only be three tread patterns. That's laughable to think about, in light of reality, because we have a confusing array of tires for every different situation. Too many choices. Somewhere between "three" choices and a "gazillion" is where the truth lays.

There are a few things people get wrong when it comes to bicycle tires, and the most egregious thing, in my opinion, is when people try to tie the attributes of motorized vehicle tires to bicycle tires. While there are a few obvious parallels, the comparisons are like comparing a deep sea fishing rod to a Tenkara rod. Similar in some ways, yes, but the design intentions and performance parameters are so different that the only remaining similarities are in basic form and name.

They say you don't need tread on a gravel road going tire? Hmm.....
So, I'm not one to say that some form of tire usage outside of the cycling world is a parallel to what works on bicycles. It isn't a good analogy and what does actually work is more specific and specialized to cycling than what you'd find outside of this sport. To that end, I've discovered some traits of tires that seem to lend a helping hand to riders on dirt and gravel over the years. Some things are obvious, some not so much.

In the gravel going arena, I find that a tire totally devoid of tread isn't the very best idea, and neither is one that has all sorts of tread on the casing. Just like with the tread design choices, there is a middle ground somewhere that actually works well. However; it is something else that also needs to be there, which if not included, will make or break a tire's performance on gravel roads. That is the casing's shape, or the way the casing and the tread form a shape which hits the road.

In all of my gravel miles, the tires that perform best seem to all have a shape which isn't really "round" in cross section. Something "less C shaped" and more squared off or flattish seems to really tame loose stuff. You can get there several ways. Sometimes air pressure and rim width can do this. Sometimes tire design gets you this trait, and many times a clever use of smooth and treaded design in the right spots gets you there. Many times bits of all of the above come together to get a tire which rides wonderfully on gravel.

The thing is, a "standard", roundish shape tends to plow, like the bow of a boat, through looser gravel. This is most evident when tire pressures are too high. The resulting ride is not unlike a skinny tire on gravel. There is a lot of vibration, lateral movement, and the rider has to correct the front end much more than one should. I call it "herding" the bike instead of riding it. A tire with a flatter profile, maybe with lateral tread blocks on the sides, gives the tire an ability to float over gravel, and the flatter profile also cuts way down on the "bow effect". There is a lot less "herding" the bike and far more riding it.

So, maybe you have a different idea? Fine. That's why they make a gazillion different tire choices.

9 comments:

Ari said...

I think we can make a top ten list to give riders an idea.

Adam said...

I can't help but feel like this is a not-so-subtle jab at Jan's post from last week: https://janheine.wordpress.com/2017/01/30/why-we-dont-make-gravel-tires/

If it is, I agree with you.

I've been surprised at how good the smooth, knobless Compass tires are in some off-road situations (particularly slightly damp and sticky "hero dirt"); they've made me reconsider a lot about what I thought I knew about tires. But there are also a lot of situations in which they're pretty bad - particularly, they're terrible on "loose over hard" type surfaces, like the dry and dusty fire roads we have out here in California. The Compass tires have no cornering grip on surfaces like this, which is terrifying when you come up on a turn in the middle of a steep descent. Not a problem I've had with knobbier tires like the Nano 40C or Bruce Gordon.

Scott said...

@Adam. This post made me think of Compass as well. Those 650b Extralight Switchback Hills sound too good to be true. Here in Oklahoma the gravel roads are so squared off you never have to worry about cornering but I still have concerns about how these treadless tires will perform in a straight line on loose over hard surfaces. I've never ridden Iowa gravel but I think tend to defer to GT over Jan when it comes to midwest gravel riding.

Scott said...

GT. This may or may not be worthy of a future post but I am curious about the following...Given your fairly strong preference for steel over carbon forks for gravel riding, I was wondering if your experience on the plus size WTB Horizons gave you any reason to reconsider your position on carbon forks as a result of running such a large tire at low pressures. In other words, any chance the softer ride of the fatter tires can offset some or all of the stiffness of a carbon fork? I feel like this might be of interest to your readers given that your Tamland now comes with a carbon fork in 2017. Thanks!

Guitar Ted said...

@Scott- The big, puffy 650B tires do a great job of smoothing out the road, but I would still prefer a fork that damped out vibrations vs one that did not. Even tires at low pressures are only going to be able to do so much. A fork that works along with that tire is always going to be a better ride than a fork that is super-stiff and unforgiving with a big, cushy tire.

Could that fork be made from carbon fiber? Sure it could be. The thing is, due to racer preferences, forks are what they are today. Stiff, efficient holders for wheels. The molds to make forks in that vein with their short-ish offsets are expensive. Cyclo Cross also has greatly influenced what we have now for carbon fork choices. I believe that if the gravel/all-road genre takes root and sustains sales numbers, or grows, there will be gravel/all road specific carbon forks that will have compliance and greater offset choices.

It took almost six years for the industry to decide that 29"ers deserved "real" suspension forks and another two to three years after that to get better forks that had geometry specific for 29"ers. So, don't be all that surprised if it takes a bit to see forks for gravel/all road bikes in carbon fiber to take a while to make it to market as well.

R said...

i think i've said it here before - but i 100% agree with your take on a flattish topped tire for the best stability on iowa gravel. your term 'herding' is what i might also describe as 'sledding'... the front end is much more volatile with a rounded tire, and extra effort to take weight off the front wheel (which we should probably be doing in the loose stuff anyway) is more urgently needed with that "c" shaped tire... that's been my experience... your mileage may vary.
-r-

Jason said...

Perhaps you want to stay away from "endorsing" particular tires, but could you give examples of tires that are flatter and less "c" shaped? Maybe you have a future post planned to highlight some of these differences.

Guitar Ted said...

@Jason. Probably the best example of tread blocks working to make this sort of profile happen is the Challenge Tires Gravel Grinder model. There are others similar to that idea- Terrene Elwood, the WTB Riddler, and one of the Arisun Gravel Plus models come to mind.

Then you can use a wider rim to make tires like the Panaracer Gravel King SK 40mm and Clement MSO 36mm tires work that way.

Essentially, as my friend MG says, wider is better and a good internal width on the rim doesn't hurt either. Casing design and tread design can work in tandem to get you this feature. Designs tend to be supporting this idea of late as well, so apparently MG and I are not the only ones thinking this way.

MG said...

Amen, Brother...