tire wear...ashphalt vs. gravel?
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tire wear...ashphalt vs. gravel?
Post by thumbies on Sept 17, 2008, 3:08pm
I do a lot or road riding to and from the trailhead. You know the old saying that road riding on knobbies wears your tires out really fast.
This makes me wonder what causes more wear: riding on the road (faster) or riding on the gravel shoulder. What do you think?
thanks,
Dave
Re: tire wear...ashphalt vs. gravel?
Post by lexus on Sept 17, 2008, 7:09pm
i don't think you should ride your mountain bike on the road!!
you know they make these things called cars that get you to and from the trails!!
Re: tire wear...ashphalt vs. gravel?
Post by sewerurchin on Sept 17, 2008, 8:33pm
Road causes more wear on knobbies. There's a greater contact area with the road, and more stress applied to the knobs. Also if the tires are made of a sticky compound, they'll stick better to asphalt then gravel.
Re: tire wear...ashphalt vs. gravel?
Post by thumbies on Sept 17, 2008, 10:14pm
Sept 17, 2008, 8:33pm, sewerurchin wrote:
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I think that for a given amount of saddle time, road riding probably wears tires faster (because you go much farther). But why is it that you can go faster and farther on the road than the shoulder? reduced friction maybe?
Since 'weight' is the same, a smaller contact patch on gravel would actually mean a greater force/stress (per unit area of tire-to-ground contact).
hmmm.....
Re: tire wear...ashphalt vs. gravel?
Post by sewerurchin on Sept 18, 2008, 11:15am
Sept 17, 2008, 10:14pm, thumbies wrote:
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The friction caused by the stickiness of the rubber on the road is less then the friction caused by the gravel. The biker is at times peddling into the pebbles, over them, or moving them.
Sept 17, 2008, 10:14pm, thumbies wrote:
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Ignore what I stated in the previous post about contact area. I was thinking of something else.
But how is the force applied to the knobs? It's easier for the knobbies to deform to the contact area of gravel then the road. When pebbles fall between the knobs, stress is distributed both to the tires (non knobby area) and sides of the knobs. The distribution is even better when the tip of the knobs still has contact with the ground. Distribution is again further improved if the rubber is of a "soft" composition as it helps the tire to deform to the shape of the ground and pebbles.
When on the road, the knobs are having to support the whole weight of the rider and bike. The knobs will most likely bend, and bend a lot to match the flat surface of the road. If the rubber is of a soft composition then the bending would be too much. If the rubber is of a sticky composition then it would find the pavement an ideal surface to stick to, thus applying further stress on the knobs as it has to be peeled off the road.
For the road, a hard rubber knobby tire like your Tioga Factory DH would be more suitable then a soft composition tire.
Re: tire wear...ashphalt vs. gravel?
Post by thumbies on Sept 18, 2008, 7:16pm
[quote author=sewerurchin
For the road, a hard rubber knobby tire like your Tioga Factory DH would be more suitable then a soft composition tire.[/quote]
yeah, except for the 200 or so screws in each of them
Re: tire wear...ashphalt vs. gravel?
Post by thumbies on Sept 19, 2008, 2:54pm
this is not scientific...just casual observation but today Stoner and i were riding down a gentle incline, with him on the road (cause you know he's a roadie at heart) and me on the gravel shoulder. We were both riding the similar tires (Nevegals) and we traveled for a surprising distance going exactly the same speed...near the end he began pulling away (but this was expected since he's a little bit heavier).
makes me wonder if the perceived slowness of gravel is due to more difficulty pedaling (less traction). I've noticed this before, where i will be coasting down a gentle hill on the road and then move onto the shoulder and see no reduction in speed...until i have to start pedaling.
what's my point you ask?
I'm not sure, just food for thought.
D.
Re: tire wear...ashphalt vs. gravel?
Post by sewerurchin on Sept 21, 2008, 11:01am
While singlespeeding on a rigid bike, I read on mtbr that wider/fatter tires are faster then skinny tires off-road. I initially thought the only benefit was that they act as a form of suspension . . .
Wider/fatter tires tend to weigh more then skinny tires and tend to have a greater rolling resistance. BUT, when the air pressure is low enough, they tend to deform better to the shape of the off-road ground and roll right over things. As a result, the total friction / resistance is less then a skinny tire. There was actually a formal study on this somewhere, but I can't remember the link. Edit: Not the link I was looking for but here's an interesting link.
http://www.schwalbetires.com/tech_info/rolling_resistance
Many rigid singlespeeders at MTBR reported that fat/wide tires plus low PSI is faster for single speeding off-road then skinny tires. In my experience, this is true especially when using low weight (~600-800g) fatty tires.
However, the benefits may not be there for those on geared front/full suspension bikes. They can use skinny tires at higher PSI, which reduces rolling resistance, and let the bike absorb the bumps.
In the end, there are too many variables to take into account :/.
Re: tire wear...ashphalt vs. gravel?
Post by stoner on Sept 21, 2008, 7:39pm
Yes, I know. You're surprised that I haven't weighed in on this topic yet. I've just been so busy at work.
There are a lot of variables in this problem. I think that you'd be faster on the road because in gravel you sort if sink in and you loose energy as you push the gravel around. It adds an element of damping. That action would be very abrasive to the tire but I don't know if it would be worse that on the road. On the road your toroidal shaped tire deforms into a flat spot. As the tire rotates this flat spot flexes and the knobs would be subjected to a front to back shearing force which would be very abrasive.
A friend of mine read an article where they looked at the rolling resistance of various bike wheels / tire combos. They put a wheel against a large drum and rotated it and measured the drag. The conclusion was that the lowest resistance tire was the one that had a small contact patch - high pressure and small diameter - the BMX tire!
Paul
Re: tire wear...ashphalt vs. gravel?
Post by g on Sept 24, 2008, 10:29am
I can't believe this thread exsists.....
-G
Re: tire wear...ashphalt vs. gravel?
Post by lexus on Sept 24, 2008, 8:14pm
AMEN brother!!