Tyre wear - mileages

For discussions about bikes and equipment.
User avatar
Mick F
Spambuster
Posts: 46797
Joined: 7 Jan 2007, 11:24am
Location: Tamar Valley, Cornwall

Tyre wear - mileages

Postby Mick F » 9 Nov 2019, 12:49pm

I've just replaced the rear tyre on Moulton (again).

Mileage out of the rears is about 1,600miles. Could get more, but the tread goes and the rubber gets very thin, and once I was down to the canvass in a couple of places.

Mileage from Mercian for rear tyres is about 5,000miles.

Considering that Moulton's rolling diameter is 18.2" and Mercian's is 26.5" it means (by using Pi) that Moulton's circumference is 57" and Mercian's 83"
Works out as about (round numbers) 1.5 times bigger.

1.5 times bigger in circumference.
1.5 x 1,600miles = 2,400miles

Why do I get three times the Moulton mileage out of Mercian?
Is there something going on that tyre wear on smaller wheels isn't proportional to circumference?

Am I getting confused here?
Is my point pointless? :wink:
Mick F. Cornwall

Brucey
Posts: 35936
Joined: 4 Jan 2012, 6:25pm

Re: Tyre wear - mileages

Postby Brucey » 9 Nov 2019, 12:59pm

that is quite a big difference. I'd say there is probably something going on there, either to do with the wheel size/tyres or the way the bike is used.

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

User avatar
Mick F
Spambuster
Posts: 46797
Joined: 7 Jan 2007, 11:24am
Location: Tamar Valley, Cornwall

Re: Tyre wear - mileages

Postby Mick F » 9 Nov 2019, 2:18pm

I could have said that, before I even posted! :wink:
"Something going on" ............. what is it?

Continental Sports Contact 406-28 vs Vittoria Rubino Pro 622-23
Mick F. Cornwall

User avatar
Chris Jeggo
Posts: 150
Joined: 3 Jul 2010, 9:44am
Location: Woking

Re: Tyre wear - mileages

Postby Chris Jeggo » 9 Nov 2019, 2:22pm

One cause of tyre wear is rubbing contact between tyre and road, because arc length and chord length between two points on the circumference are not the same. If the two tyres (Moulton and Mercian) are the same width and running at the same pressure then the lengths of the footprints will be roughly the same, so the arc subtended by the contact patch will be larger for Moulton than for Mercian. The difference between arc length and chord length goes as the cube of the angle (for small angles). This is all a simplification, but I suspect that it is an important part of the explanation for your observations.

User avatar
fausto99
Posts: 426
Joined: 19 Sep 2011, 10:06am

Re: Tyre wear - mileages

Postby fausto99 » 9 Nov 2019, 3:38pm

Chris Jeggo wrote:One cause of tyre wear is rubbing contact between tyre and road, because arc length and chord length between two points on the circumference are not the same.

Can you expand on this a bit? How do you define rubbing contact? How does the difference in arc to chord length affect the rubbing contact?

Jamesh
Posts: 681
Joined: 2 Jan 2017, 5:56pm

Re: Tyre wear - mileages

Postby Jamesh » 9 Nov 2019, 4:40pm

Could it be that the smaller diameter wheel scrubs more as it had less inertia?

Rather like a hgv wheel scrubs when turning?

Cheers James

reohn2
Posts: 36363
Joined: 26 Jun 2009, 8:21pm

Re: Tyre wear - mileages

Postby reohn2 » 9 Nov 2019, 4:44pm

fausto99 wrote:
Chris Jeggo wrote:One cause of tyre wear is rubbing contact between tyre and road, because arc length and chord length between two points on the circumference are not the same.

Can you expand on this a bit? How do you define rubbing contact? How does the difference in arc to chord length affect the rubbing contact?

There's more tyre on the road at any given time on a smaller wheel,on the drive wheel that means the same friction over a great arc of the smaller tyre.
-----------------------------------------------------------
I cycle therefore I am.

User avatar
Chris Jeggo
Posts: 150
Joined: 3 Jul 2010, 9:44am
Location: Woking

Re: Tyre wear - mileages

Postby Chris Jeggo » 9 Nov 2019, 4:46pm

fausto99 wrote:
Chris Jeggo wrote:One cause of tyre wear is rubbing contact between tyre and road, because arc length and chord length between two points on the circumference are not the same.

Can you expand on this a bit? How do you define rubbing contact? How does the difference in arc to chord length affect the rubbing contact?

Try this explanation. The roll-out method of cycle computer calibration consists of marking a point on the tread of the relevant tyre, marking where it touches the road surface, rolling the bike forward one revolution, marking where it next touches the road, and measuring the separation of the two marks. If you do this with the bike loaded and unloaded you get two different results, because of the flattening of the tyre at the bottom. (So for best calibration you should be sitting on the bike.) Now think about a small patch of the tyre as the wheel rolls along. While the patch is out of contact with the road it is always the same length (measured along the circumference), but as it goes through the flat contact area it has to shorten and then lengthen again, which must cause some rubbing. I would not care to estimate how far a given point on a tyre rubs along the road surface, because we are in the real world, with doughnut-shaped tyres with complex elastic properties, not in a 2-D geometric world with perfect circles and straight lines, but there has to be a close relationship.

mig
Posts: 2062
Joined: 19 Oct 2011, 9:39pm

Re: Tyre wear - mileages

Postby mig » 9 Nov 2019, 4:49pm

you're smoother on the mercian.

User avatar
Tigerbiten
Posts: 1923
Joined: 29 Jun 2009, 6:49am

Re: Tyre wear - mileages

Postby Tigerbiten » 9 Nov 2019, 6:13pm

What kills a tyre is the amount of slippage against the road.
The lower gears on the Brompton encourage this type micro/macro slippage going uphill.
As you live where it's hilly, the rear tyre suffers.
The rear wheel on my bent trike also suffers from this type of wear due to the lack of weight on it.
I've worn a new tyre out in under 1,000 mile due to a lot of hill climbing on damp roads.
This is the reason I use a Big Apple tyre on my bent trike, it has more rubber to wear off before reaching the carcass.

Luck ...... :D

User avatar
Mick F
Spambuster
Posts: 46797
Joined: 7 Jan 2007, 11:24am
Location: Tamar Valley, Cornwall

Re: Tyre wear - mileages

Postby Mick F » 9 Nov 2019, 8:07pm

mig wrote:you're smoother on the mercian.
This seems a good statement.

Why am I more smooth on a 700c 531c road bike, than on a suspended 20" Moulton?
Same geometry, same bloke in the same kit, riding the same roads.

Seems a good statement, but why three times the mileage on the rear tyres?
Mick F. Cornwall

User avatar
foxyrider
Posts: 4541
Joined: 29 Aug 2011, 10:25am
Location: Sheffield, South Yorkshire

Re: Tyre wear - mileages

Postby foxyrider » 9 Nov 2019, 9:02pm

i get a similar disparity between my Airnimal running 520 tyres and my big wheelers. It doesn't just run to tyre wear - i also seem to get far more punctures in the smaller tyres. :(
Convention? what's that then?
Airnimal Chameleon touring, Orbit Pro hack, Orbit Photon audax, Focus Mares AX tour, Peugeot Carbon sportive, Owen Blower vintage race - all running Tulio's finest!

User avatar
NUKe
Posts: 3739
Joined: 23 Apr 2007, 11:07pm
Location: Suffolk

Re: Tyre wear - mileages

Postby NUKe » 9 Nov 2019, 9:09pm

Mick F wrote:I could have said that, before I even posted! :wink:
"Something going on" ............. what is it?

Continental Sports Contact 406-28 vs Vittoria Rubino Pro 622-23

And there. Is the answer different tyres different compounds
NUKe
_____________________________________

iandriver
Posts: 2177
Joined: 10 Jun 2009, 2:09pm
Location: Cambridge.

Re: Tyre wear - mileages

Postby iandriver » 9 Nov 2019, 9:13pm

Hmm, random theory with no basis in science or suggestions I know what I'm talking about.

Heat making the rubber softer in a smaller tyre.

Pressures and the contact patch size.

More brake bias towards the rear. Dragging the back brake, different braking strategy on the small wheeler.
Supporter of the A10 corridor cycling campaign serving Royston to Cambridge http://a10corridorcycle.com. Never knew gardening secateurs were an essential part of the on bike tool kit until I took up campaigning.....

User avatar
Mick F
Spambuster
Posts: 46797
Joined: 7 Jan 2007, 11:24am
Location: Tamar Valley, Cornwall

Re: Tyre wear - mileages

Postby Mick F » 9 Nov 2019, 9:25pm

iandriver wrote:Hmm, random theory with no basis in science or suggestions I know what I'm talking about.

All I can say, is that I get three times the mileage on one bike than the other.

Big difference.
Mick F. Cornwall