http://citycyclingedinburgh.info/bbpress/ CityCyclingEdinburgh Forum » Topic: Contact patches en Wed, 13 May 2026 05:34:01 +0000 http://citycyclingedinburgh.info/bbpress/topic.php?id=12911#post-155733 Tue, 03 Jun 2014 14:48:28 +0000 I were right about that saddle 155733@http://citycyclingedinburgh.info/bbpress/ <p>@Arellcat</p> <p>Thanks - really interesting.</p> <p>You know you still want to join me, acsimpson and wingpig with a pile of bricks and shower cubicle doors though, don't you? </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=12911#post-155731 Tue, 03 Jun 2014 14:40:38 +0000 Arellcat 155731@http://citycyclingedinburgh.info/bbpress/ <p>Tulyar and I discussed this a while ago in relation to friction of surfaces (eg tarmac vs steel rails).</p> <p>From Continental:</p> <p><img src="http://blog.evanscycles.com/wp-content/uploads/2012/06/conti-e1340122349149.jpg"></p> <p>and possibly more than you wanted to know about contact patch shape, and how pressure influences the shape, and how shape influences rolling resistance (as does carcass ply direction and sidewall TPI).</p> <p><a href="http://flocycling.blogspot.co.uk/2011/11/flo-cyling-contact-patch-why-wider-is.html" rel="nofollow">http://flocycling.blogspot.co.uk/2011/11/flo-cyling-contact-patch-why-wider-is.html</a> </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=12911#post-155703 Tue, 03 Jun 2014 13:19:46 +0000 Dangerous 155703@http://citycyclingedinburgh.info/bbpress/ <p>There is a good reason that the formula is touted in the motorcycle world. It's called Physics.</p> <p><a href="http://en.wikipedia.org/wiki/Pressure" rel="nofollow">http://en.wikipedia.org/wiki/Pressure</a></p> <p>Pressure = Force / Area </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=12911#post-155695 Tue, 03 Jun 2014 12:25:46 +0000 acsimpson 155695@http://citycyclingedinburgh.info/bbpress/ <p>With two shower screens you could put the acetate between the layers. </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=12911#post-155690 Tue, 03 Jun 2014 11:49:25 +0000 wingpig 155690@http://citycyclingedinburgh.info/bbpress/ <p><blockquote><em>"How best to get a millimeter grid onto the glass?"</em></blockquote></p> <p>Print one out on acetate or just glue two perpendicular rulers on the underside and Photoshopically extend lines from each into a grid? </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=12911#post-155688 Tue, 03 Jun 2014 11:19:33 +0000 I were right about that saddle 155688@http://citycyclingedinburgh.info/bbpress/ <p>@wingpig</p> <p>Game on. I've got a very accurate schraeder tyre pressure gauge and a presta track pump with a decent gauge built in. Bathroom scales...anyone got a digital set?</p> <p>Only the rear wheel needs to go on the glass - photograph the contact patch and let the tyre down in 5psi increments until the rim touches down - plot up the resulting 1/pressure vs area curve. Should be linear, with a slope equal to the weight on the wheel if the theory is correct....</p> <p>How best to get a millimeter grid onto the glass? </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=12911#post-155684 Tue, 03 Jun 2014 10:50:39 +0000 wingpig 155684@http://citycyclingedinburgh.info/bbpress/ <p>Film it from the side riding past a tape measure to get the maximal fore-aft length of the contact areas and ride through a small puddle then a dusting of flour to get the maximal width? May require assuming the contact area to be elliptical.</p> <p><blockquote><em>"Is there anywhere you can ride a bike over a plate glass surface and observe it from underneath?"</em></blockquote></p> <p>I have two expired glass shower screens and some bricks in my back garden which could, if properly arranged, support a bike on top with a camera underneath. </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=12911#post-155681 Tue, 03 Jun 2014 10:39:30 +0000 I were right about that saddle 155681@http://citycyclingedinburgh.info/bbpress/ <p>That formula is touted in the motorcycle world (where the contact patch is about the size of an adult male hand). I reckon it would be right for a latex tyre with no inherent stiffness, provided you measure the air pressure while sitting on the bike.</p> <p>I'm an empiricist though, and am now tempted to make the actual measurements. Is there anywhere you can ride a bike over a plate glass surface and observe it from underneath? Can't be bothered getting paint on my tyres.... </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=12911#post-155667 Mon, 02 Jun 2014 22:07:03 +0000 Snowy 155667@http://citycyclingedinburgh.info/bbpress/ <p>I read something this evening that intrigued me and I thought I'd run it past people with knowledge of such things.</p> <p>It went like this: the weight of a vehicle (including driver/rider) in pounds, can be be divided by the PSI of the tyres, to give the size of the vehicle's contact patch with the road. You would then divide by the number of tyres to get the size of the contact patch for each tyre. </p> <p>Apparently this gets you within 10% of the right value, due to factors like variation in sidewall stiffness.</p> <p>So if my bike plus myself weighs 220 pounds (cough) and I run my tyres at 110 PSI, I have a contact area of 2 square inches, or 1 square inch per tyre.</p> <p>This seems somewhat small. Can this be right? If so, I have a new found respect for the gripiness of my tyres... </p>