# Which design to maximize friction for a device standing on concrete?

I have a device 4cm X 5cm X 15cm that stands on asphalt/concrete/road. So, the device is taller than its base which makes contact with the asphalt.

I want to maximize the friction so that the device stands as well as possible without any attachment.

I'm considering a thin rubber add-on attached at the bottom of the device and I'm wondering what is the best design for such rubber to maximize the friction with asphalt.

I selected rubber because it has the highest friction coefficient with asphalt - there is a reason why tires are made of rubber...

But how should I design the bottom side of this rubber part that will be in contact with the asphalt? Here is an idea which I got inspiration from a bathtub mat. What is the best pattern possible? And what should be the pattern size (small or big relative to the 5cm X 4cm area)?

I would use three(triangulated) very sharp tip toes, stainless steel conical points so that they dig into the asphalt a little bit with a little pressure from the installer :-) I don't know if they have them anymore, but track and field shoes use to have threaded conical spikes with the shoe soles having threaded inserts to receive the spikes. You could use something similar. Me thinks this will grip the ground better than a textured rubber pad.

• Thanks for the answer. Very interesting. I didn't think about track shoes (I was thinking more of bathtub mat) and it's a very good idea. The point of track shoes is that there is a lot of pressure to stick to the ground. – gregoiregentil Mar 26 '19 at 14:29
• @gregoiregentil If you like my answer you can check it off as accepted ;-) – William Hird Mar 26 '19 at 23:20
• @gregoiregentil If you have to use a rubber bottom , use the softest durometer Sorbothane , it is very tacky . Or if you want to get crazy and can market the product with an add-on, have your device come with sticky pads on the bottom, with the protective layer of course, you peel the layer off to stick the device to the asphalt . – William Hird Mar 28 '19 at 15:10
• Another interesting comment. I will ask my Chinese manufacturer if they can get such rubber. For the peeling, it's not a one-time but yes, it's a good idea. – gregoiregentil Mar 28 '19 at 22:41

If you have a rubber that you believe has the best coefficient of friction possible then it wont matter too much how it is shaped unless you need to deal with water or mud like a car tire. The best way to increase the force of friction is to add weight. As you probably know the friction equation is $$F=\mu N$$ $$(F=$$Friction Force, $$\mu=$$friction coefficient, $$N=$$normal force) Friction force

I don't know what this device does, but if it sees side load and is top heavy it is more likely to tip with a gripy base.

If the issue is that you don't want it to fall over when you set it down... then I'd guess you need this base to help counteract the variation in how level the ground is? In this case, my shot in the dark is three bumps so you just get the minimum three points of contact. Three-legged tables don't wobble.

But if you take nothing else away from this and are simply looking for rubber pattern advice I'd say lighting bolts... Lightning bolts are badass.

• Thanks for that answer. Very useful. The concrete is always flat and the gravity center of the device is perfectly aligned with the middle of base and is not so high. Still, a very strong outdoor wind could tip the device. I know that rubber won't be the perfect fix but the more it can "stick", the better. – gregoiregentil Mar 26 '19 at 14:26