I came across this video today. It is not long but I am glad I watched it to the end. It is a deep dive into the topic of tire pressures and how different decision points affect whether to run higher or lower pressures. 

I've seen this video before and it's got me thinking as I am currently adjusting to radically different tires and going through the process of trying different pressures to find what's optimal.

The first thing that stands out to me is he runs the same pressure in both tires. That's odd except for track or aggressive street riding. I looked for articles to explain why manufacturers recommend a significantly higher pressure in the rear but didn't find anything. My assumption is it's because that's where the weight of the rider, the luggage, the pillion go, towards the rear of the bike.

That would be my guess as well. 

Pure Speculation Below!

Maybe it's because of the importance of grip to each tire.

The rear is already larger, and losing grip in the rear is often recoverable or at worst a low-side.

Losing grip in the front is less recoverable and could cause a high-side.

Also, on many bikes it's easier to change the front tire than the rear tire, so longevity of the rear tire is a bit more valuable than the front.

I also wonder how the difference in volume of smaller front and larger rear relates to amount of deformation and therefore the size of the contact patch. Could be that if the tires have similar construction but different volumes, you need different pressures to achieve equal-sized contact patches (if that's even desirable?)

I think you might be on to something with that last thought.

Hmmm... I don't think we'll answer this differential pressure question with any authority. If we focus solely on contact patch size we ignore other factors such as ride comfort, durability, and handling characteristics. Also factor in the different rim sizes, air volumes, etc, and there are just too many variables. Front tires are typically larger in diameter and narrower in width to improve turning and absorb shocks better, rear tires smaller in diameter and wider to help the bike track straight, improve grip, and increase comfort. Conventional wisdom says the wider tire should have a lower pressure due to increased volume, yet it's not the case. Maybe the higher pressure helps keep the rear tire from overheating as it's under almost constant stress driving the bike forward. Too confusing.

That said - 36/42 is a pretty widely used standard. It's one I've rarely used. My Triumph had those manufacturer recommendations yet I only used them when the bike was fully loaded on long highway trips. If I was going out the the Dragon to drag a knee I'd drop to 30/30 or 32/32, and for general riding I'd run 32-33/36-39 or so.

What intrigues me is why this expert recommends going the the much higher pressure in the front tire? Increasing from 36 to 42 is going to have a significant difference in comfort and handling. Why equal pressure in both tires? Maybe I should try it. 

It just dawned on me that because of the larger size the rear tire may be constructed somewhat differently further muddying the waters. 

I typically run 32/36 on the street bikes. 

Right now it's hard to do any specific testing as we're not riding as much and the roads are so sketchy when we do. Winter time means be more cautious, days are short, starts are late, so rides are short. We're passing up on a decent day today because the roads are so heavily salted. Rain is coming through to clear it, then it looks like 65 on Saturday. 

Having the TPM's sure makes it easier to keep an eye on what's going on. I love / hate them off road - They're are great when you take a big whack on one of the wheels and are sure that's going to lead to a flat. They are a pain when the low tire pressure screen pops every up half hour telling you to stop immediately due to low tire pressure.