K60 Tyre Pressure Test

[squarebore]

After listening to concerns by other forum members about tyre temperatures going up when running at lower than recommended pressures, I decided to do some testing. The methodology was:

Almost new K60s - 1000kms on each
1/4 tank fuel and 110kg rider (no luggage except empty topbox)
pressures set cold in shed at 33f and 42r
rode to start point and stopped and checked temps on tread area (in the valley), sidewall, road and ambient
used Fluke 566 laser temp sensor
rode a 5km circuit of straights and bends
recorded temps
reduced pressure by 2 psi front and rear
continued same process for 5 laps

I have the table and charts below but my conclusion is that down to 25f and 34r you will have no significant temperature issues with the tyres. When I have more time I will continue the test for lower pressures and a loaded bike.

(Edit and P.s. The hot pressures were about 5-7 psi above cold. That's why I reduced the pressure by 2psi each time and didn't worry about the actual pressure. 42psi cold was reading as 49psi hot)

 

[martin_nj]

A laser temp reader won't tell you much.

You would want something like this http://www.longacreracing.com/products.aspx?itemid=1721&prodid=7298&pagetitle=AccuTech%E2%84%A2+Economy+Pyrometer that you can jab into the rubber and get the core temps.

 

[Checkswrecks]

What you have is interesting data and here is the type of plot that you are starting to create:

I know that heat applied to the outside of a thinner car tire can take 45-50 minutes to reach the inside. The heat we are discussing in a nice thick K60 is halfway through the carcass of the tire construction, so about the same distance through the cross section of a thin-wall car tire. In other words, your ride times are probably insufficient and the temps will go up till you've been riding for more than a half-hour.







After thinking about your previous posts, I think in the real world on a K60 that before you build enough heat to unglue the plies (the idea discussed in the previous thread), you are going to be able to run the pressure down till at some pressure you will have no problem; then a couple of psi less you either you unseat the bead, damage the rim and suddenly lose all pressure, or controllability disappears.

You may remember that I responded to your previous post that deflection is the critical value for tire design. You probably would be better served to work from that standpoint in collecting your data. The farther you have to go to reach the maximum possible speed and the less load you have, technically, the less pressure you need to get the same deflection.


My suggestion is to accurately measure your tire width and the rim height above the floor (sidewall deflection) then build a plot like this one from the bicycle world. (It just shows width.) Put the deflection on the horizontal axis and plot weights as your variable curves. When you get past the knee/bend in a curve you'll probably be where you don't want to reduce pressure further.


You are still on your own in figuring out what that least possible pressure is, but at least there'd be some logic to relate your load and deflection to tire pressure.

Till the bead unseats from low pressure and then all bets are off.

You're doing real world testing and as Dunlop states:
Underinflated tires can result in imprecise cornering, higher running temperatures, irregular tread wear, fatigue cracking, overstressing and eventual failure of the tire carcass, or loss of control, which could cause accident, injury or death.


btw - The best online tire data calculator that I personally know of is here: http://bndtechsource.ucoz.com/index/tire_data_calculator/0-20