Sorry for another DFM question.
Do DFMs have a very narrow working window for pressure?
Very occasionally I find a pressure that seems to make the rears grip up and feel like chewing gum on the track.
This only seems to last a few laps mid way into a session.
Because I muck around with the pressure and setup too much I find it hard to get back in this narrow window.
It seems to lie between 15 and 16 psi.
The rears grip like you know what to a blanket and the front understeers which never happens at any oher time.
I have only felt this grip about three times on the track.
My times are more than 1/2 second faster than my usual fastest times when it happens.
Is this a typical phenomenon with grippier tyres or just a DFM thing?
because of the shape of DFM's, I usually find that 12-14psi works for my kart. Mostly 12 psi.
Once they start to slide in the rear, they just get hotter and slide more. You will also see that not all of the tread is making contact with the track, that's why I prefer lower pressure.
I rarely have understeer, I mostly struggle with rear end grip. I'd be keen to hear what others are running
Cold pressure Ben
No knowing the DFM's, That seems very high for a cold pressure.
With the MG Reds, 12 - 14 psi, depending on conditions was what I use to used as a cool (not totally cold but some residual heat from a practice) starting tyre pressure. I would also look at 1.5 - 2 psi increase from starting to working pressure. I would expect this to be fairly consistent across most karting tyres although I believe the yellows were as low as 8psi and the SL1 up to 24psi for memory.
A pressure increase in the tyre is caused by increase in tyre (air in the tyre) temperature. If you start too high in pressure, there is less of the tyre surface doing all the work and it overheats. If the pressures are to low, there can be to much side wall movement and it causes an uneven contact pressure across the tyre, therefor not optimising the tyre grip available. (working the outer edges and the middle does little work)
So you are looking to have your tyre pressures at an optimum WORKING pressure, which will depend on the conditions a little also.
Either way, 15 - 16psi seems a little high for a med grip tyre.
Remember, its the working parameters (temp & pressure) that are important not, while its sitting in the pits.
Around 15psi Hot seems to be on the money for the DFM tyre in most circumstances. however i have seen them run successfully up has high as 22psi on a brand new track surface.