According to Miata tire calculator the difference in speed between 2457516 and 3057016 is 7.7% radius 1.2" dia. 2.3" circumference 7.4" and revs per mile 47 I get the speedo difference, not sure what the data really makes a difference in gear ratios.

But I got to thinking about this. Would changing the gear ratio in the diff make a difference?

 

Regardless of the mph, the tire diameter, the phase of the moon, the engine revolutions matter to the transmission because pressure is pressure and revolutions build pressure and spin the governor. What is being indicated to me (other than governor) is that the torque converter is hitting the crapper which is what locks up 4th gear to begin with. Pressure fellas not tire diameter dictates when the auto shifts. It's clunking into gear after the gas pedal is released......!!!!!! Slip, slip, slipping away!!!!

 

Unfortunately If I were a betting man my money would be on what scouts said, for your sake I hope he's wrong

For the speedo it is is set to the small tire size from factory, the large factory tire size 235 throws the speedo 5 MPH fast so bigger will be more off, GPS will show you how much

 

Turns out I was right about the valves being stuck. Flushed w sea foam and shifts as deigned. So the tire size isn't influencing the shifting. Still can't locate battery discharge issue. Draining the battery overnight with nothing turned on.

 

Glad you got the trans sorted, so you added sea foam, drove and drain fill? Or something done by the trans shop?

 

Trans shop drained, added sea foam, let sit overnite, ran engine, drained, refilled tranny fluid.

 

They just add one can or what?

 

@ 57 mph you should be shifting into 4th....... correct?

 

Yup right on and so smooth you can hardly tell it shifts just like it should be. So I think we have dis-spelled the myth about tire size effecting how the ZF shifts. It is as you pointed out all about pressure of fluid. If the valves are stuck (which each gear has them) then it's not going to shift properly

 

Here's what he did: the directions on sea foam tranny cleaner calls for half a can, he used the entire can. Drove it for 5-6 miles then let it sit for 2 days. Flushed and re-filled with Redline D4 fluid. Put a small amount of slack in kickdown cable.

Hope this helps others with this problem. Honestly I thought this tranny was garbage the way it acted. Now it shifts like a brand new unit. So smooth you can't even tell its shifting. Tire size has nothing to do with it.