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Old 11-16-2019, 07:04 PM
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DBU DBU is offline
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Change Tire Pressure when going from RFT to Conventional?

The title pretty much says it all. Should I change the tire pressure when going from factory RFT to conventional tires?
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Old 11-16-2019, 07:36 PM
Autoputzer Autoputzer is offline
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It's a throw of the dice. Even different brands of the same type (RFT or non-RFT) will have different optimal pressures.

Get a digital tread depth gauge (~$10 on the Interwebs) with a high-resolution display (0.001" or 0.01mm). Measure and record the circumferential channels on all the tires when they're new. Pick pressures. I start out with two PSI over what the door decal says, measured cold in the early morning. Stick with those pressures for a rotation stint (or ~5k miles). Then, measure the depths again and adjust the pressure as needed. Higher pressure causes more wear in the middle of the tire. Lower pressure causes more wear in the inside and outside channels. You need to stick with pressures for a few thousand miles, to get a correlation between pressures and measurable wear.

I've found that Goodyear and Continental tires like more pressure. Michelin and Bridgestone work at closer to the decal pressures.

My F10 535i came with the miserable Goodyear LS2 RFT's. I never could get them to wear perfectly even. I replaced them with non-RFT Michelin PSS's. They seem to wear evenly at 38 PSI in the front, 42 PSI in the rear, both of those pressures being three PSI over what the decal says for low-speed driving.

I ordered Frau Putzer's G01 X3 30i with non-RFT, all-season tires. They're Bridgestone Dueler HP Sport A/S's. The door jamb decal says 32 PSI in the front, 35 PIS in the rear. They were wearing evenly with two PSI over the decal pressures. The tires are round shouldered (started out with 9/32" depth on the inside and outside circumferential channels, 10/32" on the two middle circumferential channels). I'm trying to concentrate the wear in the middle more, so that all four channels will wear down to 3/32" of depth at the same time. So, I'm now running them at four PSI over the what the decal says. In 1500 miles, next tire rotation, I'll measure everything again and see where I stand.
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Last edited by Autoputzer; 11-16-2019 at 07:44 PM.
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Old 11-17-2019, 02:05 PM
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Thank you, Autoputzer. I'd asked Mike Miller (Roundel) the same question and he stated that there is no "set conversion" between the two tire types. He did suggest to start out at 2 PSI over the door decal/original RFT tires. Pretty much in line with your thoughts. Based on how the old tires wore down, I am running 3 PSI over in front and 2 PSI over in the rear, i.e. 35 front and 34 rear. I have recorded the depths like you described and will see how it goes. This is a very low mileage car, so it may be a year or so before I get enough meaningful data to adjust the pressures.
BTW - switched from Pirelli PZero RFT to Firestone Indy 500. The Pirelli's gave great handling and comfort but were gone after just 20,000 miles of grocery shopping. The Firestone feels a little softer going over the small bump going into my garage. They are summer tires which is all you need in SoCal. It is 90F today and rarely gets under 45F in the winter here.
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Old 11-17-2019, 02:19 PM
Autoputzer Autoputzer is offline
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With a high-resolution digital gauge, you need to pick a spot (or spots) to take the measurements. There's enough variation in channel depths around a tire that measuring at random spots will pick up that random variation of channel depths in the measurements. I measure my tires at the valve stem and 180 degrees from the valve stem, and then take the average.

Firestone's are Bridgestone's. So, they should also be happy at just a few PSI over the door jamb decal pressures.

PM me if you want a copy of my magic "tire whispering" spreadsheet. . anybody else who wants a copy, too.

The spreadsheet's particularly handy for shuffling tread depth data around after a tire rotation. It does that with two nested VLOOKUP functions. Oh, boy!
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Last edited by Autoputzer; 11-17-2019 at 03:01 PM.
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