Replaced 1 flat tire, other three still have medium tread depth. What to do?

i think they say to buy 2 and put them on the rear

how many miles on them?

 

What is the difference in depth?

I’d throw the new one in the back as they don’t have the same concerns as the ones in the front being close in diameter.

 

and one consideration is, if you rotate them, it won't matter soon enough

 

Nope.

On the back.

 

Since the front tires wear faster than the rear, it would seem reasonable to put new tires on the front. However the tire store will always install new tires on the rear axle because of the concern that oversteer (where the rear of the car slips out during a turn) is harder for most drivers to handle than understeer (where the front of the car does not take a corner as much as the steering wheel angle would indicate).

If you put new tires on the rear, the front tires should slip (causing understeer) before the rear tires do.

 

it's a conundrum. personally, i'd live with the one new tire, but i drive like a granny, and slicks would work just fine

 

Sure it’s not a grandpa.

I’d like to see what slicks look like in the Boston winter.

 

Is your TPMS working correctly?
Did you reset the TPMS with the correct PSI (door jamb or your PSI)?
The TPMS should have been triggered once PSI fell below 25% trigger. If you notice the light immediately when it is lit, and are able to quickly pull over and investigate, your tire likely could have been repaired (if the puncture was repairable).
Anytime you adjust air pressure, you should reset the TPMS, so it learns the new setting, and will adjust the 25% threshold warning parameter.

Base Gen2 Prius factory psi recommendation is 35 front/33 rear.
35psi * .75 = 26.25psi is when the front TPMS would trigger the warning light.

You may want to follow the factory psi difference of 2psi difference between front and rear. Unofficially, I notice many here seem to go 42/40 or 40/38. Ultimately your choice.

Tire manufactures recommend replacing tires in pairs. Michelin provides a good summary and explanation here.
Mixing Tires | Using Different Tires | Michelin US
I would just replace the one tire, and not rotate that side. Over time, the other three will require replacement; at this time then replace all four. Maybe hang onto this recently replaced tire as a spare, should you run into another situation that requires a single tire replacement.

 

Same thing happened to me. I just got 1 tire and am going to run the other 3 out and get another rim from the junkyard and keep the newer tire as my road hazard spare.

 

Do you have traction control?

It’s summer, just leave her up front and rotate the other 3 .

Flip her to the rear for the winter with whatever tread matches most closely

 

The missing info: how much tread depth is remaining, and what was/is the new tread depth?

If new tread depth was/is 10/32", and the remaining tires are around 8/32", I'd say just replace the one, you'll never notice it. And: throw caution to the wind, install the new one on the front, and leave it there a good while. If the tire shop refuses, do it yourself when you get home.

If the remaining tires are more like 6/32", I'd say screw it and get all new. A little early, but not worth losing sleep over it.

 

Remember, the TPMS gets triggered when it sees the PSI 25% lower, from its last forced memory setting (meaning you/someone has to rest the TPMS, to learn the new pressures for each tire).

You could have each tire at a different PSI (say 40, 35, 30, 25). As you drive, the TPMS in the wheels report the PSI they are reading. When the TPMS ECUS sees a >=25% reduction in PSI in a wheel sensor (based off the last reset memory setting), TPMS will activate the warning light, assuming the system is functioning correctly (including the light bulb in the dash).

Earlier you said 3-tires at 42PSI, one at 34PSI. I infer the 34PSI tire was inflated to 42PSI, and are wondering why the 34PSI tire did NOT trigger the TPMS? I suspect your TPMS was reset to 42 or higher. Here is why.

42 x .25 = 10.5; a loss of 10.5PSI or greater would trigger the TPMS.
42 -34 = 8; there was only a difference of 8PSI.
10.5 - 8 = 2.5; you would need to loose >=2.5PSI from that 34PSI tire to trigger the TPMS, assuming the system was reset at 42PSI.
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Do yourself a favor and set the tires to the PSI you want, then perform the TPMS reset so the sensors learn the new "ceiling". The 25% trigger gets based off this new rest/ceiling. Be sure to do this when the tires are COLD.

Page 155 from the 2007 Owner's Manual
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The factory recommended setting on the door jamb sticker for base and Touring, is 35 PSI front, 33 PSI rear; this PSI is low. Many here seem to go higher (42/40, 40/38), but still maintain the 2PSI differential between front and rear like the factory.

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