Tire thoughts: air pressure sensors (TPMS) and alternate spare tire options

[Twisted Santa]

I had a few tire related questions pop into my head when I saw someone with a flat tire waiting on the side of the road, presumably for Triple A.

(1) I haven’t heard any talk of this yet, but will the Slate have the tire air pressure sensors that communicate with the car and show a warning when a tire is going flat? Or are they being left out for sake of simplicity? Are they something that contributes to a ”top safety rating”?

(2) Most new cars don’t come with a spare nowadays. They just have a “repair kit” that inflates the tire and sprays sealant gunk in it. I like the idea of having an actual spare tire for emergencies, but I don’t want to have one hanging on my tailgate. Is there any place to squeeze in an undersized donut spare? My ’71 Super Beetle from high school had a spare in the frunk , with a little room left over for other stuff. Would a donut fit in the space behind a front seat?
Is a donut even a viable option given the weight of on EV? So many questions…

 

[KevinRS]

I think basic TPMS is required now, that just gives a warning light to check your tires, more advanced systems show pressures at all the tires.
Spare and flat tire info hasn't been given besides that there is a spare option in the maker.

 

[E90400K]

Starting with model year 2007, Tire Pressure Monitoring Systems (TPMS)/Flat Tire Monitoring (FTM) systems are Federally mandated safety systems. So, the Slate will have either TPMS or FTM (I hope they go FTM).

If you have a concern with flat tires, install run-flat tires or keep a tire inflator in the frunk.

 

[Ironman]

Hate the damn things.
I learned about 50 years ago how the vehicle feels when I had a soft tire. Presently no vehicle I own has a tire monitor in a tire, and the little red dash light is just decorative. I do a walkaround before I jump behind the wheel and if I spot a suspicious tire, I check the pressure. Then inflate if needed and decide if I have to visit the tire shop.

 

[thespacecowboy]

Hate the damn things.
I learned about 50 years ago how the vehicle feels when I had a soft tire. Presently no vehicle I own has a tire monitor in a tire, and the little red dash light is just decorative. I do a walkaround before I jump behind the wheel and if I spot a suspicious tire, I check the pressure. Then inflate if needed and decide if I have to visit the tire shop.

Quite the opposite experience here. I’ve had the TPMs alert me that a tire was low before I felt anything while driving down the freeway a few years ago. I thought it might have messed up and drove a few more minutes and then started feeling it get a little soft and pulled over to check and swapped to a spare. Just the other day I hopped into the car and it was on. Did a walk around with a gauge, and sure enough one of them was lower than the rest. Didn’t visibly look low, but modern low profile tires rarely do, and now I know to keep an eye on it to identify if it’s got an issue.

 

[MySlate]

I was wondering if run-flat tires would be an option.

 

[SparkYellow]

I have used tire pressure monitoring kits on my older cars (pre-2017). They use BT enabled valve stem caps to display the psi on a small device. The budget units (<$50) all failed within a year. The caps essentially work like the needle/pin on a tire inflator. If the cap isn't screwed on tight, it would actually cause a leak.

I will make my own full size spare and strap it down in the bed. It looks like I can make one with a $100 wheel and $70 tire.

 

[Ironman]

Quite the opposite experience here. I’ve had the TPMs alert me that a tire was low before I felt anything while driving down the freeway a few years ago. I thought it might have messed up and drove a few more minutes and then started feeling it get a little soft and pulled over to check and swapped to a spare. Just the other day I hopped into the car and it was on. Did a walk around with a gauge, and sure enough one of them was lower than the rest. Didn’t visibly look low, but modern low profile tires rarely do, and now I know to keep an eye on it to identify if it’s got an issue.

Ahh, there's the thing. I don't run modern low profile tires. I use regular tires, 15" and 17" on the Dodge 1 ton

 

[coregrind]

When I asked this week, I was told by an agent there is no stock spare. I’m definitely going aftermarket on tires & wheels and am considering going with a set of 5 so there’s a matched spare. I’m not open to the bumper mount for the spare so I’m hoping to find a secure option for the bed that will prevent it from easily wondering off. Another possibility is to skip the spare and carry a plug kit in addition to my usual pump.

 

[KevinRS]

Probably 50% or more of the flats I've had have been road hazards or sidewall punctures that required an immediate change to a spare and then replacement of the tire. Do have AAA now, so wouldn't be just stuck if Slate gets a flat, but that takes time. Probably need to plan on a spare, even if it's in the bed.

 

[pdxmotorhead]

If the bolt pattern isnt too different, might be able to buy a compact spare that has the inflater with it so it fits in a smaller footprint.

 

[kvermeer]

Modern TPMS in most vehicles are not actual air pressure sensors with wireless radios, they're just piggybacking off the ABS wheel speed sensors. Tire circumference is proportional to tire diameter is related to tire inflation pressure, so the computer can count the number of degrees each wheel rotates to estimate the air level.

If one tire does 101 revolutions while holding constant speed and not turning, and in that time the other 3 only do 100, that one's probably a little smaller in diameter and might be low on air.

I don't expect it to offer a live readout of air pressure. You can buy trailer tire monitoring kits that screw onto and extend the valve stem if you want that.

 

[ElectricShitbox]

Modern TPMS in most vehicles are not actual air pressure sensors with wireless radios, they're just piggybacking off the ABS wheel speed sensors. Tire circumference is proportional to tire diameter is related to tire inflation pressure, so the computer can count the number of degrees each wheel rotates to estimate the air level.

If one tire does 101 revolutions while holding constant speed and not turning, and in that time the other 3 only do 100, that one's probably a little smaller in diameter and might be low on air.

I don't expect it to offer a live readout of air pressure. You can buy trailer tire monitoring kits that screw onto and extend the valve stem if you want that.

GM did this in the early 2000s, but for the past 15+ years most TPMS systems use sensors in the wheels mounted to the valve stems. They directly measure pressure and temperature.

 

[kvermeer]

GM did this in the early 2000s, but for the past 15+ years most TPMS systems use sensors in the wheels mounted to the valve stems. They directly measure pressure and temperature.

Really? ....researches... Huh, I stand corrected! I'm not so far off given my own Ford has an indirect TPMS, but apparently direct-measurement systems are more common than I thought.

 

[ElectricShitbox]

Really? ....researches... Huh, I stand corrected! I'm not so far off given my own Ford has an indirect TPMS, but apparently direct-measurement systems are more common than I thought.

Upon further reading, we were both wrong, because there's a few brands that switched back to indirect measuring! I guess most VWs do indirect tpms lately!