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What A Difference 4-psi Tire Pressure Makes...

What A Difference 4-psi Tire Pressure Makes...

What a difference 4-psi tire pressure makes. I have a 10-month old 70D 19" Cyclone and regular suspension. For about 2 months I've been driving at 41-42psi tire pressure instead of 45. (What can I say, I've been avoiding gas stations, so I waited long enough for my next appt with Tesla so they can repressurise my tires.)

The other day when I got my car back from the Tesla service center, my car drove so much smoother... like driving on air. So...smooth. I felt like I was driving a new car. Especially since I just got my regular dashboard replaced with the alcantra one. Tesla's initial mistake upon delivery. Anyway, my tires were back at 45 psi. (46 when the tires are warmed.)

I can only imagine what those 21" wheels would feel like... :-( especially without the Air Suspension upgrade. Must be less-smooth like when my tires were at 41.

Last week, it was so hot when I was in Pasadena, my tire pressure went up to 48psi all by itself parked under a tree.

Smmooooooth....

70D

Chunky Jr. | 1 augusti 2016

did you notice a difference in Wh/mi?

dpena23 | 1 augusti 2016

The car makes me feel all mushy inside when I feel how soft it moves on the pavement.....

Tropopause | 1 augusti 2016

I bought the Tesla tire compressor to air up my tires at home from the 12 volt connector. The gauge is very accurate in agreeing with my hand-held gauge AND the onboard tire pressure readouts. No gas station visits for me either.

dpena23 | 1 augusti 2016

oh, the Tesla Tire Repair Kit can put air back into your tires? Woo, I better buy one... I thought the kit was just for fixing holes.

Silver2K | 2 augusti 2016

every time tesla does work on my car the tire pressure goes up.

When I first dropped it off months ago I had my 21's at 42psi and they upped it to 45psi. A month ago I dropped it off at 45psi and they upped it to 48psi. I think in 2 years I'm going to be riding on balloons.

mjwellman | 2 augusti 2016

Tropopause--THANKS. Great tip. I've got the Tesla compressor but had not thought of using it to top off my tires. I've got one tire that is down a couple of pounds and I keep forgetting to pull into a station for air.

-Gman- | 2 augusti 2016

A bicycle pump works great too!
(no gas station visits in 19 months now)

barrykmd | 2 augusti 2016

I, too, use the slime pump. Can't imagine how much pumping a bike pump would take. Can I add Presta valves to my Tesla's tires? :-)

-Gman- | 2 augusti 2016

Bike pump takes about 6 pumps per psi to top off.

Wilber | 2 augusti 2016

I can confirm what Gman says - about 6 pumps per psi. The bike pump i bought at my local Trek store has both Presta and Schrader valves on it.

vp09 | 2 augusti 2016

I use a bicycle pump. I sure like that dash feature that shows PSIs.

EVRider | 2 augusti 2016

I use a small electric air inflator at home. It's much faster than a 12V inflator, and inexpensive -- I think I paid about $50 several years ago.

dpena23 | 2 augusti 2016

Bicycle pump it is then!

barrykmd | 2 augusti 2016

Learn something every day! I would have thought that a bike pump would take forever, given the much greater volume of air in the car tires. I'll have to try it next time.

Bighorn | 2 augusti 2016

It's anecdotal and may be confounded by firmware changes, but I have noted much better efficiency after raising tire pressures by 4 PSI.

oangel | 2 augusti 2016

Good tip on using a bicycle pump. I too thought it would require too many pumps to be worthwhile.

amareshvanga | 2 augusti 2016

Tires are very important in the performance of a car.
Maintianing good tire pressures not only increases range but also the life of the tires along with performance,comfort.
Alignment and balancing are important.As long as you drive without pumping the brakes too often,taking high speed turns,running via potholes, you can get away with balancing,rotation,alignment for almost close to 12000 miles which is when they recommend first service of the vehicle anyway.
I always keep my TPS screen on my dash so that I can get accurate reading when car is cold.This is the pressure that needs to be interpreted.If you drive for little bit this will go up.Also hot temp increases this but true measure is cold temperature tire pressure.I brought a air compressor from amazon which plugs in to my 12 v outlet and works beautifully to top off the tires if the pressure falls.No gas station visits needed

Silver2K | 2 augusti 2016

@Bighorn

I tend to shift a bit in the rear of the car when I hit a bump at 48 psi. let me know if this happens to you please.

Bighorn | 2 augusti 2016

@Silver
I've never gone above 44PSI on 21s. Spec is 38/40. I could imagine a loss of traction if overinflated, though it's not data driven.

Silver2K | 2 augusti 2016

Service inflated it to 48 when they changed out my DU.
I questioned if that was the norm now and was told that's what they inflated it to.

the only things that have caused the shifting in the past with bumps are bad control arms and bad traction. I may drop them back to 44, that did very well for me.

Bighorn | 2 augusti 2016

I was happy with 44 and last time I went in, they deflated me to 38/40--time waster. I've not come across 48 though there was a brief time when 50 got published on the jamb plate for 19s. 45 is consensus.

Silver2K | 2 augusti 2016

44 it is! tanx!

bb0tin | 2 augusti 2016

I assume you are all talking about floor pumps and not hand pumps

-Gman- | 3 augusti 2016

I use the classic "T"-shaped hand-pump* but a foot-pump would work as well.

*if you buy a pump, make sure the hose is long enough to easily reach the valve when it's at the top of the wheel; some have very short hoses and require you to set it on a crate or wood block to reach.

Silver2K | 3 augusti 2016

you guys are crazy. why not just buy one of these and call it a day?

https://www.walmart.com/ip/Masterflow-12v-Basic-Air-Compressor-Inflator/...

Silver2K | 3 augusti 2016

this is what I use and have had it for over 3 years now. great for inflating pool toys also. no more light headedness after wife requests a certain toy :)

https://www.walmart.com/ip/Masterflow-12v-Portable-Air-Compressor-Inflat...

-Gman- | 3 augusti 2016

because unpacking/repacking cords is slower than just reaching for the bike pump... and I'm a lazy person.

Horsfield13 | 3 augusti 2016

Quick few questions for those of you with much more experience of this than me:

My 70D is a few weeks old (facelift model). I checked all tires with a digital pressure gauge. All tires were approx 40PSI which makes me believe that the service center set them at this level when i picked the car up from new.
I inflated the tires to 45 PSI (using 12v inflator) and confirmed 45PSI via the digital gauge. Questions a s follows:

1. Im in Colorado. Does this mean that the preferred tire pressure should be lower than the official 45PSI quoted in the car details?
2. The pressure sensor in the car shows all of the tires as 42PSI cold. This is despite the tire pump and the dedicated digital gauge showing 45PSI. Is the on board pressure sensor known to be incorrect?
3. Which pressure gauge would you believe, the onboard sensor or the hand held digital gauge?

Just about to embark on a road trip so i'd like to get the tires correctly inflated so I'm very grateful for your comments

Thx

rxlawdude | 3 augusti 2016

@Horsfield: As to 1, I'm not aware of "high altitude" adjustments like when baking.
2. You might check a third trusted gauge, but if the TPMS is reporting low, I'd take it in for service.
3. See 2.

murphyS90D | 3 augusti 2016

How much did you pay for the digital gauge? I have three low cost digital gauges and they all give different readings.

The problem I have with the TPMS readouts is they don't provide data until after the car is moving. Once the car is moving the pressure is rising because the flexing of the tire generates heat which heats the air in the tire which increases the pressure.

tom168 | 3 augusti 2016

The recommended tire pressure is listed on driver door plate. It stated 45psi for my May, 15 70D. Last year, the service center lowered my tires to 42psi without checking the door plate. I could feel the difference within a few hundred ft from the SC. I took it back right away and they corrected it. Apparantely, some of the earlier models have 42psi as the recommedned pressure.

Also, adjust the pressure when the tires are cold. The difference could be 4 to 5 psi after driving for a while.

Horsfield13 | 3 augusti 2016

All - Thx for your responses

The digital gauge is an inexpensive $15 type from Amazon. Id be surprised if it was 15% to 20% wrong but i guess its possible? Interesting that the 2nd gauge (from the 12v inflator) also was in sync with the hand held gauge. I think i'll take a ride to the gas station and test again on their commercial tire inflator.

My 70D shows 45PSI as the correct PSI on the door plate. I'm surprised that it didn't come with tires at that level from new. I did check the levels while the car was cold after being left overnight. They were all on or close to 40PSI before i re-inflated

I do have to say that the ride is much smoother with the tires at 45PSI

Thx again

txakoli | 3 augusti 2016

This is the tire gauge I use. It's easy to use and it's accurate.

https://www.amazon.com/gp/product/B00404WDUC/ref=oh_aui_search_detailpag...

barrykmd | 3 augusti 2016

Horsfield13:
1. I'm in CO, too. No altitude adjustment for tire pressure.
2/3. I use a quality gauge and my sensors read 3-4 psi lower. My flat tire/slime pump reads identical to my gauge. I believe the gauge.
Have a good trip

Davidb0229 | 3 augusti 2016

I use a digital gauge from Brookstone that I have had several years, which agrees almost perfectly with the TPMS.

As others have said, tire pressure is critical for tire longevity -- under-inflation leads to excessive wear on the edges, and over-inflation leads to excessive wear in the center. Sever under-inflation can damage the tire structure.
And as stated, pressure is a function of ambient temperature. So that means, pressures need to be checked and adjusted as the seasons change -- add more air in winter, less in summer. The wild card in all this is where is the car when the pressure is checked and what condition are the tires in. In winter, a service garage (and maybe the owner's garage) is likely warmer than the outdoors, and in summer it may be cooler. So regardless of what the garage sets it to, the pressure should be checked the next morning before being driven.
If you do not have a good digital gauge, the TPMS will display the pressures within a short drive -- fraction of a mile. That is likely close enough to cold temperature to be reliable. One exception to this is that I have found over the years that the tires can heat up from the sunlight. So if, like me, your car is parked outside, the tires on the sunny side may be 1 or 2 PSI higher than the other side, once the sun has been on the car for some period (depending upon air temperature and so on). In the summer I find that the sun can heat up the tires pretty doggone fast. So if you can, it is good to check them early in the day.
Surveys by AAA have found that people generally tend to under-inflate their tires, probably because most people rarely check them. Hence the value of the TPMS for folks like me that are a bit lazy!
Having said all this, it's still "only a car" so I try not to obsess about the pressure....

Horsfield13 | 3 augusti 2016

barrykmd - thx for your response. That makes me feel better. Seems like its a sensor complication. Im going to leave as is with 45PSI showing on the external gauges and all will be good.

Davidbo229 - good advice. I drove around for a while tonight abs the internal sensors did indeed increase from 42 to 44. Similar to my external gauges, just a little lower.

Thx again all. I'll report back if i find anything changes or matters between external and internal measurements become more clear.

rxlawdude | 3 augusti 2016

My gauge on the bicycle pump I use, and the Brookstone gauge match the TPMS reading to the pound.

If you look at both the OP and another in higher altitude Colorado, they both observe a deviation between known accurate gauges and TPMS.

I theorize, therefore, that TPMS reads low at higher altitudes. :-)

rxlawdude | 3 augusti 2016

(Forgot to mention I'm at 95ft above sea level.)

Silver2K | 3 augusti 2016

ok maybe I'm nuts but I don't see tire pressure readings anywhere on the car and as a matter of fact I've done a search and came up with people not being happy the reading are not there..

where are you reading tpms numbers?

Bighorn | 3 augusti 2016

@Silver
Your car predates the individual dash readout

miyamky | 3 augusti 2016

I'm with @silver, just went through owners manual looking and couldn't find it as well

Silver2K | 3 augusti 2016

Mother....

Sigh...

SbMD | 4 augusti 2016

I'm surprised there's no car status app that you can access when pushing the click wheel to show tire pressures.
I assume you checked this, right?

Silver2K | 4 augusti 2016

nothing on windows or android

Silver2K | 4 augusti 2016

You can purchase Bluetooth tire pressure monitors that replace the caps on each wheel, but I don't see them lasting more than a day or 2 before being lifted.

I don't understand why it's not in the settings since the car see's the tpms sensors to reset them and can tell if they are low.

Peter Gregory | 4 augusti 2016

My mechanic told me the listed air presure in the door frame of my ICE is at 32 degrees (or zero), need to pump them higher. She says 32 pounds on car, means 36 in tire.

martin | 4 augusti 2016

My MS90D has a status app in the cockpit screen...

murphyS90D | 4 augusti 2016

@Peter Gregory

You need a new mechanic. The tire pressure on the door frame is the pressure the tires are to be set to when the tire is at ambient temperature. That means they need to be adjusted at least monthly if you live where the ambient temperature changes significantly with the seasons.

Silver2K | 4 augusti 2016

martin

your MS90D can kiss my a.. :)

barrykmd | 4 augusti 2016

murphyS90D
+1

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