Change of tyre pressure if using 255/50/19 107Y due to higher load rating

[Shippy2006]

As many of us are using 255/50/19 tyres on 19 inch wheels to improve ride and cushion but why to keep the same pressure of 42 psi recommended by Tesla If tyre load rating is higher than original tyres?

I installed Michelin pilot sport 4 suv summer tyres on 19” Gemini wheels on my model Y performance 2022.
The new tyre rating is 107Y.

The original tyres on model Y performance are 255/35/21 98W and 275/35/21 103W

These tyres Load rating as per load chart corresponds to front-750 kg at 50 psi and rear 875 kg at 50 psi.
Now considering Tesla recommended pressure of 42.0 psi we can calculate the design load.

At 42.0 psi recommended pressure safe load on front axle is 1260 kg.max approx.
At 42.0 psi recommended pressure safe load on rear axle is 1470 kg max. approx.

Model Y performance maximum Laden mass is 2415 kg.Front axle max laden mass -1125 kg and rear is 1290 kg.

Even considering the max.max allowable loading limit for axle as per chart is F-1300 kg and Rear -1500 kg.So all this falls in 42.0 psi limit for original tyres.

If we consider the same design load of front - 1260 kg and rear 1470 kg then the psi required for 107 Y load rating can be calculated.
The load rating for 107y tyre is 975 kg at 50 psi.

So minimum safe front pressure for 1260 kg is 32.3 psi and rear pressure for 1470 kg is 37.7 psi.This pressure is sufficient to support the maximum limit of vehicle loading.

I kept 35.0 psi all round and the load they can support is 682.5 kg each.Total load support at this pressure is 2730 kg which is in limits.

At 35.0 psi the car drive is as good as a land cruiser or Nissan patrol.Anything above 35.0 max the ride is uncomfortable.The suspension are not suitable for comfortable suv ride at higher tyre pressures.

I am attaching some photos.Gents what is your suggestion on this.Am I wrong in any calculation?

 

[TomB985]

I think you’re pretty close, but you don’t even need to do that kind of math. The engineers who design these tires have already done it for you, and the load inflation table for the P255/50R20 is available. You’ll note the tiny difference between load ratings at a given pressure. They don’t have 107 listed, but it should be comfortably between these ranges:

At 45 PSI, those tires can handle 1,960 lbs each, or 890 kg. That’s much more than needed to support your Model Y, so I think you’re just fine with 35 PSI if you’re happy with how it rides and handles.

I kept my stock 21” tires, but found 42 PSI to be far too stiff. Using the load inflation tables for that size, I aired them down to 37 PSI and I’ve been much happier with the ride. I recommend this to anyone interested in improving their ride; the difference is huge.

 

[towndrunk]

I think you’re pretty close, but you don’t even need to do that kind of math. The engineers who design these tires have already done it for you, and the load inflation table for the P255/50R20 is available. You’ll note the tiny difference between load ratings at a given pressure. They don’t have 107 listed, but it should be comfortably between these ranges:

View attachment 928803

At 45 PSI, those tires can handle 1,960 lbs each, or 890 kg. That’s much more than needed to support your Model Y, so I think you’re just fine with 35 PSI if you’re happy with how it rides and handles.

I kept my stock 21” tires, but found 42 PSI to be far too stiff. Using the load inflation tables for that size, I aired them down to 37 PSI and I’ve been much happier with the ride. I recommend this to anyone interested in improving their ride; the difference is huge.

But what kind of mileage hit do you take at 37 PSI?

 

[TomB985]

But what kind of mileage hit do you take at 37 PSI?

It’s too early to get any firm numbers since I just adjusted pressure last week, but I haven’t noticed much of a difference. I’d say it’s almost negligible at this point.

 

[Pianewman]

Hmm...37psi is still a lot of tire pressure so I agree the efficiency penalty would be minimal. Highway cruising? I'd put it back up at 40-42psi.

 

[jadatis]

All the tires mentioned are XL, and those are allowed maxload at 160kmph/99mph AT 42 psi.
The 50 psi is the maximum allowed cold pressure, and difference is used to highen up the maxloadpressure of 42 psi, for higher speed, with a system depending on speedcode of tire, in the official used system.

And that is what you see in the pressure loadcapacity list given by TomB985.
I checked that list to be made with the official used formula used in Europe for decades for all kind of tires, and in US since 2006 for P-tires in SL and XL.

This list is minimum pressure for the load. Nowadays recomended pressure is calculated for GAWR and maximum technical carspeed. But electrical cars often higher advice for energysaving so batteryloading lasts longer.

I can make a customised pressure axleload list wich gives maximum reserve at wich comfort and gripp is still acceptable. Then still battery lasts long enaugh.
Have all the needed data, but will do it tomorrow, now sleepingtime in the Netherlands 2400 h

 

[jadatis]

Here the promessed list.
For every tire with loadindex 107 XL so at 42 psi. If you want it for higher speed, give that speed, you wont go over for even a minute, and I make a list for that.

Given in KG and LBS for the psi,
Given 90% of axleloadcapacity calculated for the psi, for max speed 160kmph/99mph, calculated with my determined safer formula then the European official used, wich is not bad.
I determined this to give maximum reserve and good milage, with still acceptable comfort and gripp, and no centrewear. Then you see that 35psi covers the GAWR rear( Gross axle weight rating) with all the reserves, and still good milage. The 42 psi is for the axiradius of the battery, and a choice to make, comfort or axiradius. You changed tires for better comfort.
Mayby the OEM tires would have given enaugh comfort with the lower pressures, nit that liw as for these, but still no 42 psi.

Rolling resistence makes about 15 to 20% of total energy use, so my 30 to 35 psi then already brings it back to 10 to 15%, and 42 psi to 7 to 12%.
Will give in next post for 98 loadindex of OEM tires, for wich the 42 psi was recomended.

So now you "ONLY" have to look back the 99%accurate determined axleloads back in the list, and use the cold psi given. Succes with that, the most tricky part in it all, and your responcibility.

In the list I gave your given GAWR's, and the max axleloads, a thing other brands dont give, but OK, Tesla will know better.

Axle Kg/ cold psi/ axle lbs
905 kg/ 20 psi / 1996 lbs
944 kg/ 21 psi / 2083 lbs
984 kg/ 22 psi / 2169 lbs
1023 kg/ 23 psi / 2256 lbs
1062 kg/ 24 psi / 2342 lbs
1101 kg/ 25 psi / 2428 lbs
1140 kg/ 26 psi / 2514 lbs/1125kg Fr
1179 kg/ 27 psi / 2600 lbs
1218 kg/ 28 psi / 2685 lbs
1256 kg/ 29 psi / 2771 lbs/Fr GAWR
1295 kg/ 30 psi / 2856 lbs/1290kg Rr
1334 kg/ 31 psi / 2941 lbs
1372 kg/ 32 psi / 3026 lbs
1411 kg/ 33 psi / 3111 lbs
1449 kg/ 34 psi / 3196 lbs
1487 kg/ 35 psi / 3280 lbs/ Rr GAWR
1526 kg/ 36 psi / 3365 lbs
1564 kg/ 37 psi / 3449 lbs
1602 kg/ 38 psi / 3534 lbs
1640 kg/ 39 psi / 3618 lbs
1678 kg/ 40 psi / 3702 lbs
1716 kg/ 41 psi / 3786 lbs
1755 kg/ 42 psi / 3870 lbs
1792 kg/ 43 psi / 3953 lbs
1830 kg/ 44 psi / 4037 lbs
1868 kg/ 45 psi / 4120 lbs
1906 kg/ 46 psi / 4204 lbs
1944 kg/ 47 psi / 4287 lbs
1982 kg/ 48 psi / 4370 lbs
2019 kg/ 49 psi / 4454 lbs
2057 kg/ 50 psi / 4537 lbs

 

[jadatis]

Here the list for 98 loadindex, 750kg/ 1653lbs AT 42 psi up to 99mph.

Kg axle/ cold psi/ LBS axle
696 kg/ 20 psi / 1534 lbs
726 kg/ 21 psi / 1601 lbs
756 kg/ 22 psi / 1668 lbs
787 kg/ 23 psi / 1734 lbs
817 kg/ 24 psi / 1801 lbs
847 kg/ 25 psi / 1867 lbs
877 kg/ 26 psi / 1933 lbs
907 kg/ 27 psi / 1999 lbs
936 kg/ 28 psi / 2064 lbs
966 kg/ 29 psi / 2130 lbs
996 kg/ 30 psi / 2196 lbs
1026 kg/ 31 psi / 2261 lbs
1055 kg/ 32 psi / 2327 lbs
1085 kg/ 33 psi / 2392 lbs
1114 kg/ 34 psi / 2457 lbs
1144 kg/ 35 psi / 2522 lbs/fr1125kg
1173 kg/ 36 psi / 2587 lbs
1203 kg/ 37 psi / 2652 lbs
1232 kg/ 38 psi / 2717 lbs
1262 kg/ 39 psi / 2781 lbs/GAWR FR
1291 kg/ 40 psi / 2846 lbs/Rr1290kg
1320 kg/ 41 psi / 2910 lbs
1350 kg/ 42 psi / 2975 lbs/ maxloadpress
1379 kg/ 43 psi / 3039 lbs
1408 kg/ 44 psi / 3104 lbs
1437 kg/ 45 psi / 3168 lbs
1466 kg/ 46 psi / 3232 lbs/GAWR Rr
1495 kg/ 47 psi / 3296 lbs
1524 kg/ 48 psi / 3360 lbs
1553 kg/ 49 psi / 3424 lbs
1582 kg/ 50 psi / 3488 lbs

 

[TomB985]

Here the list for 98 loadindex, 750kg/ 1653lbs AT 42 psi up to 99mph.

Kg axle/ cold psi/ LBS axle
696 kg/ 20 psi / 1534 lbs
726 kg/ 21 psi / 1601 lbs
756 kg/ 22 psi / 1668 lbs
787 kg/ 23 psi / 1734 lbs
817 kg/ 24 psi / 1801 lbs
847 kg/ 25 psi / 1867 lbs
877 kg/ 26 psi / 1933 lbs
907 kg/ 27 psi / 1999 lbs
936 kg/ 28 psi / 2064 lbs
966 kg/ 29 psi / 2130 lbs
996 kg/ 30 psi / 2196 lbs
1026 kg/ 31 psi / 2261 lbs
1055 kg/ 32 psi / 2327 lbs
1085 kg/ 33 psi / 2392 lbs
1114 kg/ 34 psi / 2457 lbs
1144 kg/ 35 psi / 2522 lbs/fr1125kg
1173 kg/ 36 psi / 2587 lbs
1203 kg/ 37 psi / 2652 lbs
1232 kg/ 38 psi / 2717 lbs
1262 kg/ 39 psi / 2781 lbs/GAWR FR
1291 kg/ 40 psi / 2846 lbs/Rr1290kg
1320 kg/ 41 psi / 2910 lbs
1350 kg/ 42 psi / 2975 lbs/ maxloadpress
1379 kg/ 43 psi / 3039 lbs
1408 kg/ 44 psi / 3104 lbs
1437 kg/ 45 psi / 3168 lbs
1466 kg/ 46 psi / 3232 lbs/GAWR Rr
1495 kg/ 47 psi / 3296 lbs
1524 kg/ 48 psi / 3360 lbs
1553 kg/ 49 psi / 3424 lbs
1582 kg/ 50 psi / 3488 lbs

Can you explain the difference between the tire’s rated 750 kg at 42 PSI with your chart showing it lower? 750 x 2 = 1,500. Why does the chart show only 1,350 kg for the axle?

 

[jadatis]

That is because I build in a reserve, is 90% of 1500kg.
So if your axleload is 1350kg,you will search back and find 42 psi, and so use 90% of the loadcapacity calculated for 42 psi. This gives maximum reserve but still no bad comfort.
You need that reserve for things like.
1. Pressure loss in time

2. Inacurate measurement of pressure,
3. Misyudged axleweight
4. Incidental extra weight.
5.unequall weight R/L on the axle.
6.a bit higher speed used then 99mph for more the a few minutes
7.etc.

Now you dont need to do pre calculations like adding a reserve or deviding by 2. All done for you. Yust determine axleloads as acurate as possible, and look it back in my made list. Using 90% is the same as adding 11.11% to the axleload, and then look it back in a list for 100%, so 1500kg given at 42 psi.

But if you have other ideas about the reserves, write it, and if I cant convince you that my reserves are better, I yust change the reserves in my spreadsheet, and other reserve rols out.

 

[JohnB007]

Wow way above my head... lol.

For dumb ones like me, what does all that translate to if I reduce my 19 inch CC2 tire from 42psi to 37psi?

Is it safe? Expected range drop? Comfort? Tire wear?

 

[jadatis]

If that is the 107 loadindex AT 42 psi, from the first list I gave, 37 psi is even above as needed for GAWR rear, so wil give still verry acceptable actiradius of one battery filling, but better comfort.
Front then can even be lower.
Asuming you have the same GAWR's and weights as topicstarter ( disclaimer).
You dont want an expensive luxuary car, that has comfort of an old army truck.

 

[TomB985]

I like how you did this. As I understand it, you built in a 10% buffer into the load tables for each given PSI, then multiplied by two to get a conservative max axle weight.

Can you generate charts for the other factory load ranges?

21” Front - 98
21” rears - 103
20” Induction - 101
19” Gemini - 104

 

[jadatis]

I like how you did this. As I understand it, you built in a 10% buffer into the load tables for each given PSI, then multiplied by two to get a conservative max axle weight.

Can you generate charts for the other factory load ranges?

21” Front - 98
21” rears - 103
20” Induction - 101
19” Gemini - 104

The 21 inch front 98 ( loadindex) assuming they are all XL, already given in second list.
Can make for 2 in one list, if you give if in KG or LBS. Or do you want both.

About reserve for unequall weight.
I once determined by reactions about bumping, that if less then 85% of weight calculated with the ever to be constructed ideal formula for 99mph/160kmph, that then it gives a deflection of tire at wich comfort gets unacceptable.
Now if one side 85% used so still comfort acceptable, and the other side 95%, average 90% still some reserve. Is a 47.3%/ 52.7% weight division on the axle. Centrewear of tire, I estimate will probably happen when 60% of loadcapacity for 99mph used

My tirepressure story began for Recreation vehicles, wich have extreme weightdifferences sometimes, and in US they are often weighed per axle, better per axle-end. So mayby for Cars the reserves can be less.
But cars have more variation in loading.
RV weighed once, can do for years.

 

[jadatis]

Joined in an other topic on this forum, and pointed to this topic.
Was in the UK and Ireland part, so will give the lists for KG and LBS.

1 or 2 years ago Continental introduced the HL for High Load especially for the heavyer electric cars.
Is a tire with about 3 loadindex steps higher then same sise XL tire, but maxloadpressure still 42 psi/2.9 bar.
So its possible you will read HL in front of the sises. But then, to get highest pressure with comfort, you can use the XL list with 3 loadindex steps lower then given on HL, to my opinion.

First the 103 loadindex assuming to be XL/ reinforced/Extraload AT 42 psi.
And max reserve and max speed 160kmph/99mph

KG axleload/ cold psi/LBS axleload
812 kg/ 20 psi / 1791 lbs
847 kg/ 21 psi / 1869 lbs
883 kg/ 22 psi / 1946 lbs
918 kg/ 23 psi / 2024 lbs
953 kg/ 24 psi / 2101 lbs
988 kg/ 25 psi / 2179 lbs
1023 kg/ 26 psi / 2256 lbs
1058 kg/ 27 psi / 2332 lbs
1093 kg/ 28 psi / 2409 lbs
1127 kg/ 29 psi / 2486 lbs
1162 kg/ 30 psi / 2562 lbs
1197 kg/ 31 psi / 2639 lbs
1231 kg/ 32 psi / 2715 lbs
1266 kg/ 33 psi / 2791 lbs
1300 kg/ 34 psi / 2867 lbs
1335 kg/ 35 psi / 2943 lbs
1369 kg/ 36 psi / 3019 lbs
1403 kg/ 37 psi / 3095 lbs
1438 kg/ 38 psi / 3170 lbs
1472 kg/ 39 psi / 3246 lbs
1506 kg/ 40 psi / 3321 lbs
1540 kg/ 41 psi / 3396 lbs
1575 kg/ 42 psi / 3472 lbs/maxloadpressure
1609 kg/ 43 psi / 3547 lbs
1643 kg/ 44 psi / 3622 lbs
1677 kg/ 45 psi / 3697 lbs
1711 kg/ 46 psi / 3772 lbs
1745 kg/ 47 psi / 3846 lbs
1778 kg/ 48 psi / 3921 lbs
1812 kg/ 49 psi / 3996 lbs
1846 kg/ 50 psi / 4070 lbs

 

[jadatis]

Now for 101 loadindex /maxload 825kg/1819 lbs. AT 42psi so XL

KG axleload/cold psi/LBS axleload
766 kg/ 20 psi / 1689 lbs
799 kg/ 21 psi / 1762 lbs
832 kg/ 22 psi / 1835 lbs
865 kg/ 23 psi / 1908 lbs
898 kg/ 24 psi / 1981 lbs
931 kg/ 25 psi / 2054 lbs
964 kg/ 26 psi / 2127 lbs
997 kg/ 27 psi / 2199 lbs
1030 kg/ 28 psi / 2272 lbs
1063 kg/ 29 psi / 2344 lbs
1096 kg/ 30 psi / 2416 lbs
1128 kg/ 31 psi / 2488 lbs
1161 kg/ 32 psi / 2560 lbs
1193 kg/ 33 psi / 2632 lbs
1226 kg/ 34 psi / 2704 lbs
1258 kg/ 35 psi / 2775 lbs
1291 kg/ 36 psi / 2847 lbs
1323 kg/ 37 psi / 2918 lbs
1356 kg/ 38 psi / 2989 lbs
1388 kg/ 39 psi / 3061 lbs
1420 kg/ 40 psi / 3132 lbs
1452 kg/ 41 psi / 3203 lbs
1485 kg/ 42 psi / 3274 lbs/maxloadpressure
1517 kg/ 43 psi / 3345 lbs
1549 kg/ 44 psi / 3415 lbs
1581 kg/ 45 psi / 3486 lbs
1613 kg/ 46 psi / 3557 lbs
1645 kg/ 47 psi / 3627 lbs
1677 kg/ 48 psi / 3698 lbs
1709 kg/ 49 psi / 3768 lbs
1741 kg/ 50 psi / 3838 lbs

 

[jadatis]

XL LI 104 / maxload 900kg/1984lbs AT 42 psi upto 160kmph/99mph

Kg axleload/cold psi/ Lbs axleload
835 kg/ 20 psi / 1842 lbs
872 kg/ 21 psi / 1922 lbs
908 kg/ 22 psi / 2002 lbs
944 kg/ 23 psi / 2082 lbs
980 kg/ 24 psi / 2161 lbs
1016 kg/ 25 psi / 2241 lbs
1052 kg/ 26 psi / 2320 lbs
1088 kg/ 27 psi / 2399 lbs
1124 kg/ 28 psi / 2478 lbs
1160 kg/ 29 psi / 2557 lbs
1195 kg/ 30 psi / 2636 lbs
1231 kg/ 31 psi / 2714 lbs
1266 kg/ 32 psi / 2793 lbs
1302 kg/ 33 psi / 2871 lbs
1337 kg/ 34 psi / 2949 lbs
1373 kg/ 35 psi / 3027 lbs
1408 kg/ 36 psi / 3105 lbs
1444 kg/ 37 psi / 3183 lbs
1479 kg/ 38 psi / 3261 lbs
1514 kg/ 39 psi / 3338 lbs
1549 kg/ 40 psi / 3416 lbs
1584 kg/ 41 psi / 3493 lbs
1620 kg/ 42 psi / 3571 lbs/maxloadpressure
1655 kg/ 43 psi / 3648 lbs
1690 kg/ 44 psi / 3725 lbs
1725 kg/ 45 psi / 3802 lbs
1759 kg/ 46 psi / 3879 lbs
1794 kg/ 47 psi / 3956 lbs
1829 kg/ 48 psi / 4033 lbs
1864 kg/ 49 psi / 4110 lbs
1899 kg/ 50 psi / 4186 lbs
1934 kg/ 51 psi / 4263 lbs

 

[DavidWarb]

As many of us are using 255/50/19 tyres on 19 inch wheels to improve ride and cushion but why to keep the same pressure of 42 psi recommended by Tesla If tyre load rating is higher than original tyres?

I installed Michelin pilot sport 4 suv summer tyres on 19” Gemini wheels on my model Y performance 2022.
The new tyre rating is 107Y.

The original tyres on model Y performance are 255/35/21 98W and 275/35/21 103W

These tyres Load rating as per load chart corresponds to front-750 kg at 50 psi and rear 875 kg at 50 psi.
Now considering Tesla recommended pressure of 42.0 psi we can calculate the design load.

At 42.0 psi recommended pressure safe load on front axle is 1260 kg.max approx.
At 42.0 psi recommended pressure safe load on rear axle is 1470 kg max. approx.

Model Y performance maximum Laden mass is 2415 kg.Front axle max laden mass -1125 kg and rear is 1290 kg.

Even considering the max.max allowable loading limit for axle as per chart is F-1300 kg and Rear -1500 kg.So all this falls in 42.0 psi limit for original tyres.

If we consider the same design load of front - 1260 kg and rear 1470 kg then the psi required for 107 Y load rating can be calculated.
The load rating for 107y tyre is 975 kg at 50 psi.

So minimum safe front pressure for 1260 kg is 32.3 psi and rear pressure for 1470 kg is 37.7 psi.This pressure is sufficient to support the maximum limit of vehicle loading.

I kept 35.0 psi all round and the load they can support is 682.5 kg each.Total load support at this pressure is 2730 kg which is in limits.

At 35.0 psi the car drive is as good as a land cruiser or Nissan patrol.Anything above 35.0 max the ride is uncomfortable.The suspension are not suitable for comfortable suv ride at higher tyre pressures.

I am attaching some photos.Gents what is your suggestion on this.Am I wrong in any calculation?View attachment 928776
View attachment 928777View attachment 928778

Hi Shipley. I’ m here in the UK and I’ve had my new Model Y (standard RWD, so not the Performance model) for a couple of months and I’m considering changing my tyres to 255/50/R19 to improve the comfort of the ride. Can I check that you fitted yours to the front as well as the rear, and that you (or anyone else reading this post) haven’t experienced any rubbing etc or issues with the front set? Many thanks.

 

[DavidWarb]

Hi Shipley. I’ m here in the UK and I’ve had my new Model Y (standard RWD, so not the Performance model) for a couple of months and I’m considering changing my tyres to 255/50/R19 to improve the comfort of the ride. Can I check that you fitted yours to the front as well as the rear, and that you (or anyone else reading this post) haven’t experienced any rubbing etc or issues with the front set? Many thanks.

•Shippy

 

[jadatis]

Hi Shipley. I’ m here in the UK and I’ve had my new Model Y (standard RWD, so not the Performance model) for a couple of months and I’m considering changing my tyres to 255/50/R19 to improve the comfort of the ride. Can I check that you fitted yours to the front as well as the rear, and that you (or anyone else reading this post) haven’t experienced any rubbing etc or issues with the front set? Many thanks.

You could try out first, to lower the pressure with use of my list. Mayby that is already enaugh for better comfort.

And mind that wider tyre needs wider rimm. I made rimmwidth calculator, after contact with Vredestein, and uses ratio's from desighners guide of ETRTO.
Also aspect ratio is important in that ( the hight/width division, your /50 in the sizes).
AR /50 has less leeway from measure rimm then fi /80.