19” to 18” wheel, ideal tire pressures

[Jboyd215]

Hi all, looking for some advice on recommended Tire Pressures

I have a 2017 Audi S3 that originally had 19” OEM wheels with DWS 235/35/19 - 8width

After blowing out my tires from hitting a pothole earlier this year decided to go with 18” wheels with DWS 235/40/18 - 8.5width

The tire pressure sticker on my door reads 44 all around (supposedly for max load) but that was for my 19” wheels. Heard some recommend 38psi all around for 18” wheels, but also some say 38F and 35-36R and heard other numbers as well. I hear the Conti DWS are supposed to have a very soft sidewall and like to be inflated a little higher than normal but not sure where that lands me.

If it helps, here is the specs for my wheels and tires:

https://www.wheel-size.com/calc/?whe...cl=30mm&sr=0mm

ExtremeContact DWS06 Plus Tire Specs:
- 235/40ZR18
- Load Index: 95
- Speed Rating: Y
- Traction: AA
- Temperature: A
- Max Load: 1521 lbs
- Load Range: XL

[Rod Paine]

I had the same experience within 3 days of buying our 2019 Audi RS 3, when a pot hole did in the 235/35/19 left front tire. I installed Neuspeed RSe10 18/8.5 wheels with Michelin A/S3+ 245/40/18 and after quite a bit of back roads testing, I am running them 40 psi front and 38 psi back. Huge improvement indeed!

[Spinnetti]

Ideal for what? Potholes, handling, comfort? - Pressures different for each but It won't matter a huge deal. Given the understeery nature of these cars, I tend towards the 38-40 in the front, 35-36 in the back, but OTOH, higher pressure in the rear will make the rear rotate more and I bias to handling..

[Jboyd215]

Ideal for what? Potholes, handling, comfort? - Pressures different for each but It won't matter a huge deal. Given the understeery nature of these cars, I tend towards the 38-40 in the front, 35-36 in the back, but OTOH, higher pressure in the rear will make the rear rotate more and I bias to handling..

Is a good point, mostly want for handling and using the extra sidewall to help with potholes.

I tried running 38F and 35R but felt pretty mushy. Moved over to 40F and 38R last night, that felt much better.

[Boomerdw]

I have and always use the recommendation tire pressure on the door sticker. For 19” wheel it states 39F 36R. Look up for the 18” wheel. Further I tested the correct pressure in my previous C6 corvette. Put chalk across the tread and drive and roll forward a bit. If the chalk stays across the tread you are close. If it wears over in center your overinflated and if the edges show the caulk is worn then under inflated. I tested and ran the recommended psi and took tread depth information for a few thousand mile and later tried 5 lbs higher and ran them and took depth and it showed I was overinflated. I think the car is tested for proper inflation and noted on the door jam sticker. If you have unusual driving habits pay attention to the tire wear, it will tell the story both with inflation and Alinement.

It isn’t rocket science and the manufacturer has done the testing. You can tweak it some put will have to watch for wear, if it concerns you. For best all around performance use the recommended pressure. Potholes are best dealt with by paying attention to the road. Add a few lbs if it is a concern but do it in equal amounts all around.

[Spinnetti]

I have and always use the recommendation tire pressure on the door sticker. For 19” wheel it states 39F 36R. Look up for the 18” wheel. Further I tested the correct pressure in my previous C6 corvette. Put chalk across the tread and drive and roll forward a bit. If the chalk stays across the tread you are close. If it wears over in center your overinflated and if the edges show the caulk is worn then under inflated. I tested and ran the recommended psi and took tread depth information for a few thousand mile and later tried 5 lbs higher and ran them and took depth and it showed I was overinflated. I think the car is tested for proper inflation and noted on the door jam sticker. If you have unusual driving habits pay attention to the tire wear, it will tell the story both with inflation and Alinement.

It isn’t rocket science and the manufacturer has done the testing. You can tweak it some put will have to watch for wear, if it concerns you. For best all around performance use the recommended pressure. Potholes are best dealt with by paying attention to the road. Add a few lbs if it is a concern but do it in equal amounts all around.

1. OEM settings no longer apply when you change tire and/or wheel size
2. Tire wear isn't the only consideration. If making like the factory intended, then you wouldn't change the wheels or tires from OEM in the first place. When you make a change, you need to know what you are trying to do, and adjust the systems accordingly. Other than my R8 (and Touareg strangely enough), I've never driven a car I didn't modify extensively to make it drive how I want rather than a blah baseline that suits everybody that the OEM sells.

[Boomerdw]

1. OEM settings no longer apply when you change tire and/or wheel size
2. Tire wear isn't the only consideration. If making like the factory intended, then you wouldn't change the wheels or tires from OEM in the first place. When you make a change, you need to know what you are trying to do, and adjust the systems accordingly. Other than my R8 (and Touareg strangely enough), I've never driven a car I didn't modify extensively to make it drive how I want rather than a blah baseline that suits everybody that the OEM sells.

Ya I concur, my thought is predicated on the situation where a person would have to inquire what is the proper tire pressure. Anyone into track or strip will likely learn how to determine the needed pressure for a given situation. My thoughts where intended as a generic response for the common owner, if you will. Most people are interested ride quality and tire wear in use everyday on the streets. A small percentage of car owners every track or strip their rides, very small percentage. This is why I suggested the chalk method to find the best tire patch on road.

[morris39]

Ya I concur, my thought is predicted on the situation where a person would have to inquire what is the proper tire pressure. Anyone into track or strip will likely learn how to determine the needed pressure for a given situation. My thoughts where intended as a generic response for the common owner, if you will. Most people are interested ride quality and tire wear in use everyday on the streets. A small percentage of car owners every track or strip their rides, very small percentage. This is why I suggested the chalk method to find the best tire patch on road.

I like your idea of using chalk and in fact use it indirectly. I start with the sticker value, lower pressure in small increments and measure/observe the tire thread depth across the tire face. I will also try your way as it's faster. I have calibrated my pressures and find in general that for my service 3psi less than sticker worked for many of my cars. My criteria is as you say, comfort and wear.

I am skeptical about claims of real benefits of higher pressures (or higher perf tires) on street handling vs perception. Track days on a motorbike many moons ago convinced of the big gap between imagined and real effects.

You meant predicated?

[Rod Paine]

Now at 46,084 miles of which 33,180 miles have been very fast country back roads,
using Michelin Pilot Sport AS3+ on Neuspeed RSe10 18x8.5 alloy wheels and doing
so 3 days a week 10am-2pm only has proven to be a good series of runs thus far.

Tires are now through at 2.5 mm remaining tread depth and are being replaced
with Michelin All Season 4 as the Pilot Sport AS3+ has been discontinued. I'll
keep track of our back raod runs as I have in the past and will post our results
with these new Michelin tires. Our frequency of runs as summer moves in will
be less, simply to reduce tire wear during the summer temperatures.

[ChatYTB]

Ideal pressure 36 i have if u just driving on your own 40 if you have more than 2 people...