[MidtownMike]

Hi all, for my BMW 320i B48 M Sport I recently bought a set of 18" winter wheels and equipped them with new 225/45 R18 Continental Wintercontact TS830P SSR runflat tires with BMW certification (Star mark).

Now it turns out that BMW recommends a significantly different tire pressure on the door frame sticker than Continental does in their vehicle specific table:

BMW recommends:
Front: 2.2-2.7 bar / Rear: 2.4-3.2 bar
Continental recommends:
Front: 2.8-3.0 bar / Rear: 3.0-3.5 bar

Does anybody know how the difference can be so big? Basically Continental pressure range starts where BMW stops on the front tires... I am a bit confused. Who knows best? the tire manufacturer or the vehicle manufacturer?

[COKen]

The recommendations from the car builder or the tire manufacture are general starting points. Pick one, keep an eye on your tire wear and adjust as needed.

[MidtownMike]

Thanks COKen,
I understand that these are starting points, but what I am trying to understand is why the ranges given by the vehicle manufacturer and the tire manufacturer are so radically different? Especially since these are official BMW certified tires?

[Billfitz]

The recommendations have different criteria. The one from BMW is the range within which their testing gives the best result irrespective of the tire model. The one from Continental is the range within which their testing gives the best result for specific car models. Where the two overlap is a prudent recommendation. Is the Continental chart specific for this winter tire? Winter tires typically work better with higher pressure, which gives better grip on fresh snow and slush, while compensating for the wider daily temperature swing.

[johnung]

Originally Posted by MidtownMike

Thanks COKen,
I understand that these are starting points, but what I am trying to understand is why the ranges given by the vehicle manufacturer and the tire manufacturer are so radically different? Especially since these are official BMW certified tires?

Don't overthink it. Could be government issues, wear issues or mileage issues involved with either of specs from the car or tire manufacturers. Just start with car door pillar tire pressures and adjust from there. If it really drives you bonkers then buy a tire pyrometer to measure the temperature across the tread. And post the results.

[MidtownMike]

Thanks Billfitz and johnung for the suggestions and explanation.
Tire wear, fuel mileage and braking performance are exactly why I am wondering what recommendation to follow. Tire wear can't be measured easily over a short period of time with no reference material; fuel mileage is affected by too many factors (temperature, A/C etc); and I don't feel like doing maximum brake tests with my car on the open road.
I would expect that during the Star mark certification process BMW and Continental would collaborate to come up with a unified recommendation, but clearly that is not the case. Unfortunately the recommendations don't even overlap in some cases. Too bad...

[2017F30]

Originally Posted by MidtownMike

Thanks COKen,
I understand that these are starting points, but what I am trying to understand is why the ranges given by the vehicle manufacturer and the tire manufacturer are so radically different? Especially since these are official BMW certified tires?

BMW’s desired fuel mileage is also predicated on certain pressures.

Your specific climate and desired performance is more crucial than fuel mileage down to the decimal point.

[Billfitz]

Originally Posted by MidtownMike

Tire wear, fuel mileage and braking performance are exactly why I am wondering what recommendation to follow.

All three of those are better served with higher pressure. The negative would potentially be tread life, if the higher pressure results in faster wear in the center of the tire. I always run a few PSI higher than the car manufacturer recommendation, which is often geared towards a more comfortable ride.

[Skyhigh]

Higher pressure for more comfortable ride!? Think this through....

Tire pressure plays a role in much more than just range, fuel-economy and comfort. Traction and phenomenons such as aqua-planning are heavily influenced by the tire pressure.

I stick to the recommendation on the door frame. I have no reasons to reinvent the wheel, literally.

[MidtownMike]

I think Billfitz meant that the (lower pressure) vehicle manufacturer recommendation is often geared towards comfort.
I have been running the middle of Continental's (higher pressure) recommendation range for about a week now, which resulted in a very bouncy ride with vibrations.

Today I brought the pressure down to about the middle of BMW's recommendation range, which feels a lot better, so guess I will be sticking to that.

I would not think that climate should influence the pressure. Just choose a pressure which works and stick to it throughout the year. To keep it constant, just inflate when it gets colder in winter and deflate as it gets hotter in spring/summer.

To my knowing, braking performance is negatively affected by a higher than recommended pressure, since the contact surface area with the road decreases?

All this does not change the fact that I'm surprised that the recommended ranges are so far apart for the vehicle manufacturer and a certified OEM tire manufacturer. BMW and Conti need to get their acts together.

[rjd_F30]

I'd assume that BMW makes pressure recommendations based on the tires that the car came with. Seeing as you're not using those anymore, I'd go with the company that makes the new tires you're using, i.e. Conty.

[MidtownMike]

That was exactly my train of thought when I chose to initially inflate to Conti pressure , however it feels way too bouncy when driving.

The car originally came on 19" Styling 704M wheels (staggered) with OEM BMW GoodYear F1 Summer tires.
For winter I bought a set of 18" Styling 707 wheels (square setup as recommended for winter) and deliberately chose Conti OEM BMW tires because BMW voids warranty on drivetrain when using non-OEM tires. That is why I would expect that there would at least be some overlap in the recommended tire pressures.

[Billfitz]

Originally Posted by MidtownMike

I think Billfitz meant that the (lower pressure) vehicle manufacturer recommendation is often geared towards comfort.

Correct.

BMW voids warranty on drivetrain when using non-OEM tires.

Incorrect.

[dmaxdmax]

I'd honestly try the front tires at the pressure for fully loaded, and the rear somewhere in the middle of the range...so like 35 and 41...and see how it drives. I find doing that makes my car neutral and amenable to throttle steering. I don't like understeer.

[MidtownMike]

The head of sales at the BMW dealership where I bought my car (BMW premium pre-owned) told me that BMW AG refused warranty when one of their customers had a damaged differential. The reason they gave was that the customer had been running on tires that were not BMW approved, i.e. had no OEM star mark certification. Could it be that warranty conditions here in the European Union are different from those in the US? Here all major tire sellers have the option to filter for BMW OEM approved tires on their websites. Mercedes Benz has a similar approval/certification program.

[Wires]

Originally Posted by MidtownMike

The head of sales at the BMW dealership where I bought my car (BMW premium pre-owned) told me that BMW AG refused warranty when one of their customers had a damaged differential. The reason they gave was that the customer had been running on tires that were not BMW approved, i.e. had no OEM star mark certification. Could it be that warranty conditions here in the European Union are different from those in the US? Here all major tire sellers have the option to filter for BMW OEM approved tires on their websites. Mercedes Benz has a similar approval/certification program.

Unless they were radically larger width, etc, I cannot see how they would be able to void warranty on a differential.

...or.... they are doing a fear mongering tactic to make you buy tires from them.

Keep in mind, higher tire pressures also reduce fuel consumption (less drag). BMW will most likely have their numbers biased high to help meet regulatory commitments.

[MidtownMike]

Originally Posted by dmaxdmax

I'd honestly try the front tires at the pressure for fully loaded, and the rear somewhere in the middle of the range...so like 35 and 41...and see how it drives. I find doing that makes my car neutral and amenable to throttle steering. I don't like understeer.

Those values are exactly the middle of the range as recommended by BMW for winter tires, and happen to be exactly what I have set my pressure to today. Feels wayyy better than Conti's recommended pressure for my vehicle. Conti's high pressure was causing bouncing, vibrations and my car was more prone to breaking out in corners due to the smaller road surface contact area.

[MidtownMike]

Originally Posted by Wires

Unless they were radically larger width, etc, I cannot see how they would be able to void warranty on a differential.

...or.... they are doing a fear mongering tactic to make you buy tires from them.

Keep in mind, higher tire pressures also reduce fuel consumption (less drag). BMW will most likely have their numbers biased high to help meet regulatory commitments.

One could argue that BMW star rated tires have lower or controlled tolerances when it comes to deviations in rolling circumference, which could play a role in differential wear and tear. This is especially an issue on Xdrive vehicles.

Regarding tire pressure: BMW's recommendation is a substantially lower pressure than Conti recommends in their chart, so in this case it is not a matter of BMW trying to reduce rated fuel consumption. Of course it could be that Conti tests their tires at a unrealistically high pressure to get a better fuel economy rating, which is important selling point for tires here in Europe.

(Today's fuel price in the Netherlands: 9.10 USD/gallon for non-premium unleaded 95 RON E10 .)

[rjd_F30]

Originally Posted by MidtownMike

That was exactly my train of thought when I chose to initially inflate to Conti pressure , however it feels way too bouncy when driving.

The car originally came on 19" Styling 704M wheels (staggered) with OEM BMW GoodYear F1 Summer tires.
For winter I bought a set of 18" Styling 707 wheels (square setup as recommended for winter) and deliberately chose Conti OEM BMW tires because BMW voids warranty on drivetrain when using non-OEM tires. That is why I would expect that there would at least be some overlap in the recommended tire pressures.

Keep in mind that the bounciness could just be a characteristic of the tire, not it's pressure. All tires will ride/perform differently. My reco is to go with Conti pressures.

[eleven11]

All good points given in your replies. My initial thought is the values recommended by Continental are for winter conditions (hence the snowflake icon), which generally call for higher pressures (as noted by Bill).

[Skyhigh]

Originally Posted by eleven11

All good points given in your replies. My initial thought is the values recommended by Continental are for winter conditions (hence the snowflake icon), which generally call for higher pressures (as noted by Bill).

There are winter tires (snowflake, M+S) and summer tires.
The recommendations both on the door frame and from the manufacturer are for the respective tires and condition, grouped correspondingly.

There are no recommendations about how to drive summer tires in snow or winter tires in the desert. It is recommended not to…

There is also no recommendation to readjust pressure once you go over a patch of ice or snow and back when driving over a dry road. Winter is winter and the more critical case applies conservatively.

All-year tires are typically a compromise in all directions and not reflected.

[Wires]

Originally Posted by MidtownMike

One could argue that BMW star rated tires have lower or controlled tolerances when it comes to deviations in rolling circumference, which could play a role in differential wear and tear. This is especially an issue on Xdrive vehicles.

Regarding tire pressure: BMW's recommendation is a substantially lower pressure than Conti recommends in their chart, so in this case it is not a matter of BMW trying to reduce rated fuel consumption. Of course it could be that Conti tests their tires at a unrealistically high pressure to get a better fuel economy rating, which is important selling point for tires here in Europe.

(Today's fuel price in the Netherlands: 9.10 USD/gallon for non-premium unleaded 95 RON E10 .)

The star typically means that they meet all the performance specifications set forth for BMW. So the car handles and drives just like they designed it too. Tires wear over time, so there is a bunch of change to rolling circumference over time.

When you buy a new vehicle, the tires you get might not be the same as what a tire shop sells you. I had an Acura that came with Michelin MXM4's. Reviews always had them as amazing tires, I found them to be junk. Talking to the tire shop, he said "you got to be careful. Even though they are the same model, OEM's tend to have the tire supplier skip processes in longitivty, wear, traction to reduce cost. You'd be better to sell your new tires and replace with the same model from a tire shop". But, with the BMW star rated, you get the same tire OEM as the tire shop.

As for pressures, I'd pick the BMW one, and see how it rides and handles. If they are too low, it's going to feel like it's riding on marshmellows. Too high and it's harsh, and feels like it's on rails darting around.

Yeh, and fuel price is a bit ridiculous right now. Our equivalent is about $7.50USD/gallon right now. Normally it would have been around $5-5.50.