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I have been searching through the forums for the past couple of days but I keep finding conflicting information on this. I have Michelin PS4S tires on my e63s and I used to run them at 41/33psi cold, as the fuel door cap says but I get a lot of understeer when driving through backroads, so I read up on what the recommended tyre pressures for the PS4S are and it turns out it is mid 30s and after 38 they start understeering a lot (as explained by the person who designed them). I now have no idea what to do and would appreciate any input on the topic.
Is that the normal load or max load pressure? Tire pressure ultimately is a function of load. The heavier the vehicle the more load the tire has to be able to carry. FWIW, I run them at 33f/32r (normal load pressure as shown on my fuel door sticker) with my '19 C63S coupe, which is about 500 lbs lighter. 41 in the front vs 33 in the rear seems quite a discrepancy. Didn't think the E was so much more nose heavy. I never have understeer, but then again, my front wheels also don't have to share the grip between steering and propulsion. AWD fundamentally is more prone to understeer and the front diff with the clutch does add more weight over the front axle. FWIW, I've read that Michelin recommends about 36 psi hot pressure for track driving, so starting at 33/32 kinda gets me there. On a hot summer day it'll be closer to 40 psi hot. Starting at 41psi cold, I'm assuming your hot pressure will be quite high. Frankly, the E63S never was a canyon carver. It's more at home driving it in a straight line.
Last edited by superswiss; Mar 29, 2024 at 02:18 PM.
One more thing that might be of interest. I have switched to the BMW Star marked PS4S. BMW has worked with Michelin to make the PS4S closer in performance to the Cup 2. Since I don't drive in the wet very much, I appreciate the sharper focus on dry handling with the BMW variant. They are still very good in the wet, for example it's raining cats and dogs today and I had to go to a meeting. Car handled standing water and roads getting pounded by rain very well with no loss of traction at any point. After I had put them on earlier this year, it didn't take much driving for me to realize that the BMW PS4S is not your regular PS4S. Not sure if they are available in the sizes needed for the E63, but they happen to be available in the exact sizes I needed for my C63 coupe. Below is a great video that shows the differences between the regular PS4S and the BMW PS4S.
One more thing that might be of interest. I have switched to the BMW Star marked PS4S. BMW has worked with Michelin to make the PS4S closer in performance to the Cup 2. Since I don't drive in the wet very much, I appreciate the sharper focus on dry handling with the BMW variant. They are still very good in the wet, for example it's raining cats and dogs today and I had to go to a meeting. Car handled standing water and roads getting pounded by rain very well with no loss of traction at any point. After I had put them on earlier this year, it didn't take much driving for me to realize that the BMW PS4S is not your regular PS4S. Not sure if they are available in the sizes needed for the E63, but they happen to be available in the exact sizes I needed for my C63 coupe. Below is a great video that shows the differences between the regular PS4S and the BMW PS4S.
Good to know , looking up tires under a 213 doesn't net the bmw star ps4's . Did find pilot super sports with the bmw star in 213 sizing . Where did you source them if you don't mind me asking , sorry just noticed you have a C63.
Last edited by SilverE5588; Mar 29, 2024 at 08:21 PM.
Good to know , looking up tires under a 213 doesn't net the bmw star ps4's . Did find pilot super sports with the bmw star in 213 sizing . Where did you source them if you don't mind me asking , sorry just noticed you have a C63.
Yes, I have a C63, so the sizes line up with the BMW models. I sourced them from Tire Rack. They come up alongside the regular PS4S for my model and 19/20" staggered wheels.
One more thing that might be of interest. I have switched to the BMW Star marked PS4S. BMW has worked with Michelin to make the PS4S closer in performance to the Cup 2. Since I don't drive in the wet very much, I appreciate the sharper focus on dry handling with the BMW variant. They are still very good in the wet, for example it's raining cats and dogs today and I had to go to a meeting. Car handled standing water and roads getting pounded by rain very well with no loss of traction at any point. After I had put them on earlier this year, it didn't take much driving for me to realize that the BMW PS4S is not your regular PS4S. Not sure if they are available in the sizes needed for the E63, but they happen to be available in the exact sizes I needed for my C63 coupe. Below is a great video that shows the differences between the regular PS4S and the BMW PS4S.
From what I understand of tire pressure tuning, I would expect your configuration to have a high amount of understeer. The differential of your pressures from front to rear is way too great. I also think the cold tire pressures of your steer axle is too high.
Generally speaking, higher pressure in the rear compared to front will increase oversteer and lower pressure in the rear compared to front will decrease oversteer.
Since there are so many variables between cars and tires and how they are used, I don't think there is a number that works for everyone. I think tire pressure tuning for performance should be done by driver feel.
I suggest you drive a known road that you can drive hard on with your current configuration. Then set your pressures square (say 34 or 36 psi cold all around) and drive that same road again. Then if needed, you can tune your pressure differential from front to rear by increasing the rear pressures to increase oversteer or decrease the rear pressures to decrease oversteer.
FWIW, I run my PS4S's at 36psi cold all around and for me it's very well balanced and is a good combination of comfort while cruising and firm reactive performance driving.
If one really wants to tune the tire pressure then get an infrared thermometer and measure the tread temperature across the entire width of the tire. You want an even temperature from shoulder to shoulder. If the center is hotter than the shoulders, then the pressure is too high. If it's lower than the shoulders, then the pressure is too low. Adjust as necessary.
Generally one only goes to this length when driving on the track, and you pretty much should check it after each session. I attended an AMG driving event at the Nurburgring a little over a year ago and we hauled the GT BS around the track. During the last session as usual, the instructors took us on a taxi laps. They checked and adjusted the tire pressure after each couple of laps.
I just put these back on this past week, setting them to 37 front, 36 rear, although the sensors are reading 37 all around. If the stock TPMS are accurate I should simply drop them all to 36 or at least the rears to 36. I drive pretty sporty most of the time.
I based my PSI on reading this thread, so thank you! Last year they were set by the dealership at something like 41/36 or so, I think that's too high (and unbalanced between front/rear maybe?) based on driving sporty.
I just put these back on this past week, setting them to 37 front, 36 rear, although the sensors are reading 37 all around. If the stock TPMS are accurate I should simply drop them all to 36 or at least the rears to 36. I drive pretty sporty most of the time.
I based my PSI on reading this thread, so thank you! Last year they were set by the dealership at something like 41/36 or so, I think that's too high (and unbalanced between front/rear maybe?) based on driving sporty.
I'm interested in hearing what differences you may notice in handling and feel after the change.
When I first picked up my W213, I was throwing it around hard to get familiar with the handling and I was a bit disappointed that the handling was not as good as the W205 on coilovers I just traded in for the W213.
Within the new car excitement I didn't even think to check the tire pressures. They were 46 PSI all around (WTF??). I set them all to 36 PSI and I was surprised how much of a difference it made to this car. It then handled better than my W205 and had much more turn-in bite.
37 all round is giving me nice throttle lift oversteer to tighten a corner that has a touch too much bend for the speed. A thing of beauty. This is with horrendously loud and harsh Pirelli run flats.
I'm interested in hearing what differences you may notice in handling and feel after the change.
When I first picked up my W213, I was throwing it around hard to get familiar with the handling and I was a bit disappointed that the handling was not as good as the W205 on coilovers I just traded in for the W213.
Within the new car excitement I didn't even think to check the tire pressures. They were 46 PSI all around (WTF??). I set them all to 36 PSI and I was surprised how much of a difference it made to this car. It then handled better than my W205 and had much more turn-in bite.
Sometimes it's the simple things.
I'll definitely get back to you on that. I might (if I'm not lazy) slightly decrease my PSI by 1 or so to true 36 (sensors are saying 37ish) then I'll go for some test drives. Because you need more than one session, you know for, uh... verification purposes. And I'll report back.
So, given that all this work is done. And given that it is VERY vehicle specific. Where may we find the list of perfectly matched tires for our specific year, model and options?
So, given that all this work is done. And given that it is VERY vehicle specific. Where may we find the list of perfectly matched tires for our specific year, model and options?
intresting story. I shopped around at tire rack, tire discount, costco, sam's club etc. The most inexpensive place was at our local Mercedes Benz dealership (Feldmann's Import in Bloomington, MN).
The tires (PS4s M01), balance, install + 4 wheel alignment was $2000+ ish. Every where else was about $300-$500 more which is so odd.
I’ve gotten my last few sets of tires from the dealer when they run promo buy 3 tires get 1 free, all 4 tires don’t have to match, plus a small rebate. Price gets close to local stores or tirerack.
I had the same experience this year at a Ford dealer for our SUV. They found a couple screws in a sidewall and it forced the install of a set of tires. I have a place I trust, Ford was within 5 bucks of their price and cheaper than the internet.
If the dealers recognize that getting the vehicle in for tires gives them an extra look it becomes a bit of a Walmart 'lost leader' despite not being a loss... I'm sure not all will but its a fine comment.
I'm interested in hearing what differences you may notice in handling and feel after the change.
When I first picked up my W213, I was throwing it around hard to get familiar with the handling and I was a bit disappointed that the handling was not as good as the W205 on coilovers I just traded in for the W213.
Within the new car excitement I didn't even think to check the tire pressures. They were 46 PSI all around (WTF??). I set them all to 36 PSI and I was surprised how much of a difference it made to this car. It then handled better than my W205 and had much more turn-in bite.
Sometimes it's the simple things.
@Keith66 So I took a couple of "sporty drives" @ ~36PSI all around. Talk about fun! Compared to my last summer's pressures (~41f/36r) this hugs the road on fast & tight turns. Although turning my tires at stationary/low speeds is more difficult, I feel like that's just physics talking. I hope no one comes back and tells me something might be wrong with my car lol.
@Keith66 So I took a couple of "sporty drives" @ ~36PSI all around. Talk about fun! Compared to my last summer's pressures (~41f/36r) this hugs the road on fast & tight turns. Although turning my tires at stationary/low speeds is more difficult, I feel like that's just physics talking. I hope no one comes back and tells me something might be wrong with my car lol.
Excellent! Thanks for reporting back dude. I'm glad to hear this benefitted you also (and also I'm not crazy, lol). I hadn't noticed a difference in slow speed feel, but probably because I didn't pay attention to that.
I've spent many years focused on the hardware to improve handling and only recently have I realized that tweaking tire pressures can also have a great effect. And it's free!
I'm curious how one ends up with the wild difference between front and rear pressures that Mercedes recommends? I've never seen, or come to the same conclusion myself. Racetrack or not.
All I can come up with is some load calc on the front where more pressure is needed to produce a load spec.
Or that there's a turn-in or agility dynamic that requires that front end pressure to retain stability at speeds that aren't within non-German driving circumstances.
I'm curious how one ends up with the wild difference between front and rear pressures that Mercedes recommends? I've never seen, or come to the same conclusion myself. Racetrack or not.
All I can come up with is some load calc on the front where more pressure is needed to produce a load spec.
Or that there's a turn-in or agility dynamic that requires that front end pressure to retain stability at speeds that aren't within non-German driving circumstances.
Just guessing, but if you were to put the car on a scale and weigh each tire separately the weight bias of the car is likely toward the front. Motor being up there and not as much heavy things in the rear.
Then look at the front tire width versus the rear tire, narrower so less area in contact with the roadway. To support X lbs or kg of weight with Y square inches or meters of area, the pressure in the front tires will have to be somewhat higher in pounds per square inch or kilo pascals than for the rear tires.
The same sort of calculation is done for my F-250 and motorhome tires based on the weight distribution of the loads I'm carrying. Big heavy diesel up front in the truck with nothing in the bed is one set of pressures, fully loaded bed or trailer towing is a different set of pressures. Motorhome front tires run at a higher pressure than the rear because they are single versus duals in the rear, even though it is a diesel pusher with motor in the rear.
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