Tire Pressure with aftermarket springs

[U_SHO?]

Correct Tire Pressure with Aftermarket Suspension?

Well this should be a basic question... The plate on the car says 35psi cold all around, but I got 225/55 16s and also have Eibach/Tokicos with all the suspension upgrades.

Does this change the manufacturer's recommended psi as it is recommendation based on the softer setup with 215/60 16s? The reason I ask is I just put on Eagle F1 GS-D3s and what got me started is that on TireRacks site they are rated up to 51 psi (most other tires are 44 psi max).

Tires stick great at 35 psi but I have a feeling that at the limit they are flexing just a bit so I was thinking to put more air in but don't want to mess the tires up too fast. Search on this didn't return much. Any thoughts? Thanks

 

[SHOZ123]

IMHO the plate on the car is only for a cushy ride and only relevant to OEM tires.

I always run the fronts at or near max inflation pressure and the rears 4-6 lbs under the fronts.

 

[U_SHO?]

Running them at max psi when cold is dangerous in my opinion! What you basically do then is run them over the max recommended pressure as soon as they warm up and they can abruptly break (read: explode)

Plus what does that do to your wear pattern? I think that is too much pressure, as for the ones I've got would be around 50 psi, no sirrrrrr

 

[olympic]

From what I've read, the D3's do have a fairly soft sidewall, so a little more air pressure may be necessary. The max PSI stated on the sidewall is the max recommended COLD air pressure. The tire manufacturer knows full well that the tires heat up when driven, so you are safe inflating the D3's right up to 51psi cold. But if you can get away with less pressure and still get the handling you want then do it. It'll save a little wear and tear on your tires, wheels and suspension.

 

[AutoSHO]

Yes, as Olympic said, max pressures are rated when the tire is Cold. It is perfectly safe to inflate them to 51 psi if that is what they're rated for.

 

[U_SHO?]

I'm confused now

Does more air = bumpy ride, bad wear in the center, but more stable cornering?

I remember some autocrossers put chalk marks on the side of the tire and deflate them up until the chalk is worn until the tread line on the side of the tire but not more than that. But this is way below max psi said on the tire...

What is then ideal combination? What should I shoot for in handling vs. wear?

Thanks for all the input so far

 

[olympic]

It all depends on the characteristics of the tire. Some will handle well with less pressure, some need more. You just have to experiment until you find what works best. You generally run less pressure on the street than on a road course or autocross. A slightly softer tire will improve ride comfort and absorb large bumps easier. You don't have to worry about that on the course so you run the max pressure you can to stiffen the sidewalls.

The guy with the chalk was trying to maximize the tires contact patch(very common in drag racing). Less pressure will increase the contact patch but soften the sidewalls also so it's a matter of balancing the two. Maybe his tires had very stiff sidewalls so he could still get good handling with less pressure.

 

[Hack]

Does more air = bumpy ride, bad wear in the center, but more stable cornering?

More air as in, over the maximum cold psi, would give you accelerated wear on the center of the tire. Likewise, an under-inflated tire will wear quicker on the outside. An over-inflated tire will not provide better handling, as the contact patch is reduced. Over-inflating may cause a slight increase in harshness, but the way a particular tire "rides" is highly dependant on the stiffness of the sidewall. The shorter the sidewall, the stiffer it will probably be. This is to keep your rims from being damaged by large potholes, curbs, etc. Also, the performance oriented a tire is, the more likely that the sidewall will be stiff. This is to keeping the contact patch from "squirming" under lateral loads(ie cornering).

As has been said already, I would inflate them to the manufacturers specification. It should also be printed on the sidewall of the tire, so you can doublecheck what Tire Rack told you.

Good luck!

 

[U_SHO?]

I was trying to contact GoodYear directly but I was too late so I'll have to try this tomorrow, so sorry for the delay. TireRack recommended what was on the car plate, you guys suggest much more (which I still cannot logically accept) and talked to another member who's got more posts than all of us(you) together and he is running RE750s at 29psi, maybe 30psi on a track day on the same suspension as mine. Everything less than that and his tires wear in the middle. I guess I'll have to find out about this the hard way, by trial and error :ruhroh:

I wouldn't close this topic yet, I would like more input from others and their experience. I think this is pretty important topic and even searching the internet doesn't give a scientific reason for more or less air. TireRack thinks the weight of the car is the same so pressure should stay the same... However, wider tires than stock make a larger contact patch and to keep all the same in pressure formula (pure physics p=F/S that is F=p*S) more contact patch takes less pressure to keep force the same. However, less pressure induces heat build up in the tire that is also bad. Much more pressure, the turning response is improved but the ride is really bumpy and there is a chance of teh tire exploding when hitting an unexpected pothole.

One racing site suggested car weight/100 + 2 psi on the heavier end so it's 36psig fr/ 34psig rear, which is close to what the plate says...

 

[U_SHO?]

GoodYear said 35 psi all around...

 

[Hack]

That sounds pretty realistic to me. The 51 psi maximum rating is probably just that, a maximum. I do not think I have ever owned any passenger car tires that required inflation to 40+ psi, but my fullsize Dodge truck tires are 45 psi.

Everything less than that and his tires wear in the middle.

That is strange. Are you sure he said less than that, and not more than that? I have never heard of accelerated wear on the center of the tread with underinflated tires.

 

[U_SHO?]

my goof, he said any more than that. But you got the point. Anyway, I trust Scott a lot. I did not mean to disrespect anybbody too. I'm out of town until Sunday. I'm trying 32 psi in my tires until then... just a test

 

[U_SHO?]

Hey everyone, tried tires at 33 cold all week long and in the morning (8am) on the way to work the ride was much more comfortable but as far as handling I would say it was a little sloppier, less responsive and a little less direct. However, on the way back from work it was still more comfortable than at 35 psi but now it felt really responsive and grippy. Also no abnormal tire wear so far...

Then, this weekend after being on the interstate for a while I stopped at my friends place and picked up some dust on his driveway and we could see that tires (especially rears) still had about almost an inch from each shoulder that was not in contact with the road (like they were still overinflated) so he used to have 96 SHO (with the same Gen3 wheels I have) and he told me recommended pressure on Gen 3 was 30 psi all around (COULD SOMEBODY WITH GEN3 VERIFY THIS PLEASE?). Anyway, I decided to drop the pressure to 30 psig cold and ride home on the interstate was very comfortable, and for the first time since I put Tokicos it seemed nice on the interstate, not too bumpy and all, but then I tried a corner at about 80 and the way the rear acted really scared me... Really loose and wobbly and all around I could feel the sidewalls flex. On one open stretch I tried to quickly merge lanes and the steering feels really disconnected almost like if I had a flat tire. Also, after the ride all 4 tires felt really hot that is definitely a sign of underinflation...

1) I would still like to hear from you how do you decide what pressure to run as obviously low pressure makes a big difference in how comfortably the car rides on the interstate but gives more side play for the sidewalls... My old tires at 35 psi hadled good, very bumpy, but wore a lot in the center so I was trying to figure something better with my nice F1 GS-D3s...

2) Finally, how do you compensate for a temperature difference in the morning and afternoon? 33 psi that felt low in the morning, at 5 pm was over 36psi and felt good and responsive. Does that difference average out the tire wear as when it's cold it wears the outside more and then when it warms up it wears in the center more?

3) I did a lot of reading on this on Tirerack's site and it talks a lot about carefully checking pressure in the morning before any ride to match the factory specs, but then I don't really have the factory setup any more... Also there, I found out that BMW 330i with similar weight, suspension like on mine, and 225/50 16s recommends 29 / 33 psi front/rear... again an argument to lower our pressure from 35 psi. And why keep the pressure the same all around and not put more in the front?

Sorry for the long post but I waited for a week to get some more experience running the lower pressure

Thanks for all the help so far

This is killing me :headbang: