Here is the status:

97 I30t on Intrax Springs w/ KYB AGX. Tires are 225/50/16 Sumitomo HTR+ @ 44 psi (50 psi is max).

I was on the same rims/tires on my 96 w/ H&R springs w/ Tokico HP struts.

With the old setup, I was fairly comfortable. With the new setup, it is a little harsh. Should I trade out my springs for H&Rs or replace the tires w/ a 215/55/16 tire?

Other factors- the Intrax drop looks good and rides great on flat roads. The tires are a higher pressure (@44 psi) than most 215/55 tires will be, btu 44 is the proper pressure for this rim width.

Another factor- the Intrax are not wrapped all of the way up and will need to be pulled this summer to wrap for rubbing, b/c I am getting some noise out of them. Also, the tires will need to bve replaced in the next few months anyway.

With the OEM BBS 15" (215/60/15) the ride was not too bad- fairly close the the ride of the H&R combo, but a little bit more harsh.

Thanks for your thoughts.

 

It's gotta be the springs.

Isn't 44 psi a bit much??

 

I talked to Sumotomo's high-performance tech manager and he said that 80-85% of the max PSI is recommended on a 7.5" rim, so I am at the right pressure. Like I said, max is 50 psi for those tires.

I think that it is the springs as well, but with the look of the Intrax being what I want, do you think that switching to 215/55 tires this summer might be a good way to make it more tolerable? I will need at least 2 new tires by summer, so should I just do all 4? Or would it be best to ditch the Intrax and go to H&Rs and just replace 2 of the 4 tires?

 

I would try swaping the springs. A 215/55 tire is not going make any differene except not be as wide.

 

Sumitomo's high tech manager doesn't know much for obvious reasons. He must be use to BMWs where the normal tire pressure is in the 40s. Ours isn't. Unless you are autocrossing or roadracing you won't need pressure that high. Adjust your pressure according to your car's specifications:
http://maxmods.dyndns.org/index.php?TirePressure

Otherwise AGX are very harsh shocks, and is probably causing most of the problem. Members have even complained about AGX on H&Rs. Intrax are soft, my friend had them with tokico blues.

 

I was thinking that the 1/2 inch increase in sidewall height might make the difference and dull some of the harshness.

 

The tech manager was basing it on cars like a miata or a 3-series BMW. One thing that we do need to keep in mind is the the recommended psi on the max body is based on OEM-size and make of tire. Some tires have more sidewall stability ahnd require less tire pressure for structure, others have thinner sidewalls and require more pressure for rigidity.

I ran them at 32-35 psi and it was really soft and squishy...maybe I can drop the pressure a bit more (to 38-ish) and soften up the AGX a few clicks.

 

I thought that the shocks are one of main factors of ride quality.

Dropping PSI and moving to a smaller rim sound like a bunch of compromises to keep you from what you think you should do (or you might be avoiding?)

Would illuminas be the answer? Closer to your H&R tokico setup you said was ok. But that answer would be $$$. Note: I don't have Illuminas so I don't know the answer, just what we have read around here.

Mr.P

 

y not try dropping the air pressure to 32.
it will not cost anything

 

I agree that there is no up-front cost. But there is a cost in gas mileage and handling and perhaps unusual tire wear going from 44 psi to 32 psi with a tire that was designed (perhaps) for higher pressures.

I guess I am more focused on the engineering of the suspension parts than a hack type of fix with lowering the tire pressure.

But I guess that tires, like the AGX struts have stiffness settings.
A setting of 44 is stiff, and a setting of 32 is soft. At least the tires aren't bouncy and you know when they blow.

Mr.P

 

Stock tire pressure on a 4th gen with 16s is 33/30 from the best of my memory, that's what he should be running unless he has problems with the sidewalls rolling over. That's what I ran when I had 225/50/16 Potenza RE730s and I never had a problem with uneven wear. Running >40psi will most likely wear the center of the tire down very quickly.

I use to run 40-42psi in my 18s until I realized how much more grip AND ride comfort I got when I lowered it to about 35, which is what I should have been running in the first place.

Learn from those who learned the hard way.

 

As Drewm has already said, it's the AGX's that are causing your harsh ride. Replace them with Tokico Illuminas and you'll have a sweet ride. Drop your tire pressure down a bit too. Recommended tire pressure is 33F/30R. You shouldn't be much more then 3-5psi higher. The higher you are, the less tire contact patch you have on the road. Less contact patch means less traction. Don't let the feel of a hard tire fool you into thinking your car handles better.

 

Did you cut your bump stops? Intrax lower 1.75ish (correct if wrong) without cutting or using shorter bumpstops you don't have much suspension travel left.

44+ psi....ah...way high...you are close to 50psi hot....like Tom said max 5 psi over stock (cold)

What setting are do you have the AGX set at?

 

Definately lower your pressure a bit. Maybe even try 225-55/16s, which is what im running. Slightly bigger tire...




Eric

 

I am not trying to argue with you guys, because I am the one asking for assistance, but bear in mind that different tire designs are meant to run different pressures. Those of you running ~32-35 psi are most likely running that on tires with thicker sidewalls, thereby voiding the need for higher pressure levels to maintain sidewall rigidity. On a tire like the 730 or 950, for example, what is the recommended max pressure? Probably not as high as the 50 max on the HTR+.

I am definately dropping the pressure first, and I will fool w/ the AGX settings, but I don't want you guys to think that I am a moron for running 44 psi on those tires.

 

I just bought the car- not sure where the AGX are set, but the bump stops are intact and uncut.

 

I had Intrax and while they looked good, they reduced wheel travel to about nill. If you're running on uncut bumpstops then you're probably riding on them. I had to cut my bumpstops ~60-70% to make the ride better. The Intrax themselves are pretty harsh on anything, but a smooth road. My 1/2" higher H&Rs ride 20X better. It's a night and day difference.

As for tire pressure, the max pressure is the max "hot" psi. Running 44psi puts you very close to the max inflation on a hot tire (assuming ~48-49psi on a hot day once the tire is warm). I've had 215/55R16, 225/50R16, 235/45R17, 225/50R17, and 215/60R15. I've always found that the OEM recommendation of ~32/30psi always offers the best handling, ride, and wear.


Dave

 

I must agree with phenryiv1 though, some tires are made for a higher psi because of needing the more pressure for a stiffer sidewall. I just don't think that you can always go by the car's specs when you are not using the same type of tire that came on the car.

 

Max pressure on RE730s was 44psi, almost all tires have a max of between 44 and 50psi. All that number shows you is the maximum you should safely run to keep them from exploding.

Also keep in mind njmaxseltd runs the same tire as you (HTR+) and he runs the stock pressure. Or at least I remember him using that tire in the past. That tire should have a decently stiff sidewall already because it shows up as a "high performance tire all season"