[flash]

We all know that these cars are prone to tramlining. For those of you who don't know what tramlining is, it is the tendency for the car to dart about or wander on the road, constantly chasing every rut and groove.



Obviously the suspension bushings and such need to be up to snuff, and we won't get into that in this. We will just focus instead on the tires.



New tire compounds and the performance tires we have today don't help our problem. Exactly the things that make the newer tires grab better, also contribute to tramlining. If you run lower profile tires, or wider tires, it gets worse. Too much negative camber will also add to this problem, as will toe out settings.



Tire pressure is also one of the largest culprits here. Running a tire pressure that is too high will cause the tires to wander, but so will one that is too low.



Now that it is winter, tire pressures generally drop 3-4 lbs over what they were during the summer. It's sort of the reverse effect of a hot air balloon. Dropping tire pressure can help you on the track, as it helps with grab and expansion, but it can also lead to tramlining. Bumping up your pressure a pound or two over your summer setting can help maintain the tire pressure and help cure tramlining. In the winter you need to set your cold tire temps a bit higher than you do in the summer, because the tires won't expand as much, due to the lower ambient and road temps.



So, check your tires to make sure you haven't lost your summer pressure, and then, if your car is tramlining, add a pound or two.

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[cosimo]

What tire pressure do you reommend for winter driving (east coast)? I am running Toyos 245x45 front, 265x45 rear.

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[flash]

i have no experience with toyos. every tire reacts differently, so your starting point could easily be a couple of pounds different than a different tire. you would have to play around to see. the point of this tech tip was to say that whatever you found to be the optimal cold tire temp for summer, that first you need to check to see that the pressures are there cold, and then to bump it up a pound or two above the summer pressure to allow for the lesser expansion in the winter.



then, if the car is tramlining, try taking it up another pound or two from your cold temps in winter or summer.



but, just as a starting point, if it is a summer high performance tire, in the winter i would start at 37 or 38 cold all around and see how it behaves. if it is an all season, i have no recommendation. i've never run an all season tire on anything.

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[DaveN]

That's because you don't have any seasons! Yea, I'm jealous :-P

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[flash]

true enough. we only get about 14 days of rain here. i barely have to worry about wet traction, let alone any other kind of weather related tire issues.



that being said, i am extremely happy that i can finally get the conti sport contact 3s off the SL550 next week. those things are slicker than deer guts on a door knob in the wet.

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[cosimo]

Thanks, Flash. I do have trammling on some highways. I normally run 34 psi, so I will up it to the 37/38 and see the effects.

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[94SilverCab]

Cosimo, I ran 36 psi in my Toyos...the key was to check the pressure very regularly because the difference of 2 psi was enough that even with my uneducated sensibilities I could tell the difference.



Jay

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[tamathumper]

I'm probably one of the few on the forum who knows exactly how slick deer guts on a door knob can be?

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[flash]

as an update to the source of tramlining, the caster blocks are a primary source as well. when they go bad or get soft, it makes for toe set change as they deflect. this results in tramlining.



as it turns out, i have another worn out spherical bearing unit. that makes now both of the original ones gone bad in less than 30k miles. these are definitely not suited to street use. i am going back to OEM.

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[MCL968]

Question for the group, my Toyo Proxes say 50psi max, at a certain load limit. But, there is no minimum or normal pressure range on the sidewall. I am running them at 46. Should I use the max as the norm and run them at 50?

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[flash]

WOW! that is WAY too high.



start at 36 and go from there, seeking a pressure that results in a 4psi bump from cold to hot. you should end up somewhere between 34 and 38.

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[MCL968]

Thanks Flash, they looked better at 35-40. Is there any reason they don't put on typical pressures and not max on HP tires? The tires on our other cars tell us what the pressures should be, not what they shouldn't be.

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[flash]

they don't want you to blow them up. that could cost them money in lawsuits. the pressure you set a tire to is dependent on the make, model, weight etc of the car, and can vary widely. i've never had a tire for any car that says "set it here". they've all said "maximum". it's not like bicycle tires.

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[tryan]

The old school method is to run a chalk line across the tire but Porsche now requires little arrows on the edge of the tire to help set the pressure for your set up on factory approved rubber. There are a few videos online of how the contact patch changes with overinflation/underinflation at varying speeds.



Speed ratings are based on tire deflection(heat) so ideally one would have different optimal pressures depending on the tire. I go with the door sticker recommendation then plus two for extended high speed driving..... I am pretty anal and some cars are only driven once a month so I do a preflight check most of the time. 2psi can make a difference between doin' a high side and close ones on a sport bike so yeah, take the time and check them before every ride.

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[ds968]

Hopefully the door sticker on a Porsche is a good indicator of the ideal tire pressure, but I can say the one on our Nissan Pathfinder is suspect ( to say the least ) : it recommends 26 psi . On a SUV ?!! I thought that low of a tire pressure on a roll-over prone SUV is begging for ...a roll over , if you have to make a sudden maneuver or on a sharp turn, etc. When I asked the Nissan dealer the service manager bozo said the lower the tire pressure ( on any car ) the more stability . So for many , many years I've driven the 968 with around 28 psi , and while it felt a lot more planted I later learned that's a pretty deceiving seat of the pants thing, and tire-road contact coverage works differently. I have Michelin PS 2 on my six speed and one time when I was down at flash's house about five or six years ago he took temperature measures of the tires - we determined that on my suspension set up and with those tires the fronts should be at 31 - 31.5 and the rears at 32 - 32.5 cold.

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[flash]

even that can be misleading. keep in mind that when we did that, it was the heat of summer. the road surface was well over 100 degrees. ambient temp and road temp is everything when setting tire pressures. as an example, i have to set my winter pressures 3-4lbs higher than my summer pressures.

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[ds968]

Ah, good to know.

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[MCL968]

I don't have a door sticker on the 968. Were these put on the early 92's? It's been a long time since I had a car this old; I don't even remember if cars had door stickers on them in 92.

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[Bulti]

Mine says 2.5 bar (36 psi) front and rear.



I put in 2.7 for winter tyres (as recommended by the tire manufacturer). Not enough pressure will make the tires wear out faster and is bad for fuel comsumption, so I never go lower.

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[prj24149]

My 93 has the tire pressure sticker on the inside of the petrol fill cover.

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