tramlining and tire pressures
 

I was driving the 4.6is last night on a stretch or highway that was particularly bad for tramlining. Pretty annoying. I know all X5's the wider 19-20" tires do this to some degree, and the 4.6is is more of a worse case. I am runinng Yoko Advans with about 75% tread on them. unsure on alighment, but it was done when these tires were installed.

Anyway - driving that same stretch of road in my Audi with 235-40-18 tires shows no tramlining effect at all. But the X was pretty bad. then on another road that was smoother it was much better, so it is very much road dependant.

Are there tire pressures that will reduce the effect?

I am running 33-34 front and 36 rear currently. Maybe balance it out to 32 all around? Or is this effect more due to front tire than rear?

I'm running 32-33 in the front and 34-35 in the rear. I have the style 132 19" so there a little narrower then your tires at the front and rear but I haven't noticed any "tramlining" ever before. Maybe lowering the pressure a little will help.

While the lower tire pressures will help, the tramilining on certain road conditions is all but unavoidable with the wide, low profile tires and aggressive camber and tow settings of BMW sport suspension. Driving the same stretch or roads in my 4.6is vs a 3.0i standard suspension and 17" rims is a completely different driving experience. The 3.0i is smooth on the straight roads, the 4.6is is on rails on the turns!

Unfortunately you lose one aspect for the other...

p.s. I run my tires at 34-36 front and 38-40 rear for handling in the turns.

hmm - well I could probably give up a bit of the performance in turns - this thing is still a boat compared to my S4. What are the factory toe settings? I am thinking maybe dial that back a bit. I am guessing they must run a bit of toe out? bringing that back to 0 may help and should not hurt cornering performance much.

those numbers sound too low. whats the recommend psi on the tire? i keep mine high, in the 40's. as far as tramlining and psi, i would have to say that psi plays little effect on the tramlining. however, a low psi can cause uneven tire wear and if you have uneven wear you'll notice it more. if you can, rotate the tires. (i'll assume from left to right as they are staggered.) 75% left means 25% driven so its time for that anyhow.

BMW doesn't use negative toe on anything, still positive. And the more positive end of the specs makes it more stable on the highway, closer to 0 will be more prone to wander, but longer tire life and a hair better fuel economy.

A quick google search will bring up all kinds of info on tramlining and what has affects on it. I know tirerack has a page on it, probably wiki too. I'm sure other forums discussed this as well, good to broaden the search for the big picture. But from what I gather it is just the price to pay for bigger wheels.

Well - I am familiar with the effects - I have owned Corvettes with 285/315 and 265/295 tires and they do a similar thing. The E39 M5 did not do it much at all, and those tires are fairly wide, although quite not as wide as the 4.6is.

I just eliminated a lot of my tram'ing by installing the H&R camber bolts in the front and pulling my negative camber back to just -0.6 degrees. When it was more than -1.0 (-1.4 on one side) the truck followed every little road crown.

It isn't the tire size or the short sidewall entirely. My old Audi allroad with 255/40-18 tires never trammed like the X5 did. Even when I ran R-compound track tires on it. And my 528 with the 18" M5 wheels doesn't tram a bit. But the 19" Michelins on the X5 will follow every road imperfection if you have too much negative camber up front.

Good to know. So is camber not adjustable stock then? Is that why you need the camber bolts. Do you mean bolts or plates?

Correct, camber and caster aren't adjustable in the front. The H&R concentric bolt replaces the upper of the two large bolts that attach the spindle to the strut, and is concentric so as you turn it, you change the camber.