no traction over bumps

[joe86]

I have noticed that over small bumps when accelerating my tires lose traction. Also over large rolling bumps on the freeway while accelerating my tires loose traction. my tail end has actually kicked out doing 70 mph at wot. (dsc off of course). It feels like my shocks just aren't keeping my tires in contact with the ground very well. Maybe the biltsein sports are too stiff? Can to much rear toe-in cause this? When my car was stock it handled bumps much better. Does any body else have this problem? Is it just a negative effect of all the mods i've done to my car (handles very well on smooth road). I have Michelin pss 225/255 with about 4mm of tread left. tire psi at 38f 36r

[The Wind Breezes]

Handling is a compromise unless you have really advanced dynamic suspension, and then your compromise is complexity, cost, and maybe some additional weight.

Stiffer suspension + bumps = less traction. What's best for a smooth road will suck on real-world streets.

[joe86]

I found that my rear shocks were riding on the bump-stops. Ordered dinan rsm's and now I have much better traction and stability over bumps. I highly suggest that anyone with bilstein sport shocks and swift specr springs get the dinan rear shock mounts.

[tuj]

You have toe-in at the rear?? Why? I believe the shop spec is for slight toe-out at the rear.

How did you find out you were riding the bumpstops? (zip-tie method?)

[MightyMouseTech]

Originally Posted by tuj

You have toe-in at the rear?? Why? I believe the shop spec is for slight toe-out at the rear.

Uh, no, the factory spec is not toe out.

[tuj]

Originally Posted by MightyMouseTech

Uh, no, the factory spec is not toe out.

Would you care to share the factory specs then? I went through every post you have made where the word 'toe' was mentioned and many many E82 setup sheets. Almost all of them show rear toe out to some degree. Maybe I'm reading the specs wrong.

What is the factory spec rear toe?

EDIT: 0.2 in per wheel? Spec is total 0.2-0.4 IN?

This is strange to me. I have always read:

Lower horsepower cars tend to use zero toe in the rear, for the same drag reduction reason. Higher horsepower cars may run positive rear toe to avoid unwanted rotation under throttle when exiting corners.

[chris82]

Originally Posted by joe86

I found that my rear shocks were riding on the bump-stops. Ordered dinan rsm's and now I have much better traction and stability over bumps. I highly suggest that anyone with bilstein sport shocks and swift specr springs get the dinan rear shock mounts.

Did the comfort improve going over bumps?

[MightyMouseTech]

Originally Posted by tuj

Would you care to share the factory specs then? I went through every post you have made where the word 'toe' was mentioned and many many E82 setup sheets. Almost all of them show rear toe out to some degree. Maybe I'm reading the specs wrong.

What is the factory spec rear toe?

EDIT: 0.2 in per wheel? Spec is total 0.2-0.4 IN?

This is strange to me. I have always read:

Positive toe is toe IN, negative toe is toe OUT. Negative toe will make the car very, very hard to control under hard acceleration.

Easy way to remember.

When you walk up behind a girl and you put your hands on her waist, if your hands go out, that is negative, if your hands go in, that is positive.



Negative Toe



Positive Toe

[MightyMouseTech]

Originally Posted by tuj

What is the factory spec rear toe?

Factory toe spec for the 1er's in the rear:

1M: 0.02 to 0.15 deg (toe in per wheel)

135: 0.10 to 0.20 deg (toe in per wheel)

[tuj]

MightyMouseTech nice explanation!

I have always preferred 0 toe both front and rear on my previous cars (Miata & RX-8), but obviously those have completely different suspensions. What do you think about 0 toe on the 135i for the track?

[MightyMouseTech]

Originally Posted by tuj

MightyMouseTech nice explanation!

I have always preferred 0 toe both front and rear on my previous cars (Miata & RX-8), but obviously those have completely different suspensions. What do you think about 0 toe on the 135i for the track?

Thanks.

On my own car, I run 0 toe in the front, and now running 0.05 deg toe in (0.10 total toe in) on the rear of my 135. Basically, an aggressive 135 rear toe (outside of specs) but pretty normal for the 1M. I can get the back end to come around fairly easy at this setting, so do not want to make the car more unstable for street driving. Have experienced toe out on the car (alignment was out of spec) and it was zero fun. Spent the whole time chasing the back end when WOT.

[HP Autosport]

Originally Posted by joe86

I have noticed that over small bumps when accelerating my tires lose traction. Also over large rolling bumps on the freeway while accelerating my tires loose traction. my tail end has actually kicked out doing 70 mph at wot. (dsc off of course). It feels like my shocks just aren't keeping my tires in contact with the ground very well. Maybe the biltsein sports are too stiff? Can to much rear toe-in cause this? When my car was stock it handled bumps much better. Does any body else have this problem? Is it just a negative effect of all the mods i've done to my car (handles very well on smooth road). I have Michelin pss 225/255 with about 4mm of tread left. tire psi at 38f 36r

Toe in promotes stability so I don't think that is the case. If you examine the rear suspension, it actually adds toe in under compression.

What you may have may be dampers, are they bottoming out or running out of compression travel? In addition, if the dampers are too stiff and don't have a blow off feature(Dual Flow Valve, Digressive valving or other names).

Stock springs and anti roll bars?

[The Wind Breezes]

To add to my reply from a year ago you also need good suspension travel to deal with bumps. This car has none. No joke, my range rover keeps MUCH better contact (not peak traction) when hauling ass over some of our extremely broken roads.

[Olgeezer1]

Have you done the rear subframe bushings? That's what it sounds like to me. Really shows up if you hit some bumps mid-corner. Rear gets really loose. I've done the Bilstiens and just upgraded the brakes, RSFB's are next. Also agree with 0 toe in front and slightly in, in the rear.

[joe86]

Originally Posted by chris82

Did the comfort improve going over bumps?

Yes, mostly over medium and large bumps on the highway

[xijonix]

Swapped out my rear subframe bushings from some much higher quality stiffer bushings and it made a good deal of a difference personally so I'd say consider that if your running stock 135i rear subframe bushings. Before my car use to dance around road creases when accelerating and the rear use to follow imperfections like line cracks in the road now it's much more predictable rear wise.

[PrematureApex]

Originally Posted by MightyMouseTech

Easy way to remember.

When you walk up behind a girl and you put your hands on her waist, if your hands go out, that is negative, if your hands go in, that is positive.

OK, you win the internet for today.