What rear sway to balance front?

[Little1er]

Hey Everyone,

I'm running BMW performance suspension with the included upgraded swaybar and all M3 bits for the front with 2 degrees of camber.

I'm about to install a Quaife, powerflex subframe and differential bushings and wondering what sway bar to use to balance the car now. I'm thinking either the 15mm bar for the e90 convertible or the 20mm from the m3 coupe.

I'm open to other recommendations and just looking for some guidance for what others have used and liked.

[HP Autosport]

Originally Posted by Little1er

Hey Everyone,

I'm running BMW performance suspension with the included upgraded swaybar and all M3 bits for the front with 2 degrees of camber.

I'm about to install a Quaife, powerflex subframe and differential bushings and wondering what sway bar to use to balance the car now. I'm thinking either the 15mm bar for the e90 convertible or the 20mm from the m3 coupe.

I'm open to other recommendations and just looking for some guidance for what others have used and liked.

'Balanced' is a very subjective word. What do use the car for? Do you mean balanced as in no body roll, or stronger turn in? For daily driving you really won't notice the difference between either of the sways. Basically it comes down to how you want your car to drive and handle.

-Mike

[PrematureApex]

Big bars save lives. Remember that.

[dsh135]

I think the consensus on this forum is that on the 135 a front bar upgrade alone will reduce roll and give you less understeer. That's kind of bizarro-world as far as the conventional wisdom on sway bars (normally bigger back gives you less understeer, bigger front gives you more) but there were some arguments made as to why the front reduces understeer on this car and they seem reasonable. Still, when I did my rear subframe bushings I couldn't resist so I popped an M3 rear bar in there as well as front. For aggressive street and the odd fast-lapping day I find it well-balanced. Made a big difference to body roll, understeer is improved, and no weirdness that I have found with regard to rear wheel lift or oversteer. Whether that is still the case going all out on the track I don't know.
What also helps big-time is camber for understeer and toe-out for turn-in.

[John_01]

My guess is that it won't be ideally balanced with the PS front bar. With 2 degrees of front camber you should already have plenty of front end bite. The PS front sway bar seems a fairly subtle upgrade (I have one), and I expect the 15mm rear bar to be a lot stiffer than the stock 12mm one. When I upgraded the rear subframe bushes I added a 13mm rear bar. Together with 1 degree front camber it gave more than enough turn-in for my taste. When I add more front camber for track use, I expect to need a stiffer front bar to restore some balance.

Based on simple theory, the rear bar stiffness goes something like this:
12mm is stock (on M-sport cars)
13mm is 38% stiffer than stock
14mm is 85% stiffer than stock
15mm is 144% stiffer than stock

You might also consider the 1M rear bar, as it is different from the M3 rear bar. From what I've heard the 1M doesn't have an understeer problem. Anyway I'm very interested to know what you decide and how it turns out.

[fe1rx]

Originally Posted by dsh135

I'm a shill for Pedal Box - ask me for a review.

Despite initial appearances, you have a sense of humour. Excellent!

[Southjersey128]

I have have an e93 front and e92 rear in my 128i. Accompanying the front M3 bits and rear subframe bushings, Koni yellows with swift springs(whatever spring rate Harold at hpa recomends). I think that it's pretty balanced. I'd say I have a tad more oversteer than under steer. Which is fun, but I don't have the power to get in trouble if I'm on it too hard like in a 135i.

[John_01]

Originally Posted by Southjersey128

I have have an e93 front and e92 rear in my 128i.

Do you mean the regular E92 and E93 sway bars or M3 versions?

[SaviorXi]

Originally Posted by John_01

Do you mean the regular E92 and E93 sway bars or M3 versions?

He has the M3 ones.

[RimasRS]

I think for 1er would be nice to try 335i e93 which is 15mm

[Suds]

I installed the E93 M3 front sway bar on a 2011 m-sport, no other suspension mods., have now run two auto-x's, what a cheap solution to front understeer. I love the way the car pulls into a corner now, and It feels good on the street.

I also feel less wiggle in the rear when changing lanes under hard acceleration with non runflats. Yeah I do that shit.

[lastMleft]

Originally Posted by Suds

I installed the E93 M3 front sway bar on a 2011 m-sport, no other suspension mods., have now run two auto-x's, what a cheap solution to front understeer. I love the way the car pulls into a corner now, and It feels good on the street.

I also feel less wiggle in the rear when changing lanes under hard acceleration with non runflats. Yeah I do that shit.

Would that^be the 28mm bar from HP??

Thanks,

[Suds]

Originally Posted by Rukuss

Would that^be the 28mm bar from HP??

Thanks,

I purchased the sway bar and mounting hardware from Turner Motorsports, it is the 28mm.

P/N 31352283965 on real OEM, looks like lots of places sell it.

[lastMleft]

Originally Posted by Suds

I purchased the sway bar and mounting hardware from Turner Motorsports, it is the 28mm.

P/N 31352283965 on real OEM, looks like lots of places sell it.

thanks again

[3002 tii]

Neither, sways should always be last to fine tune. If you want more neutral balancing, add camber and get more rubber up front.