Improving convertible handling

[Lucky1]

Lately I've been toying with the idea of trading my 128i Coupe in for a 135i Convertible. One thing I am concerned about is how well the 'vert handles stock from the factory. Most people will talk about how a Convertible version of a Coupe never handles as well as the latter, and since I am of the opinion that the Coupe could do with some improvements I don't have high hopes for the Vert at least matching its capabilities. For example I read a Car and Driver article that suggested the convertible will do .86g on the skidpad while I remember reading that the coupe will do .89g.

So my question is this: do you think with the right modifications the vert could do as well (or even better, exceed) the handling of the coupe? I know it'll probably never be a Z4 but what formula of mods would it take for improvement and what do you think it would do on the skidpad afterwards?

Here's what I had in mind:

-stickier tires
-front sway bar (would the OEM M3 sway bar fit?)
-aftermarket springs

What about shocks and struts?

Prefer not to do anything that will lower the car since winter is an issue here.

Interested in people's opinions. Thanks!

[Lucky1]

Originally Posted by maxnix

It's heavier, not as rigid in torsion, so it will never handle as good as a coupe similarly equipped. If you buy the convertible, just enjoy the ride and style.

Okay, point taken. But what can be done to improve it? Is it not possible for a modified convertible to do as well or exceed a stock coupe?

[roo97ss]

right on track there.

Tires will make a big difference in ride quality and modest in handling.

e93 M3 sway bar, stiffest of them available for the heavier convert

instead of aftermarket springs as you're worried about lowering it....
i hear the 11 have linear springs which should be better, if going for other year i'd go with e92 335i sport springs. they are essentially same height as hours and higher rate, or the BMW performance, though they will lower hte car 1/2 inch.

if you don't do the springs, because you want stock height, then i would add koni shocks, probably fsd, or yellows depending on how hard core you want to be, i'd assume the fsd would be what you're looking for.

You pick up extra weight and lose some rigidity, but it will definitely handle better than your 128.

[spyderx]

my 11 135 vert is nice open top cruiser and attracts ton of you know...

but, it handles decent for a vert and I think they improved the rigidity and handling greatly from 2010 model. I had both.

It's a fun car and make sure to get a 6MT. Forget that DCT toy setup.

[BrokenVert]

The chassis doesn't decker under torsion nearly as much as the coupe guys would have you believe. However without going into custom stuff you need to do the things that coup guys do.

From and rear strut tower braces, go with stiffer sways. Either the 29 mm E93 M3 bar or the 32 mm Hotckis bar

If you want to get insane you need to make a custom roll cage and pull the popup rollbars...replace the xbrace behind the seats and run a horizontal bar from the top of the tub right behind the front seats

[Mak135i]

Change the RFT tires for sure. In my car, this has made the biggest difference by far (you need winter tires for cold weather though).
Installed the 32mm Hotchkis. Makes a bit of difference to roll but more so to steering feel, which is perfect now.
I also have the BMW performance springs which lower the car slightly (they are designed for the coupe) but no problems with winter driving or drive-ways etc.

In spring, I intend to get either the Bilstein HD struts (recommended by tire rack) or Koni FSD.

[RoundelM3]

Are you going to autocross or track it? If not, you're not going to notice the difference. I'm installing 18" wheels and wider non-runflat tires on my wife's soon-to-be-delivered 128i convertible, but that's all it's going to need.

[fancyfl1ght]

Originally Posted by Lucky1

Lately I've been toying with the idea of trading my 128i Coupe in for a 135i Convertible. One thing I am concerned about is how well the 'vert handles stock from the factory. Most people will talk about how a Convertible version of a Coupe never handles as well as the latter, and since I am of the opinion that the Coupe could do with some improvements I don't have high hopes for the Vert at least matching its capabilities. For example I read a Car and Driver article that suggested the convertible will do .86g on the skidpad while I remember reading that the coupe will do .89g.

So my question is this: do you think with the right modifications the vert could do as well (or even better, exceed) the handling of the coupe? I know it'll probably never be a Z4 but what formula of mods would it take for improvement and what do you think it would do on the skidpad afterwards?

Here's what I had in mind:

-stickier tires
-front sway bar (would the OEM M3 sway bar fit?)
-aftermarket springs

What about shocks and struts?

Prefer not to do anything that will lower the car since winter is an issue here.

Interested in people's opinions. Thanks!

I can not wait to replace my RFT tires with Michelin PS2 on APEX ARC 8 wheels!

APEX has a perfect offset fitment for the front and rear.

March is too far away!

[fancyfl1ght]

Originally Posted by Lucky1

Lately I've been toying with the idea of trading my 128i Coupe in for a 135i Convertible. One thing I am concerned about is how well the 'vert handles stock from the factory. Most people will talk about how a Convertible version of a Coupe never handles as well as the latter, and since I am of the opinion that the Coupe could do with some improvements I don't have high hopes for the Vert at least matching its capabilities. For example I read a Car and Driver article that suggested the convertible will do .86g on the skidpad while I remember reading that the coupe will do .89g.

So my question is this: do you think with the right modifications the vert could do as well (or even better, exceed) the handling of the coupe? I know it'll probably never be a Z4 but what formula of mods would it take for improvement and what do you think it would do on the skidpad afterwards?

Here's what I had in mind:

-stickier tires
-front sway bar (would the OEM M3 sway bar fit?)
-aftermarket springs

What about shocks and struts?

Prefer not to do anything that will lower the car since winter is an issue here.

Interested in people's opinions. Thanks!

I am thinking about his mod. Don't know if anyone has had any improvements though on a vert.

[fancyfl1ght]

Originally Posted by maxnix

I think I would have to add LSD right after that as the best handling improvement for dry, wet and winter (after winter tires).

Then you will really be trippin'

[Lucky1]

Originally Posted by roundel335

Are you going to autocross or track it? If not, you're not going to notice the difference. I'm installing 18" wheels and wider non-runflat tires on my wife's soon-to-be-delivered 128i convertible, but that's all it's going to need.

No plans to autocross or track it regularly.

All the same probably don't want to push a convertible too hard. What with no roof and all.

Forgot to mention that with the mods I probably don't want to sacrifice ride quality if at all possible. I'm guessing deleting the RFTs has got to at least offest any punishing changes proposed here to the suspension...

[BrokenVert]

^it will be the best desicision you make while you own your car

[akak1997]

I'd do all the mods a coupe will do first before worry about the chassis not being as rigid as the coupe. If you want to improve the chassis, I'd suggest front strut brace to enhance rigidity on the front. I'm not sure if anyone makes a rear strut brace for verts as I'm sure it doesn't have the same trunk layout as coupe coz of retracted roof storage.

As with all mods, anything is possible if you've unlimited cash. I mean you can go as far as putting a roll cage in, but that's gonna kill the looks.

Sway bar will, in general, kill ride quality (going over uneven bumps is a pita, literally). Damper and springs also hurt ride quality a bit, but unless you go will full on race setup, you'll notice the sway bar first before damper and springs.

RTF should be the first thing to go, that stuff sucks in terms of ride quality and handling.

[Prof T]

Tires are the first thing to change. Unless you are really going to push it ...anything else is not worth the time and money.

[fancyfl1ght]

unsprung weight performance gains? Any noticable impact for everyday driving?

[BrokenVert]

Originally Posted by fancyfl1ght

unsprung weight performance gains? Any noticable impact for everyday driving?

a bbk isnt worth it unless you track it regularly.

[nordique14]

Originally Posted by akak1997

I'd do all the mods a coupe will do first before worry about the chassis not being as rigid as the coupe. If you want to improve the chassis, I'd suggest front strut brace to enhance rigidity on the front. I'm not sure if anyone makes a rear strut brace for verts as I'm sure it doesn't have the same trunk layout as coupe coz of retracted roof storage.

This is correct. All of the mods that work for the coupe will work the same as on the convertible. The convertible will benefit more from a strut brace than the coupe. That is pretty much the only difference from a performance mod standpoint.

Note that if you consider an exhaust a performance mod that not all coupe exhausts will fit the convertible. The vert has additional bracing which requires some additional bends over a coupe exhaust.