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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Suspension | Brakes | Chassis > Springs & rates, Non RFT's, LM-25's,etc



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      10-03-2008, 09:02 AM   #1
ithatel
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Springs & rates, Non RFT's, LM-25's,etc

Hi All:
I just took off and discarded the stock run flat tires that finally wore out (23,000 miles) - whew !
I put on Blizzak LM-25 winter tires on all 4 corners. I used 225/40/R18 XL 92V and got them from Tire Rack.

My car is a 2007 E90 Sedan with Sports suspension (ZSP) and 6MT.

The question is why is the car so SOFT now. A fast quick turn in leaves the car with a sort of secondary oscilliation.

I have seen it written that to compensate for the lack of sidewall stiffness (that the RFT's provide) - you should stiffen up the car with stiffer springs (maybe shocks as well). When I ordered the tires, I was told that this was not necessary. Logic says to stiffen as the suspension was taylored around a tire with a stiff sidewall and now it is gone.

Is the softness coming from the winter tires - So, when I put a set of new wheels and a set of excellent street tires in the spring - will the car still be soft (not as soft) or will it be fine ??

What are the spring rates for the Stock sports suspension springs ?
Does anyone know the spring rates that go with the new "M" suspension that Mr 5 has put on his E9x ?

The same question applies to the Dinan kit as well - what are these springs rated at ?

Thanks,

Doug

BTW": I just installed UUC's black tranny mounts and Evo 3 short shifter. I will post a review shortly in the appropriate forum - but a heads up, these two upgrades are fantastic !!!
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      10-03-2008, 04:29 PM   #2
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Just to let you know, I kept the ZSP springs on my car.
I only changed out the dampers.

I don't know how to answer your question, but I thought I'd correct what you said about me changing out the springs.
Changing out the dampers to the performance dampers stiffens the rebound so there isn't a "second oscillation".

Quote:
Originally Posted by ithatel View Post
Hi All:
I just took off and discarded the stock run flat tires that finally wore out (23,000 miles) - whew !
I put on Blizzak LM-25 winter tires on all 4 corners. I used 225/40/R18 XL 92V and got them from Tire Rack.

My car is a 2007 E90 Sedan with Sports suspension (ZSP) and 6MT.

The question is why is the car so SOFT now. A fast quick turn in leaves the car with a sort of secondary oscilliation.

I have seen it written that to compensate for the lack of sidewall stiffness (that the RFT's provide) - you should stiffen up the car with stiffer springs (maybe shocks as well). When I ordered the tires, I was told that this was not necessary. Logic says to stiffen as the suspension was taylored around a tire with a stiff sidewall and now it is gone.

Is the softness coming from the winter tires - So, when I put a set of new wheels and a set of excellent street tires in the spring - will the car still be soft (not as soft) or will it be fine ??

What are the spring rates for the Stock sports suspension springs ?
Does anyone know the spring rates that go with the new "M" suspension that Mr 5 has put on his E9x ?

The same question applies to the Dinan kit as well - what are these springs rated at ?

Thanks,

Doug

BTW": I just installed UUC's black tranny mounts and Evo 3 short shifter. I will post a review shortly in the appropriate forum - but a heads up, these two upgrades are fantastic !!!
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      10-03-2008, 06:45 PM   #3
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Ithatel,

It's coming from from the "softness" of your winter tire. The sidewalls on the runflats are very stiff as you know. This helps in steering input as well...you probably noticed a general vagueness to the ride/handling as well, all due to the winter tire. I live in Chicago and run those same tires during the cold months. I was part of the Morr VS8 group buy and I just recently got my new wheels and tires(Goodyear F1 Asym.). I was really surprised by the handling difference when I drove the new tires...it's the trade-off for winter traction. By the way, I do notice when it gets down in the 20-30 degree range the Blizzaks will firm up.
As far as the spring rates for the performance suspension springs, no one knows for sure. I have spoken to two different dealers, and they can't say for sure. I'm going to be switching to the performance suspension and would like the M (yellow) spring, but there isn't much info. on it yet. Does it ride any lower, is it that much stiffer? I wish we had some good info..

Nevets1
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      10-03-2008, 07:49 PM   #4
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It's the tires. You really can feel the difference on the E9x. I can't stand anything more wintery than the V-rated, high performance 'snows' such as the Pirelli 240 sottozeros. But seeing as you live in Durango, lucky dog, you have some serious mountain snow to contend with. The LM-25s should provide a bit more traction, at the cost of increased tread block movement.

IMO the single best mod for the E9x is to swap the wheels for lightweight forged alloy rims with extreme performance non-rfts. The increase in grip and road feel, combined with the reduction in harshness, really improve the ride. But then the shortcomings of the OEM ZSP suspension become more apparent, and you will want to go M-sport/Performance or aftermarket for coilovers, sways, braces, & LSD.
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      10-03-2008, 08:49 PM   #5
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Quote:
Originally Posted by stressdoc View Post
It's the tires. You really can feel the difference on the E9x. I can't stand anything more wintery than the V-rated, high performance 'snows' such as the Pirelli 240 sottozeros. But seeing as you live in Durango, lucky dog, you have some serious mountain snow to contend with. The LM-25s should provide a bit more traction, at the cost of increased tread block movement.

IMO the single best mod for the E9x is to swap the wheels for lightweight forged alloy rims with extreme performance non-rfts. The increase in grip and road feel, combined with the reduction in harshness, really improve the ride. But then the shortcomings of the OEM ZSP suspension become more apparent, and you will want to go M-sport/Performance or aftermarket for coilovers, sways, braces, & LSD.
Thanks for that info on the tire being the issue. I was thinking that I had two problems.
We got 164" of snow where I live last winter and I can't see dropping ride height with a new suspension setup unless I have to. The BMW performance kit that Mr. 5 may be the way to go, without using a new set of springs. Oh well, another interesting problem to think about when it's snowing.
I will go with lighter wheels and extreme performance non-rfts for the spring.
Thanks,

Doug
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      10-03-2008, 09:01 PM   #6
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Quote:
Originally Posted by Mr. 5 View Post
Just to let you know, I kept the ZSP springs on my car.
I only changed out the dampers.

I don't know how to answer your question, but I thought I'd correct what you said about me changing out the springs.
Changing out the dampers to the performance dampers stiffens the rebound so there isn't a "second oscillation".
Yes, I thought you had done the springs, but I was wrong.
I heard today that stock ZSP BMW springs are soft (200 or so in the front) with a long bump rubber. So you are using the bump rubber as a spring and it is not a very good one and it eventually bottoms out. A good aftermarket set up will use springs first and bump rubber last. This came from TC Kline's shop.
I will probably move to your suspension setup in the spring. I really don't want to go to a double adjustable setup as I track the car very little and I had enough of those headaches with getting that kind of setup perfect when I was racing. Go back to the same track you were at last month and the same setting feels like crap and it's back to ground zero, again.
Keep us informed of what you learn, your posts and DIY's have been very helpful.


Doug
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      10-03-2008, 09:06 PM   #7
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Quote:
Originally Posted by nevets1 View Post
Ithatel,

It's coming from from the "softness" of your winter tire. The sidewalls on the runflats are very stiff as you know. This helps in steering input as well...you probably noticed a general vagueness to the ride/handling as well, all due to the winter tire. I live in Chicago and run those same tires during the cold months. I was part of the Morr VS8 group buy and I just recently got my new wheels and tires(Goodyear F1 Asym.). I was really surprised by the handling difference when I drove the new tires...it's the trade-off for winter traction. By the way, I do notice when it gets down in the 20-30 degree range the Blizzaks will firm up.
As far as the spring rates for the performance suspension springs, no one knows for sure. I have spoken to two different dealers, and they can't say for sure. I'm going to be switching to the performance suspension and would like the M (yellow) spring, but there isn't much info. on it yet. Does it ride any lower, is it that much stiffer? I wish we had some good info..

Nevets1
Thank you for the info on the tire, I am glad to know that in all likelihood I only have a tire issue. I can live with it for the winter.

What tire pressures are you using with these winter tires (only if yours is a sedan, as the coupe pressures are different).

I am continuing to plug along with getting answers to my questions, yours complement mine on the BMW performance suspension.

Doug
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