Spring rate differences

[bNks334]

Originally Posted by ShocknAwe

Not to drag anyone into the dirt, but they're not the only ones. Same front spring rate recommended for a E82 128i as a F80M3, not just 128i vs 135i or even 335i. Makes me question which one is correct.

Motion ratio is the same between E8x and E9x so the effect of weight is all you need to worry about. 50 extra lbs over a wheel would make a 1/4" difference in static ride height when you're talking about effective wheel rates of close to 200lb/in (4k/12k). That becomes 1/6" when talking about effective wheel rates of close to 300lb/in (6k/18k). Most E8x/E9x are also fairly neutrally balanced so you don't need to worry too much about F:R bias differences either (51/49). The only car I'd be worried about is the convertibles which carry several hundred more pounds over the rear wheels. For this reason, even BMW uses a thicker coil spring in the rear of the E93 and a higher spring rate.

F-series is a much different car and probably has a different motion ratio and wheel rate (based on sprung weight). I highly doubt E series spring rates carry over to an F series 1:1.

[John_01]

Originally Posted by bNks334

336/700 (6k/12k) is still going to understeer pretty heavily even with the front sway deleted.

What circumstances do you experience this heavy understeer?
If it is an Autocross setup, then it seem understandable.

If you drive on a road course with R-comp tires, you will generate a lot more weight transfer under braking. That always happens when more grip allows you to brake later and harder. It also occurs because at higher speed the car has more momentum so the braking distance is longer and weight transfer occurs in a more significant part of the corner. I just want to point out that its hard to generalise about what spring rate is correct and what is not. There are so many factors that affect car setup. Obviously a lot more tuning and setup that will be done according to driver preference if the car is used for more serious track driving or competition.

[bNks334]

Originally Posted by John_01

What circumstances do you experience this heavy understeer?
If it is an Autocross setup, then it seem understandable.

If you drive on a road course with R-comp tires, you will generate a lot more weight transfer under braking. That always happens when more grip allows you to brake later and harder. It also occurs because at higher speed the car has more momentum so the braking distance is longer and weight transfer occurs in a more significant part of the corner. I just want to point out that its hard to generalise about what spring rate is correct and what is not. There are so many factors that affect car setup. Obviously a lot more tuning and setup that will be done according to driver preference if the car is used for more serious track driving or competition.

Both on track and autocross... you seem to be trying to justify running a stiffer front spring rate relative to the rear when using rcomps? I am not following your logic at all...

More weight transfer to the front of the car means more front end grip and less understeer. That is not a reason to run an imbalanced spring setup... which is complete opposite of the understeer complaints. When traction does finally break you want it to happen at both tires at the same time (neutral setup). Everything being said is arguing against the common spring rate recommendation that all suggest using a massively stiffer effective front wheel rate than rear...

If you're trying to say spring rates should be dependant on how much grip you can generated then yeah you're absolutely right and no one is denying that. Rcomps will generate higher G-forces and will be able to take advantage of greater spring rates (2hz+) without the car just ice skating around. Again, there is no reason not to maintain a neutral balanced spring rate F:R (1:3). All running a stiffer front spring will do is cause the car to push at corner exit (which a slight bit of understeer is sometimes preferred on track).

Ever stop and think maybe you'd be able to turn in without braking as hard if you could actually get grip on turn in instead of understeering???? It's called slip angles... worried the car will roll too much causing camber loss? Well then add a bit of throttle mid turn to lift the front end... it's called throttle steering or "maintenance throttle"

You should be using advanced driving techniques to pivot the front/rear end not butchered spring rates...

[John_01]

Originally Posted by bNks334

More weight transfer to the front of the car means more front end grip and less understeer. That is not a reason to run an imbalanced spring setup... which is complete opposite of the understeer complaints. When traction does finally break you want it to happen at both tires at the same time (neutral setup). Everything being said is arguing against the common spring rate recommendation that all suggest using a massively stiffer effective front wheel rate than rear...

My comments are basically aimed towards creating a car that has neutral mid-corner handling, and reasonable stability in the braking zone. Probably what I didn't spell out clearly enough, is that softer tyres and/or more grip changes the setup requirement for neutral handling. If you just swap tires to ones with more grip it will feel like an instant reduction in understeer. It happens because of the way the car behaves in the braking zones. It is the greater front-to-rear weight transfer that is responsible for this. I guess we can agree on this much, but I just want to be clear.

Before we can really have a discussion about the above, I just wanted to understand about the context of your comment. I'm not saying there is anything wrong with your proposed setup. I am saying it won't be a case of one-size-fits-all.

For example, if you setup your car for Autocross, then if you take your car to a reasonable fast road course and use a nice grippy set of R-comps you may no longer be as happy with the handling balance. Rather than complaining about heavy understeer, you may be wishing for a bit more braking stability. When that happens it could be an argument for swapping to a firmer front sway bar. On the other hand, if you setup your car with a large stagger of front-to-rear tire size, and maybe use a welded diff center, then it could be a different situation entirely. There are a lot of different scenarios.

Originally Posted by bNks334

Ever stop and think maybe you'd be able to turn in without braking as hard if you could actually get grip on turn in instead of understeering???? It's called slip angles... worried the car will roll too much causing camber loss? Well then add a bit of throttle mid turn to lift the front end... it's called throttle steering or "maintenance throttle"

I am not really thinking about camber loss due to body roll, because I was assuming you will use enough static camber to compensate. If it is not the case, then it can be a good reason for running firmer front roll stiffness (Either springs or sway bar). Otherwise the shoulder of the tire will be overheated. When you make a good setup with really connected front grip, that is the time you will be able to get on the power much earlier - Use the power to stabilise the car out of the corner. Probably this is the objective, but its a question of how to reach it without making the car too nervous, hard to control, or unstable in mid corner or turn-in phases. There will be many different requirements depending on people's preference and usage. That's why I wanted to ask the context of your comments.

[bNks334]

Originally Posted by John_01

My comments are basically aimed towards creating a car that has neutral mid-corner handling, and reasonable stability in the braking zone. Probably what I didn't spell out clearly enough, is that softer tyres and/or more grip changes the setup requirement for neutral handling. If you just swap tires to ones with more grip it will feel like an instant reduction in understeer. It happens because of the way the car behaves in the braking zones. It is the greater front-to-rear weight transfer that is responsible for this. I guess we can agree on this much, but I just want to be clear.

Before we can really have a discussion about the above, I just wanted to understand about the context of your comment. I'm not saying there is anything wrong with your proposed setup. I am saying it won't be a case of one-size-fits-all.

For example, if you setup your car for Autocross, then if you take your car to a reasonable fast road course and use a nice grippy set of R-comps you may no longer be as happy with the handling balance. Rather than complaining about heavy understeer, you may be wishing for a bit more braking stability. When that happens it could be an argument for swapping to a firmer front sway bar. On the other hand, if you setup your car with a large stagger of front-to-rear tire size, and maybe use a welded diff center, then it could be a different situation entirely. There are a lot of different scenarios.



I am not really thinking about camber loss due to body roll, because I was assuming you will use enough static camber to compensate. If it is not the case, then it can be a good reason for running firmer front roll stiffness (Either springs or sway bar). Otherwise the shoulder of the tire will be overheated. When you make a good setup with really connected front grip, that is the time you will be able to get on the power much earlier - Use the power to stabilise the car out of the corner. Probably this is the objective, but its a question of how to reach it without making the car too nervous, hard to control, or unstable in mid corner or turn-in phases. There will be many different requirements depending on people's preference and usage. That's why I wanted to ask the context of your comments.

I can't really agree with much of anything you're saying. You state a few concepts I agree with but then your thoughts on how to deal with them are the complete opposite of what Ive researched. You seem to still be rooted in the misguided information that's been posted here as your basis for the changes you want to make.

All I can say is I've tried everything... base suspension, msport, bmwps, 6k/12k, 4k/12k, 4k/16k, 6k/16k, e92 m3 sway, e93 m3 sway, 27mm h&r sway, and now front sway is deleted. My car handles fantastic right now and I wouldn't go back to a terrible rate like 400/700 if you paid me. That's not just a little stiffer up front that's massively stiffer (200% stiffer front than rear)... people who went from stock suspension straight to an imbalanced rate like that have no idea what they're missing out on.

Your comment that changing tires will instantly make the car "feel less understeer" tells me you're not using the term understeer the way I am at all. Yes, stickier tires will allow you to drive the car harder without breaking traction. However, once you drive the car hard enough again to hit the limits of grip your front tires are still going to break traction first if you run imbalanced spring rates (understeer).

My personal experience agrees with the math which shows you don't need to go as stiff with the front spring rate on an e9x/e8x than on previous platforms. An E46 had a motion ratio bias of closer to 1:2 so rates like 400/700 made sense. Not so much on our cars...

[John_01]

Fair enough. I hope you continue to post your results.

[titium]

could not be happier with my setup on my e82.

swift spec r springs

3.6kg F 9kg R

m3 e92 front bar was the missing link to counter body roll.
No idea how anyone finds coilovers with twice my front spring rate comfortable for street use. I find what I've got quite firm (but not uncomfortable).

If anything my only complaint is I wish I had about 10mm more ride height.

[Ginger_Extract]

A lot of good input in this thread. I have tried deleting the front bar altogether, however, I found that the front end wanted to wander too much over rougher pavement, making the car feel very uncertain. Perhaps that was bad luck, I'll try it again.

I have modified my Eibach bar to reduce binding. Turns out, as delivered, the Eibach bar binds like crazy. Handling has improved with this change alone. Still had an understeer issue on track, but better. Everyone, check your front sways for binding!

Going to swap in the softer Swift front springs this weekend, and schedule a track day to test some things out. Want to try Eibach bar with the softer springs, stock bar, and then no bar at all. Will report with findings, including lap times.

[bNks334]

Originally Posted by Ginger_Extract

I have modified my Eibach bar to reduce binding. Turns out, as delivered, the Eibach bar binds like crazy. Handling has improved with this change alone. Still had an understeer issue on track, but better. Everyone, check your front sways for binding!

Going to swap in the softer Swift front springs this weekend, and schedule a track day to test some things out. Want to try Eibach bar with the softer springs, stock bar, and then no bar at all. Will report with findings, including lap times.

That would be awesome!

Also, I've always wondered about why people cared about swaybar binding... the stock swaybar is literally glued to the bushings. The M3 bar is free, but there are stops built into the bar to keep the bushings from sliding around.

A sway bar is a simple lever. Push on one end and the other end goes up (borrowing spring rate from the opposite wheel). The only time time swaybar binding is going to effect your ride is when both wheels are compressing the exact same amount and both ends of the swaybar are being pushed down on... bind would prevent the sway bar from pivoting in the bushings as the suspension compresses.

So yeah, I can see how if you put a big stiff sway bar on the front of the car, and it's not allowed to spin freely (it binds), then less weight transfer will occur to the front of the car under braking (swaybar would be contributing to effective wheel rate under braking) and I can see how the car would understeer upon initial turn-in...

[ShocknAwe]

Originally Posted by Ginger_Extract

A lot of good input in this thread. I have tried deleting the front bar altogether, however, I found that the front end wanted to wander too much over rougher pavement, making the car feel very uncertain. Perhaps that was bad luck, I'll try it again.

I have modified my Eibach bar to reduce binding. Turns out, as delivered, the Eibach bar binds like crazy. Handling has improved with this change alone. Still had an understeer issue on track, but better. Everyone, check your front sways for binding!

Going to swap in the softer Swift front springs this weekend, and schedule a track day to test some things out. Want to try Eibach bar with the softer springs, stock bar, and then no bar at all. Will report with findings, including lap times.

Can't wait to hear your impression of the 336lb swift springs. Have 672 rears and 396 fronts that I have held off installing. I did try taking off my H&R bar with the 350lb TCK springs on the car now, and echo your sentiments that the car felt unstable. Roads here kind of suck though. I may go back to the stock bar or possibly even a 128i front bar with the higher rate springs.

[bNks334]

Originally Posted by ShocknAwe

Can't wait to hear your impression of the 336lb swift springs. Have 672 rears and 396 fronts that I have held off installing. I did try taking off my H&R bar with the 350lb TCK springs on the car now, and echo your sentiments that the car felt unstable. Roads here kind of suck though. I may go back to the stock bar or possibly even a 128i front bar with the higher rate springs.

I felt the same way at first, but got used to the feeling. All you're feeling is the suspension allowing each wheel to move independently from one another... A swaybar links the wheels together which is actually less stable over rough pavement but obviously feels differently when both wheels are being forced to take impacts instead of just one. No swaybar = greater suspension articulation = more grip.

here is some more quick reading on the concept of wheel rates that is pretty easy to understand: http://www.autospeed.com/cms/article...l-Rates&A=2904

[Ginger_Extract]

Originally Posted by bNks334

That would be awesome!

Also, I've always wondered about why people cared about swaybar binding... the stock swaybar is literally glued to the bushings. The M3 bar is free, but there are stops built into the bar to keep the bushings from sliding around.

A sway bar is a simple lever. Push on one end and the other end goes up (borrowing spring rate from the opposite wheel). The only time time swaybar binding is going to effect your ride is when both wheels are compressing the exact same amount and both ends of the swaybar are being pushed down on... bind would prevent the sway bar from pivoting in the bushings as the suspension compresses.

So yeah, I can see how if you put a big stiff sway bar on the front of the car, and it's not allowed to spin freely (it binds), then less weight transfer will occur to the front of the car under braking (swaybar would be contributing to effective wheel rate under braking) and I can see how the car would understeer upon initial turn-in...

You pretty much nailed it. When the bar binds, it can't rotate in it's bushings. In my case, with the bar unhooked from the end links and the car in the air, the bar was so bound up I had to grab it with both hands and really wrench it to move at all! The sway bar experiences torsion/bending under load, as well. With the bar binding, it effectively becomes "infinitely" stiff. No bueno.

[ShocknAwe]

Originally Posted by bNks334

I felt the same way at first, but got used to the feeling. All you're feeling is the suspension allowing each wheel to move independently from one another... A swaybar links the wheels together which is actually less stable over rough pavement but obviously feels differently when both wheels are being forced to take impacts instead of just one. No swaybar = greater suspension articulation = more grip.

here is some more quick reading on the concept of wheel rates that is pretty easy to understand: http://www.autospeed.com/cms/article...l-Rates&A=2904

Good read. May be worth another try. Couldn't kick the thought I had without the bar was maybe a higher rate would help.

Does rake increase or decrease front bias?

[bNks334]

Originally Posted by ShocknAwe

Good read. May be worth another try. Couldn't kick the thought I had without the bar was maybe a higher rate would help.

Does rake increase or decrease front bias?

The hard part about learning this stuff is that the information you get is only as good as the person interpreting it and there are a lot of poor conclusions drawn from good information. I was just reading this thread today: https://grassrootsmotorsports.com/fo...s/43604/page2/

Half the people posting in that thread about roll center height are trying to counter what OP is saying, and posting source info from race books, but they are completely misinterpreting the data. The data they quote actually states the complete opposite of their counter points lol...

In general though, I agree with OP of the above thread. I think rake reduces under-steer (to a point like everything suspension related). By increasing rake from factory settings of pretty much 0 to .5-.75in more weight will shift forward; aiding front traction for those of us that have also put more tire up front than stock 215's. 0 rake, or negative rake, will transfer less weight forward under braking and corner loads which means more traction in the rear and less in the front (under-steer). This is done off the factory floor by BMW, and many car manufacturers, to aid straight line traction and help keep the average driver from getting into power over-steer situations.

Under-steer can be caused by too much weight transferring forward as well (no way that's the case with the majority of complaints) so you should try to control how many variables you play with on the suspension at the same time. If you're going to run rates like 450/700 you're probably also going to benefit from increasing rake to keep the rear of the car from squatting excessively mid corner (promoting under-steer).

See also: https://rennlist.com/forums/racing-a...-handling.html