Spring rates when using no arb...

[Dave_M3]

Just thinking about not running an arb in my current project as it'll give me more room for a sump if I can fit the engine further back.

Would coil-overs with stiffer springs be able to compensate for having no front arb or am I just being silly and fit the engine like everybody else does

car will be a competition drift and trackday car and occasional road car for the shits and giggles.

[billgatese30]

There's no hard and fast rule to say that you must always have roll bars. So long as you have your spring rates set correctly you should be ok.

[Dave_M3]

Yeah, was thinking that really as you often don't need to upgrade arbs if you are running coil-overs. I was just worrying if taking away the arb completely would be too drastic at the front and if it wasn't, roughly what percentage increase would I need in the spring rates to compensate. I know the rear arb isn't that important if running coilovers but I'll probably keep it as having the rear alittle stiffer will be good for drifting.


arbs and slightly softer springs are right for bumpier surfaces or a road car so you can still have decent cornering while keeping comfort rather than the car shaking to pieces around you if using just stiff springs... Being a track car and mostly on pretty good surfaces shouldn't have to worry about that though.

Having no arb will help with clearance for the extra lock too I suppose...

First things first is to see how the engine and manifolds will work out with mounting the engine abit further back anyway

[billgatese30]

arbs and slightly softer springs are right for bumpier surfaces or a road car so you can still have decent cornering while keeping comfort rather than the car shaking to pieces around you if using just stiff springs... Being a track car and mostly on pretty good surfaces shouldn't have to worry about that though.

Thats my thinking. Also if you setup your springs (sorry, not sure on how much to increase the rates by) for the best track performance and then have a heavy bar on the rear you can connect it for drifting and then disconnect for the track

[Dave_M3]

Yep, sounds like a good plan really when you think about it that way:)

Will get the engine on a stand during the week anyway and see how my idea of moving it back abit works out with the manifolds and sump by using the orginal subframe modded a little...
I know an E30 with an S50b32 with the engine moved back abit by using the complete M3 Evo front subframe and front end but I really don't like that aproach as the car sits far too high and lowering it enough for it to low right then will just mess up geometry further then.

[GeoffBob]

Dave, I currently have no ARB's on my track car, but have left the mounts intact to facilitate putting one or the other back if the need should arise (to tackle acute over or understeer problems should they arise).

However, before you decide that stiffer springs are an effective substitute for ARB's, first understand the difference between the two. Any one of the four springs on your car functions in such a way as to resist the "absolute" displacement of the attached wheel. That is to say, the force with which a spring resists the movement of the attached wheel is entirely a function of the absolute displacement of that wheel.

An ARB, on the other hand, opposes the "relative" (not absolute) displacement between two wheels. That is to say, an ARB exerts a force that is a function of the "difference" in displacement between two adjacent wheels. If both left and right wheels are raised equally high relative to the body/frame (compressing both springs) the springs will both oppose this displacement, but the ARB will exert no force on either wheel since the bar has no torsion applied to it when the left & right wheels are equally displaced. However when one wheel is raised higher than the other relative to the body/frame (as in the case of body-roll) the ARB will oppose this differential displacement with a force that acts on both wheels in an effort to bring both wheels back in line with each other.

So what does all this mean? What it means is that springs (by their very action) also work to oppose body roll since the force exerted by the spring on the raised wheel is greater than that, say, on the lower wheel (during roll). So stiffer springs can in effect be used to counter roll. The problem is that springs that are stiff enough to work effectively against roll substantially sacrifice ride comfort, and are thus generally reserved for lightweight track cars with a low COG. So long as your car is a track car only then stiffer springs in place of ARB's could work effectively, not to mention the fact the suspension components at each wheel now function independently of each other, which has numerous other advantages that I won’t go into here.

Apologies for the long boring answer. Hope I wasn’t teaching too many people to suck eggs.

[RPM]

I love reading Geoffs posts

[Dave_M3]

for the long boring answer. Hope I wasn’t teaching too many people to suck eggs.

Not at all. Have a reasonable understanding of it already but its good to get a informative second opinion when your thinking aloud about trying something

generally reserved for lightweight track cars with a low COG. So long as your car is a track car only then stiffer springs in place of ARB's could work effectively, not to mention the fact the suspension components at each wheel now function independently of each other, which has numerous other advantages that I won’t go into here.

Such as allowing each wheel as much contact with the ground as it is capable of for traction and grip entering corners

Having no arb at the back on an E30 with lots of power definitely won't be a bad thing anyway for traction off the line and out of corners etc.

[Stevin]

I would prefer to keep the front roll bar in place as it keeps the front wheels linked. In turn it stops the car from picking up the front unloaded wheel when cornering.

I on the other hand believe that running a very soft or no roll bar in the rear as it allows the rear wheels to work independently allowing the car to put the power down easier.

[AlpineAde]

As Stevin intimates, disconnecting or running next to no rear bar is a relatively common practice on road courses for a number of classes of cars ~ I am unsure of taking the front bar out of action, though. For me, it would be something I would prefer to keep.

[caneswell]

I would prefer to keep the front roll bar in place as it keeps the front wheels linked. In turn it stops the car from picking up the front unloaded wheel when cornering.

Sorry but that is completely the opposite to what happens! An ARB will tend to cause the inside wheel to be picked up more.

[billgatese30]

I would prefer to keep the front roll bar in place as it keeps the front wheels linked. In turn it stops the car from picking up the front unloaded wheel when cornering.

Sorry but that is completely the opposite to what happens! An ARB will tend to cause the inside wheel to be picked up more.

I agree with caneswell here, here is a pic of mine picking up the front wheel because the front bar is too stiff as I have springs which are still a compromise between track and road. Stiffer springs, a softer front ARB or both would have prevented the front inside wheel lifting.

http://img.photobucket.com/albums/v225/ ... C_0813.jpg

[AlpineAde]

Dave, you should have a look at some of Carroll Smith's books on chassis tuning:

http://www.carrollsmith.com/

He devotes quite a few pages to setting up a relationship between springs and bars. If you can't get your hands on any of them (you should, though ~ the guy is awesome!) let me know and I should be able to hook you up with pdf copies of a couple of things.

[billgatese30]

this one is also very good.

[Dave_M3]

Just had a quick look at the thread eariler and didn't have time to post about a arb helping keep the inside wheel down :p
This would even be more important in a drift car as you are carrying alot more lateral g into the corners and forcing the car to roll even more so.


Could always just fit the arb on the front of the subframe if I needed it anyway. as it would help with steering lock clearance on the inside wheel then too.


Might see can I pick up one of those books. I love reading up on this sort of thing.

[Motorhole]

I agree with caneswell here, here is a pic of mine picking up the front wheel because the front bar is too stiff as I have springs which are still a compromise between track and road. Stiffer springs, a softer front ARB or both would have prevented the front inside wheel lifting.

Is it just the angle of the photo or are your rear wheels toed out slightly??

Geoffbob - keep your stuff coming, I think it's awesome.

[GeoffBob]

Geoffbob - keep your stuff coming, I think it's awesome.

Very kind of you Sir! I'll do my best.

Regards
Geoff

[billgatese30]

I agree with caneswell here, here is a pic of mine picking up the front wheel because the front bar is too stiff as I have springs which are still a compromise between track and road. Stiffer springs, a softer front ARB or both would have prevented the front inside wheel lifting.

Is it just the angle of the photo or are your rear wheels toed out slightly??

Geoffbob - keep your stuff coming, I think it's awesome.

just the angle of the pic

[Stevin]

You are correct. I have no idea what I was thinking.

I guess keeping the wheel down is more a factor of your springs being to soft and your roll bar too stiff.