How Low without hurting the handling?

[Sharad]

Has anyone done any testing to determine how low you can go without adversely affecting the handling? I did a forum search and didn't find anything. My car is right at 27.25" to the fender, front and rear, with 275/35-20 tires. I'd like to go lower, but my car's sole purpose is maximum cornering grip while maintaining daily drivability, so I don't know if it would be a bad idea to go any lower.

Thoughts?

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[NightmareMoon]

That entirely depends on your road conditions. On a pefectly smooth road you dont need much travel/height. You want enough height and travel to absorb the bumps in your area without upsetting the chassis. I know thats not a the answer you were looking for.

 

[BmacIL]

No lower than ~1.5" drop, less than 1.25" recommended for good handling. It's not so much about bumps and bump stops as the geometry.

 

[Sharad]

No lower than ~1.5" drop, less than 1.25" recommended for good handling. It's not so much about bumps and bump stops as the geometry.

That's more or less what I figured, but what's your source? How do we know when the geometry starts getting undesirable?

 

[BMR Tech]

How do we know when the geometry starts getting undesirable?

You put the car on the lift and you travel the suspension.

Knowing your travel range when racing the car will come in handy, as you won't really care about what the suspension does an inch before it bottoms out.

Then there is deflection within the system that plays a factor as well.

If you are not noticing any unwanted geometry changes at say 3" bump when testing statically, that doesnt mean you won't have a compounding affect when the suspension is loaded in a corner and those awesome rubber bushings are deflecting like crazy.

For starters, get the car in the air and check the camber and toe curves.

Good luck! :cheers:

 

[BmacIL]

You put the car on the lift and you travel the suspension.

Knowing your travel range when racing the car will come in handy, as you won't really care about what the suspension does an inch before it bottoms out.

Then there is deflection within the system that plays a factor as well.

If you are not noticing any unwanted geometry changes at say 3" bump when testing statically, that doesnt mean you won't have a compounding affect when the suspension is loaded in a corner and those awesome rubber bushings are deflecting like crazy.

For starters, get the car in the air and check the camber and toe curves.

Good luck! :cheers:

This and a few other things that are harder to see: roll centers being the most significant. Once you lower too far, your roll couple (distance between roll center and CG) starts increasing significantly, making it much more difficult for the springs to control the body effectively. Your camber gain curves are not usually linear either, so once you've set a new nominal, the amount of negative camber the car loses during roll is different than it was.

 

[BMR Tech]

Yes, as well as the roll axis which will change due to the difference in geometry F/R. (arc changes)

You also have changes in wheel/working rates due to changes in leverage on the F/R bar arms.

It goes on forever, but first thing is to ensure the geometry of the wheels/knuckle assemblies are sufficient and will not act erratically during suspension loading and unloading.

 

[Sharad]

Thanks guys. This is more along the lines of what I was looking for- a more substantive conversation than "don't go too low."

I think what I'll do is try to get as much video as possible at the current ride height at Sebring in a couple weeks. I have the feeling the suspension won't travel much with the way I have the coilovers set, but that turn 17 sure is brutal.

Unfortunately, I don't think I'll be able to get the spherical bearings for all four corners installed before then. It would have been nice to eliminate that slop. I run a decent amount of negative camber on the street, and I've still gotten to the shoulders of the tires just driving on the street. (at 45psi cold)

I guess I'll do some testing of my own and see what I come up with. I won't be going low for "stance bro!" if that degrades the handling.

You put the car on the lift and you travel the suspension.

^^Obviously. But that's not exactly what I meant. Probably the best way to do this would be on an alignment rack with the springs out of the car, and chart out the alignment changes as the suspension articulates. Then compare the rate of change, starting from different ride heights.

There's still the question of which alignment changes are good or bad. Ah well. Time to test.

 

[Grintch]

Yes, as well as the roll axis which will change due to the difference in geometry F/R. (arc changes)

You also have changes in wheel/working rates due to changes in leverage on the F/R bar arms.

It goes on forever, but first thing is to ensure the geometry of the wheels/knuckle assemblies are sufficient and will not act erratically during suspension loading and unloading.

BMR has surely looked at that. Want to volunteer a good number Kelly?

Also note that how stiff your suspension is also a factor. For example, if you front suspension compresses 2" under hard braking, you need to think about that in your evaluation of where the geometry starts getting sub optimal or wonky. But it you stiffen it up so it only compresses 1" under braking, now you can potentially lower the car another inch before you get to that same point in the suspension travel.

This is one reason coil over kits typically offer more lowering than simple lowering springs.

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