I have been looking around for a BSK and I have seen two kinds. The spacers (used in front I think) and the rod type (used in rear I believe). The toe rod type seems to be legit but more suited for hardcore racers. The front on the other hand seems to be for the people who dont race or are on a budget. The thing is, I do no understand how a $115 piece of metal can actually eliminate bump-steer. Is this product legit?

 

at stock height, both the front toe rods and lower control arms travel in the same arc as it was designed to. they move in unison to one another over bumps and so no bumpsteer.

however, when you lower your car, the arc that the front toe rods travel up and down in will now be different than that of the lower control arms. this tiny offset difference in arc travel causes the steering to go left or right when hitting bumps on the road thus causing bumpsteer.

to correct this, you will need to return the arc in which the toe rods move to match that of the lower control arms. this can be done by either putting spacers under the steering rack to compensate for the lowered ride height or by putting spacers at the ends of the toe rod ball joints to correct the angle. the lower the car, the thicker the spacer should be to correct the larger change in angle. im too lazy to draw a diagram, perhaps someone can to illustrate it better.

 

Vstryker is correct as far as the front suspension goes. When you change the ride height you also need to change the height of the steering rack by the same amount to avoid bump steer. Personally I wouldn't relocate the rack unless the bumpsteer was bad enough to be a real problem, but if it is a problem, you have to move the rack just the right amount, so you need spacers that are the right size for the specific drop. If the car is dropped an inch, the rack needs to move an inch, but if the car is dropped two inches, the rack needs to move two inches. If you move the rack two inches and drop the car one inch, you're no better off, becaue the rack will still be an inch out of place relative to the wishbones. IOW, one thickness of spacer will not work on every car.

It's a little different at the back of the car. AP1's were designed with roll understeer in the back (a very common practice) so they also have bump steer in the back, becaue you can't have one without the other. The roll and bump steer do not suddenly appear when the car is lowered. Lowering DOES change the roll steer profile (a little), so it also changes the bump steer profiles (by the same amount), but the rear BSK actually eleminates the roll understeer Honda designed into the rear suspension. Honda also eleminated the roll understeer when they reworked the geometry for the AP2, but they also changed the handling bias, and the two changes work togehter. AP1's hit the bump stops in the back before the rear wheels steer enough to feel and that's the real cause of most of the reported instability over bumps, but based on the reports from some of the guys who race the car there appear to be times when the bump/roll steer actually does become an issue. Others haven't experienced any such issues, but if you do, the rear BSK is one way to eleminate the characteristic.

You can also alter the rear geometry in other ways, but the BSK is the cheapest way, and works just as well as any other in most applicaitons.

 

good read.

 

Are you sure the 1:1 ratio is true? I was always told that the more the car is lowered, the bigger the spacer must be. The only thing is, they don't make spacers too big. The biggest I have seen is 20mm and thats not even an inch of increased spacing.

 

LOL, in fact, I'm pretty sure it's not 1:1. I didn't mean for my numbers to come across as a real world example. The amount the rack has to be moved depends on both the amount of drop and the cars original geometry. If there is a straight forward way to calculate the actual amount the rack needs to be moved, short of drawing out the 3D geometry, I'm not familiar with it.

I'm dropped a little over an inch up front, and the car really doesn't have enough bump steer to worry about (at least not anywhere where I drive the car), and bump steer is something you usually don't worry about unless it becomes a problem.

Good catch S2FARSI. In re-reading my post it's obvious that this needed better clearification. Thanks.

 

MX5,

I will soon be purchasing the t1r 20mm spacers since they are the biggest I could find. I will be lowering my car soon 1.75"-2" in the near future. Hopefully I can come back to this site with some good reviews.

 

Have fun putting it in w/ the smog pump hardline there. I had a hard time w/ the spoon spacers on my friends car. He had about 1-2mm left before the rack hit the line.

 

[QUOTE=SOHCmyDOHC,Sep 26 2007, 01:08 AM]Have fun putting it in w/ the smog pump hardline there.

 

so whats the biggest space you can install with the smog pump hardline?