bump steer spacers/ steering knuckles 240z

[mark240z]

has anyone bought the arizona steering knuckles with bump steer spacers and are they any good???

im keen to get the steering knuckles machined up with the built on bump steer spacers but im not sure on the dimensions, if anyone can help me out id be grateful

thanks mark

[franky]

technically it'll depend on what suspension you're running, exact ride height etc etc.

If you're having some made you'd be best off doing some measurements on your setup.

[mark240z]

My car is miles away from being finished so I can't measure the ride hight as I haven't got any wheels yet, I've bought the mekinney motorsport coilovers, and was going to get the steering knuckles made 10mm shorter, and how does it look in the internal bore of the spacers so I can get a better idea of how it works ?? I might just being a bit stupid here ??

[franky]

Couple of good books to read here...

Competition Car Suspension: Design, Construction, Tuning: Amazon.co.uk: Allan Staniforth: Books

How to Build and Modify Sportscar and Kitcar Suspension and Brakes: For Road and Track Speedpro Series: Amazon.co.uk: Des Hammill: Books

[johnymd]

I've lowered by car more than more and yet to find the need for these spacers. I understand the principle but never found the need for them in practice. Maybe it because I get very little suspension travel on bends and avoid high speed cornering on very bumpy roads.

[franky]

why do you get little travel? Bump steer isn't just caused by bumps, its as the suspension goes through travel in bends. It all gives me a bit of a headache to be honest. With your fully adjustable setup you should be able to just about set the car up to feel however you want it to.

Basics are that with your lower wishbones level the steering arm on the rack should have a level line between the two pivot points.

[johnymd]

I get very little travel because the car rolls very little. It doesn't bounce around and I think this is when bump stear is most noticeable. My car goes round bends very smoothly. If the suspension compresses as I go into a bend the stearing will alter slightly due to the differencial angles but I am making stearing adjustments anyway so I dont notice the bumpstear effect. If maybe i go over a big undulation mid corner then yes the stearing will alter as the suspension rises and fall but I can adjust my stearing to compensate.

Because Im no expert at track work I probably dont notice the effects. Perhaps I should try some spacers and see what the effect is. But then again, I may not be good enough to notice an improvement. I guess I should fit them as everyone seams to say they work but I'm not in any hurry to do so.

[franky]

Theory goes that its more noticeable on the road. As you said though are any of us good enough to notice small geometry changes!?

If you like how your car feels there's no point fitting them, save the money towards rear tyres

[Rob Gaskin]

The spacers help to keep the tca and trackrod horizontal on a lowered car. In that position they have less effect on steering through the suspension travel.

[zbloke]

If you've got bump steer you'll know about it

As you go through a corner, either road or track, you'll be sawing at the wheel making constant corrections to the direction of travel, the amount of sawing will depend on the amount of bump steer you have

Ideally you want to have zero

[morbias]

Wouldn't having the LCA horizontal be bad for bumpsteer? I'd have thought with the angle of the LCA being what it is, having the LCA horizontal would cause the toe to change more noticably?

[franky]

Originally Posted by morbias

Wouldn't having the LCA horizontal be bad for bumpsteer? I'd have thought with the angle of the LCA being what it is, having the LCA horizontal would cause the toe to change more noticably?

Its all in relation to everything else. In the spaceframe toy cars I've had you can feel if its not quite setup right.

I'm not sure what the cars were designed to run caster/camber/toe also how much bump steer a good standard car has.

[Rob Gaskin]

Originally Posted by morbias

Wouldn't having the LCA horizontal be bad for bumpsteer? I'd have thought with the angle of the LCA being what it is, having the LCA horizontal would cause the toe to change more noticably?

Try it on a drawing.

You either want to lower the outside with a strut spacer or raise the inside mounting point on the cross-member.

If you leave the arm as is (pointing upwards if the car is lowered) bump-steer is accentuated.

[morbias]

Leaving it pointed upwards is not what I mean, surely it should be pointing down for less bumpsteer? If it's horizontal then on compression the LCA will be angled up when the tie rod is angled down as the steering rack sits slightly higher than the stock LCA pivot point, then on further compression the tie rod reaches the top of it's arc before pointing upwards with the LCA.

[franky]

Originally Posted by morbias

Leaving it pointed upwards is not what I mean, surely it should be pointing down for less bumpsteer? If it's horizontal then on compression the LCA will be angled up when the tie rod is angled down as the steering rack sits slightly higher than the stock LCA pivot point, then on further compression the tie rod reaches the top of it's arc before pointing upwards with the LCA.

I understand why you think what you do but without drawing it I can't describe it. With what you're suggesting you'd end up with even more bump steer though.

Buy the books above, good toilet reading. As Rob says a lot of race/rally cars have the lower mounting point moved to compensate for a drop in ride height.