FredR

Jeff,

No personal flame intended to you or anyone else for that matter and trust my [well intended] humour does not offend at the expense of anyone.

I personally prefer to let value be decided by the purchaser.

I do however highly value the efforts of all our "innovators" who I try to sponsor as/when possible even if it is in a modest way -I have purchased a few items from Carl, all of which I was well pleased with at the time.

For sure I enjoy reading constructive analysis- positive or negative, right or wrong and if someone deserves a good ragging then so be it.

Best wishes

Fred

IcemanG17

interesting......I have ran my racer as low as 85mm in front.....and never noticed "bump steer"....and going over the bypass at Thunderhill into the right hander clearly isn't easy on suspensions.... it just never seemed to be an issue...

I can take corners with bumps at apex at over 1.5G, at 100mph and never noticed an issue.....

69gaugeman

+1. That will work fine until it wears out. Then you can replace the joint or go back to stock.

That's because the geometry of the tie rods doesn't change as drastically in the 928 as it does in other cars with suspension travel.. As long as you are not overextending the inner joint, there really is no issue with the tie rods. If you have clearance issues, you can use this kit to fix it.

Carl Fausett

That depends what year 928 you are referring to, and what model Porsche you are comparing to.

We measured both before-and-after bump-steer on both the early cars with longer a-arms and the later cars with shorter a-arms.

As excpected, the early cars reacted less adversly to being lowered where bump steer was concerned. The longer a-arms of the early cars have less change in angle because of the longer links.

So we expected the late-model 928's with the shorter a-arms to be more greatly effected by lowering, but the amount that the toe changed thru the range surprised us. It was quite a bit more than expected.

When i get a little bit more caught-up on my other work, I can publish the pictures and the results of the testing.

I assumed (incorrectly) that because bump-steer kits are so common on any street car that is lowered and tracked - either by relocating the steering rack or relocating the tie-rod ends (when the steering rack cannot be moved, as in the 928), and because they have been in use for so many years and so popular on Porsche's that no explanation would be needed. I can see I was wrong.

Speedtoys

We agree on more than we do not, which is..well, everything.

We're saying the same thing, just different ways.


No harm seen/taken.

69gaugeman

Please do. Data is always appreciated.

Carl Fausett

And I agree - they did a fantastic job of designing our suspension.

But if you lower your car from the factory spec by an inch or more, and introduce angularity in your front tie rods ends in excess of what was intended, and by doing so, effectively shorten them, then why wouldn't you expect your toe to have been effected?

Of course it has!

If you change the length of your tie rod arm, you change the toe-in/out setting. That is in fact how the toe setting is adjusted during an alignment.

If you change the point in the arc of the suspension travel where we pass zero (the point where the bump-steer changes from toe-in to toe-out) then you have modified the bump-steer characteristics of the car.

I fully agree with you - Porsche did a great job of designing our suspension. This is not an attempt to modify their design, but rather - this is an attempt to get back to their design after you have lowered your car.

If you have lowered your car (at the springs) you have already changed your suspension geometry. Putting the suspension back into Porsche's designed arc and range is a good thing. Not a bad thing.

I will publish the test data we gathered in the next couple days. Until then, this drawing (not mine) may help explain what we are talking about.

Bart-Jan

The reason for this is very simple: by lowering, you don't change the actual length of the tie rod. Of you only measure the horizontal distance (allong the x-axis of a normal graph if you like), the length indeed has decreased. You are forgetting the the upper and lower A-arms are seeing the same angular change and therefore also a change in horizontal distance, which is in 928's case almost identical.

Your image is very nicely explaining what's going on here. If we assume in 'normal' ride height, the arms and rods are horizontal, then in lowered setting, all arms would point upwards to the top left in your image. The bump steer kit changes the position of the tie rod back to horizontal, or worse: pointing downwards. The horizontal length indeed would change and thereby adjusting the angle of the wheel seen from above: toe out. Now in static position, the car will be adjusted to the correct toe settings. If the spring then is compressed further, the toe out would increase even further! This is called bumpsteer.

I agree with previous posts: I really appreciate all efforts of developing new and or improved parts for our beloved cars. I've bought many parts from Carl allready. This item will however not be on my wish list. Other customers would probably think otherwise. That's what makes us human;-)

Mike Simard

I cannot believe you are actually trying to argue this after what I said.

This is irresponsible and absurd, that drawing is seriously flawed and would not even work in reality, it would be the poorest handling car in existance, what's it supposed to show anyway?

You have no understanding of suspension design which is fine but to attempt to sell flawed parts with safety issues and continue to do so right after it being pointed out as flawed and actually argue it with someone that implies they know the subject is reckless.

Speedtoys

Mike:

What makes this any more dangerous than a bazillion bump steer kits already in existence, and of the 10s of thousands in race use every weekend with well, the same hardware.

No rat in this race here, just curious.

Mike Simard

I'm not wasting any more time on this, I'm dedicating my experience to my customers and friends instead. Besides, it's cutting into the time I normally would be spending looking for cat videos.

Speedtoys

Uhh...ok.

Mark Anderson

This was done to my car more than a decade ago and it did help tire wear. I was getting lots of toe out under compression and this helped. I never touched it from day one so I guess that means you might want to take a closer look at things.
I see you sig says expert parts washer so I'm Assuming this is a pic from back when it was mine right

Speedtoys

Apparently, it's actually out to kill you, and steal your children.

But we wont ever hear _how_.

Rob Edwards

Maybe it's why he sold me the car so cheap (?)

I'd better go wash the tie rod ends.