The book was called Dynamic Systems and Controls published by Kettering University. Another book was called Vehicle Dynamics but I'm not sure who the publisher was. I don't remember too much about bump steer (of course maybe that was one of the days I skipped :lol: ) Anyway they both have a lot of good info on yaw rate, oversteer/us, response modeling, and that sort of stuff. I would recommend this book to anyone who has trouble sleeping. :sleep: :D

 

You better look at the publication date on that book. The late Alan Kulwicki taught me how to bump steer a car back in the late 70's so it is hardly new or cutting edge. But it is just recently that street rodders have started to learn that there is more to vehicle dynamics that just a big set of wheels and tires.


You are right that you can not have zero bump steer at both static and dynamic conditions. The problem is that you can not check for bump steer in a dynamic situtation without linear motion sensors and a data accusition package that we use on some of the race cars. At upwards of 10K for a system it is a little out of the budget for most street guys. So that leave you with a static check set-up. Bump steer will change as you turn the steering angle and suspension motion, so to try to set for zero bump steer dynamically, what steering angle do you want to use?

To concern yourself with bump steer without first making sure that everything esle on the suspension is in proper working order(zero play ball joint, low deflection bushings, ect.) is a wate of time. Bump steer is the last thing to be set on front end geometry. But it must be designed in from the start. Ride height, a-frame placement and intial alignment must be done before you can set bump steer.

As far as front steer/rear steer, you can not say that one is better than the other in all situations. There are advantages and disadvantages to both as far as caster/camber gain, caliper placement/ball joint loading is concerned. The differences between them is minimal and way past the needs of a street driven car.

There is no big difference in steering effect between a drag link design steering and a rack and pinion setup. Both must be designed and installed properly to fuction properly. Most race cars nowdays use a R&P because of the weight benifit. Winston Cup cars can not use R&P so they must have a properly designed and set-up drag link steering, and they have no problem with stability at 200MPH.

To properly design and set-up front suspension geomerty you must take into account all of the front suspension components and look at them in both static and dynamic situations through a full range of suspension movement. To focus on just one area can be very misleading.

 

amd lets not forget, we have massive bump steer in the rear too (yes, bump steer in the rear exists). our clumsy trailing arm arrangement pivots over 2 points, the frame mount and the 1/2 shafts inner joint. If you watch the rear go through the full suspension travel you'll notice the toe will change in the rear, creating bump steer. The only way to fix that is to introduce a 2nd hinge point in the trailing arm, just like the 5 link, the C4 and similar setups and have a strut on the rear or an extra one on the underside control the toe (so it remains the same over the entire suspension travel)





[Modified by Twin_Turbo, 3:58 AM 8/26/2003]

 

..this here topic is dying, NOT good :)

So, any input? Norval, Pete, Gene,.. others.....

 

Pete and Twin_Turbo, you both make some good points. The rear of the car can be just as important as the front. Depending on how balanced the car is, rear toe steer could make things rather ugly. The rear could move that balance more towards over steer and that wouldn't be pretty. Pete has also echoed my point that bushing compliance, suspension geometry, alignment and the like play a critical role in bump steer. I will reiterate my point that because of the differences in all these factors, a bump steer curve is going to be unique to an individual car. Whether it is significantly unique can only be determined once measured.

Pete, I think you could do a reasonable job of plotting dynamic bump steer without a high-end data acquisition system. Granted, the resolution of the data wouldn't be near as good but it would really only require time rather than money. A measurement scenario where you plot the bump steer vs. steering angle (say at two different points of 15 and 20 or 25 degrees) with a level chassis condition, then with the chassis at 5 degrees of body roll and another at 10 degrees. Determining which steering angle and which body roll angles can be done by finding the corners and condition that the car spends the most time at (or that will gain the most useful speed) and measuring those angles.

 

Twin_Turbo. This is a subject I enjoy talking about but I think it has run it's coarse again. It keeps popping up every now and then. I have really persued this problem this summer.
In this search for 0 bump steer I have so far, make a really good bump steer gage, bought a caster camber gage, made a really good accurate toe gage.
To the car I install adjustable upper ball joints, removed the upper A arms and slotted them to give 5 degrees of caster and minus .75 camber without shims, installed adjustable outer tie rod ends that are actually a stud and heim joints and after experimenting on the correct shims removed the steering arms and welded on the proper thickness shims and used a 5/8th bolt for a heavier solider attechment. Made 4 sets of tie rod sleeves and install 3 extra inner ball joint holes per side to try the different length of tie rods and their effect on bump steer.
I also installed a nascar style power steering pump for increased pressure and reliability,
I also installed a set of 460 springs, test drove then pulled out to re install the 280 pound morosso's.
So you can see that I have been busy trying to imporve my front end. At a car show almost none of it shows, only I know it is there but it really works on the open road and high speed. :) :) :)

 

Norval, I don't know which one of us is worse off, you-the guy who has all the gear and CAN, or me who has not quite the budget-but the desire.....

either way , we be doomed....vechicle dynamics is interesting, for sure, and yes I have a book on the subject....

Fundamentals of Vehicle Dynamics by Tom Gillespie....who teaches at Univ of Michigan, and at Ford plus others....the man has much more than this few shots to his credit, on back of the book....
MUCHO credit to the guy who can actually UNDERSTAND this book...given to my by an old old racing buddy of some decades....

OH, and yes, the pages are FULL of every one of them crazy squiggley math whatchamagiggers too.....fun reading for bed time....;-)))

GENE

 

Gene they are talking about dynamic bump steer and most have never even worried about static pump steer. If a few of us let the subject alone most would never know it existed. It is only by a few continually harping about the problem that most even begin to understand there is a problem.
Guys worry about the static first before going off in search of the more elusive dynamic.
Most of you will notice the problem in a straight line anyway, going really fast over a hill or through a dip. In the corners you are not noticing it.
Twin Turbo I will have to start check out the rear as well

 

flynhi, I’m sorry for your question getting lost in the shuffle. Basically the only adjustment on our system is at the outer tie rod pivot. It can be adjusted down, if needed, by swapping the spacer from below to above the rod end. Other spacers can be added as long as the elastic lock nut has full thread engagement. We have already made the tie rods longer. You will have to measure the bump steer to know which way you need to adjust. Be sure to do this after the alignment has been completed.

 

Eric,
So the procedure I should use is:
1. Have the car aligned to spec.
2. Measure bump toe change as per Norval's suggestions on 8-21 above.
3. Adjust location of tie rod end shim (above or below) and tie rod length to get as close as possible to no change in toe with vertical movement.

Is this it?

 

Norval-I also installed a nascar style power steering pump for increased pressure and reliability.

Tell me about this, I thought of going to a power steering pump like this but haven't had time to look at what is available yet. Is it bolt in? Does it have a remote resivoir? and does it use factory mounting bracket/pulley?

Eric, you keep mentioning that changing the relay rod or tie rod length is unit specific. Why do you make this statement? It would seem that all C-3 Corvettes that share the same front suspension would use the same length of tie rod and same 3.1" inward movement of the relay rod connection that Norval did.

Norval, Would the tie rod length and relay position change from the 3.1" in if you extended the spindles an inch as we are planning? Does the upper control arm need to be altered as well?

I have read articles in the past about G-body Malibus that use Global West extended spindles requiring a modified upper control arm to compensate for the change of using of the extended spindle. Would this be necesary for us ? Jim


JIM

 

If you get a Sweet or KRC pump get the head mount bracket and it'll fit your car really nice. They use a remote reservoir, Norval made his own reservoir (real cool looking piece).

I have a KRC pump, head mount bracket and a sweet reservoir, here's where the pump will mount on the engine:



It's the one of the far right, the one with the hoses on it

Marck

 

Twin Turbo I am sure Jim remembers my homemade resovoir but in case he missed it here is another shot.

 

Tell me about this, I thought of going to a power steering pump like this but haven't had time to look at what is available yet. Is it bolt in? Does it have a remote resivoir? and does it use factory mounting bracket/pulley?


The pump definitely needs a remote resovior and if you have a small block a flat mounting plate is easy to order. It bolts directly to the front on the block in about the stock locations. As for shimming out, you can easily make stand offs.

Norval, Would the tie rod length and relay position change from the 3.1" in if you extended the spindles an inch as we are planning? Does the upper control arm need to be altered as well?

I don't know about the tie rod length. In theory the tie rod length should equal the distance between two lines drawn through the outer tie rod pivot points and the inner frame mounted pivot points. This is the tie rod length required and spindle length should have nothing to do with it. So extending the spindles should be ok. But the outer or inner mouning height will change. The instantanous center point changes with spindle length so the tie rod end must be moved up or down to point to this new instantanous center.
I didn't know what my car wanted, just guessed and made 4 different length sets of tie rods with 4 different mounting holes in the center link then ASKED THE CAR WHAT IT WANTED. For me the 3.1 inches longer then stock gave the least bump steer. After changing the spindles to the new longer ones I will ask it again and see if the 3.1 in still the best length but in theory it should not change.

I have read articles in the past about G-body Malibus that use Global West extended spindles requiring a modified upper control arm to compensate for the change of using of the extended spindle. Would this be necesary for us ? Jim

The only thing and extended spindle does is increase the negative camber. If you started at 0 camber as the spindle length increases the camber goes more negative. It is possible to run out of adjustment. If you have alot of shims no problem but if you are already low on shims it might just make for too much negative camber.

 

Norval, about13-15 years ago on that Lemans/GTO convertible I had, I did a Global West system, with '80caddy spindles, and they supplied custom ball joint to be pressed into the lower arm...tops were easy...and yes, it did help the handling, that car was greatly improved....I think the caddy spindles were taller, but you know, I can't remember....

I couldn't think of the company name either....but you nailed them....
as I recall, I used 1Le camaro rotors on that setup also....I needed the brakes for towing that boat....had a towing version of a line lock on it too, to freeze the front calipers for up to 30 minits when on the loading dock/ramp....

NOW, Norval, I am somewhat confused about the interaction of the two mods you are doing/recommending.....I can see/understand the mods of the tall spindles...and I can see the mod of moving the top A arm back a bit for extra caster, but I do NOT understand why that alone would not be enough to make the reaction we want....or would it.??? so are the affects additive and desirable, or is one more potent than the other, or....well, what's your guess as to how this is going on...??

GENE

 

NOW, Norval, I am somewhat confused about the interaction of the two mods you are doing/recommending.....I can see/understand the mods of the tall spindles...and I can see the mod of moving the top A arm back a bit for extra caster, but I do NOT understand why that alone would not be enough to make the reaction we want....or would it.??? so are the affects additive and desirable, or is one more potent than the other, or....well, what's your guess as to how this is going on...??

GENE

You are confussing me Gene. What are you asking? Slotting the A arm cross shafts helps caster. 5 degrees no shims. The longer spindles increase the downward angle of the upper A arm making a higher roll center.
The bad part about longer spindles is it causes an increase in negative camber. If you have shims to remove that is ok but if you are almost shimmless so to speak you don't have the adjustability to remove some of the unwanted negative camber.

As far as aftermarket spindles I still can not see a simple cut a weld of the stock units. NO money involved other then the welding and welding can be done just as strong as original.
Also the loads on the top of the spindle are very minor so strength while important is not overly hard to achieve.
Gene I am not pushing anyone into making any of these modification. I am experimenting, pointing out the original problem then telling them what I have done to try and eliminate that problem.
The only thing stock after doing my spindles will be the lower A arm. Everything else is modified. Looks good though.

 

flynhi, that's how to do it. Keep in mind that the only reason you will be changing the tie rod length is to set the toe back to the original alignment. So make sure you measure the toe setting before you start. A general recommendation for alignment is to put as much positive caster in as possible (4 or 5 degrees).

PROSOUTH, I make the statement of vehicle specific lengths because of 1. The tolerances in the factory parts and mounting locations are all over the map, 2. 20 to 30 year old cars have settled, bent and loosened frames that can change the physical relationship between the frame, suspension and steering, and 3. Both the caster and camber settings affect where the steering arm hole (for the tie rod end) sits in space and where it moves during suspension travel.

For example, Norval's slotted a-arm cross shaft (a good idea, by the way) changes the pivot point of the upper a-arm in relation to the lower a-arm's pivot points. With normal shims the a-arm will act in a different movement plane when compared to a cross shaft without shims. This will change the location of the steering arm hole throughout the suspension travel (it will track differently than the setup without shims) therefore changing the bump steer curve.

 

OH, Christ, I give up allready.....I understand it all, but so it seems it would take a whole GM chassis design programme to figger all this out....
I don't have a CAD/CAM powerful enough computer....

I do like the slotted upper cross shafts though.....

GENE

 

Gene, you crack me up. Granted there are a lot of factors involved but if you just want an improved bump steer curve, just follow Norval's methodology. It will improve things but it wont make it perfect. Direct measurement of your own car and trying a few locations and lengths will make a difference. Besides, I think that as people understand more and get into measuring they will feel more comfortable expanding those measurements to include dynamic situatons.

 

For example, Norval's slotted a-arm cross shaft (a good idea, by the way) changes the pivot point of the upper a-arm in relation to the lower a-arm's pivot points. With normal shims the a-arm will act in a different movement plane when compared to a cross shaft without shims. This will change the location of the steering arm hole throughout the suspension travel (it will track differently than the setup without shims) therefore changing the bump steer curve.

This has me a little confussed. If the lower ball joint is fix and it is and I want the upper to end up 5 degrees behind the vertical line drawn through the lower ball joint and minus .75 behind the vertical line and I achieve it through milling the cross shaft mounting hole or pile shims in where is the difference in pivot points? The arc's will be the same.

My upper and lower pivot points are still in the same location. I just arrived at it differently.
I also believe that getting 5 degrees caster is impossible with just shimming and believe that the best solution is changing/milling the cross shafts.
I agree that testing and measuring are the only way to really know what your particular car needs.
Checking can be so easy I don't see why others don't try it.
Lay under the front of the car, hook a tape in the far tread and take a measurement, jack up 1 inch take another using the same points. It is crude but gets you an idea. Do it over a 3 or 4 inch lift. Just be sure to use the same measuring points and as close to the center of the tire as possible.


Gene don't give up. I have the software to run a program but find getting the numbers to plug in is the hardest part. To me it is easier to just check on the car.