Rear steering

M

msogren

New member
After looking at the replies to the rear axle bearing stuff.,I wonder why do we stiffen the rear axle bushings??
The stock bushiings allow the axle to toe out some with side load. The is helps the turn.
We spend a lot of money and time reducing the push. Some use lots of tire pressure, this results in a fine edge of control. The same with very hard rear springs. or sway bars. The result is a narrow edge and some spins.
Some use toe out and less spring and maybe tire pressure .
The solid axle bushes add to the problem or push by taking away the load induced toe out.
I think that we need a softer bushing that travels more. Than we could use less of all the other" fixes."
I will put the solo car on the weagie boards this week and measure the toe versus load.
I am running about .75in toe out per side now and the car is pretty good. The slalom is real nice but the constant pin turns are still pushy. I need a rear axle that moves toward more toe at a constant load, but stays pretty straight in the transitions. The road race cars need about the same thing, IMHO
I have visions of a hand brake lever hooked to the middle of the axle and bending it as needed.
Mike Ogren
 
Michael,
The problem is that the VW toe-control bushings are not designed for motorsports.
The VW designed geometry changes are quickly overcome by racing or rallying type stress, distorting the bushing far beyond the correct amount, resulting in large and uncontrollable geometry changes. Additionally the bushing will deteriorate with prolonged use in a race environment to the point where it is no longer able to locate the rear axle beam effectively when any stress is put on it.

I spent quite a bit of time analyzing the designs of VW racing and rally cars I found in Germany. (spent a few days at the Nurburgring 24hrs, VWMS and a hillclimb full of VWs) After talking with a few people it was clear to me that every FWD VW I examined (with the exception of the G4 Kit Car) used the same VWMS type rear suspension. See the drawing posted elsewhere in this forum.

Now some of the cars did not use the rear toe control (panhard type bars), however they all did use hard spherical bearings to fix the axle at a known point. From a known point you can at least set your alignment to compensate for toe changes due to axle beam flex (trailing portion). Axles beams are also usually strengthened longitudinally by the way. This reduces the tendancy to bend under and generate unwanted toe and camber changes.

The ultimate setup however is the triangulated beam with the toe control bars linking the center of the axle beam to a point 4" below each rear lower shock mount.
 
Bill: try convincing Bob Griffith (BHP Developments) and Jack Bahna (GT Lights Rabbit) of that. Their super-compliant trick setup seems to work pretty damned well! Although I ran spherical brgs in my axlebeam, I still wouldn't discount their approach. The more I know, the stupider I get.
 
Does someone make a soft bushing ??
I picture a guide plate and some soft material or hydralic stuff to control the swing.
The bushing is only about 1.75 in +- . If the axle moves.5 in on load, That could be usable.
BTW I have used stock axle bushings in all of my cars, fairly successfully. The front control arms are stiff tho. I could just not see the improvement in doing what I considered counter productive to what I wanted the rear to do.


Phil, I am told that you have a fast Digifant car . After working on them some in my shop, but very seldom due to the fact that they have very few problems. I want to change my Son's solo car over to Dfant from CIS-E . The book says that we can run well by reducing intake restriction. It also says that the meter doesnt affect WOT or rpm over 4500 or so. ( plus my Son found his engine code and it's 90hp, he wants the 105 hp engine):
Some times the solo car needs to rev well into the mid 7s. will the pulse percentage time keep up??
What injectors do I try , and can I pull the A/F Meter open at full throttle ? Can I change to a larger AF meter??
[email protected]
Thanks. MM
 
Mike, or anyone interested: you could call Bob at 215 838 0361 on Tues/Thus afternoons and find out what he does and what it costs (he does makea living off his brain you know) Be warned, however; I think his parents trained him not to talk to strangers!
Regarding the Digi II setup: IM me about chip tuning for Digi II. I don't have any personal experience with running the BMW AFM but I can tell you what to do. I can't imagine it's of much value unless you're making pretty big airflow numbers. And contrary to popuar belief, the AFM is still controlling AF at full load/redline and still isn't fully open. The stock sytem leans out because the fuel map in the ECM demands it.
 
I worked for VW for a while. I aquired some A2, new car tech data books. they speak of toe control rear bushes. They are basically just rubber ramps that as the axle moves laterly, under load, the bushing rubber wedges the axle towards more tow in.
I have the solo car on the aligment rack. The bushings actually dont add any toe at all, but I think that the intent is to not add any tow out. With some load , moving the axle sideways with a pry bar, there is no toe change. Pulling on the rim shows some toe out, about 1mm total , That is, the axle bends some and the bush moves a very little. The bushings and the brackets are interchangable from side to side and front to rear. I will take the brackets and swap them , along with turning the bushings around to ramp the rubber to the rear. This should increase the toe out with load. There is also the possiblity of insertiing a CV joint ball into the bracket/bushing joint to take out the slack and move the axle on the ramp, pretty well under the control of the ball and funnel shaped bushing metal. We'll do this when we change to the disc brake rear .
This wont happen until late summer tho with 15-20 baseball games in June, and some races. MM
 
>> Bill: try convincing Bob Griffith (BHP Developments) and Jack Bahna (GT Lights Rabbit) of that.

Hi Phil,
Try convincing them of what I saw? :D
Rabbits dont have a rear bushing like we're discussing.

I'm sure that other (flexy) designs are possible and may work. I'm just reporting my findings.
VWMS and the majority of cars I've studied use a solid rear bearing.
 
Last week, Michael and I installed the disc brake rear , with the flipped, stock bushings. The springs are about 400 rear with 500 front with a 16v rear bar/axle. I did the same lateral pull test , on the front end machine. The results are much better than the stock. I could get about 3mm of additional toe out with the same lateral tug on the lower shock bracket. They are still too stiff it seems to me. I have left the option of drilling thru the bushing to soften it up. But I wanted to run it stock to try it.
The total alignment ran sat and sun is ; front ; - 3.5degrees camber, 5mm toe out, Tires at 31# hot
rear ; 3.0 degrees camber, 1in toe out(.100 thou shims), tires at 46# hot
Mike and I made 26 runs total sat and sun; we corded three of the spec racer yokes within 2runs of each other. This shows a much better balance than prior.The tires had a total of about 60 runs , after taken off of some SRF, so tire life is very good.
The car was very neutral sat on the second gear track and very fast on the 80ft slolom sections. Better , but still pushy, on a single pin turn style of situation. Perfect on the 50-60mph sweepers
Sun the track was very slow with first gear areas, 70s , old school. perfect for the Vw with 85hp and decent suspension. I was about 2 sec faster repsectivly than last month, next to the other cars. I was bumped from FSP to combine with DSP(nissan 300zx) and ESP( Toyota supra). Both of these cars beat me by two - three sec on a 46 sec course. I beat them today by .3 on a 58sec course.
The added rear stear reduced the push in the very tight stuff and the sweeperes were very neutral or loose. Not loose enough to lift. but rear drive- ish.
Next ; is to soften up the bushings more and take some rear toe out. I think it has a lot of potential for a road race setup , if I can get them soft enough. I am going to read the rule book and see if I can bolt the axle brackets to the car using soft mounts, like my Ultralight airplane engine mounts. They come in different denstity ratings.MM
 
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