Front end lightness

Pushing 80 mph (in short bursts) it is amazing how light the front gets and how quickly the directional stability goes away.

Was this a the case with the originals?

And is there a way, short of sand bags in the front, to reduce the tendency to float.

1957 Beck Speedster

Original Post

 

If you don't already have a spare tire (and wheel) in the front, you've just found another reason to have one. I have a VS with the battery up front and forget if Beck puts the battery there or not. I also store some tools next to the battery.

Stability is OK in my car at 80-85, and I've touched 90 once or twice and survived, but I usually cruise at 70-75 and avoid interstates as much as possible.

Part of that "lack of directional stability" or "lightness" could be there not being enough caster. A VW barely has enough caster for 65-70 mph, and dropping the car even just a couple inches can make it hard to control even at 60 mph. To make the car safer at higher speeds your car may need a pair (or even maybe 2 pairs, depending on how low the car is and how it was lowered) of shims underneath the bottom beam of the front suspension.

http://www.geneberg.com/advanc...ster&x=3&y=7

As you can see, they're not expensive; buy 2 pairs (and the longer bolts) and if you don't use the 2nd set you can always sell them. Al

I think 80 mph was flying for a 1957 Porsche Speedster and it was heavier steel.  They had a max 90 HP!  (I think top speed was advertised as 120 mph).  A big low mounted front battery would add 40#.  A 12.5 gallon extra capacity gas tank adds maybe another 20# over a 10 gallon one.  A spare tire and Jack maybe another 40# with tools.

I had a late '65 911 and during a repaint I discovered big cast steel hunks on either side of the front bumpers which I guess were for keeping the front down and providing better balance (F to R). It also had a spare tire mounted low (as a crush zone too) , gas heater, plus jack and tools. It would do an indicated 130 mph but was scary at that speed (fortunately I-81 is pretty straight in VA).

Image result for 1966 porsche front bumper weights

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A Beck can't use caster shims as the beam is welded in as the frontmost frame crossmember.  The only way to adjust caster, short of cutting and welding, is to lower the rear of the car relative to the front.  Luckily they include adjustable spring plates, making that an easy job.  I had a similar caster issue when I first got mine, but it's easy to correct.

Jim, if you bought your car new you should have an owners manual detailing how to adjust the rear ride height.  You can also adjust the front as the car has avus adjusters on the beam.  Check with Carey if you don't have a manual, or PM me and I'll send you the instructions.  Also, your car should have a full-sized spare up front.

My JPS was scary .....till I added caster as advised by the guys in here and lowered the tire pressures to 20 psi....I thought about putting a couple sand bags in the trunk but didn't do that.... it is fine at 85 mph, any more than that is a "come to jesus moment".

I also had a 69 911 and it was very stable at top speed....it very well could have had the weights in the front as Wolfgang pointed out......but I wasn't aware of them.

Compared to any other cars I owned at that time, including Camaros and Mustangs and Corvettes, that Porsche was on rails.... 

 

 

I'm dealing with front end issues at the race track in a kart right now. My steering feels way too heavy and I want the kart to turn in faster and exit the corners faster. I was advised by a professional driver to remove a little caster and add a touch of tow out to the front wheels. This frees up the kart but makes the back end feel loose. I think the term here would be oversteer and I'm looking for a little more of that.

This must be the opposite if you want stability. As long as your top king pin angles sit behind the center of your wheels they will automatically straighten out when you let go of the steering wheel - kind of like, well just like the front wheels on a shopping cart.

The more positive caster (top of king pin pointing backwards) the more front end stability you'll have or "understeer" and this front end stability transfers to your rear wheels as well giving them more bite. The downside of understeer is how heavy it makes your steering feel in a corner.

In a kart you are in a very tight seat and you feel every move the kart makes and for me I found I prefer a little oversteer (less caster) which makes the rear feel a little to very loose but I control that. The benefit is the kart is faster going into and out of the corners and on a kart track there are a lot of corners!

In our cars you don't have that precise feel of control so I think adding more caster is a good idea - you'll have a lot more stability both front and rear but you'll have to pull the wheel a little harder and farther to get the desired effect. Make sense?

I understand there are caster shims but can't you add or subtract a little caster using the eccentrics on a VW? Seems to me the eccentric moved all the way back would add a measure of positive caster then bump the eccentric a little to the inside to give you a touch of negative camber. I'm so glad this topic came up because it's something that I'm trying to get dialed in as well!

@Jim Dunn You may have two issues going on. 1) The wind force is literally lifting the front of your car causing a "hydroplaning" effect (Not too likely). 2) You indeed may not have enough caster and the car feels uncomfortably squirrely at high speed. Squirrely doesn't necessarily mean you don't have traction it means your steering needs more attention and a very steady hand.  

If you don't have enough caster your steering will feel light and responsive at any speed. Also, you may have enough caster but you may need to angle your body such that it pushes down on the front end at high speeds if you do that a lot. Or perhaps a touch of adjustment to both. These type of issues are tough to get just right.

Jim:  The additional caster shim(s) should help a lot.  You should get the front end aligned after installing the shims, and tell the tech you want between 5º and 7º of negative caster.  Adding caster shims will make the steering heavier, especially at low speed in parking lots, but it should feel MUCH more stable at higher highway speeds.

Of course, adding balanced weight to the front is always a good thing.  Finding a place to put it can be a problem.  Porsche's weights low at the corners in front of some 911s is just about perfect placement.  We would have to do some serious fabricating of a structure to hold them on a fiberglass 356.

Caster is a bit hard to understand for sure. My take away on Jim's problem is he feels a lack of stability at higher speeds - perhaps the car feels like it wants to wander from side to side. If that is the case then "negative" caster will only worsen that condition. It may be best to google caster settings and try to get a better understanding of what the effects of positive caster versus negative caster are. From my understanding if you want your wheels to self center and have more stability then you would want to add "positive" caster.

“Aligning torque as the result of positive caster settings produces a self - centering effect which wants to return the steered wheels back to their neutral position”

Here is a good resource:

http://www.racecartuning.com/caster.html

MusbJim posted:

Jim's profile on his initial post shows that he has a Beck. Lane posted that caster on a Beck can't be adjusted by adding shims because the front beam is welded to the chassis. I'm guessing that discussing addition of shims is kinda moot.

You're right, Jim; I'd forgotten about that little tidbit! I do remember having this discussion before and someone mentioning that Becks come with more caster.

Beck Speedsters have the beam welded in, so caster shims won't work.

There is a workaround though. There are aftermarket camber adjusters that fit where the top ball joint goes into the spindle. They provide a wider range of adjustment. The free bonus here is that with a reasonable amount of camber dialed in, they automatically provide more caster. 

Nobody here has touched on toe except Rusty. You WANT toe-in on the street. Track or autocross you want zero or maybe a bit of toe-out, which makes the car easier to turn into a corner and thereby a bit unstable. Or as I like to say, flickable.

Nobody has mentioned rear toe-in. Crucial to how the car feels going down the road especially at speed! You want a bit of toe-in in the rear as well, about 1/16" total, this will also prevent that wandering feeling. I do remember one Lane Anderson having to elongate the slots in his trailing arms to get a bit of toe-in and stability.

Front end and all bushings, tie rods, and ball joints should be checked also. Don't forget the steering stabilizer! Sometimes they go bad.

I have 1/16" toe-in on both front and rear. 1.5 degrees of negative camber in front, about 3 degrees negative in the rear(swing axle). Caster is 5 or 6 degrees positive(and it is MOST definitely positive caster we want). Stable up to 125 mph in my Spyder.

Jim Dunn posted:

I do have a Beck and have lowered the rear to its max. 

I also do have the manual that Lane prepared that I will have to review.

I just don't remember anything about the front height adjustment.

 

If the front height adjustment isn't in there (memory's fuzzy), it oughta be.  I owe Carey an update and will make sure it's in the next one.

Absolutely, and I'd say 6 to 7 degrees positive front caster.  1/16" total toe in front and back is a good handling point.  Not more than 1.5 degrees front negative camber, and for a swing axle car, I'd not go more than 3 degrees negative camber. IRS rear, probably somewhat less at about 1.5 to 2 degrees rear negative camber.  Sway bars/camber compensator will also play a big role on how your speedy (or coupe) handle.  Now, I don't own a speedster, and holding out for a Beck coupe for now. Water cooled of course.  Tons of seat time in 356's and early 912/911 race cars though.  Built a fair share of Super Vee's in the distant past too.

Pretty much because the camber in a VW IRS is only dictated by raising or lowering it. Cars with a-arm setups can adjust the camber at a static ride height and also control the amount of camber through it's suspension arc. I think a safe rate is about .83* for every inch of travel.

My dad's Miata is set at about 1.5* at static ride height.

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