What are the absolute essentials for a good handling chassis?

a sweet thing next to ya always helps too. Helps my ride anyways.

 

My roadster with rear coil overs plowed(understeered) like crazy. I made a rear roll bar from 1/2 bar. Better but not right. Made a 9/16. Then a 5/8. Then a 3/4. About right now but could go to 7/8.
I checked roll stiffness by jacking the car up in the center of the front axle and sitting in the door jam and measuring the sag. Did the same thing but jacked up the rear axle instead. Originally had almost no roll stifness at all from the back. All in the front. Added the roll bar and is now about 50/50 in roll stiffness.
I enjoy a fine handling car. I have had some. The roadster is a blast on a twisty road. Going thru the turns leading down into Death Valley from the west was great. Stand on it untill the corner and let it hang out a bit and then go for the next turn. Great.

 

I love that road.

 

Great positive info, guess we can all learn something from this discussion.

 

Can't get it outta my head what Alan Moffat said. Build it from the contact patch up ( and in harmony with it).
That can still leave you plenty of scope, no matter what your approach/ needs..

 

HaHa! too true!

I've seen good handling cars beat high horsepower cars on many occasions
Moffats "Autocraft" Mustang was a good example, a 302 Boss up against Bob Janes ZL1 Camaro.
They were good racing days

There is a well known Rally Driver in NZ that read the rulebook, where it stated the "suspension was free" .

His interpretation was "only the wheels touched the ground, everything else was suspended"

I wonder if that included the engine?

 

I've had a look at your pics and you need do a lot to increase the stiffness of the frame, also as others have said ditch the friction shocks as they don't work well.
There is nothing wrong with having the tierod out front as long as you have the ackermann set correctly (the rod is longer when front mounted)
Also you need to make a proper triangulated rear as your existing top link is too short, Springs are probably the most common problem with hotrods i find, virtually everybody is oversprung, remember the springs do the springing and the dampers do the damping.

 

All good info here, I agree about being over sprung, Don't listen to the mag editors on spring rate. I softened considerably from recommended.



Ago

 

Scott, it sounds like what you are asking is how to build in straight line stability at speed on the freeway, not how to go around a bunch of cones sideways in a balls to the wall maximum effort slalom event.

The priorities are very different between high G cornering power, and high speed straight line stability on the freeway (or at Bonneville).

The very first requirement is zero bump steer, very difficult to get right in a traditional rod, but well worth whatever effort you are prepared to put into it.

The second requirement is to build in enough front end caster to make the steering self centering. And give some serious thought to front scrub radius, because this is often the unsuspected cause of the infamous "death wobble".

The third requirement is to build in some slight roll understeer at the rear. This works even with a beam axle, by making the whole rear end steer as the body rolls. On production cars with leaf springs, the rear of the leaf spring is always mounted to the body higher at the back than at the front. As the rear wheel moves up under bump, it moves slightly forward. As the rear wheel droops on the spring, it moves slightly to the rear. As the body rolls on the springs, the whole rear axle skews and steers very slightly. You can do this with coil springs too, by arranging the rear roll axis to point downwards towards the front of the car. Whatever locates the rear axle can be made to provide this sloping rear roll axis with suitable geometry.

The last thing is relative front to rear roll centre height, and relative front to rear roll stiffness. And with a beam front axle and an (often) torsionally flexy chassis, it can be very difficult. Getting this right has a lot more to do with cornering power, agility, and handling than just high speed stability.
That is why it comes last on my list. But if you can find a way to lower the front roll centre on your front beam axle that does not look too ugly or out f place, do it !

And last of all on my high speed stability wish list, reduce unsprung weight wherever possible. If you are freeway driving on a dead smooth road it probably is not that important. But if you drive fast on back roads, it will definitely improve road holding at speed if you can reduce the unsprung weight as much as possible.

 

2 Hands on the Wheel












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No matter what you do........ A Traditional built Hot Rod built in a Hot Rod way will not handle like a modern car! That's unless you want to Build a Street Rod!

HC.

 

Remember your building a box! Keep everything square and equal to the centreline. Drivetrain, Suspension and Body. Then everything works.

Good Reading or CD. Steve Smith's Advanced Race Car Suspension and design. Great Book in my day about building a chassis and suspensin from scratch. The last time I saw it advertized was in Hot Rod Mag. in a little ad in the back.

The Old Tinbasher

 

Tyre pressures too. I ran 30psi front and rear in my car, and it handled and rode like crap. Dropped it to 25psi all round and the difference was remarkable.

I also increased the rear spring rate, transverse leaf, as it was too soft. I added three leaves, but it only really needed one. Many people simply build their car, and live with the results, but you need to experiment and adjust things, fine tune it.

I may have missed it, but I can't see what your steering is set up like. Cowl steering? If you've followed the traditional 'the links must be parallel to make it steer' then that is your biggest problem. The usual result is bump steer as the various linkages rotate around different centres and move your steering without you touching anything.

http://www.rodandcustommagazine.com...d_axle_front_suspension_details/photo_11.html



PS. Your chassis is almost identical in design to the one I plan to build for my Model A Roadster Pickup. Same kick-up at the rear, Y shaped top locator, same design kick-up at the front, same suicide front end etc.

 

Give a man a fish........

Buy these. Read. Learn.

Fred Puhn How to make your car handle
http://www.amazon.com/How-Make-Your-Car-Handle/dp/0912656468

Herb Addams Chassis Engineering
http://www.amazon.com/Chassis-Engineering-HP1055-Herb-Adams/dp/1557880557/ref=pd_bxgy_b_text_b

Use this web sight for reference- even a thread on building a 30 ford hot rod there.....
http://forums.corner-carvers.com

 

4 bars not traditional? Somebody needs to call Norm Grabowski and let him know that the T(s) he built in the 1950's just don't cut it anymore.

 

If it isn't on a race track,good handling is a relative term.A car can feel good to the driver buy not have the ultimate grip at the limit.Very few people drive at the limit on the street...and shouldn't.
The needs to have have stable handling,not suddenly go from mild understeer to gross oversteer in the middle of a turn.If you lift your foot off the gas in a turn the back end shouldn't try to come around.Hard braking shouldn't upset the car in a turn causing it to increase steering angle or tend to plow ahead.
The closer the engine is to the middle of the vehicle increases the tendency to spin out without warning.

 

This statement is totally wrong!
Cars with low "Polar Moment of Inertia" [ eg: mid-engine ] are very agile and have the ability to change direction with relative ease.

Moving the engine rearward [ behind the rear wheels ] increases the tendency to spin out . Basically the front of the car goes around the corner but the heavy mass wants to go straight ahead

Hanging a fat ol' big block over the front end does the opposite [ it plows or understeers ]

Tires with low slip-angles let go with little warning [ eg; Racing tires ] they grip so much better right up to their limit, then let-go suddenly
Old bias plys are the opposite, they will howl forever as the slip angle slowly increases

 

Actually,it's totally correct.Mid engine cars are very agile and also very touchy at the limit.Ask anyone who raced mid engine cars..............

 

well I guess you've answered it yourself "Mid engine cars are very agile "

Yes I have raced them. Anything is touchy "at the limit" but the behavoir is different

It is the Tires that get very touchy at the limit.

A tire can only handle 100% of its own capabilities, that can be a combination of lateral, braking, or accelaration forces [ eg: 80% cornering and 20% braking or 100% braking 0% cornering ]

A high performance tire is more "touchy at the limit" than a lowly street tire, but the limit is usually at a higher level of grip. [ the tires will suddenly let go during a high speed corner ,usually because of driver input ]

Most understeering RWD cars can be "throttle oversteered" out of a corner [ by adding another force ] ,it is quite controllable

The classic drift out of a corner looks s.pectacular, but is definately slower.

A classic understeering car will suddenly plow if you push it over the limit.
likewise an oversteering car will suddenly gets loose

Don't confuse Understeer / Oversteer with "Low Polar Moment of Inertia" which is the cars ability to change direction quickly [ as in cornering ]

A car with a high polar moment of inertia will try to resist cornering ,It will try to understeer on corner entry and oversteer on corner exit [ usually at a far lower speed than a "mid engine" car]

 

Put a four bar on the front. A tube axle with hairpins is not the best way to go.
As Langy said, the rear top link is a bit short on radius. Anyway to get a longer arm in there?

 

I gotta admit, I'm impressed by the amount of sensible advice from knowledgeable people here. +1 on the Fred Puhn and Herb Adams books.

My $.02:
-Your frame doesn't have nearly enough beam or torsional stiffness. A frame with deeper side rails and an even deeper X member that comes up into the engine bay and near suspension pickup points would be much better.
-Hairpins and a tube axle are a bad combo. Hairpins need an I beam that offers some torsional flex. A four bar with the tube would be better.
-Rear coil shocks should be tipped in about 15 degrees or so at the top.
-My rule of thumb for unsprung weight of a 9" is 300 pounds, give or take. That's a huge proportion of the total weight of a 2400 lb car.
-I'd suggest trying the alignment at 6 deg. positive caster, 0-1/2 deg. positive camber, 1/16 inch toe in. A car will be twitchy in a straight line if it has toe out at speed. Ackerman geometry matters in tight corners, Detroit spent a lot of years ignoring it.
-I agree with everyone on the softer front spring/ lose the friction shocks/ upper rear link too short/ lower front tire pressure points.

Could you post a pic with your steering gear in place?

 

Good points and reading guys....

 

Once you get your ackerman/ bump steer issue resolved, start dropping the unsprung weight in the front and and lowering your front spring rate. You are probably going to need to buy a new front spring with a lower rate but higher arch so you save your ride height. I also subscribe to the "tube axle/ 4bar, ibeam axle/ hairpin" method. So in your case, consider getting a beam axle. Last, I would try to make that upper link in the rear at least 18" long. With that setup in the rear, you don't need a panhard rod, but if you went to a single link forward (18-24" long) and put a panhard in the rear, you could lower your rear roll center and free up the back end.

 

Any updates on your fix for your handling on your ride? Alot of good info,just curious on your out come.You put a lot of work into building a car from the ground up and not being content with the results,my hat is off to you for fixing the problem, not accepting the results. George