How does radius rod length affect handling?

[dcmengle]

How do you determine the proper length of the radius rods or hairpins and how does it affect steering and/or handling?

I'm planning on lengthening my body about 8 to 10 inches and possilby using an inline 6 engine so my frame will need to be a several inches longer than normal. Will I need to lengthen the radius rods or just relocate the point at which they attach to the frame?

I've seen pictures of buckets and rat rods that use what appear to be a standard size radius rod and others that are quite a bit longer than normal but any mention on how it affects things.

There's an article on the NTBA website that seems to imply that radius rod length can affect bumb steer but it's a short aritcle and not definitive. I've googled the subject but haven't found anything yet.

Thanks,

Doug

 

[butch27]

Maybe Ted Brown can jump in here. He uses LONG rods for handling.

 

[Hotrod46]

I don't know of any rules as to how long they have to be, but there are advantages to longer rods.

All radius rod or 4-bar type suspensions force the axle to move fore and aft as the axle moves up and down.

This is because the radius rod (or 4 link) travels in an arc. The longer the rod the less severe this arc will be. Simple geometery.

This arc also causes caster changes in radius rod or split wishbone setups. 4 bars don't suffer from this.

I'm not saying short rods don't work, but longer links will have less chance of strange handling quirks since they reduce unwanted axle movement.

Having said all that, I think longer bars look better too. Mine run all the way to the firewall and follow the same angle as the frame. I think it makes the look of the car "flow" better when viewed from the side.

I think Ted built the first CCR frame and he used long rods. I'd like to hear his reasons too.

Mike

 

[Youngster]

As a rule of thumb, if you locate the frame radius rod mount at or near the steering box mount and keep the drag link as parallel as possible, you will eliminate most all of the bump steer. This is with a side steer set up.

In therory, the longer the radius rods, the smoother the ride. With a cross steer, you can make the rods as long as you like. You will need a panhard or sway bar on the front to control bump steer with this set up.

A note on setting up your rear housing with ''hair pins''. If you fab your hair pins so they mount on the frame rail in line with your front U-joint, you will eliminate most all of the binding with the hair pins. The slip joint in the trans will compensate. Accordingly if I have to move the mounting point for the hair pins further forward, I will shorten the drive shaft so there is more ''slip'' distance for the yoke to compensate for the larger arc .

Ron

 

[Ted Brown]

Maybe Ted Brown can jump in here. He uses LONG rods for handling.

Well what luck, first look and there is my name called.. Thanks for thinking bout me... Yes I do use what look like long radius rods, but then again I have a very short wheelbase car 95 1/2"... my ft. RR are 50", rear are 43"... I myself like to make them as long as possible, well the fronts anyway, the rears are for traction, but in just a street cruiser, looks and handling is all you really need to strive for... My next T Bucket will be totally for comfort and handling... don't want to forget safety... All these new DMV rules make for a totally different ball game as far as hand built cars go...

 

[Ted Brown]

I don't know of any rules as to how long they have to be, but there are advantages to longer rods.

All radius rod or 4-bar type suspensions force the axle to move fore and aft as the axle moves up and down.

This is because the radius rod (or 4 link) travels in an arc. The longer the rod the less severe this arc will be. Simple geometery.

This arc also causes caster changes in radius rod or split wishbone setups. 4 bars don't suffer from this.

I'm not saying short rods don't work, but longer links will have less chance of strange handling quirks since they reduce unwanted axle movement.

Having said all that, I think longer bars look better too. Mine run all the way to the firewall and follow the same angle as the frame. I think it makes the look of the car "flow" better when viewed from the side.

I think Ted built the first CCR frame and he used long rods. I'd like to hear his reasons too.

Mike

Rules are to be broken, hehe well that is just me talkin here... Use my favorite word about building chassis "LEVERAGE" that pretty much tells the story, as to just what you are trying to do... unless you have a real de-tuned 4 banger, traction is still very important with a T Bucket. as without it, you are out of control, unless you keep a big block under the load pedal... to get close to finding the happy RR length (rear) you should balance the whole car with driver and passenger weight, on stands, see where it balances, % wise, if you are close to 70% on rear tires static weight, you don't want/or need shorter bars than 40 to 43 inches in length... I really hate a car that wants to swap ends with you when hard on the pedal...and to get the front wheels off the ground is also not real smart on the street, well even on the track is not great, can't steer with the wheels up... :gum: PS, That fall from the sky hurts a lot of goodies also...