[staleg]

Since I'm building with IFS and IRS I will use sway bars both front and rear. 7/8" or 1" diameter

A highboy style 34 Roadster with aluminium radiator and waterpump, headers, battery & gas tank in the trunk area will often end up with close to 50/50 weight ratio.
Sould I use same dimension on front and rear sway bars, or must the front sway bar be thicker than the rear one for some other reason?

Yes I know this is a very complicated question and there are lots of other factors here as well. Like the length of the bar, the length of the arms, the width of the suspension it is going to be mounted at etc. But I must start somewhere and then I would like to know if I should start with 7/8 rear and 1" front, or 1" both front and rear?.

[joe_padavano]

The very rough rule of thumb is that the stiffer end of the car breaks away first. If the front end of the car is stiffer, the car will understeer. If the rear is stiffer, the car will oversteer. Are you planning to fabricate the sway bars yourself? If so, the best thing to do would be to configure the arms to allow adjustment so you can change the length of the arms. As you point out, that changes the effective stiffness and will let you do some tuning.

[staleg]

Thank you for your answer, Joe.
I'm planning to use torsion bars with separate arms.
They have the adjustment possibilities you recommend.

I'm not sure what end of the car will be stiffest yet. In the front I use a Mustang II kit from Fat Man called stage III. It is with coilovers they have included in the kit based on my car.
At the rear I'm going to use a Jaguar axle. I haven't bought coilovers for it yet. But I will buy what Speedway Motors recommends for my car (34 Ford, Jaguar rear.)

A store called Stack Car Product link:
http://www.stockcarproducts.com/ftsusp.htm
sells 37,5" long torsion bars in different diameters, both tubular and solid. Maybe I'll start with 1" solid in the front and 1" tubular rear. Then I have lots of possibilities to do changes later. The tubular 1" have about the same stiffness as the solid 7/8.

Point is, It save me for lots of work to make this installation on the rear axle now on the bare frame, before I put on the body.

[seriousracer]

no offense but your not ready to figure you sway bars till you have shock spring combos . you will also need to figure the mounting placement on the suspension. the amount of bends you need to make in the sway bar. (perferrable none). you could make a generic mount and bushing setup using some of the bushing kits that are out there.

i guess really what i am trying to say is you need more info.
otherwise 3/4 solid ? or 7/8 .120 tubular ? could be your starting points... or if the spring were already to stiff you could be at a 5/8 .090 tubular sway bar.
willing to bet a 7/8 or 1" will be to stiff,.,,
need more info .
i have used sprint car torsen bars for swaybars before and have had good success in a racecar application(honda crx road race car) you need to check the spring rating on the bars your looking at.

[OneMoreTime]

I would reccomend to Go here and buy the books on handling and suspension setup..

Setting up suspension is an art of its own and while a lot of the street rodders are just happy to have springs and shocks that work there are those of us who like something just a bit "better"..

Any thing written by Carroll Smith is good although tilted toward formula cars the principles are the same..

Sam

[seriousracer]

actaully bill mitchell's stuff is alot better . carrol smith just did it in words and really does not teach you how to figure out some things.
http://www.mitchellsoftware.com/products.htm
sorry i crew scca gt1,gt3 and formula cars.
this guy is a good.. carrol smith is good to just .. not as good he touches on a lot of basics that are common sense.

[OneMoreTime]

Good one..live and learn..lot of new stuff out there..

Sam