Your Input: Front Torsion Bars, Rear Coilovers Only?
 

Hey all,

I was going to buy heavy rear torsion bars and go through the painstaking process of lowering my car, until I found Coilovers with 400 pound Springs for only a few hundred dollars more. I heard the front coilover kits can lose wheel and fender clearance, and I don't have the money for RSR front coils. This was I have the ease of coils in the rear where it really matters, and the fronts will still be easily adjustable (and cheaper) with the torsion bars.

Am I crazy to put 24 mm front torsion bars in the front only?

I plan on running the car relatively low with 17" wheels.

You will need to reinforce your rear shock towers if you install CO's. Not cheap by a long shot.
-C

It's mostly a street car that gets driven 300 miles a year, I'm going to go without the reinforcement for now until I drop the engine at some point.

With my limited experience and no knowledge of pros/cons of coil-overs, the first thing I'd ask is do you think 24 bars in front for "mostly street" might be a little stiff? ..and wouldnt it be a near necessity to have the front shock inserts re-valved to them? I could imagine the front getting a little "bouncy" without the correct rebound dampening. After completely rebuilding my suspension with Rebel Racing bushings I decided on 22 for the front(smooth roads and a good deal of track) and had the inserts revalved to their spring weight. Incredible difference from 26 year old stock.

Yes, good input, I will of course re-valve eventually too.

I would go 24mm because the rears are 400lb springs. I know someone who streets a car with 500lb front and 450lb rears and regularly drives to Florida, haha! I don't mind stiffness.

A-lot of effort for a 300 mile a year car. Why not just stockpile the parts and wait to do the work when the car finally gets driven more ? My car is very low (like 24.25" at the wheel arch) on 17's on the stock suspension no problems I know of. I see no problem what you plan, 24's will be very stiff up front if roads are rough but 300 miles won't wear out anyone sense of humor.

My car has rear coil overs and has not had the shock towers reinforced. It has been tracked off and on over the last 17 years by the previous owner and I don't see any signs of damage as a result. Is the reinforcing just a precaution? FYI I'm doing my 2nd PCA DE this weekend. Many more to follow...

The lack of miles it will be used isn't a decision point for how to install coils on a car.

Your car is designed to be carried by the torsion bars and the shocks are only dampening its movement. When you convert to coils you are going to be carrying the car by the shock mounts AND the shock mounts will still need to absorb the dampening forces.

If you don't do the RSR reinforcements you will tear apart the shock mounts and the repair plus the required reinforcement will cost lots more. A "shortcut" isn't a shortcut in car fabrication. It is a "learning experience"... $$$

Pm sent

Listen, I could care less about the shock tower reinforcement folklore. I also don't care to answer the question about why I should stockpile parts. Helpful answers to my actual question are appreciated.

FWIW, a 400 pound coilover is about the same as a 33mm torsion bar which is the biggest commonly available. I'd say 24 would be too stiff in front. I'd go 22 or 23.

Now that's helpful, thanks!

So, like 300lb equivalent in the front? Would the 24mm just make it under steer more?

Is anyone else running a similar torsion front and coil rear setup?

I run 22/31 which feels about right to me in terms of ride and handling Probably could stand to be a little stiffer in the back. I haven't revalved the dampers but it still feels alright. I don't have sway bars installed. I also have rebel racing bushings which mean I don't have the spring rate contribution of the rubber bushings.

My calculations put the wheel rates (not including the tire) at 232 lbs/in front and 328 lbs/in rear for 22mm/31mm torsion bars. This does not take into account the flex/twist of the A-arm and the torsion tube so these numbers are a bit high in that regard. 33 rear would be 422 lbs/in using the same calculations. 23 front is 278 lbs/in, 24 front is 329 lbs/in. I don't know how accurate my calcs are but I think they are in the ballpark based on my experience with my car only.

I'm not sure whether you are interested more in ride or handling when comparing coils to torsion bars but alignment and corner balance (and sway bars) will have big effects on handling so spring rates aren't the be all and end all. You generally want the rear ride frequency a little bit higher than the front to give a more comfortable (level) ride over bumps. That is where the springs and dampers will be the main variable to tune.

I just did a full suspension refresh on my '87 with 23/31 bars. In all honesty, the front is a tad stiff for my liking and I might drop to 21's. Balance is good and the adjustable Hotbits dampers make adjustment easy. I think I will convert to coils for ease of height change and no reduced droop travel on my SC in the future. I also question the need to reinforce the towers for a street car or the notion that the ride feels better on a coil-spring car because of chassis flex. I would like to see some data to prove this, not internet hearsay.

As Flieger mentioned, the wheel rates and ride frequency are rather important. Going too high with the rear will increase that ride frequency too much and cause the car to "buck" over bumps.

http://i61.tinypic.com/vie0n.jpg

Here's a chart I made based off instant g's wheel rate data and my estimated unsprung corner weights.

I'm personally at 23/33 at this time, and now that my front swaybar is no longer binding, it's pretty neutral, maybe a bit oversteery for some, though I'm running an assload of front tire (square setup.)

Don't worry too much about the coil spring / torsion bar difference. They're the same thing, they work in the same way. One is just wrapped into a spiral, the other is straight.

If you want access to the file so you can put in your own sprung weights, let me know.

"Folklore"


http://forums.pelicanparts.com/uploa...1363601470.jpg

http://forums.pelicanparts.com/uploa...1363601675.jpg

http://forums.pelicanparts.com/uploa...1363601725.jpg

Driven97, that's super interesting, how do I find my sprung weights?

Well it seems like the jury is in that 24mm from is too hard for 400lb rears, and that's essentially what I wanted to know. I'll try 23's and go from there.

Feilger I remeber you commented on my sway bar thread. Maybe this will be the perfect setup for me to test getting rid of the rear or front or both sways. Or maybe just some end links so I can adjust the stock bars a little. But that's a whole other topic, haha!

Actual corner weight minus unsprung weight (the wheels, tires, brakes, and ~ 1/2 the weight of the suspension arms.)

I think I'm just reading your post wrong, but in any case the drop links allow you to adjust the preload (to zero) but to adjust the stiffness you need levers with multiple droplink attachment holes or slots.

FWIW I've still got the unused RSR style Taretts for sale.

Cool, thanks! Thats a bit of work.