Lowering the rear... Do you really need a thicker torsion bar?
 

I want to lower the rear on my 85. It's a street car that will never see track time. Shop is saying that the stock rear bar really should be upgraded to a 26mm bar while they're in there.

Thoughts?

you do not need to change your bars to lower the car. However, the bar will have to be reindexed which makes it an ideal opportunity for upgrade/replacement.

If there is less distance to travel with the same spring, a force that would bottom out at a lowered height might not have at standard height. This is where the stiffer torsion bar comes into play.

Do you need to change? No. Should you? Who knows. There are compromises to lowering the car. What are your goals?

Would a US car benefit from the rear bar upgrade?

How far are you trying to lower it? If it's really low, the change in suspension geometry leads to an increased tendency to roll (lean sideways).
26mm isn't really even much stiffer than stock.

I lowered my 83 and kept the stick tbar with no issues. It was a street car and never once did I bottom out. Of course that has much to do with how and where you drive but I think if you're going for the "nicer" look you'll be fine.

It depends on your goals. The word "upgrade" is somewhat inappropriate in this context, as stiffer doesn't necessarily mean better. If you lower your car with the same torsion bars, the ride will be firmer. If you get thicker torsion bars after, it will be firmer still (and probably under-damped).

Most lower their cars for looks. In this case, I believe keeping the same torsion bars when doing so will impact the ride the least.

I'm surprised they didn't suggest changing the front bars, too. You would be lowering both the front and rear, so the change in forces would be comparable. I'm not expert on any of this, I just regurgitate what I read around here.

Starting in 1984, ride heights were the same for all 911s globally, so your car came at "Euro" height from the factory:

http://forums.pelicanparts.com/uploa...1452963527.gif

http://forums.pelicanparts.com/uploa...1452963541.gif

http://forums.pelicanparts.com/uploa...1452963634.gif

I'd like to have the rear tire right at the bottom of the fender. Not slammed, but fairly low.

It's a while you are in there thing. If you wanted to do it now is the time, but you don't have to.

The car is being worked on at a vintage Porsche race shop. We recently did brand new struts/shocks. Standard stuff. Bilstein Sports or something like that...

I thought it was odd too that he didn't feel the front needed anything. He did say the rear would likely wallow if we lowered it and did not put a thicker bar on. He thought 26 was appropriate to keep the performance in check, while at the same time not ruining the ride.

Make sure your spring plates are not adjustable, guessing they are not since shop thinks you need to replace the bars?

As somebody that lowered their car with stock bars, you can do it. Do you have wheels with a lower offset than the factory 7" Fuchs in the back, or are you running spacers in the back? If you do, at the ride height you are describing, you'll rub anytime you hit any kind of bump. And you rub about an inch up the fender in a spot that burns the paint if you rub for any significant amount of time.

I put 26's on mine to prevent the rubbing. I have 9" Fuchs at the back of my car. The 26mm rear bar is a nice balance paired with the stock 19's on the front. I'd imagine the shop is recommending 26's because anything bigger would necessitate larger front bars.

Typically, larger torsion bars are a handling upgrade. However, they have their place as well for airborne landings or equivalent. :-)

As imported, early US 911s sit higher than Euro spec 911s and thus lowering to those specs brings you closer to a typical 911 off the PAG assembly line. That is to say, the stock bars should be fine for looks.

Larger torsion bars don't necessarily compromise the ride as much as larger sway bars and/or stiffer shocks. They just firm up the ride whereas the aforementioned SBs, shocks as well as low profile tires can increase ride harshness.

Remember that suspension upgrades should be planned as a system with partial upgrades just another piece of the whole.

MHO,
Sherwood

The shop feels like that the USA car should have come with 26's to begin with and that they softened the car up for the Americans...

I have 16x9 et11 out back and 16x7 et23 up front. Front rubbed like crazy with the 225's. We rolled the fenders and it's still rubbing a little. Going to switch to 205-55's up front and run the back the way it is.

With the et11, the tire is still inside the fender so it shouldn't rub... Shouldn't but you know how that goes lol.

Keep in mind that the front of our cars don't have nearly as much work to do so depending on how much is done to the rear, the front may or may not need a corresponding change

Here's a couple shots of the rear as it sits now. The small height adjustment is maxed out.

http://uploads.tapatalk-cdn.com/2016...02e42407ca.jpg

http://uploads.tapatalk-cdn.com/2016...6a4ed2506e.jpg

slightly off topic but how large of a torsion bar would you guys recommend if dropping a 3.6motor?

Considering the original topic and yours and to avoid hi-jacking the OP's question, I would suggest going to a more related 3.6/torsion bar thread for that question.

Sherwood

Beautiful car deputy! So I'd bet it's safe to say the car won't be going on any hot rod diet anytime soon. Probably retaining AC, back seats, heat, & the tail hu? Maybe a little upgrade wouldn't hurt? How's the roads? Just my 2 penny's. Cheers!

Not only am I retaining the AC, I'm going to upgrade and add to it LOL.

There will likely be a subwoofer going in as well. This is strictly a blvd cruiser. The 79 is the gutted, caged track rat with probably as much bondo as metal at this point LOL.

https://lh3.googleusercontent.com/_5...=w1757-h988-no