recommend torsion bars:
04-11-2003, 12:15 AM
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recommend torsion bars:
In my '74 911, I currently run stock torsion bars in front and 26mm in rear. A 3.0 is the engine. This car is mostly used for street driving over some fairly poor roads. It has been lightened substantially.
I've been thinking of going to 22mm in front and 28mm in back. What sort of handling characterstics can I expect with this set up?
At some point, I'll also be going with Bilstein sport shocks if that helps.
My car is lowered now, and I don't see it exhibiting much body roll, so I might not swap out the old sway bars for larger diameter bars.
What do you guys think of a set up like this?
TIA
I've been thinking of going to 22mm in front and 28mm in back. What sort of handling characterstics can I expect with this set up?
At some point, I'll also be going with Bilstein sport shocks if that helps.
My car is lowered now, and I don't see it exhibiting much body roll, so I might not swap out the old sway bars for larger diameter bars.
What do you guys think of a set up like this?
TIA
04-11-2003, 02:46 AM
#2
I have driven cars with 22/28, and they feel pretty good for all around street/track. 22/28 seems to be pretty widely accepted. The ones with 22/28 that I have driven have not been lightened. So your car will be stiffer than what I have felt. My SC is lightened. Once lightened, it actually felt pretty stiff on stock bars. I presenty run 23/30 which are the largest non-hollow bars. The only reason I got that particular size combination is because they were the largest without going to the tubular. With tubular, you can go 23.5 for an effective rate of 23 which is the same as mine and 32 rear for an effective rate of 31 there. I feel that 31 might be be overkill since my rear is pretty stiff as it is. Unless you are running a 930 with the extra weight in the back. When going to 23 in the front, you have a choice of going either 29 or 30 in the back. It is sort of a compromise when compared to stock as far as spring effect percentages based on stock. Of course, you are not stock with a 26 in the back. I also felt I really needed a 23 in the front because with a lowered car, there isn't much travel left. And while that little bit works, I knew I wasn't going to avoid curbs, so I went with 23 to avoid shock bottoming. Especially since I run no snubbers in the front shocks to increase travel. With the 23, the shocks never close. Actually, with 23/30 in a lightened 911, there isn't much movement in the suspension at all. Here are some numbers that can help you out.
From a stock 911 with 18.8 front and 24.1 rear, here are the percentage increases in stiffness.
To front 22=87%
To rear 28=82%
Or
To front 23=124%
To rear 29=110%
To rear 30=140%
To rear 31=174%
The 31 isn't available in solid. And that 31 mm effective rate can only be achieved by a 32 mm tubular. The reason for the lower effective rate in comparison to real diameter is by the nature of the bar being tubular. Regardless, that sort of increase in comparison the the front can only be put to good use with a turbo motor or some serious downforce as it should substantially increase the tail happy nature of the car. My car with 30 has just the right ammount of oversteer. Enough to keep things from getting boring and at the same time negating any trace of understeer. You can also see from the chart above the reason for the popularity of 22/28. First, it isn't crazy stiff. Second, you achieve a very close spring medium increase with front to rear. 87.5 and 82 is very close. As close as you are going to get if you want something with the same relationship as stock. But then again, you are running a 26 in the back which has a different relationship than stock. For a normally aspirated 911 at least since 930's run what you run stock. Also, when you look at the chart, you see the decision of what to use in the back to match, as I mentioned earlier. For me, I didn't want anything that would even hint or suggest understeer. So 30 was an easy choice to match the 23. This is a tough decision, with many different opinions. But at least you have a percentage in stiffness increase guide to help you make the decision. Of course, the 930 turbo torsion bars you are running will make the decision harder since you have probably gotten used to that type of offset front to rear.
One question I have for you is how does it ride and handle with the 930 spec torsion bars you have in the back? I have always been curious as far as how that feels on a normally aspirated 911.
From a stock 911 with 18.8 front and 24.1 rear, here are the percentage increases in stiffness.
To front 22=87%
To rear 28=82%
Or
To front 23=124%
To rear 29=110%
To rear 30=140%
To rear 31=174%
The 31 isn't available in solid. And that 31 mm effective rate can only be achieved by a 32 mm tubular. The reason for the lower effective rate in comparison to real diameter is by the nature of the bar being tubular. Regardless, that sort of increase in comparison the the front can only be put to good use with a turbo motor or some serious downforce as it should substantially increase the tail happy nature of the car. My car with 30 has just the right ammount of oversteer. Enough to keep things from getting boring and at the same time negating any trace of understeer. You can also see from the chart above the reason for the popularity of 22/28. First, it isn't crazy stiff. Second, you achieve a very close spring medium increase with front to rear. 87.5 and 82 is very close. As close as you are going to get if you want something with the same relationship as stock. But then again, you are running a 26 in the back which has a different relationship than stock. For a normally aspirated 911 at least since 930's run what you run stock. Also, when you look at the chart, you see the decision of what to use in the back to match, as I mentioned earlier. For me, I didn't want anything that would even hint or suggest understeer. So 30 was an easy choice to match the 23. This is a tough decision, with many different opinions. But at least you have a percentage in stiffness increase guide to help you make the decision. Of course, the 930 turbo torsion bars you are running will make the decision harder since you have probably gotten used to that type of offset front to rear.
One question I have for you is how does it ride and handle with the 930 spec torsion bars you have in the back? I have always been curious as far as how that feels on a normally aspirated 911.
04-11-2003, 03:02 AM
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Hi Ed:
The ride isn't bad, and the handling is quite good. I can carve out some serious canyon meat with the way my suspension is set up now. Thing is, the rear is a little soft. I can push a knee down on the rear bumper and get much more travel than on the front, which I initially equated to the 3.0's weight until I found a 3.0 weighs less than a 3.0 turbo, and here I am running turbo-sized torsions. The rear shocks are new, so I don't know why there's so much rear-end travel in conjunction with front-end travel.
My mechanic suggests I go no larger than 26mm for a rear torsion size, and that I leave the stock front torsions in place. But like you, I'd rather have oversteer than under. My car does understeer, though I blame most of that on my 60-series Dunlop A2 Sports - they're really quite soft and scrub when pressured.
So my plan is to go with: 22mm, or maybe 23mm front; 28mm or 29mm rear, sport shocks, and eventually 55 series Bridgestones. The jury is still out on the sway bars. I see in other posts that you've left your sways alone. I don't know the diameter of my own sway bars, but they seem to work okay. My thoughts are when a person runs torsion bars as large as I'm thinking of installing, can larger sway bars be all that important in the end?
Thanks for your reply.
The ride isn't bad, and the handling is quite good. I can carve out some serious canyon meat with the way my suspension is set up now. Thing is, the rear is a little soft. I can push a knee down on the rear bumper and get much more travel than on the front, which I initially equated to the 3.0's weight until I found a 3.0 weighs less than a 3.0 turbo, and here I am running turbo-sized torsions. The rear shocks are new, so I don't know why there's so much rear-end travel in conjunction with front-end travel.
My mechanic suggests I go no larger than 26mm for a rear torsion size, and that I leave the stock front torsions in place. But like you, I'd rather have oversteer than under. My car does understeer, though I blame most of that on my 60-series Dunlop A2 Sports - they're really quite soft and scrub when pressured.
So my plan is to go with: 22mm, or maybe 23mm front; 28mm or 29mm rear, sport shocks, and eventually 55 series Bridgestones. The jury is still out on the sway bars. I see in other posts that you've left your sways alone. I don't know the diameter of my own sway bars, but they seem to work okay. My thoughts are when a person runs torsion bars as large as I'm thinking of installing, can larger sway bars be all that important in the end?
Thanks for your reply.
