Modify steering response on C5
Le Mans Master
Joined: Jul 2002
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From: Nevada and Florida
Originally Posted by leaftye
How have those Red Devil rotors been holding up?
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Joined: Jan 2004
Posts: 92
Likes: 6
From: Sacramento CA
Originally Posted by leaftye
Some autocrossers do it. JakeL is one person I know of. The T1 control arms are the same as any other C5 control arm, it just has the stiffer bushings in them.
You talk about feel and handling as if they are the same thing. While I'm with you on the steering feeling light at low speeds, but autocrossing is low speed, and I have zero complaints about the steering between 15-60 mph during autocrosses, and I did one track event where speeds were between 30-100 mph, and the steering felt great too.
If you don't mind the extra noise, and can stand extra harshness, just go for the VBP bushing kit.
Seriously though, you should do more studying before you make drastic changes. Bushings don't seem like much, but they change every aspect of handing and ride. I know I can't say I know enough to make drastic changes. So far I've only done T1 swaybars, fully knowing that they were going to add understeer with a stock wheel/tire setup. I'm also upgrading the springs, knowing it's still a compromise setup aimed for both mid 150 mph open race racing and low speed autocrosses. I haven't fully analyzed the effects of a bushing swap, but I know the options are T1, Delrin and metal sperical bushings. The last two I'd probably have to make myself unless I have get LG to sell whatever they're using to me. I also know if I'm going to mess with super stiff bushings, I'm going to nail the handling down to a tee, so that means using a bump steer kit and putting the car on a rack to check the geometry changes throughout the entire range of motion. If I'm going to install the parts that can take the suspension to the max, I'm going to use it to take it there instead of installing it and hoping for the max.
If you insist on getting max road feel and effort, install metal spherical bushings all around. Install tires with 30 series aspect or less in front, and get them wide and sticky. Check the camber rate changes throughout the range of motion for the front and rear wheels, and change to suit, remembering that you'll need less camber because the bushings won't distort anymore. Turn the caster down a couple notches and set toe to zero. Install a hard mount for the rear tie rod, and then set rear toe to zero as well. Check the "Chassis stiffness" thread in the Autocross forum and implement some of the ideas there. Take weight, a lot of weight out of the car. You can get to 2,800 lbs and still have a street legal car. You can probably get down to 2,600 lbs with a car that "looks" street legal. Do all this, and you'll have a car that'll make the term "riding on rails" sound loose and plush.
You talk about feel and handling as if they are the same thing. While I'm with you on the steering feeling light at low speeds, but autocrossing is low speed, and I have zero complaints about the steering between 15-60 mph during autocrosses, and I did one track event where speeds were between 30-100 mph, and the steering felt great too.
If you don't mind the extra noise, and can stand extra harshness, just go for the VBP bushing kit.
Seriously though, you should do more studying before you make drastic changes. Bushings don't seem like much, but they change every aspect of handing and ride. I know I can't say I know enough to make drastic changes. So far I've only done T1 swaybars, fully knowing that they were going to add understeer with a stock wheel/tire setup. I'm also upgrading the springs, knowing it's still a compromise setup aimed for both mid 150 mph open race racing and low speed autocrosses. I haven't fully analyzed the effects of a bushing swap, but I know the options are T1, Delrin and metal sperical bushings. The last two I'd probably have to make myself unless I have get LG to sell whatever they're using to me. I also know if I'm going to mess with super stiff bushings, I'm going to nail the handling down to a tee, so that means using a bump steer kit and putting the car on a rack to check the geometry changes throughout the entire range of motion. If I'm going to install the parts that can take the suspension to the max, I'm going to use it to take it there instead of installing it and hoping for the max.
If you insist on getting max road feel and effort, install metal spherical bushings all around. Install tires with 30 series aspect or less in front, and get them wide and sticky. Check the camber rate changes throughout the range of motion for the front and rear wheels, and change to suit, remembering that you'll need less camber because the bushings won't distort anymore. Turn the caster down a couple notches and set toe to zero. Install a hard mount for the rear tie rod, and then set rear toe to zero as well. Check the "Chassis stiffness" thread in the Autocross forum and implement some of the ideas there. Take weight, a lot of weight out of the car. You can get to 2,800 lbs and still have a street legal car. You can probably get down to 2,600 lbs with a car that "looks" street legal. Do all this, and you'll have a car that'll make the term "riding on rails" sound loose and plush.
leaftye -- I will be taking your advice and studying this thoroughly before changing anything. Thanks for all of your detailed input. Just to clarify my goals again, I'm looking at improving steering feel to something similar in feedback to the M3 or RX-7. I don't think that this would be very extreme, nor am I trying to achieve professional level race handling. I don't autocross (but am considering it), and mainly enjoy sprited driving on the backroads and twisties. Most of my driving enjoyment is achieved in the 20 to 70 mph range. So, weight reduction, or drastic and costly mods are not on my radar right now.
I still need to read the SAE article, but your previous posts recalls the SAE paper suggesting stiffer bushings in the front control arms to improve handling/steering. I just read another article about changes in C4 handling and steering feel though changing of front bushings. Bushings seem to be a good place to start.
I like the idea of staying factory parts and going with T1 rather than swapping just the bushings. I looked at gmpartsdirect and found T1 parts for front upper and lower control arms: (http://www.gmpartsdirect.com/perform...ATID=1392.html)
12480072* - Arm, LH Front Upper Control $160
12480073* - Arm, RH Front Upper Control $160
12480077* - Arm, LH Front Lower Control $137
12480078* - Arm, RH Front Lower Control $137
It looks like for $600 in parts, the front upper and lower arms and bushings could be done. (Can anyone verify that these are the correct part numbers?)
I just compared this cost to VBP's kit (http://www.vbandp.com/detail.aspx?ID=770) and it's priced at $250. For an additional $350 you can get the T1s with the bushings installed. And I believe someone mentioned that the T1 control arms are forged vs. cast on stock or vice versa(?) Any opinions on this?
Finally, anyone know what it costs to have this work done at a shop? I'll be getting a quote this week from a dealer as well as from a local C5 shop (MSI). Any DIYers have any words of wisdom on difficultly level? I did the Z06 sways myself, and will be doing a parking brake adjustment next week myself. Control arms may be out of my league though.
1st Gear
Joined: Sep 2004
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Steering Feel...A Geometry Problem?
I have been told that the scrub radius of the C5 front suspension is .275"--which is very low. If you could get SR to .75-1", you would increase steering feel . The easiest way that I know to increase scrub radius is to reduce the amount of positive offset in your wheels with a wheel spacer or new wheels. I have never done this myself, but it was suggested to me by the guy who designed Art Morrison's C5 subframe for his 57 Chevy.
By the way, the lower the SR, the better, as it reduces the twisting forces a tire transmits to the steering as it goes over bumps or through turns. So low SR is a good thing (I read somewhere that Trans Am cars have zero SR). However, as SR decreases, so does steering feel. Increasing SR to .75-1" will not make the car handle any worse, and it should help improve the feel. I will also say that this same guy told me that the SR is the way it is on the C5 is because of ABS--so that might be a problem, or it might not.
By the way, the lower the SR, the better, as it reduces the twisting forces a tire transmits to the steering as it goes over bumps or through turns. So low SR is a good thing (I read somewhere that Trans Am cars have zero SR). However, as SR decreases, so does steering feel. Increasing SR to .75-1" will not make the car handle any worse, and it should help improve the feel. I will also say that this same guy told me that the SR is the way it is on the C5 is because of ABS--so that might be a problem, or it might not.
Safety Car
Joined: Nov 2003
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From: San Diego, CA "leaf" "tee" "e"
Actually I think the scrub radius is only .1", but I'm not looking at the specs right now.
Undecided, if you don't mind putting in a little work, you can get used front control arms from Phoenix Performance for $45 each:
http://forums.corvetteforum.com/show...5&page=1&pp=20
Phoenix Performance has made the fastest T1 race cars for 4 out of the last 5 years, and the Heinrocket races a Phoenix built car. If Joe Aquilino gives you any advice, my advice is to heed whatever he says.
The front bushings will have a much greater effect than the rear due to braking and turning forces, and sometimes both at the same time! All control arms in all C5 suspensions from FE1 all the way to T1 are the same. The only forged piece is the front upper control arms. All other control arms, and the knuckle are cast in the same manner, but a very strong manner. The subframes use yet another casting method.
As for installation. Yeah, I think installing the bushings will be hard, and you may want/need a press, a torch, and a chisel. After that, it should get pretty easy, especially if you use the Hardbar alignment kit. I haven't used it yet, but Gary Hoffman let me know I still had a $200 balance with them, so I'll be putting it towards their lowering bolts and alignment kit, so I should let you know just how hard it is very soon....unless of coarse I decide to get those VBP bushings too....hmm...
Undecided, if you don't mind putting in a little work, you can get used front control arms from Phoenix Performance for $45 each:
http://forums.corvetteforum.com/show...5&page=1&pp=20
Phoenix Performance has made the fastest T1 race cars for 4 out of the last 5 years, and the Heinrocket races a Phoenix built car. If Joe Aquilino gives you any advice, my advice is to heed whatever he says.
The front bushings will have a much greater effect than the rear due to braking and turning forces, and sometimes both at the same time! All control arms in all C5 suspensions from FE1 all the way to T1 are the same. The only forged piece is the front upper control arms. All other control arms, and the knuckle are cast in the same manner, but a very strong manner. The subframes use yet another casting method.
As for installation. Yeah, I think installing the bushings will be hard, and you may want/need a press, a torch, and a chisel. After that, it should get pretty easy, especially if you use the Hardbar alignment kit. I haven't used it yet, but Gary Hoffman let me know I still had a $200 balance with them, so I'll be putting it towards their lowering bolts and alignment kit, so I should let you know just how hard it is very soon....unless of coarse I decide to get those VBP bushings too....hmm...
Safety Car
Joined: Nov 2003
Posts: 4,979
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From: San Diego, CA "leaf" "tee" "e"
I don't remember if I already mentioned it, but the tunnel reinforcement plate was worth 2 Hz in torsional stiffness. There are stronger tunnel plates sold by several vendors. I can't say myself if the improvement is significant, or if it's a placebo effect, but many people say it helps turn-in. I suppose there may be worth another Hz or so to pickup in the tunnel reinforcement area, or at least I think there's enough to pick up that I intend to buy a tunnel plate or make one myself....but if I make my own, it'll totally blow away anything available right now.
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Joined: Jan 2004
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From: Sacramento CA
Update
So after numerous phone calls to C5 shops, the general consensus was that it's bushings, springs/shocks, alignment, or all three. I got a good tip to inspect the condition of my current bushings for extrusion -- apparently, stock bushings tend to work themselves out. I did check mine, and found that the existing bushings were intact and in great shape.
Next, I went down to my local Chevy dealer and test drove a 2003 Z06 that had 8k miles on it. Wow. What a difference that car is from my coupe. I wish I had the $$$ to buy it! In any case, I drove it hard and did plenty of hard cornering and maneuvers in the speed range I typically drive. I found the steering feel to be just what I wanted. I am now convinced that the FE1 springs and F45 shocks are the biggest factor in that loose steering feel, since the bushings on the Z06 are supposedly the same.
Tomorrow, I'm taking advantage of the deal through FredBeans and ordering Z06 springs/shocks to complement my z06 sways. That should be the end of this story.
Next, I went down to my local Chevy dealer and test drove a 2003 Z06 that had 8k miles on it. Wow. What a difference that car is from my coupe. I wish I had the $$$ to buy it! In any case, I drove it hard and did plenty of hard cornering and maneuvers in the speed range I typically drive. I found the steering feel to be just what I wanted. I am now convinced that the FE1 springs and F45 shocks are the biggest factor in that loose steering feel, since the bushings on the Z06 are supposedly the same.
Tomorrow, I'm taking advantage of the deal through FredBeans and ordering Z06 springs/shocks to complement my z06 sways. That should be the end of this story.
Last edited by Undecided; Jan 6, 2005 at 01:53 AM.
Safety Car
Joined: Nov 2003
Posts: 4,979
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From: San Diego, CA "leaf" "tee" "e"
In addition to shocks & springs, the Z06 has bigger tires, a more aggressive alignment and stiffer swaybars too. All else suspension wise is the same....although I consider all weight to be part of the suspension, and the Z06 is lighter.
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Thread Starter
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Joined: Jan 2004
Posts: 92
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From: Sacramento CA
Originally Posted by leaftye
In addition to shocks & springs, the Z06 has bigger tires, a more aggressive alignment and stiffer swaybars too. All else suspension wise is the same....although I consider all weight to be part of the suspension, and the Z06 is lighter.
Any thoughts on alignment once I get the Z06 suspension installed? Should I get it aligned to Z06 specs even though I have stock sized non-Z06 wheels/tires?
Safety Car
Joined: Nov 2003
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From: San Diego, CA "leaf" "tee" "e"
Sure, go for it. An aggressive alignment is less brutal on skinnier tires, and the Z06 alignment is pretty mild, so go for it. It's usually possible to find Z06 wheels going for less than $1,000, sometimes much less. Good luck finding a set!
