Handling Issue - Possible caster adjustment needed?
11-16-16, 07:37 PM
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Handling Issue - Possible caster adjustment needed?
Hello all,
I've been fighting a handling issue for a while now, and would like to get a little advice from the handling guru's out there.
Some background: 94 RX7. Street driven. Suspension upgrades include Tein Street Advance coilovers, new inner and outer tie rods, new bushings, new ball joint boots, repacked ball joints and checked for play, new upper strut mounts, front and rear strut tower braces. In general, went through the front and rear suspension and replaced anything that was worn. Coilover height is set lower than factory ride height, by about an inch. Four wheel alignment done several months ago. All measurements within factory spec, save the rear camber which is at about -2.5*.
Symptom 1: Handling has felt 'off' for, some time. Not horribly out of control or anything, but not enjoyable. It's almost like I have to ride herd. Constant small eft and right adjustments in the steering wheel to keep it between the lines.
Symptom 2: Center return is present, but may not be as strong as it should be.
Symptom 3: On rough roads, it wants to .. track .. the defects in the road. Say there was a seam in the black top... If the wheels get close to it, it'll feel as though it wants to strongly track that seam, or defect.
I have a couple friends who are mechanics for a living, so I asked them to look over the work I had done, and to take it for a test drive.
Neither found anything loose, nor did they find any play in anything. All fasteners torqued to spec. Steering rack mounts in good shape and no movement in the rack during steering. They both describe the steering as tight, and say the car responds to steering input quickly. But they both felt the unnerving feeling I described. One friend wasn't sure what to make of it, and the other suspects a caster issue.
As mentioned above, all alignment values are within factory spec, except for rear camber. The technician doing the alignment ran into an issue on the rear left wheel, and could not get the camber within spec, so he set both left and right rear wheels to -2.5*. Explained this would cause better traction when going around turns at higher rates of speed, at the cost of faster tire wear, but otherwise would not cause any ill effects. I still need to investigate the cause of the alignment issue and replace whatever it is, but I'm assuming for the moment that the rear camber is not the cause of this tracking / handling feeling.
Front left caster is +6.6*, and front right caster is +6.8*. Front cross caster is -0.2*.
My friend thinks that I need to focus on the front caster adjustments. I really am not very knowledgeable on suspension geometry settings. Have read over Howard Coleman's sticky, and have searched the board to get some basic ideas about caster adjustments. I've also read some general information online, and checked out some of the digital caster/camber adjustment gauges available nowadays. Just trying to become somewhat knowledgeable so I can at least describe what's going on, etc.
I'm looking for some thoughts on whether the symptoms described could be caused by caster adjustment issues. It seems like it's a possibility, but I'm wondering if there's alternative theories that I should be investigating. If this is a likely cause, I'll try to find an alignment shop in the area that is willing to a) realize that it may take several test drives and alignment cycles before its completely worked out, and b) is willing to possibly need to take my car out of factory specs, if that's what it takes to correct the issue. But if there's other ideas of what could cause this set of symptoms, I'd value the input so I can take this into consideration.
I appreciate any input anyone may have.
Thanks!
I've been fighting a handling issue for a while now, and would like to get a little advice from the handling guru's out there.
Some background: 94 RX7. Street driven. Suspension upgrades include Tein Street Advance coilovers, new inner and outer tie rods, new bushings, new ball joint boots, repacked ball joints and checked for play, new upper strut mounts, front and rear strut tower braces. In general, went through the front and rear suspension and replaced anything that was worn. Coilover height is set lower than factory ride height, by about an inch. Four wheel alignment done several months ago. All measurements within factory spec, save the rear camber which is at about -2.5*.
Symptom 1: Handling has felt 'off' for, some time. Not horribly out of control or anything, but not enjoyable. It's almost like I have to ride herd. Constant small eft and right adjustments in the steering wheel to keep it between the lines.
Symptom 2: Center return is present, but may not be as strong as it should be.
Symptom 3: On rough roads, it wants to .. track .. the defects in the road. Say there was a seam in the black top... If the wheels get close to it, it'll feel as though it wants to strongly track that seam, or defect.
I have a couple friends who are mechanics for a living, so I asked them to look over the work I had done, and to take it for a test drive.
Neither found anything loose, nor did they find any play in anything. All fasteners torqued to spec. Steering rack mounts in good shape and no movement in the rack during steering. They both describe the steering as tight, and say the car responds to steering input quickly. But they both felt the unnerving feeling I described. One friend wasn't sure what to make of it, and the other suspects a caster issue.
As mentioned above, all alignment values are within factory spec, except for rear camber. The technician doing the alignment ran into an issue on the rear left wheel, and could not get the camber within spec, so he set both left and right rear wheels to -2.5*. Explained this would cause better traction when going around turns at higher rates of speed, at the cost of faster tire wear, but otherwise would not cause any ill effects. I still need to investigate the cause of the alignment issue and replace whatever it is, but I'm assuming for the moment that the rear camber is not the cause of this tracking / handling feeling.
Front left caster is +6.6*, and front right caster is +6.8*. Front cross caster is -0.2*.
My friend thinks that I need to focus on the front caster adjustments. I really am not very knowledgeable on suspension geometry settings. Have read over Howard Coleman's sticky, and have searched the board to get some basic ideas about caster adjustments. I've also read some general information online, and checked out some of the digital caster/camber adjustment gauges available nowadays. Just trying to become somewhat knowledgeable so I can at least describe what's going on, etc.
I'm looking for some thoughts on whether the symptoms described could be caused by caster adjustment issues. It seems like it's a possibility, but I'm wondering if there's alternative theories that I should be investigating. If this is a likely cause, I'll try to find an alignment shop in the area that is willing to a) realize that it may take several test drives and alignment cycles before its completely worked out, and b) is willing to possibly need to take my car out of factory specs, if that's what it takes to correct the issue. But if there's other ideas of what could cause this set of symptoms, I'd value the input so I can take this into consideration.
I appreciate any input anyone may have.
Thanks!
11-17-16, 06:21 AM
#5
What tires are you running and what pressures? Everything works together as a system.
The rear camber is a bit much, especially considering your front camber is basically zero. The front to rear balance is off.
Here is what I would recommend, start with the basics:
Inspect your tires to make sure they are worn somewhat evenly and no obvious defects.
Set tire pressures to 32 psi cold all around
Increase front camber, decrease rear camber. You need to have more camber in the front than in the rear, your rear camber is way too high in relation to the front. The car probably handles like ****.
Change your front toe to TOE IN. Right now you have toe out. Toe in helps keep the car straight & stable, vs toe out where the tires are constantly fighting each other, but you gain steering agility.)
Start with that and report back, this is assuming all is mechanically sound. Alignments are extremely important. They can make or break or a car and the way it drives.
The rear camber is a bit much, especially considering your front camber is basically zero. The front to rear balance is off.
Here is what I would recommend, start with the basics:
Inspect your tires to make sure they are worn somewhat evenly and no obvious defects.
Set tire pressures to 32 psi cold all around
Increase front camber, decrease rear camber. You need to have more camber in the front than in the rear, your rear camber is way too high in relation to the front. The car probably handles like ****.
Change your front toe to TOE IN. Right now you have toe out. Toe in helps keep the car straight & stable, vs toe out where the tires are constantly fighting each other, but you gain steering agility.)
Start with that and report back, this is assuming all is mechanically sound. Alignments are extremely important. They can make or break or a car and the way it drives.
11-17-16, 06:25 AM
#6
Senior Member
Yeah, I'd have them dial in +0.1 degrees total front toe-in, and maybe reduce rear toe down to 0.1 degrees total toe-in.
The car must have been a REAL mess with -2.6 degrees toe out!
With as much rear camber as you have, I think it'd be good to get around -1.5 or at least -1 up front, but I don't think that has much if anything to do with the issues you described.
Caster should be fine. Personally I like to run at the minimum end of spec, but 6.6/6.8 is well within spec and small enough spread between the two that it shouldn't be an issue at all.
Your caster
The car must have been a REAL mess with -2.6 degrees toe out!
With as much rear camber as you have, I think it'd be good to get around -1.5 or at least -1 up front, but I don't think that has much if anything to do with the issues you described.
Caster should be fine. Personally I like to run at the minimum end of spec, but 6.6/6.8 is well within spec and small enough spread between the two that it shouldn't be an issue at all.
Your caster
11-17-16, 09:54 AM
#7
fix whatever the rear issue is. Hopefully it's as easy as new eccentric bolts, but getting the rear working appropriate should be your first step.
As others mentioned, go slightly toe in on the front and reduce the toe in a bit in the rear. Having toe out in the front will definitely cause the car to dart and tramline as you're experiencing.
Caster is ok, just try to have them make it as close to equal on both sides as possible.
As others mentioned, go slightly toe in on the front and reduce the toe in a bit in the rear. Having toe out in the front will definitely cause the car to dart and tramline as you're experiencing.
Caster is ok, just try to have them make it as close to equal on both sides as possible.
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11-17-16, 07:05 PM
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Thank you all for the input. This information is great. As if you couldn't tell, I'm not the most knowledgeable when it comes to suspension and alignment details... Replacing parts is one thing... Trying to figure out why a freshly aligned car doesn't handle good is completely different. I appreciate all of the suggestions.
Tire pressure is at 35 psi all the way around. I will drop this to 32 as suggested.
Tires are wearing pretty well, but they only have a couple thousand miles on them. Previous tires wore fine, but that was before I had replaced a bunch of suspension & steering parts.
Regarding the rear camber... The reason it is at -2.5ish is because the alignment shop couldn't adjust the rear left out to factory specs, so they set it to the lest they could and matched the rear right to it. Seems that everyone agrees that either I need to get the issue fixed so that the camber can be dialed down, or that I need to add some front camber to offset the rear camber some... I'll try to go the route of fixing whatever is damaged first. The alignment shop pointed out that my trailing link was tweaked a bit. I'm sure this happened during a hundred mile tiltbed ride I had a few months before the replacement parts and alignment. I think the driver may have strapped the rear down on the trailing link. I'm sure that can't be good for getting things to align properly. I'll try to get that sorted out. Or, maybe its a cam bolt as mentioned.
Regarding toe: I'll definitely take the advice and have them toe in the front a bit more and reduce the toe in on the rear a bit.
Regarding handling like crap: Definitely. Long story short, I've been upgrading the car bit by bit for a couple years now... Mostly engine, engine management, fuel system, etc. Also fixing problems, replacing parts to increase reliability, etc. I finally got around to replacing the shocks and springs, and figured while there, I might as well replace all the other wear items and check all the other bits and pieces. By the time it was all said and done, I had replaced many of the parts, and confirmed that the remaining parts (ball joints, sway bar links, etc) were reusable. Course, I threw the alignment totally out of whack by replacing all these parts, hence the -2.6 total toe. I tried to get it close enough with tape measure, to drive it to the alignment shop, but it was bad.
The final straw was when I started thinking "Its kind of sad when my daily driven Toyota Celica handles better than my FD dream car....."
Anyway, thank you all again for all the advice. I'll start with your suggestions, and see what this does. Hopefully the snow (and salt and cinders) will stay away for the next couple weekends so I can give all of this a shot.
Will update everyone with the outcome.
Tire pressure is at 35 psi all the way around. I will drop this to 32 as suggested.
Tires are wearing pretty well, but they only have a couple thousand miles on them. Previous tires wore fine, but that was before I had replaced a bunch of suspension & steering parts.
Regarding the rear camber... The reason it is at -2.5ish is because the alignment shop couldn't adjust the rear left out to factory specs, so they set it to the lest they could and matched the rear right to it. Seems that everyone agrees that either I need to get the issue fixed so that the camber can be dialed down, or that I need to add some front camber to offset the rear camber some... I'll try to go the route of fixing whatever is damaged first. The alignment shop pointed out that my trailing link was tweaked a bit. I'm sure this happened during a hundred mile tiltbed ride I had a few months before the replacement parts and alignment. I think the driver may have strapped the rear down on the trailing link. I'm sure that can't be good for getting things to align properly. I'll try to get that sorted out. Or, maybe its a cam bolt as mentioned.
Regarding toe: I'll definitely take the advice and have them toe in the front a bit more and reduce the toe in on the rear a bit.
Regarding handling like crap: Definitely. Long story short, I've been upgrading the car bit by bit for a couple years now... Mostly engine, engine management, fuel system, etc. Also fixing problems, replacing parts to increase reliability, etc. I finally got around to replacing the shocks and springs, and figured while there, I might as well replace all the other wear items and check all the other bits and pieces. By the time it was all said and done, I had replaced many of the parts, and confirmed that the remaining parts (ball joints, sway bar links, etc) were reusable. Course, I threw the alignment totally out of whack by replacing all these parts, hence the -2.6 total toe. I tried to get it close enough with tape measure, to drive it to the alignment shop, but it was bad.
The final straw was when I started thinking "Its kind of sad when my daily driven Toyota Celica handles better than my FD dream car....."
Anyway, thank you all again for all the advice. I'll start with your suggestions, and see what this does. Hopefully the snow (and salt and cinders) will stay away for the next couple weekends so I can give all of this a shot.
Will update everyone with the outcome.
11-18-16, 04:43 AM
#9
I'm fairly confident its an alignment issue. I also wouldn't reduce your rear toe much, if at all. I'd leave the rear toe alone. Perhaps just lower the left side a little to match the right side. Toe in on the rear is good, helps keep the rear straight & stable.
Another thing to keep in mind is, all of your suspension nuts & bolts need to be torqued when the chassis is loaded at static height, or close to it.
Another thing to keep in mind is, all of your suspension nuts & bolts need to be torqued when the chassis is loaded at static height, or close to it.
11-18-16, 11:34 PM
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drop the pressures down to 32 cold, and see what its like.
tire pressure changes with temperature, so a cold tire might be 27psi, and then it'll come up to 33psi when its hot. so a track car, we'd be setting the tire pressure hot, at around 32-38psi.
on the street we don't take temps, so we set them cold, and start at 32.
