20b?
03-28-2005, 07:01 PM
#22
Senior Member
Join Date: Jun 2004
Posts: 524
[quote name='inanimate_object' date='Mar 28 2005, 03:24 AM']Like what exactly?
Mark
[/quote]
Assuming you could get the bumpsteer near correct, since hanging a rack is a non-trivial job and you would additionally have a lot of diddling to do with rack lengths, you would suffer from horrid amounts of negative Ackerman.
If you picture a car driving around a corner, you can see that the inside and outside front tires will have to describe two different arcs, since the inside tire will have a shorter radius in the corner than the outside one. Without getting into too deep of an explanation with lots of diagramming and such, if you move the rack forwards, the inside tire will not turn enough relative to the outside tire.
If you've ever wondered why 80's Mustangs felt so odd when cornering, like the harder you drive the less the steering felt sure, that is why. There is a large market for fixes for this, and a lot of road racers extensively modify the subframe to both get the rack as far back as possible, and the ball joints as far forwards as possible, assuming they don't just buy a pre-made custom job.
Mark
[snapback]691722[/snapback]
[/quote]
Assuming you could get the bumpsteer near correct, since hanging a rack is a non-trivial job and you would additionally have a lot of diddling to do with rack lengths, you would suffer from horrid amounts of negative Ackerman.
If you picture a car driving around a corner, you can see that the inside and outside front tires will have to describe two different arcs, since the inside tire will have a shorter radius in the corner than the outside one. Without getting into too deep of an explanation with lots of diagramming and such, if you move the rack forwards, the inside tire will not turn enough relative to the outside tire.
If you've ever wondered why 80's Mustangs felt so odd when cornering, like the harder you drive the less the steering felt sure, that is why. There is a large market for fixes for this, and a lot of road racers extensively modify the subframe to both get the rack as far back as possible, and the ball joints as far forwards as possible, assuming they don't just buy a pre-made custom job.
03-29-2005, 05:46 AM
#23
Senior Member
Join Date: Nov 2003
Location: Ireland
Posts: 907
[quote name='heretic' date='Mar 29 2005, 02:00 AM']Assuming you could get the bumpsteer near correct, since hanging a rack is a non-trivial job and you would additionally have a lot of diddling to do with rack lengths, you would suffer from horrid amounts of negative Ackerman.
If you picture a car driving around a corner, you can see that the inside and outside front tires will have to describe two different arcs, since the inside tire will have a shorter radius in the corner than the outside one. Without getting into too deep of an explanation with lots of diagramming and such, if you move the rack forwards, the inside tire will not turn enough relative to the outside tire.
If you've ever wondered why 80's Mustangs felt so odd when cornering, like the harder you drive the less the steering felt sure, that is why. There is a large market for fixes for this, and a lot of road racers extensively modify the subframe to both get the rack as far back as possible, and the ball joints as far forwards as possible, assuming they don't just buy a pre-made custom job.
[/quote]
Getting the rack length is simple, you keep the track rod ends in line with the suspension mounts that's all there is to eliminating bump steer. As for the ackermann problem, horrid amounts? how far forward do you have to move it? With a 20b you probably want a bit less Ackermann than stock since you'll be going that bit faster.
Mark
If you picture a car driving around a corner, you can see that the inside and outside front tires will have to describe two different arcs, since the inside tire will have a shorter radius in the corner than the outside one. Without getting into too deep of an explanation with lots of diagramming and such, if you move the rack forwards, the inside tire will not turn enough relative to the outside tire.
If you've ever wondered why 80's Mustangs felt so odd when cornering, like the harder you drive the less the steering felt sure, that is why. There is a large market for fixes for this, and a lot of road racers extensively modify the subframe to both get the rack as far back as possible, and the ball joints as far forwards as possible, assuming they don't just buy a pre-made custom job.
[snapback]692037[/snapback]
[/quote]
Getting the rack length is simple, you keep the track rod ends in line with the suspension mounts that's all there is to eliminating bump steer. As for the ackermann problem, horrid amounts? how far forward do you have to move it? With a 20b you probably want a bit less Ackermann than stock since you'll be going that bit faster.
Mark
03-29-2005, 06:21 PM
#24
Senior Member
Join Date: Jun 2004
Posts: 524
Originally Posted by inanimate_object' date='Mar 29 2005, 03:46 AM
Getting the rack length is simple, you keep the track rod ends in line with the suspension mounts that's all there is to eliminating bump steer. As for the ackermann problem, horrid amounts? how far forward do you have to move it? With a 20b you probably want a bit less Ackermann than stock since you'll be going that bit faster.
The phrase "easier said than done" comes to mind. If the rack needs to be lengthened, that can be done fairly expediently, but if it needs shortened, that's a bit more difficult to deal with.
I don't understand why you'd want to compromise the steering because the car can theoretically go faster. Won't be able to go faster in corners, anyway.
By the same token you could say that bumpsteer is not a problem because you will be using 1000lb-in springs and the suspension will barely be moving.
Also by the same token, you could say that a little reconstructive surgery on the firewall and modifying the driveshaft and PPF is much preferable to screwing around this way and that with the frontend. As a bonus, you get to shift some weight rearwards, never a bad thing. Might even compensate for the huge front-mount intercooler and huger radiator you'd probably want to install, too.
03-30-2005, 07:29 PM
#25
Senior Member
Join Date: Nov 2003
Location: Ireland
Posts: 907
[quote name='heretic' date='Mar 30 2005, 01:21 AM']The phrase "easier said than done" comes to mind. If the rack needs to be lengthened, that can be done fairly expediently, but if it needs shortened, that's a bit more difficult to deal with.
[/quote]
It's no harder to shorten the rack, the guys building the same car as is in my sig shorten the rack in their own garages without any hassle. If it's a hardened rack, generally it's just the teeth that are hardened so that's not a problem. And that's not even touching a custom rack or finding a suitable donor one which are both viable.
[quote name='heretic' date='Mar 30 2005, 01:21 AM']I don't understand why you'd want to compromise the steering because the car can theoretically go faster. Won't be able to go faster in corners, anyway.
[/quote]
I'm not talking about comprimise, chances are the 20b is not the only alteration to the car, chances are you're running bigger softer tyres too, and with the 20b you're hitting the corners faster, you probably want less Ackermann.
I'm aware there's a trade off between better roadholding and fidgity steering, but that only happens when you get into negative Ackermann. I don't know what amount of Ackermann an fd has, I'm assuming it's positive by some amount, leaving some room for moving the rack, worst case scenario you lengthen the steering arms on the uprights.
[quote name='heretic' date='Mar 30 2005, 01:21 AM']By the same token you could say that bumpsteer is not a problem because you will be using 1000lb-in springs and the suspension will barely be moving.
[/quote]
Very true, but if it can be fixed, then why not?
[quote name='heretic' date='Mar 30 2005, 01:21 AM']Also by the same token, you could say that a little reconstructive surgery on the firewall and modifying the driveshaft and PPF is much preferable to screwing around this way and that with the frontend. As a bonus, you get to shift some weight rearwards, never a bad thing. Might even compensate for the huge front-mount intercooler and huger radiator you'd probably want to install, too.
[/quote]
But what is a perfectly good car worth after all this? Although that is a fair point about shifting the weight back.
I guess we're coming at this from different angles, the real benefit of changing the rack is once you have a solution, it's the same for every other 20b fd you do - and you stand to make a bit of money selling kits.
Mark
[/quote]
It's no harder to shorten the rack, the guys building the same car as is in my sig shorten the rack in their own garages without any hassle. If it's a hardened rack, generally it's just the teeth that are hardened so that's not a problem. And that's not even touching a custom rack or finding a suitable donor one which are both viable.
[quote name='heretic' date='Mar 30 2005, 01:21 AM']I don't understand why you'd want to compromise the steering because the car can theoretically go faster. Won't be able to go faster in corners, anyway.
[/quote]
I'm not talking about comprimise, chances are the 20b is not the only alteration to the car, chances are you're running bigger softer tyres too, and with the 20b you're hitting the corners faster, you probably want less Ackermann.
I'm aware there's a trade off between better roadholding and fidgity steering, but that only happens when you get into negative Ackermann. I don't know what amount of Ackermann an fd has, I'm assuming it's positive by some amount, leaving some room for moving the rack, worst case scenario you lengthen the steering arms on the uprights.
[quote name='heretic' date='Mar 30 2005, 01:21 AM']By the same token you could say that bumpsteer is not a problem because you will be using 1000lb-in springs and the suspension will barely be moving.
[/quote]
Very true, but if it can be fixed, then why not?
[quote name='heretic' date='Mar 30 2005, 01:21 AM']Also by the same token, you could say that a little reconstructive surgery on the firewall and modifying the driveshaft and PPF is much preferable to screwing around this way and that with the frontend. As a bonus, you get to shift some weight rearwards, never a bad thing. Might even compensate for the huge front-mount intercooler and huger radiator you'd probably want to install, too.
[snapback]692458[/snapback]
[/quote]
But what is a perfectly good car worth after all this? Although that is a fair point about shifting the weight back.
I guess we're coming at this from different angles, the real benefit of changing the rack is once you have a solution, it's the same for every other 20b fd you do - and you stand to make a bit of money selling kits.
Mark
03-30-2005, 07:57 PM
#26
Senior Member
Join Date: Jun 2004
Posts: 524
Originally Posted by inanimate_object' date='Mar 30 2005, 05:28 PM
I'm not talking about comprimise, chances are the 20b is not the only alteration to the car, chances are you're running bigger softer tyres too, and with the 20b you're hitting the corners faster, you probably want less Ackermann.
I can't imagine why you would want to hamper turn-in and steering feel.
I guess we will just have to agree to disagree. I find it much easier to relocate the drivetrain than to rehang the rack, perhaps your experience is different.
03-31-2005, 06:14 AM
#27
Senior Member
Join Date: Nov 2003
Location: Ireland
Posts: 907
[quote name='heretic' date='Mar 31 2005, 02:57 AM']I can't imagine why you would want to hamper turn-in and steering feel.
I guess we will just have to agree to disagree. I find it much easier to relocate the drivetrain than to rehang the rack, perhaps your experience is different.
[/quote]
Let's not blow this out of proportion here, we're not even talking about large amounts of anti-Ackermann, which is what you'd want for the average driver to notice the difference anyway. Even if we were, I have seen plenty of race cars with anti-ackermann, so it can't be all that bad for turn in (although I won't argue over steering feel).
To be honest I think we're getting a bit trivial over this, and I actually don't disagree with anything you have said, we don't have 20b's or even rx-7's in Ireland (apart from literally 1 or 2 that have been imported
). I'm just always wondered why people put up with bump steer on these cars when as far as I can see the solution is quite simple.
Mark
I guess we will just have to agree to disagree. I find it much easier to relocate the drivetrain than to rehang the rack, perhaps your experience is different.
[snapback]693081[/snapback]
[/quote]
Let's not blow this out of proportion here, we're not even talking about large amounts of anti-Ackermann, which is what you'd want for the average driver to notice the difference anyway. Even if we were, I have seen plenty of race cars with anti-ackermann, so it can't be all that bad for turn in (although I won't argue over steering feel).
To be honest I think we're getting a bit trivial over this, and I actually don't disagree with anything you have said, we don't have 20b's or even rx-7's in Ireland (apart from literally 1 or 2 that have been imported
Mark
04-05-2005, 07:12 PM
#28
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Join Date: Nov 2002
Location: Honolulu, Hawaii USA
Posts: 925
I dunno what "horrid amounts of Ackemann" means, but anyone who brings up Ackermann in relation to a street car should be shot...
Are you moving the steering rack more than half a foot?
If so, you need better customizing skills.
-Ted
Are you moving the steering rack more than half a foot?
If so, you need better customizing skills.
-Ted
