This is the roll center, suspension pickup, and steering angle modification thread.

[racepar1]

Originally Posted by PoorMans180SX

I'm pretty sure the wheel well clearance issue would only be an issue if you were already bottoming out your shocks at the ride height you were at. Also, you are going to have more roll resistance when you raise your roll center, so this will decrease the likelihood of you running into interference issues during bump.

Bottomong the shock is not the issue. Bottoming the shock shouldn't be the issue on the front of any s-chasis car running anyone's coilovers. Although really I'm sure it is an issue because of the really cheap ass coilovers floating around like the plague. Wheelwell clearence in the front of the s-chasis cars is EXTREMELY limited. That is the only real issue limiting our available bump travel. The obvious solution is fendertubs, but fendertubs are not allowed in a lot of "racing" classes. I am absolutely 10000000% positive that with my stances and those knuckles I would have bottomed the tire on the fenderwell long before I bottomed the shock.

Now, yes correcting the roll center will cause less body roll and that would help with fender rubbing issues. The problem is that there will for absolute certain be situations in which the tire does bottom in the fenderwell both at the track and on the street. Bottoming your tire rather then your suspension is NOT a good thing. At the least it could damage the tire and at the worst it could cause you to lose control of the car.

mmdb, not checking the tire clearence after making that large of a change is not a very smart thing to do. Really that should be done when simply installing and setting up coilovers man...

[PoorMans180SX]

Originally Posted by racepar1

Bottomong the shock is not the issue. Bottoming the shock shouldn't be the issue on the front of any s-chasis car running anyone's coilovers. Although really I'm sure it is an issue because of the really cheap ass coilovers floating around like the plague. Wheelwell clearence in the front of the s-chasis cars is EXTREMELY limited. That is the only real issue limiting our available bump travel. The obvious solution is fendertubs, but fendertubs are not allowed in a lot of "racing" classes. I am absolutely 10000000% positive that with my stances and those knuckles I would have bottomed the tire on the fenderwell long before I bottomed the shock.

Now, yes correcting the roll center will cause less body roll and that would help with fender rubbing issues. The problem is that there will for absolute certain be situations in which the tire does bottom in the fenderwell both at the track and on the street. Bottoming your tire rather then your suspension is NOT a good thing. At the least it could damage the tire and at the worst it could cause you to lose control of the car.

mmdb, not checking the tire clearence after making that large of a change is not a very smart thing to do. Really that should be done when simply installing and setting up coilovers man...

Ah, I can see what you mean in mmdb's case, because he can't mess with the front height much.

But in general, if you're bottoming the tire, you should get higher spring rates or anti-roll bars. Knuckles can only help with people with height adjustable coils and low low ride height.

[mmdb]

Originally Posted by GripTerror

Does the car feel more compliant/comfortable/grippy so far in the front (I know you didnt install the rears).

Give us some beef on how it feels so far Cmon And I wouldn't raise it that's like perfect

There's much less roll throughout the turn (entry, mid, exit). I find it to be very confidence inspiring. When I purposely power oversteer during mid or corner exit I find it much easier to countersteer, recover and gain control. This because of the shorter steering ratio allows myself to quickly provide steering input via less effort.

As for comfort raising roll center adds resistance to roll. Similar to increasing spring rates, or sway bar stiffness. But in contrast to running higher spring rates, you might be able to lower your spring rate and gain driving comfort while using some sort of roll center correction. But there's also the issue of nose diving during braking, so you might not be able to lower the spring rate too much.

In summary to the roll center interests, I'd highly recommend investing into roll center correction such as what DW provides or a custom route (there's a few examples over on nissanroadracing.com, DW or others out there). I'd put it up there with running coilovers or sway bars. It's extremely effective.

Originally Posted by Def

Back to the discussion at hand... what's the weight on the rear uprights? I weighed Z32s at about 6.5 lbs less than stock iron uprights per side.

The DW rear knuckles weigh in at ~10.8lbs each. The stock knuckles surprising weighed in the same!

Originally Posted by mikerbike

MMDB, what shocks are you using? You can't raise ride height? Or you can't raise ride height enough to compensate how much the spindle raised the wheel?

On Topic, I tried 'super low' ride height on my car for a few weeks, maybe 2 months, i don't remember. The front gave me troubles at full lock, the rack didn't center itself and in the rack started moving side to side under turning load. The rear didn't feel any different. I raised the front one collar width (8mm or so) and it fixed all three problems. Definitely not worth the style.

Sadly, the reason I raised it was so I could fit a taller tire, not because I had problems. Stupid drifter..

I can adjust height, but it's maxed out... saddly lol.

[racepar1]

Originally Posted by PoorMans180SX

Ah, I can see what you mean in mmdb's case, because he can't mess with the front height much.

But in general, if you're bottoming the tire, you should get higher spring rates or anti-roll bars. Knuckles can only help with people with height adjustable coils and low low ride height.

No...

If you are bottoming the tire you SHOULD either:

1: tub your fenderwells (if allowed)

2: re-adjust your coilovers so that the shock bottoms on the bump stop just before the tire bottoms in the wheelwell. This is only possible if you have dual heighth adjustable coilovers and they have enough adjustment to compensate. Really this SHOULD be done whenever installing any coilovers just to be sure.

3: If your coilovers don't have enough adjustment you need to "re-engineer" them so that the shock bottoms just before the tire. This can be done with spacers on the upper mounts, adjustable upper mounts, thicker bump stops, or heavy fabrication.

I really don't like what they did in the front. I am quite suspicious that those front knuckles are one of those parts that work great if the rest of the car is setup for them, but not so great for the rest of us. Changing the distance between the hub mounting point and the shock mouting point is just not a great idea with as little fenderwell clearence as the car has. Every single aftermarket coilover is designed with that particular measurement in mind and we don't have the fender clearence to accomodate in all cases.

Once again, suspension "tuning" is about the whole package. To do it RIGHT the everything has to work together. Just because a part works badass for someone else doesn't mean it will for you.

[racepar1]

Originally Posted by Def

I've said it about 20 times here, but I'll say it again, the rear roll center does NOT drop as quickly as the front when lowering the car. Raising the rear roll center up to almost stock height when you've lowered the rear CG a few inches is going to create an UNFAVORABLE roll axis inclination in that it crosses through your CG axis. This causes all sorts of undesirable things to happen with your suspension.

I still have no clue why people think going to stock geometry is the right thing to do when you've now lowered your CG significantly. These two things work together, why in the world would you want to keep one the same and change the other one significantly?

Beyond that even when referring to "stock" geometry when referring to roll center people are using the wrong reference point. We keep talking about the roll center's heighth in reference to the ground. We need to be referencing the roll center heighth to the CG (like you said) even when referring to taking things "back to stock". The roll center's heighth in reference to the ground isn't nearly as important as the roll couple length and we all need to wake up to that as well as to what you posted above.

One question though, how bad would it be if someone got to the point where the roll center was actually above the CG? I wouldn't imagine that would be a good thing.

[Def]

Originally Posted by racepar1

I really don't like what they did in the front. I am quite suspicious that those front knuckles are one of those parts that work great if the rest of the car is setup for them, but not so great for the rest of us. Changing the distance between the hub mounting point and the shock mouting point is just not a great idea with as little fenderwell clearence as the car has. Every single aftermarket coilover is designed with that particular measurement in mind and we don't have the fender clearence to accomodate in all cases.

Once again, suspension "tuning" is about the whole package. To do it RIGHT the everything has to work together. Just because a part works badass for someone else doesn't mean it will for you.

I wonder what they did with the kingpin axis inclination up front. Raising the hub mounting point with keeping the strut mounting point in the same relative location to stock and at the same angle will probably increase the scrub radius a large amount.

Just another situation where "stock" starts to not be the best solution once you start changing a few important aspects of the whole suspension geometry.

[PoorMans180SX]

Originally Posted by Def

I wonder what they did with the kingpin axis inclination up front. Raising the hub mounting point with keeping the strut mounting point in the same relative location to stock and at the same angle will probably increase the scrub radius a large amount.

Just another situation where "stock" starts to not be the best solution once you start changing a few important aspects of the whole suspension geometry.

Well, I know that they changed it. These uprights are supposed to keep the outside wheel more "upright" when at maximum steering lock. If so, then it seems that the scrub radius would stay about the same.

[PoorMans180SX]

Originally Posted by racepar1

No...

If you are bottoming the tire you SHOULD either:

1: tub your fenderwells (if allowed)

2: re-adjust your coilovers so that the shock bottoms on the bump stop just before the tire bottoms in the wheelwell. This is only possible if you have dual heighth adjustable coilovers and they have enough adjustment to compensate. Really this SHOULD be done whenever installing any coilovers just to be sure.

3: If your coilovers don't have enough adjustment you need to "re-engineer" them so that the shock bottoms just before the tire. This can be done with spacers on the upper mounts, adjustable upper mounts, thicker bump stops, or heavy fabrication.

I really don't like what they did in the front. I am quite suspicious that those front knuckles are one of those parts that work great if the rest of the car is setup for them, but not so great for the rest of us. Changing the distance between the hub mounting point and the shock mouting point is just not a great idea with as little fenderwell clearence as the car has. Every single aftermarket coilover is designed with that particular measurement in mind and we don't have the fender clearence to accomodate in all cases.

Once again, suspension "tuning" is about the whole package. To do it RIGHT the everything has to work together. Just because a part works badass for someone else doesn't mean it will for you.

I still don't get why you're going on about it. If your tires are bottoming out in the well your body is rolling too much for your ride height.

There are many ways to fix this. Yours are some, and increasing the roll couple is another. You can't say I'm wrong.

[racepar1]

Originally Posted by PoorMans180SX

I still don't get why you're going on about it. If your tires are bottoming out in the well your body is rolling too much for your ride height.

There are many ways to fix this. Yours are some, and increasing the roll couple is another. You can't say I'm wrong.

I can for absolute positive certain tell you that you and anyone else who follows the line of thinking that you describe above is 100% for sure WRONG.

First of all body roll is not the only thing that can cause the suspenion to bottom. Hitting bumps and curbs (like at buttonwillow) compresses the suspension as well you know. Changing the roll couple doesn't affect how much the suspension compresses over bumps and such either, that's all spring rate.

Second, your suspension should be designed and set-up so that your tire never even gets the chance to touch the wheelwell under any conditions ideally. You always want your shock to bottom on the bumpstop before your tire bottoms in the wheelwell. Since our front wheelwell clearence is so limited you really have to split hairs and that will result in occasional light rubbing under extreme circumstances. That is simply unavoidable because of how close everything is.

It's really not that complicated... If your tire is hitting the fenderwell significantly, then your coilovers are either mis-adjusted or mis-engineered. Sure you can screw with the roll couples, spring rates, and swaybars to help, but that isn't actually solving anything. It is the automotive equivalent of trying to use a band-aid to stop arterial bleeding. Changing your roll stiffness to limit fender rubbing issues will certainly have un-wanted side-effects, and will only work marginally. Simply setting up your coilovers CORRECTLY has no negative side effects and will work correctly.

[PoorMans180SX]

I didn't really want to start a big argument in my own thread...

Here's the thing. Like you said, there are compromises to anything.

My point is that if you want your ride height really low (say tucking tire on 18's), and you're hitting your fenderwell, there are only so many ways around it.

Getting higher spring rates is one of them. I am NOT saying that this is ideal or that it's the absolute best solution, but it is a solution.

The whole point of this thread (for me at least) is to be able to have a really low track car with a proper functioning suspension (like a GT class car).

[95KA-Turbo]

Originally Posted by PoorMans180SX

I didn't really want to start a big argument in my own thread...

Here's the thing. Like you said, there are compromises to anything.

My point is that if you want your ride height really low (say tucking tire on 18's), and you're hitting your fenderwell, there are only so many ways around it.

Getting higher spring rates is one of them. I am NOT saying that this is ideal or that it's the absolute best solution, but it is a solution.

The whole point of this thread (for me at least) is to be able to have a really low track car with a proper functioning suspension (like a GT class car).

That's my whole point as well. Which is why I modified my front wheel wells so much:

[racepar1]

Originally Posted by PoorMans180SX

I didn't really want to start a big argument in my own thread...

Here's the thing. Like you said, there are compromises to anything.

My point is that if you want your ride height really low (say tucking tire on 18's), and you're hitting your fenderwell, there are only so many ways around it.

Getting higher spring rates is one of them. I am NOT saying that this is ideal or that it's the absolute best solution, but it is a solution.

The whole point of this thread (for me at least) is to be able to have a really low track car with a proper functioning suspension (like a GT class car).

Take a look at the post below yours. THAT is how you slam the car and still maintain acceptable compression travel. The way you are thinking is just not good. You need to change that. What you are talking about is a band-aid, not a solution. I don't see this as an argument at all. An argument has two sides. I do not consider half-assing a bunch of stuff and dealing with the negative side effects a valid "other side" to this "argument", especially since it didn't even fully solve the problem. If you wanna talk about how to half-ass your car together so that it sort of works then you probably shouldn't have ever started this thread in the first place. The compromises you are talking about making are not the kind that you want to have to live with.

EDIT: Beyond what I posted above, your "solution" costs more money then mine as well. You have to go out and buy stiffer springs and/or swaybars to do what you want. I just need some materials, patience, and time to do it my way. I simply do not see the logic behind your reasoning.

EDIT 2: I have been thinking about it some and I think I can see the problem. You're taking the necessary compromises to keep the SUSPENSION from bottoming with limited travel and you are applying them to keeping the TIRE off the fenderwell as if it was the same thing. It isn't the same. The suspension is MEANT to bottom out, that's what bumpstops are for. The tire ISN'T MEANT to bottom out, keeping the tire off the fenderwell is necessary no matter what. That is a safety issue, plain and simple. Keeping the suspension off the bumpstops is something completely separate and far less of a safety issue, more a performance issue. To increase travel in the front of our cars any significant amount you have to modify the fenderwells. If you can't do that you just have to find a way to deal with the limited travel, like what you suggested. If your car is slammed and your tire is 2" off the top of the fenderwell then you only have 2" of travel no matter what you do with the rest of the suspension, other then the wheelwells themselves. You can't change that, but you can at least adjust things so that you aren't tearing up your tires every time your suspension bottoms.

[PoorMans180SX]

Whatever man. I wasn't even saying you were wrong.

Of course you clearance the wheelwell and crap.

I was just saying that it's a possibility, after you try other stuff.

[racepar1]

Originally Posted by PoorMans180SX

Whatever man. I wasn't even saying you were wrong.

Of course you clearance the wheelwell and crap.

I was just saying that it's a possibility, after you try other stuff.

Read my "EDIT 2". You're simply applying the solutions for one problem to a completely different problem. You shouldn't shy away from a little debate. I have learned LOTS of things in debates in different threads. The whole point of having a discussion at all is to debate the options to figure out what is right. I am going to be very critical and elitist about suspension parts and theory, have been for quite a while. I have to be critical and elitist about those things to get the kind of performance that I am looking for out of my little s-13.

[PoorMans180SX]

Well, I completely agree with your edit 2.

[GripTerror]

Now instead of arguing how about some of you smarties who are smarter than some of us come up with solutions how to improve DW's spindles? What would you change/adjust, you know we can give them feedback or give suggestions to powered by max for the ones they're building (what the hell is up with theirs when is it coming out)... or anyone else who may be building *hint hint kuah cmon* these to do them the way we want/better/etc...

[mmdb]

Originally Posted by GripTerror

Now instead of arguing how about some of you smarties who are smarter than some of us come up with solutions how to improve DW's spindles? What would you change/adjust, you know we can give them feedback or give suggestions to powered by max for the ones they're building (what the hell is up with theirs when is it coming out)... or anyone else who may be building *hint hint kuah cmon* these to do them the way we want/better/etc...

DW would be mo betta if it had sphericals as an option. Also, different profiles in roll center adjustment would be nice. Not sure if that's feasible as it might require a total redesign of the unit. The 50mm in roll center adjustment keeps me skeptical whether it might be TOO much RC increase. Last thing I want is to be driftastically oversteering. Construction of the unit is pretty nice. Feels like it'll withstand a hard impacts. I dunno how feasible an aluminum spindle option would be, but it'll save a few pounds of unsprung weight which is always nice. And finally, it'd be nice to gain some sort of data or analysis how these affect other suspension components and alignment.

With that said, someone buy my LCA with moonface rca installed!

[PoorMans180SX]

Originally Posted by GripTerror

Now instead of arguing how about some of you smarties who are smarter than some of us come up with solutions how to improve DW's spindles? What would you change/adjust, you know we can give them feedback or give suggestions to powered by max for the ones they're building (what the hell is up with theirs when is it coming out)... or anyone else who may be building *hint hint kuah cmon* these to do them the way we want/better/etc...

I have some stuff drawn up, but it's not really accurate, as I haven't really measured anything due to lack of stock uprights that I can take measurements from.

mmdb, you mind if I steal those pics of the DW stuff to use in the original post?

[mmdb]

Originally Posted by PoorMans180SX

I have some stuff drawn up, but it's not really accurate, as I haven't really measured anything due to lack of stock uprights that I can take measurements from.

mmdb, you mind if I steal those pics of the DW stuff to use in the original post?

Sure no problemo

[racepar1]

Originally Posted by mmdb

DW would be mo betta if it had sphericals as an option. Also, different profiles in roll center adjustment would be nice. Not sure if that's feasible as it might require a total redesign of the unit. The 50mm in roll center adjustment keeps me skeptical whether it might be TOO much RC increase. Last thing I want is to be driftastically oversteering. Construction of the unit is pretty nice. Feels like it'll withstand a hard impacts. I dunno how feasible an aluminum spindle option would be, but it'll save a few pounds of unsprung weight which is always nice. And finally, it'd be nice to gain some sort of data or analysis how these affect other suspension components and alignment.

With that said, someone buy my LCA with moonface rca installed!

What he said^^^

#1: SPHERICALS

Also I wouldn't have corrected the rear roll center NEARLY as much, maybe half.

As for what I would do with the front knuckles I would have to see if there are any tire clearence issues with them. I'm strongly suspecting that there is, but without a set of my own to play with I couldn't tell you for sure. Since Def mentioned it I would also be interested in what was done with the scrub radius and KAI. I'm pretty sure that scrub radius isn't critical, but I'm also sure that you don't want it all out of whack either.

[swiftmini]

The dw hubs defo have kpi altered. Iam not sure about scrub radius or ackerman though.

Does it look like all or just most of the ackerman has been removed?


My opinion on wheel clearance is, if he is running the same ride height as before fitting the new knuckles and he had zero problems before, then he won't have any probs now. Surely its a no brainer. My coilovers have the same bump and droop at whatever ride height they are set at.

[swiftmini]

On previous pages I wrote that I had severe bumpsteer.

After reading the first post in this thread I realised that problem had come from lowering my trackrod ends in the psm knuckle mod fashion. I had pushed the tie rod and lower arm a long way out of sync.

I have since made rc correction parts to drop my lower balljoints 50mm, the same as I had dropped the track rod end.

Now the arms sit parallel to each other and also parallel to the ground. The bump steer issue has virtually gone completely and my car handles really nice.

At the back of the car I have godspeed lower arms, which lower the balljoint about 25mm and also rigid mounted subframe with riser bushes. So I have got aroung 35-40mm of rc correction in the rear of the car.

This is all I can do until I have access to corner scales and can determine c of g.

But some positive progress for me, iam mostly happy now.

[swiftmini]

For the rear suspension. To find the rc can we not just treat the upper camber arm and the lower control arm as a double wishbone setup?

Yes the traction rod and the toe arm will affect things but not by much. The toe arm should be treated the same as the tie rods and the traction rods should be treated ina simialr manor as tension rods.

That's just my opinion

[racepar1]

Originally Posted by swiftmini

The dw hubs defo have kpi altered. Iam not sure about scrub radius or ackerman though.

Does it look like all or just most of the ackerman has been removed?


My opinion on wheel clearance is, if he is running the same ride height as before fitting the new knuckles and he had zero problems before, then he won't have any probs now. Surely its a no brainer. My coilovers have the same bump and droop at whatever ride height they are set at.

If they changed the KAI then they changed the scrub radius as well. My question is, they changed it to what???

Personally I wouldn't wanna remove all the ackerman angle. That's kinda important to keep.

Think a little more about what they did with those knuckles. It surely isn't a "no brainer".

Originally Posted by swiftmini

On previous pages I wrote that I had severe bumpsteer.

After reading the first post in this thread I realised that problem had come from lowering my trackrod ends in the psm knuckle mod fashion. I had pushed the tie rod and lower arm a long way out of sync.

I have since made rc correction parts to drop my lower balljoints 50mm, the same as I had dropped the track rod end.

Now the arms sit parallel to each other and also parallel to the ground. The bump steer issue has virtually gone completely and my car handles really nice.

At the back of the car I have godspeed lower arms, which lower the balljoint about 25mm and also rigid mounted subframe with riser bushes. So I have got aroung 35-40mm of rc correction in the rear of the car.

This is all I can do until I have access to corner scales and can determine c of g.

But some positive progress for me, iam mostly happy now.

Pics of your roll center correction please...

I think you may have gone too far on the rear roll center correction at least though.

Originally Posted by swiftmini

For the rear suspension. To find the rc can we not just treat the upper camber arm and the lower control arm as a double wishbone setup?

Yes the traction rod and the toe arm will affect things but not by much. The toe arm should be treated the same as the tie rods and the traction rods should be treated ina simialr manor as tension rods.

That's just my opinion

That is exactly how you determine rear roll center to the best of my understanding...

[mmdb]

Originally Posted by swiftmini

At the back of the car I have godspeed lower arms, which lower the balljoint about 25mm and also rigid mounted subframe with riser bushes. So I have got aroung 35-40mm of rc correction in the rear of the car.

This is all I can do until I have access to corner scales and can determine c of g.

But some positive progress for me, iam mostly happy now.

Your roll correction height is similar to DW. How does your car feel at the rear with the roll correction you added?

[swiftmini]

Originally Posted by mmdb

Your roll correction height is similar to DW. How does your car feel at the rear with the roll correction you added?

Tbh I haven't driven the car hard in to corners yet.

The front tracking is along way out at the moment. I just did a few miles on the road to feel the car, also checked bump steer by eye before I took the car out of the work shop. I did take the car to my local parking lot to see what it handled like sideways. The car felt superb compared to how it was previously, even with the terrible toe in.

The rear of the car has had the same setup for about 9 months, although I did recently swap from an s13 subframe to an s14 frame. The rear has always felt fine. But I ruined the front end as soon as I made the knuckle mods. Now that the front has a better rc, the car feels better as a whole.

I will be doing some track testing very soon.

[swiftmini]

Originally Posted by racepar1

1. If they changed the KAI then they changed the scrub radius as well. My question is, they changed it to what???

2. Personally I wouldn't wanna remove all the ackerman angle. That's kinda important to keep.

3. Think a little more about what they did with those knuckles. It surely isn't a "no brainer".



4. Pics of your roll center correction please...

5. I think you may have gone too far on the rear roll center correction at least though.



6. That is exactly how you determine rear roll center to the best of my understanding...

1. Yes of course , I have actually altered my kpi and scrub radius. I had to fit 10mm shims between the disc and the hub, because the bottom ball joint collided with the disc.

2. Maybe iam wrong then, I will go back and look longer and harder at the pics.

3. I agree with that, I have removed some but not all. I think it helps with smooth transitions whilst drifting and also is better for turn in. However I know there are a lot of peeps that swear by zero ackerman.

4. I haven't got any, but I will post some up. The only problem is that the method I used and the parts I made are essentially a bodge, I only intend to use them to prove the problems I had. Now that I have answer I can start maing new lower arms. I will make them simialr to the godspeed arms, but I will use quality bearings (pillowballs) and build in some kind of rc adjustment.

5. I agree with this but iam willing to leave it as it is until I determine c of g or become a better driver.

6. Yay I am only 85% retarded

[GripTerror]

swiftmini post up pix of your mods and how you did what, sounds interesting

[mikerbike]

Originally Posted by racepar1

If your car is slammed and your tire is 2" off the top of the fenderwell

Is that some sort of joke?

Originally Posted by GripTerror

swiftmini post up pix of your mods and how you did what, sounds interesting

Yes Please!

[swiftmini]

Double post