Need Suspension Education

[bgettel]

Hey Folks,

I have a tubular k-member for my 85GT (weight savings). I need help understanding my options for the rest of the front suspension.

What other front suspension pieces am I required to change? I'm a little confused about the control arms as I see they come with or without spring perches.

Is it possible to keep the stock control arms until I'm ready to convert to coilovers?

[86lx]

I’m about 99% certain that most tubular k-members are designed to accommodate stock control arms. I would reach out to whoever made the one you have to be 100% certain.


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[massacre]

You didn’t say which K member you have, but it makes it easier if you know what your suspension setup is going to be.
For instance, Team Z makes control arms that are 1” shorter, to keep the Fox tread width when using ‘94-95 spindles. I knew I wanted to use the 94-95 spindles to have bigger front disc brakes, but also did not want the front tires to be wider.

There is lots of info out there, this might help get you started

https://www.maximummotorsports.com/F...Tech-C565.aspx

[TxMike64]

You could use stock control arms, but I don't think the tubular k-members have upper spring perches. BMR's K-member has an option to add spring perches and also have control arms that can use a conventional spring.

I kind of like the idea of using conventional springs, as I don't see the advantage to coilovers.

[massacre]

I like coilovers for setting ride height

[TxMike64]

I like coilovers for setting ride height

Is that the only advantage? I can't imagine the net change in unspring weight is that great for a street cruiser.

/sorry for the thread-jack

[massacre]

Is that the only advantage? I can't imagine the net change in unspring weight is that great for a street cruiser.

/sorry for the thread-jack

Easier to change springs as well.

[TxMike64]

I've used conventional drop springs and have been happy with the results. Setting ride height with coilovers seems tedious - even to just get the car even side-to-side - but that may just be my inexperience with them. I suppose it does sometimes happen with conventional spring that ride height is uneven side-to-side - but I don't know how often it happens and I've not had it happen.

I suppose it all comes down to the purposed intent of the modification: my intent for a k-member is to lighten the from some and give clearance for longtubes. And I'd be happy with a 1-1.5 drop I'd get from regular drop springs.

We need to know the OPs intent. The MM link is a great source of info.

[bgettel]

We need to know the OPs intent. The MM link is a great source of info.

The car will be a street car 95% of the time. Handling w/o completely sacrificing ride comfort is the goal, and lightening the front end will help. I just don't know suspension stuff very well, and the budget is not unlimited. I'm just trying to understand what I can and can't do, starting with what I have today.

I'll try and get more info and/or a pic of the K member that I have. It's almost 3AM else I'd do it now.

Thanks for the responses thus far.

BG

[Hammer Down]

Unless it’s a MM or Griggs k-member it probably won’t help handling. But it will save a lot of weight and room.

[Jack Hidley]

You absolutely should install coilovers in the front of the car along with tubular FCAs, before you install a tubular k-member. There are far more benefits from this as well as more weight savings.

Virtually no production vehicle made today puts the springs on the control arms in the suspension. This is because it results in a low motion ratio for the spring. The result of this is that the spring needs to be heavier because it must be stiffer to achieve the same wheel rate. The control arm must be heavier because it must be able to handle the bending load of the spring being placed on it. Putting the spring on the control arm causes friction in all of the suspension pviots. This is bad for performance in every way. With the spring mounted concentrically with the damper, there is no added friction in the damper seals, ball joints or control arm bushings. This makes ride quality and traction better, because the suspension isn't locked up going over small bumps.

Building a tubular k-member with upper spring perches so that it can accept the stock FCAs is a very, very poor decision in my opinion. You have made the entire system heavier and the performance worse for no reason.

[bgettel]

Building a tubular k-member with upper spring perches so that it can accept the stock FCAs is a very, very poor decision in my opinion. You have made the entire system heavier and the performance worse for no reason.

OK, I'm listening. First, I should provide pics of the K member and control arms that I want to put on the car. But I can't seem to get any photos to post, and I'm following the instructions listed in the Board Help forum.

Jack - can I send them to you via email @ Maximum Motorsports?

BG

[Shauncb]

I had a long phone call with one of the guys from MM about all this and he made a very good point, with the a stock spring the control arm bushings are being forced down as is the ball joint, with a coil over the weight of the car is on the spindle and tire so the control arm and ball joint just float along reducing friction.

I have an aje k member with stock springs, the ONLY reason I want to stay stock springs is because I've read so many times that the early fox chassis aren't as strong as the later chassis and I'm afraid that the strut mount will crack by that area holding the weight of the car.

[Jack Hidley]

BG. Yes.

[wraithracing]

I had a long phone call with one of the guys from MM about all this and he made a very good point, with the a stock spring the control arm bushings are being forced down as is the ball joint, with a coil over the weight of the car is on the spindle and tire so the control arm and ball joint just float along reducing friction.

I have an aje k member with stock springs, the ONLY reason I want to stay stock springs is because I've read so many times that the early fox chassis aren't as strong as the later chassis and I'm afraid that the strut mount will crack by that area holding the weight of the car.

First assuming the Unibody of the Fox is in good condition with no rust issues that would compromise the structural integrity of the vehicle. There are plenty of road racers across the nation that have been running coil over front suspensions on the Fox bodies literally for decades now. I personally don't know of any that have had structural issues in the strut mount area due to the coil over design. Keep in mind that the vast majority of these cars are running spring rates of 400+ lbs which most likely would be higher than what you might need for your setup. I personally have MM coil over setup on 3 of my Foxes and have had zero issues with the strut tower areas. With that said, I do also run MM C/C Plates and most of their other hardware. I have no experience with the AJE K member, but I doubt that would cause any issues with the strut tower. My understanding is the AJE K member has additional reinforcements if the K member is used for road racing.

Oh and by the way, my 86 Road Racer project that I am working on is running 400lb front coil over springs, so definitely on the upper end of the range for a street car. Good Luck!

[bgettel]

BG. Yes.

Jack - I found the info on my K. It's a PA Racing tubular K member and I also have their tubular control arms.

K member: https://paracing.com/product/79-93-mustang-k-member/

Control arms: https://paracing.com/product/79-93-m...ubular-a-arms/

If you have a chance you can read up on the specs there. Feel free to PM me if you'd rather not respond here on the thread.

Thanks, Jack.

[Shauncb]

First assuming the Unibody of the Fox is in good condition with no rust issues that would compromise the structural integrity of the vehicle. There are plenty of road racers across the nation that have been running coil over front suspensions on the Fox bodies literally for decades now. I personally don't know of any that have had structural issues in the strut mount area due to the coil over design. Keep in mind that the vast majority of these cars are running spring rates of 400+ lbs which most likely would be higher than what you might need for your setup. I personally have MM coil over setup on 3 of my Foxes and have had zero issues with the strut tower areas. With that said, I do also run MM C/C Plates and most of their other hardware. I have no experience with the AJE K member, but I doubt that would cause any issues with the strut tower. My understanding is the AJE K member has additional reinforcements if the K member is used for road racing.

Oh and by the way, my 86 Road Racer project that I am working on is running 400lb front coil over springs, so definitely on the upper end of the range for a street car. Good Luck!

I might be wrong but I'm not sure that there are pot holes on road courses, is just worried about street driving and the super smooth roads we all have.

[wraithracing]

I might be wrong but I'm not sure that there are pot holes on road courses, is just worried about street driving and the super smooth roads we all have.

First I recommend trying to avoid the pot holes rather than driving over them. Not good for any suspension.

Second if that is a major concern than I don't know that the AJE K member is the best option for the street either since it is really designed for drag racing. As you stated there aren't many pot holes on race tracks nor most drag strips.

If terrible road conditions and pot holes are standard driving conditions then truthfully a stock K member, stock A arms and stock style springs are probably the best options for the wear and tear they will have to endure. I lived in Texas for over 30 years and have been back many times over the past several years, although there are bad roads like any state, overall your road quality is better than most. Good luck!

[86FOX4EYE]

K member: https://paracing.com/product/79-93-mustang-k-member/

Control arms: https://paracing.com/product/79-93-m...ubular-a-arms/

bgettel,

I would seriously reconsider the design of the lower arm you have posted for street driving. Especially for a car that weighs 3000+ pounds. Or even 2700 lbs.

In my experience, for a strong light lower control arm (at least the ones I have designed) the arm legs need to be straight with cross bracing to form a triangle. The front and rear legs act in tension and compression to counteract the fore and aft forces of acceleration and especially breaking. For this reason any bends in the legs tend to weaken the arm as well as add flex to the legs.

The other thing to consider with a lower arm is the use of rod ends to pin it to the pick up points on the chassis. I am not saying it cant be done. Many designs use this approach. I am just saying that with the use of rod ends as fixing points the design is less robust than a design that utilizes sleeves and bushings. The use of rod ends as fixing points is more appropriate for a component with much lower loads. For instance the upper control arm in an SLA suspension. If you are going for zero (or close to zero) pivot deflection then use Delrin or even aluminum bushings in the sleeved design.

In many ways a street driven car can have suspension loads as high as track driven cars. Sometimes higher impact loads. Use careful consideration when selecting components.

Matthew