Suspension Questions (Not for FR-S)

[Toyarzee]

I have a 2nd gen mini tacoma that is currently under construction. It is a boosted 2rz motor, w58 trans, and all custom suspension for a 7" drop. I am looking to redo the suspension because this truck is moving from the streets to the track. Other forums aren't proving as active and helpful as this one, so I wanted to see if anyone could help me figure out how to tackle this job.

Currently, the front was converted to a QA1 coilover setup. They are 8" 600 lb springs on single adjustable shocks from a 69 camaro (part #8MB600). I only had to make custom UCA and LCA's to fit these. The springs are actually coming in at 565 lbs though, and it's far too soft and sloppy. I'm told that any 69 camaro coilovers will work, however the coils sit so close to the frame, that any larger diameter coils will hit frame - the 700 lb qa1's available are too big a diameter in the middle, plus that's not stiff enough.

The rear is being converted from a custom leaf pack to a 4-link for coilovers, though i haven't decided what to put in the rear. I know i won't need much travel and there's not a lot of weight back there, but i don't want it squatting so hard it lays frame (frame is notched and boxed in rear).

Suggestions from here? Thanks

[jdmblood]

If you have the guap get bags yo. My favorite part about companies that make bags is the attention to detail in their work. Better then trying to get old parts imo

[Toyarzee]

Lol only new parts going into the build, unless you mean new as in never built before. I will only go with static suspension parts qualified for more serious tracking. Besides, bagged setups for these trucks usually use a reverse 4 link and would make the rear squat and bounce significantly, not ideal.

[jdmblood]

just bag it yo!

[Dimman]

What kind of track? Drag or with turns?

[Toyarzee]

Turns. Hdpe, AutoX... want to run this truck at willow

[Toyarzee]

Can I just buy non qa1 coil springs that are stiffer and throw them on the shock assembly up front if the same length and diameter? Or would that create damping issues?

[Dimman]

Originally Posted by Toyarzee

Can I just buy non qa1 coil springs that are stiffer and throw them on the shock assembly up front if the same length and diameter? Or would that create damping issues?

QA1s are fully rebuildable, AFAIK. You can buy rebuild kits and shim packs to mod the damping and I think they have pretty goid tech support for that. Will tell you x shim types for damping y spring rate.

Not sure of specifics but they make at least one shock type that is made for a small diameter spring type that is popular in circle track racing. AFCO and Bilstein have similar competing products, and there is a wide range of springs rates for them. Contact QA1 and they will tell you the dimensions of springs that will fit, then you can contact Eibach and see if they have an appropriate size in the rate you want.

Do you have the basics of your truck's f:r weight split and the motion ratios of the control arms? If you do we can sort out a good starting f:r frequency and the rates needed to achieve it. Then damp it properly. (QA1 curves are nicely digressive, if I recall) From there you balance under or oversteer and roll with bars.

Curious about racing a truck, though...

[Toyarzee]

Originally Posted by Dimman

Do you have the basics of your truck's f:r weight split and the motion ratios of the control arms? If you do we can sort out a good starting f:r frequency and the rates needed to achieve it. Then damp it properly. (QA1 curves are nicely digressive, if I recall) From there you balance under or oversteer and roll with bars.

Curious about racing a truck, though...

f:r is 57/43, which will be subject to further change. I have not experimented with measuring the motion ratios, especially now that i have longer UCA/LCA's. As it was explained to me, I was told the best way to measure this is to remove the springs and take the compression of the shock over the vertical travel of the wheel, in increments of .1" to .25". I do understand the compromise of control vs. grip, but the grip is largely affected by many other factors as well...

Since the wheel base on the ext'd cabs is rather long, 122", it is very stable on the drag strip. Now that I'm interested in taking this to the next level, I'm trying to acquire as much information as possible before making hard and costly decisions, since this is widely uncharted territory especially for this particular vehicle. However, I'm excited to take on the applicable racing models with a non-traditional and unconventional approach. I have a decent knowledge of the 2rz motors, originally rated stock at 142 hp, and have managed to crank out over 400 hp on stock compression. These torque happy motors are tons of fun and take to boost well. I suppose most would throw this setup in an ae86, but i'm content with a truck body.

I guess my initial confusion with your statement above is: how does the f:r and motion ratios really affect the desired spring rate if the springs aren't even used in formulating these calculations? I'm trying to connect the dots and have much to learn. Also, what do you mean by nicely digressive curves?

Thank you for your insight.

[Dimman]

Originally Posted by Toyarzee

f:r is 57/43. I have not experimented with measuring the motion ratios, especially now that i have longer UCA/LCA's. As it was explained to me, I was told the best way to measure this is to remove the springs and take the compression of the shock over the vertical travel of the wheel. I do understand the compromise of control vs. grip, but the grip is largely affected by many other factors as well...

Since the wheel base on the ext'd cabs is rather long, 122", it is very stable on the drag strip. Now that I'm interested in taking this to the next level, I'm trying to acquire as much information as possible before making hard and costly decisions, since this is widely uncharted territory especially for this particular vehicle.

I guess my initial question is: should the f:r and motion ratios really affect the desired spring rate if the springs aren't even considered in these calculations? I'm trying to connect the dots and have much to learn.

Thank you for your insight.

Spring rates come later.

Since you are basically building your own suspension (modifications are very different than stock), you can treat it like more serious race guys do, rather than modifying. And it's not like trucks are engineered to handle from the factory anyways...

They design to a frequency which approximates 'effective stiffness' and work backwards to figure out the spring rates that achieve it.

The motion ratio changes the effective spring rate through leverage, so we need that to know the 'real' rate the suspension works with. I think solid axle is 1:1 so the rear is easy that way.

The other things you'll need are your racing weight (driver, fluids) and a pretty close estimate of unsprung weights for f and r.

With that I can put you in the ballpark for spring rates, and explain the philosophy and math. I'll have to find my old spreadsheet and go over my books again for solid axles... Then bars for adjusting roll and over or understeer and some other weight transfer stuff can be done with an estimate of tire grip efficiency.

Then you can take that base line to some better experts for 2nd, 3rd and 4th opinions. Whatever rates you settle on, QA1 can probably give you rebuild/revalve information to match. Or maybe you can send them in.



Your front suspension is independent upper and lower control arms (basically double wishbone), and rear is a four-link solid axle, correct? For serious suspension info on that combination, maybe older Trans-Am racing related stuff?

Lastly you can ask questions in the RCE/CSG Tag team suspension thread, as lots of principles are universal. And just read through the whole thing anyways since there is a lot of good stuff in there.

What you may find though is a conflict between older solid axle tuning advice and modern advice. I know RCE prefers a harder spring setup with more front frequency bias and less reliance on bars. Older Trans Am stuff will encourage a softer but slightly rear frequency biased spring setup with harder adjustable bars to deal with roll and tune overall over and understeer.

What RCE's philosophy seems to be is a responsive setup with predictable motions and more steady state understeer. The Trans Am way goes after maximum front and rear grip but in a vehicle that will squat and dive more aggressively. The Trans Am way can ultimately be faster for experienced drivers that are good at managing weight transfer but maximum grip and speed often feel less predictable and lots of drivers can drive faster on a 'slower' setup because it feels more predictable and gives them confidence.

[serialk11r]

It's all about getting a custom prototype active suspension yo.

Just kidding lol. People race trucks? I didn't know this was a thing. You should put a tonneau cover to reduce drag and increase rear traction

[Dimman]

Originally Posted by serialk11r

It's all about getting a custom prototype active suspension yo.

Just kidding lol. People race trucks? I didn't know this was a thing. You should put a tonneau cover to reduce drag and increase rear traction

It's an interesting challenge. Looking at how front biased the weight is, it will be tough to dial in nicely. It's going to want to overload the front tires in steady state turning and plow like a pig. But conversely being slightly imperfect on exit with limited weight on the back the rear will step out more easily. Add to it that it's a turbo motor with less throttle control/response it will probably be a handful. I don't know what the steering ratio is either, so corrections might be even harder.

[Toyarzee]

very well put, I am glad I asked now.

I can already say that I would prefer an overly stiff vehicle with a responsive feel as well. Oversteer is expected in this setup but being able to take turns at speeds where there isn't an excessive dive and squatting will help me keep the ride height lower without needing to tub the whole damn car as well.

My buddy who has been fabricating everything for me should have access to, or a means to get the truck on a scale for these measurements. The 4-link is not complete, but wanted to know what I was getting into before it begins. I guess i will need to report back later.



I just installed a 255 walbro, -8 fuel lines, new fpr, high flow fuel rail, new 1200 injectors, .70 Precision Turbo, new tial q bov, and sticking with tial 38mm wg for now. Installing haltech (have e6x, considering updating to sprint) and that buddy i spoke of finished the 3" ic charge piping, and building new manifolds from scratch. We just got in the flanges today, and will be running an 80 mm tb. 2rz is on stock compression but will be rebuilt after completion of said suspension and some transmission matters.

Long story short, fuck yes i'ma race this truck.
(and tonneau will come later, but that will probably end up being custom as well..)

[Toyarzee]

i apologize for my noob picture attachments

and steering can be redone to an extent, at least in theory stages. We shall see where this goes i suppose.