CSG and RCE tag-team suspension Q&A thread! Ask us anything!

[midnight23]

My rear toe appears out now after the Cusco LCA install, I am on Tein Flex and already have an alignment scheduled on Friday but it is pulling left and right while driving and I can smell the rubber from the toe out, anyone have suggestions on a fix for now until I take it in?

TL;DR

How to fix rear toe?

Thanks in advance.

[ZDan]

Originally Posted by solidONE

Since you brought up pyrometers, are those IR meters no good for taking tire temps?

Throwing in my .02:

Problem with IR pyrometers is that they only get the temp of the surface of the tire, which cools quickly. Probe pyrometers get down into the tread a little, where the temperature stays hotter longer. IR is OK for monitoring tire temps real-time, but not so much after you've brought the car into the pits/paddock.

Regarding setting pressures according to pyrometer, unless you're at the level where you can actually measure the difference in lap times with small changes in tire pressure, I wouldn't (and don't) bother. Particularly on a car that's likely to be camber-challenged anyway. Find out what hot pressures the truly fast guys are running with the tires you are running and run that hot pressure, adding ~2psi to be conservative (higher pressures are generally going to be "better" for less than optimal suspension setups, and will make the tires last longer, and worst case won't cost you much in terms of lap time).

Also, if you do use a pyrometer, be aware that "even temps across the tread" is not the ideal, and will have you running less-than-optimal camber. Optimally set up, the insides will typically run a bit hotter, as they're supporting the car's weight more of the time, including down the straights, where speeds are highest.

Optimal temperature profile and optimal tire pressure can only really be validated with lap times. If you're like me and don't get enough track time to be able to tell the *real* lap-time difference between 36psi hot and 38psi hot, you're most likely better off just running pressures a little on the high side vs. the experienced fast guys in similar cars on the same make/model tires.

[Wepeel]

Have you ever quantified how turns of the tie rod relate to toe change (i.e. one facet = x deg of toe change)?

[CSG Mike]

Originally Posted by midnight23

My rear toe appears out now after the Cusco LCA install, I am on Tein Flex and already have an alignment scheduled on Friday but it is pulling left and right while driving and I can smell the rubber from the toe out, anyone have suggestions on a fix for now until I take it in?

TL;DR

How to fix rear toe?

Thanks in advance.

You have toe adjustment from the factory. Just minimize your driving until you get it aligned.

[CSG Mike]

Originally Posted by solidONE

Since you brought up pyrometers, are those IR meters no good for taking tire temps?

They only read surface temps. You need to know the temperature under the surface, the rubber itself.

[CSG Mike]

Originally Posted by Wepeel

Have you ever quantified how turns of the tie rod relate to toe change (i.e. one facet = x deg of toe change)?

No, I leave it to our alignment guys.

Shameless plug for West End Alignment for those of you in SoCal. If you make an appointment, DO NOT DO NOT DO NOT miss it. They do not overbook, and they are booked weeks in advance for a reason.

http://www.yelp.com/biz/west-end-alignment-gardena

[Dimman]

Originally Posted by Racecomp Engineering

I would like to do an article on suspension frequencies.

Soon.

- Andy

Originally Posted by ZDan

Regarding frequencies, for each corner, you can use:
fn = [sqrt(wheel rate/sprung mass)]/2pi
Easiest if you just use metric units: wheel rate in Newtons/meter, mass in kilograms

Wheel rate is the spring rate divided by the *square* of the motion ratio.

On my FD, one corner = ~3000lb/4 = 750 lb
Unsprung mass per corner ~50 lb.
sprung mass per corner ~750-50 = 700 lb, divide by 2.205 lb/kg = 317 kg
11kgf/mm springs, multiply by 9.81N/kgf = 108 N/mm = 108,000 N/m
motion ratio ~1.6 front, so wheel rate = 108,000 N/m / 1.6^2 = 42,188 N/m
motion ratio ~1.4 rear, wheel rate = 108,000 N/m / 1.4^2 = 55,102 N/m

fn front = sqrt(42,188N/m / 317kg)/2pi = 1.8 Hz
fn rear = sqrt(55,102N/m / 317kg)/2pi = 2.1 Hz

~2Hz is a pretty damn stiff street ride, pretty damn soft track ride, a decent-enough compromise...

The difficulty will be not terrifying people with the math...

ZDan could you do this again with a stock early WRX (strut/strut so we don't need to go hunting for motion ratios) so we can compare the difference in spring rate to frequency from different weight and motion ratios.

It may be a good start for explaining that big coil rate numbers don't automatically mean super stiff rides, depending on the car's design. ie comparing spring rates between different can be useless at times.

[eckoflyte]

Question regarding Ground Control camber plates. We know that these allow the strut to be mounted higher, in effect lowering the car without sacrificing bump travel. From a geometry point of view, what would be the difference in lowering the car using the threaded shock bodies or using the GC plates? They both allow the car to be lowered without reducing shock bump travel.

[OICU812]

I'm hoping rce and CSG mike will make a thread like this for alignments and what's safe and workable. I realize people say use what works thing is there are people far more experienced with multiple setups ie: wheels sizes, tires,etc...

[ZDan]

Originally Posted by Dimman

The difficulty will be not terrifying people with the math...

Fortunately, it isn't advanced math at all! The concepts involved are subtle, but easily understandable.

ZDan could you do this again with a stock early WRX (strut/strut so we don't need to go hunting for motion ratios)

Struts have motion ratios, it shouldn't be 1:1. On my 240Z it was ~1.14 wheel/spring. Even if the strut axis intersects the ground right in the middle of the contact patch, there is kingpin inclination angle (KAI) front and rear, and also caster up front. Even when the ratio is close to 1 it's important to get it close to right because it gets squared.

It may be a good start for explaining that big coil rate numbers don't automatically mean super stiff rides, depending on the car's design. ie comparing spring rates between different can be useless at times.

Absolutely true. Spring rate says nothing without knowing the motion ratio!

[Dimman]

Originally Posted by ZDan

Fortunately, it isn't advanced math at all! The concepts involved are subtle, but easily understandable.

Struts have motion ratios, it shouldn't be 1:1. On my 240Z it was ~1.14 wheel/spring. Even if the strut axis intersects the ground right in the middle of the contact patch, there is kingpin inclination angle (KAI) front and rear, and also caster up front. Even when the ratio is close to 1 it's important to get it close to right because it gets squared.


Absolutely true. Spring rate says nothing without knowing the motion ratio!

Any math beyond quoting some numbers they read will terrify people. Heh...

I put together a spread sheet for my own use, but my unsprung weight figures are estimates, as are the motion ratios I use. But it still gives me a better idea of how different spring rates can affect different cars.

About the struts, I've been using 1:1, what are the actual points we need to use?

[solidONE]

Originally Posted by 448hpsti

Thanks in advance:
So what's a good entry level pyrometer for the guy jot newvto cars but new to stuff like tire temp monitoring

... I know my IR temp gun is crap when it comes to tires, we don't want surface temp ...

Check this one out: http://www.soloperformance.com/Joes-...FUfZQgodFzoAfA Joe's Racing is a pretty highly regarded brand. Little cheaper than the Longacre dual function unit, but should work just as well.

Originally Posted by ZDan

Throwing in my .02:

Problem with IR pyrometers is that they only get the temp of the surface of the tire, which cools quickly. Probe pyrometers get down into the tread a little, where the temperature stays hotter longer. IR is OK for monitoring tire temps real-time, but not so much after you've brought the car into the pits/paddock.

Regarding setting pressures according to pyrometer, unless you're at the level where you can actually measure the difference in lap times with small changes in tire pressure, I wouldn't (and don't) bother. Particularly on a car that's likely to be camber-challenged anyway. Find out what hot pressures the truly fast guys are running with the tires you are running and run that hot pressure, adding ~2psi to be conservative (higher pressures are generally going to be "better" for less than optimal suspension setups, and will make the tires last longer, and worst case won't cost you much in terms of lap time).

Also, if you do use a pyrometer, be aware that "even temps across the tread" is not the ideal, and will have you running less-than-optimal camber. Optimally set up, the insides will typically run a bit hotter, as they're supporting the car's weight more of the time, including down the straights, where speeds are highest.

Optimal temperature profile and optimal tire pressure can only really be validated with lap times. If you're like me and don't get enough track time to be able to tell the *real* lap-time difference between 36psi hot and 38psi hot, you're most likely better off just running pressures a little on the high side vs. the experienced fast guys in similar cars on the same make/model tires.

Any hard numbers in terms of temp differential between the inside, center and outer portions of the tires tread? What would be ideal when trying to determining camber?

[ZDan]

Originally Posted by Dimman

I put together a spread sheet for my own use, but my unsprung weight figures are estimates, as are the motion ratios I use. But it still gives me a better idea of how different spring rates can affect different cars.
About the struts, I've been using 1:1, what are the actual points we need to use?

I don't know, quick search didn't yield anything concrete, either. You might just assume 0.9:1 for the front struts, should be a much better estimate than 1:1. 1:1 says a 500 lb/in spring gives a 500 lb/in wheel rate, 0.9:1 => 500*0.9^2 = 405 lb/in wheel rate, so it makes a big difference.

[ZDan]

Originally Posted by solidONE

Any hard numbers in terms of temp differential between the inside, center and outer portions of the tires tread? What would be ideal when trying to determining camber?

There are no hard numbers on optimal tread temperature profile, it's going to depend heavily on the car and the setup. ~15F hotter on the inside than the outside *might* be an OK rule of thumb.