Race car suspension Class

[Savem c10]

So there two types of roll center geometry that I know of. Most common is kinetic roll center does work. But over the last year I’ve been working with jacking force geometry on and off and found it works better than a kinetic based roll center geometry. Does anyone on here know of racers using jacking force geometry and have knowledge on or know of any literature to read on it . Rm… Mender ??

 

[Ranger Mike]

By kinetic i take it you are using the automation mode on software like Performance Trends that show Roll center migration on roll and dive, right? Is the jacking force function on some other software?

 

[Savem c10]

By kinetic i take it you are using the automation mode on software like Performance Trends that show Roll center migration on roll and dive, right? Is the jacking force function on some other software?

I don’t have any computer software as of yet iv always mapped roll centers out life size on paper. I have no way of knowing migration . Based on recommended starting points for roll centers is what I’ve done. I do not know if there is a function for that type of geometry u would know better as u have the software.

 

[alpharomeofifetwo]

Tie down shock keeps weight on rt ft forever .

Finally got to run Saturday night.

Through processes of elimination, I firmly believe a shock change is due.

Shop work
Double checked all chassis mounts/measurements to make sure everything was square. Ran rear roll steer numbers and got about a 1/4” max trail in dynamic on RR
0 lead/trail on LR. Rescaled car. Stiffened up springs

Track/chassis adjustments
We stiffened up the front 200lbs each spring, stiffened LR to a 20” 125#, softened up RR to a 200, moved LR in 1”, moved RR out 1” via offsets, moved lead lower 8-10”, tightened chain on LR RR and LF, cranked cross / bite in it. Pulled a 50lbs lead chunk off the right side low. No matter the change, we still got the same results.

Race day notes
Bumped those tire air pressures up to 17-22 psi, Couldn’t get an accurate temp readout due to the infield being very wet from rain during the week. But we burnt the rr up and every other tire looked exactly the same as it went on the track, No feathering on any tire except RR. I think we had it set to 22psi and noticed it did wear significantly more across the center treads so might’ve been a tad much on air. Started the race with 1/4” of reverse stagger just to try a last ditch effort

Car had “the usual” handling; great getting in, lacking drive mid off… even with all the “positive” changes. I’m chalking this whole issue up to the shock package and shipping them off today to be redone like I mentioned in a prior post .

 

[Ranger Mike]

Right rear is worn out because it is not hooked up. Still loose off. Why? front springs too soft plus you have no arb. Good news is the car is going In ok. No traction corner off.

 

[Ranger Mike]

https://www.msn.com/en-us/sports/ot...1&cvid=523a751deaa848d0bc475e3efe569885&ei=17

one fine racer, mill be missed

 

[alpharomeofifetwo]

I’m chalking this whole issue up to the shock package and shipping them off today to be redone like I mentioned in a prior post .

Reference: https://www.physicsforums.com/threads/race-car-suspension-class.326355/page-51

Sent the shocks off to be redone and the shock expert said exactly what we were thinking. It was holding too much load for too long on the RF and not getting any back to the LR.

They made a huge difference on the track this past Saturday! Without changing much other than shocks, it handled really decent compared to before,I’m just fighting a loose entry/ RR tire hot problem still. It was loose to the point I had to run the very top high side where the banking was the steepest to keep from losing grip on the entry to mid part of the corner/ braking going straight before turning. I believe ballast placement is the next area that needs to be addressed. I have roughly 200lbs directly above the rear end center section just below the decking.

Tire temps were equal across the tread so I’ll just abbreviate the avg per wheel:
LF 110 RF 127
LR 125 RR 175

 

[Ranger Mike]

LF 110 RF 127
LR 125 RR 175


RF to lft rear temp should be with in 6 to 10°, is is 2°, not enough cross weight - LOOSE


RR to Rt Front ave temp , the rt rear should be 10° cooler, it is 48° hotter ..LOOSE


rt rear not getting enough traction, it is spinning and heating up. It needs more weight so ft springs are too soft.

 

[alpharomeofifetwo]

So how would I differentiate between the RR getting too much vs too little dynamic load? I was under the impression I was transferring too much load laterally and sliding the tire. The feathers on rr are toward the centerline of the chassis (laterally, not longitudinally)

 

[Ranger Mike]

Your tire is shredding due to lateral momentum. The tire can not provide grip due to not enough downforce on it when you get on the gas at corner exit. Read post 1519 on page 44.


Why not enough down force. The car body has finished rolling over to provide down force and traction for the right front tire on corner exit. You still do not have enough weight on the right rear tire.

Your springs reason - too weak on rt front spring rate , too stiff on rt rear spring rate. .

 

[alpharomeofifetwo]

Your tire is shredding due to lateral momentum. The tire can not provide grip due to not enough downforce on it when you get on the gas at corner exit. Read post 1519 on page 44.


Why not enough down force. The car body has finished rolling over to provide down force and traction for the right front tire on corner exit. You still do not have enough weight on the right rear tire.

Your springs reason - too weak on rt front spring rate , too stiff on rt rear spring rate. .

 

[alpharomeofifetwo]

Yeah I had a ton of RF travel (outboard mounted shocks, see motion ratio from earlier post) RF 6” LF 3”

Going to stiffen RF from 650 to 800, LF 700 to 900, RR from 200 to 175

 

[Ranger Mike]

a great start. Please only do one side at a time. Stay with right side changes and try it, take tire temps. add cross weight at the track. run it. get 6 to 10 degree Average from lF rear to right front. car is balanced.
then worry about lft frt tire. see if you improve drive off better with this setup , then we can work on super fine tuning. I suspect you will be carrying the lft ft tire like the old sprint cars and lft ft will have less temp. This is good. next we can make lft ft tire do more work. but we have to make calculated, slow changes one at a time. I like the 25# lesson rt rear idea. not major change but gradual. good job!

 

[alpharomeofifetwo]

you should see what I’m looking at on my screen… I purchased the Performance trend software and the front roll center is ugly. 2.5” high, 12” right (this is what it was from the previous race)

 

[Ranger Mike]

Front roll center offset too far to right will lift up the left side of the car. Has too much leverage. This will load the right rear tire heavily under acceleration. This will heat up the right rear tire and make you loose traction to the point that you totally loose all traction on that tire. From earlier conversations I thought you had the roll center pretty on track? Do not make major changes until you fox the frt roll center offset to 3 to 3.5 inch to right. You can change the rear spring to go a little softer but we do not know is causing rt rear tire temp to be so big? Could be roll center or springs. In any event you have to fix the ft roll center first. Then spring swap is easy.

 

[alpharomeofifetwo]

I did have it set pretty well but we’ve rescaled it and lowered the car 1/4” since. Also took my measurements without someone sitting in the car so I’m sure it’s off a tad. I’m going to take another look at in today and rerun the numbers.

 

[Ranger Mike]

Why RC location can be too offset
Let us look at a Late model asphalt Car weighing in at 2800 lbs. with 66" track width. If we calculate the unsprung weight total we have about 500 lbs. leaving 2300 sprung weight.


If we place the front Roll Center (RC) mid point we have it located 33" from the center-line of the left front tire. If we place the 2300 lbs sprung weight on the chassis we will see that half of this weight will rotate thru the RC to plant down force on the right front tire during cornering. The other half will push sideways with lateral momentum. In simple terms we have 1150 lbs. (half of 2300) acting thru a 33" (2.75 ft.) lever (2.75 x 1150 lbs. = 4,125 foot lbs. of torque.

A pound-foot (lb⋅ft), abbreviated from pound-force foot (lbf · ft), is a unit of torque representing one pound of force acting at a perpendicular distance of one foot from a pivot point. Conversely one foot pound-force (ft · lbf) is the moment about an axis that applies one pound-force at a radius of one foot.

​

If we move the RC to the right by 3", we now have 1150 lbs. times 36" (3 ft.) = 3,450-foot lbs. torque because we now have 54% of the unsprung weight rotating thru the RC to plant down force on the right front tire.

Now we find the front RC is 12" offset to the right! Our RC is located 45" (3.75ft) from the center-line of the left front tire. We have a whopping 68% (45" divided by 66" track width) of the unsprung weight rotating thru the RC to plant down force on the right front tire.

3.75 x 1150 = 4,312 foot lbs. torque. This is toque will lift the left front of the car and add down force to the right rear tire. The rt rear tire will quickly overheat and loose grip or traction. Car will be real fast for a few laps then drop off the cliff!

But wait there's more! This assumes we have 50-50% left to right side weight. What if we have 58% left side weight? These figures will be much greater.

The point of this post is to show you the importance of proper RC location as step one of any successful chassis setup.

Unsprung weight table from "Short track chassis set-up" by Duke Southard
other pic from Steve Smith- Paved Track Stock Car Racing Technology -

 

[alpharomeofifetwo]

I’m completely bamboozled at this point then. I reset RC to be dead center, up 3”.

Raced tonight and still had excessive roll and lateral load transfer. Very loose mid/off. (Turned 4th quickest and finished p4)
LF OAT+5° RF 130°
LR 130° RR 180°
Feathering laterally across tires (RR Extreme)

Even changed up my rear set up to the following after qualifying
LR 100lbs 20” RR 225 w red Longacre rubber
Static load LR 600lbs RR 225+rubber
LR 83” tire on 3” offset
RR 86” tire on 4” offset (with 1/4 spacer so 3.75”)

 

[Ranger Mike]

written 21 August 2024 above
LF 110 RF 127
LR 125 RR 175


RF to lft rear temp should be with in 6 to 10°, is is 2°, not enough cross weight - LOOSE


RR to Rt Front ave temp , the rt rear should be 10° cooler, it is 48° hotter ..LOOSE


rt rear not getting enough traction, it is spinning and heating up. It needs more weight so ft springs are too soft.


ft Springs are too soft and you need RC offset to right 3" to put down force on Rt ft tire. and you stiffened the rt rear spring!! ??????

 

[alpharomeofifetwo]

written 21 August 2024 above
LF 110 RF 127
LR 125 RR 175


RF to lft rear temp should be with in 6 to 10°, is is 2°, not enough cross weight - LOOSE


RR to Rt Front ave temp , the rt rear should be 10° cooler, it is 48° hotter ..LOOSE


rt rear not getting enough traction, it is spinning and heating up. It needs more weight so ft springs are too soft.


ft Springs are too soft and you need RC offset to right 3" to put down force on Rt ft tire. and you stiffened the rt rear spring!! ??????

We went up on the front springs
900 LF / 800 RF

Had a test session Friday night and tried a 175lbs spring on the rr and had the same results tire temp wise. I was getting 5-6” of dynamic spring compression on the RR. LR was static loaded to 600lbs and getting 700-800lbs total of dynamic load.

I just wonder if my lead is mounted too high and rolling over. Using the “crank + 5in” for CG height, I’ve got all my lead mounted above this by 6-7” (200lbs)

 

[Ranger Mike]

Look amigo, I am trying to help you but you are not taking any advice to heart. i told you back in June, rt ft needs a 1050# spring lft frt needs a 1000# spring lft WITH a sway bar (ARB) which you do not have.
Why in the hel* are your running a left front spring stiffer than the rt ft? Rt frt tire is always the hottest tire temp. Put a 1050# spring in the right front and 1000# spring in lft ft and run it AFTER you fix the RC location to 3 inch rt side offset. Still will not be right due to absence of the additional ARB with additional spring rate ( 220 #) but will get you a whole lot closer to winning.
https://www.google.com/search?clien...ate=ive&vld=cid:5a6efc51,vid:V2f-MZ2HRHQ,st:0

 

[Ranger Mike]

Happy Labor Day 2024.

How about a single piston costing you $ 65,000!
Thats $ 520,000 for 8 slugs..a little out of my racing budget!!

 

[Cape15]

This may not be the right thread for this, but does anyone have any advice on what is the best bearing setup for wide 5 hubs? I was ideally looking for ceramic ball bearings but not seeing much results and was curious if anyone on here could share or recommend something! Thank you in advance!

 

[Ranger Mike]

We ran ceramic bearings on all four corners of the Formula Car. May have been a slight advantage due to less friction but in my opinion not worth the big expense. Metal bearings are a lot more forgiving and last longer. Was a nice thought but no real lap time advantage.

Now if you are going for land speed record at Bonneville over 300 mph or racing a car over 175 mph for hours, then the ceramic bearing will make sense. Less thermal growth than steel (see table). This means the inner and outer bearing race and the ball bearing itself will GROW with temperature. So if the bearing components will grow 0.0001" in size for every 72° F increase, things will get real tight real quick. We have all seen the right front hub of round track cars getting red hot on a long green run. Nascar right front wheels are 1200° F! Brakes play a huge part of this so we have cooling hoses blowing on the brake rotors.
A number of things can alter the radial play during the fitting process. A tight shaft fit where the shaft is slightly larger than the bearing inner ring (often called an interference fit or a press fit) will stretch the inner ring so making it bigger. This reduces radial play by up to 80% of the interference fit. A similar thing occurs if the outer ring is a tight fit in the housing. A difference between the shaft and housing temperatures can also be a problem. If a bearing inner ring gets hotter than the outer ring, it will expand more and reduce radial play. This can be calculated as follows:
Chrome Steel: 0.0000125 x (inner ring temp - outer ring temp °C) x outer ring raceway diameter* in mm.
440 Stainless Steel: 0.0000103 x (inner ring temp - outer ring temp °C) x outer ring raceway diameter* in mm.
* The outer ring raceway diameter can be roughly calculated as: 0.2 x (d + 4D) where d is the bore in mm and D is the outer diameter in mm.


There can also be problems where, for example, the shaft is made of different material to the bearing and housing and expands more due to a different expansion coefficient. In such a case, a bearing with a looser radial play may be needed.


A standard radial play is usually suitable and these bearings are more readily available but, sometimes, a non-standard clearance is recommended. A tight radial play is better for low noise, greater rigidity and running accuracy if the load is purely radial. A loose radial play is preferable for high axial loads as it increases the bearing's axial load capacity. It will also better accommodate misalignment between the shaft and housing.

An 80 mm diameter "loose " bearing ( high load applications) has 0.0007" play built in. Now you can see effect of thermal growth of inner , outer races and the bearings themselves.

nominal bore	C2 (tight)	CN (normal)	C3 (loose)	C4 (looser)
Over	Incl.	Metric .001mm	Inch .0001”	Metric .001mm	Inch .0001”	Metric .001mm	Inch .0001”	Metric .001mm	Inch .0001”
_	10	0-7	0-3	2-13	1-5	8-23	3-9	14-29	6-11
10	18	0-9	0-3.5	3-18	1-7	11-25	4-10	18-33	7-13
18	24	0-10	0-4	5-20	2-8	13-28	5--11	20-36	8-14
24	30	1-11	0-4.5	5-20	2-8	13-28	5-11	23-41	9-16
30	40	1-11	0-4.5	6-20	2-8	15-33	6-13	28-46	11-18
40	50	1-11	0-4.5	6-23	2-9	18-36	7-14	30-51	12-20
50	65	1-15	0-6	8-28	3-11	23-43	9-17	38-61	15-24
65	80	1-15	0-6	10-30	4-12	25-51	10-20	46-71	18-28
80	100	1-18	0-7	12-36	5-14	30-58	12-23	53-84	21-34

Less temperature disfussion ( runs cooler ) , lighter weight per bearing.
Make sense?