Been thinking again about suspensions

Basically what I was thinking about was tall front uprights for camber control. Basically the taller the upright the less the suspension arms change the camber of the wheel because the side to side motion induced by the arms rotates the upright in the camber plane in inverse proportion to the distance between the ball joints.


Camber – The angle between the tire and the road surface. Positive is the top of the tire tilted away from the center of the car, negative tilts toward the center of the car. This is backwards because positive camber is almost universally bad for tire grip and is therefore a negative, but the terms were defined prior to the invention of the pneumatic tire and now we are stuck with them.

Kingpin inclination – Another term that is archaic because kingpins are from solid axles except for a very tiny number of early independent front suspensions. It refers to the angle of the axis of steering rotation for front wheels between the upper and lower ball joints.

Scrub radius – The distance between the intersection of the steering axis with the ground and the center of the wheel. Basically this is the moment arm of the force generated by the brakes through the steering system. The greater the absolute value of this number the larger the force felt at the steering wheel under braking. The direction of this force depends on the positive or negative value of the radius. If positive the steering wheel will turn in the direction of the greatest braking force, and opposite if negative. Now there are schools of thought that if the system is designed to turn away from the stronger braking force it will be self-correcting in the case of brake failure. There are other schools of thought that drivers will instinctively turn away from forces trying to steer the car so positive scrub radius is better, with the debate coming down to do you want your driver to be an active part of the car.

Upright height – The distance between the upper and lower ball joints of an independent front suspension

This is a hypothetical discussion because the front suspension for the Sprint-T has been frozen as a straight axle, and because my fabrication tools are not up to building suspension uprights. So theory only. No labs for this lesson (shoutout to my teacher friends who “get” this joke). Theory for this starts with the statement from the opening paragraph camber change is inversely proportional to the distance between the ball joints. Second is that the position of the bottom joint is constrained by the dimensions of the wheel used, because kingpin inclination and reducing scrub radius dictate the location somewhere inside the wheel. Excessive positive scrub radius has been proven bad experimentally by excessively increasing the force required to steer under braking.

And it just dawned on me this post needs a glossary to keep track of all the technical terms. We already have camber, kingpin inclination, and scrub radius besides upright height. Basically I’m assuming my reader has a working knowledge of terms used in suspension design, which is probably not the case. So I’m inserting one following the first paragraph. It’s there now but wasn’t before I started this paragraph.

Anywho, the design parameters basically dictate the lower ball joint be as far inside the wheel as possible constricted by the brake disk because of scrub radius minimization. It doesn’t matter if you want positive or negative scrub radius, you still want it to be small or variations in braking force caused by changes in road surface can tear the steering wheel out of the driver’s hands which is bad no matter how you look at it.

Also, the amount of camber change caused by body roll is proportional to the ratio of the distance between pivot points on the frame and the distance between the pivot points on the upright. Desirable geometry of defining the instant center dictate this is going to be close to unity and usually less than 1:1. There are some old GM cars that had this greater than 1:1 and they understeered excessively with the outside front wheel riding on the sidewall of the tire. Look for images of the late ’60s Chevelles making hard turns and you can see this in action, but not many of those pictures made it to the internet and the only ones I have are in paper books on suspension and my cell phone camera did not get a good picture of the picture. One of the things about having the ratio between the distance of the suspension pivots greater than unity is the front roll center is underground, which causes the body to roll excessively and further causes the car to ride on the sidewall of the outside front tire. This meant that racers using this car as a base for stock cars had to crank in ridiculous amounts of static camber and excessive amounts of roll stiffness to keep the car driving on the tire treads instead of the sidewalls. They made it work but it would have been easier if the front suspension was designed right in the first place.

Getting back on track for this essay without any more digression (squirrel!), we want to basically define a height range for the front upright. Too tall and either we get “funny” geometry in the suspension or we get the pivots for the upper suspension arm somewhere in the boonies, which technically is “funny” geometry. Too short and we get poorly controlled camber as the car goes through bump and/or roll. My personal take is I design about the same as the inside diameter of the front wheel as my max, and about 8″ as my minimum except for suspension karts. No matter what you do those are “funny” because no room.

And I seem to have lost the point of this post except that I woke up in the middle of the night thinking about front suspension uprights. So since we hit over 1000 words this seems like a good place to stop and hope I get my train of thought back on the rails for a future post.

Still thinking, remain in cover until the all clear has been given

I’m still reading my new book about suspension geometry and contemplating the information, but it hasn’t resulted in any changes to the Sprint-T. The front is still a tube with fore and aft location by parallel 4-bar and laterally by a bent Panhard rod to clear frame members, rear is still fore and aft by dual trailing links and laterally by a Watt’s link and a torque arm for control of reaction torque from the engine. And torque reaction links for the brakes. All rotational reaction forces are isolated from the suspension to prevent locking up the suspension from either engine torque or brake torque, allowing the suspension to move freely at all times. The front springs are mounted as close to the ends of the axle as will clear moving parts, and the rear springs are mounted to the trailing links originally designed for swingarm suspensions of much heavier vehicles on rough tracks. This allows easier tuning of suspension stiffness by changing the motion ratio for the springs as there is quite a bit of motion ratio to play with.

To clarify that, the bottom of the spring mount moves less than the wheel in both single wheel and double wheel bumps. This means I can get smaller changes in wheel rate than steps in spring rate which gives me finer control over wheel rate. Also the total travel of the shock is less than the travel of the wheel which reduces the amount of force per inch of wheel travel. There is a formula that gives us the effective wheel rate when the spring rate is known (mr2*Spring Rate) or the square of the motion ratio times the spring rate. On the rear suspension for the Sprint-T there are two motion ratios, the motion ratio for a single-wheel bump or body roll and the motion ratio for a two-wheel bump which is just the motion ratio of the swingarm. The single wheel bump is the swingarm ratio times (the distance from the far wheel to where the swing arm attaches to the axle housing divided by the track).

OK engineering problem here

I have been thinking about the front suspension of the Sprint-T, specifically how to get anti-dive without getting bump steer. Since this is a solid axle technically I could just change the angles on the links of the 4-bar same as if it was a rear axle trying to get anti-squat, except that moves the axle differently back and forth and changes how the wheels point depending on how hard the brakes are pushed. And since the wheels don’t change camber with bump there’s really no reason to have anti-dive in the front suspension, except to not have the front suspension travel under braking.

And really I don’t have any reason to do that, there’s nothing close to the ground up front that might hit under heavy braking. The only thing even close is the front lip of the nose, and it is about 6″ off the ground at ride height, and not very far from the front tires. The actual position is even with the fairing in the front fenders or about 5″ from the front edge of the tire, or about 18½” from the center of the front axle. To get the lip to hit would take both tires being about half flat and extremely heavy braking enough to use all the travel available in the front suspension. So really there’s no reason beyond only having a little bit of travel left in the front suspension. So, it is an intellectual exercise that won’t be used on the Sprint -T and has only served to keep my mind occupied so it doesn’t wander off and leave me without a mind. Because that would be bad.

Again I feel compelled to write but don’t have anything to write about

I have to write something again but (again) I don’t have anything new I can write about. I have a subject but (still) can’t write about it in this blog. I wrote about the Shadowrun game already, that’s covered. I wrote about the LS engine I lust after, and the transmission to go with it. I wrote recently about how much I miss riding since my hip started having problems so I can’t get on the bike anymore.

That remains the same, I still miss riding. I miss having my heart pound after a climb and the thrill of a fast downhill. I miss getting to choose when I leave the house because I can get home whenever I want to. My miserly side misses being able to go across town for no more than the cost of a Gatorade or a candybar. And I miss getting cardio everyday while I got around.

Getting around now is exhausting because walking is so hard with my hips getting bad. I spend all my energy just trying to stay upright even just walking across the room. My glutes hurt all the time now, and I don’t know what to do about them. I really need to get a massage and get the tired out of them.

Simple game for me

We had a fun game today, I wasn’t very busy but everybody had a chance to do something. I used my new rigger skills to pilot us out of danger, our technomage did matrix combat to thwart people trying to track us, our other street samurai shot the helicopter that was following us and disabled the rotor controls and made it crash, our mage made us invisible and levitated our van over a roadblock. Our other mage used a summoned spirit to wreak havoc on their shooters who couldn’t shoot at us, and the Faraday cage in my garage isolated our quarry from all electronic signals when we got home. The one mage that was the reason why we had to make this run had to change residence and temporarily move into my basement because Mitsuhama wants access to her research but doesn’t want to pay for it.

Anywho, we have the guy isolated while we question him and find out how much he told the corp about our mage he recognized on our previous run. And the one mage moving into my basement is probably getting an upgrade because the basement in my compound is pretty plush in game. It’s not as nice as my house because it’s emergency housing for trolls and orcs during a disaster, but it’s still pretty nice in that it is sometimes hard to get the trolls and orcs to leave and go home when the disaster they had to evacuate their homes for is over. And that is canon in game.

Allergies are kicking everyone’s butts here

I’m up way early because I ended up going to bed at 1930 and waking up about 0200 ±. Mrs. the Poet is also having an allergy attack that made her face swell until she couldn’t see past her swollen cheeks and it was painful to her eyes. That’s why I was so off on going to bed, I had to stay up to get her to the doctor, then I took a nap from 1200 to about 1600 to go grocery shopping, then fell asleep during the Cup race last night. I managed to last until the end of the first stage, but was too zonked to last any longer so I went to bed early, or late depending on your time orientation. My normal “day” I get to bed about 0600 and get up about 1200-1400 depending on if I have anything to do that day that requires getting up before noon.

And I was looking at the dyno charts for the various engines that can be built from that 4.2″ bore LS block and I think the best one for the Sprint-T is the 4.2″ bore with the 4″ stroke. Compared with the 3.26″ stroke engine with the same cam the difference in torque below 5000 RPM where the Sprint-T will spend most of a lap around an autocross course is enormous. Which proves the adage “There’s no replacement for displacement”. And with a good flowing head I can spin up past 6500 RPM without losing power. So when I’m bucks up I’m making the 443 cubic inch LS with the LS7 heads that maybe are ported to breathe at 7K RPM.

In a few hours we play Shadowrun again if the GM has replenished his supply of medications that allow him to function, but we won’t know until time to play.

And speaking of “functioning” I need to take another nap.

Got a new book

I bought Advanced Race Car Chassis Technology HP1562 for the Kindle a few weeks ago and I’ve been absorbing it a little at a time. It’s a complex subject, but from what I’ve been able to read so far, if I get it right I don’t need to make the frame all that torsionally rigid. If I’m reading this right there’s no twisting load on the frame if I have the suspension geometry right and tuned the spring rates. If my sums are close there will be about 300 pounds ± on the springs of the front corners, and about 350 ± on each rear. That’s not a good sprung/unsprung ratio, but that’s what I’m stuck with.

The front axle weighs about 65 pounds plus the hubs and brakes, because it’s a honkin’ huge chunk of iron steel with tons of thick brackets welded to it, and the spindles are likewise big chunks of forged steel. The rear axle is right at 100 with the diff and and axles (drive) but without the hubs and brakes, which are almost the same weight for both ends. The rears are a touch lighter than the fronts because the rear disks are 11.75″ and the fronts are 12.19″. All of that is unsprung (bad) weight, axles, drive axles, hubs, brakes, the whole shootin’ match all bad weight. Well none of it is good but unsprung weight is super bad compared to sprung weight. Like excess unsprung weight causes tires to lose contact with the ground over a bumpy road even if the bumps aren’t that big, bad. And a lightweight car makes unsprung weight even worse because sprung weight pushes the unsprung into the road and not having enough sprung weight means the unsprung weight is just kinda floating out in space. It only contacts the ground intermittently because the two weights, sprung and unsprung, are just oscillating independently. I’m getting close to that condition with the front of the Sprint-T. If I understand the theory right the only thing you can do with a car that has sprung:unsprung ratio approaching unity is make the dampers stiffer to prevent oscillation from setting in, assuming there’s nothing to do to make the unsprung weight less. Right now the only option I have is to use “drillium” in the front axle, that is to remove weight by drilling the front axle full of holes. Since this axle was designed for a car almost twice as heavy as the Sprint-T this is actually an option.

As far as the geometries of both ends are concerned, the front end will not have any adjustability beyond caster and toe, the roll center height will be fixed to prevent the front axle moving under load and changing the steering angle. But the rear axle will be located by a Watt’s link with the pivot located by a nut on a threaded bolt that adjusts up and down to change the balance of the car for different conditions, like understeering for highway travel, neutral for road courses, and slightly oversteering for autocross. That can be done by turning the bolt to move the rear roll center up and down.

Oh, here’s the link to the build video for the GenIII Hemi™ giveaway. Lotsa power and torque from a nearly 600 pound engine.

Still thinking, take cover

I’m one of those people that is always thinking about something, like what I will do if I don’t win the GenIII Hemi™ being given away by POWERNATION. Obviously I get what’s cheap from a junkyard unless I win the lottery. At this point GenIII and GenIV LS engines are the cheap alternative for making reliable power from the junkyard.

I have to also go for the possibility I won’t need to install an automatic transmission. The main reason I can’t go with a manual is lack of space in the footbox for a clutch pedal, but if I get a transmission that can be shifted without using a clutch except for starting I can use a hand clutch for starting out, and use the “clutchless” shifting to change gears. I mostly will race in first gear so once I leave the starting line I’m good and never have to use the clutch until I cross the finish. Driving on the highway is different because I will have to get to top gear somehow, and if I have a regular transmission I will have to use both hands to shift and let go of the steering wheel. This is ungood for obvious reasons, but if I can just lift throttle for a bit and slam the shifter into the next gear until I get to cruise speed I’m good. I just need to get a transmission that I can shift without using the clutch. Also manual transmissions are lighter than automatics in almost every case, the T-10 with an aluminum case coming in at just 70 pounds wet compared to the 4l60e at 176. That doesn’t include the flywheel and clutch for the manual, but it also doesn’t include the flex plate and roughly 50 pound torque converter for the automatic. And I can use a lightweight “button” clutch on a flex place instead of the torque convertor to save a few pound over the flywheel/clutch, saving a few pounds of rotating weight. That adds a lot of cost though.

That T-10 can be purchased with an overdrive gear in the 3rd position retaining the 1:1 4th. This results in a strange shift pattern that has the top gear above third, but that can be adapted to with seat time. The jump from 1st to 2nd will have to be figured out, but if I gear 1st to top out at 40 MPH, for street and highway I can skip shift from 1st to OD 3rd or 4th. I was just now looking and if I flop the 3-4 shift lever it will swap the 3rd and 4th gears in the shift pattern. This requires a bit of cutting and welding on the shift arm, but well within my skills as a metal fabricator.

Looking at the costs of bellhousings and other support equipment to install a T-10 to an LS compared to the price for a 4l60, that’s a ton of $ to save 50 or so pounds, but I’ll have to keep it in mind as an option. Basically the flywheel, clutch and bellhousing to bolt a T-10 to an LS are more than a performance remanufactured 4l60e, and that’s not including the cost of the T-10.

But if I get the money to do it that is the way I would go. I would get that 4.2″ bore LS block and a 3.26″ stroke crankshaft from a 4.8 liter truck engine, and a set of LS7 heads and the stuff to make it run, and have a 361 cubic inch engine that keeps breathing past 7000 RPM, fit it with the T10 and the OD 3rd cog and the swapped 3-4 shifting arm, and then have a 1700 pound car on the starting line with an easy 500 HP, that cruises at a low RPM to get good gas mileage and range. Obviously that is going to require I win the Powerball or Lotto, and I may have burned most of my luck out just surviving the wreck, but I have to think winning is a possibility, or why continue with the build?

Been a while, but stuff has happened

First things first, we tried to play Shadowrun on Sunday but health issues came up for a couple of our players. One is recovering from C-19 and got tired really quick, and the other ran out of brain meds because insurance and was not managing to think straight, so we quit early because tired and not thinking straight makes the game not fun for everybody. We did get my character sheet fixed before then and basically I’m a street samurai with a minor in rigging, level 6 pilot ground car. That makes me level 6 guns, blades, and ground vehicles which if I understand the rules is as high as I can go in all of those.

Other things, I’m still plugging away at that engine giveaway. The build video has been released and the engine pulls to 7000 RPM and makes over 500 HP and also good low-end torque, so aside from weighing close to 600 pounds would be really good for the Sprint-T. Also POWERNATION has announced the winner of the 5 liter Ford giveaway and it wasn’t me >sigh<.

Now I was doing some research and the biggest bore available with an aluminum LS block is 4.2", which combines with the OEM cranks of 3.26", 3.622", and 4", results in displacements of 361, 401, and 443 cubic inches respectively, and they would all weigh about 415-420 pounds depending on the FEAD I pick. Now that 4.2" bore block runs about $6k bare but fully machined, so unless I win the lottery this one is an exercise in possibilities, not realities. I could walk to the local C-store (just barely) and get a ticket today for tonight's drawing, making this something that could happen IRL for me. But it's dark now so I have to wait for sunrise to leave so the C-store will be open. The good thing is we are post a cold front passing through so it's not ghastly hot today. Today's Powerball is $388 million for a $2 ticket and the Lotto is $15.25 million for a $1 ticket. I just have to wait until sunrise…

Another case of needing to write but not having anything to say

I have this compulsion to sit down and write something at least every two or three days. Even when I don’t have anything in particular to say, I still have to write. The compare-contrast to the Harlan Ellison short story continues.

One thing I’m steamed about is I now live in a state that has made abortion illegal. I’m trying to think of anything that happens only to men that can be similarly restricted and beyond prostate issues I’m drawing a huge blank. The problem with prostate issues is they can be ignored for decades with no risk to the man, unlike a problem pregnancy which has a built-in time limit. I can’t think of anything that potentially threatens a man’s life or livelyhood like pregnancy but has a time limit to treat like pregnancy and only affects males or AMAB. I suspect that the men who voted for this are not getting any from their wives and have to either pay for it or do without. The poet in me wants to deny those who voted for this law or signed it into law access to all medical care, permanently. This is denying women medical care by law, so they shouldn’t get any medical care either.

Other than that I don’t have anything of importance to relay here. Still trying to win an engine from POWERBLOCK, a 6.4l GenIII Hemi™ this time and you can help by clicking the link. The best native automatic transmission (one that can be installed without an adapter or modification) looks like the NAG1 5 speed automatic. It has a 3.59 first gear which combined with the 0.83 overdrive gives a 1772 RPM cruise at 60 MPH with the street tires and race gears in the rear end. That means I have to tune 1700 through 2200 RPM really lean for good highway mileage. The ECM they’re using has tune by gear so we can restrict the lean tune to 1700-2200 in fifth. Also the NAG is much lighter than any native transmission and also somewhat lighter than any other transmission that can adapt to the GenIII Hemi™. In another week I’ll be able to link the build video to a post so everybody can see what I’m gunning for. The build sheet looked pretty good.