Forum: HoseHeads Sprint Car General Forum (go)
Moderators: dirtonly  /  dmantx  /  hosehead

anyone have any designs for a torsion bar tester? any info would be helpful

Cheapest way is to make a torsion tube fixture table and just put a scale under the end of the your torsion arm and jack weight into your stop and record how much weigh it puts on the scale. You can baseline bars pretty good that way.

You might also want to try to find a used Intercomp coil sprint tester (eBay) and use it with the same type of torsion tube fixture set up and jack up with the spring tester instead to record the weight and compression as if you were testing a coil spring. Plus then you could also test coil springs with it if you needed to.

Intercomp also makes a purpose built torsion bar test but it is three grand. You might be able to find a used one of them somewhere. Roehrig and Maxwell also make them but they are thousands of dollars.

I was wondering how to make a cheap one also. At work we have tiny devices called load cells.

You could probably find one on ebay. I really don't know what "lbs" you would need. But the devices are little blocks, maybe 2" X 1" X 1" in size with a couple of wires that go to a meter to read the lbs pushed on them.

1) I would place the load cell under the stop/bolt where you twist wt into the sprint car.

2) Next get a big degree wheel, like one about 2 ft in diameter and place it where the torsion bar arm

connects to the axel. You would probably have to remove the axel...lol!

3) Figure out a way to pull on the attach point, torsion bar arm to axel for a certain amount of degrees,

then read the load cell reading in lbs.

a) Pull the control arm in the opposite direction, using the big degree wheel as a guide and pull

it the exact same amount of degrees in the opposite direction and read the load cell/lbs.

b) The two load cell reading should not vary by 10%. If they do you have a bad torsion bar arm.

Sincerely,

Larry Otani.

P.S. I figure you could jury rig a setup for about 100 dollars.

doesnt a bar tester record the bars exact static load , as to, where the bar originally started its twist and how quickley It returns to that form ? thus the charicter of the bar? I belive a back yard mechanic (such as many of us) could rig something up to tell if a bar is starting to go, if testing frequently , thanks for the input, I often wondered the same thing. but, theres got to be a reason these testers are worth so much ?

i am no expert but steve watt from maxwell explained to me that when he tests a bar on his machine he can compute the total spring rate of the entire system, not just the bar. he related that when a bar is checked with the correct arm and stop that it is going to be in stalled in the car with, the actual deflection of the arm, stop and the bending of the bar as it twists all add up to provide the spring rate. also as stated above, the rate that the bar rebounds back to its static state is measured as well.

to indy and beyond!!

Interesting post! I think "Buzz" hit the nail on the head. The bar's ability to rebound, is probably more important than the actual spring rate. In fact some bars can pass the spring rate test, but will flunk the rebound test. Lazy bars are just as bad as a bar that has lost it's spring rate.

I also disagree with the comment about using a load cell under the torsion bar stop. The load cell might work, but the measuring needs to happen on the arm end of the bar, not under the stop.

Another rant; It's amazing how many race teams take out loans to purchase fancy enclosed trailers, yet their bars and shocks are crap! I'm confused...

expert or not ,its usefull information,

the way I look at it is, a bar is only as good as a car it is going in , there is so many other variables , call me crazy, ive got two "old" bars I have used in my RR as compaired to the "new" bar of the same dimension, the two "old" ones are softer and read lightly inbetween the next step down , needless to say, we always resort back to old trusty, and the "new" one lays in the trailer more often than not, keep in mind we dont run alot of nights (time) on our equipment in one season up here, Most importantly is to catch a bar acting funny before it catches you , Wilfred Brimley would say "check it often" or eat more oats r something like that ?

Excellent information on bars whether you test them yourself, build your own tester or send them out.

It's always fun to be a bench racer and I think that is what these message boards are all about.

The point about Fancy trailers has always intriqued me. Some people would rather buy a new car rather than go get a medical checkup or go fix their teeth/see a dentist.

Some people would rather be with a beautiful babe even though she may not have nickel sense..

So in essense, I think some people buy fancy trailers because it make them feel good or important

and not buy those new bars even though it would be a smarter choice.

Vanity is something women spend millions on and if you have the money to go racing some don't care if you win or loose. They just want to be seen with people who look rich/good...lol!

Larry Otani

Thanks for all the great info...I think i'll make a jig to hold the bar with a scale under the arm at the load point...thanks again to all

With regular torsion bar checkers a lot of people preload the bars two degrees, re-zero, and then wrap up another five degrees and record the torque.

After you build yours you might want to figure out how many turns it takes to twist the bar both two and five degrees with a smart level as well, and then follow the same procedure to keep yourself somewhat standard...preload two degrees-rezero-twist five more degrees-record.

You'll be reading pounds on the scale instead of torque, but you'll at least be able to do the math backwords (dependent on arm length) to calculate the spring rate in both torque/degrees and pounds/inch if you wanted to.

Only difference with yours, arm flex will be added in as well because you're checking it with the arm, plus any flex you have in your torsion tube fixture table will also soften the rate...it should be pretty sturdy.

Good luck.

I can't help but comment on all this very good information>

I really like the information on how fast the bar reacts/a slow moving bar.

But something is coming into  voque here or hinted about. I have noticed when you try to tweak bars or dial in wt into your bars a lot of things are happening or not happening.

1) How much slop is in those plastic cups that go around and in the ends of the torsion bar tubes?

2) How much slop or twist is in your frame/front end of the chassis/as you twist in wt are you really seeing anything at the wheels or opposite diagonal wheel your are trying to affect/load up with the turning of the screws?

     a) If you are lucky you have a brand new chassis or one that is really rigid, but if you don't

         you might want to add in a new diagonal tube to the chassis  with the heims joints at

         each end that you can twist to make the chassis a little stiffer so when you dial in wt

         you actually see some at the wheels.

These posts are really educational and yeah, if you have torsion bar arms that bend and are not very rigid you also loose some of the twist you are trying to dial into your chassis.

Larryoracing,

I agree with most of your statements, but I want to encourage everyone to keep things in perspective. Sure chassis flex, arm flex, etc. can/will affect overall bar rate, but lets not "kid" ourselves, those variables will have little affect on our overal performance. None of us are that good at what we do.

The point I'm trying to make, is we need to keep things simple, especially at the grassroots level. Is the bar good or is the bar bad, should replace, "the deflection of the left front torsion bar arm reduces the spring rate of the bar by .0255 pounds". Give me a freaking break! lol

Building a tester might be kind of fun, but I would recommend paying your local speedshop 5 dollars per bar and have them tested at the beginning and middle of each season, and again immediately following any kind of a crash; more frequently if you race more than two nights a week.

If your bars are good, forget all that other crap; clean em, grease em, and race em. If their bad, replace them, but don't make things complicated.

If your not on a budget, buy new bars every ten shows and sell your used ones to the guys who are trying to measure their's with the wife's bathroom scale!

Keep it simple...stupid!

pitnote, I think you nailed the idea right on the head, honestly we just kept making changes until we seen a driveable improvement, now, we know our baseline , remember, the driver HAS to feel the change in order to perfect it , chassis flex,arm deflection ect proubly can play a part but not the major differance most will notice , One thing stated earlier about the bushings is, I preferr the bronze type as compaired to the plastic, anyone care to differ? when confused, I try to resort to the most important information. K-I-S-S!

LOL! All very good points.

1) One of the things I have noticed about all my friends is they love to talk about racing. How many hours do you guys spend talking to all your buddies about all this stuff. To me that is a lot of fun, very amusing and  very complicated. So if you can keep it simple, by all means that is the fastest way to successs, right?

2) Another thing that amazes me is how much money my friends spend on all this crap.

3) Yep, my friends have bought shock dynos. Yes, they have bought torsion bar dynos and yes

they love to debate and talk about all the technical as well as practical ways to set up a race car

through all their years of experience. As a rookie in this sport I love bringing up a question and if I'm lucky they will be stumped in their tracks and stop to think about an idea or two. That is a lot of fun to try to question somebody authority or knowledge about a setup, a theory or a change they wish to make in a car. That is a lot of fun and is called bench racing and that is what we do when we are not at the track.Every once in a while they will steal an idea I have dream't up. Now that is the most rewarding of all...lol!

Personally the bushings that have always intriqued me are the BK ones that are needle bearings. Those seems to have  some merit.

And it has been fun and thanks for all the ideas. It makes us better racers.

Sincerely,

Larry Otani

My Dad and I made one with load cells that works well. Had to build a pretty beefy frame for it cause initial design flexed way too much. Prob cost us about 600-700 bucks for material load cells and everything