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Teching Ride Heights


NickHolt

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Ride Heights - What's the best way to check 'em in tech?

 

When I was at SAS, we went to the trouble to construct two level spots in the asphalt on the flat just past the turn four pit entrance. As the cars lined up for their races, at least two of us would put the wheels under the cars. If too low, they were sent to the pits. If OK, they lined up for the start.

 

This worked OK until one day I discovered a couple of balsa wood (or something like balsa wood) spring spacers at the edge of turn one. Hmmmm... So much for pre-teching for ride height.

 

Part of the high cost of shocks these days has to do with engineering shocks with enough static compression to hold the car up for tech and not so much rebound that the car is prevented from returning to "legal ride height" after the race (maybe with a little "lift" provided by team members as the car is pushed around to tech). That's because many of today's cars basically run on shock shims or chassis bump stops and not the suspension springs - a good example are cars running what's known as the Big Bar/soft spring setup which is commonly used in classes where body rules allow teams to generate aero downforce through the turns. These cars typically use low front and side air dams to create a partial vacuum under the car to provide the needed downforce through the turns. Of course, the lowered Center of Gravity height through the turns is a big plus too.

 

So, you'll hear arguments from many of these BB/ss teams asking for "pre-race height checks." They usually argue that the car could "settle" during the race and it would be unfair to DQ a car that "settles." Yeah, right... They want it pre-checked so they can be on the ground during the race without having to worry about post-race height checks.

 

From the suspension engineering point of view, the lower the Center of Gravity height, the more cornering force you can obtain from a car because less weight is being transfered from the left side to the right side in the turn at a given G-force if all else is equal. So, in other words, the low CG car can go faster through the turns than a car with a higher CG. This is algebra 101 since weight transfered equals CG times the total weight of the car times the G-force being generated, all divided by the track width of the car. The car with the lower CQ will transfer less weight than a car with a higher CG. Period. Of course, there is more to it than that, roll centers, moment arms, etc., but the basic weight transfer formula still applies.

 

Soooo..... with the above in mind, what would be the best way to tech ride heights? Let the dicussion begin.

 

NOTE: This is not intended to be a bitch session, but rather a discussion that may produce some valuable results for those tracks that are interested in such things. Be warned ahead of time - complaints and recounting of sorrowful tales of being DQ'd unjustly, etc. will be removed.

 

Nick

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We've been doing Jacks ride height check, after the race for 10 years now. Thank god my bro is so on top of things because two weeks ago we checked ride height after the car being loose in practice. Come to find out we had a leaf spring going soft. We had to raise the car for that night to make sure we would pass.

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Oh, I see keyboards smoking already.

 

LMAO @ Kathy :lol::lol: ....and Nick's finger poised on the delete button...

 

Since I'm no longer a weekly racer, my opinion is just that.....

 

.....but if the "intent" of the rule is to keep frame/chassis heights at a set point, or fixed body panels at a specific height, then that's what it should be. If you have a bolt, or broken/damaged panel hanging lower, that's certainly no performance advantage, and provisions could be made at the discretion of the tech man....That however, leaves things open for interpretation and the tech man open to calls of favoritism. If a precident were to be set for any non-performance enhancing infraction, it should be the same for all. Taking a few seconds to look for a bolt or broken body bracket is easily done...I would think.

 

Now that being said, I've clearly seen many SLM's, Mods, Trucks and even some local LM's at SAS pulling the body up pre and post race tech.....do other classes do it too? Not sure, usually not able to see the tech area until after the last races. At SAS you could easily watch from the media booth or grandstands or pre-race at the tech pad.

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At THR, there is a line on the floor where your bumper must be during the ride height check. I believe the line is there because Jack has found that area of the floor to be level (or close at least.) Jack then rolls his tool under the car at several random points starting just in front of the LR tire and working his way clockwise around the car (nose included) until he reaches the area just in front of the RR tire. That's how it's done at THR.

 

Now for a little history - years ago, Jack used to get down on his hands and knees and push a height checker (fancy term) under the frame rails to check ride height. As the story goes, somebody made fun of the tech man having to get on his hands and knees to check ride height. After that, Jack built the current tools he uses, which are basically aluminum wheels with handles attached long enough to allow him to roll the car standing up. When he started using these tools, he told all of us that he would no longer get down on his hands and knees to see what, if anything, the wheel was hitting. If it hit, you were disqualified. The only exception he ever agreed to was the exhaust. I know, I know, that would require looking to verify, but thank goodness for that because most of the exhausts won't clear the rule. On our car, the wheel doesn't go under the car far enough to reach the exhaust, so it's never been an issue as far as the headers are concerned.

 

Thanks to the driving abilities of my younger brother, I've spent a lot of time in the tech garage during these inspections. I've seen multiple cars disqualified during ride height check for objects other than the frame being below the height limit.

 

Now here is my question, and I've wondered this many times but never asked Jack. Why have a ride height rule at all? I've never been a tech man and don't want the thankless job, but some folks on here (hint Nick) have done it before. Why do we really need a ride height rule anyway?

 

We've been doing Jacks ride height check, after the race for 10 years now. Thank god my bro is so on top of things because two weeks ago we checked ride height after the car being loose in practice. Come to find out we had a leaf spring going soft. We had to raise the car for that night to make sure we would pass.

 

Now the cat's out of the bag. :D At a wedding last weekend, Matt Banker told me that he wondered why we rolled over the scales so many times. I never told him that we were fighting a ride height issue during the weekend he was talking about. We werent' really concerned about the scales - just the height wheel! :lol:

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Now here is my question, and I've wondered this many times but never asked Jack. Why have a ride height rule at all? I've never been a tech man and don't want the thankless job, but some folks on here (hint Nick) have done it before. Why do we really need a ride height rule anyway?

 

I really don't think a ride height rule is particularly needed in any top racing division that uses an aero setup. These cars (and trucks) are designed to run with the nose on the ground and the tail in the air to take advantage of the downforce the body design generates when air is kept from entering under the car or truck.

 

Why make the teams in these division go through four inches of suspension travel four times a lap?

 

You've probably noticed that most of the BB/ss cars "twitch" going into a turn and exiting a turn. That's partly due to the abrupt suspension geometry changes that the chassis must endure on decelleration and acceleration. If there were no ride height rules for those classes, they could design their chassis to run on the stops all the way around the track with the geometry set for the turn they feel is critical. If developed properly and if the track is fast enough to generate enough downforce, they could actually remove the shocks and springs and have a rather large go kart with no suspension travel whatsoever.

 

However, on classes which do not have the aero bodies, the BB/ss setup is not quite as effective since air flows much more freely under these cars preventing high levels of aero downforce. Since the aero advantage is less dramatic, the real advantage would be in lowering the CG in these classes. Lowering the chassis to gain a CG advantage involves a lot of engineering (if done properly) and is beyond the means of most people competing in these racing divisions. By having and enforcing a ride height rule that is appropriate for that class, teams are discouraged from cutting and dropping the center third of the frame, for example, to lower the CG height. And since CG height so critical to handling performance, it should be regulated by sanctioning bodies with enthusiasm.

 

As I recall, I used to have three ride height wheels - 4 inches, 5 inches and 6 inches - depending on the classs.

 

Nick

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The rule says everything but the exhaust must clear 4 IN. Body skirting bolts and all. Just because he doesnt check it does that mean it is legal???? Does it also mean pop ups are legal just becuase Jack doesnt check them? Has Jack actually said in a drivers meeting that everything behind the front of the rear tire will not be included in the ride height rule?

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Has Jack actually said in a drivers meeting that everything behind the front of the rear tire will not be included in the ride height rule?

 

Absolutely not. The question was asked earlier in the thred about how it is checked. I just tried to answer the question.

 

You could knit-pick the ride height rule to death. Maybe that's why Jack checks it the same way every time - so we understand the way he intends to enforce the rule. The area you asked about is probably the lowest part of the entire car, but it's behind the frame kick-up. I figure that's why you picked that area to point out. The fact is - the factory frame on these cars kicks up in front of the rear axle. Maybe that's why he doesn't check any further back than that? But only Jack could tell us that.

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Does it also mean pop ups are legal just becuase Jack doesnt check them?

 

Actually, he does check for domed pistons. That's part of the inspection that happens when the heads come off - love that one! :D

 

Thanks ss99.

 

You bet. But you know the answers to all these questions Curtis. So you must just be bored like me. Got to get back to work. ;)

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Nick, as you of all people know,shocks have many different oils in them. Some thicker than others. As oil heats up as in a long race , could it be possible that some teams have figured out on a dyno that the oil gets thinner as it heats up, therefore creating less friction when pushed through the shock shim. Which in return could possibly make a car on the so called bb/ss set up be a touch lower? Maybe this is why some teams want it checked before the race.

 

Hey ss99 Who is Curtis?????????

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Do the u-bolts that hold the leaf spring to the rearend have to clear Jacks wheel?

 

OK soaker, today is a new day (with a little more time to play with.) Just for you, I checked the clearance under the leaf spring u-bolts. They are well above the 4.5" minimum ride height rule (at least on our car.)

 

Now I feel better. :lol:

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I dont have aproblem with the ride height rule, however it always seem to affect someone unintentionaly(sp?). Frame heights, yes, bolt heads, no. I have also had problems in the past passing the wheel mostly because the geometry of my car is better the lower I get it so I always try to get as close to the edge as possible. I donot understand the "settling" theory as Nick stated. The only reason a car can loose height after a race would be a collapsed spring or damage. Once you take 35 or more pounds of gas out of the car it will ALWAYS raise. The front will not drop due to the cell being back so far so its not shifting. All in all Jack does an exceptional job of teching our cars, so I have no real complaints. Just my 2 cents, since Im all out of dollars.

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