Thoughts on LR travel

[Matt49]

LR travel is always (according to most) supposed to be measured while the car is on jack stands with both sides just hanging. Which is incidentally not a position the suspension would be in on the race track. Well...suffice to say that if it is, you're having a really bad day. But seriously, why do we measure it this way? My (and most everybody's) travel limiter is mounted inboard of the birdcage. So ANY travel that the RR experiences is going to affect the LR birdcage (and wheel) travel. We only measure travel from the axle tube to the chassis (which is usually where the limiter is mounted) but that doesn't tell the entire story now does it?
Thoughts?

[JHobbs26]

I've always measured my drop by jacking the car up under the seat

[TheJet-09]

I thought about this too, or at least along the same lines, over the winter. My LR travel limiter was well inboard of the LR birdcage, actually right against the left hand rearend bell. That to me created a "teeter totter" effect based on the RR travel, and consequently affects the LR. Theoretically, wouldn't we want the LR travel limiter in the center of the LR contact patch (I know, impossible)? I spent a fair amount of time making an outboard mount on my chassis that ran on an angle down to the rearend, and had to make sure it cleared the brake hose and LR shock. Then I got the nice updated rules from UMP, which they sent out two weeks before they took effect by the way, only to realize we now have to run the limiter as close to vertical as possible. Whatever!!!

[Kromulous]

I think taking the measurement the same way everyime is the key for adjustments, but for design its definitely flawed.

In the shop i jack it up in front of the LR or under the seat like Jhobbs said, but it would be neat to have a car on a pull down rig and simulate some on track attitudes.

[fastford]

I do the same thing krom, except I have a good idea where the right rear is when going thru turn, so I undo the right rear shock and put another jack under the right rear bird cage and jack it up, gives you a better idea where everything is on left rear while going thru turn.....

[lindsey97]

I pull the right front shock off and let the car down to the ride height the car travels in the corner. Then jack up under the LR 4 bar mount. I think that gets it closer to actual. There is a difference in chain lengths, and you can learn more about the rear movement. I haven't done it yet, but pulling the RR down to actual would be good also. I have gotten my wife to sit on the RR before. :)

[Bubstr]

I was thinking about this a couple years ago. If you made a pull point at the center of gravity and use a L shaped hook attached to a chain tie down and a hydraulic ram to tighten chain. By moving car in relationship to side force, you could not only get real drop but dynamic wheel weights on the out side wheels or rear, depending on where the pull point is. A poor mans pull down rig. One of the low tech frame machines that most body shops are replacing would be great and straighten that bent frame too. Force on the COG is what makes the roll. Smarter guys than me in here. Take the idea if you think it's good.

[Matt49]

I do the same thing krom, except I have a good idea where the right rear is when going thru turn, so I undo the right rear shock and put another jack under the right rear bird cage and jack it up, gives you a better idea where everything is on left rear while going thru turn.....

This is exactly what I've started doing and the results are pretty interesting.

[Austin34471]

We check "droop" like this because someone started checking it like that 30 years ago and people followed suit. Everything we check at the shop is just a reference point and 95% of it is not representative of what's actually going on while racing. Most racers don't have data aq or a pull down so the mindset is "well let's add a 1/2" of LR hike up based on this arbitrary measurement and see what it does this week!" If it's faster then GREAT, if not, change it back.

[a25rjr]

We bought a used Rocket a couple years ago. Since it was a roller without shocks, the previous owner had taken 1.25" tubing, smashed the ends flat in a press, then drilled the holes the right length according to ride height. I took it a step further and made a set trying to match the dynamic ride height while on the track. Of course its not perfect but you'll learn a few things if you do it this way.

[Kwoods25]

If you run a limiter on the RR. You would get about exact measurement.

[a25rjr]

If you run a limiter on the RR. You would get about exact measurement.

True.....you don't see too much discussion about dynamic bar lengths, which affects roll steer and indexing.

[fastford]

We bought a used Rocket a couple years ago. Since it was a roller without shocks, the previous owner had taken 1.25" tubing, smashed the ends flat in a press, then drilled the holes the right length according to ride height. I took it a step further and made a set trying to match the dynamic ride height while on the track. Of course its not perfect but you'll learn a few things if you do it this way.

if you want to take it a step farther, take it to the track you race on, with your dynamic tubing's on, when no ones there and pull it slowly through the turns with a four wheeler , you would be amazed what you can learn with out spending hardly any thing.

[collateralDamage]

In my experience, when the rear end hanging is relatively flat, it is much easier to get a consistent droop reference week to week. Not saying what is right or wrong, just saying use a method that you can duplicate easily at the track and the shop the same.

The position of the RR greatly impacts the measured droop, even more so when you account for the location of the limiter on the axle tube relative to the birdcage/wheel. If the attitude of the RR isn't exactly the same every time you measure, it won't be consistent regardless of the method you use.

Also think about any angle the LR limiter chain may have and how it affects droop when the lift bar is in motion......

[RacerX10]

How much change at the LR drop measurement does it take to notice a difference on the track ?

What are the symptoms of too much drop ? too little drop ?

[collateralDamage]

How much change at the LR drop measurement does it take to notice a difference on the track ?

What are the symptoms of too much drop ? too little drop ?

How much change largely depends on the pivot point (location of the limiter on the axle). I would consider 1/4" a noticeable change.

too much droop/drop can over-rotate the birdcage. too little may not transfer enough weight.

[Matt49]

How much change largely depends on the pivot point (location of the limiter on the axle). I would consider 1/4" a noticeable change.

too much droop/drop can over-rotate the birdcage. too little may not transfer enough weight.

1/4 inch of travel at the chain could mean 1/2 inch at the tire. Food for thought.

[collateralDamage]

1/4 inch of travel at the chain could mean 1/2 inch at the tire. Food for thought.

Absolutely agree. it could be a lot more than that in some cases. the closer the "pivot" (lower drop limter on the axle) is to the bell, the more affect on actual LR contact patch movement. The more angle of the chain - left to right - the more pinion movement influences the LR contact patch as well. Combine the two and there is a whole lot going on there.

[slmcrewchief99]

There are several different ways to do this. Some I am sure are better than others. As long as you do it the same way every week at the shop, you should be ok. That's the way we did our Mastersbilt when we had them. We would change it at the track from night to night but at the shop we put it right back to "scale settings" as we called it. We don't have to worry about it with our Black Diamond. We don't have a chain on it.....

[Kromulous]

Whats the at the track adjustments do for ya? adding droop etc?

Seems to be a lot of information that contradicts each other.

[Matt49]

Adding droop at the track can be a pretty effective adjustment as the track slicks off. Adds rear steer, adds LR anti-squat, raises vertical CoG raises rear deck height. All good things in slick track conditions.

[Kromulous]

I agree, i add for the slick usually. I was told that was backwards...loose roll steer.

I guess there is a point at which the advantages, starts to turn into disadvantages, via dding to much droop.

[Matt49]

I personally think the term "loose roll steer" is a misnomer and confuses people. You WANT roll steer when the track is slick. As opposed to having to slide the tires sideways to change the direction of the car. On a slick track, once you've started sliding, you can forget having any forward bite to get you off the corner.
Watch the best in the business and their car is never actually sideways in the corner when the track is slick. If it looks sideways, that's purely the way it is tracking due to the roll steer. The rear tires are almost always pointed the direction the car is going. Very limited slip angle maximizes grip.

[a25rjr]

It appears to me, the cars are getting more and more hike, and still have plenty of drive off. If you look at some of the pics, the lr upper bar angle seems to be a lot more than in the past.

[Kromulous]

Yes, more hike, more rod angle, to work harder against the right front stack, thats how i see it anyway.

Bloomquist was the last hold out on lower LR hike. Now he is hiking it up a lot more for all the benefits Matt49 posted earlier. Last year his car was lower on the LR, and just didnt seem to be able to drive as hard off the corners as others.

I agree with Matt49 too, there cars arnt sideways, there just "dog tracking" thru the corners. Sliding is out, and slow.

[manwplan]

So where do you think max bar angle should stop? For ever the rule of thumb was don't go over 47 degrees. Some cars look like they are almost 90.

[Kromulous]

I noticed that too, the last stand is over indexing the cage, so i guess that is the limit.

Seems like some are running more lower bar angle to help stop over indexing the cage, so they can gain more total angle in the top bar.

[dirtslinger4]

Just curious what everyone is running on the left rear upper angle at ride height and also at full hike. Been playing with some things just wondering if I am getting too far.