Droop Limiting and Bumps.

So I have been away from here for a while. Had to eat my words about calling guys who run bumps on dirt crazy, because as I found out, running bumps on the RF in a dry slick greatly helps keep the car tight in the middle when transition handling would normally change from tight in to loose off due to the static cross weight setting. I did find out that contrary to what I thought running a lot less static bite on the slick, when running a bump was what was needed, not the other way around. Obvious blonde moment was me tuning crossweight for the amount it would decrease with the soft RF ride spring rate when weight transferred, and not the amount it would increase when it got onto the bump. Figured it out right away when I came in with a cold LF tire. Derp. Anyways I could go on and on, thing is, I was wrong and I have to say anyone that I argued with about bumps being stupid on dirt, I'm stupid lol. I was thinking now, (here we go again), with how stiff the RF and LR corners are becoming, due to bump devices and chassis hike like never before, the LF and RR corners begin to seem fairly soft, even if we are looking at the heavy RR spring setups. I have read somewhere that the tethers have been used in different types of racing to run the same springs on a car in a much more pre-loaded state in order to change the handling characteristics as well as responsiveness of the car. So aside from using the tether to actually help keep the LF down, this is just my brain kinda going off on a tangent here, do you think that using the tether setup on the LF (and RR, I suppose too) is one way of making sure these two corners are working at a rate that is functional with the increased wheel rates at the RF and LR corners we have been seeing over time? Is the RR tether just to keep the RR corner from coming off the spring like a LR? Or are guys actually pre-loading the living hell out of their springs these days? When I watch the WOO late models even on bumpy tracks it looks like the cars barely break their platform, like the car itself is actually really stiff lol. Anyways. Hopefully someone can come along and tell me I'm an idiot or I'm kinda on the right track. Thanks in advance.

I guess another point to add in there would also be the use of the very pre-loaded soft ride spring on the RF and soft LR springs guys are using as well, is there something to matching the pre-load of the four corners perhaps?

I think your thoughts on bump stops are way too absolute. It depends on what you are using and how you use it. I been using them for years and I have been on high bite and low bite with them. The rest of the puzzle still matters.

This was just from my experience with the RF being on a bump: I set my bite high because I figured the soft ride spring with a stiffer RR than normal would cut a lot of cross out of the car. Little did I know, I was quite loose in when on the brakes coming into the corner. My left front had barely any heat and the RR was blistering hot. I made adjustments by taking bite out of the car, the cold LF was my indicator the bite was off, something I had actually been prepared for by making the adjustment at the shop, so I knew what I had to do in order to get back down to the 50-75lb range. When I set it down there, the car was much tighter coming in, which is what I needed, and once the car would get down into the bump rubber harder, it would tighten up in the middle. For the dry slick aspect of using a bump, for myself, I most likely will not run up high for bite again. It really sucked on entry. Just adjusting the cross from high to low, on this surface anyways with the RF bump rubber, I went from over 8 seconds behind the leader, in the first nights main, to 1.7 seconds ahead of the second place guy the next night and took my first win of the season finally after playing with bumps. If the track was already really tight then I could see myself running the higher bite to get into the corner better on that surface, but for a dry slick, I just couldn't see myself going back to running a high bite number.

There are plenty of really fast cars out there with RF bump stops and upward of 100 pounds static LR. Like MBR said, there's a lot more to the puzzle. There are ways to tighten entry without dropping wedge down that low.
On the tethering thing, there's a lot to that, but tethering a corner doesn't change that corner's spring rate. It's a travel limiter, plain and simple. The trick then is just understanding what happens dynamically when the travel stops. On the LF, there's some gains to be made. On the RR, if you're using it in the slick to tighten exit, it may be an indication that your car needs work in other areas...just my opinion. And be careful tethering the RR on any track that is a little rough. That can be a handful in a big hurry.

I would think tethering the LF and RR down to zero droop travel from ride height would make the car extremely tight on the throttle. Basicly setting up a pivot axis for the LR to push against the RF corner, the only thing that could extend would be the LR shock, and the only thing compress would be the RF. Thats just pure speculation.

We tried the LF limiter and it made the car really loose on entry, but i didnt have enough adjustability there and just took it off. This year i will redo it all so i can adjust it. We ran the RR limiter late last year, and liked it, but not a huge difference, but i wasnt bound down real tight either, 1 droop at ride height.

I would tend to think, binding the RR and adding some preload would be the best of both worlds. Softer spring to keep the packed rate down, and still get the car to enter well. But finding that number may prove costly, your base starting point.

i have started setting my static cross weight with the rt frt spring off and sitting on the bump stop, is any one else doing this and if so , what does your bite look like?

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Originally Posted by Matt49

There are plenty of really fast cars out there with RF bump stops and upward of 100 pounds static LR. Like MBR said, there's a lot more to the puzzle. There are ways to tighten entry without dropping wedge down that low.On the tethering thing, there's a lot to that, but tethering a corner doesn't change that corner's spring rate. It's a travel limiter, plain and simple. The trick then is just understanding what happens dynamically when the travel stops. On the LF, there's some gains to be made. On the RR, if you're using it in the slick to tighten exit, it may be an indication that your car needs work in other areas...just my opinion. And be careful tethering the RR on any track that is a little rough. That can be a handful in a big hurry.

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I was up at 232lbs of bite before I dropped it down on this setup.

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Originally Posted by Kromulous

I would think tethering the LF and RR down to zero droop travel from ride height would make the car extremely tight on the throttle. Basicly setting up a pivot axis for the LR to push against the RF corner, the only thing that could extend would be the LR shock, and the only thing compress would be the RF. Thats just pure speculation.We tried the LF limiter and it made the car really loose on entry, but i didnt have enough adjustability there and just took it off. This year i will redo it all so i can adjust it. We ran the RR limiter late last year, and liked it, but not a huge difference, but i wasnt bound down real tight either, 1 droop at ride height.I would tend to think, binding the RR and adding some preload would be the best of both worlds. Softer spring to keep the packed rate down, and still get the car to enter well. But finding that number may prove costly, your base starting point.

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I think the idea is to increase roll stiffness to increase aero platform (chassis roll especially LF corner rising up too high gets air under the car). At the same time because the stiffness is from the tether, not an anti roll bar, when the left front tire hits a bump it doesn't load and unload the RF like a pavement BBSS setup. It does give the corner the ability to lift sooner, but with the increase in aero, as well as the lower mass concentration height in the front, the likeliness of the LF lifting goes down and when it does happen I don't believe it's as exaggerated as the days of the past where you carry the tire half way around the track and can read the brand of the tire lol. This is also due to the fact the RF corner is slammed down so low too majority of the time. That has been one of the things with working the LF more is getting the RF down lower when hiking the LR so high. I might be wrong here but that's kinda the jist of what I've found for information.

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Originally Posted by fastford

i have started setting my static cross weight with the rt frt spring off and sitting on the bump stop, is any one else doing this and if so , what does your bite look like?

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Not sure I understand this. I realize our cars are never at static ride height while we're racing but dynamically, the spring doesn't go away just because you're on the bump. It is still providing a force feedback to the tire.
I'm trying to ask this in a way that doesn't sound like I'm trying to be a smart ass because I'm sure there is something to be learned here...but why are you scaling it this way? Or in other words, what is the thought process? It certainly is interesting.
There are already a million things that we've all argued about over the years on how to properly scale...might as well be a million and one I guess :-)

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Originally Posted by Matt49

Not sure I understand this. I realize our cars are never at static ride height while we're racing but dynamically, the spring doesn't go away just because you're on the bump. It is still providing a force feedback to the tire.
I'm trying to ask this in a way that doesn't sound like I'm trying to be a smart ass because I'm sure there is something to be learned here...but why are you scaling it this way? Or in other words, what is the thought process? It certainly is interesting.
There are already a million things that we've all argued about over the years on how to properly scale...might as well be a million and one I guess :-)

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It's an asphalt thing Matt I've done it on bumps in asphalt yoh set the car on the stops and see the cross they don't want cross changing from
Static

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Originally Posted by Matt49

Not sure I understand this. I realize our cars are never at static ride height while we're racing but dynamically, the spring doesn't go away just because you're on the bump. It is still providing a force feedback to the tire.
I'm trying to ask this in a way that doesn't sound like I'm trying to be a smart ass because I'm sure there is something to be learned here...but why are you scaling it this way? Or in other words, what is the thought process? It certainly is interesting.
There are already a million things that we've all argued about over the years on how to properly scale...might as well be a million and one I guess :-)

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i dont know if it makes a difference or not , but my theory is in dynamic roll onto the rt frt , static weight is actually decreasing on the left rear , especially with soft left rear , now i understand that mechanical load from the bars is a factor, but i feel i get a better or more consistent base line setting by doing it this way. im working on a single spring to use on the 2 stage set up to be able to do basicaly the same procedure to simulate when its on the second stage. i by no means consider my self an expert on all this, but i do like to experiment and i do belive this is better for me. im not here to argue about this , but would appreciate any input.

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Originally Posted by 7uptruckracer

It's an asphalt thing Matt I've done it on bumps in asphalt yoh set the car on the stops and see the cross they don't want cross changing from
Static

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thanks 7up , this is actually what got me thinking about this.

I got to pondering this roll resistance thing (Ken777 above), i know dangerous... but given the same car (weight) and same track (centrifugal force applied) limiting the LF and the RR are going to change the application of said centrifugal force, not so much the RR except maybe for entry.

Your basically going to direct it to apply the force to the RF. It has to move somewhere, the same force is being applied.

I have always thought the purpose of the RF, i know aero is a big deal, but i always thought it was to make room for the LR to be hiked up and then once you gain a lot of bar angle the resistance kicks in, bump stop, dual stage spring, so the LR begins to dig harder against that stop thus creating more pressure on the RF tire and LR tire simultaneously.

If i am in left field, let me know.

LOL, Krom.

here is something to try that might help some one understand what im doing a little better, put car on scales with ride heights close, now remove rt frt spring and let it down on bump , now set your rear neutral (no bite) , now put spring back in and look at how much your bite is now, you would be surprised. mine is way more than i ever ran on conventional rt frt spring. im not gone tell every thing im doing on here , but i think around 50 lbs of bite on the bump is a good starting point and work on that mid turn throttle push by adjusting bars. JMO

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Originally Posted by fastford

here is something to try that might help some one understand what im doing a little better, put car on scales with ride heights close, now remove rt frt spring and let it down on bump , now set your rear neutral (no bite) , now put spring back in and look at how much your bite is now, you would be surprised. mine is way more than i ever ran on conventional rt frt spring. im not gone tell every thing im doing on here , but i think around 50 lbs of bite on the bump is a good starting point and work on that mid turn throttle push by adjusting bars. JMO

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We all know dynamic ride height changes changes bite. I try to set it at dynamic heights and see where the cross is migrating. Things to keep in mind. Are my bump or stack setup for wheel loading or travel limitation. Its good to know where dynamic bite is going and with some of the new tools you can simulate rear end loading into the equation as well with pull down rigs and actuators on the lift arm etc On asphalt we get the static loads then depending on the bump setup set the car on the bumps, account for tire sqrunch and check valance clearance and you can add or subtract shims ot change dynamic bite on the bumps or total clearance if you are too high or low. In short its all about shop work and the more you know and try to more things you can rule out or go into deeper

I'm seeing the word "dynamic" a lot but none of what is being described actually simulates the "dynamics" that happen on the race track. Ride height changes on the race track because of induced forces (deceleration, engine torque, centrifugal, etc.) not because a spring got pulled out or an arm got moved. These induced forces have a very real impact on the loading of each tire and that can't be simulated sitting in the shop regardless of how many pull downs and jacks you have. I'm not saying there isn't something to be learned by doing this stuff but to think that it simulates some on-track situation seems like nonsense to me.

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Originally Posted by Matt49

I'm seeing the word "dynamic" a lot but none of what is being described actually simulates the "dynamics" that happen on the race track. Ride height changes on the race track because of induced forces (deceleration, engine torque, centrifugal, etc.) not because a spring got pulled out or an arm got moved. These induced forces have a very real impact on the loading of each tire and that can't be simulated sitting in the shop regardless of how many pull downs and jacks you have. I'm not saying there isn't something to be learned by doing this stuff but to think that it simulates some on-track situation seems like nonsense to me.

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Some guys are using actuators on the lift arms and pullbars to simulate engine torque that is supposed to load the rear tires like engine torque would I think I mentioned it in my post but Ive seen it on the pull down Rig you also have to account for lateral forces that are hard to simulate and aero

Matt49, you can actually simulate lateral loading on a pull down rig. I think. Here is my idea. Lol. You need an accelerometer or a g force meter and a TPS and BPS in your car on a test day, maybe put a go pro in the thing and have it watch the meter so you can pay attention and drive the car hard. You will need to figure out what your baseline for banking will be. You will also need to figure out the exact centre of gravity on your car. You can determine lateral and longitudinal location by static scale numbers and you can figure out the height if you replace all your coils and shocks (including the 5th coil and 6th coil) with solid bars, place the car on scales and lift each end. There's some formulas that you can run that give you CG height based on the scale number changes. The higher each end can get lifted the better. From that point you'll need to mount a clevice of some kind so that you can attach a cable and a winch. Your cornering force is almost never at 90 degrees so the rig will have to tilt to simulate banking. Put a pull scale on the winch and cable on the car and apply the force you need to the center of gravity. You might need to make a better surface to keep the car from sliding off (this can be done). if you really wanna get carried away you could install wheel dyno on pads on the rear with a track so the LR and RR tires could move while you rev the crap out of the car. it would be quite the endeavour and while technically what I am talking about isnt really a pull down rig, you could probably just run a tilt on a pull down rig and use the pull scale and cable at CG to get somewhat close. The other thing is the torque from the rear end always tries to push the LR down and unload the RR, due to its rotation, while at the front trying to lift the LF and load the RF. so to get real dynamics you need the car on scales while it's running under load as well as applying force to CG AND aero, so you would need to simulate a surface under the car as well. THEN you would need to have this entire setup on a four post shaker as well as the rest so you could simulate wheel loads not just on a smooth surface but to see what happens over imperfections.

Oh and instead of a cable/winch pull scale you could use a pendulum style hydraulic arm that could apply not only lateral force but forward and rearward force to, to simulate braking and acceleration.