Hard tire, lots of Lead, too much Rear % ?

[north louisiana dirt]

how much Rear % is too much on a dirt mod ? we have added so much lead to make it go forward, we had to raise the Left Side % to get it to turn....need the forward bite because of the tire, but need ideas to get it without the extra weight.... we are about 300# over min required...... solid pull bar required by rules.... 3 link , j bar , springs on housing, hard tire ( asphalt pull off ) required by (rules)

[skicker]

Ran as much as 64% rear weight at one point.
Bought a restrictor plate and started dropping weight off. Car was much faster. .02

[billetbirdcage]

Unless it's a paper clip track or completely one lane where the person in front of you dictates your entry speed, then corner speed trumps forward bite any day. Not saying it's your case but guys get so carried up in forward drive that they miss where the real speed is.

[north louisiana dirt]

Yes Sir... thanks for that... I agree , that is what I see..... I have been giving every driver I have worked with for the last 5 yrs your article on "Trail Braking".... I now see the difference between a driver and a "Real Modified Driver" :-) and now in a new class with a harder tire.. I believe it is even more important to get that corner speed up so you don't have to fight forward bite... but , I am not a stake holder in the team, so my input is just mild fussing and trying to beat ideas into some set in stone old theories.... Like loading a car up with lead... thanks for the articles, forum post and education....

[stock car driver]

Unless it's a paper clip track or completely one lane where the person in front of you dictates your entry speed, then corner speed trumps forward bite any day. Not saying it's your case but guys get so carried up in forward drive that they miss where the real speed is.

4 corners
2 straights

[Bmod141]

I have been giving every driver I have worked with for the last 5 yrs your article on "Trail Braking".... I now see the difference between a driver and a "Real Modified Driver" :-)

Where can this be found?

[billetbirdcage]

Where can this be found?

Keep in mind I wrote then well over 10 years ago and things change or need to be updated but you can get the jest of it.

Trail braking

I have had a couple of requests to explain this, so I'm putting this here:

This is probably one of the least understood aspects of driving. This is incredibly hard to learn and do effectively after you have been racing a while. Be prepared to spend alot of time learning this as it isn't something your going to learn in a couple of races.

One thing is you should be easing off the gas similar to the way you would apply it in the slick. Now if it is tacky you can throw alot of this out the window as it not as big a deal.

The idea is to remove some or all of the engine braking from the car. "Engine Braking" : The decelleration of the car thru the rear tires causes by the engine. This is just the engine (shut throttle) slowing the car down. If you where to stay in the throttle (partially) enough to match the RPM of the engine to the rate of decelleration, you can remove some or all of the decelleration force from the engine. Basically the car is free wheeling into the corner with no decelleration from the engine.

You don't necessarily go into the corner harder or faster, but since you have removed a large force of decelleration (engine braking) you will likely need to use more brakes to slow the car down to the speed at which you want to enter the corner.

So how does this help?: First, staying in the throttle some and removing some engine braking will noticiably tighten the car on entry. Engine braking is 100% thru the rear tires, so if you remove some of it and then use more brakes (which are not ever 100% rear) you have reduced the total amount of slowing by the rear tires. This will tighten entry. The big benefit comes from being able to vary the amount of engine braking by varing the throttle. If the car is too tight on entry you just get out of the throttle more to loosen entry or if the car is loose you try to stay in the throttle and remove all of the engine braking. It also allows you to make the car tighter or looser at any point on corner entry. This just means I could trail brake more early entry (tightening car) and then closer to the middle trail brake less (loosening car) to make the car rotate.

This is something that if you are not doing, you are leaving something on the table. You are never going to have perfect car every night, ever wonder why the big guys never seem to show really big handling problems. This is because they can adjust driving to make the car do what they need to. It also allows you to have a larger sweet spot for the car, as the driver can adjust entry one way or the other if needed as the track changes.

This is harder to do on some tracks then other and does take a while to learn and use on a regular basis. If you don't think this makes alot of difference, sometime on a practice night turn the idle up the engine to 3500 RPM and go right back out and you see how much tighter the car is on entry. Once you are able to do this you will likey have the car freed up on entry a fair amount from what you used to run because you will be tightening the car with the trail braking.

That's the best way I can think of to descibe it.

Billet

[Bmod141]

Thank you sir.

[7uptruckracer]

Thats the best written example of balancing the car and loading the car with the brakes I've see, Its hard to try to explain to others how to balance the car on the brakes thats definitely something that needs to be cut, pasted and saved! Awesome

[north louisiana dirt]

Trust Me on this.... Out of the 5 drivers I have tried to advance this theory and make the car better and faster.... None of them can handle this part of the Trail Braking Idea !! >>>>>>>> Once you are able to do this you will likey have the car freed up on entry a fair amount from what you used to run because you will be tightening the car with the trail braking.>>>>> they can talk the theory till you wear yourself out showing them the car is really not free enough yet with bias bar settings and RF brake shut offs...most drivers need the security blanket feeling they get with a slightly snug car.... and there in lies the problem with getting a driver to trail brake and stay with it till they learn it......

[turtle1hp]

I have always been concerned more with corner entry and through the middle speeds of the turn. I have tried to trail brake a few different times and it made the car feel to tight. I like the explanation of freeing up the car and using/learning trail braking to use as track conditions change. I just hope I can get through this learning curve without tearing up mine or someone else's car. Any advice on how to approach this?

[turtle1hp]

I have always been concerned more with corner entry and through the middle speeds of the turn. I have tried to trail brake a few different times and it made the car feel to tight. I like the explanation of freeing up the car and using/learning trail braking to use as track conditions change. I just hope I can get through this learning curve without tearing up mine or someone else's car. Any advice on how to approach this?

[north louisiana dirt]

sounds like your taking the correct approach....you have felt the need for "freeing up" the car... so you have confidence now the car will stay up under you when you do it right.... for me as a crew guy , you can't "Tell" the driver what he is feeling...he has to feel it... it's kind of a " what came first, the chicken or the egg"...... so you trail brake and " feel" it tightens the car, then you have the ability to loosen the car up some more...so the driver can use the technique to make the car faster through the corner..... using the gas, brake and all the tools available to adjust the "tight and loose" in any given corner where the other cars are not.

[billetbirdcage]

I'm just going to copy and paste some replies I made over the years to further explain some questions

Adjusting the idle:

Is really just a way of showing some of the effects of trail braking and is really just to pass across the idea of the effect to someone, so it isn't mean as an adjustment. I have adjusted it up or down some to help out but as high as I have stated (3500 would be excessive). I have adjusted them between 1000 and 1800 to help.

I have went as far as hooking a A/C solenoid to a guys car that increased the idle to 3000 when switched on. This are a small solenoid that came on quadrajets in the mid 70's that when powered extends the arm of the solenoid and holds the throttle open when powered. They have a travel of around 3/8" and have a threaded adjuster in the end of the arm that allows you to set the desired idle when the arm extended (powered). I installed it on a guys car that couldn't grasp or ride the gas to see how big an effect it has, I did this so if the car was loose going into the corner he just had to flip the switch on and increase the idea to help tighten the car. This way is all or nothing and doesn't allow you to adjust the car at different points on the track. It was meant as a learning tool. However this isn't the safest way of doing things and wouldn't recommend doing this.

If you runs taller gear then most people or have heavy rotating assemblies in your engines you will see less engine braking from the engine due to the high gear and heavy components. When I started I was running a limited engine where we were on 7.5 pounds per cubic inch with a 2400# minimum. I used a 311 cid engine with really light internals, high compression and a lot of gear (8600+) and I injured my back and had touring LM guy drive the car and he won with it but complained about the car stopping when you got out of the gas. We ended up taking about 6 tenths of gear out of it to help, as he wasn't used to running a car with that light of a rotating assembly and a ton of gear. I was winning most of the races there, so it was just a difference in what you are used to. I like an extremely loose car on entry where he likes a really tight car and the light rotating and extra gear made the car to loose for him.

So just remember the internal components of the engine, flywheel and clutch, rotating weight of the driveline, and rear end rotating components along with gearing are all going to effect the engine braking to that car.

Another reply

Let me start again,


Picture driving a normal car (with a stick trans) down the road at 60 MPH and let off the gas, the car will decellerate from friction of the rotating parts, aerodynamics, and the engine slowing the car. If you were to kick it into neutral or depress the clutch the car would decellerate less, because you removed the engine braking. This is the force we are talking about, you can also remove some or all of this force by not lifting on the gas all the way. You stay into the gas just enuff to not accellerate the car but enuff to not allow the engine to slow the car down.

Since you will need to slow the racecar down into the corner and lets say that is 5 MPH per 10 foot. If you stayed in the throttle or kicked it into neutral you would now (with the same amount of brakeing from the brakes) be slowing down less then that 5 mph per 10 foot. To get back to the same slowing rate you have to use the brakes more.

Basically you are using more brakes and less engine braking to get the same slowing rate. You just vary the amount of engine braking by the throttle and then use the correct brake brakeing needed to get the same over all slowing rate.

Yes, you should be getting out of the throttle smoothly. If you don't do this you will likely need more LR compression to counter the hike down from jumping out of the throttle. This is way I reccommend more compression on the LR for less experienced drivers then my more experienced ones.

Another reply

Just lift on the throttle to 1/4 throttle and see were your at. If you have a practice day drive into the corner (lifting early on the straight for this test) and then stay partially in the throttle to see how much you need to make the car free wheel going to the corner. It is an experience deal to tell you how much you need to make the car free wheel as speed and gearing effect this. After a while you will start to get a feel for different speeds and gearing to know approximatey how much you need to be in the throttle to remove the engine braking.

Like I said this will take a pretty long time to learn and do effectively.

[let-r-eat]

The fastest race car will vary it's speed the least. Would you rather maintain 65mph for 1320ft or vary your speed from 45mph to 80 mph to average the same lap time?

Think about that concept for slick tracks?