Truck Rake

[JOHNBOY]

nuthin mouthy here - just asked for sumthin other than retorts and denigration to peoples posts and questions
I have heard him spout before, on other threads n still waitin for the backup - tellin me he is summ kinda engineer dont mean sheet to me

Show me the money

prove to me empirically and theoretically and for real that rake doesnt matter and I will retract my post AND apologize

given the number of raked trucks that outrun the not raked trucks i have seen - for whatever reasons - I dont see that data forthcoming

prove physics wrong and show me that changin the centre of gravity doesnt change the lift characteristics and thereby the minor increases in traction - inches matter in pulling - hell tenths of inches matter

Here is the problem with that. If your using a floating draw bar hitch I can see how that could be. But you still need something to set the height of the draw bar on the end of the frame. When the chain is hooked it will be pulling down and back on the drawbar. The support use to sey the height will load the frame with down pressure causing most of the advantage in of the drawbar to be wasted. Now if you can angle the drawbar so it has the same angle as the hooked chain then you can keep the load off the rear support. That would work but all sled chains ould need the same length.

But all that really does not matter as we have "receiver" hitches.

By the rules our hitch can only be so high and only so far from the rear axle. The examples below our the actual dimensions of my truck. Raising the frame does not change the force triangles because the hitch is till in the same spot.

 

[brushpuller]

^^^Does your rules say you can angle your reese hitch in the frame???

 

[brushpuller]

Ok you cant compare tube frame trucks with true pulling hitches and front stops to what most of us have DD

Not all mod trucks have tube frames and the ones that have factoy frames are running level!

Talking about front stops...why can't a DD have them...thats verry easy to do and undo...

 

[malibu795]

Not all mod trucks have tube frames and the ones that have factoy frames are running level!

Talking about front stops...why can't a DD have them...thats verry easy to do and undo...

is there anything limmiting front end travel?

 

[brushpuller]

Don't know if i understand your question...but no...thats what front stops do is limit the front sag when weight is put out front.

 

[Blackdog]

Ok, here is my .02. I say raked and here is why. From all my years of stock and antique tractor pulling we ran the biggest rear tire the classes would allow and small tires in the front to create a "Rake". The hitches were parallel and not angled. Weight is the key. When pulling tractors you want to keep as much weight on the rear tires as possible and the exact amount and placement on the front so the front tires just skim the dirt. If the front comes up you loose all the pressure the sled is transferring to the back tires thus taking away your traction.

I put this knowledge to truck pulling. Rake the rear with a parallel hitch because you want the pressure from the sled on the rear which is doing most of the work anyway. Weight placement on the front as far forward and as much to make weight to keep front down and the front tires diggin. Traction bar mount point on the frame so they are transferring pressure towards the front of the truck and not bending the frame due to front and rear pressure created. This is why front weight placement is my key to keep th front down.

The question was about rake and this is my answer. Mod trucks are a different breed of cat and I would compare them to SS tractors.

 

[seeker1056]

the second pic isnt accurate - if the weight at the front was attached exactly the same way as the first pic - the weight would be lower to the ground, and so would the motor etc, - which moves the centre of gravity forward and down - which makes it harder to pull up over centre thereby increasin traction
it also shows the frame being slightly higher over the wheel which also would not be accurrate because as you tip the truck forward the suspension tends to compress slightly more makin the rake even more
the second pic if drawn accurrately would have the weight right on the ground or just - which would be about perfect

So if you redraw that second pic and the centre of gravity line? (yellow one from rear wheel to weight) - you will see it relocates substantially over the centreline of the front wheel

Awesum that you took the time to draw it though - took some thought and energy

the tractor example is exactly correct
2 wheelers are the same

and as to why mod trucks dont have rake - I suspect they already have the centre of gravity as far forward as it is possible to get , because of the huge weight bar etc - whereass a DD cant move much weight around physically or within the rules and thats why rake works on them because you are artificially movin the centre of gravity forward and down

 

[JOHNBOY]

the second pic isnt accurate - if the weight at the front was attached exactly the same way as the first pic - the weight would be lower to the ground, and so would the motor etc, - which moves the centre of gravity forward and down - which makes it harder to pull up over centre thereby increasin traction
it also shows the frame being slightly higher over the wheel which also would not be accurrate because as you tip the truck forward the suspension tends to compress slightly more makin the rake even more
the second pic if drawn accurrately would have the weight right on the ground or just - which would be about perfect
You can only go so low with the frame. I attached a drawing with it lower to the same over center height as the first pic. The weight placement doesnot change because that is as low as it can go an still get on the trailer and scales. Around he they might DQ you if you weight bangs the scales getting on. Bang Sledpullers scales and see how freindly he is.:kick:

So if you redraw that second pic and the centre of gravity line? (yellow one from rear wheel to weight) - you will see it relocates substantially over the centreline of the front wheel

Awesum that you took the time to draw it though - took some thought and energy

the tractor example is exactly correct
2 wheelers are the same

and as to why mod trucks dont have rake - I suspect they already have the centre of gravity as far forward as it is possible to get , because of the huge weight bar etc - whereass a DD cant move much weight around physically or within the rules and thats why rake works on them because you are artificially movin the centre of gravity forward and down

The yellow lines are just triangles I drew in to figure lengths for doing calculations. The center of the back tire contact patch is the pivot point. The force of the weight pulls downward at the angle of the chain. No matter what you do with the rake the back triangle does not change. Its sides are set by Max hitch height(26") and min. length from the center of axle (45"). The front one will change until your to the point where it cant go lower. The angle of the frame below is 8*. In the first pic above it is .85*. That is a pretty good difference. But the length of the front triangle side are the same because that is all the lower the weight can feasablily go. So you can take the length and plug them into a calculator like this.
Calculator

Using the lenghts in the picture 227" and 45" with a 1000% endweight you get a hitch force of 5044% It is the same no matter the rake. Now if you do what Troy Wakeman supposedly did and have a 20" shorter hitch it would be 9080%. Big difference!

 

[SmokeShow]

Very nice explaination. Thanks JB.

 

[seeker1056]

Any of the following will give you a minor understanding of the dynamic loads involved with raking a vehicle from front to back, wether at stand still ,forward motion, braking.

Ignore the side to side, and cornering sections of the various acrticles as they are not relevent to this disscussion

The weight transfer from Cg is a very good article

Longacre Racing Online -- Tech Article

http://www.geocities.com/MotorCity/4014/cgrav.html

CG Height Calculator

Weight transfer from centre of gravity

401 Unauthorized

although it may not seem relevent because most of the articles are based on rear weight transfer, you will obsrve that the tilted calculations prove my point quite well, not to mention tha trearward motion is a very real dynamic in pulling in order to keep the front tires loaded, without unloading the rear tires

 

[brushpuller]

^^^ op:

 

[JOHNBOY]

Any of the following will give you a minor understanding of the dynamic loads involved with raking a vehicle from front to back, wether at stand still ,forward motion, braking.

Ignore the side to side, and cornering sections of the various acrticles as they are not relevent to this disscussion

The weight transfer from Cg is a very good article

Longacre Racing Online -- Tech Article

http://www.geocities.com/MotorCity/4014/cgrav.html

CG Height Calculator

Weight transfer from centre of gravity

401 Unauthorized

although it may not seem relevent because most of the articles are based on rear weight transfer, you will obsrve that the tilted calculations prove my point quite well, not to mention tha trearward motion is a very real dynamic in pulling in order to keep the front tires loaded, without unloading the rear tires

I am familiar with those formulas. They are very useful when looking at rear bite in a drag car or dirt car. Getting the weight of the car to transfer and help plant the tires. I think your way over valuing the usefulness of that. The reasoning being that will only really apply when the is moving upward upon launch at the line. Once leveled out it all about the leverages and weights. The other really big thing missing from all those equation is this.

Getting the most of leverage out of the weights you have. When you start raking the truck it compromises that.
Now I have put up pictures drawings and done math in effort to explain my point of view. You keep mentioning your "15 years of experience" So sure you can add in some values to those formulas form all that pulling experience you have. While your working on that how about posting up some examples of your truck feats. I mean you keep saying nwpadmax is has no idea what he is talking about. But he has the wins, top 5s, and the championship jacket to back him up how about you? Your turn to put up!oke:

 

[seeker1056]

I have nuthin to prove and so far nobody here has put forward "anything" other than conjecture, and unsupported statements


except for the gentleman who drew the pictures - at least he tried

When someone actually puts something concrete forward then you can diss me all you like until then - show me the money -

as for engineers - there are a gazzillion kinds and mostly for roads n construction - if your friend is an automotive engineer then he has my apologies - but still waitin on his backup info - which as Isaid - in several threads - have yet to see

by the way

2wd street class - never defeated

4x4 street class - 70% win ratio

curcuit 5500 class - third and fourth in points

super stock in five years of pullin, 3 - 4th place overall finishes in points, and the last year I ran was 1st in points till i walked away pissed at politics,

street racing - never defeated,

sand drags, 1st, and 3rd place finsihes in B/Mod

last year would have been second in points in prostreet in two divisions - but I was a day hooker so could not accummulate points

What have you done?????

 

[JOHNBOY]

I have nuthin to prove and so far nobody here has put forward "anything" other than conjecture, and unsupported statements
You have statements you made that need backing up. You posted those formulas. So us your skills and use them. I did what you asked. Now it is your turn you have something to prove. Saying you dont is just a cop out.


except for the gentleman who drew the pictures - at least he tried

When someone actually puts something concrete forward then you can diss me all you like until then - show me the money -

as for engineers - there are a gazzillion kinds and mostly for roads n construction - if your friend is an automotive engineer then he has my apologies - but still waitin on his backup info - which as Isaid - in several threads - have yet to see
After the wondeful comments you made about how much water you dont melt with your Air to Water IC I think he pretty much wrote you off as I am about to do.
You have not proven anything. I put a good bit of effort into those drawings. Right or wrong I tried. All you have done is spout at the keyboard. Apply those nifty formulas you linked. Do the math so us the work. Prove me wrong.

by the way

2wd street class - never defeated

4x4 street class - 70% win ratio

curcuit 5500 class - third and fourth in points

super stock in five years of pullin, 3 - 4th place overall finishes in points, and the last year I ran was 1st in points till i walked away pissed at politics,

street racing - never defeated,

sand drags, 1st, and 3rd place finsihes in B/Mod

last year would have been second in points in prostreet in two divisions - but I was a day hooker so could not accummulate points
Where do you run in all these classes?
What have you done?????

Not much just practice what I preach and apply what I learn.
3rd overall in DHRA WS points in 2006. This my first year in FPP Prostreet currently 7th in points currently. Point Standings...

I am working on shorting my hitch. Not going to waste my time with raising the back of truck. I have already proven to myself that it pulls much better with the truck lowered. You can find my vids here. YouTube - UNCOMMONDIESEL's Channel

nwpadmax was runner up in FPP Street in 2006, Champ in 2007, Numerous wins and top 5s. Several top 5s in DHRA 2.8" He won NADM Superstreet at Stoneboro in 2008. No Brush pull crap. In a truck with no rake.

Watch him win here.
YouTube - Bunker Hill (Goshen Twp.) Ohio Oct. 2008
and here,
YouTube - NADM July 12, 2008
and here,
YouTube - Mercer Pa 2007 Street diesel

Just a bunch bench pullers.:hehe:


A no rake gasser for good measure.
tthomp:rockwoot:
YouTube - tthomp Truck Pulls PC Fair 08 By: Diesel Bombers

I guess we are all doing it wrong.:bang

 

[longhorn859]

yeah but that gasser has his weights hung sideways lol

 

[brushpuller]

How can anyone argue with those vidio's! Great running trucks!

 

[zstroken]

the second pic isnt accurate - if the weight at the front was attached exactly the same way as the first pic - the weight would be lower to the ground, and so would the motor etc, - which moves the centre of gravity forward and down - which makes it harder to pull up over centre thereby increasin traction
it also shows the frame being slightly higher over the wheel which also would not be accurrate because as you tip the truck forward the suspension tends to compress slightly more makin the rake even more
the second pic if drawn accurrately would have the weight right on the ground or just - which would be about perfect

So if you redraw that second pic and the centre of gravity line? (yellow one from rear wheel to weight) - you will see it relocates substantially over the centreline of the front wheel

Awesum that you took the time to draw it though - took some thought and energy

the tractor example is exactly correct
2 wheelers are the same

and as to why mod trucks dont have rake - I suspect they already have the centre of gravity as far forward as it is possible to get , because of the huge weight bar etc - whereass a DD cant move much weight around physically or within the rules and thats why rake works on them because you are artificially movin the centre of gravity forward and down

How does it move the center of gravity forward?

I can see it lowering the CG, which in acceleration a lower CG would be slightly better, but miniscule. Lowering the center of gravity when the front raises 2" it raises the CG a given amount regardless if the CG is on the ground or 10 feet in the air.

Your fish scale was a decent idea, but did you actually verify that your pulling at the exact same rate? Pulling up at exactly the same angle?

To accurately represent that you need to be pulling at the similar point that the truck pulls at.

If you are pulling straight up and the rake is lower part of your force used to pull up is being pushed against the nail.

Do the same test and pull down at a similar angle as the chain pulls and record the results.

 

[Sledpuller]

Not much just practice what I preach and apply what I learn.
No Brush pull crap. In a truck with no rake.




A no rake gasser for good measure.

I guess we are all doing it wrong.:bang

Wrong? No. But for you to claim ANY of those trucks in the videos, let alone ALL have NO rake, your are smoking the crack pipe with Coopers engineers degree for baccy.:hehe::hehe:

Chevys by design have prebuilt rake, right into them as do most full size trucks. Each of those trucks in the videos clearly indicate asses up!!!:shake:

That is rake.

 

[JOHNBOY]

Wrong? No. But for you to claim ANY of those trucks in the videos, let alone ALL have NO rake, your are smoking the crack pipe with Coopers engineers degree for baccy.:hehe::hehe:

Chevys by design have prebuilt rake, right into them as do most full size trucks. Each of those trucks in the videos clearly indicate asses up!!!:shake:

That is rake.

Yes they have some rake but actually both of Cooper and myself have done things to lower the backend. Doubt you ever noticed. I have lowered the back of my truck 3" Not sure how much lower Mat's is.

 

[06RAMCTD]

I am familiar with those formulas. They are very useful when looking at rear bite in a drag car or dirt car. Getting the weight of the car to transfer and help plant the tires. I think your way over valuing the usefulness of that. The reasoning being that will only really apply when the is moving upward upon launch at the line. Once leveled out it all about the leverages and weights. The other really big thing missing from all those equation is this.

:hehe: