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Author
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Topic: wheel base
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jsracingbbf
Gearhead Posts: 1217
From: Batesville,MS. , U.S.A.
Registered: Mar 2002
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posted 04-28-2002 01:00 AM
   
Hey Any one have an opinion on increasing the wheel base of a drag car? Since my wreck I have ordered and recieved a new front frame kit w/ new forward roll bars. The car was not damaged from the A pillar back. I decided to put a whole new front clip under her with a VFN all fiberglass front. Now I set the 1 piece front end on to locate the center of the front tires AND i measured from rear wheels the proper wheel base. I also held a WELD racing wheel up inside the opening and realized I had plenty, if not too much room. Now the idea hit me to stretch the wheelbase 2". I held the tire an rim in the opening again this time a couple inches forward and guess what? You can't tell the difference. So theoretically I could do it, no probs. But I was wondering how much would it help weight transfer. I heard it once said that for every inch you move your motor back its worth 50lbs. Now I know this cant be true for every motor. Does anyone have experience with this?
Thanks! 
Jerry
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Larry Jennings
Gearhead Posts: 540
From: Redwood City, Ca. USA
Registered: Apr 2000
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posted 04-28-2002 02:59 AM
A longer wheelbase does everything slower, takes longer to get crossed up, and takes longer to transfer weight. Making your car longer will bias some weight to the rear but the advantage would be greater if you keep the wheelbase stock and move the engine back by the same percentages.------------------
No matter what's happening, there's always somebody that takes it way too seriously.
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jsracingbbf
Gearhead Posts: 1217
From: Batesville,MS. , U.S.A.
Registered: Mar 2002
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posted 04-28-2002 03:31 AM
Larry,
Motor is already WAY back as far as it will go. #1 plug was even with spindle. we were going to put it back the same OR even further behind the spindle if wheelbas was slightly longer.
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Larry Jennings
Gearhead Posts: 540
From: Redwood City, Ca. USA
Registered: Apr 2000
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posted 04-28-2002 04:27 AM
Slower weight transfer is the only theoretic downside to making it longer, and at a whopping 2" increase I'm not sure you'll ever be able to see a big change for the good or bad. How'd it get into the rail? Was it witchy or did something help you turn it?------------------
No matter what's happening, there's always somebody that takes it way too seriously.
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jkilroy
Gearhead Posts: 1636
From: Vicksburg, MS
Registered: Dec 99
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posted 04-28-2002 10:06 AM
A longer wheelbase does track better at high speeds, no matter the location of your engine. If you are rebuilding the front end and have the room I don't really see any downsides.------------------
Jay Kilroy
68' Fastback GT 390
"No such thing as a cam thats too big"
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jsracingbbf
Gearhead Posts: 1217
From: Batesville,MS. , U.S.A.
Registered: Mar 2002
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posted 04-28-2002 11:05 AM
Larry,
Rear springs ( coilovers ) were too stiff is what I am thinking. Plus I wasn't running enough caster in the front end. I could only get about 2 degrees.
Jerry
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kid vishus
Gearhead Posts: 3894
From: middle of NC
Registered: Oct 2000
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posted 04-28-2002 11:30 AM
Here's my opinion, it seems like the guys who build tube chassis cars like to extend the wheelbase, especially if the car has a four link. One buddy who had a 2000 Firebird bodied tube car last year is just finishing a '63 vette bodied car for this year, (should run 5 teens) and the wheelbase on it is 120", and I'm sure a stock vette didnt have that much wheelbase. Plus he moved his motor forward 4 inches per Jerry Bickels' suggestion. So, I guess what I am saying, is I see no reason why 2" should have any negative affects on the car.
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Larry Jennings
Gearhead Posts: 540
From: Redwood City, Ca. USA
Registered: Apr 2000
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posted 04-28-2002 01:54 PM
I think if you had a 4 link that put the instant center ahead of the motor on a chassis that worked with the horsepower assigned to it you would be quicker with the motor forward because you could use the motor weight through it's horsepower to plant the car and then sorta move the motor off the rear to loosen the car up and carry the motor weight more on 4 wheels for the charge, by setup.
I'm more interested in the front end and all the mistakes we see that take an otherwise killer car and make it a nightmare to drive. If you get some wood or heavy cardboard and make a working model this "principal" is gonna be easy to see. The front of an everyday car has "Ackerman". This is what makes the car turn soft and smooth so you don't spill your coffee. And it is well known we don't want Ackerman in a racer because it turns the front wheels in different directions! The big mistake you'll see on drag cars a bunch is what I call anti Ackerman, that's when the tie rod mounting points are moved too far in on the front or out on the rear of the spindle which causes the outside wheel to try and push the front into a turn and makes the car tippy, this in turn causes the driver to run into things trying to keep the rubber side down when the car is crossed up and the crew (most of which don't drive) to say the driver is a dolt because they can neither see or feel the tip. Butcher and I watched a Pro Stocker roll at about 30 MPH from this very thing.
So get some material and make a model axle with wheels and move the mounting point or spindle steering arm in and out so you can see just how mild to wild you steering can get, and then go about making your front wheels remain parallel lock to lock. Sorry bout the long windedness but the reason I know this is because I got it way wrong once  . ------------------
No matter what's happening, there's always somebody that takes it way too seriously.
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jsracingbbf
Gearhead Posts: 1217
From: Batesville,MS. , U.S.A.
Registered: Mar 2002
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posted 04-29-2002 12:36 AM
Larry you wrote "The big mistake you'll see on drag cars a bunch is what I call anti Ackerman, that's when the tie rod mounting points are moved too far in on the front or out on the rear of the spindle which causes the outside wheel to try and push the front into a turn and makes the car tippy,"
Ok what is Ackerman? Is this like Bumpsteer? And what turns? I only want to make 5mph turns. Tie rod mounts are in the same place a regular mustang 2 set up is. It is a A Arm style front with tubular upper and lower control arms. It utilizes a standard mustang 2 type rack and pinion and spindles. The entire front end can be seen in the frames section at www.autoweldchassis.com Larry I thought if the tie rod ends were mounted too far in that would be considered "toe in " ?
Jerry
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Larry Jennings
Gearhead Posts: 540
From: Redwood City, Ca. USA
Registered: Apr 2000
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posted 04-29-2002 04:12 PM
The turns I'm talkin about are the ones you sometimes have to make under power to keep it between the walls .
The Ackerman principal is, if we drew a sketch looking down on a frame with wheels and axles, and then drew 2 lines (one each side front to rear) from the pinion nut across the spindle pivot center, the line forms a V and the line crosses the mounting point for the steering arms or tie rod ends. The points would be closer to the center of the car than the spindle pivot if it has the steering behind the front wheels or wider if it's a front steer.
With all this in place the inside wheel (left wheel on a left turn and vice versa) will turn more than the outside wheel (right wheel on a left turn) this pulls the front of the car gently into a turn, this is the Ackerman principal.
However if the car is under power and that power is enough to bring the car around this Ackerman will have the front wheels pointed in 2 different directions and the rear will find it's own way, this is called "outta control" .
Since each car has its own length and width this principal is not a set formula that you can move the arms, say 1 3/4 inch in or out for all cars.
Some chassis builders will just mount the steering arms where they fall and many times "where they fall" is the other side of this Ackerman principal (anti Ackerman?) so the inside wheel turns less than the outside wheel and the outside wheel tries to go under the car and it feels tippy (which it is) so the only right way to have the car steer straight without Ackerman is to map the front in the shop (I map mine with a plywood template so I only have to build one set of spindles, arms and tie rods after I get it figured out). It is a lot of head scratching and figure scribbling but it only has to be done once and the car will drive super great.
PS I don't know that Ackerman is spelled right here. And this principal can be looked up at a library and might be much clearer than I can describe it. ------------------
No matter what's happening, there's always somebody that takes it way too seriously.
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jsracingbbf
Gearhead Posts: 1217
From: Batesville,MS. , U.S.A.
Registered: Mar 2002
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posted 04-30-2002 02:20 AM
I am still clueless, but I am thinking the good folks at Autoweld would not have a bogus front end out there on all the drag cars they sell front end kits for. This thing came factory welded all I have to do is weld it to the rear frame? They bassiclly mimic a Mustang 2 factory set up. Heck even I cant mess this up. ( I hope ) Anyway thanks for the lesson on Ackerman. Put me down for a D minus.
Jerry
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Larry Jennings
Gearhead Posts: 540
From: Redwood City, Ca. USA
Registered: Apr 2000
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posted 04-30-2002 02:36 AM
I did not mean to insinuate "Autoweld" is peddeling an inferior product, knowingly or otherwise. ------------------
No matter what's happening, there's always somebody that takes it way too seriously.
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Just Strokin
Gearhead Posts: 754
From: Tuscaloosa, Alabama
Registered: Dec 2001
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posted 04-30-2002 07:17 AM
On my old 86 Tbird, I increased the wheel base 2 inches. And also had one side closer to 2.5", to give more roll out. The car never twitched from day one while running 5.80's at 124 in an 1/8. Never did get the 4link right since never had any help at the track. Tuff running a fast car with no help.You run into the bump-steer problem when you mount your rack/pinion too high or too low...or the mounting point on the spindles is too high or too low with a stock draglink/tie rods. Bump-steer causes the wheels to toe-in or toe-out as the front a-arms travel thru their arc, i.e., the chassis rising on acceleration or nose diving on braking. This a-arm arc is out of sync/alignment with the inner tie rod mounting point. Ask TomP about his buddies car and this problem. A great book to get is Dave Morgan's Door Slammer handbook. A lot of info in it to digest, but once you do, it explains a lot of things you were wondering about. By the way, when Dave wrote columns for National Dragster, I wrote in and asked him about a 4 link setup on my Tbird. He had the question in his article and said it was not uncommon to have the instant center of a 4 link in front of the front tires and even underground. If you do plot the IC's of your 4link, anything about the 'neutral line' will cause the rear end to lift, anything below the 'neutral line' with plant the rear end. A good set of 4 pad weight cales is sometimes worth their cost when setting up a car. [This message has been edited by Just Strokin (edited 04-30-2002).]
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jsracingbbf
Gearhead Posts: 1217
From: Batesville,MS. , U.S.A.
Registered: Mar 2002
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posted 04-30-2002 08:15 AM
My car is a ladder bar set up. The tracks around here aren't very good except for Memphis and Hattiesburg. Also I agree about Dave Morgan's book. I have a copy. I originally was wondering about wheel base. The rack is mounted ahead of the spindles same as stock location for a mustang 2. Also Larry I didn't think you insulted Autoweld. I thank you for trying to inform me.
Jerry
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Larry Jennings
Gearhead Posts: 540
From: Redwood City, Ca. USA
Registered: Apr 2000
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posted 04-30-2002 01:15 PM
Bump steer is a whole nuther subject, not even related to Ackerman!------------------
No matter what's happening, there's always somebody that takes it way too seriously.
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jsracingbbf
Gearhead Posts: 1217
From: Batesville,MS. , U.S.A.
Registered: Mar 2002
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posted 04-30-2002 11:55 PM
Larry, you will be glad to know that I got out my old Dave's doorslammers book and blew the dust off of it. Yes, I read all about Ackerman and bumpster. You can now re-test me and I should make an A or B. I also checked my car the way Dave explained, and also called the chassis manufaturer. It was made with the outer tie rod ends and lower control arm parrallel to help prevent bumpsteer. The suspension has a small amount of Ackerman built in to help steer at slow speeds. Mr Morgan says to reduce tire scrub. According to Dave "Some racers feel it improves responsiveness to steering input during an evasive situation, but tire compliance or slip angles overcome most of this effect. He goes on to say that "bumpsteer" is a much more common problem and easier to occur. He writes that "bad" Ackerman can be attributed to racers mixing up rear steer racks and boxes with front. Since mine is an off the shelf front steer " just like a Mustang 2 " I should not have any trouble with Ackerman. I hope. Thanks for making me look this up!
Jerry
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Larry Jennings
Gearhead Posts: 540
From: Redwood City, Ca. USA
Registered: Apr 2000
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posted 05-01-2002 12:00 AM
Put yerself down for an A+! I didn't know Morgan covered it. But I do now. Thanks .------------------
No matter what's happening, there's always somebody that takes it way too seriously.
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steve'66
Gearhead Posts: 5659
From: Sonoma,CA,USA
Registered: Mar 2000
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posted 05-01-2002 12:03 AM
Jerry,
Larry is a Guru!
I'm very glad to have had his personal assistance over the last couple years, along with Butch.  They really know what they're talking 'bout.
SteveW
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Larry Jennings
Gearhead Posts: 540
From: Redwood City, Ca. USA
Registered: Apr 2000
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posted 05-01-2002 01:22 AM
Thanks Steve I think, aint a guru one of them weirdo's that sits on a hill pondering the meaning of life?
------------------
No matter what's happening, there's always somebody that takes it way too seriously.
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Just Strokin
Gearhead Posts: 754
From: Tuscaloosa, Alabama
Registered: Dec 2001
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posted 05-01-2002 10:04 AM
I knew the two weren't related Larry. And as was stated later that bump steer is a more common problem than Ackerman is why I broached the subject.
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steve'66
Gearhead Posts: 5659
From: Sonoma,CA,USA
Registered: Mar 2000
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posted 05-01-2002 10:30 AM
quote:
Originally posted by Larry Jennings:
Thanks Steve I think, aint a guru one of them weirdo's that sits on a hill pondering the meaning of life?
Yep, Like why are we forced to run Petro-fuels instead of alky in our street cars?
SteveW
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Larry Jennings
Gearhead Posts: 540
From: Redwood City, Ca. USA
Registered: Apr 2000
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posted 05-01-2002 01:37 PM
OK Steve! So I am a weirdo, but I don't sit on no hill .
Strokin! What can I say? Sometimes I read a post and miss the whole point .------------------
No matter what's happening, there's always somebody that takes it way too seriously.
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n2oMike
Gearhead Posts: 1367
From: Spencer, WV
Registered: Jan 2001
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posted 05-01-2002 02:03 PM
I'll give another recommendation for Dave Morgan's book, "Doorslammers". He lives here in West Virginia, and I attended a couple of his chassis seminars. He definitely knows his stuff. The book costs $30, and is well worth it! He pointed out a few typos in the first edition... but, I'd have to look at my notes to be sure what they were. He sure did stress shock tuning in the seminars.Larry, you know so much more than most of us about suspension systems, that to us, you are indeed a guru. Larry mentioned Ackerman, but to put it in the simplest possible terms... Both front wheels don't move the same amount when the steering wheel is turned. The linkage is designed to make the inside wheel turn further than the outside. If the outside wheel turned MORE than the inside, it would try and tuck the outside wheel up under the body and make the car want to roll over. (feel tippy) Get it? Good Luck! ------------------
Mike Burch
66 mustang real street
302 4-speed 289 heads
10.63 @ 129.3
http://www.geocities.com/carbedstangs/cmml_mburch.html
http://www.fortunecity.com/silverstone/healey/367
http://www.mustangworks.com/cgi-bin/moi-display.cgi?220
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Butch Jennings
Gearhead Posts: 534
From: California
Registered: Apr 2000
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posted 05-01-2002 03:20 PM
quote:
Originally posted by n2oMike:
If the outside wheel turned MORE than the inside, it would try and tuck the outside wheel up under the body and make the car want to roll over. (feel tippy)
You would be amazed at how many tube cars do this, I've seen more cars wrecked or nearly wreck do to this alone. Larry drilled me with "The Akerman Principle" until I was ready to puke! Once I started looking a little closer at "pro built" cars, I realized that this is a big problem. Most chassis guys I've talked to about it say something to the effect of "you don't have to worry about Akerman in a car that goes straight"....that's if they even know what I'm talking about when I mention Akerman. But then we know that a fast drag car doesn't always go straight, at least mine doesn't....I guess that doesn't count to these guys. "Drag cars go straight....PERIOD!!!" A pretty ignorant attitude if you ask me. ------------------
Butch
460 powered 1967 Comet Cyclone
10.271 @ 130.069
Butcher's Home Page
"Friends don't let friends drive Chevys"
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n2oMike
Gearhead Posts: 1367
From: Spencer, WV
Registered: Jan 2001
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posted 05-01-2002 04:58 PM
Some might ask... "Why does the inside tire need to turn more than the outside one?"Well, picture the car driving in a circle... The inside wheels turn in a smaller circle than the outside, so to avoid the tires skidding (scrubbing as some say), the inside tire MUST move more when the steering wheel is turned. If both front tires turned the same amount when the steering wheel was turned, the INSIDE front wheel would try and tuck under the front end, making the car want to roll over. (get tippy) Positive ackerman (the inside wheel turning more than the outside) is a GOOD thing. There's a LOT to a proper front suspension and steering linkage system. Do your homework. Good Luck! ------------------
Mike Burch
66 mustang real street
302 4-speed 289 heads
10.63 @ 129.3
http://www.geocities.com/carbedstangs/cmml_mburch.html
http://www.fortunecity.com/silverstone/healey/367
http://www.mustangworks.com/cgi-bin/moi-display.cgi?220
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