LegendsRacer - Legends & Bandolero Racing Forum
LEGENDS => Drivetrain & Gearing => Topic started by: DARK AGE 53 on May 22, 2007, 03:53:40 am
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Anyone know?
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2.5°-3°
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Hi Al,
Are you asking about the actual pinion angle, or the angle of the top link? I'm getting ready to mount my rear end and am also curious.
Dwarf Car Technology, by Steve Smith, recomends the top link be 7 to 10 degrees.
" The upper link should be angled downhill (towards the front of the car) at a seven-degree to ten-degree angle. This promotes good traction without the problems associated with rear end lightness and wheel hop. On a Dwarf Car, with the rear pivot point of the upper trailing link setting 9 inches above the axle centerline, a 7-degree downhill angle creates 21 percent anti-squat. A 10-degree downhill angle creates 28.5 percent anti-squat."
(page 52 in my book)
Most of the info in the book relates to both Dwarf and Legends Cars. Not a lot of difference that I can see. Legends Cars have stricter rules governing what parts must be used.
Hope this info helps.
My best to you this season.
Steve
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2.5°-3°
Thanks for the info, I was at less then 2.5 so I turned the top link to get me closer to those numbers.
Hey Steve, Good info also, I marked the top link just in case I need to turn it back some.
What gear are you installing, it looks like people have anywhere from two to three different gears for there cars.
Regards,
Al
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Steve, I can't figure how I could change the 3rd link angle. On my car, the lollypop and the 3rd link bracket on the rear end pumpkin are not adjustable. All I can do is alter the length of the rod, which changes the angle, but only slightly.
Al, it is important that you check the squareness of rear end when you change the third link length. You have to get the angle right AND get the axle square. That is often a tricky thing .
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Al, it is important that you check the squareness of rear end when you change the third link length. You have to get the angle right AND get the axle square. That is often a tricky thing .
Tom, Why would adjusting the upper rear link affect the axle squareness , I could see if you adjusted one of the trailing arms it could affect the squareness of the axle. Thanks.
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Hi Tom,
The front mounting bracket has several different holes, so can be adjusted up or down. This is on a Dwarf, with a solid top link. I wasn't sure if the Legends ran the same set up. I was looking at the pic on www.littleracecars.com. Looked like similar set up as mine.
Sounds like your set up works slightly different. I would think that the principle is the same, moving the pinion angle either up or down.
I'd like to get a better look at the Legends Car suspention, both front and rear. Unfortunately, up here in Montana, I don't get to see many Dwarfs or Legends Cars. The few Dwarf Cars I've seen here use very crude leaf springs in the rear. Probably not legal anywhere. I heard that they race Legends Cars in Kalispell, but that's a 4 hour drive from where I live. I started building my car when I lived in Nebraska. What I'll most likely do is run SCCA autocross. Not too many options for me right now, unless I can get the local track interested.
I do appreciate this forum; as I get some great ideas, as I continue my build. I try to share what I can. If it helps Great! If not, Sorry! Don't want to upset anyone.
Best of luck to all this season.
Steve
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Hey Steve,
I'll take a bunch of pics today of the front and rear suspentions and e-mail them to you later.
Al
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Al,
Thanks for the pics. !!!
I'm guessing Tom is using a rubber torque link. My set up is similar to yours except for the front mount has multiple mounting holes. Either way, as you shorten the link, the pinion angle moves downward and the rear of the link move upward. The rubber doughnut would allow the angle to change slightly during acceleration and brakeing.
I do have one of those rubber torque links also. Do you think it is the better compromise between acceleration and brakeing? Sounds reasonable.
Curious,
Steve
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I'm not exactly sure why, but I measured it, so I know it is happens.
Here is my explanation. May be right, may be wrong.
As you alter the third link length, it twists the axle housing, which changes the angle of the radius rod bracket on the bottom of the axle to lean toward, or away from the radius rod lollypop on the chassis. That changes the distance between the centerline of the axle and the lollypop. If you have different radius rod lengths or angles to begin with, it will effect each side a little differently. It is the same as changing radius rod lengths. When you change them, you are changing the arc of travel and effecting the rear steer of the car. I am VERY particular about knowing the squareness of my car's rear end.
How much or how little these things will change and the magnitude of their effect is something that I do not know how to calculate. I probably could if I really wanted to, but I'm still dealing with bigger fish with respect to setup. I do know, however, that my son can tell when I change the RR radius rod length by as little as 1/2 of a turn. You can see it on the clock and you hear about it when he comes off.
Thanks for the explanation Steve. Your info and insight has me questioning things, and that is what I need. I'm not going to learn a darn thing doing everything the same way over and over.
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Al,
Thanks for the pics. !!!
I'm guessing Tom is using a rubber torque link. My set up is similar to yours except for the front mount has multiple mounting holes. Either way, as you shorten the link, the pinion angle moves downward and the rear of the link move upward. The rubber doughnut would allow the angle to change slightly during acceleration and brakeing.
I do have one of those rubber torque links also. Do you think it is the better compromise between acceleration and brakeing? Sounds reasonable.
Curious,
Steve
Steve,
I must be missing something here, what rubber doughnut are you talking about...the only doughnuts I know about are the dozen glazed doughnuts I bought today. BTW, I'm sure my doughnuts taste better then any rubber doughnuts also. ;D
Al
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I hear ya on that glazed doughnut ;D
I think it called a biscuit bar. It's similar to your upper link, but one end has hard rubber doughnuts. somewhat like a strut or lower control arm brace on a street vehicle.
Doughnuts, Biscuits .... I'm getting hungry! ;D
Steve
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The angle of the third link is very important, I was getting into a 4 wheel drift in the middle of the corner because I had to little angle on the third link, moving the angle to be more down towards the from of the cars stop the rear end from lifting under braking and keeping me planted to the track with on the brakes hard, beware that to much angle will rob horsepower because it put the driveshaft in a bind, I measure mine from the distance from the frame rail to the u-joint, nothing closer than 1 and 1/2 inches.
Later boys,
Mike
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Mike, what you are describing is the pinion angle. What was confusing us was Steve's description of the third link angle change. In other words, the angle of the aluminum bar. Since, on a Legends car, the third link mounting brackets are in fixed positions, the angle only changes based on length adjustment, which is not as substantial as it would be if you could change the height of the lollypop on the chassis or if the bracket on the rear end pumpkin had several holes from which to choose.
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You guys are making this too complicated. get a smart tool (digital level) or an angle finder. put it on the bottom of the third member (rear end gear) with the car on a level surface. Get it close to 2-2.5 degrees. after you get this correct, do as admin said and recheck square. It should not have moved unless you have a bent heim or mounting tab onthe housing, but it is good to check, since almost everycar has a slight variation.
As far as the top link, whatever it takes to get the pinion angle you need is where it should be. Legends have fixed mounting points so you can't adjust it other then lenght.
Brad
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I use a smart tool (digital angle finder) exactly as you described. It also works great for setting caster and camber.
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Something to keep in mind, when adjusting the third link you are rotating the rear end, this also will change the wheel base length and can also effect the frame heights in the rear of the car.
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Something to keep in mind, when adjusting the third link you are rotating the rear end, this also will change the wheel base length and can also effect the frame heights in the rear of the car.
I didn't find any difference in wheel base length after I adjusted the angle, it seems the rear trailing arms would prevent that from happening. JMO
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When you adjust the third link it rotates the rear end on the lower trailing arms attach points which are two inches lower than the axle tubes and are stationary so the wheel base will change + or - depending on your pinion angle. Also when the rear end is rotated the lower shock mounts move higher or lower when measured from the ground which will effect your frame height. Granted the change will not be great and you may need a tape measure to see it but if your running close to the limits and make an adjustment at the track you could end up DQed in tech. Something else, if you change your wheel base length guess what it does to your pinion angle?
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My Guess is that if you increase the wheelbase and don't touch the third link, your pinion angle will increase and if you decrease your wheelbase it will decrease your pinion angle.
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Heh, bringing a topic back from the dead :)
Rotating the pinion up or down is really just a reference point. By reducing the length of the upper links, you are affecting what is known as Antisquat. * hey, i see you snickering over there.. * This is a very important term in suspension dynamics. antisquat or AS, is when the rotational force of the axle is distributed to the suspension. When you take off in a legends and have really good traction, the ass end sags down a little, the nose picks up and you take off like a starwars ship jumping to hyperspace ;) . The ass end squats down because all that rotational force has to find the best path to travel. This is into your suspension, then your frame THEN to the road.
The pinion wants to rotate down with that twisting motion, with pulls on the links, with makes the car squat.
The trick is to turn this into traction.
A lower pinion means shorter upper links. Less squatting. More power to the ground. This can cause hopping, due to the axle pushing itself to the ground. Best setup for low traction like dirt tracks.
Higher pinion, longer upper links, less power to the ground, less likely to hop under throttle. But, there is less bite. This is better for pavement where you have gobs of traction.
A good all around figure is about 80% Antisquat. Our cars, are about 83% to 95% according to what I can see.
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I sniggered really quietly. You shouldn't have heard me. You spying on me? This 'puter have spy stuff on it?
Good explanation.
Mike
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One question Pegalis...
How do you translate % of AS to degrees of pinion angle?
Thanks,
Mike
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Mike,
Your going to love this!
"The angle of the upper link in a 3 point system has a very important influence on the performance of the chassis under braking and acceleration. If the upper link is mounted at a downhill angle towards the front of the car, this will promote more anti-squat under acceleration. This means the rearward pitching moment of the car under acceleration is reacted by the mechanical leverage of the suspension arms and thus causes additional downforce to be placed on the rear tires. However, the drawback of this is the opposite and equal reaction under braking. A large amount of anti-squat (downhill angle of the upper link) will cause rear end lightness and and rear end hop under braking The more downhill angle of the upper link, the more severe the problem will be.
An uphill angle of the upper link will promote good firm traction of the rear wheels under braking. But, it has a big drawback under acceleration - It promotes pro-squat, which lifts the rear wheels up under acceleration and diminishes traction.
The answer is a compromise.................."
Source: "Dwarf Car Technology" by Steve Smith
I could get out several of the other books on suspension theory and design; But I think that explains it pretty well.
Simple physics; "For every action, there is an opposite and equal reaction."
Tell You What I'm Gonna Do - ;)
I'm gonna buy you the book and send it to you, in exchange for that right front spindle.
Sound Fair?
Steve
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That's a beauty and I love the trade idea. Not to forget though that Inex Legends don't allow you to change the angle of the upper link. One mounting point, not variable mounting points.
Shortening and lengthening the upper link will change the pinion angle, but how does +3 degree angle translate into Percent of AS?
Mike
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My Guess is that if you increase the wheelbase and don't touch the third link, your pinion angle will increase and if you decrease your wheelbase it will decrease your pinion angle.
Read all the posts in this thread. There is some Great info and insite!
True;
My suspension will have multiple mounting points. NOT Legal for the Legends Cars.
Think about how changes to the lower links, or upper link, change the angle. Even if only slightly. ;)
Steve
PS.
I'll get on that book for you.
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Ah, but you are moving the link mount when you change the pinion angle. Drop the pinion, and you have just moved the upper link pivot point on the axle forward, and the lower backward. Reverse for upping the angle.
On a long WB car, this 1/2" of pivot location adjustment would do little. But on a short WB car, with short suspension links, its a world of difference.
The shorter the suspension links, the less adjustment is needed to see results.
A good example: Take a drinking straw. Loosely grip one end with your thumb and index finer, about 1" from the end. Now pivot the straw from the long end with your other hand, and note the distance the short end moves in relation to the long end. For every 1" of movement on the long end, there is only 1/8" on the short end. Now, do the same thing, only pivot the straw from about 1" away from your other fingers. now, its suddenly 1/8" to 1/8" relation.
Long links, bigger adjustments. Short links, little adjustment.
Mind you, the percentage you can get from our suspensions is only + or - 6 or 7%. But that 6 or 7% can be the few needed seconds on the track you need to win!
As for calculating the % of AS on our chassis, I have fabricated enough custom 3 and 4 link suspensions to get a good feel for it just by looking at the link locations in relation the the axle and frame.
If you want, ill dig up the numbers and calculations and get some exact figures for you.
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That would be great Pegalis. Just trying to wrap my mind around the geometry of the linkages so I can think through what advantages I can get from adjustments. It's one thing to read what everything does and remembering it, but another thing entirely to truly understanding it. If I can understand it properly, I can make changes much easier to effect the results I want.
Mike