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70/30 Racing
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nice information, way to start out your posting here with a bang.

ditto for the roll center. i didnt think it was as much of a problem with our cars as it is, with say, mustangs. you can definetly see the conrtrol arms sitting at an angle to the ground with it lowered about 2-3", one of the reasons i dont lower my car too much (the other being the axles).
 

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Always Different !
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In addition. if you flip the steering end over you do loose the taper, however this is easy to fix. Go to the machine shop type sales outlets and get yourself a 3/8 to 5/8 inch 8 degree tapered reamer with a 3/8 or 1/2 inch shank. Remove the spindle and using a hand drill you can reface the taper. be careful though as if you get greedy with the drill it bites hard and can break you wrist. Even better if you do it in a propper press and vise. Do not try to cut the full taper depth because you will end up boring out the spindle as the tapers meet from opposite ends. Just bet about 1/4 to 5/16 deep into it and the steering end fits just perfect with no problem and full thread engagement.
The ultimate would be to tune the bump steer out with spherical rod ends, but there is a catch to this. The thread on the end of the sentra steering rack arms is a metric bastard and you will find it difficult to get a tap to make the adapter for the rod end. The other thing if you go this way is that the male rod end plus an adapter becomes too long an assembly and if you insist on going this way you have to shorten and re-thread the arms.
If you can, shorten the rack on both ends by an equal amount, this would give less vertical movement of the ends relative to the same degree of movement. You would then need to use longer arms on the rack and you could fabricate the spherical rod ends into the assembly for the perfect race set up.
The numbers I quoted are relative to a 4.5 degree camber on left and 4 on the right. Cannot remember the caster settings.
Obviously not reccomended for the road.
bigtoe
 

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Discussion Starter · #43 · (Edited)
bigtoe said:
When the car is off the ground it looks freaky because it toes out like crazy.
Yeah, we noticed this on Jeff's car. On the lift it looks like 3 or 4 inches of toe out. I was like "Gaaah, that doesn't look right", but then magic happens. :)

Good info. We're going to flip it to the underside and use a new joint so we can space it even lower and measure the bump steer. One of these days, but I need to work on the NX first... still one race left this season.

bigtoe said:
The ultimate would be to tune the bump steer out with spherical rod ends, but there is a catch to this. The thread on the end of the sentra steering rack arms is a metric bastard and you will find it difficult to get a tap to make the adapter for the rod end.
That's our plan. I think the rod is 12x1.25 or maybe 14. I'm just going to take it out to a machine shop to get done. I think it will be cheap to make a sleeve with 12 x 1.25 on one end and a standard size on the other so we can just grab off-the-shelf rod ends that are available everywhere. Then you'll just need to hone out the spindle (probably 5/8ths) and get a long bolt with some spacers to you can move things around. Kinda like this:

 

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Always Different !
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The 12x1.25 is a very close match. But when it's tapped out and you screw it on you get some slop on the thread. When you start tightening the back up nut it feels like its going to push off the sleeve. It may be worth checking the English UNF range of threads for the correct fit. The Japs sometimes use UNC and UNF for critical threads. I have a set of those spherical rod ends in my tool box for this same reason, mines are blue with 1/2in rod ends.
Got some realy good suspension mods and designs if interested.
I have DMS 50mm Giants back and front, complete chromoly tubular front and rear control arms and parallel links with rod ends on both inboard and outboard ends, including the the lower ball joint. Tricked out adjustable ball joint height adjustment and scrub radius adjustment. Camber plate sits ABOVE the apron on top of 1in spacers (like the WRC Rally Cars). Back strut tops are pillow ball as well. Trailing link torsion bar with additional stabiliser bar on rear end, works in conjuction with the parralel arms and allows full range of motion with adjustable toe, camber and bump steer as well.
I run a 98 B12 chassis. "The ultimate home built Sentra Race car" all built, designed, tuned, wired, maintained by myself.
If interested you can log onto http://www.fastbrakes.com. look at the 1991 B13 front brake upgrade and there is a photo of the car. One sweet N/A 53J DET motor as well.
bigtoe
 

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Discussion Starter · #45 ·
bigtoe said:
I run a 98 B12 chassis. "The ultimate home built Sentra Race car" all built, designed, tuned, wired, maintained by myself.
If interested you can log onto http://www.fastbrakes.com. look at the 1991 B13 front brake upgrade and there is a photo of the car. One sweet N/A 53J DET motor as well.bigtoe
Looks great! http://www.fastbrakes.com/images/photos/On Trailer3.JPG

What do you race it in? Do you have more pictures of the suspension mods you've done?

My main concern is getting something that is easy to do for the SR cars- which means opening the rules since you're not allowed to modify anything as it is now. We'd like to keep costs low, so that means doing the minimum required to fix the problem.

But I'm interested in what you've done because Jeff's car is in the unlimited class. You can see it here: http://buckfang.com or in the August Sport Compact Car magazine. You and Jeff must have been brothers in a past life since he's done all of the build on his car, too. :)
 

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Maybe Jeff will chime in on these threads, more minds, more ideas, more speed!!. I too have a custom ratio PAR gear set, but had a problem with the vertical alignmnet of 2nd through to 5th gear. It's back at PAR as we speak, but due back in about two weeks. I run a 16plate 60 degree 1.5way LSD unit in place of the OEM VLSD. Also have the clutch actuated by a pull type hydraulic cylinder on custom brackets. Which transmission is Jeff running, the 8 hole crown wheel LSD or the 14 hole LSD. 18 or 24 spline input shaft. PAR say that they have never seen my transmission model with the 14 hole LSD. It's JDM and I do not know if it was ever exported, at least not to Australia.
Just about to upgrade to a custom Z10 Motorsports dry sump system on the motor as well.
Do you know anyone who has played with the JWTC6M Cams, I'll have them next week and want to try them in place of my Tomei iron.
I can share photographs but would have to go to personal e-mail for that........newbie and all, do not know the ropes on the site yet.
[email protected]
 

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bigtoe said:
The problem here is that as the cradle flattens out the instantaneous roll center moves closer to the cg in the horizontal plane and higher off the ground in the vertical plane.
Um, the roll center moves downward when the car is lowered. I havent plotted it but it probably moves downward less quickly when lowering the car than the CG so the roll couple and the roll moment are reduced not incresed.
 

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"The problem here is that as the cradle flattens out the instantaneous roll center moves closer to the cg in the horizontal plane and (LOWER TO) the ground in the vertical plane."
Well spotted choaderboy2......... BUT.
I am talking about the Instantaneous Roll Center, not static Roll Center. As the suspension geometry moves the Roll Center is useless. In very simplistic terms if the IRC is above the CG in the vertical plane it is harder to roll than if it were below the CG. Agreed the CG needs to be low, but again if the geometry is compromised by the IRC going below the ground (as it does when you allow the cradle to go acute, or point up) then the car wants to roll over as weight is transfered laterally by an amount prportional to the height of the CG above the IRC and the distance away the IRC is from the CG. Some trigs and it's fairly easy to calculate.
If you draw a line perpendicular to the strut centerline and extend it till it touches the road surface, then draw a line through the cradle until it intersects the first line then you can see that the IRC would go lower to and then below the ground as the cradle moves upards, BUT it does move outwards which is good. If you have the cradle pointing downward the intersection point is higher off to start with and moves outwards and downward as the suspension rolls....a better position to start out with.
The other thing is that as the cradle points downward from the chassis you get negative camber gain (good) on bump/roll, the opposite when the cradle is parallel or points upward (very bad). The Mc Phearson or Chapman Strut is a wonderful cheap package for the OEM to produce a simple suspension system, but it is poor at maintaining satisfactory geometry in a performance application. Hence Honda's use of a psuedo double A-Arm set up and higher end sports cars use real double A-Arm set ups.
Slam a stinking fast sentra on good shocks and springs with good rubber and let it loose behind buckfangs SER on some twisties, watch it understeer, scrub out, wobble and twist, bounce and misbehave as buckfang's high rise rocket walks away. No disrespect intended, just looking for a good basis to compare.
 

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bigtoe said:
I am talking about the Instantaneous Roll Center, not static Roll Center. As the suspension geometry moves the Roll Center is useless. In very simplistic terms if the IRC is above the CG in the vertical plane it is harder to roll than if it were below the CG. Agreed the CG needs to be low, but again if the geometry is compromised by the IRC going below the ground (as it does when you allow the cradle to go acute, or point up) then the car wants to roll over as weight is transfered laterally by an amount prportional to the height of the CG above the IRC and the distance away the IRC is from the CG. Some trigs and it's fairly easy to calculate.
Please explain IRC to me. To me the IRC is where the roll center ends up dynamicaly as the car rolls. I think you are discribing the instant center of the suspension which is different from the roll center. To find the roll center of a strut car you must first plot the IC on both sides by the way you describe and draw a line through them parralel to the ground. Where this line intersects the vertical line drawn through the CG to the ground, this is the roll center. The distance between the two is the roll couple or the lever arm that the CG works on the RC to create a torque couple to roll the car over.

As a car is lowered, the IC and also by effect the RC gets lower. If the IC is too low, a large roll couple is produced as well as a loss of negative camber under roll. If its too high, the roll couple is reduced but a jacking effect can be produced, a la corvair or VW where the car can actualy flip.
 

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Right you are. What I describe as the IRC is what you think it is, but in roll. The behavior of the leverage forces acting on the CG in parallel (left and right) bump or re-bound will move the IC in an arc described by the radius of the lines of intersection. This is what you are describing as the car is lowered or raised. The term IRC is used in the texts I have read to describe the movement of the IC as the car rolls. Not only does the IC make an arc, but now it moves laterally either away from or closer to the CG. This happens because the imaginary interseting lines are now changing their point of intersection (also describing an arc) but moving laterally as the strut's included angle to the road surface changes, remember this is why we have camber. As well it moves latterally in an arc described by the radius of the line from strut top to contact patch, and the top imaginary line is always perpendicular to the centerline of the strut. The top and bottom lines on both sides of the car move angularlly in equally opposite proportion (assuming there is absolutely zero tyre and bushing defelction).
This is the advantage of the double a-arm, because by varying the length of the upper a-arm relative to the lower and by setting a "king pin" angle at rest and ride height, you have geometric control of the movement of the IRC within alot narrower range than the strut. With the double a-arm it tries to behave like you describe when the car is lowered or raised (parallel bump or rebound). Alot of texts describe things differently and use loose terms based on country of origin and who knows what else(Brits vs US for example). I would get my mind around the influences of lateral movement of what you describe as the IC and leave it at that. F1 or Indy cars have the IRC located huge distances from the CG in the horizontal plane, in the 80's on F1 ground effects cars they were up to 150 from the CG. Think of trying to roll that.
The corvair and the VW is a bit different. Becasue the angle of the wheel to the road surface (camber) was a function of the very short lever of the drive axle, equidistant from center and fixed at all times, the jacking and massive scrub radius movement is what caused the problems, the longer the axle and the wider the track the less the effect. Thought of another way, it's why the NASCAR guys build long trailing links, it controls a solid back end in the vertical plane by controling arcing of the wheel base axially to the centerline of the car. If it were short the movement would be way more exagerated. Like they do on 4 link drag car rear ends, these exagerate movement and allow the CG to shift axially as the rear end dives, hence their 2 million adjustment points. This is why we go into cv joints and telescoping axles (glenzer spicer etc) on rear ends. The dynamics of the non-turning rear end vertical movements should not be confused with the turning, higher degree of freedom, more complex geometry of the front end. I have not descibed the influences of toe and caster, but these to effect significant changes in the dynamics of the front end, both in parallel movement and equally opposite roll.
bigtoe
 

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Here's a crappy camera phone picture of our tie rods on the mazda 6:



one day I'll remember to have my real camera at work when I've got the wheels off :)

It is a long spacer, but plenty strong. It's been wrecked once already and it just twisted the upright as opposed to breaking the bolt or something. Without a standardized ride height or an easy way for everyone to measure bumpsteer it may not be easy to make a one-size-fits-all solution. I guess it could just provide moderate correction and just be "better than nothing."

andris
 

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note: that is one solid spacer as opposed to a stack of shims. I got it in the ballpark with a big stack of nuts/washers and then shaved the aluminum one little by little in the lathe until it was right on. We do not adjust it once the car is built.

andris
 

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SE-R GREEK
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!!!!

Long it is!!

Chris

PS> Andris, I might be getting a new "family" car if/when it hits our side of the globe and it is your Mazdaspeed 6. DO you have any suggestion of a decent forum/site/list I may be watching to "prep" myself?
 

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choaderboy2 said:
I have been considering making a new subframe that relocates the engine and transmission for better axle angularity, the lower control arms for negative camber gain under roll and a more favorable roll center and a relocated steering rack for less bumpsteer.

I have been talking to Jay Hassigner about it.
It is amazing how such a comment goes unnoticed for days and will soon be lost in this thread when it goes off the screen!!!

So Mike, has there been any progress on the talks?

Chris
 

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I don't. I think there is a site like mazda6tech.com, but I have never been there. Our development is basically done in a vacuum relative to street cars, so I am pretty clueless about the street car internet culture. The Mazdaspeed 6 looks like it is going to be a good deal; it has the same 2.3l 4cyl as the base car, but it is turbo and AWD. original conservative numbers released to the media were 260 hp, but I have info that it will have at least 275 when released, and the pre-prod. cars are at that now. The engine bay is gigantic, so it is a pleasure to work on the 4cyl car.

Ok, back to bumpsteer!

andris
 

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andris said:
Here's a crappy camera phone picture of our tie rods on the mazda 6:



one day I'll remember to have my real camera at work when I've got the wheels off :)

It is a long spacer, but plenty strong. It's been wrecked once already and it just twisted the upright as opposed to breaking the bolt or something. Without a standardized ride height or an easy way for everyone to measure bumpsteer it may not be easy to make a one-size-fits-all solution. I guess it could just provide moderate correction and just be "better than nothing."

andris
Damn Andris is that in single shear? That violates all of the race car fabrication rules I know of. Well you build WC cars and I don't. I would be scared to attempt that myself, more scared of breaking the spindle than shearing the bolt.
 

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hpro123 said:
It is amazing how such a comment goes unnoticed for days and will soon be lost in this thread when it goes off the screen!!!

So Mike, has there been any progress on the talks?

Chris
Jay and I just intialy discussed it. He might get around to this project when he has time. I don't think there will be much interest. Msot Sentra customers are too cheap or don't understand the signifcance of such a part.
 

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choaderboy2 said:
Damn Andris is that in single shear? That violates all of the race car fabrication rules I know of. Well you build WC cars and I don't. I would be scared to attempt that myself, more scared of breaking the spindle than shearing the bolt.
Yeah, I know it looks scary. The spindles are forged and are more prone to just deform than break. Under normal conditions there isn't all that much load on the tie rods to steer the car. When the car gets hit is when you need to worry. It has been hit hard enough to take it out of a race, and it just twisted the steering arm on the upright maybe 5-10 degrees, but didn't break anything. In hindsight, if we had enough spare tires in the hot pits to get the car back out there, we would have just eyeballed the toe back straight and run the rest of the race. We thought we were done so we didn't bother. I guess my point is that in a hard impact, there is plenty of other stuff that can and will fail on any car. On other cars I've seen tie rod failures (the joints), failed balljoints, broken or bent struts, brake rotors separate from hats, failed control arm links, etc. from similar impacts. I feel like the level of risk is no greater than any other component of the suspension/steering system for that type of crash. Any of those will end a race or cause a big accident. One example is last year at Atlanta - Bob Endicott had a minor crunch and kept going. Coming down the hill either a brake or tie rod gave up from the previous impact and he entered the hot pits at speed and went into the wall.

I totally acknowledge that it looks bad from an engineering standpoint. The other option would be to raise the rack, but it would cause a lot of other problems and interference. One other thing to note is that this car is REALLY slammed. Most of the time the spacer would be much shorter.. On the Proteges, there is no spacer - we mount the tie rods on the bottom and adjust bumpsteer with the (small) spacer on the lower balljoint. 6 one, half-dozen the other I guess.

The roundy-round guys have been doing this type of thing for a long time, though I don't know if their uprights are better suited to accept twisting loads on the steering arm. Well I guess not :) I just looked at Coleman, and their generic kit uses the same size bolt (5/8) and is supposed to be for stock Pinto spindles! They use a stack of skinny steel spacer bushings to fine tune bump steer. Not trying to say "well if circle track guys do it, it must be safe!" , just trying to add another data point.

andris
 

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andris said:
Yeah, I know it looks scary. The spindles are forged and are more prone to just deform than break. Under normal conditions there isn't all that much load on the tie rods to steer the car. When the car gets hit is when you need to worry. It has been hit hard enough to take it out of a race, and it just twisted the steering arm on the upright maybe 5-10 degrees, but didn't break anything. In hindsight, if we had enough spare tires in the hot pits to get the car back out there, we would have just eyeballed the toe back straight and run the rest of the race. We thought we were done so we didn't bother. I guess my point is that in a hard impact, there is plenty of other stuff that can and will fail on any car. On other cars I've seen tie rod failures (the joints), failed balljoints, broken or bent struts, brake rotors separate from hats, failed control arm links, etc. from similar impacts. I feel like the level of risk is no greater than any other component of the suspension/steering system for that type of crash. Any of those will end a race or cause a big accident. One example is last year at Atlanta - Bob Endicott had a minor crunch and kept going. Coming down the hill either a brake or tie rod gave up from the previous impact and he entered the hot pits at speed and went into the wall.

I totally acknowledge that it looks bad from an engineering standpoint. The other option would be to raise the rack, but it would cause a lot of other problems and interference. One other thing to note is that this car is REALLY slammed. Most of the time the spacer would be much shorter.. On the Proteges, there is no spacer - we mount the tie rods on the bottom and adjust bumpsteer with the (small) spacer on the lower balljoint. 6 one, half-dozen the other I guess.

The roundy-round guys have been doing this type of thing for a long time, though I don't know if their uprights are better suited to accept twisting loads on the steering arm. Well I guess not :) I just looked at Coleman, and their generic kit uses the same size bolt (5/8) and is supposed to be for stock Pinto spindles! They use a stack of skinny steel spacer bushings to fine tune bump steer. Not trying to say "well if circle track guys do it, it must be safe!" , just trying to add another data point.

andris
Haha, do you have a reamer? Help me make one for the new car!
 
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