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BillyShope
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Posted: Mon Apr 27, 2009 7:10 am |
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Joined: Sat Sep 22, 2007 7:05 am Posts: 88 Location: Orlando, FL
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shrinker wrote: [T]he tyre contact patch is indeed the force exertion point upon the ground BUT it is not the force exertion point into the chassis. The axle centerline is actually the place where the reaction of the tyre contact patch is distributed into chassis. The chassis does not react about the tyre contact patch it reacts about the axle. This is my biggest bone of contention to the books written on the subject. There are other things I think are wrong in the books too but that's a good one to start discussion with. The chassis does not react "about" anything. It reacts to the forces and moments imposed upon it. In this case, it reacts to the force vector at the tire patch as it acts along a line through the instant center. http://home.earthlink.net/~whshopeover 140,000 page views
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BillyShope
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Posted: Mon Apr 27, 2009 7:20 am |
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Joined: Sat Sep 22, 2007 7:05 am Posts: 88 Location: Orlando, FL
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Bubstr wrote: If you are getting compression in the rear, that is a spring storing weight/ energy and not putting it at the tire contact patch. If a spring is compressed, the forces at BOTH ends are changing. There's no need to concern yourself with energy, the compressed spring indicates increased down force on the tires. Weight transfer is always going to find its way to the rear tire patches. There's no way to stop it. It isn't possible to "store" it somewhere as "energy" and extract it later. With 100% antisquat, all the weight transfer is carried through the links. With values other than 100%, compression or extension of the rear springs indicate they are playing a part in the weight transfer. http://home.earthlink.net/~whshopeover 140,000 page views
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shrinker
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Posted: Mon Apr 27, 2009 7:29 am |
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Joined: Sat Feb 07, 2009 4:12 pm Posts: 1215 Location: Adelaide Australia
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Billy; the first column is the gearbox input torque, second is the axle lifting force(the weight that's resisting the torque) you might view it as antisquat, the third is the total weight transfer of the car. It doesnt print out as it is on my spread sheet. If I knew how to do that it would be clear and I could post the rest of the info. Beretta posted the gear ratios etc. It wont resolve to a constant CGH as you go down the rows because the CGH rises as the car moves. As the car lifts, the fourlink geometry changes IC etc.
How do you explain a theoretical car where the rear axle weight is zero, there would be no torque imposed upon the CG by the acceleration inertia of the axle, so in that situation there would only be a forward force imparted to the body at the axle height and a need for axle torque reaction as well. If the rear axle height is above the CGH then explain that please.
Also our car has an instant center of 35.5" and 7.75" high at rest and I dont know anyone with a ladder bar car that short with 870HP and 2385 lbs weight. That ladder bar car would severely jerk off of the line and bounce the tyres etc, yet the fourlink doesnt. We use light resistance shocks too, we dont tie it down with shock resistance. In fact the shocks wore out once and were virtually useless and the car was fine. It was only because of dynoing the shocks before and after rebuild that we found out they were way off. The car is not slow either it 60's at 1.151 (current best). So what gives? I think a fourlink is totally different deal to a ladder bar.
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BillyShope
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Posted: Mon Apr 27, 2009 8:08 am |
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Joined: Sat Sep 22, 2007 7:05 am Posts: 88 Location: Orlando, FL
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shrinker wrote: The reason why I do all the measurements from the ground and from the axle centerline is the axle is the thing that pushes the car forwards and applies a torque reaction that has to be resisted by the four link. The centerline of the axle is where everything starts from. There are 2 places on the car that the physics start from, one is the axle centerline and the other is the crankshaft. I dont mean to upset anyone but I argue that the concept of working out thrust lines or antisquat etc from the tyre contact patch is not correct. The tyre thrust occurs at the axle, thats where the forces come into play, not at the tread. I always find it useful to exaggerate the design or shape of things in order to better understand them So consider this, you take the rear wheels off your drag car and install monster truck wheels. You also install lower gears in the diff so that the final torque applied to the tread is the same as you have now. Then you alter the fourlink so that its still got the same IC. Now who recons that car will launch the same and have the lift etc? As my posts immediately above would indicate, I've been looking back at early posts in this thread. (Bubstr alerted me to this thread long after its beginning.) The post quoted above is particularly interesting. The problem appears to be that Shrinker attributes more intelligence to the chassis than would I. I would maintain that the chassis has no idea where the axle housing is located. How could it when its only connection with the rear axle assembly is either 2 (ladder bar) or 4 (4link) pivot points? All the chassis "knows" is that it is receiving forces at these pivot points. The rear axle assembly is experiencing many internal forces as the car launches. The ring gear teeth are engaging those of the pinion gear, the housing is deflecting, the bearings have increased loads, etc. But, all of these internal forces are canceled (reacted) within the assembly and do not influence analysis. The rear axle assembly's contacts with the outside world are through the shocks and springs, the suspension linkage, and the tire patches. Since the shocks and springs are incapable of lateral forces, it follows that the entire rear axle assembly reduces to a simple link, with one pivot point at the tire patch and the other at the instant center. (For the ladder, the IC would be the pivot point.) The tire patch force vector, then, acts on a line through the tire patch and the instant center. This line is further described as a line of constant percent antisquat. (If the inertial force, generated by the weight of the rear axle assembly, is taken into account, the line of constant percent antisquat passes an inch or so below the rear tire patch.) The preceding comments reflect the views of suspension engineers, established, now, for a century. This is not to say that Maurice Olley...and others of his ilk...could not have been mistaken in all of this, but this should give some indication of the work that lies ahead of you if a century's work is to all be overturned. http://home.earthlink.net/~whshopeover 140,000 page views
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shrinker
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Posted: Mon Apr 27, 2009 8:30 am |
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Joined: Sat Feb 07, 2009 4:12 pm Posts: 1215 Location: Adelaide Australia
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This is an interesting discussion but Just because there is an accepted way of doing things doesnt mean its right. I stand humbly ready to be corrected on any issue as thats the best way to learn I think.
I once built a test rig for sprintcar wings. We mounted it on a car and drove at race speeds on the road. we measured the downforce directly onto scales. The wing manufacturers used a NACA 4412 design and that predicted a downforce of 230 lbs for our test conditions. The real downforce was 125lbs. So i designed my own profile. It produced 335lbs with a small flap and with less drag than the naca 4412 fitted with 60 degree flaps so as to max its downforce at 225lbs. (we had to flap the NACA 4412 it to get it to the theoretical downforce of an unflapped wing) we continued to use our design from that day onward, we won lots of stuff. We even had to tame it down as too much downforce wasn't always good. So I am well aware of how some things can be incorrectly applied. Billy please consider this and fully explain where I go wrong in your or others opinion please----If both fourlink bars are facing downward at a considerable angle (but a sensible IC is created) the forward thrust of the axle will force the body down will it not??? That force must be accounted for in the final sprung mass reacted position.
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BillyShope
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Posted: Tue Apr 28, 2009 12:24 am |
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Joined: Sat Sep 22, 2007 7:05 am Posts: 88 Location: Orlando, FL
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I've just added a page (Page 38) to my site which should serve to clarify matters. The spreadsheet allows the user to place the IC anywhere, adjust the link spread and rear pivot locations, and change the link lengths. But, the tire patch force vector is shown to ALWAYS pass through the instant center. http://home.earthlink.net/~whshopeover 140,000 page views
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Scott Smith
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Posted: Tue Apr 28, 2009 12:21 pm |
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Joined: Sun Nov 11, 2007 10:33 am Posts: 1293 Location: Montgomery, Alabama
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Quote: Is it possible to post a column of numbers etc? There is a lot more other factors to see than this but it wont make sense if it just comes out the way it is for me at the moment. Surround your colums with the code brackets. *code* */code* (Repalace the * with [ ] Like this: Code: Psn Driver Vehicle ET Speed 1. Greg Anderson Summit Racing Equipment GXP 6.574@ 210.93& 2. Johnny Gray Johnny Gray Racing Stratus 6.599 209.14 3. Jason Line Summit Racing Equipment GXP 6.600 210.05 4. Allen Johnson Mopar/J & J Racing Stratus 6.607 208.78 5. Jeg Coughlin Jegs.com Cobalt 6.613 209.72 6. Greg Stanfield Attitude Apparel GXP 6.617 209.43 7. Warren Johnson K&N Filters GXP 6.628 209.98 8. Larry Morgan Lucas Oil Stratus 6.629 208.71 9. Kurt Johnson AC Delco Cobalt 6.632 209.10 10. Justin Humphreys RaceRedi Motorsports GXP 6.648 207.66 11. Steve Spiess Spiess Construction Cobalt 6.656 207.66 12. Ron Krisher Valvoline Cobalt 6.658 209.30 --------- Not Qualified --------- 13. Rodger Brogdon Charter GXP 6.661 208.04 14. Tom Hammonds Race For Achievement Cobalt 6.663 206.45 15. V. Gaines Kendall Oil Stratus 6.669 206.83 16. Ronnie Humphrey Troy Humphrey Stratus 6.670 207.56 17. Dave Northrop Nitro Fish Wear Stratus 6.751 205.91 18. Erica Enders Dragstar Racing Mustang 6.765 203.71 19. John Gaydosh Jr Gaydosh Performance GTO 6.864 203.58 20. Rickie Jones Quarter-Max/RJ Stratus 10.961 80.81 21. Mike Edwards Young Life/Penhall GXP 12.406 63.37 @ = Track ET Record
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Beretta
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Posted: Wed Apr 29, 2009 5:51 am |
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Joined: Wed Apr 19, 2006 8:20 pm Posts: 5852 Location: N.J.
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Beretta wrote: Bubstr wrote: Barry, Are you going to share what adjustments you made to see improvement and what kind of ET did you gain? Dennis, Last week it had the 4.30 gears in the rear and did work well as it just touched the wheelee bars and short times were better. So this week I put the 4.57 gears in and short times were better and tightened up the extension and the compression up on the rear shocks and both were run with a IC of 55" and 4" off the ground..... The chassis/motor likes the lower bar a 4 1/2* down and 6psi of air any less air and I got tire shake....The air was in the 2500 range as last week it was 1800 range...Last week the short times were in the 1.25 range but this week in two rounds they were 1.239 and 1.242.........With the 4.57 gears....I am going to try a longer and shorter IC with trying to keep the height the same.... No Comments???
_________________  running E85 Best ET 8.07 Best MPH 170.71 Barry
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shrinker
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Posted: Wed Apr 29, 2009 6:17 am |
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Joined: Sat Feb 07, 2009 4:12 pm Posts: 1215 Location: Adelaide Australia
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Code: torque axle lift w/ trans 0 0.0 0.0 50 66.9 99.6 100 138.4 204.6 150 215.4 316.0 200 298.7 434.6 250 389.5 562.0 300 489.6 699.9 350 597.6 840.6 400 721.5 1004.6 450 732.5 1184.8 500 854.4 1108.0 550 970.9 1108.0 600 1095.7 1108.0 650 1229.7 1108.0 700 1374.1 1108.0 750 1530.5 1108.0 800 1700.5 1108.0 850 1886.2 1108.0 900 2090.3 1108.0 950 2316.0 1108.0
Ok this is the best way i can figure to post the numbers. I have to do it in sections Boy is this tedious. i cant get it to post the columns how they appear for me . Anyway to explain these numbers. The column torque is the gearbox input shaft torque You can see it ranges from zero to 950 ft lbs. If its a converter car it can get to that with 600 ft lbs engine on the stall. I assume beretta's engine is about that power. The axle lift column is the upward force of torque reaction at the geometry the four link would be at within the dynamic movement of the car. If the engine is outputting 500 ft lbs the car will accelerate and the forces involved will cause certain movements and this is what I think will be the result. The weight transfer column is the total weight transfer of the car. I assumed 14"cgh. you gotta start somewhere.
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shrinker
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Posted: Wed Apr 29, 2009 6:30 am |
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Joined: Sat Feb 07, 2009 4:12 pm Posts: 1215 Location: Adelaide Australia
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Code: torque G's body drop front lift separation 0 0 0.000 0.000 0.000 50 0.134918617 0.126 0.181093619 0.155 100 0.269837234 0.264 0.372064773 0.328 150 0.404755851 0.418 0.574466006 0.522 200 0.539674468 0.590 0.790237325 0.739 250 0.674593085 0.784 1.021849749 0.987 300 0.809511701 1.003 1.272524355 1.269 350 0.944430318 1.275 1.528309593 1.612 400 1.079348935 1.567 1.826548867 1.993 450 1.214267552 1.351 0.139657138 1.837 500 1.349186169 1.861 0.153483004 2.348 550 1.484104786 2.201 0.441192618 2.687 600 1.619023403 2.569 0.747704532 3.055 650 1.75394202 2.968 1.07531499 3.454 700 1.888860637 3.402 1.426739582 3.889 750 2.023779254 1.805219174 800 2.15869787 2.214660087 850 2.293616487 2.659821623 900 2.428535104 3.146569239 950 2.563453721 3.682218211
Ok the torque column is the gearbox input shaft torque again, the G's column is the g force of the car. The body drop column is the distance the body at the rear axle point will get closer to the ground, this is the total of the tyre squash and spring reaction etc. The front lift column is the lift at the front axle location, the row 400 ft/lbs is 1.82" then the next row is 0.13". this is because the front wheels are still on the ground at 400 ft lbs but at 450 ft/lbs they will be just in the air by 0.13". If the front shock extend more than necessary to achieve zero weight at full extension then you wont see the front wheels in the air at this point of the run. The separation column is the distance of diff to body separation. Its the extension of the shocks on beretta's design rear end.
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Beretta
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Posted: Wed Apr 29, 2009 6:36 am |
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Joined: Wed Apr 19, 2006 8:20 pm Posts: 5852 Location: N.J.
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Shrinker my logger shows 2gs just after hit...
_________________  running E85 Best ET 8.07 Best MPH 170.71 Barry
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shrinker
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Posted: Wed Apr 29, 2009 6:46 am |
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Joined: Sat Feb 07, 2009 4:12 pm Posts: 1215 Location: Adelaide Australia
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Code: torque traction% start traction% axle torque spring load 0 0.0% 0.0% 0 1053 50 10.1% 11.1% 402 1019 100 18.5% 22.2% 804 981 150 25.6% 33.2% 1206 938 200 31.4% 44.3% 1609 890 250 36.1% 55.4% 2011 836 300 39.9% 66.5% 2413 774 350 43.1% 77.5% 2815 698 400 45.3% 88.6% 3217 615 450 48.6% 99.7% 3619 619 500 54.0% 110.8% 4022 537 550 59.4% 121.8% 4424 462 600 64.8% 132.9% 4826 381 650 70.2% 144.0% 5228 293 700 75.6% 155.1% 5630 197 750 81.0% 166.1% 6032 93 800 86.3% 177.2% 6435 -22 850 91.7% 188.3% 6837 -149 900 97.1% 199.4% 7239 -289 950 102.5% 210.4% 7641 -446
The torque is the gearbox input torque. The traction% column is the tyre traction used up when the car has its weight transfered. Note the car gets to 100% around the 950 FT/lbs point. I used a traction coefficient of 2.5 as this is near the best I have seen on our car. So this car doesnt have enough engine torque to spin the wheels once the car has moved off the line unless the torque converter multiplication kicks in. If the traction is less then it would turn the tyre a bit. The start traction column is the tyre traction when the car is relaxed on the line before any power is applied. Note how its 100% at 450 ft/lbs so this car can easily snap the tyre into wheel spin if the power is too violent. Our car has better start line traction than this car and we even have narrower tyres. Its interesting to compare results like this. The axle torque column is the torque at the axle, The spring load column is the weight supported by both springs. This data is what I use to work out our car, it works for me and I see the car do what these calcs are etc.
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shrinker
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Posted: Wed Apr 29, 2009 6:56 am |
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Joined: Sat Feb 07, 2009 4:12 pm Posts: 1215 Location: Adelaide Australia
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Things like diff separation can be different to these calc due to shocker dampening. i cant work out that stuff and how to put it into the spreadsheet. Beretta's 2 g just after launch is what i would expect from his type of car. I have adjusted our car by altering the ride height at the rear .100" and the car responds with answers that i can predict with my spreadsheet. The driver certainly feels the differences. I hope what I have posted is interesting to others. I dont proclaim it to a definative answer but I use it as a tool. The way most drag racers do it is to look at the IC and where it moves around to under dynamic loadings. What I do is approach it this way, its different to see the info in the style that the data logger and video shows.
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shrinker
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Posted: Wed Apr 29, 2009 5:16 pm |
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Joined: Sat Feb 07, 2009 4:12 pm Posts: 1215 Location: Adelaide Australia
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Beretta has posted that his car does a peak of 2 g just after hit. What i suspect is that the g stops there because the tyres start to spin excessive. Thats exactly what i see on our car, the G peaks and the tyre starts spinning. The car reduces G's then and the torque converter starts to loose multiplication as the output shaft speeds up and the tyre regains grip. When i use traction coefficient of 2 in my prog it shows the tyre maxed out the traction at 741 Ft/lbs input shaft torque in first gear (Thats easily achieved with a torque converter), it shows the front wheels at 1.74" in the air and a spring load of 115 lbs in the rear springs. The diff separation is at 4.28" but that would be dampened by the shock resistance so Its not reaching that probably. A video of the front and back wheels at launch is good have and confirm things that are happening.
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ADAMSVEGA
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Posted: Fri Sep 14, 2012 1:15 pm |
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Joined: Mon Sep 10, 2012 4:08 pm Posts: 39
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after ten pages of this and i'm still shakin my head .wow theres more than one guy throwing the box away besides me  } heavy short springs are for super gas guys to go red! by what the car is saying to me stick with the lighter spring rate and set ride height . its saying it wants more torque application for the geometry set up. do you know what converter k numbers and tq. multiplication your getting ,is it spragless? do you have room for a steeper rear or first gear ? if not then it looks like adding some weight back and higher will help . as long as your not folding the tire and running over sidewall. or its squatin bad when weight transfers .you could start with 20 # as far back as you can. if better add 20# to cross bar,seat brace. or x brace high is ideal. we found in the summer time when we need more bottle and more timer it was 75 h/p progressive to 125 right off the brake . this made our car dance a straight line and 60ft .were mirrors we mounted 2 bottles opposite of seat . the added weight worked it beter with the shot and we just kept it on 75 shot and used timer to make index . that little bit of weight and added tq. really made it consistent.
_________________ 
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