October 10, 2007
tire grip
I've made a spreadsheet to try a few different "what if" scenarios (adjusting corner weights, Center of gravity, downforce, and power), and it all hinges on getting a good ballpark coefficient of friction for the tire. I know it's impossible for me to get an accurate model due to all the variables that can change (i.e. I don't have $20k to have Calspan model my Kumhos!) but I'd like to get a ballpark curve so I can at least see what a change will do.
So far from Herb Adams book, he's got a table on page 2 with traction vs weight:
0:0
500:275 (coef of friction is 1.81)
700:500 (1.4)
1000:1000 (1)
1280:1500 (.85)
1500:1900(.79)
The polynomial I got from an excel trendline is:
-.00028*X^2+1.261*X+73
Milliken has a few charts on p78 and 79 of slip angle vs lateral force that has several curves based on vertical load for the 275 goodyear eagle ZR, a 27x14.5 Champ car rear tire, and a 25x9-13 F1 front tire. I'll get the numbers from that in a few nights when I have a chance.
The goal of all this is to figure out that 300 lbs of downforce will give me an extra 200 lbs of grip, which will let me corner at .2 more g's, which gives 4 mph faster exit speed, and saves 3 seconds per lap (purely made up numbers, but should be ballpark). Or see that ditching the 150 lbs of turbo gear on the nose and losing 250 hp will not slow me down.
Posted by Z28tt at 10:31 AM
May 9, 2007
3rd Link Excel Spreadsheet
Posted by Z28tt at 8:26 AM
November 2, 2006
Rear brakes
I might as well measure the rear rotor, while the spare is on the workbench, for balance calcs this winter. The application is for a 94-97 F-body.
Here goes:
Swept Surface OD: 11.5"
ID: 7-15/16" (8-5/8" actual)
Thickness: .785"
Centerbore: 2.787"
Posted by Z28tt at 4:45 PM
October 25, 2006
Moser 35 Spline Axles
The 9" rear has 35 spline Moser Engineering rear axles, with a 5x4.75" bolt circle. Centerbore at the brake rotor is 2.772" and necks down to 2.758" for the wheel. The torque rating is 9600 ft-lbs per axle.
http://www.moserengineering.com/Pages/axletech.html
They originally came with ARP studs, 2.5" long, M12x1.5 thread, .505 knurl, .484 drilled hole, Moser p/n 8255, $17.50/10. The interference fit is .021"
Replaced with GM late model ARP studs, 2.5" long, M12x1.5 thread, .509 knurl, .315 knurl length, 100-7708, $16/5
ARP Techline recommended a .005 interference fit for steel flanges and .007-.008 for aluminum. Moser had a .021 interference. Corner-carver mustang guys use a 15.5mm (.610) reamer for the .625 knurl and .015 interference fit.
I ended up drilling the hole with a 1/2" stubby, with the hand drill (the belt on the drill press kept slipping). The holes measured .500 to .503, and I gave it a shot (.012 interference based on my measured .512 knurl OD, with the garage calipers). The studs pulled right in, no binding, nice and straight on the drivers side. I did the passenger side with the axle still in the rear end housing, and the studs went just as smoothly.
Posted by Z28tt at 5:37 PM
May 11, 2006
3rd Link, Day Five
Justin Bertolotti (from the local Connecticut F-body Association club) stopped by to lend a hand, and get the rear end back in the car quickly. We welded the 3rd link bracket on, did a quick coat of black rustoleum, and popped everything back in the car by 2pm.
Tonight I cut and welded the 3rd link and tube ends, and set the pinion angle to match the tailshaft angle. All thats left to do is pop the axles back in, bolt on the brake calipers, and tighten the LCA/PHR/shock bolts, and the new 3 link rear suspension is complete.
Some Weights:
Moser Torque Arm Bracket, and 3 bolts - 14.5 lbs
Center section, Nodular Iron, with gears and a spool - 73 lbs
Axle housing, with 3rd link bracket - 63 lbs
3rd link bracket, undrilled - 3.5 lbs
35 spline Moser axle with bearing, ARP studs, and brake bracket - 27.5 lbs each
QA1 XM 10-12 rod ends - .57 each
3rd link, 8" of 1.25x.095 4130 Cromoly tubing, with TIG welded 3/4" thread tube ends - about 2 lbs
Front bracket, about 1/2 lbs
23" of 1.75x.095 4130 Cromo tubing, welded to the floor and cage
5x5x.125 plate welded to the floor
--
Total weight of the rear end - 194.5 lbs
QA1 XMR Rod End Specs:
Right Left B W A D C Thread Misalign. Ult. Radial Approx.
Hand Hand +.0015 ±.005 ±.015 ±.010 +.062 UNF-3A Angle Static Brg. Wgt.
-.0005 -.031 aº Load Lbs. Lbs.
XMR10-12 XML10-12 0.6250 0.750 2.875 1.750 1.750 3/4-16 13 40,572 0.57
Posted by Z28tt at 9:40 AM
May 10, 2006
3rd Link, Night Four
Today the 1.25x.095 4130 Cromoly tube finally arrived from Arundel/Autofab Race Cars (the first one had been sawed in half by their shipping department to fit in the box!), so progress resumed. The 3/4-16" left and right tube ends were from F.K. Bearings, part no. 2708 and 2798L.
11pm - Complete rear end was removed from the Camaro (about 1 hour of work), with the brakes hanging from zipties and still connected.
11:30 - Axles removed from the rear end housing, so the inside of the axle tube can get wiped clean before welding. By having the oily metal burn on the inside, the carbon can diffuse into the heat affected zone, causing the steel to become much more brittle. Drivers axle has a "1" stamped on the inside end, and the passenger side has "2". They are 35 spline Moser axles, by the way. Also noticed the wheel studs are 2.5" long ARP with an M12x1.5 thread.
11:45 - Setting up the hydraulic press to press out the leaking drivers side axle bearing. The passenger side was replaced about 100 miles ago (or 2 years).
1am - The old bearing is pressed out, and the new one is pressed back on, using a ring JeffD & I made while I was still at Mallory Industries. The new bearing's seals on both sides didn't look quite right, so I took a few pictures. The rubber outer section isn't completely flush with the outer edge of the bearing, and looks like it's on crooked. Hopefully it'll still seal OK, as I don't have time to get a replacement before the f-body event at Indy in less than a week.
1:45 - The center section of the 9" rear is removed, and still looks brand new. I wiped down the inside of the housing, so the oil won't contaminate the welds for the 3rd link bracket. Tomorrow I'll get the bracket welded on, score a center section seal from Acme Autoparts, and get it back together and in the car.
Posted by Z28tt at 11:22 PM
May 3, 2006
3rd Link, Night Three
Today I fabbed the brackets that attach the third link to the rear axle. The horizontal offset is 10.5" towards the passenger side. This packaging places it just beyond the edge of the gas tank. Checking the anti-squat numbers on the spreadsheet, I needed as short a link as possible, so I angled the mount 20 degrees forward. This actually places the mount through the rear firewall, so a larger access hole has to be cut. The nice part is that it leaves plenty of clearance for the fuel tank.
The A1 Racing mount needs some clearance in the rear, so the vertical tube needs to be about 3.5" in front of the main roll bar hoop, centerline to centerline.
Time to take a dinner break, and resume after some pasta...
For the rest of the evening, I fabbed the vertical bar for the front link. Usually, this would be easy, but not when half of your tools are in the new garage, and the other half, are at the old house. In this case, the base to my JD Squared mandrel bender was not here. I've got the manual version, that does not have hydraulics, so it requires a good anchor point, and a long breaker bar (about 4' works well). Since the 10' base used to anchor it to the trailer hitch was MIA, I decided to grab some 8' long 2x3x3/16" angle iron, and clamp the contraption to the trailer. I got about 10 degrees into the bend, and the clamps kept loosening up. Tighten them, and go again. Loose. Damn. The clamps are breaking. One of the clamps had a crack running through the webbing, and the other was just very bent. That's not working, but the fix, as always, is to weld something. I wasn't about to ruin the powdercoat on the trailer by welding directly, but I did make a bracket to bolt the bender to the angle iron, and TIG'd this outside, on the trailer (thank goodness it finally stopped raining!). This time everything went smoothly, I put the 40 degree bend in there, and packed everything back inside the garage (3 hours for one bend!). Afterwards, I notched the tube in the drill press with a hole saw to mate with the roll cage's cross bar, and then cut a 30 degree mitre on the bottom of the vertical bar to match the floorpan. This was definitely trial and error, as I didn't want to take a chance of cutting too much off, and needing to start over with another length of tube.
Posted by Z28tt at 7:13 PM
3rd Link, Night Two
The A1 Racing Panhard Bar Adjuster arrived today, for the front of the third link. The QA1 XMR 10-12 rod ends should arrive tomorrow, which leaves just the tube and tube ends. Tonight I cut the access hole for the third-link through the rear firewall. The Cummins nibbler wasn't even up to the task of cutting through thin sheetmetal, so that's going back. After messing with the anti-squat numbers in the spreadsheet, it looks like the 20" link I planned will need to be as short as possible - 12" would be ideal, but 15-17" will be necessary. This is due to the very short 19.25" lower control arms that are on the 82-up Camaro/Firebirds. The 20" long arms varied the antisquat % by nearly 100% over 4" of suspension travel, while a 12" link varied only 30%. Some long lower control arms may be in my future...
Posted by Z28tt at 1:07 AM
April 25, 2006
Rear axle bearing specs:
Bearings from Moser Engineering (260.726.6689):
9508T Big Ford & Olds/Pontiac Ball Bearing
1.562 ID x 3.150 OD, with O-ring
Green Bearing Company, RW508ER1562 A1021A
Axle ends shown on p.4 of Wilwoods brake install manual:
www.wilwood.org/ds113.pdf
The flange dimensions are close to the Chevy bolt pattern, in the above link.
O-ring on bearing goes toward outside of flange.
Posted by Z28tt at 10:56 PM
April 23, 2006
More 3 link links
Bill Shope's page: http://home.earthlink.net/~whshope/id5.html
Rear Wheel Brake Hop And Anti-squat (more Shope):http://corner-carvers.com/forums/showthread.php?t=2800
4 Link thoughts (more Shope)http://corner-carvers.com/forums/showthread.php?t=2474
Posted by Z28tt at 12:27 AM
April 25, 2005
Mustang 3 link
http://members.webpathway.com/dougnsteph@webpathway.com/mustang/rear-suspension.html
Posted by Z28tt at 10:34 AM
April 22, 2005
3rd Link Design
I removed the Herb Adams decoupled torque arm, as it had massive rear end rise under braking, was very heavy, and had a poor design with large stress concentrations (that resulted in a snapped bracket and destroyed a driveshaft).
There was some great discussion about geometry on Corner-carvers.com on the following posts:
2002 http://corner-carvers.com/forums/showthread.php?t=5322
Decoupled TA http://corner-carvers.com/forums/showthread.php?p=49371
3 link http://corner-carvers.com/forums/showthread.php?s=&threadid=2242
3 link http://corner-carvers.com/forums/showthread.php?s=&threadid=5223
EVM proto http://corner-carvers.com/forums/showthread.php?t=11730
http://www.evolutionmsport.com/evmCart/index.php?main_page=evm_pages&pag=59
EVM final http://www.evolutionmsport.com/evmCart/index.php?main_page=product_info&cPath=1&products_id=2
71 Mustang 3 link http://corner-carvers.com/forums/showthread.php?t=21114
A Sedan Camaro http://corner-carvers.com/forums/showthread.php?t=20867
Bill Mitchel SVD http://web.archive.org/web/20030622220451/http://billmitchellsvd.com/camaroproductsandservices.html
FFR pictures http://www.norcal-cobras.com/projects/3-link/index.htm
Forces depend on the acceleration of the car, and torque at the axles, which will be highest in 1st gear. Assume 800 ft-lbs engine torque to be conservative, 2.66 1st gear (T56 ratios at http://www.sallee-chevrolet.com/ChevyTransmissions/gmt56.html), 3.70 rear-end gear ratio, and 26" diameter tire.
To minimize the tension/compression forces on the 3rd link, move it higher from the axle centerline.
If the third link is located towards the passenger side, it counteracts the torque about the rear axle under acceleration. Location depends on rear axle ratio.
Thoughts to consider:
Upper arm length (usually 65% of LCA), which affects pinion angle from suspension travel. The stock LCA's are 19.5" long.
Angle, adjustable to set the anti-squat percentage
Location left/right for rear axle roll.
Posted by Z28tt at 11:44 AM