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Yes. Once I really got to hammer the car last year I couldn't help but be impressed by the corner exit grip. No waiting, just gas and go.
This isn't my first go round with this king of rear suspension. I had exactly the same thing in an autox mustang and that is the reason I went with it for this car. With spherical bearings there is zero bind, very easy to adjust and cheap to build.
Cool! I assume you put spherical bearings in all of the links? Did you put the suspension in any 3 link calculator programs?
Cool! I assume you put spherical bearings in all of the links? Did you put the suspension in any 3 link calculator programs?
Yes - all Aurora rod ends - 5/8 bore/shank on lower control arms - 1/2 bore/5/8 shank on third link. At the chassis, I had bronze spacers made so that I could use the factory 14mm bolts with the 5/8 bore rod ends.
No, applied monkey see, monkey do logic after studying this suspension design back in the 90s on late model stock cars and GT1 road race cars.
Also considered the triangulated design that SirLaughsAllot is using on his car. Exhaust packaging nixed that option for me, but it appears that SirLaughs has a solution. You will see this suspension design on allot of tube frame GT cars at the track - especially the small bore cars. In fact, I share shop space with a GT Lite Toyota that uses this rear suspension. It was also used on several C Prepared solo cars I used to compete against.
Yes - all Aurora rod ends - 5/8 bore/shank on lower control arms - 1/2 bore/5/8 shank on third link. At the chassis, I had bronze spacers made so that I could use the factory 14mm bolts with the 5/8 bore rod ends.
No, applied monkey see, monkey do logic after studying this suspension design back in the 90s on late model stock cars and GT1 road race cars.
Also considered the triangulated design that SirLaughsAllot is using on his car. Exhaust packaging nixed that option for me, but it appears that SirLaughs has a solution. You will see this suspension design on allot of tube frame GT cars at the track - especially the small bore cars. In fact, I share shop space with a GT Lite Toyota that uses this rear suspension. It was also used on several C Prepared solo cars I used to compete against.
Thanks for all the info! I am familiar with triangulated designs from the offroad world, they work really well. I think I will do the non triangulated version instead though. There is a guy I work with that runs IT7 and just went to a trilink and panhard setup as well, and is very happy with it
Just as a random thought... I'm looking at a different solution for the EProd car build I'm doing, but mostly because Prod doesn't let you move the front pivot of the third link to where it really wants to be. I'm going to try to get that to where I'm working on the unibody this week even if it's just doing 3d scans - should probably do a thread.
The triangulated 4 link setup can work well too obviously (if unconstrained by rules) but I'd really like to see the lower links go to one big spherical instead of two spaced a bit apart... I know it's probably fine, but it just seems like it's going to have to tweak things a little to have the axle roll vs the body.
Yes - all Aurora rod ends - 5/8 bore/shank on lower control arms - 1/2 bore/5/8 shank on third link. At the chassis, I had bronze spacers made so that I could use the factory 14mm bolts with the 5/8 bore rod ends.
No, applied monkey see, monkey do logic after studying this suspension design back in the 90s on late model stock cars and GT1 road race cars.
Also considered the triangulated design that SirLaughsAllot is using on his car. Exhaust packaging nixed that option for me, but it appears that SirLaughs has a solution. You will see this suspension design on allot of tube frame GT cars at the track - especially the small bore cars. In fact, I share shop space with a GT Lite Toyota that uses this rear suspension. It was also used on several C Prepared solo cars I used to compete against.
I'm always down to chat suspension configuration. My exhaust system is simply 4" downpipe to dual 3" to get over/around the Toyota 8" solid axle and it's 6.15" stroke coilovers. Ideally I want to merge dual 3" back into a single 4" outlet at the very end. Fingers crossed on that one.
For those of you who haven't seen this already, my YouTube Channel has a bunch of videos of what we're talking about:
Just as a random thought... I'm looking at a different solution for the EProd car build I'm doing, but mostly because Prod doesn't let you move the front pivot of the third link to where it really wants to be. I'm going to try to get that to where I'm working on the unibody this week even if it's just doing 3d scans - should probably do a thread.
The triangulated 4 link setup can work well too obviously (if unconstrained by rules) but I'd really like to see the lower links go to one big spherical instead of two spaced a bit apart... I know it's probably fine, but it just seems like it's going to have to tweak things a little to have the axle roll vs the body.
The C Prepared Mustangs I used to compete against used a single mount on the bottom of the rear end housing when they ran a triangulated 3 link. Specifically Frank Stagnaro's 65 Fastback. Currently i believe that car runs a three link like the one I built.
Two other concerns. First is roll center adjustment - you could lower roll center but not raise it unless you also change tire diameter. The second is ground clearance. On the Mustangs this was not a big deal because they ran 27" tall rear tires. E Production cars run a 23-23.5" tall tire. Also, on an autocross mustang ground clearance in the center of the rear axle was not a big deal. On a car that can get driven off the track or over a curb.....this could be a problem.
Regarding three link location that the trans tunnel....reread the Production rules. You get to add clearance for the driveshaft....just saying.
Sorry, separate thoughts. I wouldn't do a triangulated 4 link in prod, just saying for that design I prefer one triangle to two links firming a virtual triangle. Probably just nitpicking though.
I'm friends with one of the guys on the prod committee who used to run a 1st gen - I'm pretty sure adding "clearance for the driveshaft" enough to get the front pivot where I'd like it is a bridge too far. I'm actually thinking torque arm.
I have the gforce trilink and panhard in my car. I saw that you had it also. Did you do anything to quiet it down? The way jim designed it make it really noisy, the rod end hits the bracket and basically chatters at certain loads. Its made me nervous a few times thinking something was wrong. It really doesn’t seem like the bracket design is ideal.
That aluminium work is what im talking about. To get into bending welding and machining that is a pretty steep entry cost.
Kenku check out pendantic publishing on youtube. They have some cool videos that illustrate how our suspension works. Its stuff we know already but the visual is cool
I have the gforce trilink and panhard in my car. I saw that you had it also. Did you do anything to quiet it down? The way jim designed it make it really noisy, the rod end hits the bracket and basically chatters at certain loads. Its made me nervous a few times thinking something was wrong. It really doesn’t seem like the bracket design is ideal.
That aluminium work is what im talking about. To get into bending welding and machining that is a pretty steep entry cost.
Spherical bearings naturally transfer road noise that is why they are not typically used on street cars. There is no way to change this. The thing I remember about the tri-link I had was that the mount on the chassis tended to come loose because it was in single shear. I had to tighten it once a race weekend. On a street car, it could be worse so keep an eye on it as well as all of the rod end attachment points.
The road noise transfer isnt what i was referring to. Only the drivers side of the panhard is single shear but ill keep an eye on that.
Not really a street car by the way. I built the car to be competitive in csp 10 uears ago. No easy feat given the miatas dominance of the class. Im transitioning it to a road racing car now. First event was a few weeks ago. Quite a different experience and demand on the car.
Part of the problem with the G-Force trilink is that it was designed for Improved Touring, where there's *really* no allowance to move the sheetmetal around to get stuff to fit. If I recall correctly, there was specific wording at the time that required it to be bolt-in rather than weld-in too. I think that's as far as you can really move the side view instant center with a 3-link, without going through the trans tunnel - fine for IT but maybe less fine with an extra hundred horsepower. If you keep extrapolating it upwards in power, GT-1/Trans Am the upper links are much longer and much more parallel to the lower links.
Id think as long as the length was equal it would be ok. Also if you could draw a straight line from the front mount to the rear mount it may be more parallel than it appears.
its location does cause issues with the lower end of ride height and you cannot adjust the 3rd link without removing ine end. That alone is a bummer. Im putting close to 200rwhp on some 13x10’s through mine and it behaves well so far. Im not driving near the cars limit yet to be fair. A road race is not the same animal as an autox
Id think as long as the length was equal it would be ok. Also if you could draw a straight line from the front mount to the rear mount it may be more parallel than it appears.
its location does cause issues with the lower end of ride height and you cannot adjust the 3rd link without removing ine end. That alone is a bummer. Im putting close to 200rwhp on some 13x10’s through mine and it behaves well so far. Im not driving near the cars limit yet to be fair. A road race is not the same animal as an autox
Kenku is right. Several of E Production RX7s in KC started life as IT cars with Tri-links. The addition of 100 HP made them slow in corner exit. The fix was a modified 4 link or a three link that mounts higher in the car than the tri-link.
Regarding solo and the Street Prep rules. Your ability to run a 10" wide wheel and a Hoosier A7 in CSP covers up allot of suspension sins. However, your car would be even better if the chassis mount for your tri-link could be raised and you were able to lower the control arm mounts on the rear axle housing. By contrast, road race RX7s in IT, E Production and STU don't get much tire or wheel. So the suspension has got to be right to put the power down.
I autox'd for a long time before starting in club racing. My experience was with a Fox mustang in C Prepared using a three link with the right geometry. The traction was so good that my mustang would pull the unloaded front tire 6-8" off the ground on corner exit or slalom pivot. At an event at Forbes Field in Topeka it was so extreme that I literally could not see where I was going until the front end came down. I fixed it with a rear sway bar and allot more rear spring rate. Traction was not affected.
What road racing class are you putting your car in?
I ran in the bay area region. Castle afb was my chapters location. Biggest space the scca had at the time. Great fun.
Im working towards TT with nasa. Nola is the nearest track and im not seeing any real scca presance here. Once i get some more experience under my belt. Ill probably venture outside of tt. I want even sure if i wanted to campaign the 1st gen anymore untill i got back behind its wheel in may. Its just a great feeling car.
I actually wonder what Prather is doing on his new EProd 1st gen. The old one was straight G-Force solutions but that was a heck of a lot of years ago - last pictures I have of that one were 2004. Maybe I'm crazy but I feel like the 1st gen can still be competitive in EProd, just that there's a need to move beyond some of the old solutions. I think you posted pictures at one point of where some of the KC EProd cars moved the upper links.
I actually wonder what Prather is doing on his new EProd 1st gen. The old one was straight G-Force solutions but that was a heck of a lot of years ago - last pictures I have of that one were 2004. Maybe I'm crazy but I feel like the 1st gen can still be competitive in EProd, just that there's a need to move beyond some of the old solutions. I think you posted pictures at one point of where some of the KC EProd cars moved the upper links.
The pictures are in Post #13.
Those suspension pictures are from the car that won the RunOffs in 2011. Charlie Clark from KC Raceware built the car for a former KC area racer named David Long. David later sold the car to Justin Pritchard in early 2011. Give Charlie a call, I am sure he would be happy to talk about this suspension design and what he is using now.
At Indy most of the EP field consisted of 1st Gen RX7s. And yeah, I think they are competitive and for sure economical.
I ran in the bay area region. Castle afb was my chapters location. Biggest space the scca had at the time. Great fun.
Im working towards TT with nasa. Nola is the nearest track and im not seeing any real scca presance here. Once i get some more experience under my belt. Ill probably venture outside of tt. I want even sure if i wanted to campaign the 1st gen anymore untill i got back behind its wheel in may. Its just a great feeling car.
Cool! An RX7 is an excellent choice for TT and club racing. Engines last a long time (if you keep them cool) and they burn cheap gas. If you can keep your tire budget under control you can do allot of racing with an RX7.
The pictures are in Post #13.
Those suspension pictures are from the car that won the RunOffs in 2011. Charlie Clark from KC Raceware built the car for a former KC area racer named David Long. David later sold the car to Justin Pritchard in early 2011. Give Charlie a call, I am sure he would be happy to talk about this suspension design and what he is using now.
At Indy most of the EP field consisted of 1st Gen RX7s. And yeah, I think they are competitive and for sure economical.
Oh yeah, duh, Pritchard. I remember the runoffs win, I was watching from turn 5. We were there ostensibly with Jim Simaris (inherited a bunch of parts when he got out of 7s, I think he's just getting his FP car done after a couple false starts on what to run next) but really just spectating. Also friends with the Olsens and Hummel if you know them.
I should call Charlie anyway as I need a set of hubs, but I always feel weird calling when I don't have cash at hand.
I met Ron Olsen at the RunOffs - he sold me the clutch I just installed. I may have met Hummel too as I was hanging out at Olsen's trailer trying to solve my flywheel issues. Everybody was super helpful. One of my shop mates has a Barrington trans in his EP RX7 so the Olsens are well known.
Ron knows Charlie too, asked me if he still runs his shop out of a cave in KC. Which he does and I rent space from him too.
Installed the KC Raceware 2 piece rotors on my car. I would guess-timate the weight savings to be 1.5lbs per rotor. The Rotor Hats are based on the ones KC Raceware makes for the rear brake E Production kit on their web site, The rotors are custom spec'd rotors from Coleman Machine. Kind of spendy but the rotor material is better than auto parts store rotors and a weight savings is always welcome. Also, with this kit, I only have to purchase the hats once.
OE style cast iron rotors (right) compared to the KC Raceware 2 piece rotors (left). Note that the Coleman Machine rotors have a thinner friction surface and fewer vanes than the aftermarket all cast iron piece. Apologies - the Coleman rotors are a little rusty from sitting around in the shop while I finished my engine.
To fit my car, I have the OE replacement rotors drilled to a 4x100 pattern on a CNC Mill. The KC Raceware hats are dual drilled 4x100 and 4x114.3.
Back Side
How are you guys dealing with head room? Scca cage rules say the bars have to be 2" above the helmet. Did you do a floorpan drop plate?
You are not reading the rule correctly. The rule you are referencing applies to open cockpit Production, GT, and Touring cars. You need to adhere to rule 9.4.B.1.a for the main hoop and any other rules related to closed cockpit cars that fall within the class you are building for. The 2" rule is mentioned in 9.4.B.1.b and 9.4.B.1.c. which applies to open cars.
1. The main hoop (behind the driver) must be the full width of the cockpit for all cars. It must be one continuous length of tubing with smooth bends and no evidence of crimping or wall failure. The main hoop must maintain a single plane.a. On all closed cars, the main hoop must be as close as possible to the roof and “B” pillars.b. Open cars without the windshield frame may use an asymmetric main hoop. The main hoop must be full width to the passenger side of the car. On the passenger side of the car the hoop must be at least as high as the top of the rear corner of the door as illustrated in figure 9.The main hoop must be high enough that a straight line drawn from the top of the main hoop to the top of the front hoop would pass over the driver’s helmet and steering wheel when the driver is seated in the normal driving position. Additionally, the top of the main hoop must be at least 2 inches above the driver’s helmet as illustrated in figure 10.
c. On open cars retaining the windshield frame the main hoop must be full height for the entire width of the hoop. The top of the main hoop must be at least 2 inches above the driver’s helmet as illustrated in figure 11.
The only builders that I know of that have had to alter the floor are over 6ft tall. I am 5'8" (and shrinking with age!) and I did not modify the floor for clearance. I did put the front of my seat pretty close to the factor cross structure and I also surrounded it with rectangular tubing. The seat is mounted on the sides using brackets that sit on the rectangle structure as well as a mount on the seat back to the cage.
The SCCA recently added language specific to Spec Miata and Touring class cars (read the latest Fastrack - June 2018 https://www.scca.com/pages/fastrack-news) that allows the floor to be lowered for seat clearance. The floor may not be pushed lower than the bottom of the frame rails/rocker on the car.
If you do this, be advised that you will need to put structure back in the car so that the lowered floor that the seat attaches too is more than just a flat piece of sheet metal. The factory floor has structure that needs to be retained/enhanced where possible. Case in point, we had a tall driver in KC that build an FB and he lowered the floor for his seat. He did not put enough structure back in place to support this modification. Later that car was backed into a wall by its next owner and the floor flexed enough that the seat back hit the roll cage and so did the driver's head. Netted him a brain bleed. Be safe...............
06-12-18, 07:25 AM
