Project BLUEprint, 1965 Falcon

[carnalsupply]

PM Sent.

Thanks much.

[carnalsupply]

When I first began looking into Watts Links a year or so ago I came across these .gifs, which I totally forgot about until you mentioned you're mounting your prop on the chassis, which made me scratch my head for a second.

Watts Link mounted on Diff Housing


Watts Link mounted on Chassis

From a mechanical standpoint, do you think there's any real difference in the effectiveness between the two different mounting points? From my way of thinking the chassis mount is easier to fabricate and reduces a bit of un-sprung weight as opposed to the diff mounted but will need to have various vertically spaced mounting positions to accommodate varying ride heights.

[Bryce]

Yes, I think chassis mounted watts prop are better than axle mounted. If you are driving the car the axle has a constant height to the ground except for tire sidewall deflection, so minimal height changes. The body moves up and down +-3". When the body moves up or down the center of gravity changes (CG). Since the body/chassis weighs more than the rearend the CG follows the body movement, but not exactly since the rearend does have weight. The watts link pivot point on the prop defines the roll center of the rear suspension. I think it is better to keep the roll center and CG height seperation the same throughout the suspension travel. The reason why; the sway bar is dialed in for that distance between CG and RC. I think it will give you more consistent handling during the suspension travel.

I hope it made sence, I am off to work and just took my first sip of coffee.

[carnalsupply]

Yeah, it makes perfect sense, which is kind of frightening, actually!

One thing I don't have ready access to is a machine shop, so fabbing up parts can be a pain in the butt, so I've found a couple companies that manufacture Watt's Link kits, one that mounts to the chassis and one that mounts to the rear housing, and based on your explanation and the fact I think the chassis mounting will allow me to more neatly package the suspension components, I'll probably go with the chassis mounted set-up as well.

Thanks for the time and effort, I really appreciate it.

Bob

[Bjkadron]

Awesome! Wheels and Parts! You are making a LOT more progress than I am! Looking great!

[Bryce]

Awesome! Wheels and Parts! You are making a LOT more progress than I am! Looking great!

Thanks Benjamin,

Still long ways away from driving it again. But small progress is still progress. Good luck with your build.

[Bryce]

Yeah, it makes perfect sense, which is kind of frightening, actually!

One thing I don't have ready access to is a machine shop, so fabbing up parts can be a pain in the butt, so I've found a couple companies that manufacture Watt's Link kits, one that mounts to the chassis and one that mounts to the rear housing, and based on your explanation and the fact I think the chassis mounting will allow me to more neatly package the suspension components, I'll probably go with the chassis mounted set-up as well.

Thanks for the time and effort, I really appreciate it.

Bob

I have a full machine shop at work but no mill or lathe at home. I desing with my limitations in mind. I never lack on the engineering side and I dont sacrafice weight or asthetics. Once I get my prop built I will post pictures and an explanation of how I built it.

[65BBODY]

super curious to see the new wheels on your car!!!
Put em on!! or at least lets see them mocked up?? Thanks,

[Bryce]

I am driving up to Driverzinc today to get the tire mounted. So pictures will follow tonight!

[PhillipM]

Hey Bryce, just got back in town from a trip over the weekend. That stuff looks great. It is interesting, as a lot of those parts look like UB Machine or Speedway Engineering parts that you got from TCI.

[Bryce]

Hey Bryce, just got back in town from a trip over the weekend. That stuff looks great. It is interesting, as a lot of those parts look like UB Machine or Speedway Engineering parts that you got from TCI.

Actually only the cradle is from TCI. The other pieces are from speedway.

All of them will be modified for my applcation.

[PhillipM]

Lol! Okay. Sorry if you mentioned that earlier. I was just glancing at the pictures

[65BBODY]

pictures????

[Bryce]

pictures????

Not yet. I know I am boring. I am still waiting for valve stems from centerline. None of the ones i have fit the wheel lip shape. So I cant mount the tires until I get the valve stems. They were supposed to ship friday from 100 miles away. I guess I am making a call today.

[PhillipM]

"I will have 4" of travel 2" up and 2" down. I am mounting the cradle and prop to the chassis, so I wont tie into the UCA housing mount. But I am tying into the rear coilover crossmember."

I don't know Bryce... That seems like very little travel.?.

[Bryce]

You think so Phillip? Shooting from the hip I dont think I will have any issues with that amount of travel. It will be a street car but not a lot of street miles. I hope to see more track and autocross time withe the car.

[Bryce]

So I gave it some thought and decided to do some calculations. Rear end weight is 1250lbs with approx 250lbs in unsprung weight. Lets say the springs (coilovers) are 1:1 motion ratio and vertical. I want to design in enough spring and travel to handle a 1G bump. My sprung mass is 1000lbs or 500 per side, spring rate is 200lbs and my travel is two inches.

F=kx
F=500lbsx1G=500
k=200
x=? how much travel do I need

x=F/k
x=500/200=2.5"

Therefore, I might hit the bumpstops on a 1G bump. So I can lighten the rearend, increase rear spring stiffness but consider spring frequencies before I make changes there. Or I can increase travel of the spring before the bumps stops make contact. Or live with the fact that I might be using my bumpstops.

Here is an example. My daily driver, a lowered 95 mustang, has stock spring rates in the back with 0.5" of travel before I contact the bumpstops. It compresses the bumpstops about 0.5" as well. The ride is fine under 95% of all driving with only me in the car. When I see a huge bump I slow down. It seems to work just fine for me.

[PhillipM]

So I gave it some thought and decided to do some calculations. Rear end weight is 1250lbs with approx 250lbs in unsprung weight. Lets say the springs (coilovers) are 1:1 motion ratio and vertical. I want to design in enough spring and travel to handle a 1G bump. My sprung mass is 1000lbs or 500 per side, spring rate is 200lbs and my travel is two inches.

F=kx
F=500lbsx1G=500
k=200
x=? how much travel do I need

x=F/k
x=500/200=2.5"

Therefore, I might hit the bumpstops on a 1G bump. So I can lighten the rearend, increase rear spring stiffness but consider spring frequencies before I make changes there. Or I can increase travel of the spring before the bumps stops make contact. Or live with the fact that I might be using my bumpstops.

Here is an example. My daily driver, a lowered 95 mustang, has stock spring rates in the back with 0.5" of travel before I contact the bumpstops. It compresses the bumpstops about 0.5" as well. The ride is fine under 95% of all driving with only me in the car. When I see a huge bump I slow down. It seems to work just fine for me.

It's definitely up to you, and it sounds like you have it all under control. Our Oldsmobile had about 2.5" of bump in it until I C notched it. Now it has 4" and rides awesome. I don't have any math to back it up but real world testing around town and on Power Tour has taught me to go with 7" travel shocks and at least 3.5" of bump for a smooth uninterrupted ride. If you plan to keep yours on the track more than this will not be as important.

[craigs73]

Not yet. I know I am boring.

[Bryce]

Dude, Im driving up saturday to pick up the tires. Hopefully I will have some valvestems. I cant seem to find any that fit the wheels.