Setting up 4 bar rear end

[ekjim]

I've changed the rear axle setup on my Anglia from leaf springs and telescopic shocks to 4 bar with coil over shocks . Does anyone have any information as to getting the best setting for drag racing .
At the moment my bottom links are almost parallel to the ground and the top links are pointing down , this was my guess when the rear end was getting fabricated last year, I'm  hoping to make it adjustable to get the best setup for launching .

[BigBubba]

Link bars should be parallel to each other otherwise it'll bind.  You could play around with the pinion angle to improve traction when launching, but rear damping and spring rate will have most effect.  When you say you're 4 linking it, don't forget the panhard rod/watts linkage to stop lateral movement of the axle.

[PaulMags]

the top bar needs to come down the further it comes down the more it'll act like a ladder bar which is mainly for straight line speed but you'll have to adjust the angle of your diff.If you use your car on the road at speed it struggles a bit round corners ect but its ok.

[ekjim]

Thanks for the replies,

 

I've fitted a panhard rod , the 4 bars are 20.5 inches long, the top bars do point down but I would think there is about 4inches between the bars at the front.  Would moving the top bars down an inch make any difference? Is there a formula for working this out?   I'll try to get a couple of pictures up .  Does anyone have any pictures of their 4 bar setup ?

[katana]

Here's  some info that disproves the statement that the bars need to be parallel.....http://www.how-to-build-hotrods.com/tuning-4-link.html

Parallel bars ideal for two way axle control but drag racing axle control is pretty much single purpose primarily for launch traction.

[BigBubba]

Here's  some info that disproves the statement that the bars need to be parallel.....http://www.how-to-build-hotrods.com/tuning-4-link.html

Parallel bars ideal for two way axle control but drag racing axle control is pretty much single purpose primarily for launch traction.

 

Yeah, totally agree, but was just referring to the "standard" grp4 set up, which giver greater suspension travel. A drag set up will will of-course be different, which is why I mentioned about playing with the pinion angle. In theory though if it's 4 linked, however set, it's gonna stop axle wind up, but if it binds, and doesn't allow any vertical movement, then it's gonna break traction pretty quickly.

[ekjim]

The article Katana put up is what I was looking for, I'll just need to try and get my head round it. I had the car at Shakespeare last September's OSF meet, my clutch was slipping and I wasn't getting very good launches, I'm not sure if the rear of the car squatted or lifted on launch, this would have been a good starting point. I had set the shocks at their softest settings, should I have done this? Any further advice is most appreciated.

 

Thanks again.

[katana]

If you don't possess a data logger the next cheapest alternative is take a friend with a startline pass and have them video the launch and up to the 330' mark - it really helps! Or mount a Go-Pro camera under the car to watch the rear end - its fascinating in a nerdy kinda way!

Shocks for drag racing ideally NEED both compression AND rebound damping adjustments and you tend to want moderate compression on launch so you don't smack into the bumpstops causing the axle to 'bounce' off and unload it then the rebound takes over to slow the extension of the shock to keep the weight transfer over the axle, slowly rising down track.

[ekjim]

Thanks Katana, every days a school day.

[BigBubba]

Spring rate will have a greater effect than damper settings i would've thought? 

[ekjim]

Im not sure if the spring rate has a greater effect or not , maybe someone else knows . My car has 220lbs two and a quarter inch coilovers, it feels fine on the road not much different from the way it was with the telescopic shocks and leaf springs .

[over_head_cam]

I don't know much, but I seem to remember hearing that softer rear springs allow the car to move a little more so transferring more weight to the driven wheels. I may be wrong of course lol

[turnover]

For the weight of your Anglia you would need around 100 to 120lbs max

[BigBubba]

Is the general rule not that the rear should be 2/3 of the front rate?

 

So 120lb at the rear and 180lb at the front, with the bump/rebound set to suit.

 

Does that sound about right??

[ekjim]

Ive got 225 at the front , I thought going much lighter at the back may just compress the spring. What poundage of spring are Escorts running on rear coilovers ?

[BigBubba]

Ive got 225 at the front , I thought going much lighter at the back may just compress the spring. What poundage of spring are Escorts running on rear coilovers ?

Going with the 2/3 idea, you would be looking at 148lb or whatever was closest to that figure.

Remember the rear is a great deal lighter than the front, and the Anglia is a great deal lighter than an Escort.

Suspension is a minefield! Whatever set up is recommended may not be the best set up for you personally.