Sport Mod rear suspension

[aw10]

I have a 2003 Jet Viper that's converted to a Sport Mod per IMCA rules. The lower rear link mounts are mounted with a 5'' difference, with the 5'' more forward on the right. I fabricated a new mount for the right side to extend it back so both rear links would be the same in length. I would like to know what effect it will have if remove it. Right side link is 21'' and left is 17'' without the extra bracket. I am also thinking of extending the left lower mount upward to get more bar angle. I run a small 1/4 mile track in Ca. and is almost always dry slick at feature time. Car is always loose. Great when track is heavy-tacky. I have the following springs currently, 750lf,700rf,225lr,175rr. Any help would be greatly appreciated. Thanks!

[72Dubya]

Less split in the rear will help. 200 RR spring. I may be wrong. Someone will jump in with better info on what rates, but that 50lb split in the rear may be some of it.

[Duckhnter83]

OK the shorter bar will react faster and the more angle you put in it the more drive it will have. Is this a metric or chevelle car? My sport mod is running 650 rf 600 lf and 200 RR 150 lr it is a chevelle and we almost always turn dry slick in the feature and car handles well.

[7uptruckracer]

Softer on the RR is correct for loose off not heavier that will load the RR more and make it looser. The longer RR bar is so you don't have more thrust angle on that tire going to a shorter one will make it gain more angle and thus more thrust and make it looser off, changes you can make are drop RR bar angle when it slicks, add more LR bite. Take away stagger. Lower your rear roll center (Straight or Jbar) if a three link lower top link (more downard) angle. I forget what the spot mod suspension rules are is it metric, 3 link or 4 link, Jbar, or straight bar? None the less your goal here is to balance the drive you LR and RR have. The heavy track has a ton of grip the slick none. So you need either LESS RR drive or MORE LR drive. Link angle in a simple sense gives that tire more drive, it will add rear steer but the link angle normally is a bigger change in most aspects. Post more info. Corner weights, shocks, stagger etc

[clbaker25x]

We have run JET mods the last few years in that class.Here is what I would do with your car:Soften front end springs by at least 100 pounds, increase your left rear bite by at least 100 pounds, soften your left rear spring to at most a 175, we run softer than that last year in our sportmod. PM me if you want more information on the exact setup we run on a very similar car.

[aw10]

Here are some numbers from my car: Weights-lf 553 rf 544 lr704 rr604. Shocks lf 74 rf 753 or 735 when dry lr 93 rr 953, Cross-51.89 Left side 52.26 I weigh 180 lbs,Rear% 54.38 100lbs of bite. Thanks for everyones input!

[clbaker25x]

Download a copy of the JET racing setup book and start with their baseline for a setup. PM me if you want info on what we did with our JET northern sportmod.

[RaceMentally]

Here are some numbers from my car: Weights-lf 553 rf 544 lr704 rr604. Shocks lf 74 rf 753 or 735 when dry lr 93 rr 953, Cross-51.89 Left side 52.26 I weigh 180 lbs,Rear% 54.38 100lbs of bite. Thanks for everyones input!What tracks do you run?

[aw10]

Merced Speedway, Chowchilla Speedway, California, 1/4 & 1/3 MI. Dry slick normally.

[Nick Tucker Motorsports]

Extending the LR bracket would be a great benefit, so u can get the bar angle up to atleast 20*. When the track slicks up u wanna add more side bite to the car and more LR drive. Side bite (move panhard bar down on rearend) which will put more angle in the bar which plants the RR in the track harder, lowering the bar at the rearend lowers the rear roll center which helps transfer more weight to the rr which also plants the tire more. Adding more bite gives the LR more weight which drives the LR tire more, More angle in the LR bar will give the LR more drive (forward bite) Springs, bite and shocks pm me. I live in the area if u need anything

[aw10]

All my springs shocks bite numbers are 5 posts up Thanks. Ooops except springs LF 700 RF 650 LR 200 RR175 Thanks

[Nick Tucker Motorsports]

I meant pm me and I will give u those numbers

[purestock45]

this is a great post,lots of good info...I have a chevelle clip sport mod,and our track really slicked of at the end of this season.i moved my panhardbar down on the pinion 1 hole under the center and it really helped my side bite through the center.only problem I had was it made my rr tire rub frame rail...how far should I set my axle over to avoid this?as my car is setting how room should I have between my tire and frame rail?...thanks again .

[Nick Tucker Motorsports]

purestock45

When u lowered ur panhard bar it moved the rear end to the left. U have to move the rearend back to where it was before u moved the bar by lengthening ur panhard bar. More angle in the bar = shorter distance from heim bolt hole to heim bolt hole. U should have a measurement u take for the rear end to be set in the car, from chassis builder. So whenever u move ur panhard bar u set the rear end at that measurement. The only way for this not to happen is if ur bracket has the holes at the right arch. Most cars don't.

[Dirtrunner35]

[QUOTE=Nick Tucker Motorsports;1759849]Extending the LR bracket would be a great benefit, so u can get the bar angle up to atleast 20*. When the track slicks up u wanna add more side bite to the car and more LR drive. Side bite (move panhard bar down on rearend) which will put more angle in the bar which plants the RR in the track harder, lowering the bar at the rearend lowers the rear roll center which helps transfer more weight to the rr which also plants the tire more. Adding more bite gives the LR more weight which drives the LR tire more, More angle in the LR bar will give the LR more drive (forward bite) Springs, bite and shocks pm me. I live in the area if u need anything[D

Doesn't lowering the rear roll center give you more body roll but less weight transfer to the rr

[clbaker25x]

Never been a big fan of dropping panhard bar to add side bite. We didn't ever change ours last year and our car was fast in the slick. I believe that other things are much better for helping the car get over (go to a tie down on RR, soften RF spring, soften RR spring, lower right side bar on the chassis).

[Nick Tucker Motorsports]

[QUOTE=Nick Tucker Motorsports;1759849]Extending the LR bracket would be a great benefit, so u can get the bar angle up to atleast 20*. When the track slicks up u wanna add more side bite to the car and more LR drive. Side bite (move panhard bar down on rearend) which will put more angle in the bar which plants the RR in the track harder, lowering the bar at the rearend lowers the rear roll center which helps transfer more weight to the rr which also plants the tire more. Adding more bite gives the LR more weight which drives the LR tire more, More angle in the LR bar will give the LR more drive (forward bite) Springs, bite and shocks pm me. I live in the area if u need anything[D

Doesn't lowering the rear roll center give you more body roll but less weight transfer to the rr

Isn't body roll chassis roll? Chassis rolls over on the rr spring harder. In my experience raising the panhard on the chassis puts more side bite in the car but tightens the car from the center off. By lowering it on the rearend it seems to give u more side bite from entry to the center and keeps center through exit the same

[anissa5]

I think what dirtrunner35 is trying to say when you lower the pan-hard bar the car will roll more but the weight will stay on the lr tightening the car not the right rear . Just like when you soften the rr spring the car will roll more but tighten the car off the corner loading the lr when you raise the pan-hard bar that will loosen the car because it loads the right rear more just like stiffening the right rear spring.Just because the car rolls more does not mean you loading the right rear. Is this right I have no ideal I have heard it both ways I am not claiming I know this of anyway.anissa5

[Nick Tucker Motorsports]

I think what dirtrunner35 is trying to say when you lower the pan-hard bar the car will roll more but the weight will stay on the lr tightening the car not the right rear . Just like when you soften the rr spring the car will roll more but tighten the car off the corner loading the lr when you raise the pan-hard bar that will loosen the car because it loads the right rear more just like stiffening the right rear spring.Just because the car rolls more does not mean you loading the right rear. Is this right I have no ideal I have heard it both ways I am not claiming I know this of anyway.anissa5

The panhard bar only affects entry to the middle. So with more angle in bar it makes the car tighter on entry to the middle cause it's digging the rr into the track harder. With less angle in the bar it makes entry to the middle looser cause it's not digging the rr in the track as hard. My theory with lowering the panhard bar at the rearend is that the roll center is lower so the car rolls the weight over to the rr more causing the car to drive the rr harder than it was with the roll center higher. Yes a softer spring makes less drive because the weight of the car on the rr is compressing the spring more instead of pushing the weight down on the tire. A stiffer spring does not have as much of a compressed rate as a softer spring which makes it push more weight to the tire.

[Dirtrunner35]

I think what dirtrunner35 is trying to say when you lower the pan-hard bar the car will roll more but the weight will stay on the lr tightening the car not the right rear . Just like when you soften the rr spring the car will roll more but tighten the car off the corner loading the lr when you raise the pan-hard bar that will loosen the car because it loads the right rear more just like stiffening the right rear spring.Just because the car rolls more does not mean you loading the right rear. Is this right I have no ideal I have heard it both ways I am not claiming I know this of anyway.anissa5


You are correct