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Post by powercar82 on Aug 12, 2013 8:48:00 GMT -6
A couple of questions:
I have a three link USRA b-mod with the LR spring in front and RR on top of the housing. I have had a habitual problem with this car where I cannot get the LR to hike up, and on Dry slick I feel like I’m giving up some speed in the middle of the corner on out since I have very little rear steer and am not able to plant my LR. MY LR arm is about 20 degrees. My Springs are LF 600, RF 650, LR 200, RR 150. I have checked and rechecked for any binds in the system and everything is free moving.
I think I may be on to something why my LR isn’t getting much hike… My left rear spring (currently in front on the “hook”) is a 10.5” 200# spring. The reason I went with a short one is because my frame mount limited my space. Is it possible that with the short spring, I “run out” of rate too quickly before it can get up on the bar? I know 200 lbs/inch is what it is whether it’s a 5 inch spring or 30 inch spring, but just curious if anyone has any thoughts on that? How about going with a lighter spring that will compress more at ride height to store more kinetic energy?
I am thinking of putting a 15 inch spring in there by redoing the frame mount to allow more room for my slider. In doing so, I am contemplating switching to a swingarm LR. Assuming the spring rate at the wheel is identical between an “on the hook” setup and a swingarm, what difference in handling will a swingarm produce? Besides adding a lot more bite in the car, what other changes in setup would a swingarm LR require?
Thank you all for any input!
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Post by powercar82 on Aug 12, 2013 8:56:22 GMT -6
And I forgot to mention that my 19 inch J-bar is mounted 3 inches below the pinion centerline on the rearend and has about 7 inches of rake in it...
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Post by clbaker25x on Aug 12, 2013 15:47:01 GMT -6
Here is a video of our car:
This is from a night that we finished 1st at Eagle Raceway, Eagle, NE.
We are running a 125 pound left rear spring in this video. I would recommend going to a 150 as it will probably work good and help your car get up on the bar and stay there. We run a traction shock, but it is not overly agressive (8/3 with 150 pounds of rod pressure).
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Post by clbaker25x on Aug 12, 2013 15:51:10 GMT -6
To the part of your question about the spring rate, you will need to calculate the motion ratio of the swing arm and the actual effective rate that you will have at the wheel. That is why most cars run much stiffer left rear springs on swing arm cars.
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Post by powercar82 on Aug 13, 2013 8:18:46 GMT -6
Thank you for the reply! I will probably just try a 125 or 150 16" spring to begin with before switching to Swingarm. So it's safe to say that the lighter the spring, the more stored energy when compressed at ride height... correct?
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Post by clbaker25x on Aug 13, 2013 8:42:10 GMT -6
Definetly much more stored engery the more you compress the spring. The other nice thing is that as the car jacks on the left rear and decompresses the left rear spring you don't lose effect at the wheel as quickly because the rate at which the 125 will be losing compression is slower than the rate a 200 is losing compression. I also really like this on corner entry because I believe it helps keep the car from shocking the left rear on corner entry when it drops as you get off the gas.
The only bad thing is you have to be a little careful with them going flat. We were running a 16" 125 last year and could get about 20 nights out of our left rear spring before we would replace them. This year running the 13" 125 we have been replacing left rear springs about every 12-15 nights.
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Post by powercar82 on Aug 13, 2013 20:42:16 GMT -6
Thank you for the reply! Wondering if I could ask what RR spring you run? Also, how is your panhard bar set up? At what position on the pinion and how much rake?
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Post by clbaker25x on Aug 13, 2013 23:05:02 GMT -6
This is with the panhard bar behind and flat. As short as IMCA Sportmod rules allow and close to even with the axle tube.
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Post by Toywagon on Sept 4, 2013 18:33:15 GMT -6
The hike your looking for is a result of forward bite, chassis roll, and the right front's ability to compress. Some things to check. RF shock travel compression RR shock travel compression On the Left Rear Shock, you have to have enough shock extension to allow the LR to climb the bars. Once that shock tops out, you have no more hike available. ( Unless you get more rr compression travel ) If your chassis is underslung, once the rear end housing contacts the chassis, you have no more hike. ( Unless you get more RR compression travel.) Even with a 15 inch spring, but especially with a 10 inch spring, you can get enough hike to come up off the spring completely. RR bar angle creates lift as well, depending on the amount of bar angle you run. The tricky part is getting the hike without 3 wheeling too much. =) I don't know how to post a pic to this reply, but here is a link to my B mod up on the bars. Hope some of this is helpful. isemanracing.com/irace28.jpgJim
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Post by Toywagon on Sept 4, 2013 18:44:41 GMT -6
Loved the video dbaker!
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Post by powercar82 on Sept 5, 2013 8:18:11 GMT -6
Thank you all! I didn't respond but when I went to a 16" 125# spring, I was able to hike up to the point where it hit the underslung. That is all it took to get me to turn in the center.
Went out and the first race won my heat by a straightaway and finished 3rd in the feature. Finally felt comfortable in this car!
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Post by clbaker25x on Sept 5, 2013 10:31:13 GMT -6
Nice, glad that you got your car going! The added roll steer is what helped your car get through the corner and carry much more speed. I am glad you tried the soft spring and it helped.
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Post by flipflopoo1oo on Mar 8, 2014 17:08:45 GMT -6
A swing arm as to location and weight leverage can need more than double the poundage depending on where you were to start with but a definite plus on the left! While spring rates or trickier at times, the simplest adjustment works with out changing so much in ride heights changing angles! 4 rounds down can change 20 factors to loosen some designs!
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Post by ellisonmotorsports9 on Mar 27, 2018 9:25:46 GMT -6
When running the light LR spring such as the 16" #150 how much LR bite are you guys running?
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