Debate: RR set ups

[save the racers]

Well before SCD completely derails this thread lets TRY to somewhat get back on track.

For a common denominator. Lets say you have a RR with 17in upper and 15in lower. The upper bar has 18degrees and the lower has 5 degree. The shock mount is 6inches below the axle centerline(i believe that is close to standard on most cages). The wheel compresses 3inches. how far does the front mount travel and how much does the rear travel?

[Matt49]

Well before SCD completely derails this thread lets TRY to somewhat get back on track.

For a common denominator. Lets say you have a RR with 17in upper and 15in lower. The upper bar has 18degrees and the lower has 5 degree. The shock mount is 6inches below the axle centerline(i believe that is close to standard on most cages). The wheel compresses 3inches. how far does the front mount travel and how much does the rear travel?

This could be very easily modeled. But I would need to also know how far the shock mounts are ahead or behind the axle centerline as this also affects the motion ratios.

[save the racers]

I figured someone with CAD or something similiar could do it pretty easy. I will get that other measurement tonight. I have a couple other things to throw in i'm curious about if you have a program and dont mind me pm'ing you.

And to the person who tried to red rep me for trying to keep this one topic please get real.

[JustAddDirt]

I would have to say a 5/5, or 6/6 shock would do the trick. based off the theory that I use a 4/4 valve shock on RR.


I am thinking this because your shock may movement is decreased by 1/3 or more with the indexing. so in theory you would bump up 1-2 steps in valving to compensate for the lack of indexing.


just my opinion.

[Matt49]

I figured someone with CAD or something similiar could do it pretty easy. I will get that other measurement tonight. I have a couple other things to throw in i'm curious about if you have a program and dont mind me pm'ing you.

And to the person who tried to red rep me for trying to keep this one topic please get real.

I actually use a free program called SketchUp to do this kind of stuff. I know there is software out there but I enjoy working with this program. It takes some tedious work to figure it out but I have most of it down pat.

[Matt49]

I'm going to go with the assumption that your shock eyes are 4 inches ahead of and behind the centerline of the axle.
You said 6 inches below centerline.
I'm assuming birdcage radius rods pickups are at the standard 6 inches from centerline.
17" upper bar at 18 degrees static angle (uphill)
15" lower bar at 5 degrees static angle (uphill)
At 3 degrees of axle bump, the front shock mount will have traveled 3.234" and the rear shock mount will have only traveled 2.766".

[MasterSbilt_Racer]

I'm going to go with the assumption that your shock eyes are 4 inches ahead of and behind the centerline of the axle.
You said 6 inches below centerline.
I'm assuming birdcage radius rods pickups are at the standard 6 inches from centerline.
17" upper bar at 18 degrees static angle (uphill)
15" lower bar at 5 degrees static angle (uphill)
At 3 degrees of axle bump, the front shock mount will have traveled 3.234" and the rear shock mount will have only traveled 2.766".

Aren't rod distances from centerline normally 4.5"?

[DirtRacer9x]

Just getting back on here and reading what you guys are doing. I haven't had time to throw the number down and see what to start or go with either. Haven't seen this discussed much or really known about by many shock builders and they're somewhat shocked haha when I ask for a certain valvin in rr when I tried it. But like I said shock builders I've talked with and very big companies haven't got a clue. Not naming names but they're calling around trying to figure it out themself when I'm there and ask. Kinda a disappointment if you ask me but I guess as the racer we have to figure it out and they just build em right. Anyways if anyone has some decent info to share I'd appreciate a PM. BTW threw a green rep thing back at someone. Get outta here stocky stay loose after 5 laps Cali boy and keep that 1/2 second slower on the clock too 👍. Bet that's news to you haha. You're welcome.

[powerslide]

Matt when you say 3 degrees of axle bump is that inches of travel at the wheel?

[Matt49]

3 degrees should have said 3 inches of bump.
Birdcage pickups at 6 inches above and below centerline? Oops...ran that using the last birdcage model I was using...which I guess kind of gives away something I was working on...
I'll re-run that with the "standard" 9 inch tall (4.5 inches from centerline) birdcage.

[save the racers]

Your pm folder is full Matt. let me know when you get it rerun closer to "standard" and then what you come up with on what we discussed. Thanks

[Matt49]

I cleared out some inbox space.

[DirtRacer9x]

Bumping this thread back up. Seeing if anyone can inbox me some info they may have. Worked with 2 shock guys on the phone regarding the changes needed to compensate and wanting to compare notes.

[hucktyson]

9x the reason they don't have an answer for you is that don't have a model of your specific suspension so calculate the percentage of difference that would be need to achieve the same dampening. The entire purpose of going shock behind on the RR is to
Make the car react differently than with shock in front . With that being the case put a shock on and see how it feels and adjust from there . There's no saying the standard valving for a front shock is ideal or correct for your driving style or tracks you race on.