Negative LR Bite?

[Matt49]

We're on a stiffer bump stop than ever before and struggled big time with side bite. Has anyone else found that you need a significantly higher RR static load number to get side bite back in the car? This would make sense to me but in going back to what the scale numbers would look like it is going to have negative LR bite on the scales. Or should I just do what a buddy of mine said and throw away the scales and just give the car what it needs on the smasher?

[MasterSbilt_Racer]

We're on a stiffer bump stop than ever before and struggled big time with side bite. Has anyone else found that you need a significantly higher RR static load number to get side bite back in the car? This would make sense to me but in going back to what the scale numbers would look like it is going to have negative LR bite on the scales. Or should I just do what a buddy of mine said and throw away the scales and just give the car what it needs on the smasher?

I have never run static RR. I know for a fact that it is done with success by some people. But, from a load transfer standpoint, it doesn't make good sense in my mind.

[CCHIEF]

Kind of a loaded question with out track condition, assume slick with the season we are in? You running higher dynamic wheel load @ RF or bump with a higher rate? A real stiff bump rate greatly narrows the (already narrow) tuning window on RF travel. I gotten myself into a tight/loose, inconsistent situation with real stiff solid bumps. You in a crate/limited or a true super? Solid or spring bump?

[7uptruckracer]

I’ve heard of this in OWM can’t say I have in LM much. Except Crate. I have seen a really new car with a lot lower then traditional overall Jbar height, same rake just both pickup points about 1.5” lower. Might be to counteract what you describe. I had a DLM this weekend on a red Penske bump on a 225 with 2750 load. And had a similar issue late. Entry to middle wanted to skate but I just attributed it to the driver, let’s be honest 75% of handling issues are driver induced lol.

We're on a stiffer bump stop than ever before and struggled big time with side bite. Has anyone else found that you need a significantly higher RR static load number to get side bite back in the car? This would make sense to me but in going back to what the scale numbers would look like it is going to have negative LR bite on the scales. Or should I just do what a buddy of mine said and throw away the scales and just give the car what it needs on the smasher?

[Matt49]

Yeah I should have added this is with a crate motor. I never post setup stuff in the CLM section as it seems to be way more engine focused which is fine. And this is in slick track conditions that I'm having the NO side bite problem. Went to the stiffer bump to get more RF feel off the corner when the track is fast which worked like a charm but as soon as the track blew off we were junk. The only way I finally got some side bit in the car was to drop the lower right bar all the way down, drop the j-bar to 2" below pinion, and took all compression out of RR shock. It was actually pretty good in the slick then but this seems like a series of crutches so I'm just looking to get some balance back in the car. I've done quite a bit with dual-stage springs in the past but just not much with bumps and I'm thinking this increased dynamic wedge now has me messed up. I haven't been this far out in left field in 8 years :-)

[billetbirdcage]

Yeah I should have added this is with a crate motor. I never post setup stuff in the CLM section as it seems to be way more engine focused which is fine. And this is in slick track conditions that I'm having the NO side bite problem. Went to the stiffer bump to get more RF feel off the corner when the track is fast which worked like a charm but as soon as the track blew off we were junk. The only way I finally got some side bit in the car was to drop the lower right bar all the way down, drop the j-bar to 2" below pinion, and took all compression out of RR shock. It was actually pretty good in the slick then but this seems like a series of crutches so I'm just looking to get some balance back in the car. I've done quite a bit with dual-stage springs in the past but just not much with bumps and I'm thinking this increased dynamic wedge now has me messed up. I haven't been this far out in left field in 8 years :-)

First question I'd ask is: How much if any did your actual RF travel change? If it reduced with the harder bump, then yes most likely you need to increase the static or dymanic RR load but I'd be more inclined to just adjust the dynamic personally.

[billetbirdcage]

Matt, also since you don't run bumps much I'm guessing you may not have a travel indicator and it's a must that you have on on bumps.

I hate the ones you buy, they always bend or get hung up and bend. I prefer to just make them with a washer and 1/4" steel rod. Then cut a piece of tubing in half to make a C and weld a tab with 1/4" hole in it and hose clamp on the upper rail. Use a simple wire tire for a marker

See attached crappy drawing but should get the point across

https://i.imgur.com/nIREKga.png

Just add the lollipop looking rod to the lower bolt for the shock with an additional lock nut so it can pivot in and out.

https://i.imgur.com/2ISmV09.png

Cheap and easy, just make rod long enough that when RF drops when jacking that it don't fall out of the upper hole. I add a tether to RF right at the extended length of RF shock to stop it from falling out and making reinstalling shock easier.

[Matt49]

My RF travel is a little less. We were on a Penske black bump and we were bottoming the nose pretty bad. At the recommendation of a very reputable setup guy, we switched to the Penske blue rather than add more packers than we already had. Fixed our bottoming problem and the nose just barely grazes the track now.
Probably going to look into increasing RR spring rate or adding rubbers to what we have and play with that in the smasher to get a curve that looks decent.
I have one of the travel indicators that RE Suspension sells but I haven't had it on at all this year. Sounds like I need to re-install it to see exactly where we are or use your idea, billet. I don't have any tubing but I could just use a ballast bracket and attach a piece of angle to it with a hole in it for the rod. I like the idea of a travel limiter that is more independent of the shock. Thanks for the input.

[fastford]

before all these new set ups , ie : bumps and 2 stage , we won races with reverse wedge , never over 75# though , but with soft rt front set up , we never had any success trying it , with a heaver rt rear spring and a bunch of rt frt dive , we run more static left rear than ever before....

[billetbirdcage]

My RF travel is a little less. We were on a Penske black bump and we were bottoming the nose pretty bad. At the recommendation of a very reputable setup guy, we switched to the Penske blue rather than add more packers than we already had. Fixed our bottoming problem and the nose just barely grazes the track now.
Probably going to look into increasing RR spring rate or adding rubbers to what we have and play with that in the smasher to get a curve that looks decent.
I have one of the travel indicators that RE Suspension sells but I haven't had it on at all this year. Sounds like I need to re-install it to see exactly where we are or use your idea, billet. I don't have any tubing but I could just use a ballast bracket and attach a piece of angle to it with a hole in it for the rod. I like the idea of a travel limiter that is more independent of the shock. Thanks for the input.

On a side note: after you get the travel indicator on it, check how much you are actually compressing the bump (would be better to have some data to get a more true idea of variance on actual travel not just the max travel). Without looking up the blue penske (don't use it a lot so don't know off the top of my head) I'm not 100% on this number but for the black if you aren't in the 1.375" range of compression, you really need to pay attention to time on it and variances in those bumps as they seem to vary a ton in the lighter travels on rates a bunch now. Typically they need to be replaced about every 6 races or so, but that varies with how your using them.

Variances: What I mean is they vary in rates a fair amount between them as a manufacturing tolerance, mostly at travels under 1". So if you are only traveling it lightly, then the variance at those light travels can mess you up some when replacing it. I would suspect the blue is slight better about this but don't have enough data on them to say that with 100% confidence. Most of the time you can just put in your hand and squeeze and feel the difference for the first 3/8" of travel pretty easy over a new one.

[Matt49]

I'll keep an eye on that. This is really kinda temporary as I would like to move to a bump spring or back to dual stage stuff but I'm giving this a try.
I can tell you this about the black when we ran it the one night we did. It was fast and holding the car up for about 3 laps and then the nose started plowing. The plowing got progressively worse as the heat race went on...to the point that I was having to slow corner entry way down just to get the car to turn without plowing the nose. They way it was explained to me by the same person that told me to switch to the blue was that we were just packing it down more and more as the race went on. Got rained out after heats so that was the end of that on the black.
With the blue, we did not seem to have this affect. Once we finally got some side bite in the car for the B-main we drove away from everybody and the nose height was consistent throughout the race on corner entry. I made an error on setup and tire selection for the feature and pulled off after about 5 laps but I could still use more side bite. Thinking I'm just going to need to work on getting more dynamic RR but I am going to start with more static. I have a myriad of ways to add drive to the car so I'm not worried to much about the low bite at this point...at least I hope not.

[7uptruckracer]

Did you have the bleed almost closed off? Sounds like it ratcheted itself down? Now I'm curious to compare my red bump to what you've been on lol.


I'll keep an eye on that. This is really kinda temporary as I would like to move to a bump spring or back to dual stage stuff but I'm giving this a try.
I can tell you this about the black when we ran it the one night we did. It was fast and holding the car up for about 3 laps and then the nose started plowing. The plowing got progressively worse as the heat race went on...to the point that I was having to slow corner entry way down just to get the car to turn without plowing the nose. They way it was explained to me by the same person that told me to switch to the blue was that we were just packing it down more and more as the race went on. Got rained out after heats so that was the end of that on the black.
With the blue, we did not seem to have this affect. Once we finally got some side bite in the car for the B-main we drove away from everybody and the nose height was consistent throughout the race on corner entry. I made an error on setup and tire selection for the feature and pulled off after about 5 laps but I could still use more side bite. Thinking I'm just going to need to work on getting more dynamic RR but I am going to start with more static. I have a myriad of ways to add drive to the car so I'm not worried to much about the low bite at this point...at least I hope not.

[hucktyson]

What kind of zero point and 3” numbers did you have that it was packing down further and further ?

[a25rjr]

Back in the day, Bill Frye swore he run 60 lbs rr heavy!

[Matt49]

7up,
Rebound was 4 clicks off full stiff per builder.

Huck,
If you mean shock numbers, the dyno sheet is showing in the 775 neighborhood for zero point and about 950 for 3 in/sec.

[hucktyson]

That just doesn’t seem like enough to ratchet it down like that. Is the track a circular bullring where you are always turned left and hard over on the RF ? I could see with 775+ zero point and 1600@3” and climbing from there.

[billetbirdcage]

Matt, did you have a washer under bump or using a bump cup?

If not that explains why it was didn't bottom for 3 laps or so.

[Matt49]

Bump was in a cup with a washer between the bump and the packers (packers on top obviously).

[billetbirdcage]

Bump was in a cup with a washer between the bump and the packers (packers on top obviously).

OK, it's common for people to not use one and the bump will push over the nut and increase gap 1/4" or more. it usually takes a few laps for it to push over it and gain gap, so I figured that might have happened and thus increased you travel where it bottomed out after a few laps.

[Matt49]

OK, it's common for people to not use one and the bump will push over the nut and increase gap 1/4" or more. it usually takes a few laps for it to push over it and gain gap, so I figured that might have happened and thus increased you travel where it bottomed out after a few laps.

The bottom of our shocks' spring cups actually cover up the jam nut but I figured it would be best to use a cup to prevent the bump from getting pinched down into the slot in the spring cup. Same thing with the washer on top...I figured the point was to avoid rubber pinching up into the slot in your packers. Frankly, I'm already looking forward to trying something far less progressive like a bump spring or going back to stack. It seems like it will be far easier to tune for less than perfect track conditions.

[fastford]

we have not tried the bump spring yet , if the track is super smooth , which ours usually is not , i still like the reg bump , but most of the time , because of a lot of whats happening to you , we stay on the two stage . My question is , will the bump spring ratchet down on a rougher track like the rubber one?

[Matt49]

we have not tried the bump spring yet , if the track is super smooth , which ours usually is not , i still like the reg bump , but most of the time , because of a lot of whats happening to you , we stay on the two stage . My question is , will the bump spring ratchet down on a rougher track like the rubber one?

I could be wrong but I don't think the bump spring would ratchet down like a bump rubber. A spring has more of an elastic recoil. The rubber tends to stay a little crunched even after you take all the weight of it. Stores the energy longer...if that makes sense.
I've witnessed this on the smasher when bringing back up from full load. After the packers stop touching the body of the shock and it goes about 1/4 gap, stop the smasher and you can watch the packers close the gap as the bump expands. I can't imagine there is a steel spring in the world that would behave this way.