small 1/4mile oval tips, transitioning from road racing

[rob burgoon]

6. A LR floater applies force to the chassis through braking energy, keeping weight over on the RF, and keeping the LR from settling as far on entry braking.

Drew the picture. This checks out. Sitting outside of the LR tire looking at the tire and brake with the brake fixed to the axle, the tire rotates CCW, the brake exerts force CW, the reaction on the brake caliper mounts (the axle) is twisted CCW.

With a brake floater, the reaction force on the floater is still CCW, if you attach it on top using an upward inclined rod, wham-bam you're now attempting to lift the rear end using the brake pedal. Clever.

[Bcollins82]

Run a bar 2" longer than your upper 4 link bar, and run it parallel to your upper 4 link bar. The floater rod has a lot of force on it so they can over center or "cam over" the longer rod elimates that trouble.

[rob burgoon]

1. You are correct on LR upper angle. That is why most people suggest 45 degrees of angle at maximum droop. After that seems to be the point of diminishing return.

I don't think 45 is the limit I'm running into. Once you use up your travel, *clang* the axle smacks into the limiter (undertube in my case). Once this happens, changing the static angle on the LR bar to be steeper won't change much. When the clang happens, the angle on the bar could be 30, 35, 45, but none of those should be very different other than how fast the rear of the car came up.

Adding more droop travel should allow the clang to occur later and for more dynamic LR bite from the "vertical force".

[Bcollins82]

I don't think 45 is the limit I'm running into. Once you use up your travel, *clang* the axle smacks into the limiter (undertube in my case). Once this happens, changing the static angle on the LR bar to be steeper won't change much. When the clang happens, the angle on the bar could be 30, 35, 45, but none of those should be very different other than how fast the rear of the car came up.

Adding more droop travel should allow the clang to occur later and for more dynamic LR bite from the "vertical force".

That's correct. No more dynamic loading if its against a travel stop and staying there no matter what spring, shock, or bar angle you have in the LR. You effectively make the LR solid on throttle. Watch your LR in the under car video you posted before. The LR stays pretty much solid on throttle. The RR is the only one moving as you are on throttle. That is why LR drop is a very critical and effective adjustment on these cars.

[Toywagon]

I want to throw out something, even tho it is slightly bringing up the gear ratio topic again......

I run on mostly flat and medium banked 1/4 bullrings. Almost all of them go to dry slick, or even dusty slick at times.

I do not gear for maximum power/rpm/mph at the end of the straightaway on these bullrings. IMO having the most mph or track speed at corner entry isn't as much of an advantage as being able to drive from mid corner and off with a bit deeper gear as well as being in a better rpm range etc.

I do not like changing gears on a 9 inch either. During hotlaps, and if we manage to get a tacky track for heat races, I just lift up off the throttle slightly as I near the end of the straight away if I run up on the chip. I don't lift much, just enough to let the engine stop climbing or just banging on the chip.

IMO on these bullrings, it just works better for me to get from the middle of the corner to mid straightaway better than the other guys. Maybe something for you to try when you put the 6.20 in and it gets on the chip too soon.

Jim

[rob burgoon]

Thanks Jim, I'll make the change in the offseason.

The season is done, for the last test day I played around with more rear steer and that seemed to make the car more controllable while sliding midcorner. Entered the last race of the season, race was fun, but the car got way too pushy on entry. I let the RF tire get too worn and that killed the car's ability to rotate I think. The track ended up semi-tacky. I'm bummed I didn't run a better RF tire since I think the setup was close to being somewhat viable.

More recently I made a model of the 4 bar suspension using pined paper and learned how the thing moves with different angles. Interesting stuff. I had no idea how much indexing increases when you point the lower bar lower to reduce rear steer.

[JustAddDirt]

Ron,
Looks like you have learned quite a bit from your test sessions.

[rob burgoon]

Getting there. One thing my dad picked out from a video is that my car's rear squirts out on throttle application more than anyone else's in the field, despite my short gearing and weak engine, even on fresh tires.

I was watching some videos of other mods on tracks elsewhere in the country and saw that out of the entire field, not a single car's RR moved appreciably within the wheel well. Comparing to my rear axle video, my car gets up on its RR noticeably.

For the next event I'm going to reduce the angle of the RR upper bar to reduce downforce and steer on the RR. My suspicion is that the balance between LR and RR is wrong when I get on the gas.

[rob burgoon]

6.2 is in the car, rev limiter raised to 6,200, removed a spacer from the RF just for fun. Was on 3 new tires and a used LF in very good shape. 0 stagger unfortunately, a tire wasn't holding air and had to change it last minute.

Engine didn't blow up. Seems like I'm on the limiter for most of the straight, but I think that's mostly wheelspin.

Includes warmup, race begins at 9:45
https://youtu.be/2FiC1SRAqIk

Seems like the LR comes up at 15% throttle, I *think* the RR comes up at 60-70% throttle. Gonna screw around with spacers and some stagger next time.

I suspect I'm tight on entry and mid.

[stock car driver]

I watched first few laps of your video, looks like too much gear to me now.

fyi when your on the chip like that your not gaining speed anymore so don't be scared to stay wide open and drive thru the corner. when the track is like the one you were on you should easily be able to flat foot it all the way around, theres plenty of cushion, moist dirt to help you turn. you were staying in the middle off the good of the track.

You could go in low like you were wide open and slide up to the cushion and arch the corner or just go in higher like the cars in front of you on the restart and arch the whole thing around.

Id only cut down to the bottom on a track like that if my gear was limiting me or I was passing cars.

[JustAddDirt]

Getting there. One thing my dad picked out from a video is that my car's rear squirts out on throttle application more than anyone else's in the field, despite my short gearing and weak engine, even on fresh tires.

I was watching some videos of other mods on tracks elsewhere in the country and saw that out of the entire field, not a single car's RR moved appreciably within the wheel well. Comparing to my rear axle video, my car gets up on its RR noticeably.

For the next event I'm going to reduce the angle of the RR upper bar to reduce downforce and steer on the RR. My suspicion is that the balance between LR and RR is wrong when I get on the gas.

You could also leave it like it is and limit up travel with a limiting chain like on the LR.
But if you have a lot of up angle, in top bar, that may be why the rear end squirts out on throttle. loading rr to quick

[rob burgoon]

You could also leave it like it is and limit up travel with a limiting chain like on the LR.
But if you have a lot of up angle, in top bar, that may be why the rear end squirts out on throttle. loading rr to quick

That's not a bad thought, chaining the RR, then you can dictate the final dynamic bite while on the gas hard.

In all conditions I believe the rear likes to squirt out if you gas it early and mid corner, but when the track has been watered better the rear seemed to take the power well on exit. I'm happy to try less RR upper bar, but I worry that will make the midcorner push worse and make the exit worse too since the RR coming up later means the rear steer stays around later in the corner.

[stock car driver]

rr chain only works on a smooth track it will make your car dump truck tight if theres moisture

[JustAddDirt]

rr chain only works on a smooth track it will make your car dump truck tight if theres moisture

True, but mine are adjustable, so when track is wet I loosen chain up, as it slicks off It tighten it up. I have marks for the sweet spots on both lengths.

[powerslide]

how much difference between the two marks JAD?

[rob burgoon]

True, but mine are adjustable, so when track is wet I loosen chain up, as it slicks off It tighten it up. I have marks for the sweet spots on both lengths.

Looser RR chain means when on the gas hard, rear weights closer to equal, tighter RR chain means more LR bite (weight bias)?

Or is it just poor performance over bumps with a shorter chained RR when on the gas hard?

[JustAddDirt]

how much difference between the two marks JAD?

bout 1"
when track is slick I have very little slack, chassis will move up maybe a shade more than 1/8 before chain gets tight.

I loosen it up when track is rough/wet.

I have done it several ways:

1/2" X 5"bolt with a chain welded to it going down to rear end.
on chassis have a tube going threw frame rail, or welded to side of rail with a 1/2" ID (like a leftover piece of steering shaft tube) use a locknut on top to adjust up and down on threads of 1/2 bolt. I mark the bolt with the 2 heights with a piece of electric tape around the 1/2" bolt.

[JustAddDirt]

Looser RR chain means when on the gas hard, rear weights closer to equal, tighter RR chain means more LR bite (weight bias)?

Or is it just poor performance over bumps with a shorter chained RR when on the gas hard?

1. yes, essentially..When car climbs on bars on rr it is planting the RR tire harder.

2. when chained down on RR in rough/wet tire will not conform to bumps or run in track as well, and tends to hop the RR, because of no drop (rebound)
Also, when chained down it tries to plant the LR harder till it maxes out travel. (may cause push when throttle first applied, which is also about mid corner and it will shove nose up track)

One think you never want is a tight racecar with a crate motor.

[powerslide]

Thanks JAD we will give that a try sometime this season.

[stock car driver]

True, but mine are adjustable, so when track is wet I loosen chain up, as it slicks off It tighten it up. I have marks for the sweet spots on both lengths.

of course it is adjustable all of ours are adjustable. I used old school wrenches for a while on all thread but have this now.. http://www.speedwaymotors.com/Wehrs-...CA,112640.html much easier to just pull the pin when you need to adjust the drop or adjust bars and need the spring unloaded...

for the track he was on it would be junk tightened up on rr