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Post by otiscampbell on Aug 17, 2013 23:07:21 GMT -6
We run a class that is basically old asphalt late models on dirt. Our particular car has a 3-link with a pull bar and a J-Bar in back. It has Rocket Black front spindles up front.
We ran the setup below for the last race and did relatively well (2nd). The track was dry/slick and the car was a bit snug in the turns but it was drivable. Tonight, with the exact same setup but a tacky track, the car was really tight on entry, apex and off and we finished mid-pack.
Now I realize that differing track conditions call for different setups, but I'm not sure what to change and in what order to change it. Can you take a look at the setup below and give me some pointers? My thoughts were:
1. More camber in the RF.
2. Take some LR Bite out of the car.
3. Move the RR radius rod up a hole on the chassis side to add "drive" to that wheel and promote rear-steer...?
4. Reduce J-Bar angle.
Let me know if I'm even in the ballpark...
Thanks,
Otis
CASTER
LF: +1.5 RF: +3.5
CAMBER
LF: +1.5 RF: -3.5
TOE: 3/8" OUT
RIDE HEIGHTS
LF: 5" RF: 5-1/2"
LR: 6" RR: 5-3/4"
SPRINGS
LF: 525 RF: 600
LR: 225 RR: 250
SCALE NUMBERS (WITH DRIVER AND 20 GALLONS OF FUEL - 22 GALLON CELL)
LS%: 53.5%
REAR%: 52%
LR BITE: 131#
TOTAL WEIGHT: 3130 (WITH DRIVER AND 20 GALLONS OF FUEL)
WHEELS
5" OFFSET ON ALL 4 CORNERS
TRACK WIDTH
FRONT: 81" (1/2" SPACER ON EACH SIDE--REQUIRED ON RF TO PREVENT TIRE RUB WITH UPPER CONTROL ARM.)
REAR: 78-7/8" (1/2" SPACER ON EACH SIDE--REQUIRED ON RR TO PREVENT TIRE RUB WITH CHASSIS.)
J-BAR
EVEN WITH THE PINION (STEEL/HEAVY QUICK-CHANGE), APPROX. 4-6" OF RAKE.
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Post by confused on Aug 18, 2013 10:26:43 GMT -6
I wouldn't change the front except maybe to widen it more. The changes I would make are remove the spacer from the LR and put it on the RR. Also raise the RR bar for more roll steer on entry.
Raising the LR bar will add roll steer under throttle. It will also load the LR tire more.
Doesn't look like it has enough rear percent either.
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Post by otiscampbell on Sept 1, 2013 7:20:18 GMT -6
We finally got to race this weekend after raining out last week so sorry for the delay in my response. Since entry seemed to be our biggest issue, I swapped the rear springs and re-scaled the car thinking that the spring change would both help the car turn on entry and will help drive off. My thinking wasn't off, the changes worked for entry and my driver was much happier with entry to the apex. Not wanting to change too many things at once (and against my better judgement), I decided not to make a J-bar change to tighten the car up for the track that was getting slicker as each class raced. The end-result was that the car was extremely loose at the apex. Even on the wet/tacky track for practice, I think the car is still a bit free at the apex so I've been contemplating raising the J-bar for our baseline setup but I haven't wanted to make too many changes at once for fear of not knowing which changes worked and which did not. (This is an old asphalt car--there is no starting setting for J-bar since it didn't come with one from the chassis builder.)
If my theory is correct with the J-bar change helping the apex and the spring swap fixed entry, now I need to concentrate on the exit of the turns. (Keep in mind that I do realize that most setup changes typically are a compromise--so where I've helped a certain area of the turn, I might hurt another and the key is to pick the best combination that works for our car, our driver and the current track conditions.) Having written that, back to the exit of the turns... On a wet/tacky track and on a slick/semi-slick track (so practically always), we seem to be lacking drive off of the turn. I realize that you have to enter and make it through the apex properly to have a good exit but I feel like there were times in this past race where that happened, only to have us struggle on exit. Confused mentioned rear percentage before and this is another area I've been hoping to work on once I got a better handle on the car overall. Unlike others in our class (I think), our car is fairly light so I don't think I'll have an issue getting more rear percentage in the car since there is approx. 100# of lead to move around. My driver has lost weight recently, too, which helps the cause even more. Here are the scale numbers from this past race with 20 gallons of fuel and the driver in the car after setting ride heights:
LF: 850 RF: 646
LR: 866 RR: 737
Total: 3099
LS%: 55.37%
REAR%: 51.72%
CROSS: 48.78%
LR BITE: 129# (I was shooting for 130#.)
My question is, how much rear percentage am I shooting for and how will moving weight to the rear affect other areas of the turn? One of the chassis seminars I attended said to "put just enough rear percentage to prevent buzzing the tires off the turn". Without a whole lot of race time left this season, it would be helpful to have a number to aim for and I can fine-tune it from there. I also don't know if the same rules apply for a 3-link versus a 4-bar car which was the main focus of the chassis school.
Sorry for the long dissertation--I just like for you all to see my thought process so you can correct any misconceptions I have. I've made some assumptions over the years that I've later found out were incorrect.
Thanks,
Otis
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Post by otiscampbell on Sept 1, 2013 7:49:30 GMT -6
One more thought: I have approx. 60# of lead I can move without adding any additional weight. I could probably stand to add 20# more since we can't have more than 10 gallons of fuel burn-off without being close on weight (the car must weigh 3100# after the race). If what I've been taught is correct, the only way to add rear percentage (only) is to move the lead from where it is now on the car to even with or behind the rear axle. I already have approx. 50# of lead in the fuel cell area now (as I said, this car is light). If I move another 80# back to even with or behind the rear axle that will take my rear percentage to 54.29% which seems better than the current 51.72%, however, what other adverse handling effects will moving that much weight cause? I've heard of the pendulum effect...if I keep the lead over the rear axles, is it better than having it further back in the chassis? One other thought...moving this much lead around also gives me the chance to change Left % as well...what should I be aiming for there? I was told 55% by someone who raced this car before...not sure if that is correct or not.
Thanks, again, for listening...
Otis
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Post by confused on Sept 1, 2013 8:04:42 GMT -6
Try to get the rear up to 55-56%. This will help your drive off as well as the rest of the turn. The "pendelum effect" affects erratic drivers or a very tight stop and go track. Too much LS can also make a car loose. Is your LS with or wo=ithout the driver? If the track dries out, I would consider dropping the LS a percent or two. Your thinking is correct. One or two changes at a time. It is better to have the lead over the rearend but that is not always possible.
Set your car up for the end of the race(last 1/3). Don't set it up with a full fuel load or low air pressures. Add extra lead and don't use excess fule for ballast. Lead will sty in place but fuel moves around.
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Post by otiscampbell on Sept 1, 2013 9:31:47 GMT -6
All of the numbers I have listed are with the driver. I've always debated whether to scale with or without the driver and since this car doesn't have a baseline setup to go by that says exactly where to start with or without the driver, I figured it would be safer this way. The plan is to get the rear as close to 55-56% as I can before the next race. Without doing off-season things like moving the battery location or re-engineering the fuel cell mounts, I'll probably end up around 54% if my math is correct which will still be a considerable improvement over the 51.7% I have now. As for left side--obviously it would be much easier to move all of that lead if I didn't need to keep the left percentages at 55%--there are only so many left/rear ballast mounting locations to choose from.  Our track always slicks off by the time we race so lowering it a percent or two may not be a bad idea. Should I go to 54% or as low as 53% left? I've read somewhere that anywhere from 53.5-55% is correct... As for scaling it without fuel, I've never really known whether to scale with or without the fuel load. Our track uses time-trials to determine starting positions--we don't heat race. I assume that I simply scale the car without fuel and then don't add any fuel to it before qualifying? I then top it off for the feature so by the end of the feature, it should be at/about where it was when I scaled it? (That is what burned us last night--the car was good/better at the beginning of the run than at the end.) Or, do I get fancy and make multiple/adjustable ballast locations and try and have a wet/tacky setup and a dry/slick setup for my ballast? (I like simple, by the way...but I also want to win.) So...to recap, I'm going to get as much rear percentage as I can and lower the left side percentage a point or 2 at most. Should I even bother with making a wholesale J-bar change to help the center of the turn, too? (I was going to raise it 1/2" on the frame side and re-center the rear end.) Or do I wait to see what the weight percentage changes did? (Again, I've thought the car lacked a little side-bite but lowering the left-side percentage should help with weight-transfer, too, right?) Thanks, again, for your help! Otis |
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Post by confused on Sept 1, 2013 10:03:02 GMT -6
Weight change only. If you still need more, then adjust the j-bar. Increasing the rear and lowering the left are big changes. I think they will help considerably. I know several drivers that move/add lead when the track dries out.
p.s. I hate time trials! So do most fans.
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Post by flipflopoo1oo on Feb 26, 2014 7:00:29 GMT -6
No mention of shocks has been made in either response but that is the first thing in this first problem from the start! A shock package or just one can be a tight or loose situation when the rest is working and should do so on most any track if anywhere close to scales by laws of physics or shade tree logic! Too many factors to be considered different on every car not to mention driver knowledge! If close, changing anything one thing without consideration of the why its that way to start with and working is hard to do for me! Fuel tank location is to be considered! Any weight to the rear should over come ( pendulum ) if kept low and left to aide in traction and response to plant the left rear baring the 15-20 changes you have to deal with by doing so! A simple 1/2 inch spacer changes the world on some but 2 inches should have little affect if the rest is correct! I know any call mite help or hurt after 35 years and wish you all the good luck you can stand!
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Our track always slicks off by the time we race so lowering it a percent or two may not be a bad idea. Should I go to 54% or as low as 53% left? I've read somewhere that anywhere from 53.5-55% is correct...