Trying to Learn squat....

[Fabman]

Nothing personal here fellows! If we all agreed with each other it would be no fun.... Fabman, what are your LCAs angle up at?? (assuming that up is from the axle forward )

If I remember right you are with the Watts and torque arm?

Yes, Watts and Torque Arm.
I keep experimenting, but I'm up about 4* now.

 

[Fabman]

Nothing personal here fellows! If we all agreed with each other it would be no fun.... Fabman, what are your LCAs angle up at?? (assuming that up is from the axle forward )

If I remember right you are with the Watts and torque arm?

The trailing arm angle is much less critical with a torque arm because it is basically a lift bar.
Its lifting the body under acceleration and pushing the body down on the tires upon deceleration-best of both worlds
The trailing arm angle primarily tailors the roll steer in this case, but still adds to the anti squat, just much less than a 3 link where the 3rd link provides the lions share of anti squat. The 3rd link is basically a short lift bar, but in deceleration it lifts the rear end, so what you get on the gas-you lose on the brakes. That's one reason a torque arm is desirable, its a benefit both ways....plus it's long like a long instant center on a 3 link so it doesn't tend to shock the tires like a 3 link with a short instant center would. That's why I said to keep those angles gentile....don't get carried away with the angles.

Stock cars are almost universally 3 link cars.
That's all we do is stand on the gas twice a lap and bomb into another corner that's exactly the same lap after lap. You get a lot of experience manipulating trailing arm angles, anti squat and roll centers. Everything has multiple holes and is easily adjustable, so you get a lot of practise trying different setups. If the stop watch doesn't tell you you're going the wrong way the other cars on the track will. The effect is immediate. If you make a change and slower cars are now pulling you out of the corners, you done wrong, and it's obvious.
But hey, WTF do I know? I'm just a dumb welder.

 

[Fabman]

Here we go, this car had 6 to 10 holes on every link in the car.
3rd link, lower arms, pan hard bar (mounted diagonally) and brake floaters. (a subject for another day) Look carefully and you can see many of them. Every time that car hit the track it had a different setup and I don't mean each day, I mean each round. I'd run maybe 8 different setups a night. That's how you learn. (there are a shiznit pot of other adjustments so its super easy to find different combinations or tune yourself right out of business) I can't tell you how many times I'd show up at a track I never saw before, rip off a track record right off the trailer and then pull all the springs out of the car. Local guys would ask incredulously why I was messing with the car when I had just set a record and I'd tell them: "That's how we improve, constant exploration. If I screw it up, I know how to get it right back".

When you are in a traveling series you are running a different track every week. You get good really fast at figuring out what the car wants for each track and you never stop looking for that next tenth.

 

[Fabman]

Also, if you notice, all the holes are drilled on an arc....not just any arc-the exact arc for each arm length and position. That way when you go from the bottom hole to the top hole you aren't changing the effective length of the rod-skewing the rear end one way or another. You are only changing the effect of the angle.

 

[Mad Hatter]

Looking forward to trying these changes out on the track... More or less happy with every thing on my car so far except the steep angle of the UCA.

You can see in your photo, that the angle of the tube cars UCA is relatively shallow. Though I must admit that having the LCA above the UCA would play havoc with all the nice diagrams

 

[Mad Hatter]

Also, if you notice, all the holes are drilled on an arc....not just any arc-the exact arc for each arm length and position. That way when you go from the bottom hole to the top hole you aren't changing the effective length of the rod-skewing the rear end one way or another. You are only changing the effect of the angle.

That would be cool, because the way I am going I will spend all day under the car checking the pinion angle after every change...

 

[Fabman]

Looking forward to trying these changes out on the track... More or less happy with every thing on my car so far except the steep angle of the UCA.

You can see in your photo, that the angle of the tube cars UCA is relatively shallow. Though I must admit that having the LCA above the UCA would play havoc with all the nice diagrams

Those aren't the LCA's, those are the brake floaters.
The lower control arms are where they normally go...sort of.
The Right rear one is 48" long.

 

[Grant 302]

I could easily refute all those bullet points....but why?
You'll only do your best to discredit anything I say and then I'd have to poke holes in your argument again and you wont like that, so this is an exercise in futility.
Even 3rd party verification doesn't penetrate your armour.
Something tells me this isn't just about anti squat anymore....

I'm sorry you're upset about this. Refute away, if you care to.

But seriously, the BMR @BMRTech explanation you posted is a good example of why you can't believe everything you read on the internet. Googling for a good example diagram was tough. Lots and lots of bad or incomplete or just wrong stuff out there.

This is ALL about Mad Hatter's setup and nothing more from me. I've made suggestions on how I *think* he can duplicate the setup. You've doubted some of my suggestions and I'm doing my best just to explain why I made them. I am posting for his setup why I think some of your suggestions will not work.

You don't need to read or reply to anything I post. But you are still welcome to.

 

[Fabman]

That would be cool, because the way I am going I will spend all day under the car checking the pinion angle after every change...

That's what frustrates me with the Mustang.
Everything is heavier, more expensive and more difficult to adjust.
What would take me 60 seconds to adjust now takes me an hour and a lift.
Plus with track days there isn't enough time between rounds to get too jiggy with it.
I only got 5 track days last year and only 4 of them were with the major mods I made recently. Not a lot of opportunity to learn from it. I'd run more combinations in a day at the oval track than I did all year.
PLUS....the corners are all different so what helps in one corner may hurt in another....so lap times may not change much even though improvements were made in parts of the track....

Oval tracks you know right away, and since everybody has the same 2 corners, you better be dam good to beat the next guy because he's working it too.

 

[Albino500]

S197 cars from 2005 to 2010 use an UCA which is 9" in length between the pivot points while the 2011 to 2014 S197 with the higher horsepower Coyote/Roadrunner motors have a 10" length. LCAs are the same on both. Pivot points are the same location on the body and axle. FWIW.

 

[Mad Hatter]

View attachment 3371View attachment 3372 S197 cars from 2005 to 2010 use an UCA which is 9" in length between the pivot points while the 2011 to 2014 S197 with the higher horsepower Coyote/Roadrunner motors have a 10" length. LCAs are the same on both. Pivot points are the same location on the body and axle. FWIW.

Actually the 2011+ Mustangs have a 9.5" in long UCA. But I get your point... I am beginning to understand why the Boss came with the rear end jacked up so much. The LCA and UCA angles make for a better instant center along the 100% anti-squat line.. Assuming OEM installation points etc.

 

[Mad Hatter]

Just as a random thought.... I tried a couple hard launches with the LCA angles at 1.4 degrees up from the axle.... An noticed no squat... Probably because the #350 springs? or being on street tires... Will be raising the rear shortly... Increasing LCA angle and decreasing the opposite UCA angle to extend my instant center further out a tad.

 

[Grant 302]

Lol!! But then I would have to ask WHY!!! and we would have start this all over again!

The pros of torque arm is that it maintains about the same level of AS (~100% say between 90% and 110%) really well. Keeps traction levels very consistent on the road course.

That's also one of the cons of a torque arm. You'll never get the squat you're looking for unless you change the length of the arm. Longer, say, than the CorteX arm in our case to get more squat/less AS.

View attachment 3371View attachment 3372 S197 cars from 2005 to 2010 use an UCA which is 9" in length between the pivot points while the 2011 to 2014 S197 with the higher horsepower Coyote/Roadrunner motors have a 10" length. LCAs are the same on both. Pivot points are the same location on the body and axle. FWIW.

Those drawings are missing the spring reaction(s).

Add the force of the compressed spring in the squat picture.

Take away the decompressed spring force in the AS picture.

Seriously, this is *exactly* what I was talking about when I said I couldn't find a good free body diagram of the rear suspension that actually adds the spring forces in when I googled it. None. I found that exact picture in my search. Worst one is the one with the refrigerator example. I know this is not easy to digest. Most of these pictures depict the moment coming off the line at a drag strip. The shock happens in the 1/100ths to 1/10ths of a second range. All of that has very little to do with road racing.

Just look at *any* picture of AJ's car coming out of a corner lifting the opposite front tire. Is the outside rear spring (usually the right side) compressed? How much weight do you think that is? Where else does it 'go' beside right down to that rear tire?

 

[Grant 302]

Just as a random thought.... I tried a couple hard launches with the LCA angles at 1.4 degrees up from the axle.... An noticed no squat... Probably because the #350 springs? or being on street tires... Will be raising the rear shortly... Increasing LCA angle and decreasing the opposite UCA angle to extend my instant center further out a tad.

I'm glad you're willing to test this out. I don't think the springs are a problem. Stiffer will transfer the weight faster. Transferring 1,000+ lbs off would take ~2.85" of compression. Softer would take even more travel. 250lb springs would need ~4" etc, etc.

 

[racer47]

Mad Hatter, these are my numbers. I don't know the angles off hand but you can calculate them if needed. The LCA mounts are the Ford 2 hole brackets. The first plot is with the LCA in the upper of the 2 holes. The second plot is the bottom position.

I ran the car for quite a while on the lower hole, approx 100% anti squat. The forward bite was great. But ultimately it had more roll oversteer than I could tune out. So I'm now back to the upper hole but with less forward bite. I'm at 550 whp and forward bite is important. Lower power levels can get by with less anti squat.

Measuring the upper arm sucks. I ended up turning the nuts such that I could hang a box end wrench on them which would sit horizontal. Then measure the height off the ground of the wrench. Ultimate accuracy is not needed because you only have a very limited number of option. Its unlikely any of my numbers are 100% accurate, just close enough to know approx where I'm at.

This winter I bought BMRs longer upper arm and 3 position upper mount, UCM002, UTCA038. I'll see if its any better.

Lastly, I would highly caution trying to copy anyone else's setup when you only know bits and pieces of it. Everything is a trade-off and you never know what they think is worth increasing or giving up.

Example, I personally don't like 300 lb rear springs. I like 250s and a bigger rear bar. The trend (online at least) is the opposite. I don't care. I like what I have. Ultimately you need to do the same.

 

[Mad Hatter]

Thanks Racer47!! Taking time to put all these variables into the best order I can. I like airing out these things because you never now when a pearl of wisdom can open up a new way forward. Each of us are individuals with our own preferences on driving style etc. But I am happy to see other opinions and always willing to change or at least try it out!!!

 

[racer47]

Stock cars are almost universally 3 link cars.
That's all we do is stand on the gas twice a lap and bomb into another corner that's exactly the same lap after lap. You get a lot of experience manipulating trailing arm angles, anti squat and roll centers. Everything has multiple holes and is easily adjustable, so you get a lot of practise trying different setups. If the stop watch doesn't tell you you're going the wrong way the other cars on the track will. The effect is immediate. If you make a change and slower cars are now pulling you out of the corners, you done wrong, and it's obvious.
But hey, WTF do I know? I'm just a dumb welder.

This is so true that its importance is extremely hard to impress on those that have never done it. Somehow it would be nice if the internet could sort out those that have actually done things and are relaying hard earned first hand knowledge from those who have only read about it.

Road racers typically look down their noses at oval track racers, "its so simple, you are just going around in circles". But the truth is you are at the limit of traction a much greater percent of the time than at any road race track. Your setup and ability to fine tune it are much more critical than a road race car.

I'm not saying anyone is looking down at oval trackers. I'm just saying that they have a lot more experience and first hand knowledge of chassis set up than most guys that have only ever driven street cars with their very limited range of adjustments. All of Fabmans explanations have been spot on imho.

 

[Grant 302]

Stock Boss geometry:

 

[Mad Hatter]

Thanks Grant

 

[Grant 302]

Thanks Grant

Nah. Thanks to racer47 for reminding me about that calculator. Link was on my last computer that crashed. Already had the Boss LCA heights for your other thread. Perfect time to plug the data in. Control arms should be reduced for their 'projected' horizontal length, but close enough for me.

http://www.baselinesuspensions.com/instant-center_general.php