rear sway vs no rear sway FCM calculator
12-22-2011, 09:52 AM
#41
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I think Wayne means winding
When was the last time on track you were 'trying' to induce oversteer Collin? On the skid pad - before you ran over the railroad ties?
sorry, couldn't resist!
I regularily disconnect the rear sway when the track is wet which helps keeping the rear in place. I'm running 500F/300R on GCs/Koni yellows and still sometimes have understeer issues, usually going into a hairpin too hot - have Emilio's track alignment setup. In for baller Xida setup...
When was the last time on track you were 'trying' to induce oversteer Collin? On the skid pad - before you ran over the railroad ties?
sorry, couldn't resist! I regularily disconnect the rear sway when the track is wet which helps keeping the rear in place. I'm running 500F/300R on GCs/Koni yellows and still sometimes have understeer issues, usually going into a hairpin too hot - have Emilio's track alignment setup. In for baller Xida setup...
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12-22-2011, 10:02 AM
#42
I think Wayne means winding
When was the last time on track you were 'trying' to induce oversteer Collin? On the skid pad - before you ran over the railroad ties? sorry, couldn't resist!
I regularily disconnect the rear sway when the track is wet which helps keeping the rear in place. I'm running 500F/300R on GCs/Koni yellows and still sometimes have understeer issues, usually going into a hairpin too hot - have Emilio's track alignment setup. In for baller Xida setup...
When was the last time on track you were 'trying' to induce oversteer Collin? On the skid pad - before you ran over the railroad ties?
sorry, couldn't resist! I regularily disconnect the rear sway when the track is wet which helps keeping the rear in place. I'm running 500F/300R on GCs/Koni yellows and still sometimes have understeer issues, usually going into a hairpin too hot - have Emilio's track alignment setup. In for baller Xida setup...
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12-22-2011, 11:54 AM
#43
@joe & Bryan: you guys are ********...
just thought you would like to know.
bryan, I was trying to make it better, The turn in was a lot better on Sunday, but not great. but yeah, I knew I wasnt going to be able to completely fix it, this is an issue I have had for a long time. like since I have had the car kinda long time. I feel like I need to look for bent stuff tbh, but not sure where to start, or how to start.
Understeer is everywhere. turn in, mid turn, and track out. I would be full throttle through the entire turn with not even a hint of oversteer. Ride heights if I remember correctly were 4.75" from all of the pinch welds? I know it was very close to 949 reccomendation, if not right on the money, but my car does seem to sit lower than most. I'll go measure it again for the heck of it.
just thought you would like to know.
bryan, I was trying to make it better, The turn in was a lot better on Sunday, but not great. but yeah, I knew I wasnt going to be able to completely fix it, this is an issue I have had for a long time. like since I have had the car kinda long time. I feel like I need to look for bent stuff tbh, but not sure where to start, or how to start.
When do you get understeer Gryff? At turn in or track out? I ran the same setup as you, and if I even looked at the accelerator mid turn the car would have its tail out the rest of the way through.
What I have noticed is that ride heights can have a HUGE impact, no matter what springs you are running.
Zip ties are useless on a miata with GC coils. I can pretty much guarantee you that you're using the bumpstops at those rates.
What I have noticed is that ride heights can have a HUGE impact, no matter what springs you are running.
Zip ties are useless on a miata with GC coils. I can pretty much guarantee you that you're using the bumpstops at those rates.
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12-22-2011, 12:47 PM
#44
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For not-so-serious cheap redneck testing - you could sammwich in some of those rubber coilspring blocks to 'stiffen' the rear springs, but would be at a loss for what 'compareable' rates would be - not to mention adding to rear ride height. Again, it's a cheap *** thought for trying something to see what it does - just avoid the sprinkler head, wich I'm so glad you did NOT hit!
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12-22-2011, 01:13 PM
#45
For not-so-serious cheap redneck testing - you could sammwich in some of those rubber coilspring blocks to 'stiffen' the rear springs, but would be at a loss for what 'compareable' rates would be - not to mention adding to rear ride height. Again, it's a cheap *** thought for trying something to see what it does - just avoid the sprinkler head, wich I'm so glad you did NOT hit!
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12-22-2011, 02:06 PM
#49
while you can use tire pressure to change balance you generally want to set it and camber down right based on:
Tire pressure - based on conditions and temp. for full tread use.
Camber - for even or graidented tire temps.
Not sure what the f/b ratio is
Unless your rates are totally whack (230 front, 200 rear?), you probably should not have to change that either. Spring rates are usually pre-determined based on a bunch of suspension geometry stuff and bounce frequency. We got it easy, because spring rates on the beat have been beaten to death.
Which leaves sway bars. Your sway bars should be the biggest balance factors and perhaps the amount of toe you run. For the most part, the plaguing understeer we had was mostly due to shitty alignment (I fixed mine btw, I got some new toys and figured out some mistakes we made).
This part may not always apply, but I have read/heard this on a few occasions from a couple of TT and racers: If you are not particularly towards the grip limit on the tires, the car may have a tendency to understeer since that's how our suspension is setup. What it means is, avoid going slow enough to accelerate (keep maintenance throttle) before the apex (although some corners you are supposed to do that. For example turn 7 at RA, you actually start to track out before the apex).
Tire pressure - based on conditions and temp. for full tread use.
Camber - for even or graidented tire temps.
Not sure what the f/b ratio is
Unless your rates are totally whack (230 front, 200 rear?), you probably should not have to change that either. Spring rates are usually pre-determined based on a bunch of suspension geometry stuff and bounce frequency. We got it easy, because spring rates on the beat have been beaten to death.
Which leaves sway bars. Your sway bars should be the biggest balance factors and perhaps the amount of toe you run. For the most part, the plaguing understeer we had was mostly due to shitty alignment (I fixed mine btw, I got some new toys and figured out some mistakes we made).
This part may not always apply, but I have read/heard this on a few occasions from a couple of TT and racers: If you are not particularly towards the grip limit on the tires, the car may have a tendency to understeer since that's how our suspension is setup. What it means is, avoid going slow enough to accelerate (keep maintenance throttle) before the apex (although some corners you are supposed to do that. For example turn 7 at RA, you actually start to track out before the apex).
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12-26-2011, 10:50 AM
#53
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@jake: Thats what Ive been saying. I don know a good way to look into each aspect. The bumpstops make sense by using zip ties. tires shouldnt be an issue, they are not that old, and I rotated them halfway through the weekend, no change in handling. anything else to check with them?
What do I need to check with sways? lubed up right, not binding, ect?
same for diff...
As far as alignment, I told you what I had above. Im aiming for something like 2-2.5 front, 1.5 rear 0 toe front, 1/32 toe in rear. and 5 deg. caster next time I get the car aligned.
What do I need to check with sways? lubed up right, not binding, ect?
same for diff...
As far as alignment, I told you what I had above. Im aiming for something like 2-2.5 front, 1.5 rear 0 toe front, 1/32 toe in rear. and 5 deg. caster next time I get the car aligned.
WAG, Id say the only thing causing your understeer is the toe in everywhere. I know you said you tried getting rid of the front toe in to zero, but you should never want front toe in. Toe out is the way to go and it doesnt just affect turn in, it affects the entire turn. Something to do with ackerman I believe. Toe in in the back is an aid to help putting power down in corners but it doesnt sound like thats your problem so get rid of it. Never dial in rear toe in on a pushy car, it makes no sense.
There are other aspects of your set-up that could be causing the push too. You have plenty of camber all around according to your numbers. Well, you may not need it. You say street tires but what kind of street tires? All season radials or sticky extreme summer tires? If the all season variety then I would expect the push and blame the tires and you have no choice but to slow down. If you have sticky summer tires then you have a handling issue or you just need to slow down. Tire pressure could also be causing it. I would say about 30f/28r is a decent starting place. Raise rear tire pressure to help with understeer unless the fronts are rolling over.
Front shocks bottoming out, sure. How much travel do you have at static ride height before hitting the bumpstops? Easy fix to get more travel is to run NB mounts.
Sway bars I dont think would be in bind unless you have urethane bushings for body mounts. The stock bushings are rubber and dont require lube and are generally loose and get looser with use.
And take this advice FWIW. Ive never been on a track, just an autoxer. And I am not some suspension set up genius but I have had to deal with getting a car to handle like I like it and know that small adjustments make big changes.
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12-26-2011, 03:15 PM
#54
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I had problems with my front RB bar binding and then hitting the control arms, explaining gross mid-corner understeer. Once I fixed that I found the sweet-spot dean speaks of where you can increase trail-braking rotation with pedal pressure...it's a sweet feeling when you hit it You'll suddenly have a single tear in your eye, the clouds will part, horns will call out, and a sparrow will carry the message for all of the world, your glorious chariot has a arrived, behold it's glory.
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12-27-2011, 08:29 AM
#55
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I have the complete opposite experience with toe.. as long as its a degree here or there the differences are small. It can exaggerate an already present condition, but not cause terminal understeer.
But I have had the same experience as hustler with fat front swaybars. The bushing fit is usually terrible and there can be a LOT of bind in there. Its shocking how poor the fit is of the US made kits out there.
Ride height variations are also a big influence. I found that half an inch of added ride height in the rear more or less cancelled out the influence of the fatty arb up front. Make sure to measure ride height on a 100% flat surface.
But I have had the same experience as hustler with fat front swaybars. The bushing fit is usually terrible and there can be a LOT of bind in there. Its shocking how poor the fit is of the US made kits out there.
Ride height variations are also a big influence. I found that half an inch of added ride height in the rear more or less cancelled out the influence of the fatty arb up front. Make sure to measure ride height on a 100% flat surface.
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12-27-2011, 10:56 AM
#56
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Good thread.
My two cents. The FCM worksheet allows for a quick assessment of comparative setups, and what-if checks based on what you already have and what you might consider getting to change the balance. But, as mentioned there are a lot of other variables beyond springs and sways that make a big difference: front to rear rake, tire pressure, alignment, and power output to name a few. Personally I have used the spreadsheet to get my setup close, and check things like spring rate combinations. For example, if I change the front rate, what do I need to do to the rear rate to keep the same balance? Then when I get to the track I make relatively small adjustments and the car ends up being balanced to my liking.
Chronic understeer sucks. Been there. Get rid of it and you will be a lot happier.
My two cents. The FCM worksheet allows for a quick assessment of comparative setups, and what-if checks based on what you already have and what you might consider getting to change the balance. But, as mentioned there are a lot of other variables beyond springs and sways that make a big difference: front to rear rake, tire pressure, alignment, and power output to name a few. Personally I have used the spreadsheet to get my setup close, and check things like spring rate combinations. For example, if I change the front rate, what do I need to do to the rear rate to keep the same balance? Then when I get to the track I make relatively small adjustments and the car ends up being balanced to my liking.
Chronic understeer sucks. Been there. Get rid of it and you will be a lot happier.
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12-27-2011, 11:52 AM
#57
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If you run without a rear sway but also run stiffer springs, so that the FRC is the same, I believe *transient* turn in at the end of trail braking (lifting off brake), should improve because the weight transfer from front to rear is quicker and the tires get "upset" a bit more, over a shorter period of time.
If you keep your total roll resistance the same and the FRC the same, but increase spring rates (and by necessity reduce swaybar rates), the roll natural frequency remains the same but the heave (bounce) frequency and pitch frequency increase.
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12-31-2011, 03:28 AM
#58
WAG, Id say the only thing causing your understeer is the toe in everywhere. I know you said you tried getting rid of the front toe in to zero, but you should never want front toe in. Toe out is the way to go and it doesnt just affect turn in, it affects the entire turn. Something to do with ackerman I believe. Toe in in the back is an aid to help putting power down in corners but it doesnt sound like thats your problem so get rid of it. Never dial in rear toe in on a pushy car, it makes no sense.
There are other aspects of your set-up that could be causing the push too. You have plenty of camber all around according to your numbers. Well, you may not need it. You say street tires but what kind of street tires? All season radials or sticky extreme summer tires? If the all season variety then I would expect the push and blame the tires and you have no choice but to slow down. If you have sticky summer tires then you have a handling issue or you just need to slow down. Tire pressure could also be causing it. I would say about 30f/28r is a decent starting place. Raise rear tire pressure to help with understeer unless the fronts are rolling over.
There are other aspects of your set-up that could be causing the push too. You have plenty of camber all around according to your numbers. Well, you may not need it. You say street tires but what kind of street tires? All season radials or sticky extreme summer tires? If the all season variety then I would expect the push and blame the tires and you have no choice but to slow down. If you have sticky summer tires then you have a handling issue or you just need to slow down. Tire pressure could also be causing it. I would say about 30f/28r is a decent starting place. Raise rear tire pressure to help with understeer unless the fronts are rolling over.
for the record, tires were 32 psi all around, potenza re-11.
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01-01-2012, 11:46 AM
#59
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Happy New Year! @Damir, sorry I dont speak degrees in toe alignment. Im an inches kinda guy. Im a dinosaur I know, but this whole thing of degrees and minutes and seconds is too technical for me. He said he has a 1/16 of toe in each side so a total of 1/8" toe in on the rear. I would be willing to bet thats more than a degree or two and would make a noticeable difference. On the front it gets worse with a lowered car as you end up with the steering arms in an upwards arc already so toe in makes it even worse and not just in turn in but the whole turn. And you make a good point that rake affects the handling of a car and can be a helpful adjustment in balancing a car out. I forgot to mention that. Unfortunately for Gryff, I dont think he has control of his ride height from when I read his set up. If he does then definitely, jack the weight around.
And I think re11s are pretty sticky so keep tinkering with things one at a time. I know rear toe isnt easy to change and get right but front toe is. Tire pressure is easy. I dont think the FSB is binding as it is stock but if it is binding, remove it or disconnect it. However, getting rid of the front roll control it provides may not help the balance at all but at least you can try it. Good luck.
And I think re11s are pretty sticky so keep tinkering with things one at a time. I know rear toe isnt easy to change and get right but front toe is. Tire pressure is easy. I dont think the FSB is binding as it is stock but if it is binding, remove it or disconnect it. However, getting rid of the front roll control it provides may not help the balance at all but at least you can try it. Good luck.
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