STX Rules and Setup Questions

[smg1138]

Originally Posted by jbailey8748

Everything I've read about those who tear up their axels seems to suggest anything lower than 1" in the rear is too low for the axle. That beeing said I'm at 3/4" lower from stock in the rear and 1" lower in the front

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So, that would mean no lower than 25.5" in the back. I seem to remember the stock measurement being 26.5" from the ground to top of wheel well.

[strat61caster]

Originally Posted by smg1138

So, that would mean no lower than 25.5" in the back. I seem to remember the stock measurement being 26.5" from the ground to top of wheel well.

I measured the same.

There are certainly guys running much lower than that and are willing to eat the axle costs but I agree -1" is the limit for those not looking to completely evaluate the suspension from an engineering perspective to make sure they didn't screw something up. Or just trial by fire.

It isn't going to look like a racecar at that height, but hey, we're in the function > form section so it's a safe place. It also means you don't have to daily drive it in fear, although a good number of STX cars are definitely not DD's anymore.

The other factor is going lower than ~-1" in the front is the roll center gets too low and all the guys selling parts for a living point you to the whiteline roll center correction kit, but it's illegal for the Street Touring classes. It probably helps quite a bit, but I won't be finding out for myself any time soon.

Don't forget to evaluate bump stops as well. You can make your car work while sitting on the bump stops all the time, but if you're not aware of what's at play you could make a change and see an unexpected result i.e. raising the rear should increase oversteer to help an understeering car, but if raising the rear gets you out of bump stop territory you just decreased your rear spring rate decreasing oversteer and making your understeer problem worse. You could also see the opposite, lower the rear to hook it up, bump stop comes into play and you're looser than before.

Just a hypothetical I could see happening.

[xwd]

http://www.ft86club.com/forums/showthread.php?t=30303

That thread has some information on ride heights. I'm a little over an inch in front and around 1" in the back. I use the Raceseng 1" drop mounts in the rear. I don't run any bump stops.

[Silverspeed]

Originally Posted by xwd

http://www.ft86club.com/forums/showthread.php?t=30303

That thread has some information on ride heights. I'm a little over an inch in front and around 1" in the back. I use the Raceseng 1" drop mounts in the rear. I don't run any bump stops.

It's a bit dangerous to not run bump stops isn't it? I know most aftermarket shock producers frown on that. If the shock were to ever bottom out damage will ensue. The bump stops are there to protect the shock as much as they are to increase the spring rate of the last couple inches of travel. It's probably safe to cut them down a bit but I wouldn't completely remove them.

[smg1138]

Originally Posted by strat61caster

I measured the same.

There are certainly guys running much lower than that and are willing to eat the axle costs but I agree -1" is the limit for those not looking to completely evaluate the suspension from an engineering perspective to make sure they didn't screw something up. Or just trial by fire.

It isn't going to look like a racecar at that height, but hey, we're in the function > form section so it's a safe place. It also means you don't have to daily drive it in fear, although a good number of STX cars are definitely not DD's anymore.

The other factor is going lower than ~-1" in the front is the roll center gets too low and all the guys selling parts for a living point you to the whiteline roll center correction kit, but it's illegal for the Street Touring classes. It probably helps quite a bit, but I won't be finding out for myself any time soon.

Don't forget to evaluate bump stops as well. You can make your car work while sitting on the bump stops all the time, but if you're not aware of what's at play you could make a change and see an unexpected result i.e. raising the rear should increase oversteer to help an understeering car, but if raising the rear gets you out of bump stop territory you just decreased your rear spring rate decreasing oversteer and making your understeer problem worse. You could also see the opposite, lower the rear to hook it up, bump stop comes into play and you're looser than before.

Just a hypothetical I could see happening.

I just set my rear ride height to 25.5" with 1/4 tank of gas and no trunk junk. It's sits a bit lower for street driving, but I figured the most stress is put on the axles during Autocross anyway. The front is at 25.25" now too, so I'm basically 1" lower than stock all around. I think this is probably going to be the optimal amount of drop for a daily driver and STX car.

[redlined600]

Originally Posted by Silverspeed

It's a bit dangerous to not run bump stops isn't it? I know most aftermarket shock producers frown on that. If the shock were to ever bottom out damage will ensue. The bump stops are there to protect the shock as much as they are to increase the spring rate of the last couple inches of travel. It's probably safe to cut them down a bit but I wouldn't completely remove them.

Just depends on what bottoms out first.

[Silverspeed]

Originally Posted by redlined600

Just depends on what bottoms out first.

That is correct, but do you really want anything to truly "bottom out"? If you want some very abrupt change in attitude of the car mid corner then bottoming the suspension out (coil bind, shock piston to bottom of shock body) will do it for you. I'm not a suspension engineer but I'm guessing the folks who design shock/strut packages (stock or otherwise) probably know best how to deal with gradually limiting suspension movement at the last inch or 3 to not damage anything and not cause the car to completely change it's attitude because it ran out of spring rate.

Check out Fat Cat Motorsports to learn about bump stop design. Their not just lumps of rubber.

[redlined600]

Originally Posted by Silverspeed

That is correct, but do you really want anything to truly "bottom out"? If you want some very abrupt change in attitude of the car mid corner then bottoming the suspension out (coil bind, shock piston to bottom of shock body) will do it for you. I'm not a suspension engineer but I'm guessing the folks who design shock/strut packages (stock or otherwise) probably know best how to deal with gradually limiting suspension movement at the last inch or 3 to not damage anything and not cause the car to completely change it's attitude because it ran out of spring rate.

Check out Fat Cat Motorsports to learn about bump stop design. Their not just lumps of rubber.

Thanks, I am familiar with his stuff. You're right that abruptly bottoming out would not be ideal and certainly disastrous if the shock bottoms out.
It is my opinion (maybe wrong), that a car can be setup to not utilize the bumpstops and it had been my experience that this is a better handling car. Different strokes and all that

I'd be very interested to know how much, if any, bumpstop tuning goes on in higher levels of Motorsport.

[Silver Ignition]

Okay I'm at like 24 1/4" ground to fender in the front. That's no good. Front has to come up a bit huh?

[mpross]

Originally Posted by strat61caster

I measured the same.

There are certainly guys running much lower than that and are willing to eat the axle costs but I agree -1" is the limit for those not looking to completely evaluate the suspension from an engineering perspective to make sure they didn't screw something up. Or just trial by fire.

It isn't going to look like a racecar at that height, but hey, we're in the function > form section so it's a safe place. It also means you don't have to daily drive it in fear, although a good number of STX cars are definitely not DD's anymore.

The other factor is going lower than ~-1" in the front is the roll center gets too low and all the guys selling parts for a living point you to the whiteline roll center correction kit, but it's illegal for the Street Touring classes. It probably helps quite a bit, but I won't be finding out for myself any time soon.

Don't forget to evaluate bump stops as well. You can make your car work while sitting on the bump stops all the time, but if you're not aware of what's at play you could make a change and see an unexpected result i.e. raising the rear should increase oversteer to help an understeering car, but if raising the rear gets you out of bump stop territory you just decreased your rear spring rate decreasing oversteer and making your understeer problem worse. You could also see the opposite, lower the rear to hook it up, bump stop comes into play and you're looser than before.

Just a hypothetical I could see happening.

When you say "willing to eat axle costs" are you talking about guys who competitively autocross every weekend? Or even someone who autocrosses maybe 4 or 5 times a year and who isn't particularly fast? I'm definitely lower than 1" front and rear (about 1 finger gap) and it works just fine on the street and looks great. I haven't autocrossed yet since putting the coilovers on it. Do I need to raise it back up and realign it now? or face immanent parts failures?

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[mpross]

Originally Posted by strat61caster

I measured the same.

There are certainly guys running much lower than that and are willing to eat the axle costs but I agree -1" is the limit for those not looking to completely evaluate the suspension from an engineering perspective to make sure they didn't screw something up. Or just trial by fire.

It isn't going to look like a racecar at that height, but hey, we're in the function > form section so it's a safe place. It also means you don't have to daily drive it in fear, although a good number of STX cars are definitely not DD's anymore.

The other factor is going lower than ~-1" in the front is the roll center gets too low and all the guys selling parts for a living point you to the whiteline roll center correction kit, but it's illegal for the Street Touring classes. It probably helps quite a bit, but I won't be finding out for myself any time soon.

Don't forget to evaluate bump stops as well. You can make your car work while sitting on the bump stops all the time, but if you're not aware of what's at play you could make a change and see an unexpected result i.e. raising the rear should increase oversteer to help an understeering car, but if raising the rear gets you out of bump stop territory you just decreased your rear spring rate decreasing oversteer and making your understeer problem worse. You could also see the opposite, lower the rear to hook it up, bump stop comes into play and you're looser than before.

Just a hypothetical I could see happening.

When you say "willing to eat axle costs" are you talking about guys who competitively autocross every weekend? Or even someone who autocrosses maybe 4 or 5 times a year and who isn't particularly fast? I'm definitely lower than 1" front and rear (about 1 finger gap) and it works just fine on the street and looks great. I haven't autocrossed yet since putting the coilovers on it. Do I need to raise it back up and realign it now? or face immanent parts failures?

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[BlaineWasHere]

I'm about 2" lower in the rear and while I have chewed up one axel the car has 133k miles and probably over 1000 autox runs by now. I also race almost exclusively on stickier concrete. No asphalt sites in my region.


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[strat61caster]

Originally Posted by mpross

When you say "willing to eat axle costs" are you talking about guys who competitively autocross every weekend? Or even someone who autocrosses maybe 4 or 5 times a year and who isn't particularly fast? I'm definitely lower than 1" front and rear (about 1 finger gap) and it works just fine on the street and looks great. I haven't autocrossed yet since putting the coilovers on it. Do I need to raise it back up and realign it now? or face immanent parts failures?

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See Blaine's post above, breaking axles may have been overblown as I haven't seen anyone with one recently. Keep an ear out for axle ticking, buy new axle nuts if you start to hear it tick (fixed my ticking) and keep the e-brake lubed so that noise isn't throwing you off either, they rarely go without warning.

As for 'willing to eat costs', for some it's a AAA tow truck, a $140 replacement axle and a greasy afternoon, for others it's a $500-$1000 trip to the dealership. If you're a casual autocrosser I wouldn't worry about it, if you're planning on 50-100x hard launches a year on 245 RE71R/BFGRS, might be worth sacrificing the looks if you can't prove the performance benefit to yourself.

Ultimately, this is racing, take everything with a grain of salt and prove it to yourself. Do whatever feels right, if I was your buddy I'd shrug and say 'keep it low, if you bust an axle you'll know why'

Maybe it was just a bad batch and they've all been broken now, all the ones left are rock solid. In any case, useful suspension stroke keeps me from lowering the car, not the broken axle potential.

[Thorpedo]

Originally Posted by BlaineWasHere

I'm about 2" lower in the rear and while I have chewed up one axel the car has 133k miles and probably over 1000 autox runs by now. I also race almost exclusively on stickier concrete. No asphalt sites in my region.


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THIS.

People think they are statistics analysts and can figure out that their axles will fail by how many people report failures on the forum.

Relatively speaking, hardly anyone has had issues.