Honey Badger's Completely Off-the-Rails Race Car Build and Track Adventure Thread

[honeybadger]

Echoing HB a bit, but ...

Not exactly the same thing.

Overall - if you maintain the tire in a healthy part of the camber curve and reduce the time the suspension takes to settle when you change direction (steering input), your turn-in response will increase. This is largely a function of spring rate, with contributions from springs and roll bars. But tire sidewall height, alignment, and aero matter too.

Once into the corner and the car is "set," max grip can be higher with softer settings, to a point. It's like you want the softest setting that is stiff enough to maintain camber and use both inside and outside tires.

Because of the inherent weakness of a Macpherson strut, specifically that camber curve goes into positive after a certain level of suspension compression - it is usually a matter of compromising on the "too stiff" side. Too soft can hurt both turn-in and mid-corner grip by giving up negative camber (tire camber goes positive under constant lateral load). Too stiff and you "skate" because you don't transfer enough weight to fully maximize the tire grip - which usually shows up as corner entry and mid-corner understeer. But too-stiff gives better transitions and better braking, relative to too soft.

In the wet, it all changes again ...

Love the technical answers! Thanks for chiming in and helping educate

 

[Hack]

Not quite.

Hack is theoretically correct that a softer front bar can increase transient cornering grip by allowing more weight transfer onto the outside tire that's doing the work.

But, on a Macpherson strut suspension, too much roll (and, therefore, too much compression on the outside corner) moves into a positive camber gain curve, so in practice, as tires get stickier you want to limit roll more. That's why Mapherson strut cars benefit from stiffer springs and bigger sway bars up front. A softer rear bar can allow better hookup through mid-corner and exit, as long as your roll couple doesn't get really out of whack relative to the front.

It's not uncommon in BMW race cars (like my E36) to run very stiff springs all around, with a giant front sway bar and a small or no rear sway bar.

It sounds like you know a lot more than I do about this, but something you've said doesn't make sense to me.

If you have a softer front bar that means that LESS weight will transfer onto the outside front tire, doesn't it? And this would be during both transient as well as steady state cornering, wouldn't it? It also means there will be more weight on the inside front tire. Here's why I think this. If the front bar is soft, the car rolls more, so the rear bar is deflected more, so the rear tires start working harder to prevent the car from rolling. Yes, when the car rolls there is a little weight transfer due to the car rolling, but I would think in a (relatively) sporty car like the Mustang the CG is low enough and the car is wide enough that most of the added force on the tires is a reaction from cornering forces. I would think that weight transfer due to movement of the CG would be relatively small. In a double decker bus or a garbage truck, roll would put a lot more weight on the outside tires, but in our cars there isn't so much roll and the weight isn't so high.

Everything else you are saying in your post makes complete sense to me. Especially the statement about excessive rear roll stiffness limiting rear grip on corner exit. Mostly just curious about the one statement. I think excessive front roll stiffness will limit front grip just like excessive rear roll stiffness limits rear grip.

Contact patch size is a function of tire pressure and vehicle weight. The benefit of a wider tire is not a larger contact patch; it's the shape of the contact patch (wide and thin vs long and narrow). High performance tires also have stiffer sidewalls for two reasons:
1) can reduce pressure without damaging the tire and distorting the contact patch (this DOES increase contact patch size)
2) less distortion under lateral load makes the contact patch more consistent through corners

The lower profile tire also permits less slip angle, as the "twisting" of the wheel within the tire is reduced.

Thank you for teaching me something. Really well said and a clear explanation.

 

[chedder]

That's why I was asking (I want someone that knows more about this than I to respond). It's been long enough that I'm not sure, but I think if you want more front grip, you need to soften the front bar. This causes the rear bar to do more of the work of preventing roll (of course that change will reduce the amount of grip in the rear).

I believe a stiffer bar will tend to lift the inner tire more, thus reducing traction from that set of tires. Yes a stiff bar puts more weight on the outer tire, but I believe that it's better to have more balanced force on both inside and outside tires if you want the most traction possible. That is why wider tires are used rather than skinny tires (a larger contact patch is better than higher pressure for absolute grip).

Correctly stated.

 

[oldbmwfan]

It sounds like you know a lot more than I do about this, but something you've said doesn't make sense to me.

If you have a softer front bar that means that LESS weight will transfer onto the outside front tire, doesn't it? And this would be during both transient as well as steady state cornering, wouldn't it? It also means there will be more weight on the inside front tire. Here's why I think this. If the front bar is soft, the car rolls more, so the rear bar is deflected more, so the rear tires start working harder to prevent the car from rolling. Yes, when the car rolls there is a little weight transfer due to the car rolling, but I would think in a (relatively) sporty car like the Mustang the CG is low enough and the car is wide enough that most of the added force on the tires is a reaction from cornering forces. I would think that weight transfer due to movement of the CG would be relatively small. In a double decker bus or a garbage truck, roll would put a lot more weight on the outside tires, but in our cars there isn't so much roll and the weight isn't so high.

This is a fair call-out because I was lazy in my explanation (and we are quickly approaching the limits of my knowledge). Weight transfer per se is not directly affected by sway bars or springs/ shocks, because it's governed by Cg height, track width, vehicle weight, and cornering speed. Springs, shocks, and sways all affect the rate of weight transfer, and the degree of body roll experienced at a given amount of weight transfer.

It's canonically true that a big, stiff front bar can increase understeer and a big, stiff rear bar can increase oversteer. This is because all else equal, stiffening one bar will change how the total weight transferred is distributed. In the example of a stiffer front bar, it will increase the load on the outside front, and decrease the load on the outside rear, retaining more load at the inside rear ... which theoretically increases total rear grip and reduces total front grip = more understeer.

The "theoretically" separates from reality when the magnitude of body roll (not weight transfer) screws up the suspension geometry on the outside tire (control arms go past parallel and you move into positive camber gain). In this case, more roll stiffness on the front end has the effect of maintaining proper geometry, which increases available grip from that outside tire and is a net positive despite the decreased total traction at that end.

Edited - Most of what (little) I know about suspension tuning came from years of playing with my E36, which spent most of those years looking ugly but being a ton of cheap fun. Here it is at Mid-Ohio picking up an inside front wheel. This is obviously bad for total traction, but it ends up being the fastest setup for the springs and shocks I was running because of the other reasons mentioned above - big-*ss front sway bar keeping the front end flat and reducing camber gain. This is with -3.9* static camber, as well. I don't know if the S550 chassis is quite as prone to rolling over into the bad part of the camber curve; the E36 is relatively very narrow (but also much lighter).

 

[honeybadger]

Welp - unfortunately I had my fourth electrical gremlin pop up this weekend at MSR-Houston. During my 3rd session, I had the "Charging System - Service Now" error pop up. About 3-4 mins later, it started to misfire. Brought it in and read the codes - P0620, P065B, and P0023 (oye - that one looks familiar).

From what I am able to gather, charging system errors can cause other problems. When I clear the codes, the car runs awesome until the "Charging System - Service Now" error comes on, and then it starts to misfire. So I am thinking they're related. Either way, I tested the battery and alternator - both passed.

The only thing all these problems have had in common is the engine harness. So screw it. Ordered an entire new one + some other tools (including one REALLY big one). Going to drop the engine and replace the harness.

Am thinking of ceramic coating the headers. Anything else I should think about while the engine is out? Will of course investigate the clutch wear and all that good stuff. At least it's time for my annual coolant flush

 

[Epiphany]

Why ceramic coating over that of a wrap? Just curious as to your reasoning.

 

[honeybadger]

Why ceramic coating over that of a wrap? Just curious as to your reasoning.

My first feeling was to wrap the exhaust, but I've had a few folks tell me their experience with the wrap wasn't ideal. Tagging Chris so he can explain: @CSL

 

[Austinj427]

God speed man lol.

 

[honeybadger]

God speed man lol.

 

[Austinj427]

I hope that takes care of the issue.

You'll save some money on missed events, at least lol.

 

[sublime1996525]

Oh man. Hopefully the new harness works out!

 

[Hack]

Welp - unfortunately I had my fourth electrical gremlin pop up this weekend at MSR-Houston. During my 3rd session, I had the "Charging System - Service Now" error pop up. About 3-4 mins later, it started to misfire. Brought it in and read the codes - P0620, P065B, and P0023 (oye - that one looks familiar).

From what I am able to gather, charging system errors can cause other problems. When I clear the codes, the car runs awesome until the "Charging System - Service Now" error comes on, and then it starts to misfire. So I am thinking they're related. Either way, I tested the battery and alternator - both passed.

The only thing all these problems have had in common is the engine harness. So screw it. Ordered an entire new one + some other tools (including one REALLY big one). Going to drop the engine and replace the harness.

Am thinking of ceramic coating the headers. Anything else I should think about while the engine is out? Will of course investigate the clutch wear and all that good stuff. At least it's time for my annual coolant flush

Ceramic coating is a good idea.

As far as other ideas - obviously check over the bolts and make sure there are none loose or missing. I would consider making pen marks on them so if you ever have the engine out again it will be easy to see if anything is moving. Same for any senders that are on the engine.

The only other thing I can think of is looking at the engine mounts carefully. I assume they are taking a lot of abuse and there could be wear/slop developing. It would suck to have the engine bend your hood or something if a mount fails.

If you haven't done the accessory drive belt replacements this might be a good time.

That's what I've got.

 

[honeybadger]

Oh man. Hopefully the new harness works out!

That makes 2 of us!

Ceramic coating is a good idea.

As far as other ideas - obviously check over the bolts and make sure there are none loose or missing. I would consider making pen marks on them so if you ever have the engine out again it will be easy to see if anything is moving. Same for any senders that are on the engine.

The only other thing I can think of is looking at the engine mounts carefully. I assume they are taking a lot of abuse and there could be wear/slop developing. It would suck to have the engine bend your hood or something if a mount fails.

If you haven't done the accessory drive belt replacements this might be a good time.

That's what I've got.

All good insights. Been talking with other folks as - pretty sure I am going throw a billet OPG/Crank Sprocket in. Also looking at rear main seal + pilot bearing.

Also tossing around the idea of putting on a bigger bigger oil pan and oil cooler. Hmmm

 

[galaxy]

Just curious...if this is related to past issues, wouldn't warranty cover it? Trust me, I don't blame you for wanting to do the job yourself. I would as well. What's the expense for a complete harness?

 

[honeybadger]

Just curious...if this is related to past issues, wouldn't warranty cover it? Trust me, I don't blame you for wanting to do the job yourself. I would as well. What's the expense for a complete harness?

$138. Hard to justify the risk with a dealer at that price. It should be covered by the warranty - but just not worth the headache. And I know they wouldn't immediately replace the harness. They'd trace it to find the problem, fix it, and then it'd fail somewhere else (like it has 4 times now). Just not really interested in losing anymore track time. Been dragging my feet for 3 months on it. Finally decided to pull the trigger.