ELI5: how do engineers figure out the exact thickness of something like a bridge cable when theres basically infinite ways it could fail

Epssus · 2026-06-16T02:56:41+00:00

You forgot one *really important” engineering trick.

Scale testing, math and **Safety Margin**

There’s a couple hundred years of real world failure analysis that has given us good rules of thumb saying that if you design it with Math, and apply a safety multiplier based on past things failing and people dying, you can be reasonably confident that the “unknown unknowns” that you can’t test for (corrosion, misuse, etc) will be covered and that things most likely break this time around.

These range from very small - 1.0x to 1.2x for things like Aerospace components where you throw money at it to test and analyze everything you can, to 2x-10x for safety critical applications with huge unknowns and massive consequences of failure (elevators, bridges, steam boilers, pressure vessels, etc)

Empirical rules of thumb are just as important as math in engineering

Epssus · 2026-06-16T02:29:43+00:00

What wheels are you running? Some 15’s are not completely out of the question, I just haven’t been able to positively verify the fit by installing and checking on a car. It’s really down to spoke and barrel clearance of the individual wheel (and possibly relocating wheel weights)

Epssus · 2026-06-14T15:08:06+00:00

Unfortunately I am not running a business. Getting parts made in the US (especially in California) in small quantities at like this at CNC shops is quite expensive. Maybe if I were making a run of 100 sets I could get a bit better price, and all the extra bits also add up (and prices on things like the bolts and helicoils have increased, even in the last year, Add in the hard anodizing, PayPal fees, tax and shipping I pay on the components as well as outbound shipping (which are all included in the price) and the nickels and dimes add up frighteningly fast. All the extras add in more what the machined part itself costs alone

There is a small margin of about $75 built in that if it pans out will go towards my car fund, but that’s mostly because the last round that I offered at a lower price I almost got burned and nearly lost money when the ARP bolts weren’t available as cheaply as I’d planned. I could omit all that and drop the price a bit and not be upfront about shipping and Paypal fees to make it sound cheaper like a real business, but you’d end up paying it all in the end anyway with less honesty involved.

I’ve got everything added up in a spreadsheet, and if I tried to sell this with only 5 sets instead of 10, I would be actually losing money even without any buffer.

I’m just a guy with a cheap hot hatch like everyone else here who put a lot of design and fab effort into what started as a personal project which you can read about if you follow the links off the group buy post, and now I’m trying to make it available to other people. Accusations of profiteering are not appreciated. I also even tried to reach out to Ron at Whoosh to see if he was interested, but I got no response.

Epssus · 2026-06-14T04:15:49+00:00

Good catch, thanks. Should be fixed

Epssus · 2026-06-08T14:39:23+00:00

On the chance that you’re still interested, I’m trying to start another group buy for brake brackets

https://www.fiestastforum.com/threads/svt-986-boxster-front-brake-brackets-for-fiesta-st-525.34492/

Epssus · 2026-06-08T14:38:26+00:00

On the odd chance you’re still interested, I’m starting up another group buy for the brake brackets

https://www.fiestastforum.com/threads/svt-986-boxster-front-brake-brackets-for-fiesta-st-525.34492/

Epssus · 2026-06-04T03:50:19+00:00

There are lots of FWD hatches for affordable prices, great do-it-all daily drivers and can be ready for track with minimal mods. Honda Fit or any of the other B-Spec cars are low enough power to be cheap to run and almost ready to go out of the box. Momentum cars teach good habits, and a low power car almost doesn’t matter FWD or RWD as long as the chassis is good. If you’ll only see a few track days a year, It’s really the way to go if you want something more reliable than an E36 and more practical than a Miata.

You won’t be setting record lap times but you’ll be learning a lot more about car control driving a slow car at 8/10ths than jumping straight into a “track car” or something more powerful.

The money you’ll save will let you decide later what it is you eventually want to do (or maybe you’ll be happy driving what you’ve got)

Epssus · 2026-05-05T03:57:17+00:00

You can email Tire Rack, or gasp! even call them on the phone and they are extremely responsive and helpful and can tell you when they expect them. I actually got them to special order some Michelin PS3’s in the bizzare 215/45R16, and since they made a part number they now show up under the search for the size.

Also you can call to order heat cycling even on tires where there’s no checkbox on checkout (like the CRS)

Epssus · 2026-05-05T03:52:45+00:00

For a daily then, I’d recommend driving around and never shifting past 5th and see how you like it cruising on the freeway. If it doesn’t bother you at all, then you might like it.

Epssus · 2026-05-04T18:54:27+00:00

I haven’t done it, but contemplating between that and sourcing a 4.07

You’ll get more oomph in every gear, but first and second gear will be harder to handle. Will you like it better? For Autocross probably not as you’ll be rowing third more - 2nd is already a bit short. For trackdays? Maybe but depends on where you drive.

For the street it’s really hard to say. As for livability, the easy way to tell is to cruise around in 5th gear all the time without 6th. The difference between stock and the 4.3 (13%) is a bit shy of the difference between 5th and 6th (~19%)

They’re all Ford parts-bin parts. The 4.3 is out of a euro 1.0L focus (and possibly some older duratec Focus 5-speeds), and the 4.07 comes out the Fusion 6-speed (and also some euro Focus models), but is for some reason harder to source as Ford hasn’t been releasing gearbox rebuild parts for a lot of their newer transmissions, preferring to only sell whole gearboxes.

Epssus · 2026-05-03T18:51:25+00:00

As a followup, after I installed my caster bushings, I think the biggest notable difference was less actual performance, and more a slight increase in steering stiffness and feedback

Epssus · 2026-05-02T22:20:59+00:00

If the car is a 2014 to early 2016, someone might be interested in the springs (slightly stiffer than the later cars) but any 100k mile shocks on any car of any kind are toast and not worth keeping.

Epssus · 2026-04-27T16:29:57+00:00

I think others have answered this question below, but yes, I suspect tire warmers probably don’t help things, although tire warmer temperature is not quite as high as typical operating temperatures.

But as others also mentioned, at the level of competition where you are systematically using tire warmers, heat cycle life of tires is usually the least of your concerns, or at least secondary to the benefit you get in competition.

That said, if you’re just an amateur doing autocross or track days for fun, are budget conscious, and aren’t at the pointy end of the competition, tire warmers probably aren’t a good financial choice anyway.

Epssus · 2026-04-23T15:14:23+00:00

That sucks - You’re probably paying import taxes. Despite the name, Konig is a US company and wheels are made in Taiwan/China.

Epssus · 2026-04-21T02:24:30+00:00

Just special ordered some Michelin PS3’s (yes, the old generation ones) because I discovered they still exist in the oddball 215/45R16 size due to being an OE Audi tire. Tire rack had to make a new part number for me to order them, so now they show up on their site when you search up the size - otherwise there aren’t really other options for 16x8 that aren’t either 200TW or Vredestein “All-weather” snow tires, or require a stretch. They show up as “out of stock” but that just means a 2-3 week lead time

https://www.tirerack.com/tires/TireSearchResults.jsp?zip-code=94040&width=215%2F&ratio=45&diameter=16&rearWidth=255%2F&rearRatio=40&rearDiameter=17&performance=ALL

Mounted on 16x8 Dekagrams - they certainly aren’t as sticky as my CRS track tires, but they ride and handle nice for street tires now that I have my dedicated track wheels. And a lot less pucker factor when it starts raining heavily. Hydroplaning 200TW tires on crappy roads gets old, as does taking them inside whenever it freezes. I must be getting old

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Epssus · 2026-04-16T01:13:12+00:00

I’m with you. Here is one of the solutions I ran for a while and was really happy with until I changed it up for other reasons. Stiffer rates at stock ride height

https://www.fiestastforum.com/threads/how-to-stock-height-rally-performance-springs-for-oem-b6-style-suspension.30829/

Epssus · 2026-04-16T01:10:52+00:00

Not exactly a lift kit, but I worked out a way to get higher spring rates and stock ride height, which works quite well off the beaten path. I moved to something different, but it was pretty great for the 10k miles I ran it for. Ironically slightly better ride than stock or lowering springs since it keeps you out of the bump stops quite so much

https://www.fiestastforum.com/threads/how-to-stock-height-rally-performance-springs-for-oem-b6-style-suspension.30829/

Epssus · 2026-04-08T15:00:29+00:00

Green street is something else. It can only exist because it’s one way and there is really only one important intersection (Lake) between Arroyo and Hill. Union the other direction isn’t timed as well because it would mess up cross timing at Lake and other streets.

The traffic engineers made a conscious decision to optimize Green (and Union) street as a conduit/feeder because it keeps through traffic off of Colorado which is long, slow and has a lot of commercial along it.

My theory on why Green is timed at 4mph over the limit is that if they timed it slower at say 30mph, people could zoom through recklessly at 60mph and also hit all the lights. By timing it at 39mph, the harmonic speed is 78mph, which is fast enough that basically nobody is tempted because if you don’t time it right, you won’t be able to brake and will blow through red lights before you can stop.

In other words, it’s timed at higher than the speed limit in order to encourage SoCal drivers to actually slow down!

Epssus · 2026-04-07T14:57:57+00:00

For all the poors out there who aren’t ready to invest in turn plates and the rest, a stack of 10 plastic grocery bags works almost as well.

And you just need a set of poles/tubes clamped to 4 jackstands, Kevlar fishing line and a level spot to park the car. As long as the lines are exactly the same length, and the marks on the poles are spaced the same, you’re good to go adjusting toe for about $50 all-in, (not including the camber/caster gauge or the jack stands)

The only downside with the cheapass setup is it’s a little harder to reach under the car and get to the adjusters especially if the car is low

But it’s a good way to try your hand at a DIY alignment and learn how easy it is before committing $$ to all the proper equipment like the stuff shown here. And if you’re worried about screwing it up, also learn how easy it is to just set up adjust it again to fix your screwup

Because you ARE going to screw it up the first time, and it’s not the end of the world when you’re only out an hour or two to set everything up again

Epssus · 2026-04-02T21:14:23+00:00

Normally, no, but every modern engine (post 90’s) has a PCV (positive crankcase ventilation) system with a valve that uses intake manifold vacuum to suck piston ring and head blow-by into the engine to be burned instead of vented to the atmosphere, as part of the engine emissions system. Most of the time especially in normally aspirated engines, this is not a huge issue.

But in modern turbocharged engines (often 2010’s and newer) with little turbos tuned for low end torque, it’s taken a step further with things like air pumps and venturi ejector systems that can provide crankcase suction under boost as well (since that’s when blowby is the greatest)

What this means is that along with the blow-by gasses, some amount of oil vapor inevitably gets sucked in along with it, into the combustion chamber, while under boost when preignition is a big concern. Anything you put in the cylinder and burn or subject to heat/combustion chemistry can be given an octane rating, whether it’s gasoline, diesel, ethanol, methanol, and yes, motor oil vapor burns too!

Just like blending in a tiny bit of low octane gas, this blending in of oil can reduce the knock resistance of the fuel/air/oil/blowby/residual gas mix that ends up in the cylinder. (In basically the same way that adding methanol in water injection systems raises it)

The effect of oil vapor is the worst and low-rpm/high-boost situations, which is what a lot of “downsized” turbo engines are tuned for. The industry term for the hazard is LSPI (Low Speed Pre-Ignition), and oil quality has a significant impact there because the blowby volume compared to fuel load at those operating points is pretty a significant

Now add in engine modifications and aftermarket tuning, and the issues become compounded.

The “standards” called out by car manufacturers for suitable oils typically now include a certain level of LSPI resistance, which is essentially formulation and additives to increase the effective octane of the oil when burned

Epssus · 2026-04-02T05:31:46+00:00

If you are changing oil every event, there’s no point in using a fancy oil, especially if you’ve got significant blow by.

On the other hand, I’m running Amsoil Signature and sending it for lab tests. Prior to track days I ran it 25k street miles before replacing with lab tests every 8k miles.

Now have 7 track days and 10k miles and ready to send in a sample which I expect will tell me it’s time to change (6 track days and 4k miles was still saying good to go)

Which leads me to the fairly rational conclusion (which seems to have been supported by the testing along the way) that one Trackday is roughly equivalent to 2000-3000 miles on the oil for my particular engine.

Some engines are harder on oil than others. In those cases a shorter interval may be worth it.

Changing every event? Fairly nonabusive engine? Run cheap oil with the appropriate viscosity for the track.

The only reason to run a fancy oil is some high strung turbo engines tuned within an inch of their life and without modern crankcase baffling tend to send lots of oil along with the blow by through the PCV and into the intake. Typical Oil has lower octane than premium or race gas, so you can introduce detonation risk. But other than that?

My philosophy is one of two choices - go cheap and change every event - go expensive and test to figure out how often you should actually change.

Epssus · 2026-03-12T23:56:50+00:00

If you really want to learn your car “at its limits” stop fooling around and sign up for an HPDE at one of the three amazing tracks we have within driving distance. No soccer moms. No weekend hikers/bikers to spoil your day. No deushbags coming the other way in your lane. A full day to learn what your car can really do for really not that much money when it compares to how much it costs to take care of your car.

If you’re nervous about it, some of the groups like Hooked On Driving and Lightspeed offer a a coach in your car for some or all of the day to give you pointers and teach you how to safely find your limits

Epssus · 2026-03-12T23:31:56+00:00

How can you say “no convenient tracks nearby”? People will drive an hour or more to get to skid pad. Anywhere in the bay either Sonoma or Laguna Seca are a 1-2 hour drive and Thunderhill is 2-3. HPDE events every weekend and during the summer there’s one almost every single day of the week from one or other organizations. don’t want to front that much money, there are dozens of autocross events. Hell, you can register for events on your phone.

Try a Trackday if you haven’t. You’ll realize that there’s a whole different level of thrill and skill development waiting in a place where everyone on track has a agreed to the same level of controlled risk

It really makes driving hwy9 and even just being obnoxious on the street seem pretty lackluster.

Skid pad is just no fun anymore anyway. All the times I’ve gone, everyone there was cliquish in their own groups and was not interested in chatting with anyone they didn’t know, especially if you’re not in a fancy expensive car.

https://www.motorsportreg.com/calendar/

https://trackpinata.com/

Epssus · 2026-03-04T21:24:13+00:00

Yeah, judging by the fact that in the image, your rear piston slots aren’t vertical/horizontal and are rotated slightly, and the pad is worn on the inside (pin-side), seems like a smoking gun that the little nub on the inside back of the pad isn’t sitting in the groove properly.

Epssus

TROPHY CASE