Spring rate help?

BGTV8

You want not more than 10-15 degrees C total spread between inner, middle and outer tyre measurements and the spread needs to be even. If the temps inner to middle are close, you can drop some camber.

The other thing to remember is that unless your pit is closest to pit entry, you will drop temps in the time take to transit the pitlane .. can be as much as 10 degC or more.

An R-Spec tyre that measures under 65-70 DegC is probably not working hard enough to generate maximum grip.

An infra-red temp gauge is an approximation only - you want a pyrometer with a probe to get into the tread proper for accurate readings, UNLESS the IR technology you are using is top-shelf (professional motorsport quality)

GSS138

Feedback much appreciated. And that's why I am here, to discuss it . Appreciate the opinion and congeniality.

You actually raised a really good point by suggesting putting 5000 lb springs on the rear. Yes, the damn rear would skate worse than Tonya Harding at that point lol.

With a 5000 spring in the rear and a 600 lb spring in the front, the ratio would be .33. This makes me wrong. Everyone knows that a 5000 lb spring in the rear is going to make the rear un-dampable unless the rear weighs 2500 lbs per corner. That's what you are missing. The spring rate doesn't matter, it's the spring rate and the corner weight.

But that got me thinking as well. If this is an inverse function which I know it is, then it is exponential as well. Let's do the opposite of what you are suggesting and put a 100 lb spring in the front of the car with a 600 lb spring in the rear. Guess what, car understeers like whoah.

What's the ratio? .39. Wow, that's really weird, .33 is close to .39. So why does your 5000 spring in the rear make it oversteer, and my 100 lb spring in the front make it understeer?

Everyone knows that putting a 100 lb spring underneath a 750 lb corner is going to be near useless. Just like anyone that puts a 5000 lb spring under a 750 lb corner is not going to get good results.

Assuming a motion ratio of .62 at all four corners(close to oem) if the car was perfectly corner balanced at 750 lbs each, .62 * 760 = 465 lb spring. Lets put 465 lb springs on a perfectly balanced car, by my math, it would produce a ratio of 1. Let's for argument sake assume that is a very bad idea.

So, you can either stiffen the front or soften the rear. lets add 100 lbs of spring to the front. New ratio = 1.06

This will probably not have much effect, tell me if you disagree.

Lets add 100 more. New ratio = 1.15. Wow, big change(exponential actually).

My guess is that this will drastically reduce understeer Since the front will not roll over and the fronts will transfer weight to the back much easier. Tell me if you disagree.

Lets add 500 more lbs of spring. ratio 1.52.

My guess is the front of the car at this point is barely controllable and is skating all over the place , not quite as bad as Tonya at the Olympics , but is definitely prone to break loose. A 750 lb corner sitting on top of an 1150+ lb spring barely allows the dampers to do their job.


so we went from the following ratios

1.00 Not a good idea.
1.06 Not much better.
1.15 If we agree, we reduced understeer( or added oversteer)
1.52 Turned the front end into a Frisbee.

the same works in reverse

1.00 not good idea
.94 not much better
.85 Increased understeer (or removed oversteer)
.48 turned the car into a knee board with no rudder.

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wstar

Eh, I doubt there's a ton of difference in various IR temp gauges. They're just a simple scientific instrument, and they have a certain accuracy and work a certain way. My Fluke (that I originally bought for electronics stuff) claims 1%, and coming off a DE cooldown lap and all the way back into the paddock I'm sure contributes way more error than that. I get that the the pyro in the carcass in the hot pit is more-accurate, but at this level I generally don't need to be more accurate. I just want to know the general shape of the temps: which band of the tire is running hotter or colder.

This is kind of what I was talking about at one point earlier, about trying to find out what it really matters to obsess over at an amateur/learning level. There's a pretty wide gap between "what you need to measure/adjust/fix just to make the car reasonably-drivable and not destroy tires", and "what you want to do to squeeze every thousandth in tight competition". In some areas I still have no idea where to draw the line yet. But I'm pretty sure at this point that tire temps/pressures, as critical as they are to the car, can be done for DE-level stuff with just an IR temp gauge and a simple pressure gauge after getting back to your parking spot in the paddock and still get you in the ballpark well enough. Most of the time you can even see gross pressure/alignment errors visually if you just look at how the rubber melts/wears.

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BGTV8

It is not so much about differences, but the fact that an IR temp reader reads the surface temp but what you really want to know is the temp in the underbelt

Anyway, for amateur purposes, you are mostly correct - it is the relative difference between inner, md and outer temps that is key ... you want an even graduation of temps - say 5 DegC apart - across the face of the tread as a lead indicator to camber sweet spot. What I am trying to communicate is that you want to measure these differences as close to hot-track exit as you can - i.e. by the time to trundle down the put lane and turn to the paddock out-back, your graduations will have morphed significantly enough to distort the knowledge you are after. Tyre pressure will be affected as well, but nowhere near the same extent.

For example, real-time monitoring of my RHF tread surface temps at T12 at Philip Island GP circuit (290mm wide Dunlop SS12 compound slick) now shows (inner to outer) going from 88/85/82 to 108/100/94 in the space of 150 metres as the car is turned in and accelerated thru the mid-corner. Once I take steering angle out of it, the temps drop 15 DegC in the next 300 metres. I borrowed the setup from a semi-Pro team because I was blistering the inside of the RH front at PI after a track resurface a few years ago because the settings I was using from prior seasons was too agressive and we had to take a bit of camber and some toe out of the car to get the tyre to last (blistering set in with temps over 115 DegC on the SS12).

One of our 370Z owners over here (Keith Flanagan - KF365 here) had a couple of delamination/tyre failures with Dunlop DZ03G in T12 as well, because it is a very hi-speed corner and the car stays loaded for an eternity (maybe 8-10 seconds from turn-in until you pull all the steering out of the car). It is the temps in the carcass that lead to failure, not the outer tread surface ....

On a cold day where track temps are ~15DegC, by the time I exit the track and get to the top of pitlane (where crew can use a probe on the tyre), the IR surface temps can be back to 60 DegC or less but the temp under the surface layer can be up to 15 Deg higher - so it can be very easy to get confused. That is my real message !!

Toe (and caster) can also influence heat build-up on turn-in and in the case of toe-out, inner temps in straight running.

This thread had an earlier post on the inter-connected-ness of springs, suspension settings and even driver habit and if I have learned one thing in the past 40-odd years, it is that there is always something new to learn, that simple things usually work best - because us amateurs don;t have the funds to invest in full-time engineers to can run the calcs all the time. There were a couple of book titles recommended as well which are a great source of information and the basis for personal experimentation.

Keep experimenting and you acquire knowledge .... and tread your own path !!

wstar

As long as this thread is wobbling all over the place off the original topic anyways ...

Here's another question for those more-knowledgeable: does balancing wheels/tires really matter on a racecar? I've googled on this a bit and seen conflicting advice. Some seem to think it matters, others take the line that it doesn't. Those that say it doesn't matter argue that (a) You'd mostly only feel the vibration coasting at a steady speed, which you almost never do anyways, and (b) aside from a potential few uncomfortable vibrations, it doesn't really damage anything or hurt performance anyways. It would save time on the (increasingly-frequent) tire re-mountings not to bother with it, and then I wouldn't have to worry about taping down wheel weights and/or worrying about them flying off or possibly getting stuck in the brake caliper somewhere, etc. That and let's face it, with all the tire worms inside the wheel and the pickups on the outside, and probably the tire slipping into a different rotational position on the rim regularly, how well is the thing really staying in balance throughout the day anyways?

So: to balance or not to balance? What do pro race teams do?

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BGTV8

Definitely balance wheels - a wheel 50 gms out at 250kph will shake the filling out of your teeth.

j-rho

In the new Camaro Z28, Chevrolet marketing got some mileage out of how they're texturing the wheel bead surface to keep the tire from rotating too much on the wheel:
Camaro Z/28 is so grippy GM had to find way to keep tires from slipping on wheels - Autoblog
In reality this sort of thing has been happening on hard-driven cars for a long time. So if you have a tire-based imbalance, there's not much help in balancing if you have sticky tires you'll push hard.

An inherently unbalanced wheel, I suppose it could help, but balancing isn't usually done that way, and the tire has a much greater impact on the balance of the overall package.

But to each their own...

Megan370z

On slick I wouldn't run anything lower than 900 *16kg* in the front !!
Now with the aero its an ever bigger number !

as far as running an 1150+spring , Its not un-commun to see a car which can be Pro or Amateur driver with nearly as much spring rate and they wouldn't go much below than this with slicks.

and remember that 1150 spring on a 750 corner, Im pretty sure the car is moving and seeing over 1g in the corner.. isnt that bring that corner to over 1500 llbs ? then you have 1inch and half of travel due to weight transfer.. which is relatively acceptable in my book for 1g corner.

math paper talking is quite different when you are actually driving the car, it will bring you close but the rest its all feeling and how the car react.





I haven't gave my opinion on the first picture Wstar posted,
For his setup I would recommend 16kg *900* front // 12kg *672* rear with the stiffer front bar and then the stock rear.

this is my new baseline w/ aero I will be using when I'm fit enough to get back on the track. I know the front wont be enough but its a baseline.

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Shamu

For you guys who like "loose" cars what does that mean?

I like a balanced car that transitions well and is getting maximum mechnical grip from the tires. Not too much understeer and not much oversteer so I can managing turning with brakes and power application. I havent found too many road courses or hillclimbs where excessive oversteer is benificial .

So isnt what somone who is going to track wants is nuteral handling car with excellent transistory response for given tire selected? All this focus on loose or not loose seems to be foreign to me. Focusing on what spring and bar combo can slightly increase or decrease understeer and oversteer to your liking is probably better focus. Loose car as I know it isnt fast. But then I have been in very well buttoned down race cars with huge spring rates that arent "loose"

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wstar

Loose, in this context, I think, just means a tendency towards oversteer. Not the kind that will get you in trouble with big snap oversteers, but just a enough tendency that it's easy to rotate the car. I like how the car feels that way. I don't know if it's a fundamental thing that, given a perfect driver, either a loose or tight car setup is actually faster. But at least for me, being a bit loose is easier to feel and control at the limit with steering and throttle corrections, and it's easier to get the car to rotate through tight corners (both under trailing brake at the start and under throttle as you come out).

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wstar

^ I should add to the above, I think there's a distinction to be drawn between ideal situations and the real world, too.

In an ideal scenario, the pavement is perfect, there's no surprises from traffic or turtles or mud clods, I hit my reference points at precisely the correct location and speed every lap, and nothing about the car changes over the course of a session (e.g. tires warming up). If this were always the case, my inputs would always be perfect to keep the car exactly where it should be at the best slip angle for traction, and the car would always naturally track-out to the correct point at the end, etc.

In the real world, there are too many variables to even try to list, all the time. If you're consistent you've eliminated a lot of variables, but millisecond-by-millisecond you're making small (and sometimes, large) corrections to your inputs to account for all these variable things coming into play. Many of those corrections get to be a subconscious thing over time - they happen way too fast for it to even be possible that you're consciously thinking through the decision process. Either that or you drive slow enough that most of these variables don't actually matter because you're not that close to the edge.

I think when you're out there in that mode, near the edge, where you're constantly making corrections to keep the car where you want it to be and not flying off the track just because you happened to hit a blade of loose grass or dropped a couple wheels in the dirt to avoid traffic, a loose tendency is easier to control than a tight one (at least, it is for my brain, and it seems like it's not uncommon to feel that way).

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synolimit

Reading all this WTF Hotchkins? I emailed with no response awhile ago. No one wants their rear bar is seems or have to pay for it. Do we really have to buy both and trash the rear? No ones going to just buy a stiff rear bar and I don't want to screw someone just selling it to them and being like "you need this." If we pay almost $500 for the set I'd rather pay more money for just a front that's bigger and better.

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wstar

Or they could go engineer us a rear bar option that was actually weaker than stock. Then the set would be worth it.

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synolimit

Everyone email.

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GSS138

"Loose" refers to rear loose end-oversteer. I have noticed that in AutoX they tend to like it better and it definitely makes sense since they have to do a lot more dancing and sharp turns than us track guys. I have only done autox a few times and it's not my thing personally, but man you learn a lot about how the car behaves.

Megan, I will agree 1100 lb springs were a bad example above, but 5000 would cause the condition I was trying to describe-trying to demonstrate a point that there is a number, that all of the basics break down, and the problem exponentiates. With slicks and full aero, I can see 1100 being very reasonable on a 750 lb corner, especially at 1G.

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