Spring rate help?

Rangerz

Appreciate all the information in this thread guys...keep the discussion going please

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thompsontechs

I just typed a book and then erased it... here's what my gut or arse tell me... Make one change at a time drive it and then make another not forgetting the first. Everyone drives differently, I like a loose car and drive it well. If you are new, I would say you should go tight, but to think this or that is right for another driver is flawed. Don't get me wrong, if you are lost then any help is good and what some have said here can help you get where you want to go. I have driven for a living and the best car I ever had, my co claimed undrivable.

Find some numbers here and then learn what you like need to for yourself. No two cars are alike and no two drivers either.... end of line................

wstar

Yeah that's all the general idea. I prefer a slightly loose car. Step one should be downsizing or getting rid of the rear sway, but I'm also way overdue to up my spring rates as well - and while the swaybar is the bigger issue right now, dropping rate from that is going to make at least my rear springs suddenly a bigger issue, too.

So I'm probably going to end up making both changes at once. It'll be fine if it's somewhere in the ballpark of correct. So I'll do a bunch of math and season it with some random guesswork and then throw on a set of springs and see what happens

Really, the worst adaptation I've had to deal with so far was a simultaneous switch from high-treadwear tires to RS3's while also stepping down from a staggered to a square tire setup. Felt awful to me the first drive, but after a full weekend I adapted and decided I liked it better. I'm sure this sway+spring change will feel a little weird to me at first, too, but it'll probably be fine as long as I don't screw it up too badly.

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synolimit

Speaking of treadwear, do you check tire temps? I drove around the block after coil install and when checking rubbing and such when I got back I noticed the inner wall was hot as hell yet the outer was very cold. Obviously severe camber and getting it aligned tomorrow but it still made me think about temps on the track and wear. I'd assume even temps across the carcass is ideal? Thinking of buying a temp gun.

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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)

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

Yeah I use an IR temp gun to check things out sometimes. A proper pyrometer would be way better, but 9 times out of 10 the IR temp tells me what I need to know (and hell 8 times out of 10 I already know what the temp gun is going to say just by looking carefully at the rubber).

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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...

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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GSS138

I am actually going to talk to these guys the next time I run with POC. Their bars are the shizzle, custom made, easy to adjust, and they even make internally adjustable options. I doubt they will so don't get you hopes up. But I am going to ask them. If there is any other interest lemme know, it might help me try to convince them. It's just a small Porsche racing/performance shop down in SD but I know this car and have no problem approaching the guy and asking him at next event.

Tarett Engineering Competition Porsche Suspension Components

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