Just a thought... What could the factory have done to lighten then car?

[strat61caster]

Originally Posted by babydriver

Since the wheel is part of the sprung weight of the suspension, it seems to me that changing the mass of the wheel+tire would require changing the factory springs (and their rate) also. Less mass in the wheels will result in a lack of full compression of the springs and I suspect that the ride will become rather stiff and paradoxically you could lose some control and contact with the road. Am I misunderstanding something here?

Info inbound.

http://www.formula1-dictionary.net/unsprung_weight.html

You'd end up with a softer suspension as the unsprung assembly that creates traction with the ground requires less force to 'follow' the road.


http://victorylibrary.com/mopar/sprung-c.htm

The unsprung vs. sprung weight percentage also affects ride comfort, since lighter springs are needed to maintain traction and control with lighter unsprung components (alloy wheels, independent rear suspension, alloy calipers, composite springs, in-board brakes, etc.), the chassis is less disturbed by wheel movement and road surface irregularities.

Basically if you envision the body of the car sitting still and it's traveling over a bumpy road the wheels and suspension work like mad to stay in contact with the road, if the wheels and suspension are heavy they react slowly because they have high inertia and require a lot of force to change direction so you would need stiff suspension to 'push' them into the ground while simultaneously being soft enough to 'absorb' the rises in elevation, a tough compromise. With a lighter setup there's less inertia, the wheels 'track' the road with less effort, increasing traction overall. That's a very simplified explanation but the fundamentals don't change when talking about an F1 car or an off-road buggy.

Image for funsies:

[babydriver]

Originally Posted by strat61caster

Info inbound.

http://www.formula1-dictionary.net/unsprung_weight.html

You'd end up with a softer suspension as the unsprung assembly that creates traction with the ground requires less force to 'follow' the road.


http://victorylibrary.com/mopar/sprung-c.htm

The unsprung vs. sprung weight percentage also affects ride comfort, since lighter springs are needed to maintain traction and control with lighter unsprung components (alloy wheels, independent rear suspension, alloy calipers, composite springs, in-board brakes, etc.), the chassis is less disturbed by wheel movement and road surface irregularities.

Thanks! BTW, I meant to say "unsprung" rather than "sprung" earlier. The above underlined sentence was effectively my point; lighter wheels need lighter springs too.

[Bristecom]

Originally Posted by Tcoat

Between my wife and I we had 7 Mitsus over a 20 year period and other than my Talon (I consider it a Mitsu) that just died of old age we never once had to have one repaired. Not so much as a light bulb required work!

Yeah, I bought the Evo X and fourth gen Eclipse right when they were released and they were faultless for all the years I had them (6+). The ones who claim poor reliability are generally those who mod the heck out of them (add 200+ hp to stock engine) and try to blame the car itself for poor reliability. But with that said, my DD, the Eclipse GSX is getting tired at nearly 200k miles so I will inevitably have to replace it and the FR-S is by far my favorite prospect for that. Also, now that I live in Florida, I don't need AWD so much. :P

[Koa]

Originally Posted by Bristecom

Yeah, I bought the Evo X and fourth gen Eclipse right when they were released and they were faultless for all the years I had them (6+). The ones who claim poor reliability are generally those who mod the heck out of them (add 200+ hp to stock engine) and try to blame the car itself for poor reliability. But with that said, my DD, the Eclipse GSX is getting tired at nearly 200k miles so I will inevitably have to replace it and the FR-S is by far my favorite prospect for that. Also, now that I live in Florida, I don't need AWD so much. :P

I was referring to this, among other issues:

https://www.google.com/search?q=rust...oe=&gws_rd=ssl

but this doesn't apply to your sexy X

Fair disclaimer: I don't believe Subaru performance platforms are more reliable than Mitsu's performance offerings

[Tcoat]

Originally Posted by Bristecom

Yeah, I bought the Evo X and fourth gen Eclipse right when they were released and they were faultless for all the years I had them (6+). The ones who claim poor reliability are generally those who mod the heck out of them (add 200+ hp to stock engine) and try to blame the car itself for poor reliability. But with that said, my DD, the Eclipse GSX is getting tired at nearly 200k miles so I will inevitably have to replace it and the FR-S is by far my favorite prospect for that. Also, now that I live in Florida, I don't need AWD so much. :P

Obviously I am a Mitsu fan but found the FRS blows the Eclipse out of the water in every aspect even without the AWD.

[Ultramaroon]

Originally Posted by babydriver

Thanks! BTW, I meant to say "unsprung" rather than "sprung" earlier. The above underlined sentence was effectively my point; lighter wheels need lighter springs too.

I'm at work so no time to actually review but I think the article which makes that statement is incorrect.
http://victorylibrary.com/mopar/sprung-c.htm

All other parameters being equal, reduced unsprung mass does not require reduced spring rate. Actually, reduced spring rate in both cases lowers the resonant frequency of the suspension system which negatively affects the system's ability to recover quickly from a perturbation (bump). Traction is lost during that increased time required for the wheel to reverse direction and regain full contact with the road surface.

I'll wait until this evening to find out how wrong I am but for now, I'm going to stick it out there for consideration.

[babydriver]

Originally Posted by Ultramaroon

I'm at work so no time to actually review but I think the article which makes that statement is incorrect.
http://victorylibrary.com/mopar/sprung-c.htm

All other parameters being equal, reduced unsprung mass does not require reduced spring rate. Actually, reduced spring rate in both cases lowers the resonant frequency of the suspension system which negatively affects the system's ability to recover quickly from a perturbation (bump). Traction is lost during that increased time required for the wheel to reverse direction and regain full contact with the road surface.

I'll wait until this evening to find out how wrong I am but for now, I'm going to stick it out there for consideration.

Of course there is another factor at work and that is damping (the shock absorber). The damping would be enough to eliminate any oscillations from the lower rate (as you say, a lower resonant frequency too). I'm assuming though that there has to be an optimum spring rate for each unsprung mass designed to achieve certain goals of handling and traction, otherwise all car manufacturer would use the same springs. Toyota went to the trouble to change the spring rates on the 2015 FR-S compared to the two previous years to improve handling. They must have had their reasons.

I'll look forward to your later post, Ultramarine.

[totopo]

Originally Posted by babydriver

Of course there is another factor at work and that is damping (the shock absorber). The damping would be enough to eliminate any oscillations from the lower rate (as you say, a lower resonant frequency too). I'm assuming though that there has to be an optimum spring rate for each unsprung mass designed to achieve certain goals of handling and traction, otherwise all car manufacturer would use the same springs. Toyota went to the trouble to change the spring rates on the 2015 FR-S compared to the two previous years to improve handling. They must have had their reasons.

I'll look forward to your later post, Ultramarine.

Springs absorb bumps and shocks control springs and body motion.

Spring rates are mostly meaningless to talk about from a modeling perspective because of differing motion ratios for different suspensions and makes. Resonant frequency/wheel rate is the real measurement. Lighter unsprung weight is basically almost linear w increasing the wheel rate.

10% less unsprung weight is basically similar to 10% stiffer springs in terms of wheel rate. Ie if your wheel rate was 1.5, now it is 1.65

Generally lower wheel rates (like 1) makes for more comfort and better traction, but needs more suspension travel. So wheel rates are mostly governed by bump travel and expected hauling weight of the car. Most cars have rates around 1.2 or so and end up needing at least like 6 inches bump travel Minimum. Most non-aero driven pure track cars aim for 3 inches bump travel which ends up at wheel rates around 2.5. sports cars end up in the middle.

roll angle is harmless in steady state but bad in transitions and makes drivers unhappy if there is too little or too much. Anti roll bars are to control roll angles.

shocks control body motion at low shock speeds and control for bumps at high shock speeds.

Edit: the wheels also count for rotational mass, which does help acceleration and braking


second edit: I think I have something wrong with the unsprung weight. Please ignore the wrong half of this post. which half is wrong I'm not quite sure. ahaha

[Tcoat]

Damn poor Ubersuber he would have loved this!!!!!
You would all be wrong of course but he would still have loved this.

[Bristecom]

Originally Posted by Tcoat

Obviously I am a Mitsu fan but found the FRS blows the Eclipse out of the water in every aspect even without the AWD.

Pretty much except for a few of things - mid to high range torque, the raw feel/feedback of an old sports car, and traction (although sometimes you don't want this )

But don't worry, I'll be moving to an FR-S soon enough, even if they don't improve the engine at all (as much as I would like them to).

Originally Posted by Koa

I was referring to this, among other issues:

https://www.google.com/search?q=rust...oe=&gws_rd=ssl

but this doesn't apply to your sexy X

Fair disclaimer: I don't believe Subaru performance platforms are more reliable than Mitsu's performance offerings

As with any car, there can be issues but my Eclipse is nearly 17 years old, always sat outside, dealt with salty winter roads, and barely got washed, and I still don't really see much rust under it or anywhere. That's pretty impressive to me. But I have seen pictures of some that are badly rusted. I'm not sure what they're doing to get that kind of rust. Maybe they park it in a swamp? But even so, Mitsubishi has had a 10 year rust warranty for a long time. So those people still probably could have got that taken care of.

But yeah, I'm not claiming Mitsu is better or anything; it's just that I don't absolutely have to buy a new car right now. I will get the FR-S soon enough and I was considering getting it when the Monograms came out but decided to wait it out a bit longer.

[CatDaddysBBQ]

I'd say the easiest way would be to have a lightweight battery, no rear seat (parcel shelf and a wall to block off the trunk) and ditch the spare for a plug/compressor kit. Ditch the Sound tube while they're at it as well.

That'd save 100lbs or so, and the added cost of the fancy battery would be offset by the cheaper rear seat area option and the fill kit vs a wheel/tire/jack/etc combo.

[Ultramaroon]

Originally Posted by totopo

10% less unsprung weight is basically similar to 10% stiffer springs in terms of wheel rate. Ie if your wheel rate was 1.5, now it is 1.65

Isn't wheel rate simply a way to combine spring rate with the moment arm of the suspension? I don't understand how mass would figure into that.

I couldn't find my vehicle dynamics book last night. @babydriver's question is interesting and I'm taking ownership. Thank God brick & mortar libraries still exist.

[strat61caster]

Originally Posted by Ultramaroon

Isn't wheel rate simply a way to combine spring rate with the moment arm of the suspension? I don't understand how mass would figure into that.

I couldn't find my vehicle dynamics book last night. @babydriver's question is interesting and I'm taking ownership. Thank God brick & mortar libraries still exist.

You're absolutely right that lowering unsprung mass does not 'require' lowering spring rate and doing so would likely be detrimental to performance.

However it would not be detrimental to comfort and I pointed it out explicitly because it was the opposite of baby's assumption.

But of course I wouldn't mind the lesson, my class did not go that in depth.

[babydriver]

Sometimes it's helpful to me to simplify the problem somewhat.

Imagine that we have a coil spring connecting two weights, one small one on the bottom (the unsprung weight) and one very large one above the coil spring (the sprung weight). Any change in the sprung weight will either compress the coil spring more (if heavier) or less (if lighter). For the purpose of this thought experiment, we will ignore any side to side motion that may be possible; only up and down motion is "allowed".

What complicates matters further is that the lower "unsprung" weight also moves. As force is applied to it in an upward direction, the spring compresses and rebounds. A downward direction will cause stretching and then rebounding. At some critical combination of rate and weight, the unsprung weight will come into resonance with the spring's rate, allowing the greatest motion with the least effort. However, this is also the point at which the entire assembly wants to continue to oscillate at the same speed as long as there is additional energy put into the system. The shock absorber (on the car) is there to reduce this resonance (i.e. bouncing).

The question is: If the damped resonance is something that is desirable or undesirable?