Q45 lowering with larger than 15" wheels

[Q45tech]

Something poped into mind. That the camber gain curve of the angled upper link and caster induced gain when turning where optimized for a 15" Michelin Sport XGTV Tire.

A larger wheel will have a narrower sidewall which will not need as much camber gain, the Eibachs are only 15% stiffer in front so this won't reduce front body roll much.Big wheels will have way way excessive camber gain for the tires 16>17>18>20"...............the bigger the worse it gets.

There really is no easy [or hard] way to reduce the camber gain as it is a function of the 35 degrees angle of the upper link other than grossly limiting the body roll [more than Eibachs or sway bars can [with stiff coilovers]]. Adjustable front upperlinks can reduce the negative static camber and probably should be set to ZERO [no] camber with larger wheels to try to bring the camber down in turns.

The is much less camber gain on the rear [A arms type] but still low negative static camber with larger wheels.

Obviously different tires in larger diameters will have different camber requirements............the ultras would be stiffer vs high performance [need more camber] to make up for sloppy sidewalls.

I never think of big wheels since I still run 15"............even lowered my tires behave due to big sidewalls and as designed camber gain.

[Peterofdevon]

What does this mean in English? I was about to go up to17" and many folks eher run 18+

Peter

[elwesso]

I see what Tech is saying... Allow me to paraphrase... Great thoughts by the way Tech...

As we all know, camber increases (negatively, meaning that it increases in magnitude negatively, but technically its getting smaller) with body height... SO as the body leans, there is more negative camber...

The REASON that we have camber gain is, as the sidewall of the tire flexes due to the increased weight of that corner of the car on the tire, the sidewall starts to roll over (we all know this phenomenon)... So, the wheel "tilts" in order to compensate for this....

the POINT of camber is, as the body weight is transferred during a turn it maintains an ideal (or close to ideal) tire contact patch... If you have too little negative camber, the sidewall will want to roll over.. If you have too much negative camber, you will not be using all of the tire...

If the tires were infinitely stiff AND/OR there was no body roll, we would not need any camber (or very very little)... however, this is not the case in the real world.. Even the stiffest suspensions have some body roll and certainly the tire sidewall will flex... THIS IS WHY cars that have very little body roll have to run slightly more static negative camber (IE camber that you would set at an alignment shop, as the car sits).... Since there is less body roll, there will be less camber GAINED under dynamic conditions... So under full body roll, stock you may gain 4* (arbitrary value), with a heavily modified suspension, you may only get 2* (again, arbitrary)... Obviously, this is on very race type suspensions, nothing terribly applicable to Q45s...

back to the original topic:

Sidewall stiffness is generally related to the size of the sidewall.... Assuming a constant overall diameter, a 17in tire is going to have a much smaller sidewall than a 15in tire... THUS, in order to handle the stress, it has to be made stiffer to maintain a similar load capacity... we all know this because we think about how much better that 15in wheels ride than 17/18/19in wheels do....

Going back to what I was talking about earlier, since a 15in tire has less sidewall stiffness, it needs more dynamic camber to maintain a desireable contact patch..... HOWEVER, a 17in tire (for example) does not need the same amount of dynamic camber... this is because there is less sidewall flex.... The Q45 suspension was designed with the 15in tire in mind.

SO, we know that if we run a larger tire, we dont want as much dynamic camber.... so, how do we combat that?? well, camber increases as the car rolls, so if you reduce body roll, you decrease camber gained.... This is NOT possible without really stiff coilovers, as the eibach springs OR superstiff sway bars wont be enough! Although marginally effective at best, if you want to have maximum handling, you need to actually DECREASE your negative camber, by setting it closer to 0* if your running a larger tire.... Unfortunately, you will still be gaining a ton of camber as you turn, but theres really not anything we can do about it without changing the length and angle of the upper link and changing caster induced camber gain.....

So heres the cliff notes- The stock suspension gains too much camber during turns.- What does this mean for most people??? not a lot because most times Q45 owners arent concerned about these things.. However, its something that "we" (I say we because im getting closer) engineers like to think and dwell on... Something to consider when getting an alignment, might consider decreasing camber, making it closer to 0*

FOR TECH: Would be interesting to compare camber gains of 300ZX using the 16in wheels. Static camber spec is from -1.58 (-1*35') to -.08* (-05'), exactly the same on Q... hard to compare dual A arm (350Z/G35) to Q

[Jesda]

So... can you sum it up for a management major? I have two sets of 15" wheels. I'm fine with the stock specifications, correct?

[ScottJackson]

I don't have my Q nearby to look at the upper links to see if it's feasible, but you could reduce the camber gain as the suspension compresses by raising the pivot point of the upper link where it attaches to the body (non wheel end).

[ScottJackson]

to sum it even more, a tall sidewall like on a 15" tire will roll over more in a turn. We're talking about the tires on the outside of the turn. So you take a left turn and the right side tires will take most of the load because the inertia sends the weight of the car outward from the turn. Since the weight shifts to the right side, the suspension on that side compresses. When that happens, the upper link goes from a flat angle like this - to this /. When that happens, it pulls the top of the tire in toward the center of the car, tilting the top away from the outside of the turn. The bottom of the tire is grabbing the road and trying to pull the car into the turn while the weight is pulling away from it. That flexes the sidewall of the tire and pulls the inside tread of the tire up as the tire "rolls" over. A short sidewall tire won't roll nearly as much and therefore doesn't need the tire to be tilted against the turn nearly as much. Getting an equal load across the contact patch of the tire is the goal, so less camber gain with low profile tires is better.

[maxnix]

But what we are talking about here is say fewer than 5° of camber change.

So if we can compare sidewall stiffness (spring rate), then we need to reduce it to maybe 3°?

[Q45tech]

Some may be missing that the angled upper link creates increasing camber as the wheel is turned more and more.

The NEGATIVE camber gain curve increases as the steering wheel is turned due high caster and the angle.

1.25 turns [full lock] on the steering wheel turns the tire to a ~~35 degree angle.

It appears that with lowering and no static camber correction and full lock to lock the negative camber exceeds NEGATIVE 10 degrees. However most of us rarely use more than 1/2 a turn [14 degrees of tire angle] instead of 1.25 turns.

Consider stronger front tires [than oem 1521 pounds] and how they improve feel and allow higher handling G's because they produce a lower slip angle for the same amount of weight transfer. [called lateral force in pounds]

They just let you go thru a curve a few mph faster before the slip angle reaches the wash out point where friction decreases [up to a certain slip angle the friction goes up linearly then plateaus before decreasing]

This graph is of a very very well behaved tire, the higher the performance level of a tire the steeper the after plateau point FALLS........sudden let go!

The slip angle is the angle between the direction of the tire and the actual path of the car. Everytime you turn the wheel there is some amount of slip angle and optimum G's occur depending on tire at 4-8 degrees and this will vary with tread/road temperature.

Tire Self aligning torque is the steering effort as you approach, are in, and leave the optimum plateau, unfortunately the Q steering is so good it somewhat masks this important feel factor for performance driving.

Understeer is when the front slip angles might be 15 degrees and the rear is a normal 4-8.

http://www.msscca.org/msscca_autox_school_2006.ppt

In the middle of the above slides are some nice graphs and explanations.

[Jesda]

So... should I purchase bigger wheels or not?

This thread is giving me a headache. I think I'll go back to shopping for commercial real estate...

[elwesso]

So... should I purchase bigger wheels or not?

This thread is giving me a headache. I think I'll go back to shopping for commercial real estate...

The things we are discussing here really only apply to max handling... for 99% of driving, wether you have a 15in tire or an 18in tire wont really make a difference...

[ScottJackson]

Yeah, I left out the simplified explanation of how caster affects camber. Think of it as the angle between the top and bottom pivot points of the wheel. Picture a chopper motorcycle with that wheel way out front and the bars at a sharp raked back angle. You can keep the bike straight up and when you turn the front wheel, it also leans the front tire over a lot. Now take a bicycle where the forks are almost straight up and down (not nearly as much CASTER), hold it straight up and turn the front wheel. The wheel won't lean over nearly as much as the chopper motorcycle. That's how caster plays a big role in camber when you turn off of center. The more caster you have (like a chopper), the more it wants to naturally pull the wheels straight ahead and the more resistance the front wheels will have against turning. But Tech is right, it seems the Q masks this feel quite a bit. I haven't checked to see what the caster angle is, but it sounds like I'd be a little suprised even though it's sorta the norm to give "cruising" type cars quite a bit of caster so they want to track straight ahead instead of turn sharply at the slightest twitch of the steering wheel.

[Q45tech]

Actually this matters most in street driving where you turn the steering wheel more than 90 degrees with big wheels.................why they feather so badly.

[AZhitman]

So far, no issues with the Eibachs, OEM Q 18's, and 99Y load rating g-Force T/A KD's.

Certainly can see the difference tech is mentioning, even static turning lock-to-lock changes the ride height more than an inch.

[Falkdesigns]

OFF topic, but isn't there something on here about political statements in sigs? Jesda is saying Gore is a communist? Give me a break dude. I may have a picture of our Idiot in Chief, but I didn't make it up, HE did. Someone just got a picture of it.

On topic, I have no issues with my 2" drop that would ever make me go back. My tires wear incredibly evenly actually, I love driving it 5 mph, or 125 mph. No matter where, it's smooth. But maybe this info is specific to the G50? Weren't all Y33's stock with at least 16" and then 17", or did the non-T come with 15"?

[Q45tech]

Only the 90-96 Q45 [and early G20] had the twisted angle upper link. Nissan abandoned this design in 1997 when it went to MacPearson struts to save money and change package size...neither the J30 nor 300zx had this design.

To my knowlwedge no vehicle has ever had a much camber gain in turning as a 90-96 Q................impossible with unequal length A arms.

[Rex]

OFF topic, but isn't there something on here about political statements in sigs?

Good point., Jesda can you remove, if I do you're avfatar will be (unintentionally) "dropped" in the process.

On topic, I have no issues with my 2" drop that would ever make me go back. My tires wear incredibly evenly actually, I love driving it 5 mph, or 125 mph. No matter where, it's smooth. But maybe this info is specific to the G50? Weren't all Y33's stock with at least 16" and then 17", or did the non-T come with 15"?

I don't think the Y33 shares the same front upper link as the G50.

[AZhitman]

Correct - Y33 never had 15's.

[Q45tech]

At the front of the G20, a decidedly more complex suspension is needed to keep the front wheels perpinducular to the ground while allowing for the often conflicting geometry needed for straight-line stability, cornering grip, and compact dimensions. Nissan's front multi-link suspension is closely related to a double wishbone suspension. On a double wishbone suspension, the wheel is held by a hub that is attached to the car with an upper link and a lower link (these links are sometimes called wishbones because of their shape), with the upper link being shorter than the lower link. Assuming they start out parallel when the car is at rest, compressing the suspension will cause the short upper link to pull the top of the wheel in toward the car as it swings through its small-radius arc, while the longer lower link will keep the bottom of the wheel more or less in the same place. The result is increasing negative camber as the suspension compresses, and therefore the wheel staying close to perpindicular to the ground as the body rolls.

The G20's multi-link front suspension is essentially a modified version of a double wishbone. The changes that were made--the addition of a third link, and the angled position of the upper link--make ususally contradictory geometry goals possible. Each of the two wishbones is attached to the hub with a ball joint, and the position of the two ball joints determines the steering axis. The steering axis is critically important to achieving high-speed stability, reducing torque steer, and providing strong cornering. Designing a suspension with a steering axis that leans back severely (one with a lot of caster) requires mounting the upper arm back so far that it often interferes with other vital components, such as the brake mastery cylinder. Angling the steering axis so that the imaginary line between the two ball joints passes through the center of the contact patch (which is important for reducing torque steer) also requires pushing the upper arm in toward the middle of the car, often resulting in either an arm that is too short, or interference between the suspension and the engine.

To achieve the ideal steering axis without causing the associated packaging problems, Nissan developed a third link called, of all things the "third link". Instead of the steering axis being determined by the upper and lower ball joints, it is determined by the lower ball joint, and a shaft held solidly by the third link. The third link is then attached to the car by the upper link, so the third link tilts with the hub as camber changes.

With the third link in place, the upper link can then be positioned with much more freedom. One of the freedoms taken with the mounting of the upper link was angling it forward from the car to the third link, at an angle of about 35 degrees. This minor change is an incredibly clever way to make the suspension behave differently during cornering than during straight line driving.

To keep the wheel straight up and down on a double wishbone (or in this case a pseudo double wishbone) suspension, especially one with a high degree of body roll such as a performance luxury car, you have to have a relatively aggressive camber curve. When going over bumps in a straight line, though, you don't want the camber changing that much. The angled upper arm solves this problem. With the wheel pointed straight ahead, the upper arm pulls in at an angle as the suspension compresses. This still introduces some negative camber, but some of the movement is translated in to a rearward tilt instead. As the wheel is turned, it comes closer and closer to being at a right angle to the upper link, at which point all of that tilt is camber change. In other words, the camber curve increases the more the steering wheel is turned. Very clever. And as you will agree, the "multi-link" name sure beats "double wishbone with a forward-facing upper link and a third link controlling steering axis and holding the spring and damper".

http://www.se-r.net/about/g20/scc/oct98/tb.html

[Q45tech]

http://home.earthlink.net/~whshope/id21.html

free Skid pad software

http://home.earthlink.net/~whshope/inde ... ad...age=1

[elwesso]

great links tech!!!! that suspension page has a ton of great info on it... may have to harvest it.

[Jesda]

OFF topic, but isn't there something on here about political statements in sigs?

Its a very obscure inside joke among friends, almost all of whom are of your political persuasion. Chill out, JDM boy! Go put airbags on a tricycle or something.

[maxnix]

Correct - Y33 never had 15's.

But it did have the same specified 26" (or 26.1") diameter tire dimension.

[maxnix]

"Michelin introduced the Pilot Sport A/S, an ultra-high-performance all-season tire, in 2001. It was engineered to take advantage of, and in fact requires, a new, flexible manufacturing technology Michelin calls C3M. Nobody I talked to would admit to knowing what C3M is and how it works, but it has many advantages. Fundamentally, C3M yields the most uniform tire Michelin has ever made, reducing vibration and wear. C3M allows Michelin to build shorter runs of tires with greater precision for flexibility in production and more rapid product development cycles and to explore new architectures."

One thing I noticed about my PS2 that is unusual is that the inside, rather than showing the texture of the corded structure like most tires, is instead glass smooth. The sectional moldings are clearly visible on the sidewalls also.

Thanks for the links, Dennis. As always, your research is appreciated by those who follow it.

[Rex]

Its a very obscure inside joke among friends, almost all of whom are of your political persuasion. Chill out, JDM boy! Go put airbags on a tricycle or something.

Nonetheless, it's a NICO policy.

Jesda can you remove, if I do you're avatar will be (unintentionally) "dropped" in the process.

[Q45tech]

The extra expensive [another dollar] halogenated butyl rubber inner liner to protect the cords/belts from the air and moisture in the inflation gas.

Endurance and durability, kind of way over kill in these applications where the tires are usually replaced in 20k..................but not in the old Pilot H4 where in 235/60/15 you could get 40k..

Currently I have 235 on front and 215 on rear strange but not too hard to adjust style.......winter after all.