Drop Spindle Discussion

[Echo Leader]

"Spring rates"? Or "wheel rate"? I've always seen T-Bar rates expressed as "wheel" due to the lever arm contribution to the equation, but most coils are "spring". Comparing these two items without the motion ratio will negate any meaningful relationship between one of your setups and the other.

So what is the motion ratio on the Milano (same for GTV6 I'm assuming?)? If it's ration low, a 4X increase in RSR coil spring rate might only be 2.?X in wheel rate...

[genericwood]

Quote:

Originally Posted by Grant Even with the dropped spindles and huge sway bars and torsion bars, I was still rolling like a pig on tight turns. While the camber gain was fine, the center of gravity would shift so far onto the outside wheels, it would overload them and I would lose grip prematurely. After increasing the spring rates 2-3X over my old setup ( and 4-6X over stock!) I was finally happy.

[Grant]

What you're saying is correct, but according to Carol Smith, the roll related to a soft car moves the CG over the outside wheels, adding another factor to the "roll does not cause weight transfer" saying. It doesn't, but when the CG moves, more weight does move over to the outside wheels because of the shifting of the CG, and not just the cornering force.

I respect your experience racing over my experience screwing around on the internet and doing minor events. So, I'll double check my point for accuracy in my Tune to Win book later tonight when I have more time.

[Grant]

James, as usual, your points are valid. I do mean spring rate. The Shankle catalog lists the torsion bars as a spring rate to the best of my knowledge. How they actually calculated this, I do not know. I do know the listed rate for my shorter 27mm torsion bars was something to the effect of 190lbs/inch. The spring rate of the RS kit with my 11KG (actual rates are quoted as N/m or N/mm, I forget...no matter, conversion is multiply by .98, so close enough to estimate) front spring is around 650lb/inch. I'm using the amatauer approach of comparing spring rates to spring rates, which is really like comparing apples to oranges, but hey, they're both fruit right?

[genericwood]

Quote:

Originally Posted by Grant What you're saying is correct, but according to Carol Smith, the roll related to a soft car moves the CG over the outside wheels, adding another factor to the "roll does not cause weight transfer" saying..

[Echo Leader]

Good catch on the weight transfer issue, Erik. I skimmed right over that. I think I agree with you both on this one. It seems as though it might be as case where Smith himself might say "It happens, but it almost doesn't matter". I want to go look up what he actually says now...

Anyhow, Grant, I'm surprised (a bit) that Shankle was quoting a spring rate for a torsion bar. I phrase it that way, as I would think Shankle knew what they were doing, but who knows if they wanted to confuse their general readership by introducing the concept of wheel rate vs. the far more commonly discussed spring rate.

As confirmation, my calculations for a 27.3mm torsion bar on my GTV6 show a wheel rate of 191.85lbs/in. Now it seems as though the motion ratio for the GTV6 (and the Milano, I suppose) is around .49...That means that your 650lbs/in spring rate RSR setup is really a 317.75lbs/in wheel rate. This would be essentially equal to a 31mm torsion bar. More fun comparisons, I think the OEM torsions on the GTV6 (short ones) were 23.5mm? If my math is all correct, your current setup is almost exactly 3x this in wheel rate.

[Grant]

James, my coilovers don't mount exactly in the stock location. The wheel rate should be higher than you calculated.

From post #122:

116 & 119 Alfetta/GTV 6/Milano Torsion bar specifications:

GTV6 Early model:
stock bar:
Rate -- 96lbs/in Diameter -- 23.5mm Length--989mm
Sport Bar:
Rate -- 134lb/in Diameter -- 25.4mm Length -- 989mm
SS Bar:
Rate -- 179lb/in Diameter -- 27.3mm " " -- 989mm

GTV6 Late and Milano:
Stock bar:
Rate -- 93lbs/in Diameter -- 22.8mm Length -- 932mm
*No wonder I hit my oil sump so often with the stock setup!
Sport:
Rate -- 143lbs/in Diameter -- 25.4mm Length -- ""
SS:
Rate -- 191lbs/in Diameter -- 27.3mm Length -- ""

[Echo Leader]

Oh, neat....where do they mount?

I might have to take exception with those numbers....I think they used to total length of the torsion bar for the wheel rate calculation. I'm pretty sure you'll want to use an 'effective' length measurement from the 'insides' of the splines....where did those numbers come from?

[stocki33]

as a humble little engineer I agree with the effect of dropped spindles theoretically, but would rather go the uprating torsion/sway bars way practically

SZ spindles would cost about 1500 Euros, thats half the price of a decent 75 here in Europe; Welded spindles are to high of a risk to use on the street in my opinion. Furthermore I would not choose the coilovers as the 75 / Milano was not originally designed for this additional application of forces.

To understand the effect of lowering better I would be interested if the original Milano setup looks like this:



or like this:



The LCA beeing level, does the UCA point upwards or downwards ?

Cheers
Stocki

[Echo Leader]

Hi Stocki and welcome to the BB. I don't think anyone is trying to say that a person should only do drop spindles. Personally, my drop spindles (made by Richard Jemison) are going to be coupled with increased torsion and sway bar sizes.

Nice graphics, what software are you using?

[stocki33]

of course, dropped spindles are not a subsitute for a good suspension, but the spindles alone are more than a shock+spring kit. Together this will put you in 2000+ Euro Zone...

Do you use the welded spindles on public road ?

The drafts are made with Solid Edge. Not very good software for creating 2D graphics though.

Cheers
Stocki

[Echo Leader]

Yeah, the drop spindle is probably not the first modification I'd recommend to people as the price/performance ratio probably isn't as nice as that for torsion and sway bars. Though 1500 Euros for spindles seems a bit high. Is that price for the official Alfa SZ parts?

I don't have my drop spindles installed yet, but my car sees some street use. Richard Jemison has a pretty extensive history of racing with the welded spindles. Those g-forces are probably a lot higher than what my car can generate on street tires. Pot-holes are another story I suppose, but the forces in that situation shouldn't be in a direction which stresses the weld.

I've been thinking about putting together a model of the GTV6 suspension in some form of modeling software, but there doesn't seem to be a good option that doesn't cost major dollars... any thoughts?

[stocki33]

The official sale price for the SZ knuckles is 768 Euros p.p. and this was 2005. I don`t even know if the parts are still available.



Making up a simple model like the pics I posted shouldn`t be much of a problem. Any CAD software capable of dependent dimensioning can do this.
3D modeling is a different story...

Cheers
Stocki

[ToonRboy]

Dropped spindles are simply, the best engineering answer to lowering the (front) of the vehicle without changing the suspension geometry to it's detriment. Not just in terms Camber, but steering (rack angles to tie rods, & ackerman). Caster affects steering significantly as well. In 295 replies in this thread, the only references to steering made were in the context of understeer or oversteer with respect to spring rates (whether coil-over or torsion) and roll bar sizing. There is some good information posted here though. Just gotta look.

stocki33 makes an excellent point. In a market where excellent examples of these cars can barely fetch $3500.00, it seems silly to buy drop spindles on a road car where the capability to lower is built-in. You wanna win races? Different story. To me, it's the GTV6 that seems to need lowering in front (Esp. U.S. model), not really the Milano (needs azz-end lowered some tho)

Thanks to Bobsiopener, post #59 of
Suspension Modeling thread, he has provided many of the needed measurements to plug into the model. Which should answer stocki33's last question. Since the humble little engineer seems motivated enough to provide drawings, maybe he can re-do them with the proper to-scale dimensions.

On
What if you Don't lower a Milano? thread, I provide an online model where you can plug-in the values and see camber effect real-time. Remember though that if you lower by rotating the torsion bars, you'll have to correct the negative camber by cutting-down the mushroom spacers (or using a thinner set) at the LCA mounting points, thus changing the LCA pivot point inboard some.

[stocki33]

I`ve read through the mentioned articles, and maybe didn`t get it right as I thought the dimensions have been taken from a GTV6 ?

Yes I can take the drafts to actual proportions when I am back to the office in January

As for the camber effect: did you mean this:


Why correct negative camber ? I thought this is desirable, as Milanos go to positive camber on the outside wheel when cornering

Cheers
Stocki