Suspension Setups

[okayfine]

What are you measuring in the first pic at 6.5"?

ZX disc is vented and 9.9" OD. Strut tube will be 10.5" from top of hub flange to bottom of spring seat.

[amwalker]

Front: 280ZX struts, Z31 5-bolt hubs, 200lb spring on coil-over perch, Illumina insert, custom camber plate with fixed offset for more caster. Late (70-73) LCA’s w/ poly bushing (double-sheer fixture added to LCA pivot bolt) and poly T/C bushing. No Sway bar (yet) 1st gen. MR2 rack&pinion steering, 1” bump steer spacer.
Rear: Ermish QA-1 non-adjustable coil-over shock, 200lb spring, re-drilled 510 hub to 5-bolt. Slotted rear cross member, no sway bar.

I need advice in choosing the front sway bar rate. Because I moved my motor back a bit, I can’t use any of the front 510/SR sway bars that are available, so like everything else I have to make a custom one. It’s easier and maybe cheaper to go with a “speedway” style 3-piece sway bar, plus I’ll be able to tune with different bars if I choose. Can anyone offer any advice on which bar I should choose to start with. I’m going with a 1 1/4 diameter hollow bar because this is a common size and there are many rates to choose from. From Speedway I can choose wall thicknesses of .095, .120, .188, .250, and solid. There’s a rate chart here if anyone has a way to offer a rate comparison to the bar your using in your car. My thought was to start with the thinnest bar and go from there. Any other thoughts?

Did you ever find anything else out about this potential sway bar set-up? I'm planning on hauling my car up to the Speedway shop as they're only 20-30 minutes up the road and seeing if something will fit.

Adam

[S15DET]

Bottom line is that you need to decrease body roll and pitch...thus weight transfer.

decreasing body roll does almost nothing to decrease weight transfer in a steady state corner. If we run out the numbers. Let's say roll center is 6" high, and the CG is 30" high. These are way exaggerated, but we're just playing around. Even at 10° of body roll, lateral CG migration (x) will be:

Code: Select all

tan(10°)=x/(30"-6")
x=(24*tan(10))^(-1)=0.236"

This means the CG moves sideways 0.236" at a 10° roll. Track width of a stock Datsun 510 is 1280 mm, or 50.39 inches. The lateral CG migration we calculated above is about 0.468% of the track width of the car, so we've only increased weight transfer on the outside tires by double that, or 0.937% of the car's mass.

Jump in for the discussion from the "post a picture" thread...

So if we're only speeding up the weight transfer by limiting body roll, we're just making the outside tires work harder for longer?
Limiting body roll does have the benefit that others mentioned about limiting the undesireable geometry changes that occurr at full jounce on the inside suspension.

Adam, no I haven't. I decided that the TC-rod mount area was ideal for the straight Speedway bar mount location, so I went off on a tangent to design A-arm front LCA's and eliminate the TC rod. This stalled and I don't even remember where I left off. Did you ever go by Speedway to make a selection? I thought another option would be to mount the straight bar THROUGH the box section "frame rail" just above the TC mount. I even found some porsche flat perpindicular mount bushings that might make this easier. I'll have to look on my home computer.

[HudsonMC]

Bottom line is that you need to decrease body roll and pitch...thus weight transfer.

decreasing body roll does almost nothing to decrease weight transfer in a steady state corner. If we run out the numbers. Let's say roll center is 6" high, and the CG is 30" high. These are way exaggerated, but we're just playing around. Even at 10° of body roll, lateral CG migration (x) will be:

Code: Select all

tan(10°)=x/(30"-6")
x=(24*tan(10))^(-1)=0.236"

This means the CG moves sideways 0.236" at a 10° roll. Track width of a stock Datsun 510 is 1280 mm, or 50.39 inches. The lateral CG migration we calculated above is about 0.468% of the track width of the car, so we've only increased weight transfer on the outside tires by double that, or 0.937% of the car's mass.

Jump in for the discussion from the "post a picture" thread...

So if we're only speeding up the weight transfer by limiting body roll, we're just making the outside tires work harder for longer?
Limiting body roll does have the benefit that others mentioned about limiting the undesireable geometry changes that occurr at full jounce on the inside suspension.

Transient handling (as opposed to steady-state), which is what you're talking about when you begin thinking about how quickly load transfer is occurring and stuff like that, is a pretty complicated topic, and is where you really start to have to consider the oscillations (or lack thereof) of the suspension and take the damping into account. A higher spring rate will increase the frequency at which the damped spring-mass system that is your car will oscillate at, and if your dampers are tuned correctly, then yeah, pretty much, increasing the roll stiffness will speed up weight transfer.

Your "making the outside tires work harder for longer" example is a good one, and I've never really thought of it that way before. After the suspension "settles" into a steady state corner, that's basically what you're doing. A tightly sprung car, as you can imagine, will have a quicker response and respond to successive right/left/right transitions better. Another side effect is better communication with the driver, which is always nice.

It's helpful to think about the car's spring rates in this context in terms of the car's "undamped natural frequency" which is dictated by the mass and spring rates. There are some general rules of thumb for different types of cars, and for racecars the recommended frequency is around 2-3 Hz.

This is also all assuming a relatively flat course. If the track you're running on is really bumpy, it may serve you better to have a more compliant suspension.

[RonM]

HudsonMC is this the picture of the Alfa and 510 you were talking about?

[okayfine]

Probably something closer to this:



FWIW, page 162 of the How To Modify books says 150 in/lb rates at all four corners, 1" front bar originally, uprated to 1-1/8" for the second season. Forgot to find the rear bar size. Would be interesting to ask Peter about it...

[Byron510]

FWIW, page 162 of the How To Modify books says 150 in/lb rates at all four corners, 1" front bar originally, uprated to 1-1/8" for the second season. Forgot to find the rear bar size. Would be interesting to ask Peter about it...

One thing to keep in mind is that the street tires we buy today (DOT Auto X tires for example) have more stick than the race tires of the era could ever offer.
And race tires have come leaps and bounds. On today’s rubber, you can get away with 1/3 of the tire width, and still have more stick that John had back in the day.
You ever watch the Against All Odds video - I'm sure you all have. You see the drifts those cars are always in? It was a different world. A similarly set up 510 on race tires of the same width today can get over 300 lbs/in because the tires have that much more grab, and you can take advantage of it with stiffer springs, and less roll bar.

Just an observation, but the technology continues to change.

Byron

[HudsonMC]

Probably something closer to this:



FWIW, page 162 of the How To Modify books says 150 in/lb rates at all four corners, 1" front bar originally, uprated to 1-1/8" for the second season. Forgot to find the rear bar size. Would be interesting to ask Peter about it...

This is really surprising to me. If that's true, that seems really low. The tire answer Byron gives may be the answer. Pretty interesting. It would all depend on what kind of cornering force the tires of the day could generate. The lateral force is dependent on the 'g' level in the corner. Anyone know what kind of 'g' levels the BRE cars could pull back in the day on bias ply tires?

[okayfine]

I have the old Road&Track issue with the BRE, Alfa, and BMW Trans-Am cars compared, but skidpad figures are "n/a" for all three.

[HudsonMC]

I have the old Road&Track issue with the BRE, Alfa, and BMW Trans-Am cars compared, but skidpad figures are "n/a" for all three.

Oh man! So close! That's really cool though. Is that article available somewhere online or in the archives? I'd love to read through it.

[okayfine]

I'll e-mail R&T and see how they feel about it.

[RonM]

I thought only needed to check with the author for republication?

From a 1971 R&T article (Look at last paragraph) http://dimequarterly.tierranet.com/rt.html


We caught Brock and chassis expert Trevor Harris in the middle of designing a street/slalom suspension kit for the 510 and arranged to test a prototype of the kit. Our baseline on the skidpad for a stock 510 was 0.611g lateral acceleration, limited by the skinny tires and rims. Simply changing to the dealer-installed 13 x 5 1/2-in. rims and 165-13 Bridgestone radial tires jumped the figure to 0.739g. That brings us to the first step in improving the 510 - wheels and tires. They are the best possible investment for improved handling and bracking and should be the first step, as the original equipment here is strictly economy. Tires as large as 185/70-13 mounted on 13 x 5 1/2 or 6-in. rims will fit without rubbing the fenders (providing the wheels have zero offset), even with the car 1 1/2 in. lower than stock. Many of the wheels sold for 510s have too much offset and limit the size of tire that can be used. The wheel manufacturers now have realized this and have begun to make wheels with proper offset.



With the baseline tests complete, a prototype of BRE's Phase III Mulholland suspension kit was installed. The kit includes shorter, 115-lb/in. front and rear springs (stock springs are 85 lb/in.), 15/16-in. (0.94-in.) front anti-roll bar, 3/4-in. rear anti-roll bar and Koni shock absorbers; this lowers the 510 about 1 1/2 in. but keeps the center of the headlights a California-legal 24 in. above the road. Harris replaced the stock, rubber-mounted drag struts, which connect the leading edge of the lower front suspension arm to the body with a pair of ball-jointed struts. These eliminate rearward compliance in the front suspension and result in more positive steering feel at the expense of ride harshness. Using the ball joints these struts sell for $100 a set, but BRE is experimenting with Teflon to get the price down. They are not listed in the Interpart catalog yet. The suspension kit without the struts sells for $240, but it made a $2000 difference in the car and upped the skidpad number to 0.808g, still on the 165-13 radial tires.

Goodyear A70-13 bias-belted tires on 13 x 7-in. 4-spoke American Racing wheels were then bolted on a brought the lateral acceleration to 0.823g, at which point the stock carbuetor gave up. The non-baffled float bowl couldn't handle the load and caused the engine to cut out after two laps but this problem never appeared in normal driving. The ride with the Mulholland kit is slightly more harsh, but not as harsh as the factory racing suspension and although wheel travel is reduced somewhat, the benefits in handling are certainly worth the loss for those not concerned with rough-rod or full-load ride and handling.

We ran two additional suspension tests. A 510 with the factory suspension kit (new front struts with springs, rear springs, shocks and a 23-mm, 0.91-in., front anti-roll bar) and Bridgestone racing tires on 13 x 5 1/2-in. rims went around the skid pad at 0.826g. This car, with two sidedraft Mikuni-Solex carburetors, had no difficulty with fuel delivery. And BRE's number 35 Trans-Am car, during a shakedown session, went around at 1.01g on Guddyear racing tires.

[okayfine]

I thought only needed to check with the author for republication?

Maybe if I just want the text, but I'd like to scan the photos and graphs as well, which would be R&T. Besides, they don't seem to list an author for the article, and the chances of me finding him 40 years later...

E-mailed the same contact for C&D's PL510 review article as well. Might as well get these digitized if possible.

From a 1971 R&T article

The article doesn't list the skidpad diameter, which influences the results. If it's the same methodology they used a year later, it'd be a 200' diameter pad.

[HudsonMC]

Another thing to consider might be the dramatically lowered and heavily modified suspensions of the BRE cars. We know they relocated suspension pickup points in the front, Did they raise the rear crossmember at all?

Anyways, with a very low car and the mods mentioned above, it's possible that the roll center and center of gravity were very close to one another, meaning that less spring was required to limit body roll. The roll center is the instantaneous center of rotation that the body of the car rotates around. The difference between the RC and CG heights is the lever arm that centripetal force will work at to cause body roll. If they're very close together, it would not take very much roll stiffness to resist body roll.

Eventually, one of my projects is to take detailed measurements of the suspension on one of my 510s and model it to determine roll center heights and the like. Would be a fun project and would be nice to have a detailed model of the 510 to play with.

So, I dunno. 150 lbs still seems low, but 1-1/8" bar is pretty large...

[okayfine]

Another thing to consider might be the dramatically lowered and heavily modified suspensions of the BRE cars. We know they relocated suspension pickup points in the front, Did they raise the rear crossmember at all?

The 510 Archives has a bunch of build photos of the BRE car(s), and an accompanying write-up on the modifications performed. I'll give it a look, but you may also want to check out the documentation to see what I may miss...

BRE folder:
https://docs.google.com/folder/d/0ByCvx ... 1Rvdw/edit

Body And Chassis Modifications:
https://docs.google.com/folder/d/0ByCvx ... amlPX0I0Zw

They don't appear to have raised the rear crossmember, just modified the pick-up points to correct geo for lowering.