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Tender + main springs on an S30?

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Hey all,


I took my 240Z to the track last weekend, and because it was a bit wallowy at high speeds and had a lot of body roll, I'm now looking into changing up my spring rates.


Current setup:

  • 200 lb/in front springs
  • 22mm front sway bar
  • 250 lb/in rear springs
  • no rear sway bar
  • pretty thin RCAs on the front (18.5mm)
  • lowered somewhat but not a ton
  • 205/55R16 bridgestone RE-11s
  • Koni yellow single-adjustable (rebound only) race shocks
  • -2.0º camber front and rear
  • 2.5º caster (can't run more until I modify bodywork or relocate strut mounts rearward)
  • 0 toe front
  • 1/16" total toe in rear


Next steps I was initially thinking of:

  • put thicker (30mm) RCAs back on
  • increase spring rate to 300 front, 350 rear (or even 350F, 400R)
  • add a rear strut brace (front has a triangulated strut brace already)

However, I was reading about tender + main spring setups and they seem really interesting (To be clear, I'm using the same terms Eibach is here: helper springs: soft, just keep main springs seated at full droop. tender springs: have sufficient spring rate to impact driving under other conditions; I've noticed that some people use these terms the other way around).


It sounds like it could provide a good compromise between a car that corners fairly flat and doesn't move around to much on load transitions, but still has higher ability to absorb bumps well.


One setup I was thinking of was: 

350# main springs in the front, with #300 tenders, yielding an ~160# effective rate until the tenders reach coil bind. And something similar in the back.


But, I also see lots of downsides:

  1. it seems like with the simple shocks I'm using, you'll only be valved decently for either the soft or the firm part of the range.
  2. it seems like this setup would actually be worse than my current setup for high speed stability by reducing the effective rate in those conditions.
  3. the bump absorbing ability would only be improved when the suspension isn't already compressed, so it does nothing to help when cornering near the limit and hitting some uneven pavement, i.e. conditions where you actually want this.
  4. the sudden transition from 160# to 350# spring rate after an inch or so of compression sounds like a great way to unsettle the chassis.

Anyone here have any experience experimenting with a setup like this? It sounded good on the face of it, but I'm not convinced it can work. But if it can't, then why does these setups exist? Is it just another compromise between comfort and handling, or are there actual rear-world handling benefits from a setup like this?


My goals for the car are:

  • 1: fun to drive on back roads, and okay to drive on regular streets and highways.
  • and that performs well enough on the track that it's fun to push it to its traction limit (which it wasn't really with the high amount of roll and floatyness I got last weekend)
  • doesn't have be super comfortable on our pothole ridden California highways, but I do want to be able to drive it fast-ish on less than perfect surfaces, so it should be compliant enough for tires to remain in contact with the road most of the time.

Some pics to show the amount of roll:



Edited by rundwark
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I've Autocrossed, Hillclimbed and Road Raced for many years and a lot of guys up here in Vancouver run very fast 510's up here. Different area's have different setups. There is definitely a big bar/soft spring approach and a big spring/ small bar approach. Here in the PNW we have leaned towards the latter and it works very well.


I would not recommend the tender and main spring setup. Basically that gives you a progressive spring, which in theory gives you a comfortable ride ( which it does ) and a stiffer rate when you corner hard. Neat?? ... far from it. What it does do is give you a non-linear feel to the car that is difficult to drive fast. It is definitely spooky when cornering fast. The car takes a big, quick  bite on turn in as the soft coils compress, then it steadies up mid corner as the  rate increase, then on corner exit the front end suddenly unloads as the soft coils expand. It is not a good feeling. A linera spring rate front and rear is much more consistent. 


The main problems I see on your car are lack of a rear bar and too soft of front springs and too high of a CG. For track days I would try the following. Bear in mind there will probably be a dozen more suggestions. Bottom line it's all about balance. Get the car neutral and you can make it " dance " from there.


You need to reduce tire diameter. That will reduce CG, which will reduce roll dramatically. Change tires and rims to a 205/50 x15 or 225/45 -15 . 205/50x15 have a rolling diameter of 23.1" Your 205/55x16's have a diameter of 24.9". That's just too tall. The shorter tires and rims will also give you a gear ratio advantage and lesson rotational inertia. Both good points.


Edit: Just realized you must have Coil overs and Camber plates, although you didn't mention them. Lower the car some more....if you can  You can drop a Z 1.5" to 2"  from stock easily. Going lower  depends on strut clearance. You may have to shorten the struts to prevent bottoming out if you want it to competition heights.  That can get expensive.


Spring rate #300 front sounds fine. Most of the Hard Core 510 guys up here run #300 up front for street and track. And 510's are lighter on the front end than Z cars. Surprisingly it's not uncomfortable on the street. Good shocks like your Koni's 8610's are required.


#350 rear rate sounds a bit high. Stiff springs in the rear are what make for a choppy ride on the street. I would suggest anything from a #250 rear spring or a #275. #300 may be getting up there. Too much rear spring adversely affects cornering under bumps and putting power down exiting corners.  You definitely need a rear bar with the lower rate springs. 


A 22 mm front bar seems too small. You want around a 25mm for Road courses. a 22 mm front bar can work for Autocross if the car is low enough and has the proper rear bar. I would suggest a 25mm front bar with about a 20 to 22 mm rear bar. Maybe 23mm if you have a LSD Depends on your driving style. I've found that getting the rear setup correct requires much more finesse than the front. Up here in the PNW we have something called rain. You tend to go softer on roll bars in wet weather... unless you like drifting and spinning out a lot. 


Correct the front LCA angle of course as you lower car more. RCA's or by re-drilling LCA mounting holes higher in front cross member.


Tension Rods with proper ball and socket joint are ideal for track. May be a bit noisy on the  street.  Poly tension rod bushings can break the  tension rod. Some guys only install half the kit and that helps. But I'll only use new rubber bushings ( for street ) or ball and socket for Race. Personal choice. 


Camber and Castor specs seem fine. Strut braces front and rear are good. Poly rack bushings needed and in steering coupler. 

Edited by Chickenman
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Topic got me interested in some of my old Autocross cars. Attached are a couple of pictures of my 09/70 240z. I ran this in B-Mod in the PNW and it was a podium contender back in the day ( Mid 1970's ) .


Car was very low and handled like a go kart. Ride was very comfortable on street tires.


Autocross setup.


Goodyear 21x 8.0 x13 soft compound slicks on 13 x 7" rims ( Max Rim width regulated by rules ). Later on I got some Cantilever slicks. My Lord they stuck!! Street tires were 205/60x14's. That gained some ground clearance for the street.  


Nissan competition struts front and rear. Struts were pre-shortened from Nissan and had stiffer valving. These were the early models with non threaded collars, but spring seats were raised and shorter springs used to gain Tire clearance.  Rare pieces!!  Spring rates were not astronomical. Probably in the 200 to 225 lb range max.


Nissan Competition 22mm front bar. Nissan Competition 23mm rear bar.


R180 with 3.9 gears. No LSD. Interestingly, inside rear tire spin was never an issue. 


Front LCA angles corrected by drilling mount holes higher in K member. 


1/16" Toe-in front,  -2.0 Camber... Castor probably around +2.5 . I liked to keep Castor low for Autocross. easier steering. 1/8" Toe-in rear, -1.5 to -2.0 Camber.  Car turned in very rapidly with no trace of under-steer.


I apologize for the poor picture quality.  Pictures taken from old photo album. Pictures are from around 1975 to 1976 



Edited by Chickenman
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Thanks for the great post Chickenman!


Lots for me to digest and think about. Very glad you talked me out of tender springs, that doesn't sound like a good way to go at all.


A little more on the car: it does sit on coilovers, but no camber plates. I have adjustable, heim-jointed, LCAs, rear CAs and TC-rods on the car, which is what lets me dial in the alignment. current wheels are 0 offset, which puts the outside sidewall of the tires very close to the (rolled) fenders, so it's sitting as low as I can get it while not rubbing on hard corners and dips. I'm hoping to drop it further once I have stiffened up the suspension a bit. The car has a 3.54 torsen LSD, and I'm using a Delrin steering coupler. I need to check the rack bushings, but overall steering is very tight.


Lots of setups for S30s I read about (on HybridZ and other forums) use stiff rear springs and no rear sway bar, so that's what I've been using as a template so far. I'll measure my front bar, to make sure it's actually only 22mm. I'm thinking I may still try the 300/350 setup with no rear sway first, and if I don't like it, add a rear sway bar, and switch back to the 250 rear springs. It'll be a good learning experience for me to feel the difference between the two approaches in one car.


I feel like either approach could get me to a fairly neutral handing car. It seems like the main pro for the stiff rear spring approach is that by raising the frequency of the rear suspension relative to the front, there would be less pitching over bumps, causing a flatter ride. The main con seems like the overall ride would feel a bit more jarring and choppy due to the higher rear spring rate. Does my logic make sense? I also like the additional benefit of a stiffer spring rate in the rear for lowering the car further. The sway bar would only help reduce compression in corners, not with bumps while going in a straight line.


I'm into the shorter tire idea. Beyond the benefits you outlines, it would also solve my caster limitations, and let me get the car quite a bit lower without any rubbing issues. Sadly, my current tires are brand new, so I want to see what I can do in the intermediary to at least make it fun to wear them out quickly on the track :)

Edited by rundwark
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Every body has there own setup ideas. It really all depends on what you are comfortable with. Personally, I think spring rates above 300 lbs in the rear are too high for a street car or dual purpose car.  Track days do complicate the issue, because a lot of the setup depends on the Tracks you run on. Just my .02c...


Because the driver sits so far back in a Z car, you tend to feel jarring from the back more. Just my personal feeling from driving many miles on the I5. Nothing worse that that thump, thump thump in Washington State ( Concrete slab construction ) in a stiffly sprung car . I've also been driving Big HP RWD cars with beam axles for a long time. Those tend to get very skittish in the rear when spring rates get too high. Independent rear suspension tends to be more forgiving.


If you find the rear spring rate too harsh you can always swap out the springs to a lower rate and add a rear bar. You have a Torsen LSD so inside wheel spin is not an issue. Not that it ever has been an issue on any Z cars that I have driven with a rear bar and open diff. 


Another consideration is that these old chassis were never very stiff. The guys with the 510's that are running 300 lb springs up front have all seam welded the chassis and reinforced them in the spring seat area's such as front wheel well. Strut bars front and rear help a lot. Front strut bar benefits from being triangulated. 


On a personal note to my setup methology. Most of the time during my Motorsports activities  I have been driving medium to big HP RWD cars with beam axles. These get very skittish over bumps if you get the rear springs too stiff. Softer springs in the rear also allow you to put the power down sooner and harder on corner exit over a car with a more stiffly sprung rear end. Pony cars make up their time on the straights. So early power down  on corner exit is extremely important to us. Big Pony cars drivers like to Diamond the corners. They are not momentum cars like Miata's.


IRS cars are less sensitive to the bumps and put power down much better than a beam axle ( in general ). But there are Pro's and Cons for each method. 

Edited by Chickenman
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BTW, if you are looking for good springs ( Coil Overs ) at a reasonable price, check out the Circle Track suppliers. I use PitStopUSA. Hard core parts at reasonable prices, cause there are short tracks everywhere in the USA. Hypercoils are a very good brand. Cheaper than Eibach's and every bit as good. 


A nice compact camber plate can be found on E-Bay. No major cutting of wheel housing required, just some slight enlongation of center hole to allow for the shock shaft to move in and out:








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Hmm your current setup sounds fairly ideal spring rate wise. Although I think for track driving T3 was saying 225/250 would probably be better. 


I would be wary of comparing to 510 springs rates, they look to have a more compact design in the engine bay which would make me thing they could support the additional spring rate, the rear suspension also reminds me of the E30 which given the cantilever type of setup can run surprisingly stiff springs fairly comfortably.


I'm obviously not as experienced as others, but off the bat I would suggest getting a rear sway bar, the ST sway bar with the alignment fix is a pretty good piece, and possibly upping the front sway bar. Upping the spring rate will improve the body roll, but will be more or less a harder ride all the time, where as with thicker swaybars you could maintain the same ride quality while getting a little bit more help in the corners. I would kind of stay away from the stiff spring/no sway bar group. You can get there, but usually the spring rate required makes the car quite harsh unless you have some really good dampers. I would imagine if people did get there with the Z's it would be more of a trailer to and from kind of car just based off of what I have been in. Currently lacking the rear sway bar means that the suspension doesn't get any help in the corners so it would make a fair amount of sense you have quite a bit of roll. I think that spring rate is with the assumption that both bars are in play no? Curious who is running without sway bars and the spring rates they run.


Additionally, upping the front spring rate is going to have a diminishing effect after the 225lb/in rate unless you have some bracing as the chassis deflection will start to come more into play.


To quote the late John Coffey

"What works on a 240SX does not work on a 240Z. Unless your 240Z has a very effective roll cage that ties in the front strut towers, spring rates over 300 lb. in. on the front are questionable  The problem is that the front structure itself starts to flex at spring rates over 300 lb. in. (seen it and measured it). I know some road racers with 8 point cages have made 350 lb. in. front spring work with just a strut tower bar but I'm skeptical."


The tire aspect ratio seems a bit on the tall side as chicken man suggested, I was running a 215/55/15 and hated that, felt really tall and rolly. I would shoot for a 225/50/15 or something of that nature, if you step down even further to a 225/45/15 you can even run the bridegestone g-force rivals which are quite sticky.


Your reasoning is a bit off. While the spring does rebound and such you have to remember the damper is there to prevent the frequency, so more so think of it in terms of weight. When you accelerate and the weight shifts back having the slightly increased rear spring rate helps keep the car on neutral footing. Under braking you want your car to roll towards the front when you brake to load up the front so having that softer is beneficial. 


There is a good post/article on the reason the weights are what they are on the Z cars as most newer cars run backwards of what we usually see (higher springs up front, lower in the rear), I'll have to see if I can find it at a more sane hour.

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I purposely did not mention the rear suspension on the 510's because it is vastly different from the front and the Z car. Rear spring rates are often in the 800 to 1,000 . The motion ratio is around 3.8 to 1, so an 800 lb/in rear spring only equates to a 210 lb/in wheel rate. 


As for the front, the motion ratio's are virtually the same. In fact most of the hard core 510 guys here are using 280ZX struts. Those are preferred over 240Z or 280Z struts, I believe because of the KP inclination.


As for the rear spring rates, it comes down to more of a preference. Stiff rear spring no rear bar or slightly softer with a rear bar. For street or dual purpose cars I prefer the latter as it is less jarring to the driver and is more forgiving over bumps. I've raced both ways and either way can turn identical lap times. Softer springs are more forgiving though... particularly in the rain. Bear in mind that the tern " soft rear springs " are relative . A 250 lb/in rear spring is a large increase over stock rates. 


Having the nose dive under braking is not beneficial.  Weight transfer under braking naturally transfers weight to the front and reduces vertical load on the rear tires. That reduces the braking capability of the rear tires. If the car dives in the front, that changes the roll axis of the car along the center plane and the CG shifts forward. That further reduces rear braking capability as even more vertical load is removed from the rear tires. Compared to if the car remained more level.  All tires have a " Bell Curve  that equates tire grip level to vertical load. Go over or under that peak and you reduce traction. It is key element in understanding the Traction Circle. 


Most cars have Anti-dive engineered  into the front suspension. Race cars have a lot of anti-dive. However, McPherson struts do not allow a huge amount of anti-dive to be built in, as compared to a Double A-Arm or Multilink suspension. Increasing spring rate in the front relative to the rear maintains a stable platform by increasing anti-dive under braking. Since braking G-Forces can be much higher than acceleration forces, it makes sense to run a higher spring rate in front than in the rear. 


Many amateur racers have too little rear brake bias, either through chassis setup or personal driving style. What they are effectively doing is taking away a percentage of braking capability by not using the full capacity of the rear brakes. ABS takes a lot of the braking skill away from the driver as it allows the engineers to crank in more rear brake than a non-ABS car, without the fear of Grandma or GrandPa swapping ends under a panic stop.


Being able to run more rear brake bias is also handy for an experienced racer in rotating the car for corner entry. One of the reasons why you always see F1 drivers tweaking the brake balance before corner ( No ABS allowed in F1 or Indy Car ) . More rear brake bias for slow, tight corners to rotate the rear and get the nose to turn in and less rear brake bias on high speed corners because you want a tad of under-steer. 


All FWIW and just my opinions and experiences. As I mentioned, there will be lots of opinions on this and nothing sparks a discussion more than chassis setup... other than Republicans vs Democrats... but lets not go there!!! beer_yum.gif

Edited by Chickenman
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Seattlejester. I read the same articles by John Coffey and agree about the Chassis flex and spring rates over #300 in the front. The 240z is very flexy up front. The 280z is a bit better due to the thicker gauge frame rails and full length frame rails. But chassis stiffness is nothing like modern cars.


I think I've read that post about rear spring rates being higher on the rear of Z cars being higher than the front. But see if you can find it again. The one I read was talking more about Torsional chassis stiffness. The rear being stiffer, in Torsion,  than the front.  

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Yeah, my other fun car is a 510, and I have coilovers on that too. The 510 chassis is a lot stiffer in the front end. On my Z, I didn't even feel much of a difference when I went from sagging lowering springs that were on there when I bought it to the 200 lb/in springs, until I added a triangulated strut brace. The 510 feels like it can handle a lot more.


@seattlejester, I think you misunderstood what I meant. The frequency of the suspension is determined by the weight, motion ratio and spring rate. The damper limits the number of oscillations, but does not affect frequency. When going over a bump, the front wheels hit it first. So, it's actually desirable to have a slightly higher frequency in the rear, so that the rear suspension "catches up" to the front by oscillating more quickly. If the damping was ineffective, this would be a terrible idea, but since each oscillation is lower and you'd get at most three or so noticeable ones with good damping, there is less pitching of the car in a setup that has a slightly higher frequency in the rear.


Now, the 240Z should have almost identical motion ratios front and rear, and since mine has AC installed, it's probably fairly close to the stock 52/48 F/R split, which means that, if I ran the same rates front and rear, the rear suspension would still have a slightly higher frequency than the front. But running softer springs in the rear seems like it would be have a negative impact on the extent to which the chassis moves around over bumps.

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Good article. Here's the part about Spring rates /Frequency I was referring to about:




For a given wheelbase and speed, a frequency split front to rear can be calculated to minimize pitching of the body due to road bumps. A common split is 10 – 20% front to rear. The above theory was originally developed for passenger cars, where comfort takes priority over performance, which leads to low damping ratios, and minimum pitching over bumps


Racecars in general run higher damping ratios, and have a much smaller concern for comfort, leading to some racecars using higher front ride frequencies. The higher damping ratios will reduce the amount of oscillation resultant from road bumps, in return reducing the need for a flat ride. Damping ratios will be explained in the next tech tip in detail. A higher front ride frequency in a Racecar allows faster transient response at corner entry, less ride height variation on the front (the aerodynamics are usually more pitch sensitive on the front of the car) and allows for better rear wheel traction (for rear wheel drive cars) on corner exit. The ride frequency split should be chosen based on which is more important on the car you are racing, the track surface, the speed, pitch sensitivity, etc



Edited by Chickenman
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Seattlejester. I read the same articles by John Coffey and agree about the Chassis flex and spring rates over #300 in the front. The 240z is very flexy up front. The 280z is a bit better due to the thicker gauge frame rails and full length frame rails. But chassis stiffness is nothing like modern cars.


I think I've read that post about rear spring rates being higher on the rear of Z cars being higher than the front. But see if you can find it again. The one I read was talking more about Torsional chassis stiffness. The rear being stiffer, in Torsion,  than the front.  


When you say full length frame rails, do you mean the frame rails under the floor? The 280Z subframe rails are longer and beefier but they don't connect to the rear subframe, which is what I would assume you mean by 'full length'. The 280Z engine bay rails are the same as those in the 240Z, no difference in gauge that I know of, outside of the series one cars which have thinner metal, but based on pics I've seen, they do have reinforcement on the inside that is absent on 240Zs.


Regarding higher spring rates, I recall John C saying that a triangulated front strut bar (and possibly other reinforcements) allowed him to run higher spring rates, so if I'm interpreting what he said right, you don't need a full cage to run 300lb/in springs.

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I mean regarding the nose diving, as you said it is all pretty relative relative we aren't talking about inches upon inches of dive here it is still a relatively stiff spring up front at 200-225, we're talking about just a bit more load for that initial turn in, of course too soft and you risk upsetting what the rear is doing or even overcoming the traction of the front tire with too much shift. I'm in full agreement there, but the reference was to I guess more shift then dive in this situation.


I would say a macpherson can have quite a bit of anti-dive, depending on the caster. An E30 has macpherson struts up front but still manages a great deal of anti-dive. Granted an S30 is not going to have nearly as much given our shock tower limitation and just physical wheel placement limitation, just pointing out it is possible to get it though.


Will do, I found it when I was looking up spring rates and it was complete enough to make sense to me. It may take a while though given it was one of the earlier posts.


Regarding the frequency. Yes a higher spring rate is going to have a higher frequency in reaction to the bump in the speed it rebounds, but I guess I feel frequency is kind of strange word to describe the situation. It is an oscillation, but with the damper factored in we are talking about one stroke maybe some other residuals, but still the main return rate. It is a stroke vs time which I suppose the correct unit is indeed hz, but feels odd to talk about one oscillation using the turn frequency.


Bottom line is that you want to combat some rear roll. I think rather then upping your spring rate, adding an anti-roll bar would probably be a good starting point along with the suggestion of looking at a smaller profile tire for the CG and roll characteristics mentioned. Looking into tuning spring oscillations without dampers on a road car without a spring dyno seems like going to far technical here. Granted you could just try out a heavier setup and find it suits you more. 


Fun discussing this stuff, granted I'd very much more like to do more practice then bench racing. 

Edited by seattlejester
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I'm looking forward to getting the 280Z out to some Autocrosses this year. PO had the car and quite frankly it was a car show Queen. It was OK mechanically, but lack of driving and maintenance showed. I think I put more miles on it 2 short years  than PO did in the last 10 years. 


But it's coming along. lack of a garage is slowing things up. Underground parking in Apartment complex is not a good place to be swapping out suspensions etc... LOL. Plus I'm not as young as I used to be. Hopefully I'll get the coil -overs done this year and the rear disc conversion. Oh yeah, and new seats. And remove the Park bench bumpers band side skirts etc. Gettin' there...

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  • 3 weeks later...

I put the 300# front, 350# rear springs in, lowered the car some more and got the alignment dialed back in after that.


Had to add helper springs to keep the stiffer springs seated at full droop. Also added some Delrin isolators between the spring and top hat, which seem to help a lot with harshness when hitting expansion joints, lane markers, etc.


The Koni shocks are close to their stiffest rebound setting now to control the spring motion, and the ride's definitely stiffer. But thankfully it doesn't feel too choppy on the street to me. The car also feels a lot more steady at >80 mph speeds.


Took it on Laguna Seca today and it's a blast. Will share a quick 1-lap video when I succeed uploading it on hotel wifi. It's pulling 1.2G turns now without excessive body roll, so much more fun than before!


Next station: more horsepower :D

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Here's my best lap of the day, sorry for the choppy video quality. The guy talking is the instructor who rode along with me for one session (just so y'all know I'm not paying myself compliments while driving, I do that at other times, and off-camera).


Edited by rundwark
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