v12man

ninerguru

Myu opinion - you need tender (fully compressed under normal load) springs - specifically to keep the spring mounted correctly - having watched how my car now lifts a wheel when entering driveways etc, I would hate for a spring to become less than perfectly seated, and I think thats a real possiblity.

Helper springs which effectively create a variable rate spring setup I suspect would need a lot of experimentation to get to work well - and that will definately create complexity in the revalveing needed - unless you had 2 way adjustables, which would enable that easily.

The incremental cost of 4 helpers and 4 sliders is relatively speaking trivial - the other advantage to using them is that not all manufacturers of 60mm springs have product at the higer spring rates long enough to use without spacers (tender springs), so using H&R or Eibach springs gets very limiting on available spring lengths.

@himself - do you know the valving they used? it is my understanding that the bump and rebound on these shocks can be setup individually - Brian - the tech who did mine said he took a middle of the road path, but if I don't like it, he will change it to suit.

997gt3north

You are going to need Helpers / tenders with 700/900.
<------ if you look at my picture poster, this is my 900# Swift spring rear with the 168# helper.

I posted a new thread in the 997gt3 forum that has lots of links about tenders / Helpers - lots of good stuff there.

Punch line is, at those spring rates, tenders are preferred as it better manages the transitions in the full droop region (lifting rear wheel at apex / hitting curbs, etc) than very low rate Helpers.

I can't comment exactly on 996gt3s as I don't have one for spring length measurements, but absolutely order Tenders.

For the Rear, I would suggest the 224# Swift Tender and for the Front I would suggest the #168 Swift Helper (don't let the words Helper and Tender confuse you, the spring rate, the Block height, the pounds supported when fully compressed are what is important). Basically, the 911 is heavier in the rear, so use slightly higher rate Helpers in the rear to keep things balanced.

The block height of the #168 Swift Helper is .87 inches - with the supplied spacer the total blocked height will be approximately 1 inch.

The block height of the #224 Swift Tender is 1.18 inches - with the supplied spacer the total block height will be approximately 1 1/4 inches.

Your 700# front spring will compress at rest in the area of 5/8-7/8ths of an inch (depending on your corner weights). The Swift #168 front helper with compress to the 1 inch block height mentioned above. So, depending on the height where the threads are located for a 996gt3, the Top Spring Perch to Lower Perch distance for your desired ride height has to include the Uncompressed Main Spring - 3/4 inch + 1 inch = approximately Uncompressed Main Spring + 1/4 inch. If you took the measurement of your compressed stock spring before you removed everything (or someone with a stock 996gt3 can messages this for you), then basically, whatever the compressed stock spring height is, this is the length of the #700 Main that you have to order.

You do the same math for the rear and you are good to go - again, 900# will compress about 1 1/4 inches - the block height of the #224 Tender with spacer is coincidentally 1 1/4 inches, therefore whatever was the compressed stock spring height, this is the length of the Rear Main you want to order. *****BUT*****, you also have to take into account your new Tarret Spring Hat and if this is taller or shorter than what is being replaced and adjust accordingly.

To gain that last mm of performance, depending on how much your OE shocks are threaded in the upwards direction, this would allow you to run shorter Mains to reduce the weight of your suspension - ie, if your shocks are threaded to the top, you might be able to run 5 or 6 inch mains.

Hope that helps

Paul

KOAN

I had the opposite experience, if I understand 997GT3north correctly. I removed my tender springs that had a compression rate, and replaced them with "0" weight springs, which just keep the main spring in place. I removed the variable rate in my front and rear. The car takes a "set" much more quickly, and rapid right-left and left-right transitions are much faster. I can get on the throttle much faster. I am all over the curbing ( at Mid Ohio) and have no problems. It may relate to my driving style, or perhaps just to a preference, but I am much happier with my suspension now. I have 2 way motons and #800/#1000 springs, and am slightly lowered.

997gt3north

Do you know the Tender specs that you had? You may in fact be perfectly correct. In order to choose Tenders you really need to know your corner weights and the compressed block weight for your Tenders. the Tenders I recommended have compressed block weights of mid 200#s for the front and mid 300#s for the rear - so from a taking a set perspective, these Tenders will only come into play when the wheel is into the 1" of droop range - ie not the outside loaded wheels in the corners - but they will come into play.
The reason tenders are chosen is to avoid those abrupt (no rate to 800# rate transitions).

If your tenders had block rates for the front much closer to 400#s than you definitely would feel this as the sprung weight in a lightened gt3 in many situations would get you into this zone.

There is no perfect answer here - everyone likes their car to 'feel' a different way and every track has a preferred setup - no question.

My post was to first highlight that tenders / Helpers would be needed with those spring rates - and second to give 'my' opinion about the Tenders I would use.

If you have the data, what are your corner weights and do you know the Tender specs that you previously used - also, do you recall which track specifically you noticed this significant feel difference?

Thanks

Paul

KOAN

I do have that info, but not immediately available. I'll get it and post.

v12man

997gt3north - do you still have bump stops in that shock in your avatar, or have they been removed/are hidden in the picture?

The pounds supported by any tender spring when fully compressed will be effectively infinite - with only the compressibility of the steel a factor - that said, I am sure what Paul meant was that as long as the tender spring is fully compressed under normal load then you are good to go.

The weight of the car at the corner is not really that relevant when the tender spring is being used (when it is fully compressed, it is not being used, it is a spacer) while the car is being driven - what is relevant, is the weight of the rear suspension (unsprung weight - wheel, tire, suspension members etc) that the tender spring will be trying to keep on the road when the main spring is at full extension by pushing that (wheel) down into the road, against the resistance of the main spring/car (at approximately full extension).

The easy way to think of the mechanics is this - when the wheel is on the ground (which is effectivley immovable) the springs move the car up away from the ground.

When the car is in the air, the car becomes the effectivley immovable object (because of its higher inertia), and the spring forces the wheel towards the ground.

When the car is for example on a lift, all the tender spring has to do is support the weight of the main spring to keep it against the upper spring (assuming it is installed as the lower spring, which is the normal way of doing it)

The bottom line of this is - yes, you should use tender springs - there are benefits, and the cost/complexity implications are low - if you look around you will be able to find tender springs with different block heights for the same spring rate - and that you could use to your benefit if you make a small error (like me) on the calculation of lengths needed - when calculating the compression, I did not take in to account the lever arm effects of the suspension design, thus over estimating the compression a small amount - silly mistake really, I should know better.

Best of luck with your decision

Guy

KOAN

I believe my tender spring specs were 60-60-25 and 60-60-45. My main spring specs are 160-60-180 and 120-60-140. I now have 0 rate helpers. With my rebound rate, I'd have to be airborne for quite a while for my springs to go into full droop. I'm not sure this really comes into play.

IPguy

Thanks Chuck! that will be helpful information as I am going through this process now.
Mike

997gt3north

A 997gt3 has a full rear wheel droop of approximately 2.5 inches - I cant remember the front number exactly but it isn't too far off this number.

<<<<------- If you look at your own Picture, I think it is a pretty fair guess that you have almost fully unloaded your front 800# spring in this situation. If you are running Hoosiers, and you are decently fast, this is going to happen on your inside wheels, either front or rear, in most slow corners. With an 800/1000 setup, and a track weight GT3, your wheels while they have approximately 2.5 inches of downward travel, 1.5 inches+ will be supported by your helper/tender at those spring rates.

If you search 'tender springs' you will find a very interesting post about the counter intuitive physics that comes into play wrt roll center and why running a higher rate tender can offset an undesired roll center effect that happens when a non tendered main goes into being uncompressed.

I'm not 'pushing' higher rate tenders, just wanted to point out to the OP that at minimum he should do something.

997gt3north

Those Tenders, basically (150#, 250#) (f,r), seem to be the standard Porsche configuration that are installed on cup cars and after market street GT3s with Moton kits, etc.

That is basically what my suggestion was - i.e. replication of the 'Porsche Spec'.

I could argue, given the heavier weight of Street GT3s, that to effectively mimic how a Tender would work on a cup car, that you would want to slightly increase the load to block height for Tenders on Street Weight GT3s.

What your specs don't say, but I could guess, is what is the block weight required to full compress/block each spring - this number is very important, as it comes into play as car weight moves around.

For example, it is not unheard of for street GT3s to have one of the front corner weights being very close to 500#s - and this is the total corner weight. If you remove all the stuff like wheel, tire, rotors, caliper, etc, not being supported by the spring, you can easily be at 400#s of sprung weight at one of your front corners. Your 25N front tender, that you removed, could possibly have a block weight close to 300#s. You can see how 300 and 400#s isn't really that far apart and how in this situation, if you had a corner weight that was in this range, that the tender would often be active, even in normal driving. The block weight of that spring is likely only 250#s but you get the point.

himself

No helpers. Here are the part numbers:

0900.225.0900 Spring 9/900
0700.225.0700 Spring 7/700

No issues on the track 6 months in. Must faster as well.

I don't know the valving, as this was a package deal from Dan Jacobs (who has set a bunch of these up). You should give him a call, as he is quite helpful in terms of parts and setup.



-td

997gt3north

I actually spoke with Dan before starting with my re-valve on my 997gt3 2 months ago. Between Dan and a bunch of other phone calls that I made, that is how I ended up with 700/900 being a good range. The fact that he puts on 7" fronts and 9" rears on a 996, pretty much confirms that there is no difference between the 996 and the 997s. A 7" spring at 700#s for the front will put the spring collars very near the top at stock ride height without helper on a 997. At full droop, the front spring will unseat by about 10mm. A 9" 900# rear without helper would put at stock ride height in a 997gt3 approximately 1 full inch above the lowest thread - but this is with Tarett's new rear spring hat (which isn't used in the 996 setup by Dan Jacobs as it is a new part) - in the picture posted the 9" spring was put directly against Tarett's strut Monoball - using Tarett's new spring hat, in addition to the monball provides a better fit. So, without this hat, a 9" spring without new hat is really equivalent to a 7" spring if you are using the hat - a 7" main at 900#s would put the spring collar at the top end of the threaded range. In this setup, without a helper/tender, the rear would unseat by about 1 1/2 inches at full droop. Given how much of a seating ridge (or lack of) on the new Tarett spring hat, never mind the Monoball in the picture, this is not something I would do - there is too much chance that the spring would not re-seat properly.

With those spring rates (700/900), I think you can get away without a helper on the front but on the rear it is too much (in my opinion).

997gt3north

I found this useful post that explains in an understandable logic experiment another reason why you want to run a tender spring versus an untendered main if your spring rate is such that the main spring on the inside lifting wheel goes into an uncompressed state

The effect on roll center

https://rennlist.com/forums/racing-a...pension-3.html

KOAN

The theoretical example assumes that the spring is completely unsprung. I contend that unless you are airborne for a few seconds, or are not using shock absorbers, this is not likely to be encountered in the real world. If you can rapidly lift a corner of your car, see how slowly the wheel goes into full droop. It should take a second or 2. I can add to this that in my actual driving experience, removing the tenders made a clearly noticeable difference in the way the cornering improved. That being said, do what you like. It may be that driving style or preference plays a role here. But there will clearly be a non-linear spring rate. This may work well if you are driving on the street, and want to have a softer ride on bumpy roads, but on relatively smooth surfaces, I think it will be detrimental.

997gt3north

Chuck,

You make an interesting point. Using your logic, if your spring is so slow to expand given your dampening rates, the same logic could be used to ask how you felt the effect of your Tenders prior to replacing them with very low rate helpers? I think the fact that you did clearly 'feel' the different, as you say you prefer the current feel, pretty much confirms that your setup is often in droop and the feeling you prefer is the insta-firmer feeling of zero-rate becoming 800/1000 as oppose to a ramping up effect. Your brain was also likely registering the very small amount of time that you could 'feel' these much lower rates vs feeling nothing with the 'zero' rate helpers. Feel as you know is hugely important wrt inspiring confidence - and that is what it is all about.