Helper Springs vs Tender Springs - Page 2 - MR2 Owners Club Message Board
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post #21 of 33 (permalink) Old December 7th, 2011, 23:46
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Owen brought up a point I was going to make, but didn't get to it yet. By adding spring force to the extended (inside) strut you will get more body roll than before.

One thing I do remember from my suspension studies is that you can change spring rates and sway bars all you want, but the weight transfer of the car in a corner is only dependent on the location of the CG, the vehicle speed, and radius of the corner. Most of the changes I've made on my different cars has been to adjust which end of the car takes the additional weight transfer.

Another thing I noticed (and I'm still new to the MR2, so I may be completely off base) is that you're using the same spring rate front and rear. By stiffening up the rear rate, or by softening the front rate these should both have the effect of reducing front tire lift.

Again, I'm not too familiar with the MR2 yet, but I know several of the 911's that autocross tend to lift the front inner tire, and they seem to prefer it that way. The E30 and E36 cars also tend to do this. In fact, some E30's tend to lift both inside wheels off the ground

One year of our FSAE chassis would lift an inner rear tire - which is a horrible thing. But if you're not actually lifting a tire, but just lifting the spring off the seat then a light helper spring may be the easiest idea. I think the ones I got for my MKIV were about 6" long uncompressed, and maybe 1" long installed (but unloaded) and fully compressed with any weight on the suspension.

I did find the other company who made tender springs. It was Afco. But they don't list any specs beyond rate for their springs, and they aren't flat windings like the ERS tender springs.

My EG civic would lift the rear tire, but that's mostly because I had a stiff rear bar and light front bar. It was helpful to rotate the FWD platform. However, lifting the front of the MR2 is likely just going to cause a lot more understeer.
-Dan
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post #22 of 33 (permalink) Old December 8th, 2011, 01:36
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Originally Posted by Alex W
No, they are DIY koni coilovers based on the stock housings. Spring perch adjustment only.
Ok, same as KW's.
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post #23 of 33 (permalink) Old December 8th, 2011, 11:05 Thread Starter
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Quote:
Originally Posted by Owen
Share my experiences with significant helper/tender springs. I didn't like them. They acted just like progressive springs, which is probably why there aren't many companies making significant rates. Things that you may or may not have considered:

1. You are trying to "save" grip on a tire that has no appreciable vertical load, and hence, has no appreciable lateral grip to save.
2. Changing the effective rate in droop enough to change #1 means that you are making significant changes to the spring forces vs roll and pitch
3. This leads to the car having more body roll. Roll is comprised not just of the outside compressing, but also the inside extending. If you figure out what the equivelant single spring rate is based on roll stiffness you would find that most of your travel issues would be solved by going to equivelantly soft springs.
4. For gods sake only do it on one end of your car. This better be the front. Otherwise your handling can change somewhat fiercely since weight transfer can be even more seriously affected by fore/aft weight transfer.
5. Your damping will be all honked. There is no dampening that will be any good for your 115lb/in spring rate on the inside that even remotely works well with your 500lb/in outer rates (similare problem to big anti-roll bars).

Off hand the best solution sounds like shortening your struts, but failing that I would suggest that you only do one end.

O
Quote:
Originally Posted by cord4530
Owen brought up a point I was going to make, but didn't get to it yet. By adding spring force to the extended (inside) strut you will get more body roll than before.

One thing I do remember from my suspension studies is that you can change spring rates and sway bars all you want, but the weight transfer of the car in a corner is only dependent on the location of the CG, the vehicle speed, and radius of the corner. Most of the changes I've made on my different cars has been to adjust which end of the car takes the additional weight transfer.

Another thing I noticed (and I'm still new to the MR2, so I may be completely off base) is that you're using the same spring rate front and rear. By stiffening up the rear rate, or by softening the front rate these should both have the effect of reducing front tire lift.

Again, I'm not too familiar with the MR2 yet, but I know several of the 911's that autocross tend to lift the front inner tire, and they seem to prefer it that way. The E30 and E36 cars also tend to do this. In fact, some E30's tend to lift both inside wheels off the ground

One year of our FSAE chassis would lift an inner rear tire - which is a horrible thing. But if you're not actually lifting a tire, but just lifting the spring off the seat then a light helper spring may be the easiest idea. I think the ones I got for my MKIV were about 6" long uncompressed, and maybe 1" long installed (but unloaded) and fully compressed with any weight on the suspension.

I did find the other company who made tender springs. It was Afco. But they don't list any specs beyond rate for their springs, and they aren't flat windings like the ERS tender springs.

My EG civic would lift the rear tire, but that's mostly because I had a stiff rear bar and light front bar. It was helpful to rotate the FWD platform. However, lifting the front of the MR2 is likely just going to cause a lot more understeer.
-Dan

You guys bring up some good points, and reminded me of a couple things I know, but had forgotten or not thought of in this context.

Regarding #3 (and also what cord4530 was saying) that is correct, my understanding is that weight transfer is related only to CG and cornering load. Spring rates have nothing to do with it. Now, As far a i can reason the same cannot be said for sway bars, as they reduce body roll by transferring load, but that's not really the point of this discussion.

So given that weight transfer is not a function of spring rate, the only thing that spring rate does effect is body roll. So for a given weight transfer, given a certain spring rate, you will get a resultant body roll. If I effectively soften the springs (even if only in rebound), I will still be wanting to pick up that corner (if the weight transfer was enough to do so before), only it will happen at a greater body roll / greater droop amount. (This is referring to point #1). With this in mind, zero rate helper springs seem like the way to go.

#5 is true, I would hope to set the damping for the 500lb rate, and let the softer rate be over damped, on the theory that the lower rate is in use a lot less of the time.

The other side of this debate is what happens over bumps. I doubt that I am truly picking up a wheel (or at least unloading it completely) due to cornering forces alone. The track I was at when I had the spring come un-seated is quite rough, and I suspect I dropped it off while hitting a bump, or perhaps a bump mid corner when the two forces would be combined. It seems that having a softer initial rate at large droop levels would be good to provide better compliance over bumps.

With that in mind, maybe I want to run a tender that's on the soft end of the available range, say 100lb or so. This would give me most of my current travel at the main spring rate, and at extreme droop the lower rate would engage to cushion (at least slightly) larger bumps.

For example http://www.vorshlag.com/product_info...roducts_id=253 sells a tender with a rate of 114lb/in. By my calculations this would give me about .6" of front travel at the full 500lb main spring rate, and then an additional 2.7" of travel at a much lower ~95lb rate. In the rear I would have about 1" of full rate travel before engaging the tenders.

I'm pretty happy with the equal rate f/r setup. If anything (performance wise) I think a little stiffer in the front would be the way to go (others have had good luck with that setup). The stiffer rear setup is generally paired with a stiffer front sway bar, which ultimately ends up putting you back to roughly equal rates when you consider both the springs and sway bars.

Last edited by Alex W; December 8th, 2011 at 11:22.
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post #24 of 33 (permalink) Old December 8th, 2011, 11:58
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Nice find on the tender springs. I know you can machine just about anything, so some 60mm to 2.5" adapters are probably no problem for you, and I'm guessing the slightly smaller inside diameter will clear your setup okay (but it's worth checking).

Actually, as counter intuitave as it sounds, even sway bars don't change the weight transfer to the tires. That's still just a function of
(centrifugal force * CG height) / track width
Sway bars change the roll stiffness of each end of the car (effectively making the outer spring stiffer and the inner spring softer), but they don't actually change the lateral weight transfer. They do adjust the distribution of that weight transfer between the front and rear though.

I did a little more reading about tripodding. I know you mentioned you probably aren't actually lifting a wheel, so this may not apply in your situation. In general, the texts are saying to avoid it. If an inside front tire is lifting then they say the front roll stiffness is too high, or the rear roll stiffness is too low. The easiest way to think about this is that the moment the tire comes off the ground, any adjustments made to tune roll stiffness no longer have any effect on a 3-wheeled car.

However, the texts only discuss the negetive effects of tripodding on the steady-state corner speed. If the car is more of a momentum car, then corner speed is everything. But if the car is really powerful, getting a good drive out of the corner may make up for loss of mid-corner speed. I remember some coaching from a Canadian race car driver when we were on track in the Supra and he basically said "In a 'power car' like this, you should set it up to brake hard and be stable in trail braking, and to be able to put the power down as early as possible. This means less roll stiffness in the rear and more in the front." Set up as such, the car understeered in the corners, and I lost a few MPH of mid-corner speed because of it. But because there was so much more traction available at the back I could get on the throttle a lot earlier and rocket out of the corners compared to previous corner exit speeds. I suppose this was even more exagerated by the track having two fairly long straights.

I mention this because I think you have a turbo car, and if so you may be willing to give up some corner speed for improved acceleration. If you are NA, or running auto-x or tracks with very short straights then you may be willing to give up some longitudnal acceleration for improved lateral acceleration.
-Dan
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post #25 of 33 (permalink) Old December 8th, 2011, 13:10 Thread Starter
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Yeah, I suppose that makes sense about the sway bars, trading spring rate on one side for spring rate on the other. With that in mind, it seems that in a way sway bars will cause your springs to behave progressively, with the outer one stiffening and the inner one softening the more body roll you have.

I think I can make 60mm tenders work on my setup. The price is certainly attractive on them, compared to the Eibachs.

I agree on tripodding, in general it seems like it shouldn't be good. 3 tires can't possible provide as much grip as 4, plus the tuning issues you mentioned.

The ability to put down power is definitely critical in my car, with 365 at the wheels. I typically turn down the boost for road course use, but run at full power for autocross.


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post #26 of 33 (permalink) Old December 8th, 2011, 13:28
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Holy cow!! 365 at the wheels?!! I watched one of the videos of your car at autocross and it sounded pretty good. But I had no idea.

Yes, it's not often talked about, but with stiff swaybars you can really change the effective spring rate mid-corner, which makes chasing damping settings a difficult task. When I ran a non-staggered setup on my Supra I didn't use any rear sway bar at all (paired with a pretty stiff front bar). I really liked that setup. I don't know that I ever lifted a front tire though, but I suspect not.

I can't imagine you would have any problems machining a fix for the 60mm springs. If they don't clear the threaded perch you can certainly take a little off the inner diameter of your upper perches so they seat well. I'm guessing you'll have to make your own coupling spacer, but that shouldn't be too difficult either.
-Dan
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post #27 of 33 (permalink) Old December 8th, 2011, 22:14
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Quote:
Originally Posted by Alex W
I agree on tripodding, in general it seems like it shouldn't be good. 3 tires can't possible provide as much grip as 4
LOL. That's a good rule of thumb, but is doesn't HAVE to be true. There are plenty of cars that if you aren't on 3 wheels, you aren't anywhere near competative. Oddly enough, I think most mr2's fit that bill.

The simple fact is that any car that has a lot of weight on 1 end, but not a whole heck of a lot more tire on that end, will almost always be faster 3 wheeling. This includes the back end on most FWD cars, but also the front end of many rear heavy cars. It's not ideal in theory, but in a practical world it's essentially unavoidable.

O
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post #28 of 33 (permalink) Old October 8th, 2012, 09:54 Thread Starter
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So I have been running 150lb Eibach tender springs on all four corners for the last few months Overall, I am pretty happy with them. They do soften the ride a little over larger bumps, but the downside there is they also make a bit of noise over larger bumps, which is a bit annoying.

Performance wise, I can't say that I have noticed a huge difference, but it is tough when you are making other changes at the same time. The differences there are certainly subtle. It is possible that the car has a bit more body roll than before, but without hard measurements I can't say for sure. I also upped my front spring rates from 500 to 700 this summer, which of course has a big effect on that as well. One thing I have noticed, and I don't know if this is new or not, but the car seems to squat surprisingly hard on acceleration, considering the spring rates. It could be that under acceleration I am unloading the front enough to get into the tender springs, which considering the above quoted post from Rennlist, would significantly reduce my pitch resistance.

One setup difference that these have pointed out to me is how short of main springs you can get away with. My new 700lb front springs are 7" instead of 8, and I probably could have gone with 6" springs there without a problem. Same with the rear, I wish I had 7" or even 6" springs. In the rear especially it becomes a problem with my spring perches contacting the chassis at full droop because they are set so low on the strut.


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post #29 of 33 (permalink) Old October 20th, 2012, 03:31
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Originally Posted by Alex W
So I have been running 150lb Eibach tender springs on all four corners for the last few months Overall, I am pretty happy with them. They do soften the ride a little over larger bumps, but the downside there is they also make a bit of noise over larger bumps, which is a bit annoying.
I am wondering why you feel the ride is little soften over the larger bumps?

Maybe it is because when it is over larger bumps, your suspension has gone to full droop and your 150lb tender springs give you that "softer initial landing" when it start to compress before the main spring. so essentially a progress spring rate in compression only.

I think i like the tender spring concept.

that noise maybe it is the tender springs blinding/collap noise.
when it is the zero rate helper spring, maybe there is no enough force to make any noise? what do you think?
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post #30 of 33 (permalink) Old October 20th, 2012, 09:27 Thread Starter
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I am wondering why you feel the ride is little soften over the larger bumps?

Maybe it is because when it is over larger bumps, your suspension has gone to full droop and your 150lb tender springs give you that "softer initial landing" when it start to compress before the main spring. so essentially a progress spring rate in compression only.

I think i like the tender spring concept.

that noise maybe it is the tender springs blinding/collap noise.
when it is the zero rate helper spring, maybe there is no enough force to make any noise? what do you think?
I think that is exactly why it is softer. A larger bump that the wheel can either fall into or fall off the other side of is likely to engage the combined main+tend rate. I think what you meant to say is that it is progressive in rebound only. At ride height the tender is fully collapsed, so any further compression is all in the main spring, but as you rebound more than about 1/2" you start to open up the tender spring. The only unfortunate part of this (performance wise) is that this does effect body roll, as discussed earlier in this tread. It's a little counter-intuitive though.

I agree, the sound is probably from the tenders opening / closing, and it is actually surprising how little of a bump it takes to make them clatter sometimes. Runing a zero rate helper might help with that because you will have more compression in the main spring at ride height (similar to running no helper at all), so it will take a bigger bump to open the helper.
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post #31 of 33 (permalink) Old December 10th, 2013, 16:33 Thread Starter
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Quick update to this... I decided late last year (2012) that I wasn't as happy with the tender spring setup as I had previously thought, and that I would try without this year (2013).

In hind site, the tenders were terrible! Owen, you were right on all points, it just took me a season to come to that conclusion myself:

Quote:
Originally Posted by Owen
Share my experiences with significant helper/tender springs. I didn't like them. They acted just like progressive springs, which is probably why there aren't many companies making significant rates. Things that you may or may not have considered:

1. You are trying to "save" grip on a tire that has no appreciable vertical load, and hence, has no appreciable lateral grip to save.
2. Changing the effective rate in droop enough to change #1 means that you are making significant changes to the spring forces vs roll and pitch
3. This leads to the car having more body roll. Roll is comprised not just of the outside compressing, but also the inside extending. If you figure out what the equivelant single spring rate is based on roll stiffness you would find that most of your travel issues would be solved by going to equivelantly soft springs.
4. For gods sake only do it on one end of your car. This better be the front. Otherwise your handling can change somewhat fiercely since weight transfer can be even more seriously affected by fore/aft weight transfer.
5. Your damping will be all honked. There is no dampening that will be any good for your 115lb/in spring rate on the inside that even remotely works well with your 500lb/in outer rates (similare problem to big anti-roll bars).

Off hand the best solution sounds like shortening your struts, but failing that I would suggest that you only do one end.

O
Handling was MUCH more predictable without the tenders, body roll was greatly reduced, and ultimately the car was much faster. And to be honest, any improvements in ride comfort were at best very slight. Totally not worth it in that respect, if comfort was that big of a priority I would go down a few hundred lb on spring rates, and probably trade some front rate for a small front sway bar.


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post #32 of 33 (permalink) Old July 5th, 2014, 19:27
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Quick update to this... I decided late last year (2012) that I wasn't as happy with the tender spring setup as I had previously thought, and that I would try without this year (2013).

In hind site, the tenders were terrible! Owen, you were right on all points, it just took me a season to come to that conclusion myself:

Handling was MUCH more predictable without the tenders, body roll was greatly reduced, and ultimately the car was much faster. And to be honest, any improvements in ride comfort were at best very slight. Totally not worth it in that respect, if comfort was that big of a priority I would go down a few hundred lb on spring rates, and probably trade some front rate for a small front sway bar.
I know this is one hell of a thread revival, but I have a question for you: when you say you went without tenders in 2013, does that mean you went to helper springs instead, or set up your suspension to be mainspring only, in such a way as to prevent the spring from coming unseated? And are you still on Koni yellows, or did you go to Koni 8611's? Basically, what did you change from 2012 to 2013, coilover-wise? Still running no sways?
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post #33 of 33 (permalink) Old July 5th, 2014, 21:16 Thread Starter
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It was (is) main spring only. The only change I made was drilling a 1/4" hole in the upper perch and zip tying the spring to it, and removing the tender springs. The upper perch is free to slide along the damper shaft, so at full droop the damper sticks through the perch is down around the middle of the damper piston. The spring can't really come unseated, but there is some "unsprung" drop travel (about 1.5" in the rear, 2.5" in the front). That was with regular Koni yellows, but the housings were modified to get the droop numbers to look like that. It would have been about 4" in front and almost 2" in the rear otherwise. No sway bars.

I have a set of 8611's that I will be building new coilovers with for the new car, but I haven't quite gotten to it.


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