Eibach vs Tanner Springs

[J.R.]

We run Penske 7800 Quarter Midget Dampers. The two spring manufacturers that I have seen are Eibach (we ran last year) and Tanner. I haven't been able to get much out of calling manufacturers, but I was wondering if anyone knows the pros/ cons to each type.

From what I've gathered, Tanners are lighter and cheaper (~$22), and the Eibach's may be more precise, although I haven't been able to find anything to back that up. Opinions?

[J.R.]

We run Penske 7800 Quarter Midget Dampers. The two spring manufacturers that I have seen are Eibach (we ran last year) and Tanner. I haven't been able to get much out of calling manufacturers, but I was wondering if anyone knows the pros/ cons to each type.

From what I've gathered, Tanners are lighter and cheaper (~$22), and the Eibach's may be more precise, although I haven't been able to find anything to back that up. Opinions?

[HenningO]

From what remember from a material mechanics course I took a couple of years back - the spring rate is proportional to the spring volume (ie weight if same material is used). So I have a hard time understanding why the Tanner should be lighter.

[J.R.]

They look like they use less material to me. Could be wrong, I most likely am if that is the case, I had never heard that about springs before. Anything else anyone can offer about benefits to either?

[Drew Price]

Spring stiffness is calculated from:

Diameter of the wire
The winding diameter (I.D. usually what's measured)
Number of coils
Young's modulus of the material

It is possible to have the same stiffness spring with different geometry.

Best,
Drew

[HenningO]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Drew Price:
Spring stiffness is calculated from:

Diameter of the wire
The winding diameter (I.D. usually what's measured)
Number of coils
Young's modulus of the material

It is possible to have the same stiffness spring with different geometry.

Best,
Drew </div></BLOCKQUOTE>

True that, but can you have same stiffness with different weight (using same material)?

[Kirk Feldkamp]

My impression was that spring "quality" is dependent on how accurate the spring is to the indicated rate. When you buy a set of "200 lb/in" springs, they all will fall within a range that is close to 200lb /in. If the company takes the time and effort to match sets of springs in a batch to a close tolerance to the specified rate, you will pay more. If your design is relatively insensitive to variations in spring rate, then perhaps the cheaper sets would work for you without any issues. Now I'm no suspension expert by any stretch of the imagination, but with super light FSAE cars, variations in spring rates (and spring weight) would probably have a significant effect on the setup of the car. How sensitive your car is to spring rate variation, and what variations in spring rate translate to in terms of consistent lap times... well, that's the real question that you should be trying to answer. Whether or not your particular drivers actually benefit from taking the time/money/manpower to worry about it is another question worth asking.

-Kirk

[J.R.]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Kirk Feldkamp:
My impression was that spring "quality" is dependent on how accurate the spring is to the indicated rate. When you buy a set of "200 lb/in" springs, they all will fall within a range that is close to 200lb /in. If the company takes the time and effort to match sets of springs in a batch to a close tolerance to the specified rate, you will pay more. If your design is relatively insensitive to variations in spring rate, then perhaps the cheaper sets would work for you without any issues. Now I'm no suspension expert by any stretch of the imagination, but with super light FSAE cars, variations in spring rates (and spring weight) would probably have a significant effect on the setup of the car. How sensitive your car is to spring rate variation, and what variations in spring rate translate to in terms of consistent lap times... well, that's the real question that you should be trying to answer. Whether or not your particular drivers actually benefit from taking the time/money/manpower to worry about it is another question worth asking.

-Kirk </div></BLOCKQUOTE>

That was the impression that I got as well, I just can't land any accuracy figures. I heard within 2% for the Tanners, and the Eibach's were "Very Precise", in laymans engineering terms, lol.

Just trying to steer this back to these specific spring manufacturers, does anyone have experience with the two brands that can offer some advice on them. I appreciate the debate about spring rates vs weight, but it's really not helping me figure out which springs are best.

[Mike Macie]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Kirk Feldkamp:
My impression was that spring "quality" is dependent on how accurate the spring is to the indicated rate. When you buy a set of "200 lb/in" springs, they all will fall within a range that is close to 200lb /in. If the company takes the time and effort to match sets of springs in a batch to a close tolerance to the specified rate, you will pay more. If your design is relatively insensitive to variations in spring rate, then perhaps the cheaper sets would work for you without any issues. Now I'm no suspension expert by any stretch of the imagination, but with super light FSAE cars, variations in spring rates (and spring weight) would probably have a significant effect on the setup of the car. How sensitive your car is to spring rate variation, and what variations in spring rate translate to in terms of consistent lap times... well, that's the real question that you should be trying to answer. Whether or not your particular drivers actually benefit from taking the time/money/manpower to worry about it is another question worth asking.

-Kirk </div></BLOCKQUOTE>

True. The most important part is the overall Wheel Rate. To me it's a waste of time trying to figure out if one spring is more precise than the other when you are talking about 1 or 2%. There's going to be some error in your dynamic tire spring rate, cg height, chassis stiffness, mass of vehicle, and other suspension compliance that will affect your load transfer. As long as your not buying cheap chinesiumhttp://fsae.com/groupee_common/emoticons/icon_biggrin.gif springs from some unknown company I'm sure you can expect them to be close to what they say. You even have a set of eibachs to test to see what how precise they really are. But when you do the calcs a 2% error in the spring rate will result in a 1-2lb difference in load transfer. Not that much at all. Error in other places will have a much greater impact.

[Drew Price]

J.R.,

Did you call either company and ask if they have a spec of how close to the published stiffness the springs are?

I think you will be fine with either, but without any data in front of me you might have to take a chance and measure them yourself, or ask if it would be possible for them to send you matched sets, or if they'd be willing to take exchanges on springs that aren't close enough for you.

Ideally you'll be able to sweep a range of stiffnesses during testing to get the car set up, so that might not be possible, in which case I'd personally opt for whoever is more reasonably priced, or if they would be willing to give you a package deal on say 16 springs.

Best,
Drew

[J.R.]

I had someone on my team try to call them up, he said that he couldn't get manufacturers numbers. I've been to busy to look into calling them myself (I briefly searched for numbers with no luck).

16 springs would be awesome, but defiantly won't happen this year. ($$) I'll probably just stick with the designed rates and stick with the Eibachs, since they are only ~$5 more per, and I know that they worked well enough last year.

Thanks for everybody's help!

[Drew Price]

Make sure that you can't adapt your perches to fit the Cane Creek spring diameters, Motorsports Spares has an FSAE spring kit, 16 springs for $175, but they are pretty soft rates, and will depend on your setup. It's listed on their site under the FSAE page. Maybe you could use those.

Best,
Drew

[gt_biker13]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Drew Price:
Make sure that you can't adapt your perches to fit the Cane Creek spring diameters, Motorsports Spares has an FSAE spring kit, 16 springs for $175, but they are pretty soft rates, and will depend on your setup. It's listed on their site under the FSAE page. Maybe you could use those.
</div></BLOCKQUOTE>

I looked at those, they seemed too stiff to me. I ordered custom springs from Dendoff Springs. You don't need to be a spring engineer, just tell them the rate, ID, and loaded height.

-Craig

[sbrenaman]

What size springs do the 7800's take? I can't get info off Penske's website.

[J.R.]

I'm not in the shop right now, but ours are 5 in long and I think 2.5 in in ID/OD. Spring's I'm looking for are in the 125-150 lb/in range.

[Cory M]

I had one of the worst customer service experiences of my life from Tanner Racing (Mitler Bros). I won't go into details but I will never buy anything from them again.

Eibach has been around forever and has a great rep. I would go with them or Hyperco.

[rjwoods77]

You look them up based on spring ID. For Penske quarter midget shocks (7800) that is a 1.63" ID. The OD doesn't really matter since the spring perches are designed for a certain fixed ID.

http://eibach.com/eibach/img/ers-14catalog.pdf

Whats also super cool is they are making "torsion release bearings" for there entire spring lineup. Then again its just a needle thrust bearing with 2 hardened washers so you could probably source that out of mcmaster.com