Inside rear wheel unloading

[madjak]

I wonder why Japanese companies like Cusco, Tein etc have never used secondary springs on their MX5 suspension? They must have real egg on their Japanese faces since they have been proven wrong by videos and links to one single product available.

Tenders are more expensive.

Here you go: Thread summary

For any given 'Spring A' at a relatively high rate

Option 1. Run Spring A
Set spring perch to preload spring slightly

Pros: Cheap, simple
Cons: Not much droop travel

Maths:
Droop = (weight of the car / 4) / Spring Rate * 1.5
eg (1000kg / 4) / 10kg * 1.5 = 37.5 mm

Option 2. Run Spring A uncaptive
Set spring perch to be below the spring by 25mm

Pros: Cheap, Good droop travel
Cons: spring is loose when the car is jacked or in the air

Maths:
Droop =[(weight of the car / 4) / Spring Rate + 25mm] * 1.5
eg [(1000kg / 4) / 10kg + 25mm] * 1.5 = 75 mm

Option 3. Run Spring A-25mm plus a 150lbs tender
Run a 75mm tender that will compress to 25mm under the weight of the car

Pros: Best droop travel, some loading on the wheel depending on tender choice
Cons: More expensive

Maths:
Droop =[(weight of the car / 4) / Spring Rate + (75mm - 20 mm)] * 1.5
eg [(1000kg / 4) / 10kg + 50mm] * 1.5 = 112.5 mm

[madjak]

I should also point out that usable droop travel is limited by the shock itself, sway bar, spring rate and general handling of the car. Whilst Option 3 might have more theoretical droop, it's unlikely to actually get that much when the sway bar is hooked up. Also rubber bushings add an additional spring rate and if you want full droop you'll need to run urethane, delrin, sphericals or hybrid bushings like mine.

I will also say there is probably, at most only a 5-10% increase in suspension performance (my guestimate) from running a tender (option 3) over a single spring (option 1)...

[project.r.racing]

How "expensive" is expensive? My last helpers I brought were $80. But in 2005ish. Cannot imagine tenders costing much more.

And if anything prices for this stuff has come down since then. Was $250 for a pair of 62-180-07 springs in 2005, now same springs are $150.

So by my calculations. They shouldn't add too much to the final costs. So why haven't these well know companies used or started using them? Even on their high end comp spec versions?

[madjak]

Well a pair of Eibach race springs is around $200 from the USA. A pair of tenders around the $120 mark plus you need the guide collar an ideally a torrington bearing on the base (you need the bearing because the two shocks can twist under load).

So really you're adding around $200 - $300 per pair of shocks for what is only a minimal gain. Unless you are a serious racer and chasing that last 0.1 sec then really the cost / benefit isn't there... at which point you are also probably spending $2000+ for a set of shocks to match and the extra tenders don't add much to the price.

The other problem with a DIY setup is there is also the risk of getting it wrong and having to buy another set of springs, which is what I had to do. Unless you know what you are doing and know what you are trying to achieve, I'd stick to what manufacturers supply... Or just go get some Xidas.

Really this whole debate has come from Magpie's query on the rear wheel unloading and causing traction problems with the rear torsen diff. Ideally the best fix is probably a clutch pack diff which will minimise the loss of traction regardless of suspension. Like Magpie, I had a similar issue and I have managed to correct it with suspension changes by increasing rear droop and running stiffer springs all round. Generally when I encounter an issue on track that I think is losing me time and I research and try and fix it. It's the slow evolution of my car into something that is just a little bit faster that before.

[project.r.racing]

Thanks for taking the time to answer my questions. You unloaded some good info and it caused me to have more questions.

As for the diff. I did mention the diff being part of the issue on the first or second page.

[pepejesus]

I wonder why Japanese companies like Cusco, Tein etc have never used secondary springs on their MX5 suspension? They must have real egg on their Japanese faces since they have been proven wrong by videos and links to one single product available.

I hope magpie finds his own solution to his problem. I'm doubtful this thread can go much further. Hence the personal attack starting to come out. Goodluck.

Sorry mate, no personal attacks intended on my part, so apologise if that's how I came across. I admit I was getting frustrated going over things that had already been covered earlier in the thread.

[project.r.racing]

project.r.racing do you use off the shelf suspension with no modifications, that is order it, bolt it in place and forget about it?

I haven't come across one yet that didn't need some adjustments out of the box, (excluding height adjustment). They are advertised as bolt and play. But they always need fine tuning. 99% of people wouldn't notice they need fine tuning. Some have had the preload wrong on the fronts or rears. One set had the spring perch rubber put in up-side-down. That one was a PITA to fix. Some I didn't like the amount of limited camber on offer, or other tops were ordered with bigger adjustment slides etc.

[Magpie]

Good way to end the thread, thanks all.

Apologies for any frustration caused, would be good to organise a face to face round table discussion on the subject and invite some guest speakers

[Magpie]

Reduced the uncaptive amount on the front by increasing ride height. This was possible because I lowered the splitter 15mm. Put about 3mm rake (with drivers weight).

Once height was set only one chandler required to get 50/50 balance. Add 6.4 kg to RL and subtract 6.4 from FL. So 1 full turn on the rear (increase height) and 3/4 turn FL decreasing ride height.