Track Coilover - Tech Thread - proper coilover length
 

Hello from the other side of the pond!

I'm surprised that after sooo much searching I could not find this info.

I have some problems regarding my coilover setup that after some track experience I know that must be related to lack of drop travel. This car is mainly track used.
We all know that Xida is the right setup, developed to miata. In Europe unfortunatelly, with shipping and taxes is too expensive and not an option.

We have several top brands in the Europe like Ohlins, Nitron or Quantum at (more) afordable prices. Ohlins, it's good for OEM ride heights or by using the top hat mounts enabling to go lower but at the cost of drop travel. These were the only brands that provided further details about their coilovers. I'm sure that these companies provide top notch quality materials in their coilovers and with proper valving but body lenghts couldnt be more different, so its my main concern to have the balance between low ride heights and enough bump and drop travel. I was not able to find any review for the miata platform, so I must dig in the tech stuff. I must stress that I'm no expert by any means, please correct me if needed.

Ohlins coilover measures open lenths FR 438mm R 351mm. Nitron coilover measures open lenghts FR 415mm R 335mm and closed 319/239 respectivly. Shaft travel 96mm in the front and rear. Quatum coilover measures open lenghts FR 425mm R 360mm and closed 275/220. Shaft travel 150mm in the front and 120mm in the rear.I suppose that Quatum shocks are more suitable for track work at lower heights (5") ? I know that they can make changes at my request. I'm not looking for the perfect coilover kit but want a well setup suspension for my use and get rid of my current setup.

Car information if relevant:
Double dutty - fully interior ~2400lbs
~225whp
5" pinch weld
205 or 225 tyres

I have Nitron's and thanks to my local (NZ) Nitron dealer we have been working with the factory to make some "adjustments" to both the F&R setups. Expecting them to arrive on a CV-19 free plane any day.

FNFMC,

Where are you located?
NA/NB?

Probably your best source if you're in UK https://www.raceshocks.uk/mazda-mx5-shocks/
With your project parameters, I'd start with OEM NB shock dimensions and just shorten the shocks and stroke a bit. Rear stroke more critical than front. If you use bearing mounts, make sure they are the same offset dimension as the OEM NB mounts.

Emilio,

NB chassis.

Mainland Europe but UK will do. Thank you for the sugestion, I will contact them. You should think of supplying Xida through Tractive to Europe.


Quantum coils (open lenghts FR 425mm R 360mm and closed 275/220) are an inch or two smaller than OEM, am I right?

Yes both sets use bearing mounts.

Not possible to offer Xida from anywhere but here. Tractive only supplies the shocks. Like many products you buy, components come from all over the world. We have parts from 4 other countries in the Xida assembly. Each kit is configured to order, many possible combinations.
Sorry!

I did have an interesting chat with this crew. They rebuilt one of my Xidas last year that randomly had a chipped shaft, and they turned it around very quickly and professionally.

I had a detailed chat with them afterwards at Autosport regarding springs. I'd initially just asked for a price on stiffer springs since I'm rubbing shock towers in compressions while turning, with only a 205 AR1 on an 8 (I'm 700/400 and I was going to go for 900/500, who knows what will happen when I get my 245s mounted on 9J 6ULs).

They wanted to know what I was doing and what my ride frequency was, then suggested I go softer since my ride frequency was already too high! I tried to explain that I couldn't because I couldn't go higher (at ~4.5" pinch) and the ARB (supermiata 1.125" 0.188 RB/14mm) setup was already stiff relative to the springs. Perhaps they are used to proper race car setup where the kinematics of the vehicle are somewhat optimised for the purpose, rather than working around the constraints of an OEM platform.

I'm sure they could put together something that you'd be happy with at the end of the day, but Emilio's already done the hard work for you, so unless you want a damper tuning project, just get the Xidas. (unless you daily drive your car thought salted winters, in which case I don't know what to suggest)

TLDR: If you're serious enough to be considering anything other than low budget options, just buy Xidas.

@Tran my ride height its on Xida Race limits (~5"). Dont forget my car has fully interior even if stays more time on track that on the road.

The main issue is the cost. I cannot justify spending more than 3.200€ with shipping and taxes to get them in Europe.

I think that Quantum is a good base, with good measures for my ride height, nice quality and digressive valving at minus 1.000€ than Xida.

For comparison, (please correct me if wrong @emilio700 ) at my ride height (measures taken at the coilover):
Xida ~Open Length: 426/316 shaft 126/101
Quantum Open Length: 425/360 shaft 150/120

At my ride height I can measure ~370/290 coilover length. That will give me (without bump stop):
Xida: 75mm bump and 26mm droop
Quantum: 50mm bump and 70mm droop.

Being this a street driven car, I think that the Quantum length are ok, than the shorter Xida. If needed I can raise the car a bit but I think that 50mm bump will be ok.

Planning on running 700/400 springs with 1.125 RB and rear stock sway

Let me know what you think

Not sure if this is how you're doing it, but something to keep in mind is that there isn't a single universal way of measuring extended / compressed lengths that is also meaningful.

Given everyone's looking at coilover "systems," the most meaningful length is the distance from the centerline of the lower mount bolt to the top surface of the mounting flange of the top hat where it attaches to the body. Maybe that's already what you're quoting, but that is the only measurement that forces apples-to-apples comparisons.

What afm mentioned is true. Keep in mind you can alter your bump/droop ratio by altering the "depth" of the top hat (i.e. where the shaft shoulder mounts with relation to the top surface of the mounting flange of the top hat).

Collected all your provided info on a table, added the OEM NB "Sport" Bilsteins to it (my measurements, center of bottom eye mount to the shaft shoulder).

https://cimg7.ibsrv.net/gimg/www.mia...84fbd00f94.jpg

As mentioned, bump to droop ratio can be "tuned" by selecting the appropriate top hat depth. Keep also in mind that (i) you need to accommodate a bump stop which will reduce your available travel by whatever amount you choose as its "solid" length and (ii) at some point your front tire will contact your inner fender and your rear a-arm will contact the frame; you need your bump stops to stop you just before that happens. If my data are correct this occurs approximately at 280mm F/242mm R (wheel center to fender), with 205-50-15 tires.

@HarryB measures were taken from the eye mount to the lower bottom of the top hat.

As far as I know, Quantum maintains the OEM offset of the mounts.

I doubt that this happens with the Nitron, their top hats are the same as other aplications.

​​​​​You can change the top mounts to band aid some problems, but you will face other. Some top hats made to Ohlins do exactly that, trying to solve the bump travel problems.

Regarding bump stops, I dont know what length Xida uses. Quantum uses a 13mm bump stop. We can always adjust the bump stop length according to needs

With Quantum, I think the major advantage is the street use with high droop travel. To very low heights (- 4.7"), Xidas are unbeatable.

We are collecting very interesting data here!

Would be very interesting to hear more from @emilio700 as he's got more experience than we all together

From memory, the shaft shoulder should be pretty much level with the bottom side of the top hat (give or take a couple of mm, I will measure it on the weekend); so our measurements can be directly compared.

Stroke is simply the delta in exposed shaft full closed and full open. This excludes any portion of the shaft that extends out of the shock at full closed.

Bump stops can be tuned, different dimensions and durometers so they should not be factored in to stroke measurement.

Total length on an early Miata shock is the center of the lower eye to the step on shaft where the first washer sits.

The pin on the shock can be sized to use OEM bushings with the NB Mount or it could be proprietary for the shock companies own Billet mount or some other dimension. This pin configuration affects where the mount is in relation to the stroke range. This in turn affects bump and droop travel. Many aftermarket shock companies get this wrong. So when trying to determine functional lengths, you need to know the pin dimensions as well. Don't assume they are OEM dimensions.

Agreed; although the bump stops will take up some of your stroke, so need to keep that in mind. Exactly how much depends on what you just mentioned; the OP should just not forget they are there.

Everything on my measurements assumes OEM NB top hats and mounting (hence the "center of bottom eye mount to the shaft shoulder" disclaimer, where shaft shoulder is the step where the bottom washer sits). I was hoping that OPs measurements refer to the same measurement.

Pin= end of shock shaft if I am reading this correctly?

Yes, "Pin" refers to whatever shaft is above the actual bearing surface of the shaft. NC has a clevis lower mount. Most shocks are either pin, eye or clevis mount.