Hi,

I have just got some ohlins dfv (F8kg/mm and R6kg/mm {~448lb/in and ~336lb/in) second hand and have been searching for the recommend preload. After some digging i found this
Ohlins - Can anyone translate this for me? - MX-5 Miata Forum

The attached image in the OP recommends 2mm preload front and rear. I have gone through a number of threads on here and miata.net trying to find out of this is sufficient for the limited rear travel of the shocks but haven't had too much luck finding anything solid.

I daily the car and use it for track days and dirt sprints. Please note - I am in Australia! The roads can be pretty rubbish. The dirt sprints are my main concern - they're run on a hard packed dirt surface that begins to rubber up towards the end of the day, but can get fairly bump on corner entries. I have been running koni sports with 7kg/mm and 5kg/mm springs - it's not too bad, i have the adjustment on the hardest setting front and rear... anyway,

Is it advantageous to add more preload to the rear suspension to give it more bounce travel at the loss of droop?

I have done some quick calc's, but haven't include the angular correction for the shock, but it looks like to have 1/2 bump and droop travel for the shocks you need about 26mm of preload. I assume the shock only has about 56mm of available stroke - 76mm stroke (from the xida topic on miata.net) and assuming 20mm for the bump stop - this could be an underestimation.

Cheers
plohl


p.s. other information, they may/may not be useful - wheels: daily, stock 14" BBS's - crappy all rounder tyres, track 15x8 6uls with 205/50R15 advan ao48's. Engine is n/a, mild cams and haltech e6x ecu. Torsen t2 diff with 4.3, 5 speed gear box. Car was 1040kg with me in it. Measured on scales used to weigh cranes though, so tolerance is +/-10kg

 

There should not be any meaningful pre-load on the springs, either front or rear, but definitely not rear. Assemble the coilovers, then adjust the spring perch until the spring just touches and cannot rattle around. Then add 1/4 - 1/2 turn.

That is what I do.

I think there are 10 threads per inch (25.4mm), so 1 full turn = ~2.54mm.

 

Thanks wildo.

I got the spec's from ohlin's and put the coiolvers in the day after. I think i have a little more preload then 2mm front and rear.

Ran the shocks at the dirt sprints on sunday and got a pb which i was pretty happy about. The shocks performed brilliantly - i just need to learn to steer now haha.
The rebound was set a 10/32 'clicks' front and rear. I ran the same set up the next day at the queensland raceway with a varying track condition - dry - really wet - wet and finally it dried up. Was awesome. Very happy the ohlins lived up to their reputation.