Clamp / Release force comparisons - Grey vs Turbo vs RTS vs 3S
Turbo Mini Forums

This is a great thread, thank you Dave for posting this info. I have an RTS and you have answered everything I was wondering about.

Some great info there Dave. Thank you for sharing.

I'm using a 998 and a std 1275 spring in my AP based RTS and its lovely on the pedal.

When I talk about a flat spring, with regard to a Verto clutch, I am talking about the part of the diaphragm that is the 'Spring'. The fingers are the actuating levers rather than anything to do with the 'spring'. Even with the spring flat, the fingers still point upwards.

Pressure plate lift is in the region of 1.5 to 2mm, therefore, the lever ratio needs to be somewhere near 3:1 to achieve the 1.5 to 2mm pressure plate lift at a throw out of 6.5mm.

Factoring this in, even if the spring is under flat by 0.75mm, a pressure plate lift of 1.5mm will mean the spring has to go 'over centre' by 0.75mm, I think that is a given in any clutch. This might mean that the fingers end up flat. Certainly on the A Series Verto clutch, those fingers will eventually bottom out on the centre boss if you go much over the 6.5mm throw out.

From my rough measurements of the springs, the lever ratio for the AP type spring is somewhere between 2:1 and 3:1. I've never actually measured the pressure plate lift at full throw, but should be easy enough to do, and it is then equally easy to calculate the actual lever ratio in the working assembly since you can measure both throw out and lift, remembering that the first part of throw out, the fingers will deflect without much movement in the spring.

I've built a few of the RTS and everyone seems happy with the pedal feel. I myself don't think its that bad, and anything that makes life easier on the crank thrusts is a bonus in my eyes. I'm using 2x 998 springs (thickness of about 2.2mm each from memory) but not yet put any real torque through it. I' m using a 0.7" Wilwood master cylinder with the push rod cleat not quite touching the bodywork. I've got a 0.63" master to try, but not overly fussed at the moment to be messing with the hydraulics at the moment.

Rod, what was your experience of the PTFE sheet (if it saw road use?), was it better than the graphite option?

TurboDave, was there any updates on the 3S testing?