How thick do trigger wheels REALLY have to be?

[Chris Wilson]

I see lots of OE crank trigger discs only 3 mm or so thick, yet the Motec sensor info suggests 6 mm minimum thickness, with a broad tooth profile to boot. How come the OE set ups seem to work flawlessly with much thinner (and therefore lighter, with less inertia) discs? i have made mine, on an RB26 Nissan engine, to match Motec's criteria, but having just stripped my Toyota 4A-GE Formula Atlantic motor to find a less than 3 mm thick crank trigger disc running Electromotive ignition only management seemingly perfectly at up to 10,000 RPM, I don't quite understand this advice for very thick wheels? The teeth are also very short, with a "length", peripherally of less than 3 mm, too, it being a 60 - 2 wheel.

Thanks.

[SprinterTRD]

Generally chopper disks are matched to the sensor. Some sensors have small 3mm sensing area so a smaller tooth profile can be used. Other sensors have a 6mm sensing area so a larger tooth profile needs to be used.

MoTeC sells 6mm sensors which is why they reccomend the larger tooth profile.

[Chris Wilson]

Right, thanks for that, I see that the Formula Atlantic engine, with a very thin disc has a very slim (pencil thickness overall diameter) sensor. Toyota Supra MKIV's have a thin trigger wheel, too, but a very chubby sensor, but I think you can see a "pole piece" area on their face that's a pretty small diameter. It becomes very logical now, thanks for that

Is there not a desire to run a thin disc to reduce inertia though, particularly in the bigger diameters, on race type engines?