From a purely engineering perspective, it might be worth looking at how\nmuch power is needed in each class and working back from that. Right now\nwe have\n- MotoGP ~210bhp - 148Kg\n- 250 ~110bhp - 100Kg\n- 125 ~55bhp - 80Kg\n\nA prototype 500-2 engine based on the old 990 MotoGP engines ought to be\nable to make 110-125bhp fairly easily. The current MotoGP engines are\nmore exotic as the factories chase revs so a 100BHP 400-twin looks\npossible but expensive. 110BHP from a 600-4 is easy and might not\nrequire any tuning of a stock engine beyond a pipe. From there we could\nhave anything from 120 (US Superports), 135 (WSS), 150(unlimited\ntuning). Current YZF250s are making ~40BHP in tuned MX trim. ~45BHP\nlooks possible in road racing trim with the same engine. A prototype 250\nsingle might get to 50hp. That's at least in the same ballpark as\ncurrent 125GP.\n\nWhat would Ducati do? Well they built the Supermono as a V-Twin with a\nfake upright cylinder replacing it with a balancing rocker. So they know\nhow to build something by just removing the top cylinder from a\ndesmosedici. And you have to figure they could build a Supermono layout\n250 using the same top end layout.\n\nAll of this assumes that we need to keep to the 1-2-4 ratio between the\nclasses on horsepower and capacity. But that's only a relic of the old\n125-250-500 two stroke classes. Maybe 80hp-140hp-200hp would be a better\nprogression. On that basis, 400-4, 600-4, 800-4 would make more sense.\nIf production engines play a part, there's an added wrinkle. The\nJapanese have just dropped the power limits on their licensing scheme so\nthat 400 road bikes are no longer limited to 55BHP. It's quite possible\nthat in the next couple of years we'll see them building slimmed down\n400-4s with 70bhp or so for the home market. Allow WSS or slightly\nabove levels of tuning in prototype chassis on both these and 600s and\nwe have a formula. So we'd have production based 400 with WSS tune.\nproduction based 600s with WSS tune + unlimited cams and compression\nratio and 800 prototypes for MotoGP all in prototype chassis. Then put\nin weight limits and fuel limits to put a cap on expensive materials and\ntuning.\n\nWhich then brings in Dorna vs FGSport. There's some sort of agreement\nthat FGSport are the only people allowed to run world championships\nusing production based machines. But it's not clear what form that\nagreement actually takes.\n\nAnd then finally, there's the factory vs private team issue. I don't see\nprototype chassis as being a problem. There are plenty of chassis\nbuilders out there and all the suspension bits are available off the\nshelf. Engine tuning is interesting. I think it should actually be\neasier for a private team to get competitive power with a production\nbased engine than with the current 125-250 two strokes. And then there's\nelectronics. Right now, traction control is hard and expensive. Even\nwith 80hp-140hp the top teams will want to run it. You can see this as a\ngood thing as it'll promote trickle down of the technology. Or a bad\nthing because it's where the factory budget can make a difference.\n\n The EU is also looking at a similar graded license. Some markets\nalready have a 33hp limit for 2 years after passing your test. A 400cc\nlimit would be much easier to enforce. And I for one, look forward to a\nnew batch of grey import 400-4s. I think these make a much better first\nreal bike after learning on a 125 than a 600. It was quite scary enough\nwatching my son jump from a 125 to a 15 year old 400-4. The current crop\nof 600s are *way* too much for the average 20 year old road rider.\nActually they're way too much for the average born again 45year old as\nwell. But that's got nothing to do with racing.