[Dalko43]

Originally Posted by bradleyland

It doesn't matter if we're talking about GTLM, GTE, GTD, or GT3. They're all homologation race cars with minimum weight requirements. I lump them together as "GT cars", because GTLM, GTE, GTD, GT3, whatever all use conceptually similar regulations. You can get all pedantic about which regulations we're referring to, but none of that refutes the actual fact, which I will restate again below.

The weight of the production car is irrelevant, because they manufacturers are easily able to hit the weight targets using composite components. These days, GT cars contain massive amounts of carbon fiber.

Fire up a search engine some time. It's elucidating.

IMSA "Classes" page states:

GTLM WEIGHT: 2,745 minimum
GTD WEIGHT: 2,700 pounds

From there, BoP may add mass to cars based on their performance relative to competitors.

There is no problem at all getting a race version of the M6 down to those weight targets, and even if the cars don't hit those targets, BoP makes up the difference. Even if BMW started with an i3, they'd have to meet weight minimums, and BoP would be applied to bring it in line with the rest of the cars in that spec. So again, the production car weight is irrelevant.

The GTLM weight you listed is the minimum weight, so theoretically cars could be somewhat higher than that. BMW lists their GTLM m6 at ~2756lbs, empty, so they aren't far off from that. My comment on that specific issue was a question more than anything else, so I now understand the weight and BoP issues which you brought up.

BTW, BMW themselves did an interesting writeup on both their GT3 and GTLM platforms: http://www.bmw-motorsport.com/en/cars/bmw-m6-gtlm.html

Originally Posted by bradleyland

Dimensions do play a role, but if you listen to all the hype, commentary during races, etc, they all play up the longer wheelbase of the M6 as an advantage because it's more stable. The only race where it was a "concern" was at Long Beach, because the course is kind of tight in areas. It's all hype to me though, because none of it makes that much of a difference.

Well, that's why I started this post: to discuss the decision behind using the M6 and whether certain commentary was hype or legitimate analysis. The longer wheel base of the M6 was noted as a possible issue in a previous race, not just Long Beach, because I remember the commentators mentioning it (I believe it was the 12 hours of Sebring). And I wouldn't be surprised if it was brought up again for Sahlen's 6 hours of the Glen and LimeRock. That's the thing about traditional road courses; they tend to have tight turns and corners.

Originally Posted by bradleyland

The cars are all regulated and BoP'd to within a few tenths of each other. Winning and losing on race day comes down to strategy (fuel, pitting, etc), reliability, and gaming the system (knowing when to put on your best performance, and when not to). The best teams are the teams that balance all these equally. BMW is currently failing (primarily) at reliability and strategy. Tangentially, I'm not sure the M4 would have fixed either of these.

1) Strategy and reliability and playing the "game" no doubt play a part, and BoP tries to emphasize driver and team performance and strategy over simply letting the richest, best supported team dominate the series (as is the case in certain other racing organizations). But the engines, transmissions, chassis setup and the overall vehicle design still play a huge role in determining how cars perform. BoP might make the performance seem nearly equal on paper, but do you really think that the M6 GTLM handles and drives the same, or even similarly, to the older Z4 GTLM? Or to the C7.R GTLM or 911 GTLM? All of the driver interviews and commentary I've seen and read suggests that despite the BoP regulations, there is quite a bit of difference between how the different cars actually perform and handle on the track. I remember watching video where the old Z4 GTLM's high-reving V8 had trouble keeping up with the C7.R on transitions from certain corners into straight-aways because its peaky power delivery was vastly different from that of C7.R's push-rod V8. Just one example, I know, but hopefully you see what I am getting at.

2) I'm not sure that the M4 platform would have solved any of BMW's current issues either. My only reason for questioning the use of the M6, was because, engine aside, it seems like a lot more work is required to get such a big car ready for GTLM and GT3 use.

Originally Posted by bradleyland

Think of it this way, if the car you started with mattered, the Ferrari teams would be wiping the floor with the M6 by wide margins on every lap, because the 488 is such a vastly superior car in stock form, yet the top M6 qualified better than the top 488 at Daytona, Sebring, and Long Beach.

I agree that BoP equalizes some things, but I still think the inherent characteristics and pro's/con's of each car/setup play some measurable role in determining how the different teams and manufacturers perform. It's not purely about the strategy and driver skill, in the same way that something like NASCAR or DTM are.

Originally Posted by bradleyland

I don't need a citation, it's simple thermodynamics. The larger the displacement, the more power you can make (all things being equal). The displacement of the S55 is 15% smaller than any other car in the series, and is 46% smaller than the P63. It costs money to make up that deficit. When you stress components more, you have to use more expensive materials. I also didn't say "a lot" more; I only said more, because obviously we don't have any real world examples to work from.

Hasn't F1 paved the way for using small displacement turbo engines in racing applications? I thought they were employing that kind of technology back in the 80's, if not earlier?

I'm not sure if the a notional M4 GTLM would cost more than a comparable M6 GTLM; I'm asking the questions because I haven't seen much if any commentary on that subject. In general, I agree with what you are saying on this issue though; a larger displacement turbo V8 seems like a better starting point for building a race car.

Originally Posted by bradleyland

I've provided two core facts, both of which stand on their own.

1) The weight of the production car is irrelevant.
2) The M6 platform has a larger engine displacement from which BMW Motorsport can build from.

It is from this that we can draw very reasonable conclusions, but ultimately, it is speculation. The only people who can really answer your question are BMW, and they won't go on record (for obvious reasons). But you don't seem to want an answer to your question. You want to make an assertion. I wish you would just come out and say it:

"I think the M4 would have made a better racing platform."

To which I would say, " OK." Outside of the displacement issue, I don't disagree with you. I've already said once that I'd have rather seen an M4 GT car than an M6, but that's not what we got.

Like I said earlier, I can only guess and speculate as to whether the M4 would make a better racing platform. I'm trying to understand if BMW's decision to use the M6 was purely because of the better performance potential it offered or if there was some cost/marketing issues taken into account.

I agree that the M6's engine offers a better starting platform to work with (even though we have no direct comparison with a racing version of the S55).

I understand that the M6's weight can be reduced to make it at least comparable to other cars in the series.

Those 2 issues aside, what did BMW really see in the M6 that made them decide to use that as the foundation for their GT3 and GTLM cars? It just didn't seem like the obvious choice to me when they first came out with those cars.