Faisal Sheikh

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Respectfully, I work with Lexus Racing in multiple capacities. Have quite a bit of insight. The RC F was never developed from the start to race. It was modified to race. The results the team have gotten are absolutely superb considering this. Hopefully a car developed with racing part of the development is exactly what’s needed. That would be amazing. Just imagine a bespoke platform race car. Oh the possibilities.

We both are saying the same thing. I agree with second half of your statement regarding a purpose built race car for the streets (like a Porsche GT3). Hopefully, Lexus does that. Also, yes it was modified. I never said it was not (only quoted Lexus saying their development started in parallel). Just like the engine was from 5.0 Liter to 5.4 Liters while staying within the rules of how much it can deviate from the street parts. I am just going by what the official GT3 homologation rules and what Lexus' GT3 press release says (quoted above) that the basic monocogue as per the rules (I quote above), is the same as the production car, which was then modified for the racing car while staying within the homologation qualifying rules for the GT3 race car.
 
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ssun30

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IIRC one unintended benefit of using that IS-C middle section is the wheelbase is quite short which makes the RC extra agile compared to other 2+2s and on par with 2-seaters. The M4 by comparison makes a terrible race car because its wheelbase is so long.
 

Faisal Sheikh

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IIRC one unintended benefit of using that IS-C middle section is the wheelbase is quite short which makes the RC extra agile compared to other 2+2s and on par with 2-seaters. The M4 by comparison makes a terrible race car because its wheelbase is so long.

Definitely, in a race car that makes a big difference. Short wheelbase to width ratio was stated by Yaguchi as a key design highlight of the RCF (back in 2015) other than rigid structure of the core. Short and long wheelbase have their pros and cons. Short wheelbase makes the car more eager and willing to change direction at the cost of some stability/predictability. A long wheelbase gives more predictability/stable base at the cost of instantaneous turn rate/responsiveness as the car is more longitudinally stable (straight line stability). On the streets, predictability is a good thing for safety. and confidence. However, in a race car it is all about how fast the car can change direction.

Here is an interesting comparison between the dimensions of the road-going RCF and the racing RCF GT3

Road-going RCF:

Length: 185.2 inches
Width: 72.6 inches
Wheelbase: 107.5 inches
Height: 54 inches
Fuel capacity: 17.4 gallons

RCF GT3:

Length: 190.8 inches
Width: 72.6 inches
Wheelbase: 107.5 inches
Height: 50 inches
Fuel capacity: 17.4 gallons
 
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mikeavelli

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IIRC one unintended benefit of using that IS-C middle section is the wheelbase is quite short which makes the RC extra agile compared to other 2+2s and on par with 2-seaters. The M4 by comparison makes a terrible race car because its wheelbase is so long.

The entire purpose of that IS-C middle section was to produce a convertible. That was the original intent. If we all remember the LF-C2. If I recall dealers begged for a 7 seat RX and the convertible was canned. So it had that extra weight for no reason

BMW is going to race the M4, going to be interesting to see.
23F14661-F55C-4AEA-8B7F-C639A340EDED.jpeg
 

mikeavelli

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We both are saying the same thing. I agree with second half of your statement regarding a purpose built race car for the streets (like a Porsche GT3). Also, yes it was modified. I never said it was not (only quoted Lexus saying their development started in parallel). Just like the engine was from 5.0 Liter to 5.4 Liters while staying within the rules of how much it can deviate from the street parts. I am just going by what the official GT3 homologation rules and what Lexus' GT3 press release says (quoted above) that the basic monocogue as per the rules (I quote above), is the same as the production car, which was then modified for the racing car while staying within the homologation qualifying rules for the GT3 race car.

I hear ya. Good points. Need to get ya to a race!
 

Faisal Sheikh

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The entire purpose of that IS-C middle section was to produce a convertible. That was the original intent. If we all remember the LF-C2. If I recall dealers begged for a 7 seat RX and the convertible was canned. So it had that extra weight for no reason

BMW is going to race the M4, going to be interesting to see.

I have heard it does not provide any benefit, but a rigid chassis is always better than a softer chassis even at the cost of some additional weight. There are always other ways to reduce weight. Jason C wrote about how M division was unhappy with the previous F30/F80 3-series given to them by the BMW. In order to achieve a lighter chassis, they cut a lot of corners on it. I once posted a picture of an M4 vs RCF rear subframe and you can see how much engineering Lexus put into the rear subframe, which makes it ideal for coilover setup (while the M4 suffers from rear subframe cracks if punished extensively).

In the case of the RCF, a more rigid chassis keep all four wheels more planted under very high G-loads in the turn since it would resist torsional twisting of the chassis or "jiggly" behavior when tossed around. High speed stability wise 90 mph feels like 30 mph in RCF for the same reason.

I remember reading Lexus in the press back in 2015 that the chassis was so stiff that it could be made a convertible and the roof can be chopped off without a significant reduction in torsional stiffness. The convertible never got out of concept stage.

The floor pan, inner rocker structure, rear gussetts and front apron thickness were all increased to give the monocoque even higher rigidity. A good alternative example is, race cars have roll cages that adds up to 100+ lbs of weight in the car and a lot of it is much farther away from from the CoG, but it actually helps the handling of the car when pushing it to the limits (other than safety).

I hear ya. Good points. Need to get ya to a race!

Yeah, I wish. It would be incredible to be in those cool events you go to and see a GT3. Live too far away, family, kids, career yadda yadda! My RCF is a garage queen LOL There is a new track opening up in my city so hopefully I can get out there maybe, this summer (if they open it for the non-members).

Chassis.jpeg
 
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carguy420

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There are videos on Best Motoring's YT channel of a lightly tuned RC F by a tuner called MCR, with just basic suspension mods like coilovers, more aggressive wheel alignment for extra negative camber and a sticky set of 200tw high performance summer tires it not only handles really well it also still rides really well, it looks really composed even when going through bumpy, high speed corners.
It seem like extra chassis rigidity might be more beneficial than less weight if the weight penalty from the more rigid chassis isn't too significant and the majority of the weight is placed low down in the car, like look at how much better the new G80/82 M3 and M4 handles than the F80 generation despite being way heavier and having an even more powerful engine, all the F80 wants to do when you get on throttle coming out of corners is kick the rear end out in an abrupt manner even when you're not trying to slide it, while G80's rear end digs in and drives the car foward, and even when it does break loose it feels progressive and and controllable.
 

Faisal Sheikh

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There are videos on Best Motoring's YT channel of a lightly tuned RC F by a tuner called MCR, with just basic suspension mods like coilovers, more aggressive wheel alignment for extra negative camber and a sticky set of 200tw high performance summer tires it not only handles really well it also still rides really well, it looks really composed even when going through bumpy, high speed corners.
It seem like extra chassis rigidity might be more beneficial than less weight if the weight penalty from the more rigid chassis isn't too significant and the majority of the weight is placed low down in the car, like look at how much better the new G80/82 M3 and M4 handles than the F80 generation despite being way heavier and having an even more powerful engine, all the F80 wants to do when you get on throttle coming out of corners is kick the rear end out in an abrupt manner even when you're not trying to slide it, while G80's rear end digs in and drives the car foward, and even when it does break loose it feels progressive and and controllable.

Yeah, that is a good example. Tsuchiya and Orido loved it. With both cars on coil over suspension, RCF was definitely winning that one until the F30 M4 suffered failure.

You make a good point about the G-series M3/M4. Its a total beast. The G-series M3/M4 is so much better handling the F-series M3/M4 despite being around 200 lbs heavier and much bigger. Interestingly, when the journalists asked why it was so much heavier than the previous generation, BMW stated they had done extensive work to make the chassis very rigid, which ended up adding the weight, but pays dividend in the handling department.
 
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ssun30

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The ChDM F35 3 series LWB was considered the worst driving car made by BMW. Very long wheel base, lack of body rigidity (BMW China uses some low quality materials they call lightweight), no sway bar. The car handles like a boat, doesn't like to turn at all and is not stable either for cruising. This past generation of 3/4 series are definitely very underwhelming. G20 is great! The ride quality is way better and you can feel the extra ~100kg of weight making the car more planted.
 

Jezza819

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The M4 by comparison makes a terrible race car because its wheelbase is so long.

The new M4 GT3 is virtually the same dimensions, at least in wheelbase and width, as the M6 it's replacing so we will see how it performs.

Speaking of how big BMW's look on the track, this is related to the GTE/GTLM M8 but I guess we've all seen a similar meme.

3cc.png
 

mikeavelli

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The new M4 GT3 is virtually the same dimensions, at least in wheelbase and width, as the M6 it's replacing so we will see how it performs.

Speaking of how big BMW's look on the track, this is related to the GTE/GTLM M8 but I guess we've all seen a similar meme.

3cc.png

Lol I remember those. I do like how the race car looks. I still find the production car so blah and a huge missed opportunity.
 

Kelvin2020

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Toyota previews GR GT3 concept. Possible Lexus RC F GT3 replacement? It doesn't have the shape of a Supra. Unless Toyota is pulling Lexus out of racing and putting a Toyota model into the GT3 class? But you would think Lexus would announce a new replacement or update for the RC street model before the race version. This is a real head scratcher.

https://www.autoblog.com/2022/01/07/toyota-gr-gt3-concept-tuned-gr-yaris-tokyo-auto-salon-teaser/

toyota-gr-gt3-tokyo-auto-salon-2022.jpg
Maybe it’s the new 2000gt
 

mikeavelli

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carguy420

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With such a crazy long engine bay I wonder what would power it, will TGR do something silly like joining 2 G16E-GTS to make a 3.2L TT inline 6😂? I know, wishful thinking.