If you’re so inclined you could ask a friendly dealer to measure a rotor they have in stock. The easiest way IMO would be to pull yours off and measure weight.

I cant imagine VAP trying to pull the wool over anyone’s eyes on something so obvious and trivial to check.

 

Well tbh
Vap never make a claim that isn't a verified figure be it bhp or torque or weight or size so if they quote a figure u can bet your bottom dollar it's accurate

 

I have used giro discs on a 911 and on an STI. And I have brembo oem rotors (all steel) in my garage.

The fronts' measurements are correct on the VAP site in terms of weight savings. My assumption is it is mostly in the hat, but it could be slightly in the rotor internals too (more sophisticated design perhaps, who knows). I have no data there.

And GIRODISC rotors are of impeccable quality in all regards. They are top tier. As a plus, they lasted a very long time on track in my high hp 911 gt2 and I did not have issues (VIR).

For the rears, I have the 326mm sized oem rotors and they weigh the same as the girodisc 376mm larger rears.... I wish VAP could do the smaller rears but understand the market may be too small to justify it.... But I have zero doubt in their integrity on weight. They are tops and honest and make superb stuff that they stand behind. I am a customer but I have nothing in this to gain save to keep them untarnished so they stay around as I'd like them to do well.

My F type is a street only car. I might get the fronts just because I love the look...do I "need" them, nope. Do I want them, yep.

 

Well, you can choose to disregard my input as biased but yes, I have first hand experience of the relative weights because I weighed a set of (used) OEM rotors on a digital scale, and did the same with the Girodisc units. I'm sure you could +/- 1/2 a lb or so for variation in scales and material or whatever but those are the actual weights as observed and measured by myself.

I can't speak to what other companies quote for weights, but ecommerce data is not always 100% accurate. Maybe they copied that item over from another listing and didn't update it, I don't know. All I can tell you is, I weighed actual take-off parts from a car and those were the weights.

There are other things besides material type which can affect the weight. For example - there are CCM to Iron replacement options for some cars that are VERY close in weight, and it's because the annulus or swept portion of the rotor is not made to the same diametric dimensions as the OEM CCM part. Just a quick look at the pictures (again I don't have the drawings) of the FType Rears and I would say the annulus on our VAP rotors looks smaller than the OEM one-piece rotors. One of the advantages to a 2-piece design is better capacity to dissipate heat, which means that it's possible to use a smaller annulus and less material there as well.

Again - I'm not sure this is the case or not because I'm not comparing drawings but there are many areas that you can save weight effectively and the design team at Girodisc has 20 years of proven experience so that's all entrusted to them. The weights we list are pretty darn accurate.

 

The lengthy Wortec thread has some weights. It's not quite apples to apples, but much closer than apples to oranges. I didn't weigh mine, but the fronts are like manhole covers.

https://www.jaguarforums.com/forum/f...3/#post1909742

 

Firstly, the purpose of my original post was not to question the integrity of VAP. I’m a VAP customer myself and can attest to the quality of workmanship and products they produce. I have no intention of tarnishing VAP’s reputation, but as a time served Mechanical Engineer of 30 years, I have developed what you might call an ‘inquisitive’ mind. If I see an output or result that appears inconsistent with known references or benchmarks, my first action is to validate the inputs. This in essence was the purpose of my original post.

To halve the mass of a cast iron brake disc from 33lbs (15kg) to 16.4lbs (7.4kg), while retaining a cast iron rotor/annulus, is a massive engineering achievement. So, my inquisitive mind asks how can this be accomplished? If we were to manufacture the disc from Titanium (45% lighter), we would have a very expensive disc that would still weigh 18.2lbs (8.25kg). A 50% reduction of the disc’s mass by removing material, would require an enormous number of holes to be drilled, an aggressive ‘sun-cut’/wave rotor design or a smaller diameter disc.

There is no secret to Girodisc’s weight saving method as this can be found on their website; “The Girodisc will generally weigh between 4 – 8 lbs less than the oe disc it will replace. This is due to the heavy cast iron hat section being replaced with lightweight, high strength aluminum”. On this basis, the ‘variables’ that apply to the potential mass reduction of a brake disc are disc bell/hat diameter and height, which will produce a mass reduction in the range of 4 – 8lbs (1.8 – 3.6kg). A reduction of 10lbs (4.5kg) on the F-Type front disc, betters the Girodisc upper estimate by 20%, but it is acknowledged the Jaguar OEM 380mm discs are ridiculously heavy. The 376mm rear disc bell diameter is the same and the bell/hat height is a marginal 4mm higher, so from an engineering perspective you would expect a similar reduction for the 376mm disc, certainly not 16.6lbs (7.5kg), a staggering 107.5% above the quoted Girodisc upper range.

So, I return to the start of my quest, an engineering riddle and a simple question in an attempt to validate the inputs to this puzzle. As my car is fitted with 325mm rear discs, I can’t use them as a reference. There are no technical drawings available online for the Jaguar OEM 376mm disc (T2R5942), but the Brembo equivalent rear disc (09.D434.11) technical spec is available.

It's not feasible Brembo have a manufacturing process that can produce an equivalent 376mm disc of the same dimensions, from similar materials, 3.7kg (8.2lbs), lighter than Jaguar. Otherwise, why haven’t all the F-Type V8 owners invested Ł200 in a set of Brembo rear discs and saved themselves 16.4lbs of unsprung, rotating mass?

Thanks to @lizzardo , there is an independent historic measurement (Jun 2018) of the OEM 376mm rear disc, courtesy of @Unhingd , who recorded his (albeit worn) rear discs at 24.4lbs (11kg) each --> Group buy 2pc wortec rotors.

Within the same thread, there is photographic evidence provided by Wortec to @Unhingd , as part of the Wortec group buy project. Wortec measurements for new OEM 380mm/376mm discs, were 17.3kg and 11.3kg respectively --> Paul Spipaul@wortec.

Ultimately the answer lies with Jaguar. Although my local dealership wasn’t prepared to break open a new boxed set of rear discs, they did provide a picture of the package label. The packaged weight of a new pair of Jaguar 376mm rear discs (T2R5942) is 23kg (50.7lbs).

I repeat once again, the aim of my original post was not to throw stones, or imply wrongdoing. I just wanted to understand ‘how could it be done’. Based on the information/evidence I’ve been able to gather, by changing the input value, the math adds up and the riddle is solved.

 

I just replaced my worn OEM rotors last week. I still have the old rotors (380F/376R). Here's the weight of both front and rear. Front 36.00 pounds; Rear 24.50 pounds. FYI.

 

@diablo2112 "I just replaced my worn OEM rotors last week. I still have the old rotors (380F/376R). Here's the weight of both front and rear. Front 36.00 pounds; Rear 24.50 pounds. FYI." Thanks, consistent with other sources. A start value of 11.3kg (24.9lbs) for a new 376mm rear disc, generates a much more realistic saving of 3.9kg (8.5lbs).

 

To start, I am not an engineer, nor machinist, nor pro driver. So, I can just give my layman's "opinion/feel" after actively using the new 2-piece rotors on the track. I have now done Homestead, our local track FIRM, and just yesterday did Daytona. I was specifically waiting for an opportunity to test them at Daytona due to the intense speeds you can reach on the front and back straights. I was able to hit 170mph on the front and 160 on the back. Not bragging, you can probably even go faster, just those are the speeds I was able to achieve with my limited skills and butt pucker confidence. Over the course of the sessions (I was able to do 3 sessions before an issue arose having nothing to do with the brakes), I found that I was actually braking TOO early with the new rotors. Again, I am also using the kevlar race pads. Down the main straight at Daytona they have the braking zone marked with 5, 4, 3, 2, 1, with 3 being just at the start/finish line. This was where I began braking the last time I drove Daytona on stock irons. With the new 2 piece, doing race braking at 3 slowed me down almost too much and I had to let off to maintain speed and rebrake for turn 1. So, I then started braking at 2 and was able to carry much more momentum down into 1, let off, then reapply braking hard for turn 2, which is basically a second gear turn. Overall, I was much more confident in the braking (as far as heat dissipation) as I never felt any loss of stopping power due to heat fade.

Even at the "bus stop" section of the back straightway, I was able to brake the car controllably down from 160 to hit the bus stop and roll through it at speed before getting back onto the back bank.

Obviously, Daytona is an extremely fast track and you are able to maintain speeds, thus cooling the brakes more often. As I have posted previously, are you going to notice these differences on the street...probably not. I should also mention that, again, I run slicks on the track. This also helps with braking over street tires.

As far as the weight, again, I am not a technician and I just drive the car. My mechanics, who are familiar with Gyrodisc from Ferrari, were very impressed with the weight difference. As always, in my opinion, every little bit you can shed is a plus, especially from the corners.

I am by no means gentle on the F type at the track. As I mentioned above, unfortunately I did have a catastrophic issue late into session 3 accelerating out of corner 7 or 8 to get back onto the front bank. The supercharger pulley portion of the crank/supercharger pulley decided to separate itself from the crank portion. Completely sheered the supercharger belt pulley portion right off. I knew something happened instantly as I lost all bottom end torque coming out of the corner. Having dealt with a slipped supercharger belt before, I knew it had something to do with the supercharger belt/pulley system. I have sent photos to VAP that we took at the track. Hopefully my shop will be able to pull the crank portion off sometime today or tomorrow, so we can get better visualization. Luckily, the sheered portion stayed somewhat in position being held in by the supercharger belt and did not end up either flying around the engine bay or worse underneath the car and onto the track.

I can upload photos from my phone if people are interested, as I am typing this on my PC.

Hope all that rambling helps. A little discombobulated today mentally LOL

 

Would be great to see your photos of the SC pulley. If it’s the VAP griptec upper, I’m about to install mine when the weather warms up and like you the R also sees tracks. Thanks.

 

These are the ones taken at the track after we pulled the intake pipes. As you can see, just catastrophic sheering of the outer ring from the crank ring.

 

Hi Guys,

Just a heads up to say that this is something we're aware of. We have had a few customers experience cracking around the outer ring, in early 2023 (never complete separation like this, but then, most people aren't sustaining 150+MPH either!) Design had not changed since 2015 and across 2000+ parts, and we found all the issues were confined to a specific production run from late 2022. Although we concluded that the source was a materials consistency issue, once we had run into more than a couple of failures, we opted to add some material & extra reinforcements to the design so that material consistency couldn't ever present a problem in the future.

Those updated items have been shipping since around May 2023. Anyone who experiences cracking has been provided with replacement parts + labour costs.

 

Not to hijack this thread off the topic of the rotors, but I can confirm that VAP addressed the issue with the pulley I had immediately. They explained the situation and sent me a new pulley and belt the same day (that being Tuesday after the Monday track day at Daytona). Their explanation was very consistent with what we figured...some sort of manufacturing materials issue. After receiving emails from VAP, they confirmed this and my purchase fell right in line with the lot of pulleys in question. In no way did I post these pics to dump on VAP or mean to cause anyone else concern. I had a few people ask for the pics, so I posted them. For any wondering, yes I was able to still drive the vehicle, just, obviously, no boost. So, she was able to limp home safely.

Again, I am pretty much strictly tracking my F Type at this point and expect things to happen, just the nature of racing. I wholeheartedly appreciate VAPs response and timeliness in addressing my particular issue. And, I will continue to use their products due to their outstanding customer service and willingness to provide us enthusiasts with parts for a car that most of the other parts manufacturers have ignored. When the time inevitably comes, looking forward to rebuilding the motor with their piston and rod kit.

So, hats off to Stuart and the crew at VAP. Look forward to continuing to use your products and enjoying my F Type to its fullest!!