Please read: Posts on 19" rims

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Originally Posted by rmp

The LC200 weighs just as much, is as powerful as a TDV8 let alone a 3.0 D4 (certainly won't be left behind in a drag race) and comes with 17s standard in some specs.

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Well, most mag comparos have said otherwise - in favour of the D4 ;)

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Originally Posted by rmp

It also tows 3500kg and 750kg, another brake consideration. It has larger diameter tyres so say 18s on that car gives you more sidewall than 18s on say a RRS. It's really sidewall height is the issue, not the profile % which only gives an indication.

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Yes, LR have always spec'd smaller tyres than the opposition - and made it difficult to upgrade without being illegal.

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Originally Posted by rmp

The VW Touraeg, relative of the Cayenne is another example. In its V6 diesel form it has a greater power to weight ratio than the TDV8 yet runs 17s. It is a little lighter though. The V10 monsters will slaughter any Land Rover diesel and I think they run min 19s or maybe 18s, I forget. They are just as heavy. Neither car is as good as the D4 offroad.

There is no need to run such large rims for brakes. It makes the job easier (cheaper) and looks better, but there is no engineering need.

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I've never understood the 'greater acceleration = requirement for better braking' argument. The momentum of a vehicle is based purely on it's speed and weight. Its ability to get to a particular speed has nothing to do with it. There seems to be some 'rule of thumb' that a faster accelerating car is always driven at higher speeds, therefore requires better brakes??

Aside from that, you're missing the benefits of cooling and sensitivity that come with a larger surface area on the disc - important for cars that use the ABS system for traction control off-road. The D4 has better performance in this field than a lot of the competitors due in part to it's larger discs. However, this admittedly doesn't excuse it's poor caliper design, which is one of the other reasons for the larger rim requirement, so I'd agree with you there.

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Originally Posted by rmp

Note that while the 200 has the raw grunt come the corners it'll flounder ;-)

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- it won't keep up on the straights either!!

Cheers,

Gordon

I have a feeling that the LC200 is a couple of hundred Kg heavier than the D4. As metioned in another of my posts, the D4 when put on a dyno machine, has less loss of flywheel power to the wheels.
This is why the D4 is quicker to 100Klm per hour and is more nimble on straights and hills as well.

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Originally Posted by gghaggis

However, this admittedly doesn't excuse it's poor caliper design, which is one of the other reasons for the larger rim requirement..

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I think its the other way round, with LR's priority for a minimum sidewall height for better steering precision from less tyre squirm when hurtling around corners (part of their premiumness) so stuck bumps on the calipers and brackets to prevent fitment of smaller rims.

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Originally Posted by Disco4SE

I have a feeling that the LC200 is a couple of hundred Kg heavier than the D4. As metioned in another of my posts, the D4 when put on a dyno machine, has less loss of flywheel power to the wheels.
This is why the D4 is quicker to 100Klm per hour and is more nimble on straights and hills as well.

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No, it's not that much. The exact difference depends on the spec level and engine of the cars in question. They are pretty close. What makes more of a difference is the D4's gearing, the 200's 6th gear is very tall.

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Originally Posted by gghaggis

Well, most mag comparos have said otherwise - in favour of the D4 ;)

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Having drag raced a TDV8 Vogue and a 200 diesel I know there's nothing in it. Others may have had the same personal experience and come to a different conclusion, I can't say.

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Originally Posted by gghaggis

I've never understood the 'greater acceleration = requirement for better braking' argument. The momentum of a vehicle is based purely on it's speed and weight. Its ability to get to a particular speed has nothing to do with it. There seems to be some 'rule of thumb' that a faster accelerating car is always driven at higher speeds, therefore requires better brakes??

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OK I'll explain. Two reasons.

1. A faster accelerating car will have a higher top speed, in general, which means the brakes have a lot more work to do, quite a difference in slowing from 250km/h than from 180km/h. Manufacturers must design the brakes to match the top speed.

2. The quicker car will also be capable of being driven more quickly. Therefore, it will need to slow down more often. Take a windy road, where a slow car only makes it to say 80 on a short straight, the quick one gets to 100 every time. If you corner at the same speed there's a lot more energy to get rid of. Even non-sporting drivers keeping below the limit will end up quicker in say a RRS SV8 than a RRS TDV6 2.7, so more braking power needed. So yes there is a rule the faster the car the better the brakes have to be. The slow and fast cars may stop in the same distance from 100km/h (and there are road regs that give minima), it's really about combating brake fade and giving a more sporting drive to match the acceleration.


All that means a quicker accel car does indeed need greater braking capability. Whether or not it is legal to use that speed and power is not the point, nor is whether people will actually use it. In the same way, fast cars run tyres rated to 250-300km/h even though nobody will ever use that speed.

You are quite right that in the real world, pootling around at 100km/h as we do the braking capacity requried has nothing to do with the vehicle's acceleration capability, provided you don't drive it any quicker than the slower cars. But the car still needs to be designed to handle the loads it is capable of.

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Originally Posted by gghaggis

Aside from that, you're missing the benefits of cooling and sensitivity that come with a larger surface area on the disc - important for cars that use the ABS system for traction control off-road. The D4 has better performance in this field than a lot of the competitors due in part to it's larger discs. However, this admittedly doesn't excuse it's poor caliper design, which is one of the other reasons for the larger rim requirement, so I'd agree with you there.

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I'm not missing any benefits at all, I'm well aware of the advantages of large brakes. My point is that large brakes are not required -- manufacturers could design smaller ones, but it's cheaper and easier to go for the larger ones for various reasons such as you points above and Tombie's earlier.

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Originally Posted by gghaggis

- it won't keep up on the straights either!!

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Everyon's got their own experience, I'm not about to argue other people coming to a different conclusion to me. My experience is that the two are pretty close in straight-line grunt and I'm not bothered about 0.5 of a second in stats, I don't even know what the 0-100 times are for either, probably 10 secs I expect. The 200 feels slower though as it's noisier.

I think LR designed brakes for to 5.0L V8 and just used them for the 3.0L TDV6 as it was cheaper than designing new ones for it.
As they are the same as the V8 ones I would say they must be over speced for the 3.0L.
The old V8 discs on the 3.0L would allow you to fit 18 inch and would be the right spec for the power/speed.

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Originally Posted by CaverD3

I think LR designed brakes for to 5.0L V8 and just used them for the 3.0L TDV6 as it was cheaper than designing new ones for it.
As they are the same as the V8 ones I would say they must be over speced for the 3.0L.
The old V8 discs on the 3.0L would allow you to fit 18 inch and would be the right spec for the power/speed.

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I suspect your right, but I like GraemeS' description - "We'll put fins on the calipers so those bugg*rs can't mess about with the rims" :D

Robert, thanks for the explanation of the "faster car, bigger brakes" rule. But how much I'd apply that sort of logic to the difference between a 2.7 ltr and 3.0 ltr D4 I'm not sure. A D4 and an Aston Marton, well yes!

I don't know what conditions you've raced a TDV8 and an LC200 with each other, so I can't comment. But in the mag comparos, they've all said pretty much the same thing - that the D4 just pulls away from the LC, quite significantly. I think the LC200 0~100 time is around 10s. The TDV6 3.0 is 9.3 and the TDV8 is 9.2

Cheers,

Gordon

The old D4 V LC200 debate.
I dont suppose many have had the opportunity that I have, that is having a brand new D4 & LC200 for a whole weekend in my driveway, both with tow bars.
I beleive that this is the only way to compare the two. Hook up a trailer with one then the other on the same road, hills etc. Drive the same route that you are used to with one, then the other.
Having had three LC's and being a big fan, I went for the D4 3.0Lt.
I challenge anybody to do the same and tell me they prefer the LC.

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Originally Posted by Disco4SE

The old D4 V LC200 debate.
I dont suppose many have had the opportunity that I have, that is having a brand new D4 & LC200 for a whole weekend in my driveway, both with tow bars.
I beleive that this is the only way to compare the two. Hook up a trailer with one then the other on the same road, hills etc. Drive the same route that you are used to with one, then the other.
Having had three LC's and being a big fan, I went for the D4 3.0Lt.
I challenge anybody to do the same and tell me they prefer the LC.

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The 200 vs D4 as a general comparo has already discussed already here ->

http://www.aulro.com/afvb/d3-d4-rrs/...ser-200-a.html

we're discussing here acceleration only.

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Originally Posted by gghaggis

I suspect your right, but I like GraemeS' description - "We'll put fins on the calipers so those bugg*rs can't mess about with the rims" :D

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:p indeed, but I never attribute to malice what can be explained by sheer negligence or not caring!

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Originally Posted by gghaggis

Robert, thanks for the explanation of the "faster car, bigger brakes" rule. But how much I'd apply that sort of logic to the difference between a 2.7 ltr and 3.0 ltr D4 I'm not sure. A D4 and an Aston Marton, well yes!

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Yep, well the reasons are cars are the way they are....more to do with regulations and marketing than pure engineering.

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Originally Posted by gghaggis

I don't know what conditions you've raced a TDV8 and an LC200 with each other, so I can't comment. But in the mag comparos, they've all said pretty much the same thing - that the D4 just pulls away from the LC, quite significantly. I think the LC200 0~100 time is around 10s. The TDV6 3.0 is 9.3 and the TDV8 is 9.2

Cheers,

Gordon

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Well I decided to go and check the figures. Turns out the 200 is 8.2 seconds to 100km/h. So, quicker than LR's best. I've done roll-on tests with a 200 vs a TDV8 Vogue and there was nothing significant between them, but the 200 was marginally ahead. Like I said others are welcome to their opinions, that's mine which is borne out by the stats. Perhaps they meant "left behind through the bends" -- I'd certainly agree there. Or maybe their roll-ons were such that the test managed to hit a sweet spot for the D4's engine and gearing combo.

Personally I don't think outright accel is a major factor anyway and there's so many variables involved, so I tend not to bother with it overmuch. The pleasure of a car is defined by much more than its ability churn your guts when you hit the loud pedal, for me at least.