Thread: Please read: Posts on 19" rims

Originally Posted by Disco4SE

Hi rmp, Buying a 4WD is not about 0 - 100 Kph figures. I bought mine for towing, 4WD capabilities and day to day ease of driving.
However, whoever told you that a LC 200 TDV8 can reach 0 - 100 Kph in 8.2 seconds (as quoted in the movie "The Castle") 'tell him his dreamin'.

I agree, but seeing as the subject came up we may as well discuss it.

OK, I'll let the people at Toyota know they're dreamin'.

I think it's a bit optimistic myself, but that's the figure they quote and my own experience is that the 200 is lineball with the best LR diesels for straight-line grunt. But I'm repeating myself again....

I thought thewre was an issue with the torque output being rediced untill third gear which would explain the run on response being good but the initial excelleration being poorer than the D4 3.0.

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.


I'm not sure if I've mis-interpreted your comment here but accelaration has absolutely nothing to do with top speed whatsever. At the end of the day the possible speed created by the tourque and power of an engine is limited by the gearing/torque/power/drag ratio.

A vehicle with greater acceleration will just get faster quicker, even if it can't go above 100kph...so even around town, a car with less accelaration may not get to 60kph by the end of the street, where the vehicle with greater acceleration will....so it's brakes will/may be working harder more often. My physics is a bit rusty these days but I also think that even if you have just hit/passed a certain speed and are still accelerating, the brakes need to work even harder to deal with the extra energy that comes with reducing acceleration to a constant speed or to zero.

As I said, maybe I didn't get what you were trying to say.

Regards.

Originally Posted by Celtoid

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.


I'm not sure if I've mis-interpreted your comment here but accelaration has absolutely nothing to do with top speed whatsever. At the end of the day the possible speed created by the tourque and power of an engine is limited by the gearing/torque/power/drag ratio.

Yes, I know, which is why I qualified it with "in general" just in case anyone called me on it ;-)

Despite that point being technically incorrect, in practice it does hold which is why I cited it -- I cannot recall a single vehicle with two engines where the more powerful one does not accelerater quicker and also have a higher top speed than the less powerful one. The top speed isn't usually a lot greater, thanks to the speed squared law of aerodynamics, but still more. The next reason I think is the bigger factor.

Originally Posted by Celtoid

A vehicle with greater acceleration will just get faster quicker, even if it can't go above 100kph...so even around town, a car with less accelaration may not get to 60kph by the end of the street, where the vehicle with greater acceleration will....so it's brakes will/may be working harder more often.

Exactly. In some cases the less powerful car may not even need to brake for a corner having not exceeded the corner's speed, whereas the more powerful one will. This assumes that both cars have approximately the same cornering speed. In some situations even that point is moot, a red light is a red light so you need to stop, same for a T junction and many other situations.

Originally Posted by Celtoid

My physics is a bit rusty these days but I also think that even if you have just hit/passed a certain speed and are still accelerating, the brakes need to work even harder to deal with the extra energy that comes with reducing acceleration to a constant speed or to zero.

As I said, maybe I didn't get what you were trying to say.

Regards.

OK now it's my turn to be confused...I think you're saying there that if you are accelerating as you hit 100km/h and then brake you'll use more energy than if you were steady at 100km/h and braked? Yes that is correct -- imagine you weren't going to brake to 0 at all but were acclerating really hard to a steady state of 100, you'd need to brake just to get to that stead state.

All this is quite arcane and I think the real reason manufacturers fit huge brakes (apart from the design advantages) is because the consumers like the look. Ostentantious aerofoils are out, writing "317kw" or "BOSS 290" on the side of the car is not everyone's cup of tea, so a nice big brake caliper with low-profile tyres is an understated way of saying this car is pretty damn quick.

Robert,

Where did you get the LC200 acceleration times from? If not from Australia, note that in different markets the LC is offered with different engine spec's and tune (look carefully at the quoted power outputs). I can't see any quoted specs for the LC on the Australian site, so I'm going from the road tests in Overlander and 4x4 Action, whom I presume (ever to my detriment) have some vague idea what they're doing

Cheers,

Gordon

Originally Posted by rmp

Yes, I know, which is why I qualified it with "in general" just in case anyone called me on it ;-)

Despite that point being technically incorrect, in practice it does hold which is why I cited it -- I cannot recall a single vehicle with two engines where the more powerful one does not accelerater quicker and also have a higher top speed than the less powerful one. The top speed isn't usually a lot greater, thanks to the speed squared law of aerodynamics, but still more. The next reason I think is the bigger factor.





Exactly. In some cases the less powerful car may not even need to brake for a corner having not exceeded the corner's speed, whereas the more powerful one will. This assumes that both cars have approximately the same cornering speed. In some situations even that point is moot, a red light is a red light so you need to stop, same for a T junction and many other situations.




OK now it's my turn to be confused...I think you're saying there that if you are accelerating as you hit 100km/h and then brake you'll use more energy than if you were steady at 100km/h and braked? Yes that is correct -- imagine you weren't going to brake to 0 at all but were acclerating really hard to a steady state of 100, you'd need to brake just to get to that stead state.

All this is quite arcane and I think the real reason manufacturers fit huge brakes (apart from the design advantages) is because the consumers like the look. Ostentantious aerofoils are out, writing "317kw" or "BOSS 290" on the side of the car is not everyone's cup of tea, so a nice big brake caliper with low-profile tyres is an understated way of saying this car is pretty damn quick.

I think we're on the same page Robert. Same car, different engine and in most cases you'd probably be right...gearing aside I guess.

I was thinking of the case like a motocross bike...brilliant acceleration and out of puff at 100....LOL!!!!

My point is, there are a lot of variable that create speed and acceleration and there isn't always a proportional or direct link....even in the same chasis.

Regards,

Celtoid

OK guys,

Getting back to the topic of 19" Rims and trying not to start another 'size war'......

I'm off to Fraser Island in a few weeks with a stock standard D4 SE 3.0TD. I'm running the standard 19" Rims with the Goodyear Wrangler tyres that the car came with.

I'm a tad confused with all the toe'ing and fro'ing over the tyres. I'm anticipating soft and hard sand work....what am I doing with my tyres?

Had I never read any of the threads on this topic I would have assumed I'd drop pressure whilst on the sand but I'd be asking to what pressure?....now that I have read the various opinions, not quite sure what to do. The car will be full of people and stuff but no trailer as we are staying at a house. Now I'm not so sure of the benefits of dropping pressure on a lower profile tyre.

Can somebody with real experience on this topic i.e. who has used tyres this size, clear this up for me please?

Drop pressure YES/NO?

What pressure to, if yes?

Thanks.

Regards,

Celtoid.

Originally Posted by Celtoid

OK guys,

Getting back to the topic of 19" Rims and trying not to start another 'size war'......

I'm off to Fraser Island in a few weeks with a stock standard D4 SE 3.0TD. I'm running the standard 19" Rims with the Goodyear Wrangler tyres that the car came with.

I'm a tad confused with all the toe'ing and fro'ing over the tyres. I'm anticipating soft and hard sand work....what am I doing with my tyres?

Had I never read any of the threads on this topic I would have assumed I'd drop pressure whilst on the sand but I'd be asking to what pressure?....now that I have read the various opinions, not quite sure what to do. The car will be full of people and stuff but no trailer as we are staying at a house. Now I'm not so sure of the benefits of dropping pressure on a lower profile tyre.

Can somebody with real experience on this topic i.e. who has used tyres this size, clear this up for me please?

Drop pressure YES/NO?

What pressure to, if yes?

Thanks.

Regards,

Celtoid.

Drop = Yes

Start around 22psi
Go lower if needed.

Don't forget to turn off DSC *every* time you re-start the vehicle.