Gross Vehicle Weight?

[michaelgroves]

NOTHING has a greater influence on stopping distances (of a properly functioning vehicle) than the tires that vehicle is equiped with. NOTHING.

Hmm...How would that be quantified? In other words, while no-one would argue that the worst possible tyre would be far worse than the best possible tyre, how about if the two sets of tyres are really very similar, but not identical? Does that still make more difference than, say, the mass of the vehicle?

I would agree that tyres make a very very big difference - enough so that a comparison using different tyres might be hard to interpret. However, there are very significant differences in braking distances between different vehicles even with identical tyres, so clearly other factors play a big part.

Having said that, and having owned a wide variety of Discovery 1s, 2s, RRCs and Defenders of all types, I would agree that the Defenders tend to be noticeably worse at high-speed braking than the Discoveries and RRCs. I'd say that a lot of this would be to do with the fact that they are fitted with skinny tyres optimised for long life. I don't know about actual stopping distances, but as Musky says, the Nineties are much harder to control when braking hard than the One-Tens and One-Thirties.

 

[michaelgroves]

I also heard that Range Rover Classics had better front brakes than Disco Is. I don't know what is different, but they certainly have different part numbers.

I always felt that my RRCs had better brakes, too. It might be that the booster was better (all my Discoveries have been diesels). The RRC was dual circuit too, rather than just split circuit. I wonder if the use of two circuits makes the brakes a wee bit better?

 

[muskyman]

gone

 

[R_Lefebvre]

Hmm...How would that be quantified? In other words, while no-one would argue that the worst possible tyre would be far worse than the best possible tyre, how about if the two sets of tyres are really very similar, but not identical? Does that still make more difference than, say, the mass of the vehicle?

I would agree that tyres make a very very big difference - enough so that a comparison using different tyres might be hard to interpret. However, there are very significant differences in braking distances between different vehicles even with identical tyres, so clearly other factors play a big part.

Having said that, and having owned a wide variety of Discovery 1s, 2s, RRCs and Defenders of all types, I would agree that the Defenders tend to be noticeably worse at high-speed braking than the Discoveries and RRCs. I'd say that a lot of this would be to do with the fact that they are fitted with skinny tyres optimised for long life. I don't know about actual stopping distances, but as Musky says, the Nineties are much harder to control when braking hard than the One-Tens and One-Thirties.

Well, obviously it's hard to quantify such a statement. We'd both have to get into specific details, if you want a specific answer. Obviously if the tires are very similar, their effect could be eclipsed by something else. You'd have to give very specific details on the vehicles, including measured stopping distances, and which tires you're talking about.

My statement is along the lines of assuming two identical vehicles, one shod with something like a BFG LongTrail T/A P-car tire, versus another with BFG A/T's. The difference between those two would be much more than you would see if you did a similar test between two vehicles, one with a 90" WB, the other 100", but each with the same tires.

Skinny tires, optimized for tread life, is going in the wrong direction for braking performance.

 

[michaelgroves]

Obviously if the tires are very similar, their effect could be eclipsed by something else.

Yes, of course that was what I was getting at. I just couldn't see why you picked out tyres as being the factor to hold constant in a comparative braking test. I doubt that even the Land Rover tests are done at the same time by the same team. Surface conditions would be critical, as would testing parameters (first stop vs best stop vs 10th stop vs average stop, for example). Vehicle mass is a major factor. ABS or not. Etc.

If we tested a the most basically equipped ex-factory Defender 90, unladen, against a similarly stock RRC, then I would imagine you are right - the difference in the tyres would account for the biggest discrepancy in the braking performance. But I still think there would be a very significant chunk left in favour of the RRC, if we fitted both vehicles with identical tyres.

 

[R_Lefebvre]

Yes, I'd agree with all that. There are other differences, but they are eclipsed by tire differences. I'd expect that the difference between a highway radial, and an A/T would be more than the difference between a 90, and a mythological 200" wb truck.

The testing is done by the exact same person, on the exact same day, seperated only by the time it takes to swap wheels/tires. And with a very repeatable proceedure (1st stop, 10th stop, all measured). I believe some OEM's have taken to using robots to do the testing to ensure absolute repeatability. They do similar work with shock absorbers, springs, any manner of things. Seperated only by the it takes a dedicated mechanic to swap the parts.

 

[muskyman]

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[michaelgroves]

The testing is done by the exact same person, on the exact same day, seperated only by the time it takes to swap wheels/tires. And with a very repeatable proceedure (1st stop, 10th stop, all measured). I believe some OEM's have taken to using robots to do the testing to ensure absolute repeatability. They do similar work with shock absorbers, springs, any manner of things. Seperated only by the it takes a dedicated mechanic to swap the parts.

I just meant that when you read the braking specs on different vehicles, the comparisons must always be taken with a pinch of salt because of the very different testing techniques and conditions. One variable is the fact that they use different tyres, but there are many others. I am pretty sure that current Land Rovers are tested very differently to the way they tested RRCs.

I think we've all acknowledged that tyres are a big factor, but if we're going to be sticklers over what makes the biggest difference to stopping distances, I'm going to put tyres somewhere below vehicle speed, vehicle mass, the presence of black ice, and the driver trying to read a text message on his cell phone!

 

[Hank]

Rob,
Just save yourself and admit you have no clue as to what you're talking about.

Do you even know who makes Land Rover? Do you even know the difference between a D1, DII, RRC, and a Defender?

 

[James86004]

or maybe the fact that the mentioned RRC uses a electric pump to power the brakes

Actually, my 89 Range Rover used a vacuum booster, not an electric motor. And the brake part numbers are still different from the Disco. I didn't ever really notice a difference in braking between it and my electric motor equipped 93 Range Rover either.

 

[michaelgroves]

Rob,
Just save yourself and admit you have no clue as to what you're talking about.

Do you even know who makes Land Rover? Do you even know the difference between a D1, DII, RRC, and a Defender?

Hank, why do you post this kind of stuff? It contributes nothing intelligent. Rob's assserting that tyres are the most important factor when considering braking ability. If you think he's wrong, make a reasoned argment, or, if you're too lazy to do that, just state your own opinion on the matter, and be done. Your sort of taunting and insulting is how schoolboys argue.

I'm out.

 

[Antichrist]

I've come to the conclusion, after many years of observing others on the road, that if people didn't drive like idiots, braking performance wouldn't be the big deal it is.

As for the tires vs other factors, I may be way off base, but I would think tires would only play a significant role once they've lost adhesion with the road. They would only matter at that threshold just before loss of traction. I've nearly always used tall skinny tires, 7.50x16, 7.00x15 and the like and I've very rarely lost traction, once or twice on dry pavement, a few times on ice.
When it comes to safe braking performance, the single most important thing is what's between a person's ears.

 

[R_Lefebvre]

I just meant that when you read the braking specs on different vehicles, the comparisons must always be taken with a pinch of salt because of the very different testing techniques and conditions. One variable is the fact that they use different tyres, but there are many others. I am pretty sure that current Land Rovers are tested very differently to the way they tested RRCs.

I think we've all acknowledged that tyres are a big factor, but if we're going to be sticklers over what makes the biggest difference to stopping distances, I'm going to put tyres somewhere below vehicle speed, vehicle mass, the presence of black ice, and the driver trying to read a text message on his cell phone!

Oh, yes, if you're talking about magazine number, things are a little more difficult. Better publications will try to use a standard procedure, and a standard piece of road. But, you never really know what the situation is.

And yes, all those other things would be even more important than the tires, but I had assumed the discussion was controlling for those factors.

Actually, my 89 Range Rover used a vacuum booster, not an electric motor. And the brake part numbers are still different from the Disco. I didn't ever really notice a difference in braking between it and my electric motor equipped 93 Range Rover either.

Well, isn't that interesting. Learn something new every day.

As for the tires vs other factors, I may be way off base, but I would think tires would only play a significant role once they've lost adhesion with the road.

Tom, that's the crux of the problem. Where DO they lose adhesion with the road? There are widely changing coefficients of friction amongst tires. When considering cornering force, I've seen a difference between 0.75, and 0.95 G on the same car, same road, just changing the tires. Yes, obviously driving ability plays a big role. But again, the question that started all this was, why on a controlled, *measured* stop, why does one stop so much longer than another, even though the braking system on the latter should theoretically be better.

 

[muskyman]

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[R_Lefebvre]

That's a whole other problem if the braking system is not capable of locking up the brakes.