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Cruise Control


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My LS460 is three months old and I am basically happy with the car. This ,by the way, is my fourth Lexus. My others were a 1990 LS , a 1998 LS , and a 2002 RX300. The problem, if you can call it a problem is that going downhill with cruise control on ,the auto speeds up a few miles per hour. I assume that is because there is so little engine braking, At an indicated 70 MPH the engine turns 1700 RPM .Do I have to manually change gears to stop this or is there another solution that I have not thought of.

To fill you all in, my other auto is a 2006 BMW wagon (to transport my Labradoodle).

I'm also hoping that Lexus comes out with a kit so that I have an easier time with my Ipod . Had I known better, I would have gotten the Levinson radio.

Thanks for reading. plamma

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My LS460 is three months old and I am basically happy with the car. This ,by the way, is my fourth Lexus. My others were a 1990 LS , a 1998 LS , and a 2002 RX300. The problem, if you can call it a problem is that going downhill with cruise control on ,the auto speeds up a few miles per hour. I assume that is because there is so little engine braking, At an indicated 70 MPH the engine turns 1700 RPM .Do I have to manually change gears to stop this or is there another solution that I have not thought of.

To fill you all in, my other auto is a 2006 BMW wagon (to transport my Labradoodle).

I'm also hoping that Lexus comes out with a kit so that I have an easier time with my Ipod . Had I known better, I would have gotten the Levinson radio.

Thanks for reading. plamma

I have yet to see any cruise control that would brake if you were going down a pretty steep hill. It will stop giving the engine gas but if the hill were to be steep enough the brake would need to be applied by yourself. Having the number of gears (8), there is little resistance unless you were drop it a few gears to use engine compression.

I live in Florida and for the most part it is flat with few hills that would casue my LS460 to increase in speed.

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Since late in the last century manufacturers have been doing almost everything possible, conceivable, to improve the safety factor of vehicles with automatic transmissions when operating on low traction surfaces, most especially FWD or front torque biased AWD vehicles wherein engine compression braking will be the most detrimental.

It has now become common knowledge throughout the industry that engine braking on the front wheels will oftentimes interfere with the operation of ABS to the detriment, obviously, of the owners/passengers.

For those with long term stick shifting experience think about how often you wish for a clutch as you drive along in wintertime with your automatic shift transmission, especially a FWD one.

Most new owners manuals state quite explicitly that engine braking cannot be attained absent a manual downshift and in some cases not even then unless you disable, completely turn off, cruise control.

This whole widspread episode of throttle delay, 1-2 second downshifting delay/hesitation has arisen as the result of widespread industry adoption of a new automatic transmission shift pattern/sequence adopted late in the last century.

The technique involves quickly upshifting these electronically controlled transmissions/transaxles upon any FULL lift-thottle event wherein should the current gear ratio be retained would result in a significant level of engine braking. The idea is to improve the safety factor by virtually eliminating engine braking that cannot be overcome by the operator absent a quick shift into neutral, an action currently recommended by the AAA, but of itself fraught with peril.

So, rather than retarding the timing, as was previously done, to reduce the road speed of cruise control, I wouldn't be at all surprised to see the use of rear braking only via the traction control system to initially slow the vehicle.

But it is now pretty clear that applying the brakes, in total, to do this will be potentially safer, overall, than the use of engine braking which cannot be alleviated by the anti-locking braking system should it subsequently be needed.

Even slight engine braking on an extremely slippery surface, an icy bridge deck comes to mind, can easily result in loss of control even on a RWD vehicle, but the potential for loss of control of a FWD in these insatnces rises dramatically in comparison.

Be careful out there....

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  • 2 months later...
this problem is standard on all cruise control systems. My 5 speed rx330 will increase in speed down a hill on the freeway if its steep enough.

On a 2006 BMW 330xi with manual transmission and radar cruise control, the car maintains the set speed, even when going downhill. If necessary, it will use the brakes. This and the excellent voice recognition are about the ONLY things I like about this car.

HBH

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