Adaptive Cruise Control - Speed Less Than Target

[msenske]

Hey there. I was using the adaptive cruise control functionality on one of the highway portions of my drive home from work today and I noticed that the maximum speed I would attain was always 1mph less than what I set as my target speed. As an example, I set the target speed to 70mph and the vehicle held a constant speed of 69mph and never once hit 70mph. Obviously, the workaround was to set the cruise control to 71mph if I wanted the vehicle to maintain a constant 70mph, so it isn’t as if I was unable to overcome the issue and get the desired result, but it seemed very strange to me. I’ve never had a vehicle behave this way. Has anyone else experienced the same issue?

 

[LCColorado]

Hey there. I was using the adaptive cruise control functionality on one of the highway portions of my drive home from work today and I noticed that the maximum speed I would attain was always 1mph less than what I set as my target speed. As an example, I set the target speed to 70mph and the vehicle held a constant speed of 69mph and never once hit 70mph. Obviously, the workaround was to set the cruise control to 71mph if I wanted the vehicle to maintain a constant 70mph, so it isn’t as if I was unable to overcome the issue and get the desired result, but it seemed very strange to me. I’ve never had a vehicle behave this way. Has anyone else experienced the same issue?

It’s a Toyota thing, don’t worry about it. My wife’s 22 Highlander and 24 Grand Highlander did the same thing.

 

[Pierac]

My LC does the same.... Drives me nuts!

 

[glibglob]

Our rav4 and my previous tacoma did it too.

 

[trek805]

mine too. You will need to adjust for daylight savings to correct it

 

[Ed1]

Mine does the same - 1 mph less than set - but only sometimes. It may be related to whether vehicle is on a slight upward incline, but not sure yet. Most of the time on level road it is on target.

 

[Midwest Duo]

Noticed as well.

 

[uraniumrich]

The ability of the cruise control to maintain a constant, steady speed is a function of the control system and programming of the computer. With the computing power available today, the LC should do a better job both hitting the target speed and maintaining the target speed even with gentle variations in terrain (up/down hills). My LC not only doesn't hit the target speed, but I find that the speed will vary up and down in normal use. Toyota can (and should) do better on a $70K vehicle. Yes, the LC is new, but the software running the ACC, engine/transmission programming, and MultiMedia screen feel vastly undeveloped and in need of updates right out of the starting gate (and lots of complaints in the Forum.) You can only beat a dead horse for so long, then your arm gets tired. Or something like that.

 

[LCColorado]

The ability of the cruise control to maintain a constant, steady speed is a function of the control system and programming of the computer. With the computing power available today, the LC should do a better job both hitting the target speed and maintaining the target speed even with gentle variations in terrain (up/down hills). My LC not only doesn't hit the target speed, but I find that the speed will vary up and down in normal use. Toyota can (and should) do better on a $70K vehicle. Yes, the LC is new, but the software running the ACC, engine/transmission programming, and MultiMedia screen feel vastly undeveloped and in need of updates right out of the starting gate (and lots of complaints in the Forum.) You can only beat a dead horse for so long, then your arm gets tired. Or something like that.

This isn’t an LC specific thing, this is the same TSS 3.0 system that’s in many of their other cars. Maybe I’m just used to Toyotas at this point, but I find most of the things people get worked up about to be a non issue. The old TSS 2.5 system was SIGNIFICANTLY worse than 3.0. Having now driven about 13000 miles in TSS 3.0 equipped vehicles I actually think the new system is pretty good in comparison to what most other non German manufacturers are putting out.

In what situations are you finding the speed to vary? I hate to ask, but you are aware that the cruise control is adaptive right? It will slow you down for corners and based on the cars ahead.

 

[uraniumrich]

This isn’t an LC specific thing, this is the same TSS 3.0 system that’s in many of their other cars. Maybe I’m just used to Toyotas at this point, but I find most of the things people get worked up about to be a non issue. The old TSS 2.5 system was SIGNIFICANTLY worse than 3.0. Having now driven about 13000 miles in TSS 3.0 equipped vehicles I actually think the new system is pretty good in comparison to what most other non German manufacturers are putting out.

In what situations are you finding the speed to vary? I hate to ask, but you are aware that the cruise control is adaptive right? It will slow you down for corners and based on the cars ahead.

My Honda/Acura stuff is way better than the Toyota. ACC works great, transmission is butter smooth, and CarPlay integration is simpler and better. My '21 Venza was also much better, but it did not have TSS 3.0.

 

[LCColorado]

My Honda/Acura stuff is way better than the Toyota. ACC works great, transmission is butter smooth, and CarPlay integration is simpler and better. My '21 Venza was also much better, but it did not have TSS 3.0.

I’ve never been able to get comfortable in a Honda, so I have no experience there. My wife’s 22 Highlander had TSS 2.5 and I thought it was pretty terrible, the adaptive cruise was jerky if someone pulled in front of you closer than the following distance. The lane keeping/tracing sucked. I only used it briefly if I needed to open a bottle of water. The 3.0 lane tracing has been lovely, I used it most of the drive from Oregon to Colorado when I moved. The CarPlay was fine, but honestly it’s been just as rock solid in our old Grand Highlander and now LC with the updated Toyota infotainment stack.

 

[uraniumrich]

I’ve never been able to get comfortable in a Honda, so I have no experience there. My wife’s 22 Highlander had TSS 2.5 and I thought it was pretty terrible, the adaptive cruise was jerky if someone pulled in front of you closer than the following distance. The lane keeping/tracing sucked. I only used it briefly if I needed to open a bottle of water. The 3.0 lane tracing has been lovely, I used it most of the drive from Oregon to Colorado when I moved. The CarPlay was fine, but honestly it’s been just as rock solid in our old Grand Highlander and now LC with the updated Toyota infotainment stack.

I agree, TSS 3.0 definitely improved some of the features (like lane keep/tracing). So, it's not all bad. My 2018 Accord could drive virtually hands free on the highway and kept me centered nearly perfectly without any jerkiness. The 2021 Venza wasn't quite at the same level. But, both cars did a better job of hitting and maintaining the speed set on the cruise control. From an engineering standpoint, it's not terribly hard to develop an automatic control system to maintain a set speed. Overall I'm very happy with my LC, but also surprised and disappointed that some aspects of the LC are clearly not at the same level as the rest of the machine. On the plus side, I think the source of the issues are all related to programming - ECM, CarPlay, TSS 3.0. All of these are fixable with updates from Toyota. Here's hoping they are listening to us and working on perfecting the LC.

 

[HammerTheWall]

If the speed limit is 70 I set mine to 75. Works every time!

Sometimes mine will sit 1 mph under, it depends on the road. On interstates it seems to match up fine, one 2 lane twisty or hilly roads it sometimes does the 1 mph under, sometimes not.

 

[izzysanchez]

I did notice that on long highway trips, so started to check against GPS. What I found is that if it set the cruise to 75, the speedo would show and stay on 74,. But the gps speedos would go between 74.6 to 74.9 at the same time.

 

[TakaraLC]

I remember reading years ago is this is because the car's computer operates with metric units, and that it converts numbers in MPH to KMH and than rounds it down to the nearest integer. Like setting 70 MPH gets converted/rounded down to 112 KMH, which is then set as 69 MPH by the cruise system since it cannot keep 69.6 MPH (basically rounded down twice).

 

[LCOceans]

Mine does the 1 mph under as well.
What I am really trying to figure out is - is my car in the center of the lane when using lane assist? Sometimes I feel like I am hugging the right side and not sure if my imagination, but sometimes when a car passes me on right I feel the land cruiser hugs the right even more. Lets say I never get too relaxed with that feature on.

 

[Marksman]

My FE Land Cruiser does the same, as did both of my daughter’s ‘20 and ‘24 RAV4 hybrids. My ‘23 4Runner also has the same tendency (although I rarely use cruise control on it because the tranny downshifts so frequently).

As has been said above, I think it’s just a Toyota thing. None of my GM or Jeep vehicles with adaptive cruise control have done this.

 

[DogStar84]

I just experienced the stop and go traffic cruise control. Worked great. Down to zero, back up 10 and repeat. Kept a good tight distance to car in front so people weren't constantly filling the gap.
Surprised me how much i liked it

 

[chris_in_phx]

Hey there. I was using the adaptive cruise control functionality on one of the highway portions of my drive home from work today and I noticed that the maximum speed I would attain was always 1mph less than what I set as my target speed. As an example, I set the target speed to 70mph and the vehicle held a constant speed of 69mph and never once hit 70mph. Obviously, the workaround was to set the cruise control to 71mph if I wanted the vehicle to maintain a constant 70mph, so it isn’t as if I was unable to overcome the issue and get the desired result, but it seemed very strange to me. I’ve never had a vehicle behave this way. Has anyone else experienced the same issue?

Mine does this too. Kinda funny and annoying.

 

[ultane]

Hey there. I was using the adaptive cruise control functionality on one of the highway portions of my drive home from work today and I noticed that the maximum speed I would attain was always 1mph less than what I set as my target speed. As an example, I set the target speed to 70mph and the vehicle held a constant speed of 69mph and never once hit 70mph. Obviously, the workaround was to set the cruise control to 71mph if I wanted the vehicle to maintain a constant 70mph, so it isn’t as if I was unable to overcome the issue and get the desired result, but it seemed very strange to me. I’ve never had a vehicle behave this way. Has anyone else experienced the same issue?

Miss Daisy does that too. No big deal to me..