Subaru Outback Forums banner

Do taller tires affect Eyesight ?

13K views 22 replies 7 participants last post by  zeiter 
#1 ·
Does larger diameter tire really affect Eyesight ? I was asking the dealer service manager if I went larger diameter tires if this will affect the warranty ( since there's more stress on diffs ) and he said , if it was minimal ( like in my case 10mm taller ) no problem. But he said be careful as it might mess with Eyesight, but he wasn't sure about it. Anybody went larger and had issues with Eyesight ? Thanks
 
#2 ·
Interesting question. Eyesight comes on several Subaru models. Legacy is 6" clearance and Outback 8". I wouldn't think it would affect Eyesight's distance calcs just what Eyesight could see closer to the car, the lower the Subaru the more it could detect things closer. But that would seem a minimal. If you raised the Outback to 10" it might lose sight of smaller objects closer but likely not of much consequence to safety and functionality. But just guessing at the answer.
 
#3 ·
There is a warning in the Service Manual:


5. TIRE INFLATION PRESSURE


Check the tire air pressure.


Standard:

Adjust to the specified air pressure. <Ref. to WT-2, SPECIFICATION, General Description.>

Do not install worn tire or tires with excessive wear difference.

Install tires with specified size.


ES(diag)-11




 

Attachments

#4 ·
Thanks,I read the pdf, but almost every vehicle manual recommends to use tires of specified size, and adjust tire pressure. In my case, 10mm taller tire will raise the vehicle by 5mm ( roughly 1/5 of an inch ). Same size tire will vary by that figure between new and worn 1/5 ". Also a loaded car will sit lower but I don't know by how much. Not trying to argue here, just gather some info before I do the switch, and if it does affect the system, I'll forget about going larger tires and stick to stock size. As a side example, in my previous truck ( Nissan Xterra ), going larger size from 32" tire to 33" tire, affected the sensors in a way that my stabilty or traction control sensors activated on almost every corner when going slightly fast, and I mean slightly ,with the warning light that I was losing traction ( while this was not the case at all ), and this did not happen with stock size before. maybe difference in rotation affected the sensors. ??? I included this to point to show how sensors are really calibrated for specific specs these days, but still interested in opinions of people withe ES if they did go larger.
 
#5 ·
Eyesight is a very robust system. Ride hight isn't going to affect it. If it where that sensitive, owners would be having some serious issues.
Tire size and inflation has to do with the balance to the AWD system, not Eyesigt.
 
#9 ·
Maybe it's not the ride height that can screw up Eyesight - maybe as mentioned in above post that it's the circumference or a combination of both. There must be some situation that can cause problems as the warnings are in both the Service and Owner's Manual. I can't respond from experience but I don't think you can either. The Owner's Manual contains this warning:

The system may not operate correctly under the conditions listed below.
When these conditions occur, turn off the Pre-Collision Braking System.
Also, do not use Adaptive Cruise Control.


- The tire pressure is not correct.*1
- The temporary spare tire is installed on any wheel.*1
- Tires that are worn or have large variations in wear conditions are installed.*1
- Tires other than those of the designated size are installed.*1


*1: The wheels and tires have functions that are critically important. Be sure to use the correct ones.


Could be that Subaru is just being overly fuzzy but a service department would probably tell you to remove non specified tires if you have a problem as it's part of their trouble shooting procedure.

 
  • Like
Reactions: KentuckyOutback
#6 ·
That's great news Kentucky. Remains to see if 10mm difference in overall diameter will affect the AWD system. From posts I've read here and there, nobody who installed 255/55r18 or 235/60r18 both roughly same diameter ( 10mm extra & 12mm extra )seems to complain about anything at all. So I feel GOOOOOOOOOOOOOOOOOD, and will be testing fit on my wheels of the 255 very soon for any rubbing.
 
#7 ·
Remember the car is counting wheel revolutions to determine speed. Eyesight uses your cars speed to work out a few important things.

I'm sure it can tolerate some variation, but I don't think Subaru has published any limits, so you're kind of a pioneer for figuring out what will work and what won't.
 
#8 ·
I think ( I hope ) I should be OK for that slight variation, as I calculated and found that same difference exists on the same new tire with a say 10/32 or 11/32 tread depth, till it's 4/32 and time to replace. Tire looses about 10 mm of tread depth in overall diameter from new to time to replace.
 
#11 ·
All of the on-board safety systems base their calculations on indicated speed, which is derived from wheel/tire rpm, while vehicle dynamics remain firmly tied to actual speed.

When you fit "taller" tires, with a rolling radius greater than stock, indicated speed will be less than actual speed. Actual braking distance will be longer than EyeSight and other on-board systems calculate, and time-to-collision will be less than calculated.

Non-standard tire sizes will affect EyeSight and other on-board safety systems. But the key question is, "How much is too much?" I don't know; Subaru doesn't know, since they've never tested the vehicle with your choice of tires, etc.; and you don't know, either. You are a test pilot, and you assume all the liability that comes with that. It is unlikely that EyeSight will abruptly quit working altogether, IMO, but you will have traded away some unknown portion of the safety margins EyeSight provides.
 
  • Like
Reactions: KentuckyOutback
#20 ·
All of the on-board safety systems base their calculations on indicated speed, which is derived from wheel/tire rpm, while vehicle dynamics remain firmly tied to actual speed.
I though of this as well. Then I got to thinking about how the system works. It really doesn't matter how fast the car is moving, except that the spedo triggers the system to switch on or off for monitoring. As far as monitoring and implementation, it's analyzing distance and approach velocity through the stereo cameras. When it sees that the car is approaching too fast and is getting too close, it applies the brakes, no matter how fast the car is moving, within the speed window. The only thing relative, as far as Eyesight is concerned as to how fast the car is moving, is when it's on and off. Once the car is moving over the minimum speed to activate Eyesight, the system calculates approach velocity and distance through the cameras.
Since you got me thinking about this, I can see where a much larger circumference tire could really cause the system to become dangerous, by allowing the car to go way past the speed at which it should have been turned on, and go past a safe top speed to turn off, because the spedo is now way past the calibrated speed.

I can see Subaru in the near future, installing a GPS spedo to do away with this potentially dangerous situation...
 
#12 ·
Perfect explanation, but from what Lloyd pointed in owner manual, and I should have read that, system seems to be so sensitive that if your stock tires are worn, system might not function and Subaru recommends to turn off pre- collision braking or not use adaptive cruise. Worn tires fall within 10 mm of overall radius, and if they say so, system is more sensitive and has less tolerance than I expected.
 
#13 ·
I tend to think ... and this is just my opinion ... that many of the cautions in the Owner's Manual are there simply because Subaru has never tested configurations other than stock. Indeed, it would be unreasonable to expect them to, since they can't possibly anticipate all the things owners might do to their vehicles ... even ignoring the considerable cost such testing would impose.
 
#15 ·
... they don't want you to rely on the system if your tires are worn.
They caution you; that's all. Subaru clearly requires that all four tires have closely matched rolling radii. But how close? 1 tire worn? 2 tires worn (on same axle ... on different axles)? 3 tires worn? 4 tires worn? Worn how much? Worn to the wear bars? Worn to zero tread depth? What inflation pressure spread? Many variables to test.

Subaru probably warrants satisfactory system operation with uniformly-inflated and uniformly-worn tires, from full tread depth to the wear bars, but I haven't seen anything that indicates how many configurations are tested. Turning off EyeSight and VDC seems a little extreme to me, but it's probably the most conservative option in unknown circumstances.
 
#21 ·
@zeiter
Sorry, I've been over thinking this and writing as I'm analyzing the situation. I was thinking hight, when I should have been thinking tire circumference and indicated speed inaccuracy. It's not supposed to come on under I think 7mph, and turn off above I also think, 20mph. While it does turn off the braking function, it will scream at you at highway speed if it sees you're approaching a vehicle, or object too fast. It would be a catastrophe if you installed much larger tires that threw the spedo off to the point that the system wouldn't turn off until actual vehicle speed reaches 50mph, while showing 19mph on the spedo. As well as this, it wouldn't turn on the system while the vehicle is actually going 20mph, while the speedo shows 7mph. But at 5mm, I really don't see enough of a difference to make it dangerous.
I've had allot on my mind and it took a little longer for me to get on the correct page, LOL!
 
  • Like
Reactions: zeiter
#22 ·
Eye sight system uses a 3d camera technology to not kidding here EYE ball distances and fancy computer logic then decides if there is impending doom and applies the brake etc. No ride height should not be an issue nor should it ever be an issue given optical perspective creates far far far wider range of optical views than anything that slight increase in height would cause. No its not impacted by tire size. Indicated speed is all relative doesn't matter what speed your moving as long as your path is clear.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top