Lost regen with new tires

My new Continental's came with a surprise, no regen! I don't get any error lights, but going above 25 MPH or turning to the right disables regen until I stop. Since the car needs aligned (1/8 inch difference, toed outwards), I'm wondering if that is the problem. The i-MiEV now pulls to the right, though all tire pressure equals.

UPDATE: The front left tire is larger than the right side. The size numbers are the same, but the left is larger.

UPDATE 2: Nevermind, I mis-measured. Both fronts are the same. Would slightly smaller rear wheels cause that? I thought only if the rear was spinning slower that regen would cut back.

Okay, now that I've studied the car's behavior and came off of my panic, I have a better grasp on what's going on.

Since the rear tires are smaller in circumference, the speedometer reading is now 5 mph faster than before (used to be 1-2 slow, now it's 2-3 fast). The front tires are the same size, so the car is suddenly seeing the rear tires going faster all the time, which I believe is disabling regen. That doesn't make much sense to me unless I can see how the car's coded, but if the rear tires go slower than the front (hittting bumps, slick roads), regen will get cut back then brought back up. Maybe the car is programmed to cut back regen if speed difference front to back is 2 mph or more, but not set to disable regen only if the rear tires are going slower, just a general 2 mph difference. Funny thing is, if I go around a turn for about 3 seconds with the wheel past the 10 or 2 o'clock position, regen would come back.

I've adjusted my tire pressure to help make the situation better (44 on the back, 36 on the front), but it's still not right. I'll call the local dealer (not the one I bought from) tomorrow morning to see if I can get an alignment and the speedometer calibrated. I'm not sure if the car will make it to the other dealer the way it is right now.

One interesting note, if I coast down to 25 mph or less and tap the throttle, regen comes back, even on straight stretches.

Can you try disable traction control and see if that helps any? that's a real bummer that the regen system is so sensitive. I was hoping to try some different size tires, but i guess we'll have to figure out how to deal with this first..

I'll try turning off ASC on my drive this morning. I've tried turning it off before, but regen would still cut out when I hit rough bumps when stopping.

Maybe turning it off before even moving would help.

Anybody tried to have their speedometer re-calibrated? I've been told it can't be done.

Can the MUT-III perform this?

PV1 said:

Would slightly smaller rear wheels cause that?

Click to expand...

You've changed the size of the wheels??

Details please

Don

Sorry, I meant tires. The New tires are 175/55R15, stock are 175/60R15.

We changed the rear tires back to the Dunlops, and now it works. I didn't realize how much difference there was between the two. I'll try to return them and get a pair of rear Dunlops. The front Continentals are great, though the car pulls to the right since it needs aligned. Speedometer is spot on.

Turning off ASC does NOT turn off regen.

What it does is eliminates the occasional pesky regen intermittence. For example, going into a downhill curve on a bumpy road with regen slowing the car - regen unexpectedly releases (and starts selectively applying brakes?). Disconcerting, but safe.

IMO, the car handles great in spirited driving on rough curvy roads with ASC off.

I like having ASC for my wife and I like having the ability to turn it off. Thank you Mitsubishi for providing this disable switch.

I noticed no difference in regen with my properly-sized Yokohama AVID ENVigors. I'm going back to Dunlops when these wear out.

PV1 said:

Sorry, I meant tires. The New tires are 175/55R15, stock are 175/60R15.

We changed the rear tires back to the Dunlops, and now it works. I didn't realize how much difference there was between the two. I'll try to return them and get a pair of rear Dunlops. The front Continentals are great, though the car pulls to the right since it needs aligned. Speedometer is spot on.

Click to expand...

PV1, Please specify what size combination of front and rear causes regen to be lost. The posts are not clear on that.

Those of us considering upgrading the front's need to know how much front to rear wheel % diameter mismatch does not affect regen.

New the difference is 4%.

If the engineers were being nice and the ABS allowed, they would have designed the system to allow new fronts and worn rears, or new rears and worn fronts. If that is the case the maximum range of % difference might be:

Diameter
front rear
(in) (in) % rear/front
21.9 23.3 6.39% worn front
22.4 23.3 4.02% new
22.4 22.7 1.51% worn rear

145/65R15 on front, 175/55R15 on back. The 175/55 are smaller new than worn out 175/60R15. Currently, I'm running new 145/65 up front with worn out 175/60 on back and it's fine. Much more than that will likely cause it to cut out again.

Thanks! I guessed that after reading all your posts again and assuming you tried to find OEM sizes but the correct rears where not in stock.

So this confirms that a 0.9% difference in rear/front diameter is out of range.

BTW if you combined the 175/55 rears with half worn 145/65 fronts it would only be 2% difference, so regen might work. With completely worn fronts, I am certain regen would work.

I was thinking the same thing, because I put a large gap in air pressure (44 in back, 36 up front) and that enabled regen while making sharper turns at speed, but it dropped out as soon as I straighened up. So I was really close to the threshold.

What it boiled down to was that I wasn't willing to buy Yokohamas after Joe's experience, and Dunlops are too expensive and wear out too quickly, so I went with Continental, even though the rear was the wrong size.

What is the difference with 145/65R15 up front with 175/65R15 on back? There's quite a selection at that size for the rear?

I am surprised that you are not getting any warning lights about the ABS or other systems. The I-MiEV like most other cars has a four wheel ABS system. Each wheel has a wheel speed sensor that is calibrated so that each axle on the vehicle is reporting the same speed of the tire regardless of the actual revolutions of the wheel. In other words, software in the system compensates for the rolling radius of each tire. There is some latitude in the software that allows for corrections when you put new tires on one set of axles and not the other. However, if the change is out of the range the system can compensate for, the system usually sends a warning by shutting down the ABS or some other systems like traction or stability control. For example, many vehicles will disable ABS if it sees a compact spare on one axle. I would think in this case, the ABS is sensing a tire speed difference and turning off the regen. You can get the same effect when you hit a small bump in the road during regen that momentarily changes rear wheel speed shutting of the regen.

Yeah, I've noticed that cutout, too.

I think I was in that range of no regen, but not bad enough for a warning, kind of like, "It's not a problem, but I'm not happy."

PV1 said:

I was thinking the same thing, because I put a large gap in air pressure (44 in back, 36 up front) and that enabled regen while making sharper turns at speed, but it dropped out as soon as I straighened up. So I was really close to the threshold.

What it boiled down to was that I wasn't willing to buy Yokohamas after Joe's experience, and Dunlops are too expensive and wear out too quickly, so I went with Continental, even though the rear was the wrong size.

What is the difference with 145/65R15 up front with 175/65R15 on back? There's quite a selection at that size for the rear?

Click to expand...

On radial tires, air pressure has a very small effect.

There are so many combinations that I prefer to share my excel file with the calculations. It also has a lot of other useful stuff including range calculations.
http://files.fm/g/woponqe#aa/9624Mpg_mph_imiev.xlsx

GdB said:

There are so many combinations that I prefer to share my excel file with the calculations. It also has a lot of other useful stuff including range calculations.
http://files.fm/g/woponqe#aa/9624Mpg_mph_imiev.xlsx

Click to expand...

Wow GdB, that's not a spreadsheet- it's a quick reference bible for all i-MiEV performance questions!
THANKS :ugeek:

After playing phone tag with the dealer for this whole time, my rear tires (original Dunlops) are wore to the point of being nearly smooth. With the newer Continentals on the front, I'm starting to see a drop out of regen when turning sharply. The Dunlops are wearing much faster than the Continentals.

How does this compare, time wise, to getting a replacement battery? :roll: :twisted:

PV1 said:

…my rear tires (original Dunlops) are wore to the point of being nearly smooth. With the newer Continentals on the front, I'm starting to see a drop out of regen when turning sharply. The Dunlops are wearing much faster than the Continentals.

Click to expand...

I believe that you have had your new front Continental tires for two months.
How many miles have you put on them?
How many miles do your original rear Dunlops have on them?
My original Dunlop Enasave tires still had 2/32 tread left on them at 33,000 miles.

I changed the fronts around 13,500 miles. I'm currently at 15,698 miles. The Dunlops have lost 2/32s in that time. The Continentals still look like new. I haven't measured them, though.

So, the Continentals have 2,000 miles on them.

The front Dunlops were changed at 13,500, and are nearly smooth on the inside 1/3 of the tire. The outsides still had a decent amount of tread left (my right wheel was pointed way out).

i just replaced my original rear tires at 40,996 miles--they were worn very smooth and flat, the main grooves were still showing so probably could have run them down to the bottom of the wear bars to make slicks, but there were age cracks and checking toward the inner and outer edges. i put yokohama 175/60 on this time.

i had replaced the fronts with Yokohamas, so i had nearly new front and absolutely worn out rears--and i had full regen and no issues with regen cutout.

i may try a 155/60-15 on my next front swap--it is nearly the same diameter as stock.

i still have OEM rears on kiev2 with 36k miles, plenty of tread but age cracks and checking on the edges. i will replace these with the Achilles from Amazon.

i love regen and wouldn't want to give it up, but would like to go bigger front and rear.