Prius Prime Plus in my hands

The spare tire arrived on Tuesday but I have errands to run on Wednesday. I also ordered a wheel shim kit:
144pc GOLIATH INDUSTRIAL ALIGNMENT BODY SHIM ASSORTMENT CAMBER CASTER TOE STEEL | eBay

144pc Goliath Industrial Alignment Body Shim Assortment Camber Caster Toe Steel - $16.00

For adjusting the rear toe and camber, this is not my first effort:
Tutorial: Rear tire alignment | PriusChat

Sad to say, I have yet to find web descriptions about how to use these shims to dial in a particular value of camber and toe. So let's get started:

• Camber measurement
• Camber adjustment

CAMBER MEASUREMENT

There are several dedicated camber measurement tools: magnetic base bubble scale, ~$25, and wheel rim fixture with magnetic or digital angle measurement, $200-(how much money do you have?). The magnetic base attached to the brake disk and the bubble scale reads out the camber. Mechanically simple, you read the angle with the car sitting on a level surface (is it really level?) The wheel fixture works by attaching or being held to the wheel rim, vertically, on a level surface, and measuring the angle. One attaches to disk brake and the other uses the edge of the wheel.

The first problem is making sure the car is parked on the level surface. Since we are dealing with fractions of a degree, this is not a trivial problem. My approach would be to use a long bubble level and an old book, say a phone book, as a variable shim. Measure the original bubble offset and then put enough pages down to over correct. Remove pages until the stack of paper pages and the bubble level shows it is level. Then drive the car so one tire is on the stack of pages, the paper shim. That is going to be close enough but what a lot of work!

My approach is to use the tire temperature profile to detect if the camber is off; correct, and; remeasure the temperature profile. The goal is to even the temperature distribution across all treads. We've already gotten a left and right, rear tire temperature distribution and though there is a gradient, it is even across all treads:

	driver #1	#2	#3	#4	#5		#5	#4	#3	#2	#1 passenger
1	94	95	99	99.5	101		101.5	101.5	102	99	94.5

The good news, the temperature profiles are nearly identical meaning nearly an identical amount of negative camber on both sides. The bad news is I run the tires at maximum sidewall. The earlier, 2003 Prius tests showed the right tire had a difference of ~5F yet it was corrected with a 1/32 shim. Our tires have ~6-7F difference with maximum tire pressure. So what are the options?

CAMBER ADJUSTMENT

The shim kit comes with:

	shims	1/8"	1/16"	1/32"	1/64"
1	digital	0.125	0.0625	0.03125	0.015625

So this means we can combine shims to make any depth in 1/64" (0.015625") increments. To start, the 2003 Prius, passenger side wheel camber was corrected by using a 1/32 for a 6-7F temperature difference. So well apply 1/32" shims to both rear wheels and remeasure. But it would help if we could map the shim offset to degrees of camber change.

There is an iPhone app, "Mission Level", that provides accuracy to ~0.1 degrees:

After using business card, paper shims on the desk to calibrate the side of the iPhone case, I measured the door jam angle which I suspect is off by about 0.1 degrees from true vertical. Unfortunately this app does include a calibrate function so I used the paper shims. The difference between orientations is 0.7 degrees. Half is 0.35 degrees so taking taking 0.2 - 0.35 ~= 0.15 degrees which is probably the true vertical of the door jam. It is symmetrical, 0.5 - 0.35 ~= 0.15 degrees.

So what I'll do is measure the angle change of the brake disk after installation of the 1/32" shim. At these shallow angles, the shim to angle change will be pretty much linear.

For good measure, I'll 'blue print' the axle bolt pattern. Knowing the exact hole geometry, geometry should easily generate a table of correction angles per shim size. That way if experimentally we determine that more camber correction is needed, we can dial in exactly what is needed.

PLAN

The shim kit may be here Friday or no later than Monday. So I'll be able to do the experiment early next week. In the meanwhile, my full-size spare arrived so I can do spare tire, fit tests this week.

Questions? Comments? Suggestions?

Bob Wilson

 

A question for @ericbecky and @3prongpaul about the brake pads. I was working on our 2017 Prius Prime which has disk brakes on the rear. I noticed when reassembly the rear wheel that at least one of the brake pads looked like it is broken in the middle. I then did a Google search and found images that suggest they are made this way.

So are the disk brake pads 'split'?

Is there a problem with this?

Thanks,
Bob Wilson

 

It looks like I've added about half a degree to the passenger side wheel with a 1/32" shim. The 1/16" shim would not seat the top bolts properly. I'll do the driver side this morning using the 1/64" shims, the only other size that can work. Then I'll do another tire temperature distribution and handling test.

Technical details: 2017 Prius Prime Plus

I've figured out to handle getting a VIN that should work for the Hunter system at Decatur Toyota. I'll take a photo of a 2016-2017 Prius at a local dealer and print it to size. The Prius hatchback specs should be close enough.

Bob Wilson

 

Thanks!

Google found some hits for "caliper shims" but nothing that clearly showed how they would be used. But YouTube had something useful:

(note: stupid background music, play at 0.25 speed and muted)

It looks like these shims also handle the angle offset which makes sense.

Also about Toyota brake pads:

What I'll do on the road test is see if I'm getting excessive heat on the rear disks. If so, I'll probably look at removing the outside, brake pad shim. That may shift everything out enough to bring them close enough and early wear should (and God laughs!) bring them normal to the disk. But the key will be measure and correct as necessary.

BTW, I'm not having luck finding instructions on how to measure and determine the desired, shim offset. I found one bike YouTube but it was based on easy spinning and the Prime passenger side wheel did turn easily.

Thanks again,
Bob Wilson

 

I was working on it this morning only to discover my open-end wrench set has a 'funny' set of jaws. I'll pickup a good set later today over at Harbor Freight.

I'll take out the top, slider which should allow me to rotate the caliper assembly and access the pads. I'll compress the piston, put the pads back in and I should be able to quickly reassemble the brake around the disk. Then I can do some road tests and see if I have heating problem. I've got a 5k warranty visit planned for Tuesday so I need to get it working. <GRINS>

Bob Wilson

 

Spare testing verified the Ecopia 205x65R15 worked just fine in the rear wheel well. No rubbing or evidence of a problem going over speed bumps. These are low rolling resistance tires that Bridgestone has demonstrated and supports 51 psi side wall pressure. When the OEM tires wear out, I'll replace them with these. This size has the advantage of correcting the tire revs/mile.

Adjusting the passenger side camber took several hours as I had not dealt with rear disk brakes. The driver side was much faster until I discovered I had the wrong style of metric box wrench. Lots of lessons learned and here are the results.

BEFORE


After adding 1/64" shim:


And on the other side.

BEFORE

After adding 1/32" shim:


Because of the method, it takes a couple of minutes to measure the temperatures and we start with the outmost tread, #1. So it is not unusual that the inner tread shows a cooler temperature, especially on the last pass. Yes, I would prefer a dealer/tire store machine metric but these temperature metrics are cheap and effective: Tuning Tires &#8211; Tracking tire temperatures and tuning your setup accordingly can pay dividends on the racetrack | NASA Speed News Magazine

Now I'm ready for the 5k warranty check.

Bob Wilson

 

I got a FLIR camera attachment to the iPhone:

• driver front - no problem. Some slight negative camber but not excessive.
• driver rear - has 1/64" shim. Some slight negative camber as the outside tread is a little cool
• passenger front - way too much negative camber. Will need a camber bolt
• passenger rear - 1/32" shim. Negative camber is off like the front

I have a camber bubble level coming and will do a static test of all four wheels. I can not rule out a toe problem but that takes a different approach. It is possible the passenger side toe is off from the split speed bumps.

Bob Wilson

 

Too late to edit in the previous post, I monitored the MPG at 70 mph:

This 70 mph data point was after the initial camber adjustment of the rear tires. More to come and it looks like 70 mph is an excellent data point.

FYI, I noticed the "Car and Driver" piece comparing the Prime and Volt showed the Plus having lower performance than the Premium and Advanced. At the time, I thought that was curious but now I'm wondering if the Plus may have a systemic problem of excessive, negative wheel camber.

Bob Wilson

 

Using a tripod setup, I made better photos:

• driver rear - temperature difference is greater than passenger rear. Need to replace 1/64 shim by 1/32
• passenger front - still has a negative camber issue

The driver side rear is easy to fix. An hour and it is done. The passenger side camber may take a little more effort.

There are special order, camber adjustment bolts, but before ordering one, there is manual process to move the camber to the limit of the existing bolt. A little tricky, it requires having a torque wrench to make sure the bolt is secure. Then I retest.

Bob Wilson

 

Yes but most of the time I'm driving solo. I tuned for the usual cases.

Bob Wilson

 

Retired, I can give rides in our plug-in hybrids so I gave one to a pharmacists at Propst. The problem is how to explain the difference in cost of EV versus gasoline miles? A simple formula gives the EV equivalent to the local gasoline cost:
$EV/gal = (MPG/100) * $/kWh * kWh_per_100mi

• MPG - found at www.fueleconomy.gov
• kWh_per_100mi - found at Fuel Economy
• $/kWh - local cost of electricity, $ per kWh

So this is what three popular, plug-in hybrids would cost in Huntsville, $0.10/kWh:

• $1.13/gal - 2014 BMW i3-REX
• $1.30/gal - 2017 Chevy Volt
• $1.35/gal - 2017 Toyota Prius Prime
• $2.76/gal - 2012 Toyota Plug-in PiP ($0.19/kWh)
• $1.45/gal - 2012 Toyota Plug-in PiP ($0.10/kWh)

"Driving around town in a Prime is like buying gas at $1.35/gal."

What is fascinating, the local cost of gasoline plays no part in the calculation. Just the local utility rate.

Bob Wilson

 

So last night I was drivin' around in the Prime and I realized, I really like driving it even more than the BMW i3-REx. A little lower than our past Prius, it still has that quiet confidence and efficiency. In contrast, the BMW i3-REx is kinda like a German band, Klang und Wut.

Sure the BMW i3-REx has more power and a longer range. It is more practical as transportation like a pickup truck is not that bad of vehicle. Add a receiver hitch and a pickup bed sized trailer, problem solved.

In contrast, the Prime glides like a quiet, competent, cruiser. It is the Caddy/Buick to the BMW i3-REx.

Bob Wilson