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Old 10-28-2012, 09:55 PM   #341
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Well nords, are the wheels tires bigger in diameter or width? My 50 year old toy has bigger wheels but smaller tires such that the tire diameter is about the same. However, the tires are a bit wider and barely fit in the wheel wells. It is a problem.

It's not hard to calibrate 50 year old speedo's (for a certain speed, ie. 60 mph). OK, it's not easy but it can be done. Usually because the speedo has 'lost it'. A 6% difference on a new car seems close to tolerances unless the speedo is GPS enabled.
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Old 10-28-2012, 11:15 PM   #342
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Quote:
Originally Posted by imoldernu View Post
Curiosity question for Dave....

At one time in my career... many moons ago, I was involved in a large retailer auto service think tank, with more than 200 Service Centers... (similar to the Sears Auto Service Center)s...
One of our major challenges was to increase the labor income... ie:, the profitability aside from the income from tire/battery/repair parts sales.

One of our projects was a 4 wheels off inspection of every car that ended up in our shops. It was a free 12 or 18 point inspection of the major categories... brakes, fluids, battery, tires... etc.. The inspection was followed up with a postcard reminder three weeks later. Soft sell, confidence builder.

Our Shop Managers and employees hated the program.

In the 6 months trial, our labor recovery... (labor income % to labor cost), changed from 80% to 130%. It was obviously the right thing to do, but pushback from the Managers and employees resulted in dropping the test.

This was more than 25 years ago. Now I wonder, as I see many underutilized brake and muffler and tire shops, why this free wheels off inspection is not being used.

The idea was to "show" the customer his/her problems, and use a softer sell, instead of using the fear factor.

It grates on me to see a three bay auto service with two bays empty.

Just wonderin'... Whaddya think?
Our Chevy dealer does a 27 point inspection + tire rotation which ranges in price from "free" to 30 bucks with a lube/oil/filter change that would normally run $35 all by itself. It's basically what you describe...they measure brake pads, tire tread depth, battery condition and provide a written report. Even though I do most of my own maintanance, I find it extremely valuable since we are a family of five vehicles with 3 young drivers. If they say an air filter or whatever is required, I replace it myself but I often wonder how long it would have taken me to find the burned out license plate bulb on my daughter's car. Dealer charged 4 bucks to replace and I think that was fair.....police around here just love writing $75 tickets for such things.
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Old 10-29-2012, 10:05 AM   #343
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Sounds like the shop was just trying to sell you a new rotor. The repair manual for your vehicle will have the specs and wear limits. Mine for instance 28mm normal, 26mm repair limit so it has 2mm of wear. The replacements should meet these specs even on a cheap one.
Sometimes the min thickness is also cast into the rotor on the inside hub. Keep in mind that just because it's thinner does not mean it's lower quality. Could be different material or different ventilation in between or so on.
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Old 10-29-2012, 10:08 AM   #344
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What are some typical numbers for allowable thickness on the rotors? What I'm wondering is, why not just make them a bit thicker? It seems we are talking small fractions of an inch, right?

And before you say "unsprung weight", I can't help but notice that tires on cars seem to be getting larger (and therefore heavier). Seems to me that I used to buy 14" tires on the smaller-to-midsize cars I owned, then they started coming with 15", and now 16". Upgrade beyond the base model, and you start seeing 17-18-19-20" tires.

What's up with that? It seems the larger tires go up in price significantly, yet I doubt they wear that much longer. One that I looked at (same series), had a 3% delta in Rev/Mile between a 16" and 19" rim, and the larger is 17% heavier (~ 4 #). But the 16" cost just 53% of the 19". Not sure if that is typical, but I bet it's close.

-ERD50
larger tires improved ride quality and in some cases sell more cars (people like big wheels). As far as them wearing longer, tires definitely last longer today than in the '70s...but I can't say for sure it's due to the size...the rubber and construction (move from bias ply to radial) has been a major factor.

Maybe I should do a post on how to read tire sizes...as a 15" is not always "bigger" than a 14" lol.
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Old 10-29-2012, 10:09 AM   #345
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What are some typical numbers for allowable thickness on the rotors? What I'm wondering is, why not just make them a bit thicker? It seems we are talking small fractions of an inch, right?

And before you say "unsprung weight", I can't help but notice that tires on cars seem to be getting larger (and therefore heavier). Seems to me that I used to buy 14" tires on the smaller-to-midsize cars I owned, then they started coming with 15", and now 16". Upgrade beyond the base model, and you start seeing 17-18-19-20" tires.

What's up with that? It seems the larger tires go up in price significantly, yet I doubt they wear that much longer. One that I looked at (same series), had a 3% delta in Rev/Mile between a 16" and 19" rim, and the larger is 17% heavier (~ 4 #). But the 16" cost just 53% of the 19". Not sure if that is typical, but I bet it's close.

-ERD50

I think it has to do with heat dissipation.... if you have thicker rotors, they retain heat more and eventually can affect braking....

You might be able to correct this with cross drilling, but then you have more expensive rotors....
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Old 10-29-2012, 10:10 AM   #346
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Originally Posted by rbmrtn View Post
Called plus sizing, putting larger tires on than OEM specs

+Better handling, cornering, traction etc, Looks...

- Cost a lot more for tires and wheels. performance improvement not that great,
poor ride comfort, poor winter performance

Plus sizing - Wikipedia, the free encyclopedia
Sort of

"Plus" sizing is when you go to a larger sized RIM while keeping the overall tire diameter about the same. The goal is improved looks and better handling due to less flex in the tire sidewall, which is now shorter. Right on with all your other comments.
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Old 10-29-2012, 10:15 AM   #347
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Quote:
Originally Posted by imoldernu View Post
Curiosity question for Dave....

At one time in my career... many moons ago, I was involved in a large retailer auto service think tank, with more than 200 Service Centers... (similar to the Sears Auto Service Center)s...
One of our major challenges was to increase the labor income... ie:, the profitability aside from the income from tire/battery/repair parts sales.

One of our projects was a 4 wheels off inspection of every car that ended up in our shops. It was a free 12 or 18 point inspection of the major categories... brakes, fluids, battery, tires... etc.. The inspection was followed up with a postcard reminder three weeks later. Soft sell, confidence builder.

Our Shop Managers and employees hated the program.

In the 6 months trial, our labor recovery... (labor income % to labor cost), changed from 80% to 130%. It was obviously the right thing to do, but pushback from the Managers and employees resulted in dropping the test.

This was more than 25 years ago. Now I wonder, as I see many underutilized brake and muffler and tire shops, why this free wheels off inspection is not being used.

The idea was to "show" the customer his/her problems, and use a softer sell, instead of using the fear factor.

It grates on me to see a three bay auto service with two bays empty.

Just wonderin'... Whaddya think?
That's the type of shop I used to work in...I don't even mind telling the name as it was a long time ago....

Bob Sumerel Tire & Service | Cincinnati

We did such free inspections...typically ours was when we were rotating tires...we'd check a few things even without the customer asking, and then let them know if something was "amiss".

Yes there is a fixed cost associated with those bays, nice to have them filled. In our shop, one bay was for "general repairs" with a single-post hydraulic lift, one was for front-end alignments, and one was for 4-wheel alignments...which were relatively new at that time.

I would bet that if you went to Midas and asked for a free inspection, they'd do it.
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Old 10-29-2012, 10:22 AM   #348
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The techniques in that article seem to attempt to keep the tires the same diameter. But I've seen plenty of cars where the tires are clearly bigger than the fender wells were designed to accommodate. If the diameter of the wheels is bigger, then the tires have fewer rotations per mile and the speedometer would register a lower speed. I guess going from 16" to 17" would reduce the speedometer reading by about 6%, or about 4 MPH at 60 MPH. Does this somehow get adjusted, or is it even considered significant?
The bold part is not necessarily true...as you allude to in your first sentence. As far as whether it's adjusted, it depends. WIth "plus" sizing, the overall diameter stays about the same, and no adjustment is needed. If you do go to a dramatically different tire diameter, then it depends on the type of car you have. In my case:

1) I have a '69 Camaro with larger-than-stock tires...so I changed the plastic speedometer gear to "calibrate" everything back to where it should be. GM color-coded their speedo gears based on # of teeth so this was easy.

2) I have a 2007 Mustang with larger-than-stock tires...and in this car the speedo adjustment can be made with an aftermarket tuning device that allows you to set the "revs/mile" in the car's computer. I doubt whether most shops would do this for you...but then many shops also won't put "significantly" larger diameter tires on a car due to safety concerns. Obviously if you just take the wheels in, they can't say anything....but any good service guy would advise of the dangers of doing so without some forethought.
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Old 10-29-2012, 10:26 AM   #349
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I think it has to do with heat dissipation.... if you have thicker rotors, they retain heat more and eventually can affect braking....

You might be able to correct this with cross drilling, but then you have more expensive rotors....
The main reason they don't make them thicker is weight and cost. I know it doesn't seem like much, but every little bit helps.

Actually thicker rotors will typically "handle" more heat without the associated brake fade exhibited in some cars.

As to cross drilling, there is a trade off---remember that every hole you drill also reduces surface area and creates a sharp edge where heat can crack the rotor. I've seen numerous such rotors cracked, although usually this is on "road track" cars where they do significant amounts of braking and really get them hot.
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Old 10-29-2012, 10:47 AM   #350
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Sort of

"Plus" sizing is when you go to a larger sized RIM while keeping the overall tire diameter about the same. The goal is improved looks and better handling due to less flex in the tire sidewall, which is now shorter. Right on with all your other comments.
right, usually you get a tire/wheel package to keep things roughly the same, larger rim with lower aspect tire ( larger wheel size tire that is a little shorter ). The online tire stores will do all the calcs for you. Shouldn't have to recalibrate anything with upsizing.
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Old 10-29-2012, 11:46 AM   #351
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The initial reason to increase the rim diameter was to meet new mandated braking performance. Bigger wheels allow for bigger brakes. After that, further increases in rim diameter were primarily driven by styling.
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Old 10-29-2012, 01:34 PM   #352
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The initial reason to increase the rim diameter was to meet new mandated braking performance. Bigger wheels allow for bigger brakes. After that, further increases in rim diameter were primarily driven by styling.
One of these days we'll move to electromagnetic braking completely, thus doing away with rotors and calipers. Today some of the electric cars have 'regenerative' braking, but it's supplemental to the regular brakes...thus it saves no weight/complexity/cost.
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Old 10-29-2012, 01:36 PM   #353
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20. Do you know that feeling you sometimes get in a car where you press on the brake pedal lightly to stop, and the car sort of stops and goes…almost like a vibration, but more like a “wobble”? As the car slows, the "stop and go" slows…and if you let off the brake pedal it stops completely. This is due to “rotor runout”. It’s not dangerous…so if it doesn’t bother you, keep on driving. But if you want it fixed, the proper fix is to have the rotors resurfaced, which is where they remove them from the car and grind them down flat. Unfortunately, rotors are often made so thin that they cannot be safely resurfaced, as there is a minimum thickness…and in this case you’ll have to buy new rotors. A typical rotor resurfacing would cost about $60-$80, and new rotors with labor would cost about $160 or so. You do not have to change the brake pads when you do this, but often the brake pads are either worn or glazed…so whether you do or not depends on the specific situation…talk to your mechanic and ask questions. Typically I would NOT change rotors, but completely understand there are times when you must.

If you're looking for ways to avoid having the rotor runout issue, read some of my other posts on brakes...avoid getting them hot in one place using the techniques I mentioned, use a torque wrench when tightening wheels, and avoid driving through large water puddles when the rotors are very hot.
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Old 10-29-2012, 01:38 PM   #354
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21. Ok, so related to my post on rotor runout, what causes brake rotor runout to happen? The answer is excessive heat. So why are they getting too hot? When you press on the brake pedal, two pads (or sometimes shoes) squeeze a metal disc called the rotor. You can often see the rotor if you look through your wheels…it’s shiny. That friction creates heat. The pads only squeeze it in one area making up about 20% of the total “swept area” as it rotates. Let’s say you’re going 50 mph down a hill, and there’s a traffic light at the bottom of the hill. You see the light change yellow…so you apply the brakes. Those pads squeeze the rotor…and the entire rotor heats up as the rotor “sweeps through” the pads. Then when you get to the traffic light, you hold the brake pedal on, which keeps the hot pads against that hot rotor…while the remaining 80% of the rotor sits in the open air, cooling off. Voila…you’ve created a situation where one part of the rotor is heated more, and thus it’s size/shape changes slightly, and you get rotor runout. Multiply this over the thousands of times you stop your car, and you can see how this happens.

Another potential cause is where you get the rotors hot by braking a lot, then drive through a puddle of cold water…the water splashes up on the rotor, shrinks it quickly in one area…and voila…you have rotor runout again.

Another cause could be overtightening of lug nuts whenever wheels are bolted back on the car...use a torque wrench. Proper torque varies by the type of wheel and the type of lug nut (shank lugs require more torque and actually a re-torque if new than conical lugs - although most factory lugs are conical).

So why don’t they make rotors thicker so they can handle this? Excess weight reduces fuel economy.

Is there a way to prevent it? Yes, when you stop at a traffic light after a hard stop….inch forward 2-3 inches every 10 seconds or so, exposing all parts of the rotor to the air, cooling it evenly. Or, if you are on flat ground and have a manual transmission, simply take your foot off the brake pedal. I have manual transmission cars…and I’ve not had a rotor runout issue in 25 years…ever since I learned this trick.
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Old 10-29-2012, 02:07 PM   #355
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22. Tire size/info reading - ok, rather than me writing a long expose on this, let me just provide a link.

Tire Tech Information - Tire Size Guide

LOL
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Old 10-29-2012, 02:37 PM   #356
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One of these days we'll move to electromagnetic braking completely, thus doing away with rotors and calipers. Today some of the electric cars have 'regenerative' braking, but it's supplemental to the regular brakes...thus it saves no weight/complexity/cost.
I don't know if there's a standard regenerative braking system, but the Prius only clamps the pads onto the rotors below 6 MPH-- or if the driver really stomps on the brake pedal. Otherwise the electric motor-generator does all the work when the driver's foot presses the brake pedal. It's like spinning up a heavy flywheel.

This is supposed to help the Prius brake pads last up to 100,000 miles. I guess it would minimize rotor runout too.

We'll know in about 10 more years...
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Old 10-29-2012, 03:14 PM   #357
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I don't know if there's a standard regenerative braking system, but the Prius only clamps the pads onto the rotors below 6 MPH-- or if the driver really stomps on the brake pedal. Otherwise the electric motor-generator does all the work when the driver's foot presses the brake pedal. It's like spinning up a heavy flywheel.

This is supposed to help the Prius brake pads last up to 100,000 miles. I guess it would minimize rotor runout too.

We'll know in about 10 more years...
Good info, thanks Nords. Yes and my understanding is that it charges the battery that way. What I'm not sure on is the thermal efficiency...in other words is there any heat generated during the part where the pads are not clamped? My guess would be no other than slight battery heat...but not sure.
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Old 10-29-2012, 09:43 PM   #358
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Good info, thanks Nords. Yes and my understanding is that it charges the battery that way. What I'm not sure on is the thermal efficiency...in other words is there any heat generated during the part where the pads are not clamped? My guess would be no other than slight battery heat...but not sure.
No, I think the generator is just spinning from the rotation of the front axle on the chain of the CVT that's connected to the common shaft of the generator/engine. (Not sure what's happening to the back axle.) It's a big drag, and the heat is the normal heat produced by the resistance of the generator windings and the battery's chemical reactions as the current charges the battery.

I'm not sure how much the generator weighs, or how much torque it takes to spin all the gears & shafts, but whenever the car is coasting it's spinning the generator a little (and recharging the battery a little). If the car is coasting at faster than 41 MPH, the ECU actually spins the engine as well (with no gas to the cylinders) to prevent the generator from overspeeding. (I'm not sure exactly how the gearing achieves that.) Of course the car coasts quite well, and I've coasted down off the Ko'olau at up to 75 MPH with the battery getting a ferocious charge from the spinning wheels.

When the braking shifts over from electrical/regenerative to mechanical at 6 MPH, there's this momentary feeling that the brakes have slipped. It's a little exciting the first time you experience it-- usually about 10 feet from the car in front of you. It's even more exciting when your daughter is behind the wheel learning how to drive (while you're in the passenger seat) and instinctively pulls her foot off the brake...
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Old 10-29-2012, 11:58 PM   #359
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There are highways that descend a few thousand feet non-stop in just a few miles. I have driven on some with 10% and even 16% grade.

I wonder if the EV or hybrid car batteries would have enough capacity to store all that energy that is converted to electric. If and when the battery is full, the mechanical brakes must get activated. And as there is no combustion engine in a true EV to provide the drag, the brakes must then absorb a lot more heat. And in a hybrid, the combustion engine may be too small to provide the needed drag.

I am sure car makers have worked this all out, but I am curious about the details.
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Old 10-30-2012, 07:53 AM   #360
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23. Fluids you will find in a car
a. ----
b. Windshield washer fluid is light blue translucent
c. Anti-freeze is typically green/yellow and translucent. Typically it is recommended to mix 50/50 with water, although some stores sell “pre-mixed” fluid that can be used “as is”.
d. Brake fluid is clear and slightly viscous when new, but brown and slightly viscous when used. Brake fluid will eat paint…do not get it on any car finish. Brake fluid is hydrophilic, which means it attracts moisture out of the air. Once you open a sealed can, throw away any you don’t use within about a week or so…even screwing the cap back on the can is insufficient protection.
e. Oil is light brown and viscous when new, and dark brown/black and less viscous when used…also less viscous when heated in the oil pan
f. Gear oil is typically 80W-90…very thick viscous light brown fluid.
g. Automatic transmission fluids vary widely…many of them are red translucent, but in many front wheel drive cars they use motor oil or gear oil. See your owner's manual for the correct fluid.
h. Gasoline is very slightly brown translucent and has a distinctive, well-known smell
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