Wheel Size Question

[williaty]

Typically, sidewall and carcass construction change round about the 50 aspect ratio to cope with the considerably higher abuse that comes from running a shorter sidewall. Makes the tires less likely to stay on the wheel if you try to shoehorn them onto a too-small wheel.

 

Why are you trying to go that wide on undriven wheels? You'll just be increasing the unsprung mass, which is always a bad thing, but is a REALLY bad thing on a solid rear axle like this.

[OLDSCHOOLFOOL]

1 hour ago, williaty said:

Typically, sidewall and carcass construction change round about the 50 aspect ratio to cope with the considerably higher abuse that comes from running a shorter sidewall.

 

This is good information and I thank you.

Why is simply a question of looks. There is no real benefit regarding performance. Has absolutely zero to do with performance.

[OLDSCHOOLFOOL]

17 hours ago, williaty said:

You'll just be increasing the unsprung mass, which is always a bad thing, but is a REALLY bad thing on a solid rear axle like this.

 

Out of curiosity I looked up the weights and its actually a 1 pound net improvement over the factory steel wheels with factory tires. Pretty much a wash.

16x6.5 steel (25 lbs.) + 215/55R16 (23 lbs.)

16x7 aluminum (20 lbs.) + 275/45R16 (27 lbs.)

[williaty]

5 hours ago, OLDSCHOOLFOOL said:

 

Out of curiosity I looked up the weights and its actually a 1 pound net improvement over the factory steel wheels with factory tires. Pretty much a wash.

16x6.5 steel (25 lbs.) + 215/55R16 (23 lbs.)

16x7 aluminum (20 lbs.) + 275/45R16 (27 lbs.)

Holy crap those are HEAVY! Most OEM 16x6.5 wheels that I'm used to working with are in the 16-17lbs range. I have never before heard of wheels that small weighing that much. I have to say that coming to an American car after specializing in Japanese cars is like taking a step back into the past. I'm constantly shocked by stuff like this.

 

So yeah, you definitely got away with that without much penalty.

 

1lb increase in unsprung weight is actually a big deal but, after all, this is not a performance vehicle so the only downside is going to be the ride. Now... get a 16.5lbs wheel with a 20lbs tire and drop off about 10lbs per tire and I bet you'd actually notice a big improvement in the ride and handling! I know where to find cheap wheels that light in 5x100 but I haven't looked for them in 5x108 so I don't know if they exist.

Edited February 7, 2018 by williaty

[OLDSCHOOLFOOL]

23 minutes ago, williaty said:

I know where to find cheap wheels that light in 5x100

 

If you can add to that sentence..."and that are at a minimum of 8 inches wide and aren't ugly as homemade cow pies"........then I sure would like to know where that is. I also have an 03 Outback.

Of course, light is not the real goal anyhow, appearance is. Now I can go overseas and find some things but that will cost me. And with the 5x108 it generally means custom drilling.

[Beta Don]

On 2/6/2018 at 12:32 PM, williaty said:

You'll just be increasing the unsprung mass, which is always a bad thing, but is a REALLY bad thing on a solid rear axle like this.

Typically, the solid rear axle on most RWD vehicles also includes the considerable weight of the differential and half the weight of the driveshaft, which we don't have to deal with, so no big deal (IMO) if he were to add a few pounds to the unsprung weight of the rear axle  -  It's already super-light, by comparison

 

I'm very familiar with lightweight wheels and the bad effects of high unsprung weights.  My Miata has 9 pound wheels made by BBS in Germany and they are shod with 15 pound Bridgestone tires . . . . for a total of 24 pounds per corner.  But the Miata is not a truck, and for all intents and purposes, my TC is

 

Don

[williaty]

2 hours ago, Beta Don said:

Typically, the solid rear axle on most RWD vehicles also includes the considerable weight of the differential and half the weight of the driveshaft, which we don't have to deal with, so no big deal (IMO) if he were to add a few pounds to the unsprung weight of the rear axle  -  It's already super-light, by comparison

 

I'm very familiar with lightweight wheels and the bad effects of high unsprung weights.  My Miata has 9 pound wheels made by BBS in Germany and they are shod with 15 pound Bridgestone tires . . . . for a total of 24 pounds per corner.  But the Miata is not a truck, and for all intents and purposes, my TC is

 

Don

As someone who, until recently, designed suspensions professionally, even a few pounds of unsprung weight is a big deal. The fact that the solid rear axle design is slightly lighter than a solid, live rear axle design doesn't make it a good design. That's like trying to say it's ok because you caught the good leprosy. Unsprung weight is one of the few design factors where the ONLY correct number is 0 and anything other than that is bad. The farther you are away from 0, the worse it gets. It dramatically affects the ability of the tire to track the road which leads to big changes in road-holding. This is, obviously, a handling issue but what everyone forgets is that it's also a safety issue. Cars with well optimized suspension stop better, swerve better, and are less likely to roll over. All of these things may someday make the difference between avoiding a crash and being in a life-threatening accident. Simply put, cars with better performing suspension are safer than cars compromised in the name of cost (and under the shield of customer ignorance).

 

If you guys remember when Ford brought out the new pickup trucks, they did a series of videos with Mike Rowe comparing the Ford to the competitors. They showed the trucks driving over various test tracks and real world scenarios showing how much better the Ford did than the competition. One of the big things that the videos shows was that (even though they're all using stone age technology) the Ford truck's suspension was better optimized and produced better real world results. So even in trucks, this stuff matters.

 

For that matter, even without the pumpkin, the solid rear axle is an antiquated design that should have been abandoned for all non-haulage uses around the time we got rid of steam trains. Fully independent suspension should be the only default for a passenger vehicle (and remember, these things are basically a Focus with a box on top). The problem is that a solid, undriven rear axle is cheap. Ford made the gamble that most of their consumers are uneducated about basic engineering (which is definitely true. Americans love cars but know, on average, staggeringly little about how they work) and simply wouldn't know any better. You see the same cost-cutting design in other small, cheap cars.

 

To bring this back to a context for this forum (though admittedly straying from the discussion of unsprung weight), the Connect has a solid rear axle while the... crap, whatever Dodge is calling the Fiat Doblo here in the US... has fully independent suspension. I was able to find a dealer that had both (company owned a Ford and Dodge dealership on the same parking lot) and test drive them repeatedly back to back in the hills of Appalachia. The Doblo's rear end was SUBSTANTIALLY better controlled than the Connect's and the Doblo also was much more comfortable to ride in (my Connect doesn't smooth out in the rear end until I get about 600lbs of payload in the back). From a ride quality and handling viewpoint, the Doblo was vastly superior to the Connect. However, the Doblo's windshield stopped so low that I couldn't see traffic lights when I pulled up to the stop bar, so the Connect won the shootout because of that.

[mrtn]

Excellent post, thanks. So the weird semi-rigid rear axle of the new shape Connect has all the characteristics of a live axle and none of the IRS? It feels at least a bit better than the previous generation with its leaf springs. I never push my cars to the limits so I never visit the performance limits.

 

The new Connect is actually based on S-Max, IIRC, which is (was) a sporty minivan, bigger than the Focus. Even tho it still shares a big part with it as it’s normal from the production stand point, share as much between models as possible, to the point where some parts in larger vehicles fail prematurely due to underdimensioning (wheel bearings are the most apparent).

 

There is one truck with IRS AFAIK - the Honda Ridgeline which always got crap from the real truck guys due to the missing frame and live axle.

[OLDSCHOOLFOOL]

I love the way engineering guys can go off on a tangent. The decision to use the larger tire is already made. Its just a question of how to get there. Regardless of weight. Regardless of handling. The wheel almost certainly WILL be heavier in an effort to accommodate the extra width. Matter of fact, I'd put 305/40-16s on the back if I could easily find the wheels for it with a good marriage with what is up front.

Japan Racing makes a good looking wheel in their JR15 (that weighs in at just over 19 LBS. for a 16x9), but not in 5X108 however they can be custom drilled. They offer both 16x8 and 16x9 in the same style which is rare as hen's teeth.

Ronal makes a similar setup but only offers 16x6.5 and 16x7.5 in a wheel that's not too bad looking with a van load rating. A little skinny for my tastes and while the cost per wheel is not that bad, by the time you pay shipping and duties the cost creeps up.

American Racing offers some custom drilling but their offsets tend to be so low that it creates some potential problems with the front. And over 2 grand for a set is a little hard to swallow. 

[G B L]

Great conversation. There is one more thing.  When out the door price is a top concern then the more parts you have the more chance for cheap parts that need replacement early.

[Beta Don]

The rear suspension on the Gen 2 TC's is nothing like the 'solid axle' you'll find under other Ford trucks  -  It's actually much closer to a true IRS set-up than a 'solid axle'.  There are no heavy leaf springs and the shock is outboard adjacent to the wheel where it belongs as opposed to inside the leaf spring as it is on a truck.   Even the U channel which serves as the 'axle' which connects the wheels is not part of the unsprung weight.  For a vehicle designed primarily for hauling a large amount of cargo, the rear suspension is actually pretty doggone modern and quite lightweight.  If you admire the way an F-150 handles the rough roads, you're going to love the TC

 

Don

[OLDSCHOOLFOOL]

15 minutes ago, Beta Don said:

The rear suspension on the Gen 2 TC's is nothing like the 'solid axle' you'll find under other Ford trucks  -  It's actually much closer to a true IRS set-up than a 'solid axle'.  There are no heavy leaf springs and the shock is outboard adjacent to the wheel where it belongs as opposed to inside the leaf spring as it is on a truck.   Even the U channel which serves as the 'axle' which connects the wheels is not part of the unsprung weight.  For a vehicle designed primarily for hauling a large amount of cargo, the rear suspension is actually pretty doggone modern and quite lightweight.  If you admire the way an F-150 handles the rough roads, you're going to love the TC

 

Don

 

My wife is in general not too picky about what she drives. I have noticed her "creating" reasons to drive the TC. She says it drives awesome and stops even better. She is right.

I would still trade those big brakes for the ability to run 15s though.

[OLDSCHOOLFOOL]

Dropped by the local tire shop this morning to ask about mounting the 275/45R16s on 7 inch rims. After explaining all the dimensions (which I already knew) the owner says they will try it but there might be a problem getting them to seat. The second guy sitting there never looked up the whole time simply says, "We'll get them on there." Second guy is the one who does the real work. I love those guys. They have been around for quite a while and have probably seen every odd-ball combination you can think of. Some of them for me.

[Beta Don]

I have no doubt that "they can get them on there" but they're not going to perform very well  -  That size tire belongs on a 8.5 to 10.5 inch rim and squeezing them on such a narrow rim won't allow the tread to stay flat all across the width, so you're very likely to wear out the center before you wear out the edges

 

Also, unless you are using a similar size (diameter) tire on the front , using a 7%+ too large tire on the rear is going to cause the traction control computer fits  -  You'll need to turn that off

 

But . . . . it will probably look cool as hell  -  What else matters??

 

Don

[OLDSCHOOLFOOL]

59 minutes ago, Beta Don said:

But . . . . it will probably look cool as hell  -  What else matters??

 

Don

 

There it is...........not a bloody thing! Its all just for fun.

 

I understand its going to crown a bit and may be able to compensate a little with air pressure which will probably cause me issues with the TPMS. These wheels came with the sensors in them and I'm going to see if they work or not.  No big deal if they don't because I'm not running the sensors now with the 245s. I don't know if the sensors are different or not. Bonus if they work......no loss if they don't.

 

Looking to put 225/50R16s on the front which is only a -1.6% drop in the front and +1.6% in the rear, for a total span of about 3.2% between them. Using the 215/55R16 stock as a baseline. Curious as to where you arrive at 7%? Is that the basic limit or do I possibly have my numbers wrong? Maybe I am misunderstanding what you're saying.

 

Offset in the front won't be a problem, but I will have to space it out in the back to stay off the shocks.

[williaty]

1 hour ago, Beta Don said:

Also, unless you are using a similar size (diameter) tire on the front , using a 7%+ too large tire on the rear is going to cause the traction control computer fits  -  You'll need to turn that off
 

The Traction Control System is primarily looking at wheel speed imbalances between the front two wheels (I did some testing to confirm this). The TCS is the one you can turn off via the menu system in the dash. The Vehicle Stability Control system is looking at what all 4 wheels are doing, plus steering angle, yaw angle, and a bunch of other stuff and, sadly, it can't be turned off in the Connect. I really, really wish it could be because it's a ball and chain around the ankle of a competent driver in the snow :(

 

That said, I don't know if a 7% difference will be enough to piss it off. You can get a 7% difference in effective rolling circumference just by dicking with the tire inflation so it may be able to ignore things that small.

[Beta Don]

The owners manual doesn't seem to think that's what it's for  -  Under 'Principal of Operation' it says "If the wheels spin when accelerating on slippery or loose surfaces, the system reduces engine power in order to increase traction"  -  Wheels, not one front wheel vs the other

 

The computer knows the front wheels are slipping because they're comparing the rotation speed of the front vs the rear wheels

 

I don't know about Ford, but on my electric cars, a 2% change in tire size front to rear will disable both traction control and regenerative braking because the computer thinks the drive axle is traction impaired.  At any rate, with a 7% change it would probably be a good idea to disable that feature

 

New cars are sure much pickier about such things than 'old school' cars

 

Don

Edited February 9, 2018 by Beta Don

[williaty]

41 minutes ago, Beta Don said:

The owners manual doesn't seem to think that's what it's for  -  Under 'Principal of Operation' it says "If the wheels spin when accelerating on slippery or loose surfaces, the system reduces engine power in order to increase traction"  -  Wheels, not one front wheel vs the other

 

The computer knows the front wheels are slipping because they're comparing the rotation speed of the front vs the rear wheels

 

I don't know about Ford, but on my electric cars, a 2% change in tire size front to rear will disable both traction control and regenerative braking because the computer thinks the drive axle is traction impaired.  At any rate, with a 7% change it would probably be a good idea to disable that feature

 

New cars are sure much pickier about such things than 'old school' cars

 

Don

The owner's manual is never a reliable source for technical information. It wasn't written by an engineer and wasn't even written by anyone who knows what an engineer is.

 

I tested the TCS by putting the front end of the car on the dyno and it had no problem with the rear tires not rolling when the front wheels turned. No activation of the TCS system. I added a jack to one side to reduce the contact pressure on one front wheel and the TCS system freaked out the moment the lifted wheel started to slip. Ergo, it doesn't care what the rear wheels are doing but it cares intensely about the front. If I have to deal with the stupid crap the computer wants to do, I'll at least go to significant effort to map out exactly what it cares about and doesn't care about. Interestingly, I bumped the brake pedal while doing this and the ABS/VSC system instantly freaked out because it thought the rear end was locked up and sliding.

 

I'm not at all surprised an electric or hybrid vehicle would do that. They're NOTORIOUS for being easy to get stuck because the moment one wheel slightly diverges from the others the whole thing shuts down and cries. We had a guy try to use his Prius for road rallies here. He kept getting stuck because putting the right side wheels off the road when he pulled over for checkpoints was often enough to freak out the computer and make the car refuse to move itself. It was ridiculous because you could push the car by hand about 6" to get all 4 wheels loaded evenly again and suddenly the car was happy.

Edited February 9, 2018 by williaty

[G B L]

The computer is programed by people who do not think you should drive in the snow.  With out the ability to shut off the Traction Control the TC would be almost useless in the snow.

If the programmer was  not constrained  by the lawyers there could be a snow mode that would make the Traction Control into a competent positraction  aide . 

[mrtn]

8 hours ago, G B L said:

The computer is programed by people who do not think you should drive in the snow. 

 

Probably the Spaniards.

"While you're at it, program the winter stability control as well."

"LOL, wat".

[OLDSCHOOLFOOL]

Round 4: Went with 245s all around again. Only regret is that the rear tires just aren't wide enough. I didn't mount the 275s but did put 295s on them but they were pinched a bit too much. Could have run them though. Next time.

 

[mrtn]

Did you paint the letters yourself?

[OLDSCHOOLFOOL]

34 minutes ago, mrtn said:

Did you paint the letters yourself?

Yes, you cannot buy white letter 16s that small. When I grow up I think I want to be a professional tire painter.........or a brain surgeon........or a fry cook.

[mrtn]

I would love to find RWL tires but there are less and less available as time goes on.

[OLDSCHOOLFOOL]

Marketing only wants sell what they THINK 90% of the customers want to buy. Salespersons selling a product they know nothing about. Just counting beans.