Should I Go to Court for a Speeding Ticket

[That Guy]

I'm not talking about wheel size because I don't know, but the whole mini spare has a much smaller diameter and will therefore spin at a much greater RPM than the standard tires on the vehicle.

OK, so that is what you're saying.... What I am saying is that ^this^ is not the way it is supposed to work. The vehicle manufacturer(s) is not likely to equip a vehicle with a spare (even a compact spare) that isn't designed to support the vehicle at height as the others and one that isn't going to spin at the same rate as the other regular use tires on the vehicle. So what they do is (regardless of the size of the wheel (the metal part)) the size of the outside diameter of the rubber tire matches the outside diameter of the regular use of the tires that come with the vehicle.

In other words:



The width of the tire actually is much smaller (and hence the use of "compact" in the way its described) where as it will support the vehicle at the same height as the other regular use tires, and it would spin at the same rate and hence = no speed variation.

[Mr. Knowitall]

Compare and contrast.

The tiny spares, so-called "compact temporary spares"... the instructions I've seen typically caution drivers to keep the speed low (e.g., no more than 30 MPH) and to drive no more than @50 miles. They're supposed to be inflated to about 60 PSI, and unless you keep on top of that odds are they're going to be well below that pressure when you need them. I had one of these absurd spares in a rental car once, and had to drive thirty miles on it to one of their storefronts to get a different vehicle. Few would want to drive 50+ MPH on one of these tires, especially if it's underinflated, even fewer in their own car given what could happen with a significant bump or what it could do to the differential.

I've had to drive on them a few times. Not that other people's experiences can't differ, but in mine the speedometer always worked.

[cmre3456]

Compare and contrast.

-snip-

From the link:

"The smaller-diameter tire can put a lot of stress on your differential."

"The differential has a tricky job. It transmits engine power to the wheels from the transmission, but it also lets the left and right wheels turn at different speeds. This is essential for cornering. In a turn, the path of the inside wheel is shorter than that of the outside wheel, which means they travel at different speeds. When your car is driving in a straight line, the differential isn't in use and there's little wear and tear on its gears and bearings. But because the spare is smaller than the opposing wheel on the same axle, it must turn faster to keep up with the speed of the car, making the differential work to account for the variation. It's as if the car is constantly in a turn. Leave the spare on long enough and the grease lubricating the differential will begin to break down, accelerating wear between the gears and the clutch plates if it's a limited-slip differential. For all these reasons, manufacturers suggest keeping speeds below 50 mph and using the spare tire only for limited distances if possible..."

I believe that's about what I said. Being an old hot rodder, I've rebuilt more than my share of differentials including buying and installing limited slip 3rd members. Those put traction to both wheels under hard acceleration, whereas with a "normal" differential, only one wheel will spin - the one with the least traction. Power doesn't then go to the other wheel. "Least traction" could be caused by oil or gravel on the pavement, the condition of the tires, or any number of factors. BUT, if for any reason one tire breaks loose and spins, the other will quit pulling.

This is why I bought my pickup with a limited slip rear end. When off road, if one tire wants to just spin, you're stuck until you put it in 4 wheel drive. If one tire has insufficient traction to move the pickup, the other would not pull without limited slip.

Obviously if you're drag racing, you want full power and traction to both tires. As a kid who likes to go to the strip, you're going to want to put that positraction 3rd member in there.

Even a normal differential is designed to account for cornering so the wheels can turn at different speeds. It isn't designed to do that for long periods at higher speeds due to different diameter tires.

----------------------

I should add that the steering axle should never be limited slip. That would be dangerous on slick roads. You'd step on the gas and both wheels would pull and spin and you'd lose all steering. If just one pulls and spins but the other isn't spinning, you still have steering traction in that idle wheel. Even with limited slip on the back of my pickup it can be dangerous on a slick road. Step on the gas and both rear wheels spin and the truck wants to go sideways. If only one spun, the idle wheel would be more likely to go straight.

[That Guy]

-snip-

From the link:
[I]
"The smaller-diameter tire can put a lot of stress on your differential."

SNIP back at you!

So again, under circumstances where the car manufacturer could not control how that buyer is gong to use his/her slightly smaller compact spare, and could not dictate if it is driven for 7 1/2 miles to the tire repair shop or 75 miles on the way home from a fishing trip, whether it will get driven at 30mph 0r 40mph or 70mph and for a car that is likely still under warranty for a minimum of 50k miles on some manufacturers models and up to 100k mines for others, would you risk allow that customer the slimmest opportunity to demand a replacement differential?

I know I wouldn't!

I'll still stick to my concept of OEM <===> same diameter, and hence my comment that I though it was odd that the OP had a different size.

I believe that's about what I said. Being an old hot rodder, I've rebuilt more than my share of differentials including buying and installing limited slip 3rd members. Those put traction to both wheels under hard acceleration, whereas with a "normal" differential, only one wheel will spin - the one with the least traction. Power doesn't then go to the other wheel. "Least traction" could be caused by oil or gravel on the pavement, the condition of the tires, or any number of factors. BUT, if for any reason one tire breaks loose and spins, the other will quit pulling.

This is why I bought my pickup with a limited slip rear end. When off road, if one tire wants to just spin, you're stuck until you put it in 4 wheel drive. If one tire has insufficient traction to move the pickup, the other would not pull without limited slip.

Obviously if you're drag racing, you want full power and traction to both tires. As a kid who likes to go to the strip, you're going to want to put that positraction 3rd member in there.

Even a normal differential is designed to account for cornering so the wheels can turn at different speeds. It isn't designed to do that for long periods at higher speeds due to different diameter tires.

I should have snipped that too... But that is some great info... OK, OK... I'm just saying that! I think you lost track of the topic at hand so which part of it is discussing a smaller temporary tire?

I should add that the steering axle should never be limited slip. That would be dangerous on slick roads. You'd step on the gas and both wheels would pull and spin and you'd lose all steering. If just one pulls and spins but the other isn't spinning, you still have steering traction in that idle wheel. Even with limited slip on the back of my pickup it can be dangerous on a slick road. Step on the gas and both rear wheels spin and the truck wants to go sideways. If only one spun, the idle wheel would be more likely to go straight.

LSD is for cars with a little OOMF! And with or without "LSD" you wouldn't want a car with oomf to have front wheel drive, anyway!

[cmre3456]

I should have snipped that too... But that is some great info... OK, OK... I'm just saying that! I think you lost track of the topic at hand so which part of it is discussing a smaller temporary tire?

Just don't get me started about hot rods, Harleys, antique Schwinn bicycles, guns or computers or we'll be here all day, LOL.

LSD is for cars with a little OOMF! And with or without "LSD" you wouldn't want a car with oomf to have front wheel drive, anyway!

So which part of that is discussing "Should I Go to Court for a Speeding Ticket?"