Out of curiosity, why are most space-saver spare tires limited to such low speeds? I think the one that came with my Civic says not to exceed 50 or 55 mph. Is it primarily due to the handling difference when the spare is installed or is it actually because of technical limitations of the tires themselves?
Speed restriction on space-saver spares
- Thread starter rationull
- Start date
- Status
Drive fast on those and BAM!
They overheat and shread. (big time)
Seen it hundreds of times. Esp in the Summer.
Bill
They overheat and shread. (big time)
Seen it hundreds of times. Esp in the Summer.
Bill
The technical explanation is this:
There are 3 things that considered when setting up a load table (for a given tire size, the load vs inflation pressure relationship.):
Speed, road surface uniformity, intended length of service
In the case of minispares, the intended length of service is short, so they allow a lot of deflection (load compared with the inflation pressure). This generates heat, so in order to keep the physical size down, they also restrict the speed.
If you look up fatigue in Wikipedia, they give a pretty good rundown on the issue. In particular, pay attention to the S-N curve. If you have a lot of stress, then you can't cycle something very many times. And if you want something to cycle a lot, then you have to reduce the stress. in tires, that means deflection. BTW, 50K miles is about 60 million cycles. (6X10^7)
In other words, they are designed specifically that way.
For aircraft tires, while the speed is high, the speed is short duration. Runways are also very smooth. And while a failure is very bad, the tire doesn't operate very long.
Trucks on the other hand go a very long way when in operation, and the roadways aren't always smooth. So deflection is relativelt small. This is one of the reasons why you'll see good rolling resistance values for truck tires - compared to passenger car tires, the load is sizewise smaller.
There are 3 things that considered when setting up a load table (for a given tire size, the load vs inflation pressure relationship.):
Speed, road surface uniformity, intended length of service
In the case of minispares, the intended length of service is short, so they allow a lot of deflection (load compared with the inflation pressure). This generates heat, so in order to keep the physical size down, they also restrict the speed.
If you look up fatigue in Wikipedia, they give a pretty good rundown on the issue. In particular, pay attention to the S-N curve. If you have a lot of stress, then you can't cycle something very many times. And if you want something to cycle a lot, then you have to reduce the stress. in tires, that means deflection. BTW, 50K miles is about 60 million cycles. (6X10^7)
In other words, they are designed specifically that way.
For aircraft tires, while the speed is high, the speed is short duration. Runways are also very smooth. And while a failure is very bad, the tire doesn't operate very long.
Trucks on the other hand go a very long way when in operation, and the roadways aren't always smooth. So deflection is relativelt small. This is one of the reasons why you'll see good rolling resistance values for truck tires - compared to passenger car tires, the load is sizewise smaller.
Also on this subject, if you must use your space-saver spare, do not mount it on an axle with an active differential.
For example, if the vehicle is front wheel drive and you have a flat on one of the front wheels, better to remove a rear wheel, mount the S-S'er, and then put the full size on the front. It will prevent damage to the differential.
Still, get the full size repaired ASAP.
For example, if the vehicle is front wheel drive and you have a flat on one of the front wheels, better to remove a rear wheel, mount the S-S'er, and then put the full size on the front. It will prevent damage to the differential.
Still, get the full size repaired ASAP.
"For example, if the vehicle is front wheel drive and you have a flat on one of the front wheels, better to remove a rear wheel, mount the S-S'er, and then put the full size on the front. It will prevent damage to the differential."
This ridiculousness is actually in the S2000 manual. One of your rear
tires blown? You're in for a real treat.
This ridiculousness is actually in the S2000 manual. One of your rear
True story--- we were moving from CA to TX, and were stopped at a truck stop to let the dog out and go poop. Lady drives up with an old Mark VIII with an absolutely destroyed tire. I offer to help her change to her spare, so she could make it 30 miles down the road to El Paso. Her left-rear was shredded, so I offered to unpack my larger jack and move one of the front tires to the back to prevent any issues with the differential. She said no, it'll be fine.
Get the spare on the rear, and check her other pressures--other tires were at 50-60psi, "'cause that's where my husband set them to get good gas mileage" (it was 100+ degrees out, no wonder those old tires blew!).
They drive off, we follow about 15 minutes later. We catch up to them in El Paso, stranded on the side of the road, blown differential.....oh well.
Don't speed and don't put donuts on your drive wheels.
Get the spare on the rear, and check her other pressures--other tires were at 50-60psi, "'cause that's where my husband set them to get good gas mileage" (it was 100+ degrees out, no wonder those old tires blew!).
They drive off, we follow about 15 minutes later. We catch up to them in El Paso, stranded on the side of the road, blown differential.....oh well.
Don't speed and don't put donuts on your drive wheels.
Kestas
Staff member
I always thought the speed limitation with the donut spare was bacause handling was compromised, and unsafe for emergency maneuvers at higher speeds.
Interesting. I don't think I remember seeing anything in the manual for my car regarding not putting the spare on the drive wheels (front wheels) but I could've just missed it.
BTW, I'm not using my space-saver right now, just got curious. I did use it once when I noticed a puncture at home, to drive into town and to the tire shop, about 12 miles total.
It didn't occur to me that they could be designed for shorter distance driven before failure, too. How do you tell if a SS spare is still fit for service. Still just go by treadwear and tire age?
BTW, I'm not using my space-saver right now, just got curious. I did use it once when I noticed a puncture at home, to drive into town and to the tire shop, about 12 miles total.
It didn't occur to me that they could be designed for shorter distance driven before failure, too. How do you tell if a SS spare is still fit for service. Still just go by treadwear and tire age?
Originally Posted By: Kestas
I always thought the speed limitation with the donut spare was bacause handling was compromised, and unsafe for emergency maneuvers at higher speeds.
ever work in retail where you could give the real reason, or a quick reason that people wont question. thats what i would use for option 2 when people ask.
I always thought the speed limitation with the donut spare was bacause handling was compromised, and unsafe for emergency maneuvers at higher speeds.
ever work in retail where you could give the real reason, or a quick reason that people wont question. thats what i would use for option 2 when people ask.
Originally Posted By: paul246
Also on this subject, if you must use your space-saver spare, do not mount it on an axle with an active differential.
For example, if the vehicle is front wheel drive and you have a flat on one of the front wheels, better to remove a rear wheel, mount the S-S'er, and then put the full size on the front. It will prevent damage to the differential.
Still, get the full size repaired ASAP.
2004 Subaru Impreza WRX w/ 5-sp manual transmission. Obviously all-wheel drive and allegedly a 50/50 power split front/rear. Comes with a compact spare. No FWD fuse to electronically force the transmission into front-wheel drive mode as with some Subaru automatic transmissions.
From what I understand, differential wear isn't much of an issue if the vehicle travels under the 50 MPH recommended speed for using the spare.
Also on this subject, if you must use your space-saver spare, do not mount it on an axle with an active differential.
For example, if the vehicle is front wheel drive and you have a flat on one of the front wheels, better to remove a rear wheel, mount the S-S'er, and then put the full size on the front. It will prevent damage to the differential.
Still, get the full size repaired ASAP.
2004 Subaru Impreza WRX w/ 5-sp manual transmission. Obviously all-wheel drive and allegedly a 50/50 power split front/rear. Comes with a compact spare. No FWD fuse to electronically force the transmission into front-wheel drive mode as with some Subaru automatic transmissions.
From what I understand, differential wear isn't much of an issue if the vehicle travels under the 50 MPH recommended speed for using the spare.
- Joined
- Jun 2, 2003
- Messages
- 23,587
My A4 quattro came with a donut. There's no warning regarding differential wear when using the donut. It only says the donut is for temporary use and that 50 mph are not to be exceeded. The manual also advises to avoid unnecessary hard acceleration, breaking and cornering.
Both the Subaru and Audi get the repair done quickly.
My Outback is auto and they put on new tire on the left rear. It was the same size and brand model. Drove like [censored] and AWD light came on within 5 miles. Pulled the fuse and all was ok till I replaced all 4.
The new tire was 1/2 inch total out. The AWD systems are very picky about all tires being the same when in AWD.
Bill
My Outback is auto and they put on new tire on the left rear. It was the same size and brand model. Drove like [censored] and AWD light came on within 5 miles. Pulled the fuse and all was ok till I replaced all 4.
The new tire was 1/2 inch total out. The AWD systems are very picky about all tires being the same when in AWD.
Bill
- Joined
- Jun 2, 2003
- Messages
- 23,587
I drove the A4 with the donut mounted for at least 80 miles without issues. I did however get a full size spare after that incident, because driving around with a donut is embarrassing and unnecessary.
On my Tribute, the "temporal" space-saver spare is the same size (diameter) as the other tires, just a smaller tire with skinnier width and bigger overall steel wheel size. I guess they do this for the AWD.
While I wouldn't drive to Alaska on it, it doesn't look as cr@ppy as the tiny "donut" style on cars. The spare tire well can hold a full size, but the temp spare is a heck of a lot lighter=better fuel economy over the life of the vehicle.
While I wouldn't drive to Alaska on it, it doesn't look as cr@ppy as the tiny "donut" style on cars. The spare tire well can hold a full size, but the temp spare is a heck of a lot lighter=better fuel economy over the life of the vehicle.
- Joined
- Jun 2, 2003
- Messages
- 23,587
I don't remember if the donut had the same circumference as the regular tire. I suppose so, because Audi says (not in the manual!) all tires' circumference must at all times remain within 3% of each other. I believe I do remember that the donut was just as tight a fit in the spare tire well. I did only have to remove some EVA foam spacers from the bottom of the well.
Kestas
Staff member
Twice on interstate trips (loaded car) I've had tires that fell apart and needed replacement with a donut spare. One I drove for four hours, the other I drove 700 miles before proper service. Of course I made sure the donut was on the non-drive axle.
I heard of one compact car that was driven in the "lap around America" with donut spares to prove the durability of these tires.
I heard of one compact car that was driven in the "lap around America" with donut spares to prove the durability of these tires.
Originally Posted By: Bill in Utah
Both the Subaru and Audi get the repair done quickly.
My Outback is auto and they put on new tire on the left rear. It was the same size and brand model. Drove like [censored] and AWD light came on within 5 miles. Pulled the fuse and all was ok till I replaced all 4.
The new tire was 1/2 inch total out. The AWD systems are very picky about all tires being the same when in AWD.
Bill
The automatics (esp the 4EAT and 5 EAT) are supposed to be extremely sensitive to tire circumference. It doesn't have a center diff per se. Something about going batty when it's constantly sensing differences in wheel speed. It should be able to handle occasional differences like in low traction conditions.
I believe the manual transmission versions use simpler and more robust mechanical diffs. Perhaps not as technologically advanced, but they get the job done.
Both the Subaru and Audi get the repair done quickly.
My Outback is auto and they put on new tire on the left rear. It was the same size and brand model. Drove like [censored] and AWD light came on within 5 miles. Pulled the fuse and all was ok till I replaced all 4.
The new tire was 1/2 inch total out. The AWD systems are very picky about all tires being the same when in AWD.
Bill
The automatics (esp the 4EAT and 5 EAT) are supposed to be extremely sensitive to tire circumference. It doesn't have a center diff per se. Something about going batty when it's constantly sensing differences in wheel speed. It should be able to handle occasional differences like in low traction conditions.
I believe the manual transmission versions use simpler and more robust mechanical diffs. Perhaps not as technologically advanced, but they get the job done.
Generic Ford temporary tire boilerplate from the manual.
Note the difference between the "T-type" mini spare and the "Full-size disimilar spare" with and without label.
///
A dissimilar spare tire/wheel is defined as a spare tire and/or wheel that is different in brand, size or appearance from the road tires and wheels and can be one of three types:
1. T-type mini-spare: This spare tire begins with the letter “T” for tire size and may have “Temporary Use Only” molded in the sidewall
2. Full-size dissimilar spare with label on wheel: This spare tire has a label on the wheel that states: “THIS TIRE AND WHEEL FOR TEMPORARY USE ONLY”
When driving with one of the dissimilar spare tires listed above, do not:
² Exceed 50 mph (80 km/h)
² Load the vehicle beyond maximum vehicle load rating listed on the Safety Compliance Label
² Tow a trailer
² Use snow chains on the end of the vehicle with the dissimilar spare tire
² Use more than one dissimilar spare tire at a time
² Use commercial car washing equipment
² Try to repair the dissimilar spare tire
Use of one of the dissimilar spare tires listed above at any one wheel location can lead to impairment of the following:
² Handling, stability and braking performance
² Comfort and noise
² Ground clearance and parking at curbs
² Winter weather driving capability
² Wet weather driving capability
For vehicles equipped with 4WD, it is not recommended that the vehicle be operated in 4WD modes with a temporary emergency spare tire. If 4WD operation is necessary, do not operate above speeds of 10 mph (16km/h) or for distances above 50 miles (80 km).
3. Full-size dissimilar spare without label on wheel
When driving with the full-size dissimilar spare tire/wheel, do not:
² Exceed 70 mph (113 km/h)
² Use more than one dissimilar spare tire/wheel at a time
² Use commercial car washing equipment
² Use snow chains on the end of the vehicle with the dissimilar spare tire/wheel
///
Note the difference between the "T-type" mini spare and the "Full-size disimilar spare" with and without label.
///
A dissimilar spare tire/wheel is defined as a spare tire and/or wheel that is different in brand, size or appearance from the road tires and wheels and can be one of three types:
1. T-type mini-spare: This spare tire begins with the letter “T” for tire size and may have “Temporary Use Only” molded in the sidewall
2. Full-size dissimilar spare with label on wheel: This spare tire has a label on the wheel that states: “THIS TIRE AND WHEEL FOR TEMPORARY USE ONLY”
When driving with one of the dissimilar spare tires listed above, do not:
² Exceed 50 mph (80 km/h)
² Load the vehicle beyond maximum vehicle load rating listed on the Safety Compliance Label
² Tow a trailer
² Use snow chains on the end of the vehicle with the dissimilar spare tire
² Use more than one dissimilar spare tire at a time
² Use commercial car washing equipment
² Try to repair the dissimilar spare tire
Use of one of the dissimilar spare tires listed above at any one wheel location can lead to impairment of the following:
² Handling, stability and braking performance
² Comfort and noise
² Ground clearance and parking at curbs
² Winter weather driving capability
² Wet weather driving capability
For vehicles equipped with 4WD, it is not recommended that the vehicle be operated in 4WD modes with a temporary emergency spare tire. If 4WD operation is necessary, do not operate above speeds of 10 mph (16km/h) or for distances above 50 miles (80 km).
3. Full-size dissimilar spare without label on wheel
When driving with the full-size dissimilar spare tire/wheel, do not:
² Exceed 70 mph (113 km/h)
² Use more than one dissimilar spare tire/wheel at a time
² Use commercial car washing equipment
² Use snow chains on the end of the vehicle with the dissimilar spare tire/wheel
///
- Status
