Spare Tire Diameters w/Posi Unit

[Jon69RagTop]

I'm trying to organize a spare tire combo unit that works with the big brake set-up I have. I've purchased a 2005-07 GTO spare, and with a 1" wheel adapter the rim fits over brakes both front and back. (KORE 3) The wheels adapter is barely necessary, and some might hack on the caliper but I'm not.

The temporary tires diameter is 25.375, but the rear tires on my car are 26.5" tall> I've found a M H front drag skinny which fits the GTO rim-185/55R17, and the diameter of this tire is 26.0.

My question is would this diameter be close enough, and not create stress for the posi-unit given the need for temporary driving in case of a flat tire?

I'd appreciate any other ideas or feedback.

Thanks

[ProTouring442]

Frankly, I do not plan on running a spare. 1) They are heavy, 2) The posi problem, 3) they take up a lot of room in the trunk.

Instead, I will carry 2 cans of good Fix-A-Flat, and a connection from my on-board air compressor. If you do not have an air source, I would look at a couple of the GM nitrogen canisters. You can frequently get them from the junkyard out of a car with a collapsible spare.

Shiny Side Up!
Bill

[oestek]

^^^what he said, and a AAA card!

[streetk14]

If you are set on having a spare, that is the way to go. Would 1/2" of tire diameter be a problem with the limited slip? Hard to say, but I'd think it would be ok if it was ONLY to get you to a tire shop, etc. I thought about going this route as well, but then thought about the trunk space I'd lose, the weight and the fact that the spare isn't going to work too well with my huge tires.

Another thing you could look into would be an ///M mobility kit from BMW. You could either buy one new or get one out of a wrecked M3 or M5. It is a neat and compact system that includes an electric air pump that injects sealant into the tire. M cars do not have any type of spare tire, so you either use the sealant or call a flat-bed.

I think I'm gonna get one for my '67.

[novaderrik]

having a spare tire that is a little bit shorter than the regular tire won't hurt anything- the diff will just think you are driving in a big circle until you get the proper tire back on.
without a spare, you will have all sorts of problems if you have a tire decide to really blow out and it won't matter how good your fix-a-flat or onboard air compressor is.

[ProTouring442]

having a spare tire that is a little bit shorter than the regular tire won't hurt anything- the diff will just think you are driving in a big circle until you get the proper tire back on.
without a spare, you will have all sorts of problems if you have a tire decide to really blow out and it won't matter how good your fix-a-flat or onboard air compressor is.

yes, but driving for any real length of time with the posi slipping can destroy the clutches if it is a clutch type. If it is a locker, you will probably be OK, but it will be a very interesting drive as the car first pulls to one side, then "clank!" the unit unlocks and the car pulls to the other side, then back again.

You make a good point concerning a blow out, but how often does that happen any more? The last time I had a blow out was over 15 years ago! Still, in the event of a blow out, that's what they make cell phones for!

Shiny Side Up!
Bill

[Jon69RagTop]

Thanks for your feedback guys. Regarding weight, the combination I'm putting together is not that heavy, under 50lbs with jack included. Also the GTO rim is only 5 inches wide, so the dimension of trunk space is rather minimal.

I will only carry the spare for road trips, when heading down the interstate between corn fields. That's a lonely place to be waiting for a flat-bed. Hell those small towns might not even have a flatbed, and the thought of them using the old style lift belts scares me to death.

I do apprecaite the different points of view, which is why I posted here. Hope to see some of you on the Power Tour.

Jonathan

[Rhino]

In my 4th Gen Camaro, the manual states to put the spare on the front, put the good front on the back, then drive wherever you're needing to go.

As long as your front and rear tires are of a similar size, this works well.
However, I realize that this isn't an option for a lot of the cars we see here. I'm choosing my wheel/tire combo with this process in mind.

[b-man]

I'm running 18X9s all the way around with C6 Z06 brakes, I really had no other option but to buy a 5th 18X9 for a spare. Not a bad way to go, at least I'll have a spare rim if I happen to damage one. My '64 Tempest has plenty of room in the trunk for a full-size spare, I know the F-body guys aren't as lucky.

I'm running 275/40s in the back (listed at 26.6" tall) and 245/40s in the front (25.7" tall).

For a spare tire I chose a 245/45 that's listed at 26.7" tall. In actuality it's the same exact height as my 275/40s, they both measure very close to 26.75" unloaded.

I have enough clearance to use the 245/45 up front as a spare, but maybe not enough room to use that size up front all the time as it may rub in tighter corners. If I do in fact find that the 245/45 seems to be a good fit, I'll buy 2 new 245/45s for the front the next time I need new front tires. I haven't been able to drive the car yet to see exactly what's what.

A can of fix-a-flat will work in a pinch I suppose (anything beats being stranded), but it will eat your flat tire from the inside and ruin it. Any chance of patching that flat tire and using it again will be lost, you could have saved your 'still good' flat tire by having a spare tire setup for your car instead.

[GetMore]

Jonathan, most wreckers use something called a "wheel lift" instead of that belt sling. They lift one end of the car by the tires, which places almost no stress on the car.
It really is a toss-up as to what method is better for most cars.
If a car it towed for long distances and/or high speeds then the drive wheels should not be on the ground unless the driveshaft is disconnected. So, if the car is lowered or has a low air dam you probably wouldn't wheel lift it from the rear. However, winching that same car up onto a flatbed could do some damage to the air dam or valence, since the winch is always higher than the vehicle is and you've got to make the transition from the car being on the ground to it being on the bed. Once it's on the bed there usually isn't a clearance problem. If you've got aluminum control arms then the winch can not be hooked to them and another hook point must be found. This isn't an issue on most GM vehicles, but can be on others. Obviously most late models have taken this into consideration and it's not an issue.

[zman1969]

there is always RFT or run flat tires if not the spare will be OK must of us car guys (I think) know its for temporary use only not for 2-3 months until they pop from being worn out from never getting it fixed or replaced. - Oh BTW I put 2 late F-body spares on the back of my minitubbed T/A clone as roll arounds (due to the LS1 rear discs) and thay look flat silly with like 6-8" of room from them to the fenders. Good luck with your project!

[ProTouring442]

A can of fix-a-flat will work in a pinch I suppose (anything beats being stranded), but it will eat your flat tire from the inside and ruin it. Any chance of patching that flat tire and using it again will be lost, you could have saved your 'still good' flat tire by having a spare tire setup for your car instead.

GM must not think so as they utilize a can of fix-a-flat as the spare tire in the new Corvettes!

Further, back when I was a mechanic, we repaired many a tire previously sealed with fix-a-flat. Do however make sure that the tire repair product you use does not contain an inflammable gas as a propellant.

Shiny Side Up!
Bill