Matching Spare Tire Diameter - Cadillac ELR

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Jun 17, 2013
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Texas
Picked up a spare tire for my dad's 2014 Cadillac ELR off of a Cadillac DTS. The diameter of the spare from the DTS (125/70/17 and 23.9") is significantly smaller than the diameter of the tire/wheel combo on the ELR (245/40/20 and 27.7")

I can find new spare tires that will mount just fine to the spare wheel that more closely match the diameter of the normal tire/wheel setup from Tirerack. What I'm wondering is how close I should get the diameter to match?? There's two sizes that are within 1% of the standard diameter but the size that is closest is currently back ordered through Tirerack so I may have to go with the other size. Since it's within 1%, don't know if it'll matter anyway.
 
Will the bigger spare still fit in the trunk well? Unless you have a posi-traction differential there will be no harm running the smaller tire diameter. You should run it slower and get tire fixed ASAP.
 
ELR... that's the Fancy Volt right?

Will the bigger spare still fit in the trunk well? Unless you have a posi-traction differential there will be no harm running the smaller tire diameter. You should run it slower and get tire fixed ASAP.
I know my brother, for his Volt got an extra Volt wheel, and tire and keeps it in a tire sleeve thingy in the back seat. ( no factory spare, so no tire well)
 
its almost 15% smaller being that far off you may have issues with abs/sensors and it shouldnt be on a driven wheel. is the elr fwd rwd or awd?

I wouldnt run it myself.
 
You need to have the spare the exact same diameter as the original wheels or very very close. If you are only 1% different you should be ok especially if you drive a short distance in order to get a repair or replacement in case of emergencies. I run good tires on my vehicles and have not had an on the road flat for over 30 years. Slow leaks yes but a complete flat has not happened. My Corvette doesn't even have a spare tire. At a 1% difference I would think you could drive a 100 miles or more without damaging your vehicle but I wouldn't drive much further than that.
 
If you ever get a flat front tire and need to use the spare, just put the spare on the rear, and move a good rear tire to the front. You will have no problem as long as the drive wheels are the correct size.

And of course, if the flat is in the back, you can use the spare back there with no problem.

Will a full-size spare fit in the ELR trunk? :unsure:

its almost 15% smaller being that far off you may have issues with abs/sensors and it shouldnt be on a driven wheel. is the elr fwd rwd or awd?

I wouldnt run it myself.

It's FWD
 
If you ever get a flat front tire and need to use the spare, just put the spare on the rear, and move a good rear tire to the front. You will have no problem as long as the drive wheels are the correct size.

And of course, if the flat is in the back, you can use the spare back there with no problem.

Will a full-size spare fit in the ELR trunk? :unsure:



It's FWD
then I certainly wouldnt ever use it on the front. might be ok in the back with only odd braking behavior etc.
 
Will the bigger spare still fit in the trunk well? Unless you have a posi-traction differential there will be no harm running the smaller tire diameter. You should run it slower and get tire fixed ASAP.
The spare is going to have to live in a tire bag in the trunk regardless of tire size. There's no room under the trunk floor sadly. My dad uses the vehicle pretty much solely as a commuter so having some trunk space taken up isn't too big of a deal.
 
ELR... that's the Fancy Volt right?


I know my brother, for his Volt got an extra Volt wheel, and tire and keeps it in a tire sleeve thingy in the back seat. ( no factory spare, so no tire well)
Yes, the fancy ELR.
Thought about getting an extra full size wheel but a space saver spare wheel that fits was $13 from the local pick n pull. A new spare tire that provides the correct diameter will be under $120 installed.
 
its almost 15% smaller being that far off you may have issues with abs/sensors and it shouldnt be on a driven wheel. is the elr fwd rwd or awd?

I wouldnt run it myself.
Yeah, don't want to run this tire specifically. Just need to know how close I need to match the diameter in general so I can order the correct size spare tire to mount on the spare wheel. The ELR is FWD.
 
You need to have the spare the exact same diameter as the original wheels or very very close. If you are only 1% different you should be ok especially if you drive a short distance in order to get a repair or replacement in case of emergencies. I run good tires on my vehicles and have not had an on the road flat for over 30 years. Slow leaks yes but a complete flat has not happened. My Corvette doesn't even have a spare tire. At a 1% difference I would think you could drive a 100 miles or more without damaging your vehicle but I wouldn't drive much further than that.
I'm in Texas and for whatever reason, my family and I seem to pick up nails/screws often enough to warrant a spare. I once had a nail that wasn't leaking blast out of a tire due to the high heat while on a 6 hr road trip. The spare was priceless.

I'm going to try and get a tire size that brings the radius to within 1%. Just don't know what an acceptable tolerance is for diameter difference. There's quite a bit of different sizes that are also within 3% difference.
 
If you ever get a flat front tire and need to use the spare, just put the spare on the rear, and move a good rear tire to the front. You will have no problem as long as the drive wheels are the correct size.

And of course, if the flat is in the back, you can use the spare back there with no problem.

Will a full-size spare fit in the ELR trunk? :unsure:



It's FWD
Worst case scenario, that's what I was figuring could be done. Don't know if the rear ABS/Traction control sensors would freak out about the mismatched wheel speeds.
Thought about getting an extra full size wheel but a space saver spare wheel that fits was $13 from the local pick n pull. A new spare tire that provides the correct diameter will be under $120 installed. A full size spare will be quite a bit more. Also, there's no tire well to store it. It's going to have to live in a tire bag/tote in the trunk.
 
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