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Old 11-30-2015, 01:17 PM
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285/50r20 spare

I am upgrading from stock 18" tires to new 20x9 rims with 285/50r20 tires. But I still have the stock 18" spare. There seems to be conflicting reports on if this spare will work or not. I do not want to wreck my drivetrain.

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Old 11-30-2015, 01:24 PM
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Re: 285/50r20 spare

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Originally Posted by rlefig View Post
I am upgrading from stock 18" tires to new 20x9 rims with 285/50r20 tires. But I still have the stock 18" spare. There seems to be conflicting reports on if this spare will work or not. I do not want to wreck my drivetrain.
The 'tow package' spare is the same whether you have 20" or 18" tires.
As long as you are using the OEM 20" tire size, then the overall diameter (30.5") should be the same no matter if you have 18s or 20s.
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Old 11-30-2015, 02:33 PM
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Re: 285/50r20 spare

How do you calculate the overall diameter?
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Old 11-30-2015, 02:35 PM
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Re: 285/50r20 spare

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Originally Posted by macgeng View Post
How do you calculate the overall diameter?
http://www.discounttire.com/dtcs/infoTireMath.do
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Old 11-30-2015, 02:41 PM
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Re: 285/50r20 spare

MOFsteel I was just looking there and the change in diameter is .79"

There are other 18" spares that are in the 31" range. Like 265/65R18
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Old 11-30-2015, 03:45 PM
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Re: 285/50r20 spare

I will only run the spare in an emergency and get another tire ASAP. But again don't want to do damage in case it happens. Let's hope I don't jinx it
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Old 11-30-2015, 08:57 PM
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Re: 285/50r20 spare

The wheel size is immaterial. The tire diameter is what counts and your spare must match your normal "shoes" for tire diameter to avoid potential damage to your drive train. If you run 285/50/20, then you will need to change out the spare to a tire that matches the diameter of that tire...your OEM spare is 30.6" in diameter which matches the OEM 265/50/20 (as well as the OEM tires that come on the 18 wheel option)
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Old 12-01-2015, 06:25 AM
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Re: 285/50r20 spare

Right, I understand the overall diameter is the critical factor. I just saw many in this group talk about switching to the 285/50r20 and maybe I pulled the trigger on that switch too early.

Did all the other folks who switched to the larger tires also switch the spare? If so, what size spare?

Thanks
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Old 12-01-2015, 06:49 AM
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Re: 285/50r20 spare

Looks like the 255/65r18 Is 1mm less in overall diameter than the 285/50r20 so that could be a possible spare. I believe there is also a 1mm difference between the stock 20's and the spare


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Old 12-01-2015, 10:14 AM
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Re: 285/50r20 spare

As long as it's 3% or less difference, you should be fine.

I suspect there are many folks who up-size their regular tires and "forget" to deal with the spare...
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Old 12-01-2015, 10:19 AM
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Re: 285/50r20 spare

Thanks Jim. The Stock spare is 2.6% difference in diameter. Swapping to a 255/65r18 spare would be a .3% difference according to

https://tiresize.com/calculator/
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Old 12-01-2015, 03:16 PM
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Re: 285/50r20 spare

I'd personally go with the swap, despite the cost...which is probably a lot less expensive than fixing a drive train!
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