Quick question about changing from stock 18” to 20” wheels.

[steve16gt]

I have searched all over the site and can not find the answer to my question. I currently have the 245/45/18 wheels on my car and just purchased a set of Velgens 20” staggered. They are 275/35/20 up front and 305/35/20 in back. My question is do I need to do anything to compensate the different diameter size? Up front is about .9” larger and in back is 1.7” larger in diameter. Thanks for the help and suggestions in advance.

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[BmacIL]

I have searched all over the site and can not find the answer to my question. I currently have the 245/45/18 wheels on my car and just purchased a set of Velgens 20” staggered. They are 275/35/20 up front and 305/35/20 in back. My question is do I need to do anything to compensate the different diameter size? Up front is about .9” larger and in back is 1.7” larger in diameter. Thanks for the help and suggestions in advance.

Your speedometer will be pretty far off from the stock 235/50R18 calibration (like 6-7 mph at highway speed), and if you're lowered you definitely will rub.

305/30R20 was the correct size to go to 305 width on 20" wheels, FYI. 30 is the aspect ratio, not the sidewall height.

 

[steve16gt]

I ordered them as a set from LMR. It was the tires and wheels combo. They are on there way and I was just trying to be prepared. So if the calibration is off. What do I need to do in order to fix the issue?

 

[BmacIL]

I ordered them as a set from LMR. It was the tires and wheels combo. They are on there way and I was just trying to be prepared. So if the calibration is off. What do I need to do in order to fix the issue?

Wow, really LMR? :tsk:

The Whipple Flare Tool or modification of the as-built data can address it, but I would not drive on them and see if a shop can change them for 305/30R20s. I'd try to get LMR to pay for giving you a size that is pretty much incompatible. I guess you knowingly ordered it, but they should know better.

 

[plc268]

Chill. Plenty of people drive on 305/35/20 tires. It's not a big deal.

And no you won't rub on a modest drop with those tires. I ran steeda progressives and Mickey Thompson street comps at 305/35/20 and never rubbed.

Yes it's oversized, and yes it'll mess with your speedometer, but there are ways to fix that.

 

[WhiteyDog]

I'm lowered on an Eibach Pro-Kit and running a 20x10 wheel with 285/35's in front, and a 20x11 wheel with 315/35's in the rear and never rubbed anywhere, ever.

 

[steve16gt]

Thanks for the feedback. What are my options for calibrating the speedo? I assume it is by getting a tuner but which tuner did you use to resolve the issue?

 

[WhiteyDog]

I have a Lund tune and seem to remember some questions regarding tire size along with whatever other mods I have on the car so he could figure those things into the tune. I'm guessing all of the tuners would ask those things I suppose. I really like my Lund tune as well as many others, but the other guys are good, too.

 

[SVT-DADDY]

The 305/30/20's would be about 1/2 shorter than the fronts, the 35 series will look better. Here is a handy tool for figuring it out.

https://tiresize.com/comparison/

Lund just released functionality for the Ngauge to correct for tire sizes. If it were me I'd get a tune and fix your speedo as well! The Whipple flare tool will do the same but no other real benefits for you.

 

[steve16gt]

Thanks for all the help. I will be buying a tuner to change the tire size. But now to decide which one.

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