Tire size questions - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**thedudeabides86** · 09-05-2019, 09:28 PM

Hey Everybody!

I might have already covered this somewhere on the board, but I came across some new Goodyear tires for $75/pair. They're 215/60/R16. Are these tires safe for 16 x 6.5 steelie rims on a '72 C20 RWD? I'd like to put them on the front and eventually the same size on the back. What's the widest tire I can put on the back on a 16 x 6.5 rim? If anyone would drop any advice, criticism, and opinions, that would be helpful. Thanks!!

rpmerf · 09-06-2019, 06:20 AM

Widest suggested you can go on a 6.5" rim is around 245. Factory should be 235 on a 6", which is wider than suggested for that size rim. Typically 225 is the widest you should go on a 6" rim. I think it is basically, you want the tire width to be less than 1.5x the width of the rim.

215 - 8.77"
225 - 8.85"
235 - 9.25"
245 - 9.64"
255 - 10.04"

6" * 1.5 = 9"
6.5" * 1.5 = 9.75"

Stock tire on a 72 C20 should be 235/85R16, which are 31.7". The 215/60R16 tires are 26.2". Your speedo will be way off unless it has been changed from stock. You will run at a higher RPM on the highway.

**thedudeabides86** · 09-06-2019, 10:32 PM

Quote:

Originally Posted by rpmerf

Widest suggested you can go on a 6.5" rim is around 245. Factory should be 235 on a 6", which is wider than suggested for that size rim. Typically 225 is the widest you should go on a 6" rim. I think it is basically, you want the tire width to be less than 1.5x the width of the rim.

215 - 8.77"
225 - 8.85"
235 - 9.25"
245 - 9.64"
255 - 10.04"

6" * 1.5 = 9"
6.5" * 1.5 = 9.75"

Stock tire on a 72 C20 should be 235/85R16, which are 31.7". The 215/60R16 tires are 26.2". Your speedo will be way off unless it has been changed from stock. You will run at a higher RPM on the highway.

Um, ya lost me. Sorry, I'm not a tire guy. Could I do the 215's on the front and 235's on the back and keep the speedo accurate?

PepperTreeGarage · 09-06-2019, 11:36 PM

I used a "Tire Size Calculator". https://tiresize.com/calculator/ Worked great to determine the tire and wheel sizes on our C20.

siggyfreud · 09-07-2019, 11:08 AM

If you look up the tire size you want to run on TireRack or Discount Tire it gives you a wheel width range that tire will work on.

rpmerf · 09-09-2019, 07:16 AM

Quote:

Originally Posted by thedudeabides86

Um, ya lost me. Sorry, I'm not a tire guy. Could I do the 215's on the front and 235's on the back and keep the speedo accurate?

Speedo is calculated off the rear, so that could work. The front tires will be 5.5" smaller though.

**thedudeabides86** · 09-19-2019, 10:13 PM

So, update on the tire ordeal. I gotta tire guy. A husband of my wife's coworker has suggested a 255/70/R16. Claims smooth ride and a little lower for a cooler look. The speedo might be off by 5mph at 60 mph or so, but meh. No biggie. Whatcha all think? What brand of tires are you running that look cool? I imagine it'll be a long time before I wear these tires down as I only drive it spring through fall on weekends, really. Finally got the old steelies powder coated. I'll have to post the pics when I get a chance.

09-05-2019, 09:28 PM	#1
thedudeabides86 Active Member Join Date: Jan 2016 Location: Albertville, MN Posts: 186	Tire size questions Hey Everybody! I might have already covered this somewhere on the board, but I came across some new Goodyear tires for $75/pair. They're 215/60/R16. Are these tires safe for 16 x 6.5 steelie rims on a '72 C20 RWD? I'd like to put them on the front and eventually the same size on the back. What's the widest tire I can put on the back on a 16 x 6.5 rim? If anyone would drop any advice, criticism, and opinions, that would be helpful. Thanks!! __________________ The Dude abides.

09-06-2019, 06:20 AM	#2
rpmerf Registered User Join Date: Feb 2011 Location: Parkville, MD Posts: 1,024	Re: Tire size questions Widest suggested you can go on a 6.5" rim is around 245. Factory should be 235 on a 6", which is wider than suggested for that size rim. Typically 225 is the widest you should go on a 6" rim. I think it is basically, you want the tire width to be less than 1.5x the width of the rim. 215 - 8.77" 225 - 8.85" 235 - 9.25" 245 - 9.64" 255 - 10.04" 6" * 1.5 = 9" 6.5" * 1.5 = 9.75" Stock tire on a 72 C20 should be 235/85R16, which are 31.7". The 215/60R16 tires are 26.2". Your speedo will be way off unless it has been changed from stock. You will run at a higher RPM on the highway. __________________ 1970 C20 Custom Camper - 350, TH350 1997 GMC Suburban 1994 Acura Integra GSR 1987 Dodge Daytona Shelby Z

09-06-2019, 11:36 PM	#4
PepperTreeGarage Registered User Join Date: Jan 2014 Location: SoCal Posts: 281	Re: Tire size questions I used a "Tire Size Calculator". https://tiresize.com/calculator/ Worked great to determine the tire and wheel sizes on our C20. Attached Images

09-07-2019, 11:08 AM	#5
siggyfreud Registered User Join Date: Jun 2012 Location: Portland Posts: 1,330	Re: Tire size questions If you look up the tire size you want to run on TireRack or Discount Tire it gives you a wheel width range that tire will work on. __________________ Current Build - Project "Ghost of Poseidon" 72 C10 Pro-touring build Previous Build - 66 GMC Pro-touring build. Sold.

09-19-2019, 10:13 PM	#7
thedudeabides86 Active Member Join Date: Jan 2016 Location: Albertville, MN Posts: 186	Re: Tire size questions So, update on the tire ordeal. I gotta tire guy. A husband of my wife's coworker has suggested a 255/70/R16. Claims smooth ride and a little lower for a cooler look. The speedo might be off by 5mph at 60 mph or so, but meh. No biggie. Whatcha all think? What brand of tires are you running that look cool? I imagine it'll be a long time before I wear these tires down as I only drive it spring through fall on weekends, really. Finally got the old steelies powder coated. I'll have to post the pics when I get a chance. __________________ The Dude abides.



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