Tire recommendations??? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Stranny64 · 07-19-2014, 01:40 PM

Buying tires this week for the 68 C20. I have a 327, turbo 350, and 4.10 gears. Tire shop says I should get 265/75/R16's that are 31.7 tall. I'm looking at P265/70R16's that are 30.6 tall. Plans are to lower the truck with coil springs too. I will drive on the highway a bit so I do want something driveable. Is the advertised tire diameter the tire off the truck or on it compressed with the weight of the truck? Any thoughts on this since I'm no tire expert??? Thanks!!!

geezer#99 · 07-19-2014, 02:30 PM

The advertised tire diameter is always off the truck.

Stranny64 · 07-19-2014, 07:27 PM

So it will compress a bit? My concern is that if I put too tall of tires on I won't be able to lower it much and if I put too short of tires on it the truck will be winding rpm's too high down the highway. Just wondering what other people are running on there trucks with similar motor, trans, gears for tire sizes. Thanks!!!

**DreamRyder1963** · 07-19-2014, 08:05 PM

How low are you wanting to go?

davepl · 07-19-2014, 08:07 PM

That's a little taller than mine, which work fine on my 3/4 ton. Solution is simple. Don't lower it. But if you must I'd do the suspension part before the tire part so that you know it'll fit.

Funny how about half of the people install lift kits and about half lower their trucks. I figure on average, stock ride height must be correct :-)

geezer#99 · 07-19-2014, 08:20 PM

Quote:

Originally Posted by Stranny64

So it will compress a bit? My concern is that if I put too tall of tires on I won't be able to lower it much and if I put too short of tires on it the truck will be winding rpm's too high down the highway. Just wondering what other people are running on there trucks with similar motor, trans, gears for tire sizes. Thanks!!!

The advertised height is a mathematical equation.
Depending on the type of tire or who makes it will determine the installed height.
A p-metric (passenger car) tire will have a shorter installed height than an LT (light truck) designated tire in the same size. Due to tire construction. Side wall stiffness is greater in the Lt tire. So it squishes less.
Usually a tallish tire won't be a problem up in the wheelwell. Interference is a problem on the lower fender front and rear of the tire.

Vintage Windmills · 07-19-2014, 08:23 PM

You'll want LT series if your towing or hauling heavy. Those gears are pretty low for a non OD trannsimission. At least you have the rev happiest motor! Welcome from MN!

71tahoe · 07-19-2014, 08:24 PM

Quote:

Originally Posted by Stranny64

So it will compress a bit? My concern is that if I put too tall of tires on I won't be able to lower it much and if I put too short of tires on it the truck will be winding rpm's too high down the highway. Just wondering what other people are running on there trucks with similar motor, trans, gears for tire sizes. Thanks!!!

It's a 327, let-r-wind!

Stranny64 · 07-19-2014, 09:05 PM

I'm hoping to lower 2" in the front and 4" in the rear. I'm thinking I will do the tires first and then do some measuring. If I can't do the 2/4, I'll have to go less but I need to have it drive able. Thanks!!!

geezer#99 · 07-19-2014, 09:34 PM

Here's a neat link. Just to see what wheels and lowering does for you. This is one of many on the web.
http://tbcwheels.ridestyler.com/?mode=webbot

SS Tim · 07-19-2014, 09:57 PM

There is only about a 100rpm difference (2824 &2926 @65) between those two tire diameters.
A tire manufacturers diameter (from their specs table) is the tire mounted on the recommended size wheel, inflated but unloaded.
While you can use the "formula" to size up a tire the actual measurements are the numbers to use.

With 4.10 gears you are not going to be loafing down the highway. It was set up to carry a load. If it helps any most 68s had 4.57 gears with the 4.10s optional.

http://www.summitracing.com/expertad...tio-calculator

07-19-2014, 01:40 PM	#1
Stranny64 Registered User Join Date: Jul 2014 Location: Mora MN Posts: 172	Tire recommendations??? Buying tires this week for the 68 C20. I have a 327, turbo 350, and 4.10 gears. Tire shop says I should get 265/75/R16's that are 31.7 tall. I'm looking at P265/70R16's that are 30.6 tall. Plans are to lower the truck with coil springs too. I will drive on the highway a bit so I do want something driveable. Is the advertised tire diameter the tire off the truck or on it compressed with the weight of the truck? Any thoughts on this since I'm no tire expert??? Thanks!!!

07-19-2014, 02:30 PM	#2
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,546	Re: Tire recommendations??? The advertised tire diameter is always off the truck.

07-19-2014, 07:27 PM	#3
Stranny64 Registered User Join Date: Jul 2014 Location: Mora MN Posts: 172	Re: Tire recommendations??? So it will compress a bit? My concern is that if I put too tall of tires on I won't be able to lower it much and if I put too short of tires on it the truck will be winding rpm's too high down the highway. Just wondering what other people are running on there trucks with similar motor, trans, gears for tire sizes. Thanks!!!

07-19-2014, 08:05 PM	#4
DreamRyder1963 Senior Member Join Date: Jul 2012 Location: Knoxville, TN Posts: 499	Re: Tire recommendations??? How low are you wanting to go? __________________ 1971 Chevy C10 Cheyenne (sold for Mazda) 1963 Chevy Corvair Pro-Touring Project 2012 Mazda 3 i Sport sedan http://www.dracoautodesigns.com/

07-19-2014, 08:07 PM	#5
davepl Registered User Join Date: Aug 2006 Location: Redmond, WA Posts: 6,332	Re: Tire recommendations??? That's a little taller than mine, which work fine on my 3/4 ton. Solution is simple. Don't lower it. But if you must I'd do the suspension part before the tire part so that you know it'll fit. Funny how about half of the people install lift kits and about half lower their trucks. I figure on average, stock ride height must be correct :-) __________________ 1970 GMC Sierra Grande Custom Camper - Built, not Bought 1969 Pontiac 2+2 427/390 4-speed Coupe 1969 Pontiac 2+2 427/390 4-speed Convertible

07-19-2014, 08:23 PM	#7
Vintage Windmills Vintage 4x4s Join Date: Sep 2010 Location: Prior Lake, MN Posts: 4,305	Re: Tire recommendations??? You'll want LT series if your towing or hauling heavy. Those gears are pretty low for a non OD trannsimission. At least you have the rev happiest motor! Welcome from MN! __________________ 67 GMC K1500 Custom- 305V6 SM420, PTO, Ram Assist, yellow (the outcast) (project period correct upgrades) 67 GMC C2500 351V6 TH400, AC, PS, PB (can't decide what to do with. Update, decided to keep and will restore ) 86 CHV K30 502 th400, apple red NEW 71 CHV K20 350 SM465, ochre (saved work truck) 71 CHV K20 292 SM465, white, tach, PTO, (future project) 72 CHV K20 350 350th, medium blue (project stocker) 01 CHV K2500hd crew, indigo blue ^3 dont run and the others don't see winter either '86 K30 Cummins "Fireside" thread: http://67-72chevytrucks.com/vboard/s...d.php?t=649649 '71 K20 "get driveable" thread: http://67-72chevytrucks.com/vboard/s...d.php?t=590642 '72 K20 Build Thread: http://67-72chevytrucks.com/vboard/s...=493477&page=6

07-19-2014, 09:05 PM	#9
Stranny64 Registered User Join Date: Jul 2014 Location: Mora MN Posts: 172	Re: Tire recommendations??? I'm hoping to lower 2" in the front and 4" in the rear. I'm thinking I will do the tires first and then do some measuring. If I can't do the 2/4, I'll have to go less but I need to have it drive able. Thanks!!!

07-19-2014, 09:34 PM	#10
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,546	Re: Tire recommendations??? Here's a neat link. Just to see what wheels and lowering does for you. This is one of many on the web. http://tbcwheels.ridestyler.com/?mode=webbot

07-19-2014, 09:57 PM	#11
SS Tim Registered User Join Date: Aug 2010 Location: Edwards, CA Posts: 7,503	Re: Tire recommendations??? There is only about a 100rpm difference (2824 &2926 @65) between those two tire diameters. A tire manufacturers diameter (from their specs table) is the tire mounted on the recommended size wheel, inflated but unloaded. While you can use the "formula" to size up a tire the actual measurements are the numbers to use. With 4.10 gears you are not going to be loafing down the highway. It was set up to carry a load. If it helps any most 68s had 4.57 gears with the 4.10s optional. http://www.summitracing.com/expertad...tio-calculator __________________ Thanks, Tim * VIN/Model Decoders * Power Team Charts (engine/transmission/gear ratio) * Post Your Pickup SPID Blazer SPID Suburban/Panel SPID * RTFM ... Read The Factory Manuals... download 'em here Highlanders Do you have a 1972 Plaid Pickup? Plaid Blazer ** Plaid Suburban



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