Home page
SPONSOR AD SPONSOR AD

Topic: Tire sizes, what changed?

in Forum: C3 Engines, Driveline and Handling


Tire sizes, what changed?

Posted: 4/3/08 3:59pm Message 1 of 10
Profile Pic
Lifetime MemberLifetime Member
Send PM
Waterford, MI - USA
Joined: 9/13/2002
Posts: 1755
Vette(s): 1973 Red coupe

I just replaced my Goodyear ST 225/60-15's with BF Goodridge Radial TA's 235/60-15's. So why are the TA's tires shorter then the ST's?

I measured the ST's from ground to the top at 26.5 inches and the TA's at barely 26 inches.

 

Just curious

 

Redwingvette2008-04-03 16:00:58


Brian - NCM Lifetime Member

73 coupe L48, Flat-top pistons, Performer RPM Heads, Crane Cam and roller rockers, Holley 650 vac sec. Performer intake,
3.55 gear BTO 200-4R trans,
Leather seats, Seatbelt Plus 3point seatbelts, Pioneer CD player
Magnaflow Exhuast System

Dewitt radiator and dual electric fans
Borgeson Steering box
 


SPONSOR AD:: (Our Sponsors help support C3VR)

Tire sizes, what changed?

Posted: 4/3/08 7:03pm Message 2 of 10
Profile Pic
Former Member
Send PM
Frederick, MD - USA
Joined: 9/8/2003
Posts: 3398
Vette(s): 1969 convertible L71 427/435 4-speed black interior
It could be the differences in manufacturing tolerances and specs.  The measurements in the tire refer to inside measurements.  There could be a difference in tread depth, tread thickness, number of plies beneath the tread, etc.


Tire sizes, what changed?

Posted: 4/3/08 7:52pm Message 3 of 10
Profile Pic
Standard Member
Send PM
Victor, NY - USA
Joined: 7/12/2004
Posts: 6842
Vette(s): 2004 Commemorative Edition Coupe, Auto w/HUD. 13K miles in 2015. Sold 1982 Red Coupe
Brian,
You gotta pump'em up more.LOL
 
Is your speedo off too?



 
Save the Wave!
Support the National Corvette Museum   

Tire sizes, what changed?

Posted: 4/4/08 8:25am Message 4 of 10
Profile Pic
Former Member
Send PM
Oklahoma City, OK - USA
Joined: 4/1/2007
Posts: 432
Vette(s): 1972 LS5 Convertible,Auto.Targa Blue with Black Interior.
On your old 225's your sidewall should have been 5.3 in, diameter 25.6 in.
235's should be sidewall 5.6 in. diameter 26.1 in.. I'm not sure why the Goodyears were so tall.
Lonnie



Tire sizes, what changed?

Posted: 4/4/08 9:30am Message 5 of 10
Profile Pic
Lifetime MemberLifetime Member
Send PM
Waterford, MI - USA
Joined: 9/13/2002
Posts: 1755
Vette(s): 1973 Red coupe
I had checked all the web sites and talked to the guys and new they were smaller, not enough to worry about. I am glad I didn't order the 225's which today seem to be alot smaller then the ST's of years ago. I bought that set in 1995.
I just ordered new KYB GR2 Twin-tube shocks to go with the new tires. Hopefully they will be here so I can install them this weekend.
 
 



Brian - NCM Lifetime Member

73 coupe L48, Flat-top pistons, Performer RPM Heads, Crane Cam and roller rockers, Holley 650 vac sec. Performer intake,
3.55 gear BTO 200-4R trans,
Leather seats, Seatbelt Plus 3point seatbelts, Pioneer CD player
Magnaflow Exhuast System

Dewitt radiator and dual electric fans
Borgeson Steering box
 


Tire sizes, what changed?

Posted: 4/8/08 8:22am Message 6 of 10
Former Member
Send PM
Momence, IL - USA
Joined: 3/11/2008
Posts: 28
Vette(s): 1977 Corvette Coupe Light Corvette Blue
The number one rule to rember when changing tire size is plus 10, minus 5.  IE. if you have a 225/60r15 the proper tires sizes to change to would be 235/55r15 or 215/65r15.  The first number is the with of the tire tread in millimeters.  The second number is the aspect ratio.  It is a percent of the first number.  for example with a 225/60r15 the side wall would be 135mm, the 235/60r15's sidewall would be 141mm.  If you hade cone with a 235/55r15 the sidewall would have been 129mm which is closer than the 141 of the 60 series tire.  Your speedo should be off also, the 55 series would have kepted it closer.  The forumula to figure the sidewall size is 235 times 60 devided by 100.  Hope this helps.  I have a link that will tell you your speedo error when changing tires but I have to find it.  Mike


Tire sizes, what changed?

Posted: 4/8/08 6:14pm Message 7 of 10
Profile Pic
Lifetime MemberLifetime Member
Send PM
Waterford, MI - USA
Joined: 9/13/2002
Posts: 1755
Vette(s): 1973 Red coupe
I agree, but that doesn't answer the question as to why the Goodyear ST 225/60r15's that I had are 26.5" tall and the new 225/60r15's listed as only 25.6" tall. Which if you do the math come out to the 25.6". Now my new TA's 235/60r15's are only 26" tall.
What/why did the tire manufactures change? I know that I could have gotten a tire the 26.5" if I wanted but no one had any in the store for me to measure to see what the actual heigth was so I just ordered what others said they were using.



Brian - NCM Lifetime Member

73 coupe L48, Flat-top pistons, Performer RPM Heads, Crane Cam and roller rockers, Holley 650 vac sec. Performer intake,
3.55 gear BTO 200-4R trans,
Leather seats, Seatbelt Plus 3point seatbelts, Pioneer CD player
Magnaflow Exhuast System

Dewitt radiator and dual electric fans
Borgeson Steering box
 


Tire sizes, what changed?

Posted: 4/9/08 6:31am Message 8 of 10
Former Member
Send PM
Momence, IL - USA
Joined: 3/11/2008
Posts: 28
Vette(s): 1977 Corvette Coupe Light Corvette Blue
In that case I am not sure, I am going to talk to a buddy of mine who is a goodyear dealer and see what he says.  Mike


Tire sizes, what changed?

Posted: 4/9/08 3:16pm Message 9 of 10
Profile Pic
Gold MemberGold Member
Send PM
San Pedro, CA - USA
Joined: 5/26/2005
Posts: 239
Vette(s): 1971, LT-1, T-top, 4-speed (M21), Mulsanne Blue, 3.70 rear, mostly original (sidepipes). 2006, Daytona Sunset Orange Coupe.
Oh, by the way, I am pretty sure that aspect ratio has to do with section width (sidewall-to-sidewall), not tread width. You can have two tires from different manufactures, both say 245/45/ZR17, and they can have tread widths that differ.


Tire sizes, what changed?

Posted: 4/9/08 4:03pm Message 10 of 10
Profile Pic
Former Member
Send PM
Frederick, MD - USA
Joined: 9/8/2003
Posts: 3398
Vette(s): 1969 convertible L71 427/435 4-speed black interior
From the Yokohama website (please don't flame me for picking a non-American tire...it's simply the first definition when I googled it):


Often referred to as the profile or series, the aspect ratio of a tire is determined by dividing a tire's section height by its section width when the tire is: Inflated to maximum air pressure, Mounted on the approved measuring rim, and Under no load.

The lower aspect ratio responds to lateral force more effectively than a tire with a higher aspect ratio.

The aspect ratio affects steering stability. Generally, the shorter the sidewall, or the lower the aspect ratio, the less time it takes to transmit the steering input from the wheel to the tread. The result is quicker steering response.

Aspect ratio also affects the tread contact patch. As a rule, a low profile tire produces a wider tread contact patch. This wider tread contact patch creates a stiffer footprint that reduces distortion and provides improved cornering traction. Aspect ratio also impacts ride. A low profile tire usually has a stiffer ride than the standard aspect ratio of 75 or more.



Also, tread width can differ between two different makes or models of tires the same nominal size.  When I was researching tires for my wife's SUV, I checked out a really great sale price at a tire chain store.  It turned out the tires were a good name (Continental), and the right size, but had narrow tread and sharply inclined shoulders compared to other makes and models.  That was how they could sell them cheaper...making a narrower tread saved a lot of rubber and costs. 



in Forum: C3 Engines, Driveline and Handling


SPONSOR AD: (Our Sponsors help support C3VR)