Tire Size Experts - Step Inside
Thread Starter
Melting Slicks
Joined: May 2006
Posts: 2,257
Likes: 26
From: Delaware
Tire Size Experts - Step Inside
Ok, going to be getting some new wheels for my Vette. Already have them picked out, TSW Interlagos in 19X9 and 20X10.5
I had picked Michelin Pilot Super Sports in 265/35R19 and 305/30R20. My problem is the 305's are on national backorder with no ETA as to when they will be available so I'm looking at alternate sizes. I want to stay with the Pilot Super Sport so that limits me to 265/40R19 and 295/35R20 or 275/40R19 and 315/35R20. Looking at the specs for the two rear tire sizes, Tirerack has the tread width listed as 11.5 for both sizes.
How can a 295 series and a 315 series tire have the same tread width???? Doesn't make sense to me. If the 315 isn't any wider than the 295 I'll just go with the 295 series. Any thoughts???
I had picked Michelin Pilot Super Sports in 265/35R19 and 305/30R20. My problem is the 305's are on national backorder with no ETA as to when they will be available so I'm looking at alternate sizes. I want to stay with the Pilot Super Sport so that limits me to 265/40R19 and 295/35R20 or 275/40R19 and 315/35R20. Looking at the specs for the two rear tire sizes, Tirerack has the tread width listed as 11.5 for both sizes.
How can a 295 series and a 315 series tire have the same tread width???? Doesn't make sense to me. If the 315 isn't any wider than the 295 I'll just go with the 295 series. Any thoughts???
Melting Slicks
Joined: Jul 2004
Posts: 3,092
Likes: 120
From: orlando florida
St. Jude Donor '15
I'll explain as this is in my wheelhouse. The 295 and 315 are the measurements from sidewall to sidewall of the tire. Each manufacturer decides what percentage tread width they want. Some use 80%, some use 95%, and some use anywhere in between. Also rim width can change tread width slightly.
When you compare the 295 to the 315 of the same aspect ratio (the 35 number), there will be a different tire height.
One other point. Generally, the taller the sidewall, the less tread width manufacturers will use. As evidence by the tires you have selected.
When you compare the 295 to the 315 of the same aspect ratio (the 35 number), there will be a different tire height.
One other point. Generally, the taller the sidewall, the less tread width manufacturers will use. As evidence by the tires you have selected.
Last edited by mrr23; Sep 20, 2015 at 09:00 AM.
Thread Starter
Melting Slicks
Joined: May 2006
Posts: 2,257
Likes: 26
From: Delaware
I'll explain as this is in my wheelhouse. The 295 and 315 are the measurements from sidewall to sidewall of the tire. Each manufacturer decides what percentage tread width they want. Some use 80%, some use 95%, and some use anywhere in between. Also rim width can change tread width slightly.
When you compare the 295 to the 315 of the same aspect ratio (the 35 number), there will be a different tire height.
One other point. Generally, the taller the sidewall, the less tread width manufacturers will use. As evidence by the tires you have selected.
When you compare the 295 to the 315 of the same aspect ratio (the 35 number), there will be a different tire height.
One other point. Generally, the taller the sidewall, the less tread width manufacturers will use. As evidence by the tires you have selected.
Thread Starter
Melting Slicks
Joined: May 2006
Posts: 2,257
Likes: 26
From: Delaware
In my experience, which is very little, the tread width is what gives the overall appearance of width to the tire. The higher the tread width number the wider the tire appears. So in this case since the tread width number is the same for both tires, the 295 should appear to be the same width as the 315.
Last edited by GTJim; Sep 20, 2015 at 12:10 PM.
Thread Starter
Melting Slicks
Joined: May 2006
Posts: 2,257
Likes: 26
From: Delaware
Very nice, thanks for posting!!! 
What wheels are you running and do you have any shots from the rear? Just trying to see how wide they look and if they are flush with the fenders.
Edit: Just noticed they are TSW's
What wheels are you running and do you have any shots from the rear? Just trying to see how wide they look and if they are flush with the fenders.
Edit: Just noticed they are TSW's
Last edited by GTJim; Sep 20, 2015 at 02:37 PM.
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Melting Slicks
Joined: Apr 2004
Posts: 2,301
Likes: 199
From: Valencia CA
Sorry I don't have any other pics and I'm not with the car today. I can shoot some Monday. Having the tires flush with the fenders was one of my primary concerns, and they are.
The wheels are TSW Nurburgring in std C5 offsets.
The wheels are TSW Nurburgring in std C5 offsets.
Le Mans Master
Joined: Sep 2014
Posts: 5,278
Likes: 539
From: Kelowna BC
Have you considered the gear ratio change and speedo re-calibration effects from going to such a larger diameter tire? Speedo; easy fix.
Gears; either you'll have to live with the change (slower off the line in theory) or change the gears to get you back to your base line.
Stock tires base model 275/40/18 = 26.66 OD (Z06 tires 295/35/18 = 26.13 OD)
Assuming yours is a base model your circumference = 83.75.
295/35/20 OD = 28.13 OD, C = 88.37
83.75/88.37; your 3.42 gear (example) just became a 3.24 gear
315/35/20 OD = 28.68 OD, C = 90.10
83.75/90.10; your 3.42 gear is now 3.18
Gears; either you'll have to live with the change (slower off the line in theory) or change the gears to get you back to your base line.
Stock tires base model 275/40/18 = 26.66 OD (Z06 tires 295/35/18 = 26.13 OD)
Assuming yours is a base model your circumference = 83.75.
295/35/20 OD = 28.13 OD, C = 88.37
83.75/88.37; your 3.42 gear (example) just became a 3.24 gear
315/35/20 OD = 28.68 OD, C = 90.10
83.75/90.10; your 3.42 gear is now 3.18
Thread Starter
Melting Slicks
Joined: May 2006
Posts: 2,257
Likes: 26
From: Delaware
Have you considered the gear ratio change and speedo re-calibration effects from going to such a larger diameter tire? Speedo; easy fix.
Gears; either you'll have to live with the change (slower off the line in theory) or change the gears to get you back to your base line.
Stock tires base model 275/40/18 = 26.66 OD (Z06 tires 295/35/18 = 26.13 OD)
Assuming yours is a base model your circumference = 83.75.
295/35/20 OD = 28.13 OD, C = 88.37
83.75/88.37; your 3.42 gear (example) just became a 3.24 gear
315/35/20 OD = 28.68 OD, C = 90.10
83.75/90.10; your 3.42 gear is now 3.18
Gears; either you'll have to live with the change (slower off the line in theory) or change the gears to get you back to your base line.
Stock tires base model 275/40/18 = 26.66 OD (Z06 tires 295/35/18 = 26.13 OD)
Assuming yours is a base model your circumference = 83.75.
295/35/20 OD = 28.13 OD, C = 88.37
83.75/88.37; your 3.42 gear (example) just became a 3.24 gear
315/35/20 OD = 28.68 OD, C = 90.10
83.75/90.10; your 3.42 gear is now 3.18
Thread Starter
Melting Slicks
Joined: May 2006
Posts: 2,257
Likes: 26
From: Delaware
Here's a pic of the car. Running 265/40R17 and 295/35R18. Car is lowered all the way on stock bolts. With this combo it sits way too low and scrapes every where. What I'm trying to do is raise the car up with the larger diameter wheel and tire combo. I'm thinking about an inch will do it.
I could always adjust the bolts but then I end up with too much wheel gap for my taste.
Melting Slicks
Joined: Apr 2004
Posts: 2,301
Likes: 199
From: Valencia CA
Here's a pic of the car. Running 265/40R17 and 295/35R18. Car is lowered all the way on stock bolts. With this combo it sits way too low and scrapes every where. What I'm trying to do is raise the car up with the larger diameter wheel and tire combo. I'm thinking about an inch will do it.
I could always adjust the bolts but then I end up with too much wheel gap for my taste.
I tried 18-19 combo on my Vert. It looks good, In fact a lot better than stock, but a little more sidewall height than I was looking for.
For the Z06 I chose the same tire combo I have on the Vert, but in 1" larger rims, which essentially reduced the sidewalk by 1/2" per side.
IMHO,
The 19-20 combo is what the car should have come with stock.
Thread Starter
Melting Slicks
Joined: May 2006
Posts: 2,257
Likes: 26
From: Delaware
This shows exactly what I was talking about, 295/30R20 Michelin Pilot Super Sport, all the same size and manufacturer but three different tread widths. The two tires will definitely look wider than the one but the other two the difference is so small you wouldn't notice it. 11.5 inches wide is pretty wide for a 295 tire, it actually has the same tread width as the PSS in 315/35R20.
Melting Slicks
Joined: Apr 2004
Posts: 2,301
Likes: 199
From: Valencia CA
I agonized over the tread width issue before and after the purchase. There is no clear cut part #. Who is to say the guy in the warehouse ships any 295-30-20 he feels like. For the rears, I purchased the 11.5 tread width version.
You will find the same issue with the fronts. I purchased the Porsche version.
You will find the same issue with the fronts. I purchased the Porsche version.
Thread Starter
Melting Slicks
Joined: May 2006
Posts: 2,257
Likes: 26
From: Delaware
I agonized over the tread width issue before and after the purchase. There is no clear cut part #. Who is to say the guy in the warehouse ships any 295-30-20 he feels like. For the rears, I purchased the 11.5 tread width version.
You will find the same issue with the fronts. I purchased the Porsche version.
You will find the same issue with the fronts. I purchased the Porsche version.