Help with tire sizes......

[Zixxer]

I've searched the forums with a wealth of responses on types, rates, preferences, etc., but this question is purely technical as I've already decided what I want, just don't know if it will work:

I have a 1996 LT1, stock rims...the swirl type.....those are going, hate them.

I bought a set of rims off a 2001, the five spoke thin type:

17x8.5 fronts
18.9.5 rears

Now I'm looking at tires and I like the Kumho Supra 712s but they don't carry the size I need and I'm not sure how much of difference ratio will make in appearance and fit....I don't want to wind up with too much difference in sidewall height, at least nothing that stands out...I'm going for an improved look, not a distraction. So the question is, if stock tires are:

245/45ZR 17 front
275/40ZR 18 rear

can I get away with the following:

245/45WR 17 front
275/35WR 18 rear

speed rating is not the issue, just the difference in 40 v. 35 on the rear tires. If anyone has experience with this, or can recommend a different combination of sizes that will work for those rims in either a Kumho or a Falken tire I sure would appreciate it.

Thanks Rick

 

[ErnieN85]

The easiest way to check is to look up the specs for the tires on the tire rack click on the specs for the tire and see ho close the two sizes are in revs per mile

 

[WradDad]

Rick,

A change in tire diameter will change your overall drive ratio, throwing off your speedo reading. Here's what Tire Rack's web site says about your choices:

285/40 17 (the stock tire) diameter is 26.1 inches
275/40 18 diameter is 26.8 inches
275/35 18 diameter is 25.5

Hopefully the math wizs can jump in here and tell us if that's significant or not.

Barry

 

[Zixxer]

Thanks, yes, please let the math wiz chime in

I certainly don't think it would be wise to drop down in size so I better keep looking for the exact size.

 

[Zixxer]

Rick,

A change in tire diameter will change your overall drive ratio, throwing off your speedo reading. Here's what Tire Rack's web site says about your choices:

285/40 17 (the stock tire) diameter is 26.1 inches
275/40 18 diameter is 26.8 inches
275/35 18 diameter is 25.5

Hopefully the math wizs can jump in here and tell us if that's significant or not.

Barry

Where did you find that info? I'm on their site and clicking away but I'm pretty much just reading articles.

 

[Zixxer]

Thanks for the responses...it prompted me to find a tire size calculator which has helped greatly....the 35 would have given me a shorter tire in the rear v. the front, not a look I'm going for.

 

[c4cruiser]

When you go to the Tire Rack main page, use the blue "Products" button at the top and go down to "Tires" and click there. Select "Browse by Tire Brand" on the right side about 2/3 the way down that page.

Select a tire brand and then a type or model name. Most of the Ultra High Performance types are where you'll find excellent Vette tires. When that tire page comes up, you'll find a row of buttons like "sizes and pricing", "reviews" and on the right, "Specs". This spec page will, in most cases, have data for all sizes offered to include the overall diameter and revs per mile.

I use those two columns to determine the sizes that will show the correct speedo readings based on the OEM tire size and brand. Not all brands will have the same measurements for similar tire sizes so you just have to sort thru the information.

Of of the best tires going right now are the Goodyear Eagle F1 Supercar tires that come on the Z06, the Eagle GS-D3's or the BFG g-Force KD's. You should be able to find sizes to fit your new wheels.

 

[Vette_Newb]

I just bought a set of chrome 2000 C5 knockoffs, 17/18. I used 275-40-17 and 275-40-18 on them. I expect the speedo to be off by a couple mph, but the look and ride is great. I also plan to go up to 3:54 gears and add some NOS, so after that is done I will have a new PROM burned with all the updates and the speedo will be fine again.

Also, you do know it is almost mandatory to paint the brake calipers with these wheels right? hehe.

 

[Rich96c4ce]

Make sure that you buy tires that are very close to the same diameter. This is very important for the ABS to work correctly. The diameter does not need to be the same as the OEM diameters, it just needs to be the same between all the new tires.

Also, make sure that the load capacity in pounds is at least the same as the OEM tires.

 

[Hrtbeat1]

Size help

As you decrease the tire size (diameter) you increase the RPM at a given speed. Effectively lowering (raising numerically) your final drive ratio ... I think that is right. I would try and find sizes closer to the stock height. Then again each tire will fit each wheel a little differently. So there can be a variance in size there ... Going from one manufacturer to another. Also loaded weight will have a change on overall diameter. My 275 40 17's measure 25.66 inches doing the math. Actual measured diameter 25.25 inches.

I noticed you didn't want a skinny rear and going by the sizes you say you have (245 45 17 / 275 40 18) you could go with something like 275 40 17 fronts (sidewall of 4.33 inches) and 315 35 18 rear (sidewall of 4.34 inches). If you ask anyone that has the ZR-1 11 inch rear wheels they will tell you there is something about having 315's out back. The 275's are the same size as the Z51 option ... just a thought. It wouldn't be as noticeable going from a 40 on the front and a 35 on the rear vs. going from a 45 front and 35 rear.

 

[Hrtbeat1]

My bad I just noticed that you have 9.5 rears. I don't think 315's will fit. I know 275's will. You will have to do the math and find a combination as close to stock as you can.
example of the size calculator
275 (size in mm) 40 (aspect ratio) 17 (wheel size)
275 / 25.4 (convert mm to inches) = 10.827
* .4 (aspect ratio) = 4.3307
* 2 (two sidewalls) = 8.6614
+ 17 (wheel size) = 25.66

 

[vette1985]

hey, you might want to consider a 285/35-18 for the rear. That is the size I found on the new Z06. If you do let me know, I have a pair of rears I am selling. I put about 100 miles on them. They are dunlop SP9000. Will sell for $225.00 for the pair. Let me know. As for the front, 275/40-17. I don't have any experiance with Kumho, but I do with Falken. I feel that 502 Ziex are ok, but the better choice would be the GRB-451. If you consider my rears I am sure you could get someone to match tire rack price on the fronts. Dunlops are a better choice. I sold my 18s to get an original set of ZR-1 wheels. In the future take a look at the BFG KD line, they are nice.