Brian... THANKS for referencing 'the tire calculator' on this site..as I had never explored the site and seen that. I WILL use that information now.. so Thanks again!
Brian... THANKS for referencing 'the tire calculator' on this site..
My wheels are C5 replicas with 50mm offset. I need to check the offset because I recall them saying they were "C4 offset" which was 56mm, but they were also 9.5" wide. I thought I measured them once and they were 50mm offset. I'll check again.Originally Posted by BamaNomad
I never understood why guys talk about "wheels" fitting. It's the TIRES that cause the problem. You can use a 9.5" wheel with a 245 tire and it will fit...try a 275 tire on the same wheel and it likely won't fit. Newman used to recommend 245 tires on 9.5" wheels but I personally think the wheel is too wide for that tire. I think the tire should be the same width or wider than the wheel.I like the 90 Corvette wheels utilized by Custer55 but I was a bit surprised that 9.5" would work on the front.
That's another issue. My calculations only show whether a wheel/tire combo will fit ONCE INSTALLED. Getting them on is another issue, and is more difficult on some cars than others. I used a longer coilover and I'm able to remove the 295 rear tires without disconnecting the shocks. A larger wheel also helps since it has a bigger hole in the center.I also would prefer to be able to mount/dismount a wheel/tire without issues (loosening lower shock mount, etc).
56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension
Other vehicles:
56 Chevy 2-door BelAir sedan
56 Chevy 210 4-door sedan
57 Chevy 210 4-door sedan
1962 327/340HP Corvette
1961 Willys CJ3B Jeep
2001 Porsche Boxster S
2003 Chevy Silverado 2500 HD Duramax
2019 GMC Sierra Denali Duramax
Bamanomad, that calculator is based on the one I put together years ago in Excel format. Someone else put it into the format it's in. Some of the information in that one is slightly off. For example, the early C4 rear is 62.25" wide and the late rear is 63.25" wide according to my most recent measurements. Also my measurements show the early C4 front width at 61" and the late front width at 62" but the numbers in the calculator are close.Brian... THANKS for referencing 'the tire calculator' on this site..
That calculator uses backspacing which I don't like to use. Offset makes more sense to me and my original spreadsheet allowed the user to input offset or backspacing and calculate the other parameter. Not sure why he chose to use backspacing.
Also, body measurements should be taken off of your car. My 56 Nomad rear fenderwell lips are 71 11/16" wide. I just measured a 55 in the shop and they're 71 1/4" wide. Others have measured their cars as wide as 72". If you're really trying to squeeze a tire in, that difference is significant.
56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension
Other vehicles:
56 Chevy 2-door BelAir sedan
56 Chevy 210 4-door sedan
57 Chevy 210 4-door sedan
1962 327/340HP Corvette
1961 Willys CJ3B Jeep
2001 Porsche Boxster S
2003 Chevy Silverado 2500 HD Duramax
2019 GMC Sierra Denali Duramax
It appears my RR C4 frame has been narrowed in that area for inboard tire clearance.
IMG_1005.JPG
For anyone that might not know, production wheels have the offset marked on the wheel. Here is a 20 x 8.5 inch wheel with a +44mm offset. Regardless of backspacing, it's any change in the offset is what affects the more important track width, which needs to be considered too.
IMG_1008.JPG
Last edited by 55 Rescue Dog; 04-03-2017 at 02:51 PM.
For a given wheel width, if offset changes backspacing changes by the same amount. An 8" wheel with zero offset has 4.5" backspacing. If you increase offset to +.5" backspacing is now 5". Offset and backspacing are directly related.
If you stay inside the confines of the car's sheetmetal, track width can't be changed very much. You have a certain sized wheelwell, and if you maximize tire size the track width is pretty much fixed. A narrow tire pushed outboard as far as possible (still inside the wheelwell) maximizes the calculated track width, but how does that help anything? For example, a 255 rear tire with 1/2" wheelwell lip clearance results in a track width of about 60.5" assuming a 71.5" wheelwell lip width. A 295 tire with the same clearance results in a track width of 58.5". Which is going to perform better, the 255 or the 295?
56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension
Other vehicles:
56 Chevy 2-door BelAir sedan
56 Chevy 210 4-door sedan
57 Chevy 210 4-door sedan
1962 327/340HP Corvette
1961 Willys CJ3B Jeep
2001 Porsche Boxster S
2003 Chevy Silverado 2500 HD Duramax
2019 GMC Sierra Denali Duramax
Well, as far as cornering goes I would have to say the wider track/narrower tire could corner faster than a narrow track/wider tire would. Otherwise, I guess I didn't know that a narrower track width was better for cornering loads on the tire.
How could a wider track/narrower tire corner better than a wider tire, when BOTH tire outside edges are at the same width? The wider tire also has more traction.
If what you say is true and a narrower tire with a wider track is better, you should be using a 195 rear tire pushed out to within 1/2" of the wheelwell lip to get a track width of 62.8". That's even better than the 255 by 2.3"!!
Try that.
56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension
Other vehicles:
56 Chevy 2-door BelAir sedan
56 Chevy 210 4-door sedan
57 Chevy 210 4-door sedan
1962 327/340HP Corvette
1961 Willys CJ3B Jeep
2001 Porsche Boxster S
2003 Chevy Silverado 2500 HD Duramax
2019 GMC Sierra Denali Duramax
I think I have to agree with CN on this one..
Think of it this way. As the tires wear on a race car the lap times slow down. The suspension design doesn't change, the only difference is the amount of traction the tire has to the racing surface. A wider tire given the same tire compound/design will always have more traction.
Brian
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