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  #481  
Old 08-27-2014, 07:43 AM
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We are all moved in now and working on home renovation projects so I expect she will continue to collect rust and dust most of this year.
Congrats on the new home and move! I understand where you're at on this, having to wait until some house projects are done before you can work on the car again. It seemed like it took forever when we moved before I could work on anything cool again.

The Nova looks great sitting on all fours again. Are the Convo-Pro's eventually going to get replaced? I think of them more as a drag racing wheel than something on a corner carver.

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  #482  
Old 08-27-2014, 11:54 AM
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Given the limited tire options for 15" wheels, I'm sure new wheels are on the far horizon. I would like to get something with a vintage look because I'm sure whatever I pick out of the currently-popular pro-touring lineup will look dated and out of place in a few years, while something vintage to the original period of the car wont be unexpected. History has shown convos from the 80s, the billet wheels of the 90s pro-street craze, etc have all gone out of style with time (although I still like the convos, many people don't). I am leaning toward a 17" magnum 500 style wheel. Every one of the big 3 used a variant of this style and they came in a 14" on the SS Novas of my generation. American Racing makes one that is polished and Year One makes one with a brushed finish. I'm wondering if either might look more appropriate with the outside lip / ring powdercoated black to make the wheel look smaller. I just like the big sidewall look on these old cars.

Attached is a '68 Nova with 17" American Racing VN500s. I think they look a little too big for this car, but I will trade the classic 15" look to get a performance tire.
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  #483  
Old 08-27-2014, 12:20 PM
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Personally I would keep the C/lines because they look right on the car and to heck with what is in vogue at the moment...
As for tyre size, to look and handle on out deteriorating streets, not to mention ride quality your choice in tire really isn't limited that much...

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  #484  
Old 08-27-2014, 12:50 PM
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Originally Posted by TheBandit View Post
I think they look a little too big for this car...
I agree with that assessment. A lot of the scaled up vintage-style wheels just don't look right.

I don't dislike the Convo-Pro's. My fingers still hurt at the thought of polishing them, though. I helped with a drag car when I was in high school and often got put on wheel detail.

Actually, the thought behind my question was just due to if they were the right wheel for street/autocross/track day use. Weld Racing has a disclaimer in their catalog that some of their wheels are drag race only, and not intended for turning corners...but I just checked Center Line's website and they don't.
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  #485  
Old 08-27-2014, 01:12 PM
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I haven't seen any disclaimers from Centerline to that effect on these sizes, but I'm sure the original design was intended for drag racing, not this type of use. Their website says max load rating of 1,525lb per tire. I guess I could calculate the load from lateral and braking gs to see if I'm near that, but I'm guessing that rating is based on vertical load / static weight? Also since i have no tire date it would be tough to solve for dynamic tire loads.
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  #486  
Old 08-27-2014, 01:44 PM
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I'm not completely sure how they arrive at those load ratings, if it's some sort of a Tire & Rim Manufacturer's Association standard, or if it varies by manufacturer. If I still worked at my old job, I would offer to dig into it further, but I don't have access to the Tire & Rim specs anymore.

You could ballpark the vertical load on each corner with a bit of an assumption about the percent front lateral transfer (which is a function of springs, bars and geometry).

Dynamic Fz = Static Fz + (Pct Front Transfer / 100) * (Lateral Accel * CG Height * Total Weight) / Track Width

That's for a front wheel, where your lateral acceleration is in G's. It's not exact but a pretty decent approximation.
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  #487  
Old 08-27-2014, 02:37 PM
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For the purposes of approximation I'll estimate a total weight of 3150lb, front static weight of 1700lb (850 per front tire), CG 24", and track width (center-to-center of tires) 55". I'm really not sure what to approximate for the front % transfer. I don't know the front and rear roll stiffness. Any thoughts?

I'm doubtful the load ratings have anything to do with dynamic use, side loading, etc, but maybe?
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  #488  
Old 08-27-2014, 03:19 PM
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I would ballpark your percent front lateral transfer at 60%, maybe more. Stock numbers can be even more extreme because the OEM's like understeer (you see your wreck ).

I don't remember all the mods you've made, but anything to make the balance more neutral, like higher rear roll center, stiffer rear springs, or adding a rear anti-roll bar will decrease the percent front lateral transfer.

I think you're right about the load ratings not really taking lateral loading into account. Anything that imparts significant lateral load is an "at your own risk" sort of activity. Some of the sanctioning bodies (like USAC and NASCAR) have wheel specs that take some of this into account. I think NASCAR uses a fatigue test that stresses the center along with minimum weight (and paying the fee $$$). Not sure what USAC's specs are, but I believe they came up with them after a race got cancelled at Winchester due to wheel centers failing from increased lateral load on a recently repaved track.

Last edited by Graham08; 08-27-2014 at 03:23 PM.
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  #489  
Old 08-27-2014, 03:24 PM
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Okay so without any thought whatsoever and just doing "plug and chug" on the estimates above for 1 lateral g, I get

Dynamic Fz = Static Fz + (Pct Front Transfer / 100) * (Lateral Accel * CG Height * Total Weight) / Track Width
Dynamic Fz = 850lb + 0.65*1*24*3150lb/55
Dynamic Fz = 1,743lb

They give a rated load of 1,535lb which that would put me over, but I'd really need to talk to them about what the rated load means.
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  #490  
Old 08-27-2014, 03:26 PM
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For what it's worth, NASCAR wheels have to conform to SFI 35.1, which does include a fatigue spec:

http://www.sfifoundation.com/wp-cont...5.1_082608.pdf
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  #491  
Old 08-27-2014, 03:40 PM
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I called Centerline out of curiosity and their sales guy confirmed the ratings are based on static vehicle weight, but he wasn't familiar with what testing they did beyond a load to failure with some kind of safety factor. Engineering was out to lunch, but he offered to put me in touch with them if I call back, so I'll see what I can find out. He said the wheels are DOT approved for street use, but did not know what testing/standards they had to comply with for DOT approval. I'll check into it more and report back.

FWIW I do enjoy going down the rabbit hole, but given the risk I am not particularly worried about auto crossing these wheels.
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  #492  
Old 08-27-2014, 03:49 PM
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Interesting info. Yeah, it's cool to do the theoretical exercise, but I imagine if they're DOT approved there are some pretty healthy factors of safety involved in the final product. Plus, I think getting to 1g on 15" tires is going to be a challenge in and of itself.
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  #493  
Old 08-27-2014, 04:00 PM
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Plus, I think getting to 1g on 15" tires is going to be a challenge in and of itself.
1G was done decades ago.
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  #494  
Old 08-27-2014, 04:09 PM
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I would think combination of braking and turning would put the highest load on the wheel, so I may need to consider that situation as worst case, however I tend to think these wheels will be just fine until I lose a tire or clip something solid.

As far as DOT is concerend, it looks like 49 CFR 571.110 deals with rims and tires:
http://www.law.cornell.edu/cfr/text/49/571.110

SAE has a number of wheel testing standards here:
http://www.sae.org/servlets/works/do...o?comtID=TEVWC

I'll read up on them in my spare time lol
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  #495  
Old 08-27-2014, 06:08 PM
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1G was done decades ago.
Sure. Just not in a '70 Nova on street tires.

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I'll read up on them in my spare time lol
Like when you're suffering from insomnia.
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  #496  
Old 08-27-2014, 07:11 PM
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It's easy - I just hold my umbrella out the window and loop 'er around a light post.

Hotchkiss claims this Nova pulled 0.97g with street tires, but they are on 17s. Very similar suspension setup to what I'm running (leafs and all) http://www.hotchkis.net/featured_rides.html?ID=6. Maybe a similarly short sidewall on a 15" wheel would perform the same?
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  #497  
Old 08-27-2014, 07:42 PM
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Originally Posted by TheBandit View Post
It's easy - I just hold my umbrella out the window and loop 'er around a light post.

Hotchkiss claims this Nova pulled 0.97g with street tires, but they are on 17s. Very similar suspension setup to what I'm running (leafs and all) http://www.hotchkis.net/featured_rides.html?ID=6. Maybe a similarly short sidewall on a 15" wheel would perform the same?
Impressive. I would've guessed 0.85 or 0.9 would be it on street rubber. Now you need to go throw down a 1.0!
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  #498  
Old 08-28-2014, 11:37 AM
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Sure. Just not in a '70 Nova on street tires.
True 69 Camabird on shaved 50-Series street tires (poorboy rain tires) and 15" rims, about 36 years ago.
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  #499  
Old 08-28-2014, 12:17 PM
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True 69 Camabird on shaved 50-Series street tires (poorboy rain tires) and 15" rims, about 36 years ago.
You have my respect, sir.
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  #500  
Old 08-28-2014, 01:01 PM
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You have my respect, sir.
Thank You though the truth is: I was the youngest person affiliated with that team and smarter people designed and built, I made parts and polished aluminum. Mostly I learned, things like how fast 40-MPH is on a 100-foot radius and how ounces make pounds.

This Nova build is by comparison a harder build!

Fact is, it is always harder to build performance for the street, Trucks, Cars, Bikes, it makes no nevermind the street is harder until. . . you are to fast for the street

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