Hi everyone,

I just bought a set of dymag but the backspace is not the same as my oem rims. It is 5.5" while the original wheels are 7.4".
I allways read that the 17" gen1 dymag were 7" backspace so i don't know why mine are different.
it seems that they are made for 84-87 C4.

http://i59.servimg.com/u/f59/18/50/80/46/img_2010.jpg
http://i59.servimg.com/u/f59/18/50/80/46/img_2011.jpg
http://i59.servimg.com/u/f59/18/50/80/46/img_2012.jpg
http://i59.servimg.com/u/f59/18/50/80/46/img_2013.jpg

Does someone knows why these are diferent ?

 

Are they genuine Dymags or more recent offshore knockoffs?

 

seems that they are old ones. Their is one spoke with Dymag, one other with the corvette.
They look a bit old and need to be repainted and the seller told me that they were used on a race car.

I didn't know that there were other dymag than the genuine ones. What's the difference ?

 

Are these knockoffs being made currently, if so where?
Thanks,
Shawn

 

I just check the wheels and found there is the inscription G33GP4 on a spoke inside each rim.

 

You hint 17" but have you actually measured? If all four are alike measure the "TOTAL" wheel width and double check your back-spacing measurement also. Post back!

A 17" wheel is something near 18 1/2" tall and a 9 1/2" wheel is something very near 10 1/2" wide.

 

Wonder if those wheels are the Dymags that were sold by Mid-America? Those wheels had both Dymag and Corvette molded into the spokes.

I found a thread from 2002 about Dymags that may be worth reading.

 

I just checked the all 6 rims, they are 18.5" external diameter and around 10.35" wide.

 

And the back-spacing on all are the 5 1/2" you mention and not maybe something closer to 6 1/2"? A 6 1/2" or close dimension would put them near 32mm offset but the 5 1/2 dimension makes them something near 6mm or so and doesn't make any sense whatsoever.

A specialty build? Maybe. How is the hub surface that bolts to the hub constructed. If looking at it from the outside of the wheel can you see a seam with maybe a different ID.

 

they are all 5.5" backspace. The hub of the rim is impressively thick and the holes for the stud are very large compare to the original wheels.

Here is a picture of the outside of the rim :




here is are two pics of the inside of the wheel :




as you can see, it is very thick

here is how it should look (i found this on another thread)

 

The mounting hub thickness could be a tremendous "plus" for you as you could likely have the wheel machined to accommodate a very special fit to a particular car. If they're true that shouldn't be an issue, they need refinished anyway so you can spiff them right up for a very good fit. The center-bore could be important, for a C4 you want a 70.3 for the rear of the wheel and while you're doing the machine operation you could also tailor the outer center bore for a center cap of your choice.

You only need someone that understands what they're doing.

 

The current center bore is around 70.3mm that tends to confirm that they have been made for a C4. I checked the weight of the wheel, i know it is not a proof that they are true dymag but if they are heavy, they are not dymag.

The weight is 20.4 lbs.

I totaly agree with you, i think i will get it machined at the backspace to fit just right with the fender.

 

this quote comes from this thread:
https://www.corvetteforum.com/forums...ersting-2.html

Could my set of dymag be made for 87 challenge cars ?
I still don't understand why is this set different than the others.

 

1987 and 1988+ C4s had different rear suspension geometry which could have factored into why those wheels are the way they are

There wasn't an 87 Challenge car though, only 88-89, and the 17" Dymag was late to that party, not initially available or installed.

 

I hadn't mentioned earlier and maybe I actually overlooked it but you mentioned larger wheel stud bores than stock. I'm also assuming you've done nothing about refinishing/restoring them either.

I'd do this maybe, measure the bore of the wheel stud holes OR maybe gather a 14mm wheel stud, a 1/2" wheel stud and a 9/16" wheel stud and determine which the wheel was meant to be used with. That could have an impact on the value of the wheel set. If you intended on using these on a car you would need corresponding sized wheel studs to use them effectively.

Using your dimensions a 9 1/2" wheel with the back-spacing you've measured would be right at the lip of the quarter or hood edge on an '87 or earlier car, maybe a little out-board.

Would or could these be maybe "meant for competition" builds? Quite likely.

If these wheels were mounted on an '88+ car then the wheel would be something very close to 1 3/4" more out-board than that of an 11" wheel with a 50mm offset ('96 GS and similar). Well outside of the hood edge/quarter lip.

Wheel stud size and the "bulge/taper" required of the appropriate nut would determine I guess the ultimate value of the wheel. The nut needs to match the taper of the wheel.

 

Thanks for the info.
Answers are above in blue

 

I would start with a 14mm stud and "bulge nut" to attempt a fit. The 14mm is quite common on later GM and the bulge style nut would be a hard find for 9/16".

Newer Camaro/Cadillac use 14mm hardware as well as GM trucks.

If a 14mm stud and bulge nut is a match for the wheel then a good many questions are answered.

You haven't refinished/restored yet?

 

Well, it seems that i should use flange nut type because the set i have do not have the conic nut seat.
See the attached image.

I do not got it refinished yet.

I do not remember ; what is the original stud size on the C4 ?

 

I would have thought bulge/rounded BUT if they were originally done like you mention then yes a flange nut.

Original C4 wheel studs are 12mm

I mentioned the 9/16" because very early for competition wheel studs were spec'd at that dimension or greater by some associations and 14mm hardware wasn't very popular.

 

I found this nut. It seems that it could work.
http://www.nbeste.net/products/mag-l...r-1506411.html

I have to measure the stud bore first. I'd really like to know what are that rims.