There is my vette above. In the future, I am putting my L88 hood on it, and I'd like to put a set of dark charcoal racing stripes down it. Thats why I am liking the gunmetals.

 

Those are Boyd Coddington Smoothie II's. I have these in 18x9 with 0 offset and 5" back spacing on all 4 corners of my 79. With Khumo 275X 18X 40 tires on all 4 corners. No modifications required and no rubbing or interference. Really good looking wheels either way you go. I believe the gunmetals centers are powder coated so less maintenance.

 

275 on all four corners!!!!!??? I didnt think that was possible. Surely its not on an earlier C3; I heard that they have less clearance. Have any pictures of yours?

 

Oh, and what is 5" BS in 'mm' of offset? 25mm positive?

 

Mine is a 79 coupe.

My 18x9 wheels with 5" backspacing have 0 mm offset. The orginal alloys were 15x8 with 4.5 " of BS and 0 mm offset. Remember when you are comparing offset to backspacing you need to account for the thickness of the rim flange which is typically about 1/2". I bought them thru discount tire for $323 per wheel. The offset was custom ordered and required 6 to 10 weeks delivery. If I had it to do over again I would put 18x 10 on the rear once again with 5 " of backspacing but to get this you would have to have 12 or 13mm of positive? offset to maintain the 5" of backspacing. I would use 295x18 tires. This would put the outer portion of the tire and rim about even with the outer edge of the rear fender. I have pic somwhere but it won't demonstrate the fitment. Another factor may be how much you lower your car. The rear will take quite a bit of lowering without interference. I have lowered the front about 1.5" which is not a lot compared to some I have seen. I drive my car a lot and didn't want to get the front too low. I am considering lowering the front maybe another inch. Don't know if this will give interference or not.

The Boyds really look good. There are a lot of TT II's out there because they are good looking wheels. I recently read in a hot rod magazine that you could blindly fling a dead cat and hit a TT II wheel. I wanted something a little different. I think the BC's are better looking wheels than the TT II's but as they say beauty is in the eye of the beholder.

If your not clear on BS and offset concepts I can forward some tech info on this. like many subjects on the forum wheel fitment has been discussed many many times.

 

Magawatt, Do you have offset trailing arms on your vette? Rod

 

OK, I just placed the order for the polished Smoothis IIs. I went:

18x8 on the front with 245/45/R18 no offset.
18x9 on the rear with 275/40/R18 no offset.


I got them from Discount Tire for $290, and $305 each. He said they would take 2-3 weeks. Until then, I will cross my fingers so I wont have any issues. I sure dont like 'non-returnable' purchases...

 

thats a VERY good price on those, offset isnt a huge deal, its the backspacing thats a bit of a french whoooor. Id go with more to be safe, 5.5, then use a spacer if it wasnt kosher. Ive been thinking about the Boyds too, but now Ive seen em on at least 3 Vettes They are phat shoes but I dont want to be in the "new" TT II crowd.

 

Good luck on that. Mine took 5 weeks to show up. 4-5 weeks is the norm for Boyd.

 

Offset and back spacing are inseparable. If you change one you change the other. Because many wheel specs provide offset but not back spacing you need to know how to move from one to the other. The following link provides a good discussion of this. The second link is a tire size calculator which is very handy. If you don’t like this calculator just use google to search for “tire size calculator” there are several out there.

http://www.rsracing.com/tech-wheel.html

http://www.miata.net/garage/tirecalcold.html

You do not want 5.5 “ back spacing on the rear. Stick with 5” and the worst you might have to do is tie wrap the parking brake cable tight against the swing arm. This is with 18” wheels. Because of the diameter of the wheels the parking brake cable bracket will be slightly inboard of the wheel rim ID. The primary point of interference is the frame where it rises vertically and then up over the axle. If you look you will notice a hump. If you looking at the wheel from out board you will notice it’s that portion of the frame at about 2:00 to 3:00 oclock.

I don’t have offset trailing arms. If you don’t modify the hump in the frame then offset trailing arms won’t help you. Norval has modified his frame and fabricated his own offset trailing arms. That’s how he can get 10” wheels on the rear and still has the out board side wall of the tire well inboard of the fender lip.

 

Yet he remains one of, if not the only person running 10s in the back who has notched his frame!!

I know about backspacing and offset: Offset = Overall width divided by 2 and subtracting the backspacing, unless Im totally off my nut.

I dont see the problem with running 5.5 inch backspacing, the amount of positive offset is negligable. I know there are guys on this forum who are running 5.5" in the back with the double offset T arms and repositioned parking brakes and they didnt have to get into the frame. Just my thoughts on it. I mean you are right that 5" backspacing is easier, but if you dont want the damn thing sticking out you kinda have to go with the 5.5, it provides 5mm more clearence on the inside (negetive offset).

 

Without taking the time to check your equation just let me say that offset is the distance from the centerline of the wheel to the mounting surface of the wheel. If the mounting surface is moved out board from the centerline of the wheel it is positive offset.

I have spent many hours taking measurements and fitting my wheels. Now having them mounted I have done further measurements for what incremental changes could be made especially for inboard clearance. I incourage anyone who is going to fit larger tires and wheels to take the time to do serious measurements. I have my doubts about 5.5 " BS. I can crawl under my car now with the 18 " Wheels mounted and with 5" of back spacing and can't see but a little more room at least for 18 " tires. If someone out there has mounted 5.5" BS wheels without spacers I would like to hear from them.

I do have quite a bit of reference material from prevoius posts that I have saved to word . I will take a look and see if I can find an expample of 5.5" BS.

Later
Jack

 

My rear wheels are 18x10 with 5.5" backspacing. Tires are 285/35 18s. I have offset trailing arms and a shortened rear spring. No other modifications.

 

Do note that us older C3 guys especially 70-73 seem to have an easier time, not too sure why that is to be honest.

I LOVE the ride height on your car btw man, its sick, what is it sitting at, 25" or so? I thought it was airbagged at first that would have been insane.

 

So Megawatt,

When I ordedred my wheels, I ordedred them all zero offset. If I understood you correctly, this was the BS/offset I needed to fit my car? I'm getting a littel confused now..

 

Oh, and 81 Vette, I dont know if that blue vette in your gallery is yours, but I think it is sick! I love that type of stripe. What is it called?

 

You never said what backspacing you orded, and bear in mind youre only running 9 wides and those have almost no problems, especially with 5 backspacing. 0 Offset is also fine, stockers came that way too.

I just bought that baby, I actually dont know what that type is called to be honest, Im getting my seller to send me all the info. The car basically got a frame-on resto, its show quality all around, Im very excited for it. It was all done by one of the founders of the Corvette Museum over 2 years.

 

Yet he remains one of, if not the only person running 10s in the back who has notched his frame!!

I am running 6 1/2 inch backspacing to really push the tire under the fender lip. That is why the frame is also knotched.

 

I really admire the fit. I had to go 6 1/2 to get that good a fit.

 

Yea I like his car almost as much as I like mine, its a very clean ride, Im really digging the stance on it, it just screams badass.