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Discussion Starter · #1 ·
If someone could do some of the calculations for me, it would be really helpful

The rims I'm going to get getting are 20x8.5's w/ +40 mm offset in the front and the rears are 20x10" w/ +35mm offset. I have to get adapters to make them fit my bolt patterny anyways and I believe that they need to be atleast 1" according to Ed Runnion.. I don't really want to cut my studs

In the back of my car right now, I have 1 1/4 spacer on one side and 1 1/2 on the other side and it's PERFECT for my car. I want the new rims to stick out just as far... Hope this makes sense
 
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Discussion Starter · #2 ·
Note first you need to read my note on the studs from your other thread ;)

Front : 1" thick spacers

Rear (note this only applies because you have an SS....9C1 and Civie Caprice would be different.....just clarifying so someone doesn't search this thread later and order the wrong thing ;) ) : By my calculations, for a 10" wide wheel +35 offset is the same as 6.9" backspacing (I'll skip how I figured that out for now....just trust me ;) . A 1" thick spacer would effectively reduce it to 5.9" backspacing. 5.9" backspacing on a 10" wide wheel is likely to be REALLY close on at least one side....I wouldn't go any thicker than that.
 
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Discussion Starter · #3 ·
Alright.. I did some calculations on my own.... Hope they're right...

For the fronts, with +40mm offset on an 8.5" rim, I would have approxamately 6.32" of backspacing... Stock 8.5" impala rim has 5" so if I want to be about the same as stock, I would need about 1 1/3" spacers...

For the rears, on a 10" rim and + 35mm offset, I would have approxamately 6.87" of backspacing (thanks Ed ;) ) and 3.13" of rim in frontspacing... Meaning about .37" less than stock (8.5"-5"=3.5").. I would want to get my spacers in the rear probably about 1/3" larger than the ones I have now to get it to be about the same... a little less than before so I make sure I don't scrub my new rims in the fenders...

I think I got it right but I wanna make sure... Thanks for the replies on my posts Ed.
 
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Discussion Starter · #4 ·
Conformation?

I'm about to order them tomorrow... I think I'm going to go with either 1 1/4 or 1 1/3 for both the fronts and for the rears, 1.5 on one and 1.75 on the other... JR from Motorsports Tech is giving me a great deal b/c this is the second set I'm buying from him. Great quality adapters and spacers
 
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Discussion Starter · #7 ·
SSlumpin IMp- Your sig pic is 20*8.5's correct? Would you like to sell your current spacers? LMK
 
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Discussion Starter · #8 ·
Yeah the ones in my sig are 20x8.5.. and yes I am going to sell my current spacers but they weren't on when I took the pic in my sig. The spacers I'm using are from Motorsports Tech and are hub centric to the car only and not the wheel. I have never had any problems with them and the studs are thicker than the ones that come stock on our cars so I wouldn't worry about them.. and never have

I'll PM you about them and if you don't want them I'll put them in the For Sale Section with pics of how far they pushed my wheels out. I'm gonna ask 100 shipped for them. LMK
 
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Discussion Starter · #9 ·
Yeah, if you could just pm me with before and after shots from the side and back, that would be cool. Once I see them, I'll let you know. Just to clarify, the spacers attach to the car with the studs from the car going through the holes on the spacer, then the studs on the spacer hold on the wheel, correct?
 
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Discussion Starter · #10 ·
Just a reminder....been there and done this a few times, so here's a bit of info I can pass along.

Rated rim width and overall wheel width are different numbers. The rated/advertised width represents the bead seating surface of the rim. As there are many variations in rim edge design, it is impossible to know what you have as overall width without actually measuring the rim. A factory SS wheel measures about 9.6" edge to edge, but has a rated width of 8.5".

The numbers I see you using to calculate your spacers do not appear (to me) to take into account the difference in the numbers you get from offset info vs measured backspacing, since it appears you have added 3.13 (calculated from the measured B/S) & 6.87, I assume is what you actually have measured as the B/S, which ADDS the extra rim edge. Granted, it isn't much, but if you are attempting to maneuver a wheel in an opening, even 1/8" difference can dramatically change appearance.

Since you are working with a narrower front wheel, is your objective to place the outer edge of the wheel back to the same position as the OE 8.5 x 17 wheel (with +6mm offset)?

Also, don't assume your rear axle is placed properly from side to side...you might consider getting different thickness spacers (actually, you will probably be using adapters) to even up the rear wheel positions. This has seemed to be less of an issue with front wheel placement.

The other consideration is IF you are doing a pattern change to 4.75", and use anything less than a 1.5" spacer/adapter, you may find that the front brake rotor hub extends too far and hits the new wheel, but this depends on the design of the hub of the wheel you've chosen.

Careful checking is needed before you get too far into something like this, and you seem to be on the right track with the info you've provided and the discussion so far.

Hope this hasn't confused anyone!
 
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Discussion Starter · #11 ·
Alright hmm... I'm going to have to think about this for a second first because I thought I had this done right before. Right now, in the rear, I have 1/4" differce in the spacer sizes which works really well and evens them out so I can just factor that in for the rear.

I have not actually measured the rims because I don't have the rims yet but I will soon but I wanted to order the adapters now so I could put the rims on as soon as I get them. For the fronts, I just wanted to put the outer edge of the rims at the same place as the stocks. I do understand what you're saying about the brake rotor hub hitting the wheel but why 1.5"? I was going to order 1.25" for the fronts and one 1.5" and another 1.75" for the rear but now I'm not so sure because of the difference of the width that you stated for the stock rims. I think I should be able to get the backspacing measurements for the new rims and be able to figure it out from there but would I need any other info about frontspacing and offsets?
 
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Discussion Starter · #12 ·
If you run into any problems in the rears you can always go with a lil' bit of negative camber.This will bring the upper edge of the rim in and the bottom out a lil'.

[ 01-27-2005, 11:54 PM: Message edited by: KW Baraka ]
 
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Discussion Starter · #13 ·
OE rimes, at least most GM applications until the C6 came along, have had rim sections configured to accept clip-on weights--and both the inner and outer rim edge is designed for clip weights.

The GM rim design is based on some standard, which I will guess is a wheel industry or SAE spec. Aftermarket wheels and many other non-GM OE designs are no longer following these specs, especially in alloy wheels--steel is pretty much unchanged, but the desire for a cosmetically "clean" outer rim has finally become part of GM's newer aluminum wheel efforts, and provisions for balancing are elsewhere on the front half of the rim, in the case of the C6.

However, (I think) even the C6 wheels have a conventional clip-weight rim shape on the inboard side, but most of the aftermarket wheel suppliers do not, so I really think you either have to wait and measure the rim yourself, or possibly the manufacturer can tell you what the drawing dimension is, though I'd still not trust anything but actually measuring it.

As far as spacer thickness, this is more an issue with the 4.75" pattern when using OE (C5 or Camaro SS) wheels, since the hub center on these wheels is 2.75", and with less than a 1.5" spacer, there is likely to be an interference problem if you are staying with that hub size on the wheel and trying to use hub-centric spacers. If you are using a 5x5 pattern on the new wheels, do you know what the hub center bore size is supposed to be (on the wheels)? The rotor/axle hub is 77.8mm, or 3.0625", and I've seen some aftermarket wheels in 5x5 pattern with the hub bore listed as 78.1mm.
 
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Discussion Starter · #14 ·
The wheels I'm getting are 5x4.5 I believe (5x114.3). The site that I'm going by to check backspacing is http://www.rsracing.com/tech-wheel.html#wheeltrm which has 8.5" wheels w/ 5" backspacing as +6mm offset which is correct.

For a 10" rim with +35 mm offset it would calculate to 6.87" of backspace but that's now what I'm worried about. I want the front edge of my new wheels where the edge of my stocks are so is that frontspacing? I'm going to try to get all the measurements for the new rims and search for ALL the specs on stocks but I haven't found what I need to know about the diameters of the stocks with my previous searches... I'mma keep posting.. thanks for the help.. please post if you have any info for me
 
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Discussion Starter · #15 ·
If you are working with a 4.5" pattern, the front rotor hub extension definitely becomes a problem if using a hub-centric spacer/adapter under 1.5" thick.

The other concern I would have, personally, is the wheel stud size. The leverage on the studs is greater as the pattern gets smaller, and combined with your larger wheel diameter, I'd like to see you use 14mm studs in the adapter-to-wheel joint.
 
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Discussion Starter · #16 ·
Okay well I don't mind using a 1.5" spacer for the fronts because when I had dropped spindles on the car, the wheels were pushed out atleast 1/2" from their normal position and according to my calculations, that would only push them out 1/6" more than their stock position which I can live with.

The adapters I currently run are from Motorsports Tech and have 14mm studs on them so I don't doubt that the new ones will have the same but I can make sure about that.

Now I'm decided that I will run 1.5" in the front. I'm going to go ahead and call MS Tech and ask him if he could take some measurements for me on the rims.
 
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