Alright everybody, it's that time finally... I picked up a set of lightweight RX-7 FD wheels this weekend, and am getting ready to bolt them on!
The wheels are a 16x8 with an offset of +50
Right off the bat, I want to answer a few questions you may have:
1. Yes, I have 5 lug hubs on the front, that portion of the swap has been resolved.
2. No, there isn't another set of wheels that will work for my application(within budget)
I am aware that I will need spacers to make these wheels work on my MX-3. At this point I really want to see if anybody else has run similar setups, and maybe compare offset/spacer requirements, as well as ride height adjustments to accommodate the wider tires. My ride height is adjustable, and she currently sits ~3/4" below stock.
I would LOVE to know what offset you need, as I have a set of those tires sitting in my living room waiting on me to pick a rim for them...
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Josh, what tire are you running on those? Any spacers used?
215/50-16 is my last resort... I parallel park very well, but others occasionally drive my car... I'm not rushing these sexy whees that took me 4 months to source.
Reminder, I have PGT front spindles and hubs... MazdaSpeed6 rotors as well, so my setup offers more clearance than stock already... The FDs clear the strut with no spacer, as would a 205 series tire... 215s may be relatively simple to fit, but 225/50 is my goal... Patience has rewarded me thus far, as I do in fact have MazdaSpeed6 front brakes installed and waiting on suitable rubber.
The Probe hubs sit around 5mm farther out than the Mx-3 stock hubs, and the rotor hat is a bit thicker as well.
Worst case if you do find some rubbing, go get some washers to slide onto the studs. Use them as temporary spacers and just add a washer to each stud until you have enough space, then measure how much space the washers take up and that's roughly the spacer size you need.
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Better yet, try this to calculate your offset requirements. These calculations can be used to find wheels and tires, verify what tires will fit existing rims, and to calculate spacer requirements: EDITED 4/29
POSITIVE OFFSET: Nearly all front wheel drive cars with McPherson strut suspension use POSITIVE OFFSET wheels. Looking at the inside of a wheel, POSITIVE OFFSET means that the mounting surface of the wheel is spaced toward the OUTSIDE of the wheel centerline. MORE positive off set means the mounting surface is farther from the INSIDE of the wheel. Less positive offset means the mounting surface is closer to the inside of the wheel. NEGATIVE OFFSET means that the mounting surface is spaced closer to the back of the wheel than the centerline. Very wide wheels on a front drive car COULD require "0" or negative offset. THIS IS RARE!
FINDING THE NECESSARY OFFSET FOR YOUR CAR:
1. FIND THE INDEX: Use a straightedge held vertically on the front (and rear, since they are separate measurements) rotor hat WHEEL mounting surface (NOT THE HUB ITSELF!) as a baseline. Measure the distance from the straightedge to the strut (at THE WIDEST PART OF YOUR TIRE, approximately 9-1/2" to 10-1/2" from the hub center). This is your INDEX. If you have camber bolts, you will want to crank in all the available negative camber when you make this measurement so that you aren't surprised later.
2. FIND WHEEL CENTERLINE: Measure the exact installed width of the tires you intend to use, or use the manufacturer's published section width specs (not the tread width). Divide by 2 so that (example only) 8.3" section width / 2 = 4.15" wheel centerline.
3. FIND THE INSTALLED CENTERLINE: Add the tire clearance you want ( IMHO, absolutely no less than 10mm, and 15-20mm is better) to the wheel centerline to arrive at the (installed) CENTERLINE. LEAVE CLEARANCE FOR CAMBER CHANGES! if you didn't in step 1.
4. DO THE MATH: Baseline to strut = INDEX and (tire width / 2) + clearance = (installed) CENTERLINE, therefore INDEX - installed CENTERLINE= OFFSET
5. FIND THE OFFSET: The remainder from #4, in mm, is your OFFSET. A positive number is a positive offset, a negative number is a negative offset. MX-3s normally have a 45mm POSITIVE OFFSET with stock wheels, tires, and suspension. IF your calculation comes up negative, see #6. If it doesn't, read #6 anyway!
EXAMPLE: In my case: 205/40ZR17 on 7" rims = 8.3" installed width divided by 2 = 4.15" = 105.4mm plus 3/4" clearance (20mm) = a 125.4mm CENTERLINE. Measured INDEX= 155mm (LOTS of negative camber). 155mm - 125mm = ~30mm OFFSET, which is the POSITIVE OFFSET of my rims.
NOTE: if the tire does not extend beyond the rim, use the total rim width for your centerline measurement and make your index measurement at 9 inches or so from the hub center. 225s are approx. 9.1" wide, so they SHOULD extend beyond the rim, but it may be close.
6. SPACERS: On strut type cars, if the OFFSET we calculated in #4 above comes up negative, and you already have wheels, spacers are required to regain clearance. So, if you have 45mm offset wheels and your calculated OFFSET is 30mm, adding a 15mm spacer REDUCES the 45mm offset to 30mm and regains the necessary clearance.
In your case, for 225 section tires, 9.1" / 2 = 4.55" centerline plus 1/2" clearance = 5.05" installed centerline. Installed centerline + 50mm wheel offset = 178mm. Measure your index and subtract 178mm from it. I'd bet you will have a negative number, which will be your spacer requirement, probably at LEAST 25mm. You COULD reduce this requirement by maybe 5mm by using less clearance.
BTW, measured INDEX of a bone-stock RS is 171.5mm (no camber bolts). Calculations verified on an actual car. KEEP IN MIND, use the specs for YOUR tires, they vary considerably for the same tire size from manufacturer to manufacturer.
I hope this helps!
Steve
Last edited by stevesei on April 29th, 2013, 5:50 am, edited 3 times in total.
Steve Seiter
Blue '92 GS, Milly square-port DE with stainless headers, Stoker100 chip, HEI/Blaster conversion,
2.25" exhaust, High flow cat, ZX-2 shocks, short shifter, urethane front bushings, 17x7s with 595 Evos
Tried the FD rims myself last year, gave up. They did fit but rubbed on the front and steering felt very heavy. Looked sweet though!
AZ-3 1498cc Turbo! EVO 8 turbo and manifold, 5 stud swap, SSR Type C, DIYPNP seq Megasquirt Mx-3 2.5 V6 Turbo 291 BHP 251 lbft @ 8psi - Retired due to rust and back at uni View Worklog
The section width of the tires I hope to use(Kumho Ecsta ASX 225/50-16) is 9.2"
With the numbers you gave(approximately 12.5mm clearance), and my installed centerline of ~179.54mm, I should need a spacer between 8-9mm. This does not take into account the rotor hat thickness, I assume? It looks like a 10mm spacer would give me ~15mm clearance between the tire and the strut.
If I did the math properly(I'll double and triple check my measurements and math this week), then that should be a simple enough fix for me. I wouldn't even need extended lug studs to clear a 10mm spacer.
Hopefully there won't be an issue with clearance issue between the tire and the fenders. Running near-stock ride height, fender rolling may not even be required...
Fingers crossed, this looks to be coming along nicely!
1. Make sure you use YOUR INDEX number, since this will change with negative camber.
2. Rotor hat thickness has NO EFFECT on the calculation, since you are calculating from the rotor hat WHEEL mounting surface, NOT THE HUB ITSELF! If you got something different from reading the post, I need to make an edit to make sure I'm absolutely clear on that!
I hope everything works as you planned.
Steve
EDITED THE POST 4/29
Steve Seiter
Blue '92 GS, Milly square-port DE with stainless headers, Stoker100 chip, HEI/Blaster conversion,
2.25" exhaust, High flow cat, ZX-2 shocks, short shifter, urethane front bushings, 17x7s with 595 Evos
