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2” drop spindle / max tire size?


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Looking to go as tall/ wide in the front as I can.  Had some Schott rims made/ ordered that are 18” rims 8”wide x 4.75 b.s. but I then decided to go all out and get a UMI full coil-over suspension along  w/ 2” front drop spindles while waiting the 8 weeks form the rims to be made and now question is will the 245/45 r18 rub on a hard turn?  
i researched and the tire/wheel combo works normally but the 2” drop spindle now makes we second guess if I know what I’m doing?  Rims just showed up and I need some skins on these shiny things!! 
 

Thanks 
Mark

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Mark,

I am running 255/60s on 15x7 rims with 4.5" bs (+12mm offset) on the front with stock spindles.  Using Tiresize.com, the Tire Size Comparison tool shows your combo is .3" shorter and .4" narrower than mine.  Then, using the Wheel Offset Calculator and Visualizer, the positioning of your combo, 245/45s on 18x8 rims with 4.75" bs (+6mm offset), will be as follows: outer sidewall is .04" further out; inner sidewall is .44" further out, top of tire is .15" lower. To me, all of that says your combo will fit and work as well as mine IF you were using stock height spindles.

Frankly, I would think the 2" drop spindle would mostly affect the clearance from the top of your tire to the top of your inner wheel well, but it may also close up some clearances at the extreme ends of your turning range.  Since I have absolutely no experience with dropped spindles, I can only guess that you will probably be okay with that combo - at least I hope so,  Good luck!

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I do love that Tire Calculator! 

I wasn't sure if i was overthinking the geometry on how the 2" lower tire would change the center of the wheel when fully turned and cause rubbing issues.  

Funny how when you put 14" calipers front/back everything snowballs from there! 

I'll report back on the set-up this spring.   What i learned on this form was invaluable when i was considering tire/rim sizes.  The back wheel are  18" x 10" w/ 6.0 b.s (+12mm)   and from installing just the back rim, it has exactly 1" clearance to the inner frame and outer fender lip.    (the actual outside of the rim measures 11" and the information i learned prior was that our cars have around 13" in the back wheel well and that's what i came up)  The 10"  wide rim w/ the 6" b.s seems to be exactly centered in the back wheel well.

thanks for the help

Mark

 

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Mark,

I appreciate your observations relative to the centering of a 10" wide rim (11" overall width) in the 13" available space between the rear quarter panel and the frame on our first gens by using a +12mm offset. 

I don't believe you mentioned the size of the tire you are planning to run on those 10" rims but the visualization tool uses the tire size (width and height) for comparisons, not the rim dimensions.  Point being, that depending on the width of the tire you mount, you could still run into some tighter clearances.  However, having the rim perfectly centered with the +12mm offset, gives you the very best latitude for some additional sidewall width.

I'm guessing you are planning to run a wider tire on the rear or you wouldn't have gone to the 10" wide rim.  I compared my 275/60s on 15x8" rims with 5" backspace (+12mm offset) with your 18x10" rims with 6" backspace (also +12mm offset) and it places a 275/45-18 in exactly the same position as my setup which I know has about 1" clearance inside and out.  I also looked at the wider and taller 285/45-18 and 295/45-18 tires which reduce the inside and outside clearances by .2" and .4" respectively.  Either should still work for you on the rear. 

This is a good example of why it is so important for positioning and clearance considerations to work with offset rather than backspace. As we both have proven with our different setups, using a +12mm offset with any rim width is what our first gens need to center the rear tire/wheel combo in the available 13" space.

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I finally settled on the tires and have some Nitto NT555 coming tomorrow.

255/45r18 front

285/40r18 rear

I did chicken out on the 295/45r18 for the back.  I read mixed opinions on the fitment of the 295 wide tires along and with the limited options most brands of summer tires had for the matching front tire i just gave up thinking the 295 were for me.    

I will get back and let you how how everything turns out with the full UMI suspension front/back and the 2" drop spindles, with this tire size  (i owe this forum that much)

My little darling is also a 70' SS with the 454 but it was rebuild in 90' for a 'hot-rod' article so the engine isn't original is why i don't feel to much guilt about putting a few modern upgrades on this beast :)

thank you.

 

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Looks like you have made some excellent tire/wheel combo choices for both front and rear, Mark! 

All four tires will be 27" tall with 10" wide treads on the front and 11.2" wide treads on the rear. I would guess that the addition of 2" drop spindles will result in a modest "rake" stance but that is probably what you are trying to achieve anyway.

The +6mm offset on your front rims gives you a bit more clearance with the frame on tight turns and the +12mm offset on the wider rear rims centers your 285/40s within the available space with approximately .8" clearance inboard and outboard. 

It all looks great "on paper"!   Looking forward to hearing and seeing how it turns out when "the rubber meets the road". 😀

Good luck and thanks for sharing!

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