3.5" or 3" backspace for a 325/50r15 tire?

[5.Z]

well I'm once again changing my combo.

 

This time im setting up the car for drag radials.

 

the rim of choice:

15x10

 

Im ordering it so i can have ANY backspace I need.

 

The car is set up with stock suspension with custom 4" flare(which im thinking of increasing to a widebody 5-6") but thats later on.

 

anyways the tire im thinking of getting:

Mickey Thompson ET Street 325/50r15

 

Im thinking since according to their website sidewall to sidewall is 13.1

 

SO on a 10" rim it will add about 1.5" additional backspace.

 

and since its an early 260z with stock suspension my clearance is 4.5" backspace or is it 5"

 

im thinking with 3" back space on the RIM and with the additional width from the tire(1.5") im at 4.5" backspace in TOTAL. which should put me close to the suspension but not enough to hit it.

 

IS THIS CORRECT?

 

whats your take?

 

 

 

PS: I know its 28" tire.

and I just like the wide tire so I KNOW I DONT NEED IT ALL. I just like it.

 

Thanks

[crazyoctopus]

4.5" is the maximum backspacing that you can run with stock struts.

 

As far and the bubble that you wan to add to the tyre... 10in rims are actually 11in wide, so instead of 1.5" you have 1.1" either end. I would say go with 2.5-3, and if there are any issues with clearance add a spacer. you may also have to worry about the growth of the tyre so 2.5 may be what you want to go with.

 

--another thing that you should think about is the unsprung rotating weight that you are adding to the car. unless you are going expensive, diamond racing wheels are not that light at 15x10 (20lbs a piece) plus there is the additional weight from the tyre, so if you want to be faster you may want to look at getting a lighter wheel instead of a wider wheel.

Edited April 6, 2010 by crazyoctopus

[5.Z]

4.5" is the maximum backspacing that you can run with stock struts.

 

As far and the bubble that you wan to add to the tyre... 10in rims are actually 11in wide, so instead of 1.5" you have 1.1" either end. I would say go with 2.5-3, and if there are any issues with clearance add a spacer. you may also have to worry about the growth of the tyre so 2.5 may be what you want to go with.

 

--another thing that you should think about is the unsprung rotating weight that you are adding to the car. unless you are going expensive, diamond racing wheels are not that light at 15x10 (20lbs a piece) plus there is the additional weight from the tyre, so if you want to be faster you may want to look at getting a lighter wheel instead of a wider wheel.

 

thanks

 

and I have considered that aswell.

 

My car will be a turbo v8 and plans on pushing 500whp-which is why im changing my combo. so im not really that worried b/c I feel that these new combo weight the same as my current one.

 

My current setup is this:

4 to 5 lug 2 piece adapter

17x10.5 cobra R

315/35/17

 

I feel that with the weight of spacer + rim + tire Its similar if NOT MORE than the diamond racing + tire setup.

 

What do you think? do you think the DR and 325 weight more?

 

 

and the plus is that I get to get rid of the spacer/adapter so I can take it to the drag strip if I want to.

[crazyoctopus]

you would search around the internets to get the real weight of the cobra wheel to compare.

 

and if you are thinking about going ridiculous i think braaap is running 12s

[19762802+2]

you would search around the internets to get the real weight of the cobra wheel to compare.

 

and if you are thinking about going ridiculous i think braaap is running 12s

 

Actually rear 13x13's and 13x10 front haha.

[crazyoctopus]

do it.

 

finding dot tyres for 13s may be harder/more expensive than 15s though; even then 15s are really limited.

[5.Z]

do it.

 

finding dot tyres for 13s may be harder/more expensive than 15s though; even then 15s are really limited.

 

 

im not worried about the tires much, since right now they have nitto/bfg/MT and I seriously doubt all of those would discontinue there tires in the 315/325 range.

 

 

Okay so I found an online link

http://www.moddedmustangs.com/forums/5-0-mustangs/141857-8-8-gt-rear-end-weight.html

 

according to that the cobra R that I have on NOW weight about 26lbs.

 

According to tirerack http://www.tirerack.com/tires/tires.jsp?tireMake=BFGoodrich&tireModel=g-Force+T%2FA+Drag+Radial+2

my gforce t/a weight in at 28lbs.

 

 

so with just tire and rim that I have now totals up to 54lbs

thats not counting the spacer.

 

 

the new set up

tire is 37

rim is 20

so thats 57

 

with the spacer my setup now would probably be around the same weight.

 

 

 

 

SO weight wise it will be thesame.

 

Except I should get better traction since theres more meat, thread width is 11.6 vs. 10.4 is about 1.2" each side gained. side wall is also thicker.

anyways overall I think its a better choice.

 

 

 

But the question is do you guys think I would be good with 3" backspacing? I DO NOT WANT TO ADD ANY SPACER.

 

what is your take? will 3" bs clear?

 

thanks

[5.Z]

4.5" is the maximum backspacing that you can run with stock struts.

 

are you 100% sure on this? Have you measured it?

 

b/c I just FINISHED measuring and looks like my 74 early 260z HAS 5+" backspacing and that a 5" spacing(including tire is just the max you can run. Are you talking about the backspace on rims im assuming?

 

 

so heres how I did the measurement.

 

I have a 3/16" spacer otherwise the cobra R rims/tire is right on the strut tower.

so without that spacer it basically rubs a little is what im saying. 3/16 is smallest size i found localy.

 

 

Measuring the rim/tire combo I got the BS of 7 5/16 to 7 6/16(lets stick with 7 5/16 since its less)

 

Im using a 2" spacer/adapter.

 

so that leaves with 5 5/16 BS

 

lets subtract 5/16 for clearance.

 

were left with 5" backspacing WITH tire mounted.

 

hopefully im still making sense here.

 

 

 

SO why wouldnt a 3.5" work? wouldnt it fit just right? assuming the tire does not grow more than 5/16?

 

so from my understanding radials arent suppose to grow correct?

and the drag slicks grow 3%?

 

so 5/16 should in theory be plenty of space?

Edited April 7, 2010 by 5.Z

[crazyoctopus]

here is 4.5in of backspacing on a 15x10 with 225.50 tyres on stock struts

 

 

you could try 5in backspacing, but why risk any type of binding or interference at all?

[5.Z]

here is 4.5in of backspacing on a 15x10 with 225.50 tyres on stock struts

you could try 5in backspacing, but why risk any type of binding or interference at all?

 

is this 4.5" BS measured from rim or measured from tire(when tires installed)?

[crazyoctopus]

this is the spec that diamond racing gives.

 

[Ed260Z]

 

The car is set up with stock suspension with custom 4" flare(which im thinking of increasing to a widebody 5-6") but thats later on.

 

 

 

I surprised you haven't changed over to coil-overs yet. You will gain more clearance. Since they take up significantly less space than the stock set up.

[5.Z]

I surprised you haven't changed over to coil-overs yet. You will gain more clearance. Since they take up significantly less space than the stock set up.

 

Well I'm aiming for as low cost as possible.

I figured I don't get that much difference in traction wise during launch so right now I can't justify coils. It cost me $50 to put that flares so it's alot cheaper than 500.

I would rather spend the money on good tires and run stock suspension than run coils and crappy tires.

[5.Z]

this is the spec that diamond racing gives.

 

 

Oh okay so it is 4.5 from rims then. Well that is perfect looks like about half to a full inch clearance.

 

I should be able to get away with 3.25 bs just to be on the safe side.

 

Thanks