Help!! 1.18???

synolimit · 06-30-2013, 12:43 AM

Can you teach me what 1.18 means? Stock tires are 245/40 and 275/35 and people say that's 1.18 but cannot find a calculator to prove this because I don't know where I saw it or what it means (been looking all day). If you go bigger you get understeer, smaller oversteer??

I know I want rpf1's. 18x10.5 +15 rear and pretty sure 18x9.5 +38 front with a 15mm spacer for a +23 overall. From all the pics I've seen this should put the wheels looking the same and just under flush with the fenders which is the look I like best.

Tires however I'm racking my brain for last 5 hours reading everything. To keep stock as much as possible it would seem a 265/40 and 295/35 would be equal since both are only going wider 20mm which might keep this 1.18. Overall height I know is going down from stock about 0.4-0.5".

If it helps I like to drag race, autox and hopefull find some track days so I'm not sure if I want a 1.18 or lower or even higher. I come from superbike racing so I guess I'm used to the back end stepping out.

FYI only 265/40, 295/35 I like and want to afford is conti DW's. had them on my WRX and loved them in a 245/35/18. I know their side walls are weak but in the 35 I never felt it but I'm not sure if they'll be up to the task of all the sporting I want to do. I also loved how light they were (weak side wall re-enforcement).

Any input?

Thanks

cooltoy · 06-30-2013, 10:07 AM

I think it's offset. 1.18 of an inch = +40.

synolimit · 06-30-2013, 11:25 AM

Quote:

Originally Posted by cooltoy

I think it's offset. 1.18 of an inch = +40.

But the fronts 47 and rear is 30. It's a 17 difference which isn't 1.18. It's some kind of ratio I can't figure out.

chrischhorn · 06-30-2013, 03:18 PM

Quote:

Originally Posted by synolimit

But the fronts 47 and rear is 30. It's a 17 difference which isn't 1.18. It's some kind of ratio I can't figure out.

closest ratio I can think of that possibly pertains to this situation is tire widths but still its still not an exact match to the 1.18. 275/245 =1.12 but with you speaking of understeer and oversteer, it pertains to the situation. Wider front tire = more understeer.

BTW I just ordered my set of tires. 275/35/18 for the front and 295/35/18 for the rears in the BFGoodrich Rivals for my 18X9.5+35 and 18X10.5+12

synolimit · 06-30-2013, 04:50 PM

Quote:

Originally Posted by chrischhorn

closest ratio I can think of that possibly pertains to this situation is tire widths but still its still not an exact match to the 1.18. 275/245 =1.12 but with you speaking of understeer and oversteer, it pertains to the situation. Wider front tire = more understeer.

BTW I just ordered my set of tires. 275/35/18 for the front and 295/35/18 for the rears in the BFGoodrich Rivals for my 18X9.5+35 and 18X10.5+12

Hmm, maybe it was 1.12 then.

Why go for understeer with the larger front tire you ordered? doing the math though 295/275 is only 1.07. so is the lower number more under or oversteer?

I looked at those sizes but I didn't want the front only being 25.6" diameter since OEM is 26.8". I don't think I could even lower the car.

chrischhorn · 06-30-2013, 06:36 PM

Quote:

Originally Posted by synolimit

Hmm, maybe it was 1.12 then.

Why go for understeer with the larger front tire you ordered? doing the math though 295/275 is only 1.07. so is the lower number more under or oversteer?

I looked at those sizes but I didn't want the front only being 25.6" diameter since OEM is 26.8". I don't think I could even lower the car.

My car is lowered about an inch, maybe a bit lower already. Our cars are front heavy and if you check the track section, most people recommend a 285 or larger for better breaking power on the front. There is a reason a lot of track members are running square setups, not even staggered anymore. Understeer/Oversteer isn't a huge factor for me right now. Having the car bite and control consistently will yield faster times then whether I have more understeer or oversteer.

122554 · 06-30-2013, 08:47 PM

It refers to the maximum difference between the circumference of the front and rear tires. Anything over this ratio will cause problems with the VDC.

It has NOTHING to do with wheel size, tire width, etc..

synolimit · 06-30-2013, 10:07 PM

Quote:

Originally Posted by 122554

It refers to the maximum difference between the circumference of the front and rear tires. Anything over this ratio will cause problems with the VDC.

It has NOTHING to do with wheel size, tire width, etc..

Hmm ok. I got 83.9 f and 83.5 rear circumference. So where's the 1.18 fall into that? Math wise, I want to see the formula. And we all turn off the VDC and unplug the YAW sensor.

SouthArk370Z · 07-01-2013, 08:43 AM

Quote:

Originally Posted by synolimit

Hmm ok. I got 83.9 f and 83.5 rear circumference. So where's the 1.18 fall into that? Math wise, I want to see the formula. And we all turn off the VDC and unplug the YAW sensor.

That gives you a ratio of 83.9:83.5 or 1.005. You are well within the limits.

The formula is divide the larger tire circ by the smaller tire circ.

synolimit · 07-01-2013, 11:41 AM

Quote:

Originally Posted by SouthArk370Z

That gives you a ratio of 83.9:83.5 or 1.005. You are well within the limits.

The formula is divide the larger tire circ by the smaller tire circ.

Yes I saw that. But I know for a fact people did not state a 1.00 number. It's was 1.18. So they must not have been talking about divided tire circumference with the OEM tires.

chrischhorn · 07-01-2013, 11:53 PM

Quote:

Originally Posted by synolimit

Yes I saw that. But I know for a fact people did not state a 1.00 number. It's was 1.18. So they must not have been talking about divided tire circumference with the OEM tires.

What he is saying is 1.18 is the max ratio you can achieve before your vehicle starts to freak out with VDC and everything else. You're goal is to not reach that 1.18 ratio, not that that is the optimal ratio.

binary0x01 · 07-02-2013, 12:38 AM

VDC off... ratio obsolete

synolimit · 07-02-2013, 07:42 PM

What would you rather have for track duty??

18x9 +20 front, 18x10.5 +15 rear with 265/40, 295/35

Or

18x9 +20 front, 18x10.5 +15 rear with 275/40, 295/35

Or

18x9.5 +23 front, 18x10.5 +15 rear with 275/40, 295/35

06-30-2013, 12:43 AM	#1 (permalink)
synolimit A True Z Fanatic Join Date: May 2013 Location: Columbus, OH Posts: 5,051 Drives: 2013 Silver 370z Rep Power: 3390	Help!! 1.18??? Can you teach me what 1.18 means? Stock tires are 245/40 and 275/35 and people say that's 1.18 but cannot find a calculator to prove this because I don't know where I saw it or what it means (been looking all day). If you go bigger you get understeer, smaller oversteer?? I know I want rpf1's. 18x10.5 +15 rear and pretty sure 18x9.5 +38 front with a 15mm spacer for a +23 overall. From all the pics I've seen this should put the wheels looking the same and just under flush with the fenders which is the look I like best. Tires however I'm racking my brain for last 5 hours reading everything. To keep stock as much as possible it would seem a 265/40 and 295/35 would be equal since both are only going wider 20mm which might keep this 1.18. Overall height I know is going down from stock about 0.4-0.5". If it helps I like to drag race, autox and hopefull find some track days so I'm not sure if I want a 1.18 or lower or even higher. I come from superbike racing so I guess I'm used to the back end stepping out. FYI only 265/40, 295/35 I like and want to afford is conti DW's. had them on my WRX and loved them in a 245/35/18. I know their side walls are weak but in the 35 I never felt it but I'm not sure if they'll be up to the task of all the sporting I want to do. I also loved how light they were (weak side wall re-enforcement). Any input? Thanks __________________ 13 370z-

06-30-2013, 08:47 PM	#7 (permalink)
122554 Track Member Join Date: Jan 2013 Location: My own world Posts: 506 Drives: 2010 Nismo Rep Power: 14	It refers to the maximum difference between the circumference of the front and rear tires. Anything over this ratio will cause problems with the VDC. It has NOTHING to do with wheel size, tire width, etc.. __________________ I don't normally drink beer, but when I do....i drink a lot!

07-02-2013, 12:38 AM	#12 (permalink)
binary0x01 Track Member Join Date: Jun 2012 Location: Idaho Posts: 892 Drives: 2012 6-SPEED 3.7L Z Rep Power: 15	VDC off... ratio obsolete SouthArk370Z likes this. __________________ Tune (by Seb@SpecialtyZ) -- Upgraded Parts List : When in doubt, use brute force; if it doesn't work, you aren't using enough.

07-02-2013, 07:42 PM	#13 (permalink)
synolimit A True Z Fanatic Join Date: May 2013 Location: Columbus, OH Posts: 5,051 Drives: 2013 Silver 370z Rep Power: 3390	What would you rather have for track duty?? 18x9 +20 front, 18x10.5 +15 rear with 265/40, 295/35 Or 18x9 +20 front, 18x10.5 +15 rear with 275/40, 295/35 Or 18x9.5 +23 front, 18x10.5 +15 rear with 275/40, 295/35 __________________ 13 370z-

06-30-2013, 10:07 AM	#2 (permalink)
cooltoy Elite Member Join Date: Jun 2012 Location: Calgary Posts: 14,006 Drives: 14 PW 370Z S/T MT Rep Power: 243724	I think it's offset. 1.18 of an inch = +40.