CYD

In hopes of finding the right offsets for new wheels I used a couple of the excel docs and I found I liked the Question Eliminator the best...

I have Tanabe race springs with Tokico illumina struts. Brakes are stock except for the brembo rotors. Eventually plan to get a BBK so clearance is a concern.

So moving right along I am on the fence on whether to get 18" or 19" Wheels...adding rear flares is part of the equation. So I am not too concerned with Frontspacing except for the front lock-lock clearance issues.

If I go 18" wheels my choices from Rishis are the following:
F-18x10 +48mm offset (3.61 fsp / 7.39 bsp)
R-18x12.5 +11 offset (6.32 fsp / 7.18 bsp)

According to the Question Eliminator 3000, the fronts' there is too much backspacing on the front and too much frontspacing in the rear.
If i get +42 on the front it says they will fit, but I don't know if I can get it in that size or if it is necessary.

Damian runs 7.5" backspacing Front and Rear. So does that mean 7.39" backspacing will work on the front but I will need to roll/flare the front?

AllRotor93 is running 18x12 +18, so .5" is 12.7mm so say -6.3mm each way give or take would but 18x12.5 at approx +11mm offset right? So by that comparison +11mm would work maybe?

Also read a post by 13bhavoc, that an 18x12 +25mm would work which doing the math again for 18x12.5 would be +12.3mm offset

Finally Rynberg, the authority on offsets(Who didn't respond to my PM, sorry for some reason the $250 didn't go through not sure why) , mentions "To clear the rear suspension with 12.5" wide wheels, you would need an offset of approximately +12 or less. "

Max Cooper (yet another big name when it comes to offsets), mentions: "Anything more than 7.75" probably won't fit. 7.5" is good." So 7.5" or less will fit? If that's the case, does that logic only apply to rears or for front scrub/turn in/lock-lock clearance as well?

Thanks,

~CYD

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So I've searched for "Minimum Backspacing" and came up with 2 threads...

https://www.rx7club.com/showthread.p...um+Backspacing
https://www.rx7club.com/showthread.p...um+Backspacing

Neither really helped as I saw both 7.5" and 7" backspacing mentioned.

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https://www.rx7club.com/showthread.p...hlight=18x12.5

gooichimotors

well im in the same boat as you! someone needs to get on here and start answering some questions!

dradon03

iTrader: (2)

CYD, how have you been I am waiting for GT5 so we can do some more challenges.

I just want to let you know that unless you have 700 hp or it will be a track only car 12.5 rear in complete overkill.

CYD

Good to hear from you again. GT5:Prologue comes out in a month(50 cars, 7-10 tracks), it has Online racing, unfortunately there are no RX7's in that demo. I am still going to get it though! It should tide me over until GT5 comes out.

I wouldn't put any arbitrary magic HP number to warrant 12-13" wide wheels.

Granted, there are obvious disadvantages and advantages in any scenario, overkill is relative to each individual application. I prefer not to debate or argue my reasoning. However, if you want to PM me about my reasoning, I'd be happy to discuss/debate offline. or IM. I already know about the weight disadvantages and the width disadvantage in the wet.

aim/yahoo/msn/meebo: CYDVici0us
gmail: cyd.carpediem

On a side note, I was told the offsets should work fine with the FD. So I will probably go with that. The only reason I would get 19's is to appease the wife. But I am not sure if I could live with that much additional unsprung weight just to make the wife happy.

dradon03

iTrader: (2)

Hey CYD,

Just comfort wise a 19inch rim with a 2- something sidewall is really not going to be very comfortable. Also sometimes going into a turn it is better to have more sidewall. Feel free to send me a PM and we will discuss.

dhays

iTrader: (1)

CYD, I'm curious as to what you are going for with your wheel and suspension choice? Are you going to be racing, just street, show...?

I don't know squat about wheels or suspensions, but it seems to me that (as dragon pointed out), that low a sidewall will be an awfully rough ride. Also, unless your wheels are going to be super light, 19s will be quite a bit heavier than most 17s. Doesn't putting more weight farther out from the center of the wheel demand a lot more torque?

zenofspeed

iTrader: (1)

yeah, that is also my understanding. big wheels like that are mostly show.

CYD

The wheels will be 5-6lbs heavier than stock. Depending on what ratios you use, its probably about 200+lbs of equivalent sprung weight, not to mention the additional weight of the tires.

The car makes a comfortable amount of power, that I am not too concerned with the extra weight. But who knows. My opinion can change on a dime if all manner of handling goes out the window.

Regarding stiffness, it is already stiff with 45s...but there are folks out there running on a 30 profile tire that don't complain.

PureRX7 runs a 30 profile and said moving from a 35-30 made hardly any difference in ride comfort. Not to mention he's balling on 19's.

Charlie is also running a 30 profile tire, and it looks Great, and I haven't heard him complain about the stiffness of the 30 profile.

My focus is primarily lateral grip. Whether it be on the track at PIR or on a nice canyon back road out in Eastern Oregon.

For the width I am getting, it will be a 30 profile tire front and rear. I hope that the rears do not sit lower than the fronts as Charlies do.

~CYD

dradon03

iTrader: (2)

Purerx7 has a showcar not a race car. Albeit a very beautiful car with even more beautiful rims!

Honestly CYD, I say if it floats your boat go with 19's you know what I think, did you consider that you will have to run higher on your suspension to not rub on contraction (at least I think).

If you want grip I would do exactly as Damian has maybe it will match the grip and weight/performance feilds. If you wanted to make me endlessly jealous it would be 18*10 and 18*12 Fikse FM-10's, you got the power.

purerx7

iTrader: (61)

Thanks for the kind words, makes me wonder why i am selling my rims. I have had NO problems with 19s, i am running on the stock suspension and stock rear 1/4 as the front has r-magic fenders. I noticed NO difference going from a 35 series to a 30 series tire, this also might be because i went from a nitto tire to a toyo. Dradon03 is completely correct though, I would never bring the fd to the track on 19s, it would destroy my fenders, but have yet to have any problems on the street.