Help with rear wheels please! 18x10 et45 or 17x9.5 et38 best for over 500bhp

[rwdwiganer]

I\'m hoping someone may be able to give me a bit of advice with this, I\'ve been searching and reading on other RX7 forums too and tying myself up a bit with it all!
My car is struggling with traction, it is making just over 500bhp and 500ft/lb at the moment but I will be looking to turn up the boost when I have decided which rear wheel will be best to go for.
I\'m not planning to roll my rear arches so have been looking at 18x10 et45 Rota MXR\'s or 17x9.5 et38 Enkei RPF1\'s for the rear.
I am aware that there are more options available with the 18" wider semi slick tyres compared to 17" tyres- but keep reading that a larger side wall will help with traction- a slightly larger sidewall I will be able to run with the 17" wheel...
I really do want to compromise a bit and not roll the rear arches; can anybody help with this please?

[najiru]

I have 400 at the wheels, just under 500 at the fly, and I run 17 x 9.5 on the rear with 255/40\'s and they put the power down well but don\'t forget you may need to do a bit of setup trial and error to get it working well. With warm tyres, in the dry I can put my foot flat in 2nd and it\'s fine in a straight line ie after the hairpin in this vid...except the second time round when I still had a wheel on the curb lol

http://youtu.be/LN2jzqkQJd4

[boosted]

:3gears-lh:driving  sweet really liked that vid...cars looks well sorted!

[najiru]

Thanks! I have one from the last round which was Silverstone national to edit and get up but it\'s just not as interesting a circuit hence not as interesting a video lol

[rwdwiganer]

Thanks for that, I\'m still trying to decide so I suppose the more I read and ask the better!
I\'m planning on going with 275 Toyo R888\'s on the back, but if I go with 17" wheels that is the widest tyre available for a 17" wheel.
I\'m just a little worried that going 17" will restrict my tyre choice options.
I don\'t really want to go down the arch rolling route so if 18" 285\'s wouldn\'t fit under my standard arches anyway (with a 9.5" et38 rim or 10" et45 rim) maybe there won\'t be any advantage going for 18" wheels anyway- unless anyone knows any better? I\'m still looking for answers myself searching the net but if anyone knows for sure I would really appreciate any help!

[boosted]

Thats some serious wide tyres! Have you looked at alignment as well. If your alignment is out dont matter what width you put on will struggle with grip.

[Ed_RX7]

Did I read right 500 ft lbs of torque.... Is the engine a v8?

[neil_jdmr]

Sounds like crazy talk

[rwdwiganer]

Sorry, I hate to say it (as I know this is Mazdarotaryclub after all!) but it is a 2JZ Toyota engine with a GT35r turbo. The car has just been set up on a Dynodynamics dyno at wastegate spring pressure 1 bar spring, just over 500bhp, 500ft/lb. I am looking to increase the boost- hence needing the wider wheels...
I still really need help deciding which wheels to go for- I have read the Enkei RPF1 9.5x17 ET38 and Rota MXR 10x18 ET45 will fit on the back without any arch work with a 275 (30 for 18", 40 for 17") but can anyone please help and confirm this? I would really appreciate any help with this.

[neil_jdmr]

Well done for the conversion mate and that\'s some serious power.

[rwdwiganer]

Thanks for that! To be honest I haven\'t had much of a positive response overall from doing the swap and understand why! This forum is really good for any infomation I need on various things and there are lots of people in the know on here! The car was in a sorry state when I bought it, the engine was blown etc...
I really do need to find out about what wheels I can actually fit under these standard rear arches though... I must admit I\'m more tempted to go with the 9.5 17" et38 Enkei\'s RPF1\'s simply because I know they will fit a 275 40 without rolling the arch- and the slightly taller profile should help with traction, BUT because R888\'s aren\'t available in a 285 17 I\'m still unsure as by going 17@ I could be limiting myself to 275 tyres? Does anyone know if I could actually fit a 285 on the rear for sure without modifying the rear arches in anyway?

[rwdwiganer]

Boosted- I will get the alignment done as soon as my new coilovers, wheels and tyres are fitted too- IF I ever work out what will be best- my knowledge of wheels and tyres isn\'t one of my strong points unfortunately...

[neil_jdmr]

I\'ve got 9.5 x 17s on the rear on mine with a 25 offset and a good less hp than you and I break traction in the bone dry in second in a straight line tbh

[boosted]

Sounds like a lot of fun...cant help you with wheel tyre combo max i had on my fd was 255  40 18s but cant remember the offset.
http://www.1010tires.com/Tools/Wheel-Offset-Calculator

This is a handy tool to compare existing combo and size comparison as it gives you more and less inner and outer measurements.

[rwdwiganer]

Thanks for your replies, I am 99% sure I will be going for 17x9.5" rears but a higher offset- et38 to fit the 275\'s on there