Hey 8Club!

This question is for anyone who's experimented with 11" or wider wheels on a RX8. I know there's owners who've fitted 18x11 with 295/30 but has anyone been able to fit 18x12 with 315/30?

I'm considering picking up a new wheel set (18x11 or 18x12 ) to do some experimentation with to compare respective lap times / available mechanical grip to my current 17x10 with 255/40 combo. Current combo weighs 42.8 lbs and given a similar setup will weigh within 5 lbs I'm curious if there's any advantage that the larger setup will bring (if any, other than a greater thermal mass potential / general lap consistency). I'd also be curious to compare impressions of the larger contact patch area on wider tires and how that affects the vehicles' driving dynamics in regards to moi, steering input, etc.

1. 17x10 (255/40)​​​​
2. 18x11 (295/30)
3. 18x12 (315/30)

tire lower section width: (1) 265mm (static), 289.2mm (dynamic), (2) 300mm (static), 320.8mm (dynamic), (3) 325mm (static), 349.5 mm (dynamic)
tire stiffness rate: (1) 34.5 kg/mm (static), 30.4 kg/mm (dynamic), (2) 38.7 kg/mm (static), 34.1 kg/mm (dynamic), (3) 37.2 kg/mm (static), 32.7 kg/mm (dynamic)
contact patch width: (1) 257mm, (2) 304mm, (3) 332mm
contact patch length: (1) 115mm, (2) 118mm, (3) 121mm
contact patch area: (1) 295.09 cm2, (2) 357.77 cm2, (3) 400.03 cm2

https://bndtechsource.ucoz.com/index...alculator/0-20

Please note this is for a DE vehicle so no rules apply and any constructive input is greatly appreciated.

Thanks for looking!

 

Someone locally was running 315's on their rx8 here for autocross, I don't know if they were 11's or 12's though. Their fenders were modified to be wider within the DSP class limits and I believe they also had a speedway style swaybar that limited their turning angle. Not sure if that helps but they were and that car still is a class leader in DSP with those width tires.

 

Would you happen to know of any media on that vehicle? If so, I might be able to discern some info just by looking at it. Which reminds me that there was a guy who I believe was running an 11" set, I'll dig through some old tube vids and see what I find.

Also, I'm 99% certain oem fenders accommodate up to 11" with no issue. My r3 has a wide body kit, cut rear quarters and SPL arms so there's definitely room for adjustability, just not sure on how the 12" would sit.

 

Bueller?

Pretty sure the car I was looking for / thinking of was a silver s1 with basically a sprint car wing on the front (plus lower splitter I imagine, don't recall). Anyways, I've had zero luck finding it.

I did come across a conversation in a thread concerning track wheel selection, etc and there was a purported theory around an equation (it was not stated, just the general theory) that takes overall vehicle weight with distribution and correlates 1 kg to every cm of tire width to find the ideal wheel size to weight ratio.

Anyone else heard about this? I'd be real curious to see what calculations people came up with for their own specific setup. Purely for educational purposes and rx8club prosperity.

 

Found the car I was thinking of.

https://grassrootsmotorsports.com/ne...-8-fastfriday/

 

Yup that's Dallas Reed lol

 

I'd think going wider at rx8 power levels won't really benefit you on track with all that additional weight. Tamra was running the 315's for autox and they found it helped them out in that style racing, but not sure I've found anybody putting over 10" wide wheels at stock power levels and benefiting from it.

Would be interesting to see some results and examples though.

 

Yeah it rang a bell in my head once I came across it; been around for awhile now. Incredibly unique but kind of an odd project and goes into the respect all builds category for me. The stages of development are pretty cool though. I'm sure it's beyond insane fast if that's your thing.

Few years back when I was preparing my car to be a dedicated track vehicle, I went through a lot of effort to reduce curb weight. Although that project fell though, I'm fairly certain my DE prepped r3 ended up becoming the lightest road legal RX8 in the states after all the composite work (currently sits at 2856 lbs sans driver + 1/2 tank). Next round of mod installments should put me well into the 27xx lbs and that would still be with the additional mass of 18x11 with 295/30 tires. Also worth note is that I really only drive Laguna and Sonoma and imo they're all about entry / exit speeds and negotiating transient response / weight transfer. Of course loads of power is always helpful reducing lap times, I've seen plenty of lower powered momentum cars put down what I feel are unbelievable lap times for what they're working with. My last outing at Sonoma with my RX8 was in '22 at 1:55.6 running equal to nasa/scca club driver with Cayman S on Ohlins DFV (Apex wheels I forget the tire, I was running r888r). Cool guy, super fun day. A lot of work has gone into the car since then and I'm curious how it's going to perform. I picked up a set of RE-71rs to try out (heat cycled, heard many great things about them) and patently waiting for some upcoming May DE events. It'll be interesting to see how this new setup compares for lap times.

But I don't think I'll be able to order the wheels up for at least a few months (at earliest) and when I eventually acquire a new larger set I'll share my data here (Garmin catalyst + personal observations).

 

You'll love the stones, they're in a whole other league.

 

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https://www.rx8club.com/series-i-tec...1/#post4914674
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I use 10.5J ET35 F/R