9291150

Any pic's on stock rims?

Plus, any ideas on what 245's would be in terms of extra weight or drag? I'm not sure it's a win win.

Wider 40's might not bode well for ride quality either, which has always been an advantage of the 8 over its competition, part of the reason it makes for such a great daily driver.

Anyone notice a change in fuel economy, or is it negligible?

Jedi54

iTrader: (7)

BOTH cars in this picture are using 245 / 40's.

AlexCisneros

Mugato must be on something! I'd say "Houston we definitely have a problem"

pussywillow1972

I've been thinking of going to that size in a couple of months when I'm due for new tires. My only question is how would it affect the steering response when used on the stock wheels? When i went from 215s to 235s on my Jeep the feel changed, (though for the better.) Just wondering if it would make much difference, good or bad, on such a low profile tire.

Jedi54

iTrader: (7)

steering response still feels GREAT!

pussywillow1972

Well then, I may just have to go with the 245s!

StewC625

Hi - here's photos of mine right after I put them on. I'll upload more later this afternoon. http://public.fotki.com/fotkistewc625/rx-8/

Also, answering questions:

1) Ride quality improved. I think it's the tire more than the aspect ratio/section width. Don't forget that the aspect ratio refers to the ratio between the high of the sidewall to the section width of the tire. If you multiply the section width (for example 225) by the aspect converted to a decimal (.45), that yields sidewall height - and sidewall height is directly related (although not entirely controlling of...) ride quality - taller sidewalls generally equal softer ride when comparing identical brand/models of tires. Therefore, the sidewall height of the 225/45-18s is 101.25MM, and the sidewall height of the 245-40/18s is 98 mm - 3 mm difference isn't one the "butt o meter" is going to feel. The Bridgestones are stiffer tires than the Pirellis I have.

2) As I recall, each tire weighs about a pound more. TireRack.com has a full stat comparison tool thing on their site - you can compare there. But that's a negligible difference in unsprung weight.

3) Drag - Oh, I'm sure you could measure it with a wind-tunnel, but nothing us earth-bound folks would worry about.

4) Gas Mileage - slight improvement due to less rolling resistance of my replacement tires. Again, more about the tires than the size.

Ok, take this as the advice it is: You're overthinking this. They will work - don't sweat it.

mdw1000

I have the same tires as Stew and I really like them. The little bit wider tire gives the car a little bit more aggresive look, IMHO. And I also think the ride quality is better than the stock dunlops. Not by a whole lot, but a bit.

StewC625

Yup - same tires as me. Buy yours at TireRack?

Elara

I have the same tires as Stew as well- in fact, just had my second set put on yesterday. Ordered from Tire Rack both times.

Raptor75

Agreed, Tire rack will tell you every thing (track width, diameter, weight, ect...) I put on Avon All season performance tires that are 40/245/18. One good point not yet mentioned is that the larger tires on stock rim over hang the rims a little which helps protect the rims from scratching on curbs.

05rx8mazda

iTrader: (4)

i just got these tires put in they are the potenzas RE 01 R they are baaaadd!!! lol they are 245/40/18 and they are much better!!!!! beter grip lol havent had any issues its all good i greatly advise that lol

05rx8mazda

iTrader: (4)

if u want bigger wheels on the rear my friend that own protech he put i think 275/30/19 i think and he says that its a perfect fit lol

9291150

Thanks for the info. Stew, well put. The ride vs. handling is just too perfect on the 8 that I cringe at doing anything to mess it up, though it doesn't appear that 245's would do it.

lshu

I'm sorry, I going to have to throw a rod in everyone's gears and give my personal experience about wider tires on stock rims. I got Goodyear GS-3Ds 245/40R18 for my stock 8" rims, and while I got much better grip, the steering response/directional precision also went down a considerable amount, to the point where I did not feel confident pushing it around turns. The ride felt more supple and softer, but the extra weight of the tires can be felt when going over ruts and bumps. I am thinking that the sidewalls on these tires are not that stiff, so for different tires YMMV. I recently just got the lighter wider Enkei RPF1s 18x9.5" to remedy my situation and I must say that I am very happy with the result. It's still not as responsive as my previous almost-bald stock Dunlops (225/45R18) but response is much improved and there's alot more grip.

Silver_Surfer

LOL! Your royal highness.

titaniumgr3y

guys whats the PRESSURE we should use for this size?

i ve installed them yestarday and they look and feel awesome on my 8

mdw1000

Sorry, Stew, forgot to check this thread for a couple days. I got mine at Discount Tire. I've had good luck with them, but I've only been to one store so I can't speak for all.

As far as the question about psi, DT told me to run them at 32 psi, just like stock.

mdw1000

As far as pictures go, I have this pic but I don't think you can really tell the difference in the tires because the car was in the shade at the time.

Rhythmic

Are you still using the F1 GS D3's in 245/40 on those RPF1's? I'm thinking of going the same route, but was unsure of the fitment and ride and response. Are they really stretched?

BTW, these tires seem to respond well to changes in PSI, did you try experimenting with that before on the stock wheels? I don't have any problem with precision/response with mine.

titaniumgr3y

i ve used 32psi just like stocks but i am not sure if this is the correct amount.

StewC625

On the PSI issue, I did a range of tests on PSI and found that 32 PSI rear, 35 PSI front gives the ideal set up for me on my car for my driving style. Note the last part of that sentence. I like having just a touch less pressure in the rear - allows me to "steer" the car more with the throttle (yes, you can do this even with DSC involved) and the car seems to be more balanced and less prone to oversteer in a hot corner. Also, you don't get that feeling on a long/hot on ramp run that the front tires are rolling onto the sidewalls - I proved that with the chalk test, actually.

I'm continually amazed at how sensitive low profile tires are to pressure changes. I've autocrossed the car a few times, and tweaking the tire pressures a couple of pounds makes a huge difference. For example, the SCCA chapter here in the area seems to have preference for courses that are long and skinny, with slaloms, fast corners and chicanes in line out to a big second gear sweeper to the left, followed by the same thing coming back to the staging area. One of the hot shoes there recommended I over pressure the right front tire (compared to the other three tires) by two pounds and I'd get through that corner a lot better. He was totally correct.

So, I run: 35 psi fronts, 32 psi rears.

StewC625

Oh, chalk test: You take a big piece of sidewalk chalk like the kids use and you color a stripe of chalk from the second rib of the tread, over the shoulder of the tire and about an inch down the sidewall. Then you go do a run and check it - if you've got your inflation right for the speed and course, the chalk will be gone on the tread and onto the shoulder of the tire, and the chalk will be there on the sidewall below the tread.

Any scratches in the chalk on the sidewall means you need more pressure, as the tire is deforming too far and rolling onto the upper sidewall and if the chalk isn't gone or at least rubbed on the shoulder rib means you're over-inflated and need to lower pressure to broaden the contact patch.

Make sense?

lshu

Yep, I'm using the same tires and I did try varying pressures on the stock rims, from 32-36 psi. At 36 the responsiveness did improve substantially, but was still way too squishy for my taste.

The tires look pretty stretched on the rim, maybe a tad too much for my taste, but overall it still looks awesome. You can see the sidewall curve out from the tread to the edge of the rim, but the rim doesn't just stick out of the tire, the rubber flange comfortably encases the edge of the rim. I really need to post a photo. I just like getting the most responsiveness I can out of the tire. Finally feels good again to flick it through traffic!

Rhythmic

Yes, please post a photo