Mani 9 Report post Posted September 23, 2021 Hi All I am looking to upgrade from stock wheels and considering alloys with the following specs - 18 x 8.5J ET 35 What size tyres should I go for? Also Michelin PS4 seems to be the popular choice, but are there any others I should explore thank you in advance for the suggestions Share this post Link to post Share on other sites
Booboo 11 Report post Posted September 23, 2021 I've recently tyred the same size wheel and it took me a while to decide. First thing up is recommended sized tyre width for the wheel. 225 is min and 255 your max. Rolling radius is next up. Enter stock sizes then ones you would prefer to check differences in this example website https://www.tyresave.co.uk/tyre-size-calculator/ I discounted the 225 from the off and although they would have been the lightest and most playable set up I figured the stretch would be too much Having already ran a 245 on a 17x9 wheel (245x40x17) I fancied going down to a 235 to reduce not only width but weight. Unfortunately matching a 235x40x18 to the stock size means running a 20mm larger rolling radius which I personaly didn't fancy. In the end I went 245x35x18 which is only a 4mm difference. Tyre choice Michelin PS4 as I had already run a set on the car and liked them. Share this post Link to post Share on other sites
Mani 9 Report post Posted September 23, 2021 @Booboo .. thanks for sharing - it is good to know that some is running the same alloy specs. also the link was handy … I spent sometime this afternoon considering various combinations factoring the rolling radius and seems like there are only two options within the tolerances 235/35/18 (-4mm) 245/35/18 (3mm) also I am on coilovers and lowered by 15/20 mm I think - would that have any impact on the rolling radius - should I be factoring this in or lowered stance wouldnt matter? Share this post Link to post Share on other sites
Leeky 84 Report post Posted September 23, 2021 I have 18x8.5J ET42’s and I run 235/40R18’s. Share this post Link to post Share on other sites
Jay 37 Report post Posted September 23, 2021 3 hours ago, Mani said: ...also I am on coilovers and lowered by 15/20 mm I think - would that have any impact on the rolling radius - should I be factoring this in or lowered stance wouldnt matter? Nope! The circumference of the tyre cannot be affected by ride height. 😉 Share this post Link to post Share on other sites
Mani 9 Report post Posted September 24, 2021 9 hours ago, Leeky said: I have 18x8.5J ET42’s and I run 235/40R18’s. Thanks @Leeky … have u had any issues running those tyres Someone at a car meet did recommend me those tyre specs but the calculations below threw me off Share this post Link to post Share on other sites
Mani 9 Report post Posted September 24, 2021 7 hours ago, Jay said: Nope! The circumference of the tyre cannot be affected by ride height. 😉 Thanks @Jay … Share this post Link to post Share on other sites
Leeky 84 Report post Posted September 24, 2021 2 hours ago, Mani said: Thanks @Leeky … have u had any issues running those tyres Someone at a car meet did recommend me those tyre specs but the calculations below threw me off Nope they’ve been fine even on track days. Zero rubbing on any part of the tyre even under full lock. I didn't want to go any lower than a 40 profile as factory ride is already quite stiff. The ride with these is only noticeably a little harder over bumps but still quite acceptable as the sidewall is only slightly smaller than stock. Only drawback is that ride height has increased almost 1cm (but thats fine by me). On the plus side the speedo is now more accurate as the speedos over read on the stock tyre size. Share this post Link to post Share on other sites
spikyone 139 Report post Posted September 24, 2021 I have 225/40 on an 8.5 rim and it's fine. As a heads-up, other sizes of suitable tyre are much more expensive. I don't think the stretch looks particularly extreme; you will lose a little rim protection, but I've used my car on track and never had any concerns about the stretch causing a problem. Bear in mind that going wider will make the car harder to unsettle on the throttle, so if you like a throttle-adjustable balance you won't want to go too wide anyway. A 225 PS4 has as much grip as I need, and that's running ~290bhp with a supercharger. I posted costs for different tyre sizes a little while back, along with photos of my tyres. Share this post Link to post Share on other sites
Mani 9 Report post Posted September 25, 2021 Thanks @spikyone … I had looked at the previous link and thought the stretch looked ok i did a bit of digging around on tyre prices and below are the best deals I am getting for the options (fully fitted) 225/40/18 (350.04 Black circles) 235/40/18 (399.92 Costco) - about £50 more than 225 245/35/18 (3mm) (478.64 Costco) - about £130 more than 225 Which one do u guys thinks is best size for the cost? Share this post Link to post Share on other sites
Leeky 84 Report post Posted September 25, 2021 I guess it all depends on which tyre you are going for. I personally run Goodyear Eagle F1 Aym5’s. And I chose the size based on clearance/width/comfort rather than price. But I remember I paid only £360 for my set of 4x tyres from blackcircles. Then £40 cash to get them fitted by my local place. Share this post Link to post Share on other sites
Mani 9 Report post Posted September 25, 2021 Was planning to go down the Michelin PS4 route and thought that the prices quoted were reasonable … I was expecting it be around the 400-500 mark Not sure how i can test them for comfort on my setup unless I buy one the question I have is whether 245 is worth the extra spend or 235 seems to be the happy middle ground …. Share this post Link to post Share on other sites
Leeky 84 Report post Posted September 25, 2021 245 is gonna give you a bigger contact patch than 235’s for sure but the wider you go the heavier the steering will be, the more it’ll tramline and the thirstier it’ll become. I haven’t tried 245’s myself so I can’t comment on how that size makes the car feel, but having had 235’s for a while now I’m very happy with this size. Share this post Link to post Share on other sites
MartinT 514 Report post Posted September 25, 2021 I run 235 18s on 8.75 wheels. The balance of grip and handling is really good and I can still get very playful with the supercharger. My traction control light comes on a bit. Sent from my Oppo X3 using Tapatalk Share this post Link to post Share on other sites
Mani 9 Report post Posted September 25, 2021 Thanks @Leeky and @MartinT … 235 seems to be the tyre of choice 👍 1 Leeky reacted to this Share this post Link to post Share on other sites
Booboo 11 Report post Posted September 27, 2021 Have you checked out the Camskill site? They are offering an instant £60 cash back on most Michelin tyres including PS4's. I got my set of 245x35x18 PS4's for £496.20 MINUS the £60 so came in at £436.20 Put your order in, pay the full total and it automatically refunds the £60 to same account you pay on Share this post Link to post Share on other sites
Mani 9 Report post Posted September 27, 2021 I checked out the Camskill site just now and current deal on the 245x35x18 PS4 is £533 (including shipping) - less £60 comes to about £473 225/40/18 comes to £290 235/40/18 comes to £394 You definitely got a better deal 😜 since I will have to pay fitting costs on top, Costco is still coming out as a better deal (£478 fitted for 245 and 400 fitted for 235) thanks @Booboo for keeping an eye out Share this post Link to post Share on other sites