17 inch wheels vs 18 inch wheels

I found out today that my passenger side SSR GT7 is cracked. Fun. Apparently no one stocks this wheel anymore. It's in pretty bad shape (slow leak on the tire, and a bald spot to the cords from where the dent in the rim was) so I'm going to need to replace it soon. I've been thinking of going 18" for a while now, but I've been worried that they would dent easier than 17". Is this true? Driving the war scarred streets of Boston, I'd probably be better off in a hummer than something with 45 series tires, but is there really a big difference between 17" wheels and 18" wheels when it comes to surviving potholes? And does anyone have a need for three SSR GT7's ?

there would be less rubber on a set of 18"s ..so .. it will probably take less impact to dent the rim. that's what i think. whether it's true or not is a different story.

Not sure how to put this but if you're careful how you drive you should be fine with 18s, if your sketched out get more 17s with a meatier tire.

If you're going 18", depending on width, 235/40/18 would be a nice size since it's got a thick sidewall.

 

A major aspect of preventing wheel damage when going over bumps and potholes is tire pressure so make sure that's in check..

If you're going 18", depending on width, 235/40/18 would be a nice size since it's got a thick sidewall.

 

A major aspect of preventing wheel damage when going over bumps and potholes is tire pressure so make sure that's in check..

^^^Truth. I believe a 235/40/18 has the same sidewall height as a 215/45/17.

Here this will help http://www.miata.net/garage/tirecalc.html

Assuming a +1 fitment, the same make and model 18" wheel will be heavier (with more mass near the tread) and more expensive than a 17" wheel. An 18" tire will almost certainly be more expensive as well, possibly heavier, with its mass also closer to the tread. This extra weight will result in less responsive suspension movement and a slight decrease in acceleration, both from increased linear and rotational inertia. As other posters have noted you are more at risk of bent rims with 18's vs 17's, assuming the same make/model tire and attention to tire pressures. A good 17" option would be 17x8's w/ 235 or 245/40-17 tires. This combo would negate some of the weight difference between the stock 17" and a +1 fitment, but would get you the increased tread width while maintaining rim-friendly sidewall height. My $.02...

Probably get longer stopping distances with the 18"s due to more rotational weight too, everything else being equal - no?

Probably get longer stopping distances with the 18"s due to more rotational weight too, everything else being equal - no?

 

Yes, again it would be slight, roughly equivalent to the decrease in acceleration, but more critical. If you reach 60mph a few feet sooner great, but if you stop from 60 a few feet shorter - well, that could make all the difference.

Here's a guy in the same boat as you. Can't tell what these are on. Maybe ya'll can make a deal?

Helpful tip: Google 'anything site:craigslist.org' to check ALL craigslist sites. Also, this guy is local for me. If you make a deal and he doesn't want to deal with a remote buyer or ship maybe we can work something out.

Here's a guy in the same boat as you. Can't tell what these are on. Maybe ya'll can make a deal?

Helpful tip: Google 'anything site:craigslist.org' to check ALL craigslist sites. Also, this guy is local for me. If you make a deal and he doesn't want to deal with a remote buyer or ship maybe we can work something out.

Thanks a ton for the help. I think those are 18's but I'll use your tip to keep searching craigslist. I think I'll go with 17's, as there are no real benefit to 18's other than they look pretty, and there are a ton of drawbacks.

Even with 235/40/18's on PFF7's I'm scared sh!tless of denting them - so I'm going to 17" STI BBS's this year to try it out. Did notice that the larger tires didn't help with acceleration or braking though - it is noticeable.

There's an excellent article on this very subject in the newest (May '10) issue of C&D. Here's the Clif Notes version:

 

Wheel/tire size in 1" increments: 195/65R-15 to 235/35R-19

Cost: $227 (16") to $359 (19")

Wheel/tire weight: 40 to 54 lb.

0-60 accel: 7.6 to 7.9 s

0-100 accel: 22.3 to 23.4 s

60-0 braking: 130 (15"), 133 (16") to 126 ft.

Skidpad: 0.83g to 0.88 g

Mileage: 23.3 to 21.1 mpg

 

Note that the improvement in braking and cornering is due to the increase in tire width. A +0 fitment (same diameter but wider wheel and tire) would likely achieve the same results w/o as much deterioration in other areas.

Probably should have posted the relevant results:

Wheel size - 17x8 vs 18x8

Tire size - 225/45-17 vs 225/40-18

Cost - $261 vs $291

Weight - 48 lb vs 51 lb

0-60 - 7.8s vs 7.9s

1/4 mile - 16.0s vs 16.1s

0-100 - 22.7 vs 23.3

60-0 - 128 ft vs 126 ft

Skidpad - 0.85g vs 0.89g

Mileage - 22.8mpg vs 21.9mpg

 

Note that the load rating of the 17" tire is 91V vs 92W for the 18" so this could account for the improvements in braking and skidpad.

Thanks for the interesting information. Does it indicate what tires were used for both sizes?

Assuming a +1 fitment, the same make and model 18" wheel will be heavier (with more mass near the tread) and more expensive than a 17" wheel. An 18" tire will almost certainly be more expensive as well, possibly heavier, with its mass also closer to the tread. This extra weight will result in less responsive suspension movement and a slight decrease in acceleration, both from increased linear and rotational inertia. As other posters have noted you are more at risk of bent rims with 18's vs 17's, assuming the same make/model tire and attention to tire pressures. A good 17" option would be 17x8's w/ 235 or 245/40-17 tires. This combo would negate some of the weight difference between the stock 17" and a +1 fitment, but would get you the increased tread width while maintaining rim-friendly sidewall height. My $.02...

 

I actually run a 225/45/17 on a 17x7.5 rim. I run this for many of the reasons you listed above. I haven't gone to a wider set up because with a top of the line 225/45 tire and a good alignment with some negative camber, the grip is more than ample for public roads. Plus, you need to run an aggressive alignment to make full use of a 245 tire.

^^^ What rim you running?

 

Cheers,

Mike

Thanks for the interesting information. Does it indicate what tires were used for both sizes?

 

Goodyear Eagle GT UHP A/S tires, ASA GT1 cast Al rims. 15-17" tires are V rated, 18-19" W rated.