Downsizing from 18” to 17”

[cestjoel]

I have the Sport and would like to go down in size from an 18” wheel to an 17”, Mainly to get a more comfortable ride:

- What wheel specs are ideal?
- What size tires are ideal?
- Most improtantly, will going to a 17” wheel actually give me a softer, more comfortable ride?

Thanks in advance!

Joel

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[charleswrivers]

As to the comfort part...

Passenger cars wheel size has gotten excessive IMO. People want the look of a big wheel and a low profile tire. In the 80s, sport cars were being equipped with 15-17" wheels. Passenger cars 14-16 generally. I think all my Zs had 16s. Even my twin turbo came with 16s and 225-50-R16 rubber in '94.

You'll have more sidewall to flex, so you'll incur more body roll. Handling will diminish slightly. Because there's more sidewall to flex, you're ride will be a touch smoother on a rough road. The difference won't be *crazy* dramatic though. Going for a larger circumference wheel has a profound effect on rough roads, as the larger tire tends to not 'fall' into the holes so much... but this also slows down the car by raising the effective gearing and will throw off your speedo too.

Here's a good article from a few years back that did a comparison. IMO, I don't think a passenger car oughta be riding on much more than a 16" wheel... but car manufacturers seem like that's the minimum size, and be them... you're getting the most base model with steel wheels and plastic hubcaps vice a nice light set of aluminum wheels. The tires are mich cheaper in the smaller sizes... though the price for low profile tires has really come down over the years. The OEM aluminum wheels on my RSX were *light* compared to the boat anchors on my Si.

https://www.caranddriver.com/features/effects-of-upsized-wheels-and-tires-tested

 

[charleswrivers]

Unless you don't like your wheels, I'd save the cash and buy a comfort oriented set of tires on your existing wheels. Your money on rims would cover a good set of tires.

I'm not sure what tire you have stock... but if they're the Contenential Pro Contacts, which I had as both the OEM tire on my '15 Si and my '14 Odyssey... they're not a very good tire. A different tire still on the 18" rim can make a world of difference. You can still get a crap ride that is loud, has poor wet/dry traction is isn't all that smooth on a 17" rim if the tire isn't up.to the task.

 

[cestjoel]

Unless you don't like your wheels, I'd save the cash and buy a comfort oriented set of tires on your existing wheels. Your money on rims would cover a good set of tires.

I'm not sure what tire you have stock... but if they're the Contenential Pro Contacts, which I had as both the OEM tire on my '15 Si and my '14 Odyssey... they're not a very good tire. A different tire still on the 18" rim can make a world of difference. You can still get a crap ride that is loud, has poor wet/dry traction is isn't all that smooth on a 17" rim if the tire isn't up.to the task.

I actually had the Continental ProContacs that come with the Sport wheels. And i agree - they’re terrible tires. I ended up buying a set of the OEM tires that come with the Si - Goodyear Eagle Sport. They were a small improvement, but I’m thinking that it could feel better if I go to a smaller wheel? I don’t mind sacrificing size for comfort.

Ps. I'm reading the article you posted.

 

[charleswrivers]

You're free to give 17s a whirl.

If you're on a budget... you might look to see if someone has a nice set of 16-17" wheels off another car like the aforementioned RSX that have some good rubber on them still. You can probably grab a set w/decent tires still on them for less than the cost of new rims alone, not mentioning that cost of tires. I'd check out Craiglist. I've gotten a few sets like that over the years. I bought a set of rims of stock Prelude rims w/some winter tires w/good tread on them for the RSX I had at the time for $200 bucks when I was living in NY. Again... just a suggestion if you want a low cost if entry to see if it's for you.

The ProContacts were loud, actually had a lot of sidewall flex for what they were, had poor wet and dry traction, and had issues where the sidewall would bulge and split between two different sets of tires on 2 different vehicles that were sized much differently. I'd chuck chose things as soon as your budget allows. In the meantime, I'd also recommend you examine the sidewall closely during normal maintenance... and make sure the inside sidewall gets a good look too... not just the outside. The internet is filled with complaints about those ProContacts. They are an abysmal tire.

 

[sgk1503]

You're free to give 17s a whirl.

If you're on a budget... you might look to see if someone has a nice set of 16-17" wheels off another car like the aforementioned RSX that have some good rubber on them still. You can probably grab a set w/decent tires still on them for less than the cost of new rims alone, not mentioning that cost of tires. I'd check out Craiglist. I've gotten a few sets like that over the years. I bought a set of rims of stock Prelude rims w/some winter tires w/good tread on them for the RSX I had at the time for $200 bucks when I was living in NY. Again... just a suggestion if you want a low cost if entry to see if it's for you.

The ProContacts were loud, actually had a lot of sidewall flex for what they were, had poor wet and dry traction, and had issues where the sidewall would bulge and split between two different sets of tires on 2 different vehicles that were sized much differently. I'd chuck chose things as soon as your budget allows. In the meantime, I'd also recommend you examine the sidewall closely during normal maintenance... and make sure the inside sidewall gets a good look too... not just the outside. The internet is filled with complaints about those ProContacts. They are an abysmal tire.

I saw your upper post and this one too about down-sizing. So what about upsizing @charleswrivers ? I just bought an 18 SI's rims from a guy and planning to put summer tires in for my 17 Civic Ex-t, do you think it's still ok about the speedo, etc.??

 

[charleswrivers]

It's not the wheel that matters, it's the circumference of the tire.

If you Google, you find a million speedo error calculators where you can put in your OEM tire size and the aftermarket and determine the amount it will be off. Unless you go crazy, it won't be more than a few percent off. Generally if you stick to a wheel/tire combo that was for a car across multiple trims, the tires are all going to be almost the exact same circumference.

Body roll and skidpad times improve with a lower profile tire on a bigger wheel, but, all things being equal, the same wheel as a 17 going to an 18 is going to be a bit heavier... so you fuel economy (more city in the stop and go) is going to worse. Assuming the tires are no wider, generally the stopping distances should get worse as that's more unsprung weight spinning the brakes have to stop (going wider would improve them though... as the contact patch gets larger and usually you go wider as you go bigger by a bit), and acceleration gets worse as it's, again, more unsprung weight.

Going up or down 1 inch across the same wheel isn't a huge change. Going from heavy to light, regardless of what wheel we're talking about makes a big difference in braking/acceleration. Big... well... as in noticable. Going wider will improve overall performance. Narrow tires tend to let you reach the limits on a FWD where you tend to understeer and get more tire noise on hard cornering comparatively.

I'd always try a different tire on the stock rim personally... as, if nothing else, the stock rims are durable and it's 'cheaper to keep her' and throw good money at good tires if you're unhappy how it's performing. Tires should make more of a difference in ride/handling/noise if we're talking about changing by 1".

 

[BarracksSi]

You can go down to 15s or 16s if you want comfort. The widths available in sizes that are good for our cars are limited in 15" or 16" sizes, though. Doesn't matter much if you do mail order, but it would matter if you have a flat somewhere and want to locate a replacement tire quickly.

FWIW, my winter wheelset has 215/55-16 tires on 16" steel wheels. Still lighter than the stock 18s (no kidding!) and still performs well enough for street driving.

 

[SandyEggoSi]

To keep tire diameter the same at 25.3", you can do a 235/45/17. Lots of options in that size. =)

 

[cestjoel]

To keep tire diameter the same at 25.3", you can do a 235/45/17. Lots of options in that size. =)

Thank you! I was actually thinking of getting the Touring sedan wheels to see how they feel in the Sport.

 

[gtman]

If you're downsizing and looking for a more cushy ride why wouldn't you just go with the stock 17" tire size... 215/50-17?

 

[BarracksSi]

If you're downsizing and looking for a more cushy ride why wouldn't you just go with the stock 17" tire size... 215/50-17?

215/50-17 has about the same sidewall depth as 235/45-17. Remember, the "50" means that the sidewall is 50% of the tire width. 215mm * 50% = 107mm; 235mm * 45% = 105mm.

If the wheels are 8" wide, it'd be better to use 235-width tires; if the wheels are 7", then use 215-width. Or, really, I view it from the other direction, starting with the tires I want -- if I want to use 235s, I know that I should get 8" wheels.

 

[totopo]

As to the comfort part...

Passenger cars wheel size has gotten excessive IMO. People want the look of a big wheel and a low profile tire. In the 80s, sport cars were being equipped with 15-17" wheels. Passenger cars 14-16 generally. I think all my Zs had 16s. Even my twin turbo came with 16s and 225-50-R16 rubber in '94.

You'll have more sidewall to flex, so you'll incur more body roll. Handling will diminish slightly. Because there's more sidewall to flex, you're ride will be a touch smoother on a rough road. The difference won't be *crazy* dramatic though. Going for a larger circumference wheel has a profound effect on rough roads, as the larger tire tends to not 'fall' into the holes so much... but this also slows down the car by raising the effective gearing and will throw off your speedo too.

Here's a good article from a few years back that did a comparison. IMO, I don't think a passenger car oughta be riding on much more than a 16" wheel... but car manufacturers seem like that's the minimum size, and be them... you're getting the most base model with steel wheels and plastic hubcaps vice a nice light set of aluminum wheels. The tires are mich cheaper in the smaller sizes... though the price for low profile tires has really come down over the years. The OEM aluminum wheels on my RSX were *light* compared to the boat anchors on my Si.

https://www.caranddriver.com/features/effects-of-upsized-wheels-and-tires-tested

You're free to give 17s a whirl.

If you're on a budget... you might look to see if someone has a nice set of 16-17" wheels off another car like the aforementioned RSX that have some good rubber on them still. You can probably grab a set w/decent tires still on them for less than the cost of new rims alone, not mentioning that cost of tires. I'd check out Craiglist. I've gotten a few sets like that over the years. I bought a set of rims of stock Prelude rims w/some winter tires w/good tread on them for the RSX I had at the time for $200 bucks when I was living in NY. Again... just a suggestion if you want a low cost if entry to see if it's for you.

The ProContacts were loud, actually had a lot of sidewall flex for what they were, had poor wet and dry traction, and had issues where the sidewall would bulge and split between two different sets of tires on 2 different vehicles that were sized much differently. I'd chuck chose things as soon as your budget allows. In the meantime, I'd also recommend you examine the sidewall closely during normal maintenance... and make sure the inside sidewall gets a good look too... not just the outside. The internet is filled with complaints about those ProContacts. They are an abysmal tire.

Body roll has nothing to do with sidewall flex. Body roll has to do with weight transfer (lateral g's vs wheelbase vs. center of gravity), and the countering springs/anti-roll bars. More sidewall flex does make it feel less responsive.

I am doubtful of the old school thinking of smaller sidewalls = better cornering. I feel like there is a definite optimum. With modern tires, it seems like from tracking and autocross, all the competitive people like the smallest wheels you can fit around your brake disk while having the widest tires you can squeeze in. That car and driver article is not great since their smaller tires are super skinny, and they chose relatively heavy smaller diameter wheels. So they don't get as much weight savings as they could have and they end up with skinny bike tires. There is a reason why super wide 14-16" enkis rpf1's are the stereotypical track car wheel.

 

[BarracksSi]

That car and driver article is not great since their smaller tires are super skinny, and they chose relatively heavy smaller diameter wheels.

Yup. Not really a scientific test.

I think we've gone over this before, but I've seen maybe one article from a car mag that talked about bigger versus smaller wheels except with the same tread width (and same model of wheel). These numbers may not be the same, but they had 15", 16", and 17" wheels, all wearing 235-width tires, and their aspect ratios were chosen so that the rolling circumferences were all the same (or at least as close as they could get) -- so the 15" wheelset had taller sidewalls, and the 17" set's sidewalls were shorter.

If I remember right, they got the fastest lap times on the 15" wheels, but it was easier to be consistent with the 17" wheels. That would line up with the 15" set being lighter overall, and therefore ultimately faster, but the squidgier sidewalls were a little harder to control.

 

[charleswrivers]

Body roll has nothing to do with sidewall flex. Body roll has to do with weight transfer (lateral g's vs wheelbase vs. center of gravity), and the countering springs/anti-roll bars. More sidewall flex does make it feel less responsive.

I am doubtful of the old school thinking of smaller sidewalls = better cornering. I feel like there is a definite optimum. With modern tires, it seems like from tracking and autocross, all the competitive people like the smallest wheels you can fit around your brake disk while having the widest tires you can squeeze in. That car and driver article is not great since their smaller tires are super skinny, and they chose relatively heavy smaller diameter wheels. So they don't get as much weight savings as they could have and they end up with skinny bike tires. There is a reason why super wide 14-16" enkis rpf1's are the stereotypical track car wheel.

Yep...

and usually you go wider as you go bigger by a bit

I will disagree with you that a tall sidewall does not translate to more roll... though I'll agree it is essentially separate from the sprung weight laying down in cornering. Your suspension is based around your OEM wheel/tire size. Change nothing but the wheel/tire combo... going down on wheel size and up on the sidewall keep the overall circumference the same while retaining essentially the same tire width to... your body roll will definitely increase. I can flex a sidewall with my bare hands... but I haven't spent enough time in the gym to do the same trick with steel/aluminum wheels. Take a hard corner on a tall tire... not only does the body lay down on it's suspension, it'll squish down the taller sidewall on the outside wheels, and the tires will actually bend with the road... magnifying the effect.

Going wider definitely helps hold the tires from flexing so bad.

I have got 2 sets of rims for my Z... running the stock 225-50-R16s and I got some late model 350Z running 245-40-R18s (pretty much all I run anymore). The car definitely has more roll with the higher sidewall 16s. Same experience when I went back and forth between the 16s I had all seasons on and the 18s I had summer tires on the RSX. Far more body roll. Yes... both are wider tires too which is a huge contributor.

The article I posted was an old thing I remembered and, it is ashamed they couldn't maintain tire width constant as a control... but it's what I remembered having seen way back when.

Here's a decent vid of sidewall flex on a car in motion...



Unfortunately I can't find a comparo video really... showing something like a 16 vs an 18 with the tire having the same circumference and same width.

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