Rim Size: Pros and Cons

[Nylate]

Alright,
So I've begun the daunting decision of picking aftermarket rims
What i'm interested in knowing / getting opinions on is the affects of wheel size + width
Whether its performance, increased fuel consumption, weight etc.

Owning a dc5s, i was planning on going from the stock 17" to 18's. Mainly for personal reasons; filling the guards better, stance, grip and overall appearance.

A few of my friends are against the upsize, and i can't personally see the major downside/s!

[mrntegra]

cost of tyres are alot more mate. thats a major downside if you have to run decent camber.

[Apu]

Weight? Unless you buy a lighter set which cost megabucks, tyres cost more, scrubbing, less efficient is you use "oversized" tyres, etc etc.

I think the biggest downside is just weight and that has an impact on performance.

I "upgraded" my MX5 from 16s to 15s and the handling is much improved, and a large number of MX5 owners who are track enthusiasts have done the same. If you've driven a few back to back, you'll see how significant these changes are on a small, light car.

You're less likely to feel it on a heavier car, but it still has an impact.

[tinkerbell]

when i change my street 16's (6kg+) to my track 15's (3.9kg) i notice immediate improvements in the steering effor and feel, sensitivity increases as does the accuracy of my inputs even at low speed.

i know this is a pretty stark comparison, but the differences will exist mostly based on weight alone...

[45SET]

I haven't been one for weights, but I've noticed a massive difference when changing rim width and offset... tyres also make a MASSIVE difference.

[Pizzo321]

I haven't been one for weights, but I've noticed a massive difference when changing rim width and offset... tyres also make a MASSIVE difference.

They sure do man when I went from a 18x9+35 235/40 to a 18x9+20 and a 235/40 I dropped 11kw..

[tinkerbell]

They sure do man when I went from a 18x9+35 235/40 to a 18x9+20 and a 235/40 I dropped 11kw..

was this back-to-back? same day?

[Pizzo321]

Maybe a week apart, can't really say 100% that's what caused the loss, could of been a number of things that affected the dyno run, but majorly the weight of the Rotas against my ce28s would of
Been the main cause I'm guessing

[tinkerbell]

close enough, forged vs cast is always going to go the way of forged...

weight is the enemy, unsprung weight is the devil...

[Karl]

this may help with weight
http://hondaswap.com/reference-mater...weights-28665/

[Apu]

An increase in weight isn't going to cause a loss in power but it will reduce acceleration times.

As for forged vs cast, well a well made cast wheel can be better than a poorly made forged wheel...though you're less likely to come across that scenario. That said, you can get well made cast wheels that are light, and at a fraction of the cost of forged wheels.

Tyre width and offset can also drastically affect steering feel and effectiveness. Just consider track width as an example - don't match it up right when going for wider wheels and you could actually narrow your track width.

[andrew84tran]

Weight and rolling diameter are probably the biggest considerations when deciding to go 17 or 18. 18s will naturally weigh more than 17s (assuming same brand and wheel). With 18s you'd have to run a smaller tyre profile to keep the rolling diameter in check (so it doesnt affect your gearing). Now you're looking at decreased ride comfort because of the the smaller profile and then the higher cost of tyres in the long run.

[Norm]

I'm going to fall victim to this topic. Changing soon from a 17inch 7.5width +47 to a 18inch 10.5width +23. So I'll be able to even give some brief experience. From my assumptions, the car is going to be more stable, from increase width of offset and width of the rim. However its going to come at a cost of reduced speed of revolutions of the rim turning as the outer perimeter of the rim is going to increase and also weight as well of larger tyres and rim size. The handling i'm going to assume is going to be slightly heavier as there is now more mass or should I say contact between the ground and tyres and hence greater friction. Steering response is not going to be as agile and may be slightly dulled. All of these factors as mentioned by my peers in this topic, I will soon experience.

Norm

[ChargeR]

An increase in weight isn't going to cause a loss in power but it will reduce acceleration times.

As for forged vs cast, well a well made cast wheel can be better than a poorly made forged wheel...though you're less likely to come across that scenario. That said, you can get well made cast wheels that are light, and at a fraction of the cost of forged wheels.

Tyre width and offset can also drastically affect steering feel and effectiveness. Just consider track width as an example - don't match it up right when going for wider wheels and you could actually narrow your track width.

An increase in drivetrain inertia, as in heavier wheels, will decrease the power that actually reaches the road surface and accelerates the car. So while the power of the engine hasn't decreased, the measurable power that the car can apply has.

Also it is pretty hard on most of our cars to decrease the track width when changing to a wider wheel because in many cases much more than an inch wider whilst maintaining OEM offset will result in interference issues between the wheel and suspension. So most people elect to go for a lower offset than OEM, thus widening the track.

I'm going to fall victim to this topic. Changing soon from a 17inch 7.5width +47 to a 18inch 10.5width +23. So I'll be able to even give some brief experience. From my assumptions, the car is going to be more stable, from increase width of offset and width of the rim. However its going to come at a cost of reduced speed of revolutions of the rim turning as the outer perimeter of the rim is going to increase and also weight as well of larger tyres and rim size. The handling i'm going to assume is going to be slightly heavier as there is now more mass or should I say contact between the ground and tyres and hence greater friction. Steering response is not going to be as agile and may be slightly dulled. All of these factors as mentioned by my peers in this topic, I will soon experience.

Norm

Nothing stopping you from getting the correct sized tyres so the diameter does not increase! Also the Works you are getting will be fairly hefty I think, especially given the massive increase in width, so be sure to report back on how much difference the mass and tyre profile change affects your bump compliance.

[tinkerbell]

An increase in drivetrain inertia, as in heavier wheels, will decrease the power that actually reaches the road surface and accelerates the car. So while the power of the engine hasn't decreased, the measurable power that the car can apply has.

spot on.

now - how about a bit of talk about 'contact patch'

a wider tyre increases contact patch width, but reduces contact patch lenght.

going wider can actually reduce mechanical grip!

rememebr that a sidewall is very important to handling, and that 'profile' is a % of width,

going 10.5in wide will create a very wide, but very short contact patch, making for a very small lateral contact patch under cornering (as the tyre will 'lean').

so depending on the sidewall, you may actually have less contact patch when cornering with very low profile tyres...

and this means mech. grip is lower, and obviously peak cornering speed is reduced...

but it all depends!

Nothing stopping you from getting the correct sized tyres so the diameter does not increase!

comparing 225/45-17 to a 10in wide tyre, say 295-18 - you would need 30 profile tyres!

yikes!