Major difference between 17" and 18" rims?

[Jzza4]

Going to purchase new rims/tires within the next week and wanted some feedback regarding this. Do I lose much power moving up in rim size? Will I need to install anything else with the larger rims (spacers, etc)? The Sachs suspension kit will be installed before adding the new rims, does this change things?


Thanks

[pundit]

Going to purchase new rims/tires within the next week and wanted some feedback regarding this. Do I lose much power moving up in rim size? Will I need to install anything else with the larger rims (spacers, etc)? The Sachs suspension kit will be installed before adding the new rims, does this change things?
Thanks

As the tyre aspect ratio (profile) changes bewteen 17" & 18" rims the overall diameter, and hence the effective gearing, will be the same. However three main points to consider are...

1. Generally larger rims are heavier which = more mass = reduced acceleration and increased braking distances. This maybe quite marginal depending on the wheels.
Also any increased unsprung weight will have a negative effect on the ability of the suspension & dampners to control the wheel motion over irregularites

2. Larger rim size require lower profile tyres which means less sidewall and less cushioning over bumps. So expect a harsher ride with larger wheels and possible a greater risk of rim damage when hitting obstacles or potholes etc.

3. 18" tyres cost more than 17" tyres.

4. Wider low profile tyres are more sensitive to wheel alignment errors and tend wear more rapidly if not accuratley aligned.
E34's tend to have slight rear negative camber which is made worse when the vehicle is lowered. This will definately accelerate rear tyre wear.
I suggested investigating camber adjusters.

In the end it's your choice. Many like 18"s for the extra 'cool' factor. I personally think 17"s are more than enough for E34's.
I did notice quite a drop in ride quality going from the standard 15"s to 17"s... and that's with standard suspension and genuine 'T' Stars which are a lightweight forged wheel.

Anyway that's my 2c worth. Others, I'm sure, will disagree!

[Zeuk in Oz]

Going to purchase new rims/tires within the next week and wanted some feedback regarding this. Do I lose much power moving up in rim size? Will I need to install anything else with the larger rims (spacers, etc)? The Sachs suspension kit will be installed before adding the new rims, does this change things?


Thanks

My understanding (not experience as I run 15" bottlecaps) is that the wider / larger / heavier the wheels the more often you have to replace steering and suspension components - worth a thought ?

[joshua43214]

Don't forget that when it comes time for tire replacement, the poor slob stuck with your 18" rims will curse you and all your off spring for 10 generations. then he will ding all 4 of your rims and the shop will claim it was prior damage and refuse to fix it.

You will make fewer enemies with 17's

[Gayle]

Don't forget that when it comes time for tire replacement, the poor slob stuck with your 18" rims will curse you and all your off spring for 10 generations. then he will ding all 4 of your rims and the shop will claim it was prior damage and refuse to fix it.

You will make fewer enemies with 17's

I can testify to that. On Tuesday, Omar the installer hated me. Didn't ding them though. Guess I was really lucky.

Edit: and I can also testify that what ffong777 says below is true--that the 18s are expensive.

[mike wong]

Jzza4,

what size are you currently running?
225/60-15?

you can select 17 and 18" tires that will have similar diameters as what you currently use - so that your speedometer won't be thrown off.

enclosed is a tire size comparer:

http://www.1010tires.com/TireSizeCalculator.asp

for example 225/60-15 tire can be upgraded to a plus 2: 235/45-17 or plus 3: 235/40-18 without radically changing diameters (so your car won't be lowered)

you won't lose power unless you get larger diameter tires, which can effectively increase the rear end ratio.

pay heed to what pundit mentioned. choose your tires carefully.
also note that wider tread tires may be susceptible to tramlining.
make sure your suspension components - control arms, bushings, rear pitman arms (AKA dogbones) are in good condition. even your wheel alignment.

hope you are buying hubcentric wheels !!!!!
if not, buy hubcentric spacer rings (recommend metal over plastic).
get a quality balancing job. Hunter 9700 Road Force balancers are state of the art. check their website for locations.

pay attention to the offset of the wheel. depending upon the width of the rim; 15-22mm offset should fit. you don't want the tire to 'stick out' and rub fenderwell or rub inside against the strut tower.

please don't buy knock off/ copies of expensive wheels. generally, they may be of lesser castings and be prone to bending

good luck - post photos of your car wearing new shoes!

[uscharalph]

Going to purchase new rims/tires within the next week and wanted some feedback regarding this. Do I lose much power moving up in rim size? Will I need to install anything else with the larger rims (spacers, etc)? The Sachs suspension kit will be installed before adding the new rims, does this change things?


Thanks

18" is just too much IMHO. When i get new rims it'll be no larger than 17".

[Alexlind123]

17'' m-pars...yummy

[fkong777]

i had both 17" and now running 18"
Ride and comfort wise it isnt much difference.

18"
Good - good looks
Bad - tire prices are much higher than 17"

17"
Good - cheaper tires
Bad - a little average for today standard. Most sedans comes 17" oem now.

[onewhippedpuppy]

I just went from 16" style 8s to 17" M-Contour replicas from Tire Rack. From a non-looks perspective, the 17s made the car more responsive, but also made a noticable increase in harshness. It's not entirely a bad thing, the car is nicely firm, but going up another size I think would start to become harsh. I gained nearly 10lbs of unsprung weight per wheel, not a good thing if you track your car. In addition, it made my 55 MPH shimmy far worse, more of a shake now. That extra weight out there increases the moment about your suspension mounting points, so it's bound to wear them quicker. I'm not the only person that has had this problem, in fact I've seen it recomended that you go to M5 thrust arm bushings if you have larger than a 17" wheel.

Other than that I'm happy, they just look "right" for the E34. It's not a modern car, and I don't think it pulls off the large wheels like an E39 or E60 does. Just my opinion, but I think 17" is a good compromise all around. If you get them, check out the General UHP thread on here. $76 each at Tire Rack, and Qube really seems to like them. I went with Avon Tech M550s and love them, but they're $100 each, still not bad.