Lame Question

[1985 Gripen]

Sorry to be so lame, but I have been wondering: what is the advantage of larger-diameter wheels and really low tire sidewall thickness?

I've seen people with those tricked-out Bimmers with huge wheels and what look like little black rubber bands around them. I know the disadvantage is that the ride is really rough, but is there an advantage other than the fact that it looks pretty cool?

Does the bigger wheel translate to more distance covered per revolution or something? Is that more efficient?

[ctrlz]

Less sidewall flex.

[AeroMiami]

Not lame at all. I was at the Saab Aero Academy at Road Atlanta, which is next door to BBS USA Headquarters. One of the instructors is the National Sales Manager for BBS USA and I asked him the same question.

He said BBS has done tests and that above 18 there is no use on the racetrack. They recommend cars on the race track to run on 17s or 18s and they tested both on an identical car, a Mustang GT. They did tests on ten novice drivers and ten professional drivers. The Mustang ran faster times on the 17s when driven by a novice and ran faster times on 18s when driven by a professional driver. 19's and above are more for looks than performance he claims.

This is how it was told to me, I'm no expert, just explaining what was told to me. Hope it helps.

[johnnyrocket]

Looks would be the biggest reason. Because big wheels are the fad right now. People try to stuff the biggest wheel in the space they have. So they need smaller and smaller tires to accomadate. Like ctrlz said you get less sidewall flex which = rougher ride. Plus you don't want to change the overall diameter of your wheels or else you will throw off your speedo.

[Old Goat]

When they get too large, with less and less rubber, I think it throws the looks of the car off. You don't want it to look like you are riding on baby carrage wheels.

As to the speedo, you can get it changed at a SAAB dealer to match the wheels you have on.

[1985 Gripen]

So it's really just a looks thing? There's no functional advantage of having 18" wheels with thin rubber over say, a 16" tire with thick rubber?

Now what if I were to theoretically put 18" wheels with thin little rubber on my car, but compensate for the lack of sidewall flex and rougher ride by installing really soft dampers? Would that work?

[hkayssi]

It's not for looks! Some people do it for looks though.It depends on what you want from your car.

-- If you like a cushy ride, you're not an agressive driver and you don't turn fast on corners, then take a higher wall wheel with a smaller diameter rim. In our ng900 og9-3s, that would be 15" to 16" rims. Again depending on driving style and needs.

-- If on the other hand, you drive agressivly, turn sharp corners fast and drive fast on twisted roads, then get a set of low profile tires with bigger rims (17"-18") that handle better since there not too much flex in the tires thus less body roll.

It's a trade off as with the cushy tire you're more comftable but handle worse!

Obviously, if you go that route (low profile tires on bigger rims), you need good suspension and a good sway bar, steering brace and the 4 or 6 point frame brace or you won't see significant improvements in handling.

You can always lower the car as well to help lower the center of gravity on the car and make it less prone to body roll and grip more on the road. but that stiffens the ride even more and the rear camber causes the tires to wear unevenly and prematurely on the inside (but there's a kit out there now that fixes this undesirable side effect).

[1985 Gripen]

Thanks for the info, all. I have to say that those tricked-out Bimmers I see with the big wheels and thin tires sure do look sharp. I just don't know if my rear-end could handle that kind of ride day-in and day-out. My car isn't a "track car", it's a daily driver...

[hkayssi]

By the way you don't necessarily change the speedo when you put the right size tire.

On a 900 NG for example

Say you have 195/60R15s and you put 225/35R18s, does the speedo change? Nope

Try this calculator to see if you need to recalibrate your speedo or not

http://www.miata.net/garage/tirecalcold.html

I hope that helps

[hkayssi]

Originally Posted by 1985 Gripen

Thanks for the info, all. I have to say that those tricked-out Bimmers I see with the big wheels and thin tires sure do look sharp. I just don't know if my rear-end could handle that kind of ride day-in and day-out. My car isn't a "track car", it's a daily driver...

I know what you mean those are mostly for looks I agree. They spend k$ on stupid useless mods then hit a pebble in the road and the car flies and hits a light poll

[ragtopcav]

With 225 - 40 - 18" rubber the 900 speedo is actually correct.

The issue with large wheels is weight, nothing else.

[hkayssi]

Originally Posted by ragtopcav

With 225 - 40 - 18" rubber the 900 speedo is actually correct.

The issue with large wheels is weight, nothing else.

Go on a diet man you'll neutralize the effect

[ragtopcav]

Originally Posted by hkayssi

Go on a diet man you'll neutralize the effect

Bet you won't, unless you tie yourself to the outside of a rim first; losing a couple of kilos in this critical zone can have a staggering effect even on a fairly ordinary car..

[CleveSaab]

I have a lowered Saab with 16's and 205/55's. There is hadly any space in the wheel well... and I am starting to hate the ride. I'll give up 5 mph in the corners for a cushier ride. Anyone have any OEM springs for a coupe laying around after an upgrade?

[ragtopcav]

Originally Posted by CleveSaab

I have a lowered Saab with 16's and 205/55's. There is hadly any space in the wheel well... and I am starting to hate the ride. I'll give up 5 mph in the corners for a cushier ride. Anyone have any OEM springs for a coupe laying around after an upgrade?

IIRC you've got lowered springs with stock shocks right? Probably the worst combination for ride [especially if you factor in the US spec 'wallow'].
lowered springs have less turns with space [pitch] to offer control too and hence rely more heavily on the damper for control or ride quality.

You'd probably be better off with a Caddy Catera

[lowbudgethero]

that must have a good of a ride as my leaf spring pick up truck... that car literally gave me back problems

[Old Goat]

I would imagine that tire blow out from hitting a deep pothole would be easier with larger rims/less side wall. That is what would worry me more. We seem to have PLENTY of manly pot holes around here from all the salt we use in winter.

[johnnyrocket]

I see my words are gettting a little twisted. For what the OP was asking those people merely do those mods for looks. In my book an 18'' wheel with a 225/35r18 tire is not a small sidewall. To me that is about right. The OP I figured, especially when he mentioned bimmers was talking about 20'' or bigger wheels with rubberbands on them as to which there is no advantage to them but looks. Does Saab recalibrate speedo's for free? I know on my previous car it was a pretty hefty chunk of change to get this done. That actually makes me glad to know that Saab can do this.

[hkayssi]

SAAB can do this speedo recalibration, but not for free I'm affraid. Chances are it'll cost $$$

[dasaabguy]

how do we explain it to these guys...... HIDEOUS