FAQ: Wheel & Tire, Lug, Bolt Pattern, Offset, Center Bore Info

charlieRobinson wrote:

Maybe, but then why does OEM specs call for 30psi all the way around? You think theyd consider curb weight prior to putting a number on this, yeah?

Tires have a maximum load rating at a certain psi. Tires today list higher pressure maximums than in past years. That doesn't mean that you have to run the maximum, just that the tire is capable of supporting a higher load. You can adjust handling characteristics by adjusting air pressures front to rear. You can reduce understeer by running higher pressure in the front verses the rear, for instance. Higher pressure can produce a harsher ride, but reduced rolling resistance for better MPG. The Riviera was a luxury car, so soft ride was priority for Buick. 30 psi front rear was what Buick listed for the best overall ride and handling. You can experiment though..

Quote :

The Riviera was a luxury car, so soft ride was priority for Buick. 30 psi front rear was what Buick listed for the best overall ride and handling.

Exactly - soft ride comfort was priority for '90s Buick not handling performance. A lot has changed in 15 years. Cars typically have lower profile tires now with bigger wheels. You can see from the side of the car the contact patch is much bigger up front than in rear. Even though the pressures are the same, the load is greater up front. When you think about weight transfer during a hard stop, the ratio of grip becomes even more unevenly distributed.

Question, i noticed dodges have the same bolt pattern, the chargers, but instead of the 40 offset they have a 20 offset... does that mean one would have to run a spacer to push the wheels out or am i missing something, for instance the wheel i was looking at has a 20 mm offset with a 5.28 backspacing.....

The term offset is confusing to some people. There is positive offset and negative offset. Offset is the distance from THE CENTER LINE OF the wheel, to the mounting surface. With the older cars like my 70, I encourage guys to use back spacing measurements. Back spacing is the distance from the back side of the rim to the mounting surface. If the offset you are talking about is positive, less offset would move the wheel further outboard. A spacer would move it even further out board. Measure the back spacing of your Riviera wheels, and compare it to the Mopar wheels. You would also need to consider the width of both wheels to make an accurate comparison.

http://www.tirerack.com/wheels/tech/techpage.jsp?techid=101

It would be great, but perhaps hard/time-consuming, to put together a x-reference of all OEM Buick 1995+ 16,17,18 wheels that are a known bolt-on fit for the 95-99 Rivieras.

There seem to be quite a few questions posted about "Does Buick X wheel fit" along with the aftermarket questions.

The specs are in this thread about the correct bolt pattern, hub diameter and stock offset of course. But if we had a thread/FAQ that was updated as folks verified certain Buick wheels, that might be helpful.

Just a thought.
Al

I think any 5x115 (or 5x114.3) bolt pattern wheel would work with the correct positive offset. There were 5x115 on many GM cars in the '80s and '90s that could fit. Problem is, some wheels may stick out past the fender, or too far inside, which may not appeal to some. They technically fit, but would not be ideal. Also there are different wheel widths that could fit, but depending on the tire chosen may rub the inner fender up front. Hard to know which ones will work without trying them all.

We do have a good idea of some aftermarket wheel and tire combos that will fit the Riv in this thread:

https://rivperformance.editboard.com/t1080-faq-big-wheels-questionwill-they-fit

AA wrote:

al_roethlisberger wrote:

Has anyone tried the 17" Buick LaCrosse wheels from 2007/2008? Wondering if the bolt patter and offset are compatible.

The listing I've seen says they are 5x115, but I see that some later LaCrosse wheels are 5x120.

Thanks
Al

The Lacrosse bolt pattern is 5x120, though some incorrectly assume (and list) them to be 5x115. One of our members actually tried a set to find they wouldn't fit.

I was checking the Tire Rack x-ref and it shows 5x115 for the 2007 through 2009 Lacrosse, but goes to 5x120 in 2010.

A large wheel vendor on eBay also indicated the same. I wonder if the Lacrosse changed in 2010?

The 2007/08 Lacrosse wheel is 17x6.5 with a 52mm offset and 70.3mm hub. If the pattern is 5x115, I wonder how well a 52mm offset will setup on the Riviera.


Al

I stand corrected, Al. I think you're right, the bolt pattern did change after 2008. I think you're safe trying 2007/2008 LaCrosse rims with 5x115.

2009-up looks like they're 5x120 (probably due to increased wheel sizes).

al_roethlisberger wrote:

AA wrote:

al_roethlisberger wrote:

Has anyone tried the 17" Buick LaCrosse wheels from 2007/2008? Wondering if the bolt patter and offset are compatible.

The listing I've seen says they are 5x115, but I see that some later LaCrosse wheels are 5x120.

Thanks
Al

The Lacrosse bolt pattern is 5x120, though some incorrectly assume (and list) them to be 5x115. One of our members actually tried a set to find they wouldn't fit.

I was checking the Tire Rack x-ref and it shows 5x115 for the 2007 through 2009 Lacrosse, but goes to 5x120 in 2010.

A large wheel vendor on eBay also indicated the same. I wonder if the Lacrosse changed in 2010?

The 2007/08 Lacrosse wheel is 17x6.5 with a 52mm offset and 70.3mm hub. If the pattern is 5x115, I wonder how well a 52mm offset will setup on the Riviera.


Al

Al,
Offset is pretty useless when talking about wheels. There is positive and negative offset. I really don't know why they even list it. Back spacing is much easier to understand and measure. Most of the Riviera wheels I see listed have a back spacing of 5.6" -6". Increasing positive offset increases back spacing. 10mm is less than half an inch.

http://www.tirerack.com/wheels/results.jsp?autoMake=Buick&autoModel=Riviera&autoYear=1998&autoModClar=

Thanks, of course the bottom line is that someone (perhaps me) will just have to try one to know for sure how it fits and looks. Thanks! Al

Regarding the +52mm offset, it can be meaningful if you have a reference, and you know the width of the wheel. There is some metric conversion needed to calculate this. With positive offset, the value is in knowing how close the inside rim will come to the fender well. With negative offset, the value is in knowing how far the outside rim will protrude from the body (skateboard effect).

The OEM offset is +32 mm. Wheel width being the same, we can say a change to +40 mm offset will result in the inside rim being .315" closer to the fender well. If using an 8" wide wheel in place of 6.5" wide, that number would be about 1" closer with +40 mm offset. Tire diameter also factors in, but it is more difficult to calculate, as the fender well is a continuously curving surface.

+52 mm offset with a 6.5" wide wheel would result in the inside rim being .787" closer to the inside wheel well. I think that would work fine, but you should do some careful calculating before trying a 7 or 7.5" rim with +52 mm offset, to ensure against rubbing during full wheel lock or in very hard corners.

Perhaps defining offset and back spacing can be of some help. Some use the terms interchangeably, and they are not the same.

Back spacing is the distance between the inside bead surface of the wheel, and the mounting surface of the wheel (the surface that sits right up against the brake drum or rotor). Measuring back spacing is EASY. Simply put the wheel outside face down. Put a straight edge across from one bead to the other, and measure down to the mounting surface.

Offset is the distance from the CENTER of the wheel to the mounting surface of the wheel. There is positive offset, and negative offset. Positive offset moves the entire wheel towards the center line of the car. Negative offset moves out away from the center line of the car.

For example, a 7 inch wheel's center would be 3 1/2". If the mounting surface was 1" towards the outside of the wheel, the wheel would have 1" positive offset. If it was 1" towards the inner surface of the wheel, it would have 1" of negative offset. My first example would have 4 1/2" of back spacing, the second would have 2 1/2" of back spacing respectively.

Back spacing is way easier to measure and tells you more IMHO.

Right, they are not the same, but they both achieve the same purpose. Two different ways of saying the same thing.

I agree backspacing is an easier concept to grasp and understand, and it's easier to measure backspace from your existing wheels, but most aftermarket wheel specs and tire/wheel comparator programs I've used list offset values rather than backspace values. In order to know backspacing for aftermarket wheels, you'd need to convert.

So if your existing wheel offset needs to be measured, and you're looking for replacements, maybe working in backspace is better. But if the existing offset is known, it might make sense to stick with offset values, avoiding the need to convert to backspace. Also it depends on which wheels you chose and how their specs are listed.

Looks like the 06-11 Lucerne 17x7 wheels may fit too. Tirerack says they are 5x115 and the backspacing is similar to the Riviera spec.

al_roethlisberger wrote:

Looks like the 06-11 Lucerne 17x7 wheels may fit too. Tirerack says they are 5x115 and the backspacing is similar to the Riviera spec.

I was looking at the Lucerne rims and I believe they have a 42mm offset compared to our 32mm offset. They have the same 5x115 bolt pattern and are 7 inches wide. Would there be any problems running this rim?

Those should fit just fine. +42mm offset would move the wheel inward 10mm compared to stock.

98riv wrote:

al_roethlisberger wrote:

Looks like the 06-11 Lucerne 17x7 wheels may fit too. Tirerack says they are 5x115 and the backspacing is similar to the Riviera spec.

I was looking at these Rims and I believe they have a 42mm offset compared to our 32mm offset. They have the same 5x115 bolt pattern and are 7 inches wide. Would there be any problems running this rim?

10 mm is less than 1/2" The stock Riv wheels are 6" wide, correct? A 7" wheel would need about 1/2" more back spacing or offset. Sounds about right.

Thanks!

Just out of curiosity, what tire/wheel combinations are you running other than the stock 225/60R15?

Got pictures of them?  How does this affect the speedometer, MPG, etc.?

15? mine came with 16s. its 225/60r16 i think. i want 18s and somewhere here is a thing aa made of the "upsize" calculations to keep the spedo in check

You can get those measurements pretty much everywhere. IMO 17's look perfect, and they should be 16's (at least mine were).

Rivnut - a couple threads in the Exterior forum you may be interested in reading:

https://rivperformance.editboard.com/t594-faq-rims-wheels-that-look-good-on-the-riv

https://rivperformance.editboard.com/t1080-faq-big-wheels-questionwill-they-fit

Quote :

i want 18s and somewhere here is a thing aa made of the "upsize" calculations to keep the spedo in check

You'll need a tuner (DHP/HPT) to change the pulses per mile value. It's based on tire size, not the rim. Stock value for 60R16 is 23314. For 45R18 I use 22880. Other tires will vary slightly, but that's probably close enough for most.

NEWS FLASH: New Cadillac ATS 5x115 bolt pattern. Initial searching at Tire Rack indicates the offset for ATS is similar to Riviera (40-45mm). This may be a good thing for Riviera owners looking for wheels with some fresh style!

AA wrote:

NEWS FLASH: New Cadillac ATS 5x115 bolt pattern. Initial searching at Tire Rack indicates the offset for ATS is similar to Riviera (40-45mm). This may be a good thing for Riviera owners looking for wheels with some fresh style!

No doubt, will hopefully drive the wheel manufacturers to add more options

The ATS is going to be a hit, and lots of owners will want to customize the wheels. And given the ATS' performance credibility, we may have more performance (forged light weight, strong and maybe less expensive due to volume) options as well.

Al

Here is another website that I found to compare tire sizes and how much it could change your speedometer. http://tire-size-conversion.com/tire-size-calculator/