Wheels and Upgrades

update 1/31/05

Stock Wheels

The 3rd Generation comes with 16x6.5" wide cast aluminum which are durable, light-weight and high quality giving a good ride because they are narrow (cushy sidewalls) and good linear acceleration because of their light weight. The 96-98 rims come in two finishes, a brushed aluminum satin finish or chrome. In 96-98 the SHO rim was exclusive to the SHO, and the only optional rim for the SHO was the chrome rim of the size. `99 SHOs come with a slightly different appearing chrome rim that has no center cap but I suspect has the same weight and size. In 99 the SHO rim is an option on the SE Sport and no longer exclusive. No 3rd generation factory rim is directional. Any rim can be used at any location.

Why upgrade?

Several reasons quickly come to mind.  The factory rims are the minimum width for the factory size tires. Big improvements in handling are possible with wider rims.  Aluminum rims don't like a tire monkey changing summer-to-winter then winter-to-summer tires every year. It is expensive ( mount and balance ~ $20 a tire), inconvenient, and hard on the rims. Running all season tires year round compromises both summer and winter performance. While adequate they are far from optimal and well off the performance pace. Worse my all season tires always have too much tread to replace but not enough tread depth in the fall to trust for the winter. The narrow factory rims give a good ride in winter when road conditions are not conductive to road fun. The temptation to get performance rims (and tires) just for summer is not only more fun but makes good business sense.  Bend a rim and find out just how expensive the factory rims are if not covered under insurance.  Some rims just look nice.  Wider, bigger, lighter rims can improve every aspect of performance including stability in severe cross winds.

What size and offset?

The factory rim is 6.5 inches wide tire bead to tire bead. The flange which holds the tire on the rim is ½" wide on both sides so a 6.5" wide rim will measure 7.5". The SHO is front wheel drive and is fussy about the wheel offset, or "dish" of the rim. Ignoring this important fact and you may experience wheel bearing problems and exaggerated torque steer. This not only cost money but involves safety and vehicle control. The factory wheel has 42 mm negative offset which means that the lug nut flange is offset 42 mm toward the street side of the wheel from center. From the street the wheel looks nearly flush, from the brake side the wheels are deeply dished. The bolt pattern (5x108 mm) is also rare, so good options don't grow on trees.

The 16" plan.

Since the factory rims are 16" an advantage exists by staying with 16" rims for a second set. Tires can be used on either set of rims and you have 4 reliable spares far better than the space saver spare if you ever had to use it. (I have it, damn thing is way too small about the size of a $2 cookie, it feels like you are driving on a rim.)  The second set of rims can be much wider giving a healthy performance improvement in handling especially with performance summer tires. The 16" tires and rims are also lighter than 17" rims giving better breaking and acceleration. Other advantages, the quality ride is preserved, the tires and rims cost less and it is very difficult to bend a 16" rim. ( I have bent a 17" rim, recently with out knowing how or where. update -  Wheel had a bad valve stem and was low on air.)

Heavy rims actually slow down a car so, what can we get in a light affordable 16" with the correct offset? Most of my experience has been with a Company that Vadim (SHO Shop) has found called Team Dynamics. None of the wheels are too expensive or heavy, the quality and service has been good. When I call other places and ask how much the rim weighs and ask about the offset and width all I get is "this is guaranteed" to fit in our book but no other details. This is a good route to get heavy narrow expensive rims that WILL slow down your car, cost you lots of money.

A 16x6.5" wheel with 42 mm offset is replaced by a 16x7 or 16x7.5 with 45 mm offset. (update - 16x7.5 with 45 mm off set does NOT fit. It rubs the strut.) Team Dynamics makes two wheels in 16x7, the Monza and Motorsport that are beefy and made for severe use.  They weigh 22 lbs each compared to the factory rims which weigh 18.8 lbs each. They are only ½" wider the factory but they have a reputation for being strong.

Wider ( 16x7.5") and lighter (not as strong) at 19 lbs the Cosmos, Daytona, DTM, Qualifier, and Super Touring all have the correct offset and a the two big performance advantages, light weight and a ½" more in width.

What size tires ties do I use on the new 16" rims? Fred Puhn in his book on "How To Make Cars Handle In The 90's," recommends using a rim width ½" narrower that the maximum width for the tire size to achieve peak street performance.  Design rim width range for a 225 mm tire is 6.0"-8.0" inches so using the same size as the factory, 225/55- ZR16, is the perfect performance match for 7.5 rims. Great no speedometer error! Maximum speed and control in the corners!

What about 16x8" or 16x9" with the correct offset and bolt pattern? When you find them let me know….

The 17" Plan.

Offset is a function of width not diameter so you still want 45 mm offset. The same tires are available in the same widths from Team Dynamics. The HD Monza and Motorsport in 17x7" or the others in lighter 17x 7.5" size.

The advantages of 17" rims over 16" rims are a slim margin in all aspects handling.  They do feel great especially on a smooth road or ramp. Consider also the disadvantages, the rims are far more prone to incidental damage from potholes or RR crossings.  The rims and tire weigh more than the same 16" set of the same width which hinder acceleration and braking.  True high performance tires have stiff sidewalls which improve handling but also provides a firm ride.  This effect is multiplied by the way the short stiff tire sidewalls can keep the SARC system in firm mode.  In short the 17" rims trade a modest improvement in turn in and grip for a significant compromise in ride quality.  Expect to pay a lot more for a set of 17" rims and tires than you would for a set of 16" tires.

If you are committed to 17" rims what size tires?  The factory tire is 25.74" tall. A 245/45-ZR17 is 25.68" tall but the recommend rim width for that size is 7.5"-9.0". A 235/45-ZR17 comes within a ¼" of the struts all the way around but it does not move around much because it is a relatively narrow tire with a lot of air on a wide rim.  I have to think a 245/45, 10 mm wider tire is going to cut that ¼" safety margin to little or nothing. (10 mm is 2/5" of an inch, 1/5" per side, ¼ - 1/5" = .05" of clearance.)  The car may not move with the 245/45 bolted on because all four tires could rub the struts.  If it does move it, it will rub the sidewalls on the struts before long. The 235/45-ZR17 is a touch short at 25.33" however it has been my experience that the stiffer sidewalls on the 235/45-ZR17 have a shorter rolling distance per revolution but the same ride height. In other words, you don't go as far every turn but the car rides at the same height because the 17" side has little or no bulge.  Expect a 1.6% speedometer error with 235/45-17 tires. 100 mph indicated will actually be 98.4 MPH.

Using tire pressure tables to keep the same load capability as the factory size, use 34 psi compared to the factory setting of 30 psi all around.

One advantage of 17" rim is the option you have of running 13" front Baer racing brakes from the SHO Shop.  The 17"s do make a fashion statement and cut into apex . They also make the car immune to cross winds, since high winds are associated with wet roads and rain they make driving in very bad weather very easy.

What about 17x8" or 17x9" with the correct offset and bolt pattern? When you find them let me know….

The 18" Plan, and Bigger.

In theory a 18x8" rim with a 32 mm offset should clear the brakes and struts (a wheel with 35 mm may fit but it would be very close to the strut). Will it clear the fenders? I don't know, I think so! Team Dynamics makes 3 rims in that size and with 30 mm offset. DTM, Monza, and the Qualifier. (update - SHO Shop reports very poor ride quality without improved performance when they tried 18" Rims, this is a cosmetic only mod.)

Ford ( the Rage) and others have shown SHOs with 19" or bigger rims but the rumor is that the car had to be jacked up and the wheels put on in place because the wheels could not be turned or move once mounted.  If you try this, and get it work, drop us a note and tell us about.  It seems like a car show only trick.

What size 18" tire?  Minimum rim width for a 255 is 8.5" so you get you use the smaller 245/40-ZR18 which is 25.72" tall.  Design rim width for the 245 is 7.5"-9.5" so 8" wide is far from optimal so this combination is for looks only, not hot dogging chicanes and switch backs
 
 

Tire width (mm)	rim"	design rim width	rim sect w/ ratio
225	6.5	6.0-8.0	0.734
235	7.5	7.5-9.0	0.811
245	7.5	7.5-9.5	0.778
255	7.5	8.5-10.0	0.747

 

Rotating Weight Each	Rim Lbs	Tire Lbs	Rim & Tire Lbs
97 16" OEM GY	18.8	25.0	43.8
16" AVS S4	18.8	23.2	42.0
17" AVS Sports	19.2	24.8	44.0
99 OEM 16" rim	17.5

 

update 1/31/05

The '99 wheels I have are 17.5 lbs each on my digital scale. Scale resolution is .5 lb so they weigh at least 17.26 lbs and not more than 17.74 lbs.

SHOZ123

Team Dynamics wheel offset by size – 5x108 mm

SHO Shop:  (714) 894 8415, FAX:  (714) 894 8901
Team Dynamics:  (888) –384-7779, ask for Don, or (909) 947 0114, FAX:  (909) 947 5763

Links:

See http://www.rimstock.com to view Team Dynamics rims.
 

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