Gen 1 Wheel Rims and Tires

Gen 1 Wheel Rims and Tires
The OEM factory rims on a Gen 1 Prius are 14x5½JJ. Rim size 14x5½JJ features..
<br />
1 Bolt pattern: 4x100mm 4 bolts in a 100 mm diameter circle. Measured from center of bolt across wheel center to center of far bolt. <br />
2 Bolt Thread Size: M12x1.5 ISO standard. Nominal diameter (mm) x pitch (mm) <br />
3 Center Bore: 54.1mm The size of the center hole in the middle of the wheel. Measured in millimeters. Normally covered by a center cap. The wheels won't fit if the center bore of the wheels are smaller than that of your car's. If the bore is larger than that of your car's. Spigot rings needs to be fitted. Spigot rings allow the wheel to be firmly centered on the hub. <br />
4 Wheel width: 5.5inches The width of the wheel will dictate the tire sizes that will fit on the wheel. The wider the width the wider the tire size that will fit on the wheel. Wider wheels and tires gives your tires better grip on the road giving your car better road holding and braking than tires that are narrower. The trade off is wider tires have more rolling resistance (friction). Which will lower your MPG. If you want a higher MPG then get narrow tires. <br />
5 Wheel diameter: 14" Diameter of the 'rim' in inches (excluding the tire). <br />
6 Wheel Offset: ET45 45 mm distance from the center of the wheel width to the mounting face. So 140mm(5 ½") Wheel width / 2 = 70mm(2 ¾") Center + ET 45mm(1 ²⁵⁄₃₂") = Backspace of 115mm(4 ¹⁷⁄₃₂"). Did you know: 'ET' is derived from the German word 'Einpresstiefe' which translates to 'insertion depth'? <br />
7 fixme: JJ I have No idea what JJ means. ChapmanF feel free to weigh in here.

Gen 1 Prius can interchange rims with..

Prius, 2001-2003 (spare) [of course. duh.]

Toyota Tercel, 1993-1996 (spare with ABS)
Toyota Paseo, 1993-1999 (spare with ABS)

Toyota Echo sedan/coupe

Scion xA

2004-2005 Toyota Echo Hatchback

In terms of non-US vehicles, there’s the Ist (same as xA), Sienta, Raum, Passo, FunCargo, Vitz (Echo Hatchback), Platz (Echo sedan), Belta (Yaris sedan)

The dope on load/inflation minimums for P-metrics Tires

The factory tires on a Gen 1 Prius are P175/65/R14 84S. It turns out the standard specs for P-metric tires come from this outfit called the Tire and Rim Association, and they're published in the "TRA Yearbook".

The load capacities for P175/65R14s are standard, either "81" (981 lbs at 32psi, 1019 lbs at 35psi), or "84" ("XL", 981 @ 32, 1019 @ 35, 1058 @ 38, 1102 @ 41). (From Table P-1, in the 2004 yearbook on pp. 1-12 and 1-13). You can inflate either kind of tire further, up to its labeled max pressure, but with no additional capacity, so an 81 is still limited to 1019 lbs even if inflated past 35, and an 84 is still limited to 1102 even inflated above 41. At 35 and below, there's no capacity difference between an 81 and an 84. (p. 1-34) Caution:none of this is true of Euro-metric tires (sizes without a P).

Choosing a tire and an inflation pressure has to satisfy two conditions, one for maximum load and one for "normal" load. The maximum load has to be <= the full tire capacity at the chosen pressure. The normal load has to be <= 88% of the tire capacity at the chosen pressure. (p. 1-03) That's the TRA requirement; there is a more generous 94% limit in the Federal safety standard FMVSS 110 S4.2.1.2.

We can get the maximum load straight from the Gross Axle Weight Rating on the door label (divided by two for per-tire load). The "normal" load comes from the curb weight of the car plus 3 150-lb occupants, two in front and one in back. (That's the specified "normal" occupancy for a 5-passenger car.)

The "max" numbers are easy to run:

Column 1
<br />
1 gawr 1970 1685 from door label <br />
2 per tire 985 843 <br />
3 capacity [email protected] [email protected]

So the "max" condition is easily met at 35/33, for either an 81 or an 84 tire. (I used capacity @ 32 from the table b/c it doesn't show 33.)

The "normal" numbers will take a bit more doing. Have to get the front and rear axle curb weights from the New Car Features Manual, then throw in 3 150-lb occupants.

I'm going to smush the occupants into one 450 lb blob on the centerline, 2/3 of the way from the rear to front seat. Eyeballing the underbody dimensions in the collision manual, this point looks to be about 110 cm forward of the rear axle, or 43% of the wheelbase, so this weight should distribute 194 lb to the front, 256 lb to the rear.

Column 1
Column 4 <br />
1 curb weight 1700 1065 from New Car Features Manual <br />
2 std occupants 194 256 3 150-lb occupants 2 in front 1 in back <br />
3 ---- ---- <br />
4 1894 1321 <br />
5 per tire 947 661 <br />
6 capacity [email protected] [email protected] <br />
7 x 0.88 897 863 oops we're 50 lbs over in front! rear is ok. <br />
8 x 0.94 958 922 under the more generous FMVSS we're ok in front.

So because of the heavy front, no P175/65R14 tire can meet the TRA 88% normal load standard at 35/33, not even an XL tire. At 41 psi minimum in front, an XL (load 84) tire can meet this standard. A non-XL (load 81) cannot, at any inflation pressure.

Under the FMVSS 94% load limit, on the other hand, we're ok on either type of tire, even at the OEM 35/33. Obviously Toyota was able to get approval at those pressures, and tire vendors offer these tires for the application, so the FMVSS limit must be the one they have been held to.

So ... What I Learned Today (still for P-metric tires only):

users of 81 or 84 load index P-metric tires are ok under FMVSS, at 35/33 or any higher pressure
users of 81 index tires at higher pressures are still ok and probably getting better mileage, but no extra margin of load capacity
users of 84 index tires at 35/33 are still ok, but not any more ok than the 81 folks
drivers who use 84 index tires AND increase pressure to 41/39 or higher do have an extra margin of load capacity and meet the stricter 88% TRA figure.

Inflation minimums for P-metrics and Euro-metrics

Putting it all together....

Here are the minimum inflation pressures for different P-metric and Euro-metric tires on a G1 Prius to meet the normal load US federal requirement (no more than 94% of tire capacity) or the more conservative TRA target (no more than 88%).

As explained here, P-metric inflation tables depend on the tire size and load index number only; Euro-metric tables depend on the load index number and whether the tire is XL or not, but not the size.

Keep scrolling ... vBulletin didn't put this huge gap ahead of tables, but xenForo does....

Column 1
for 94% normal-load limit
for 88% normal-load target
<br />
1 capacity req'd (lbs) 1008 1077 <br />
2 P-metrics <br />
3 P175/65R14 81 35 psi - <br />
4 P175/65R14 84 (XL) 35 psi 41 psi <br />
5 non-XL Euro-metrics <br />
6 81 36 psi - <br />
7 82 35 psi - <br />
8 83 34 psi - <br />
9 84 33 psi 36 psi <br />
10 XL Euro-metrics <br />
11 81 XL 42 psi - <br />
12 82 XL 41 psi - <br />
13 83 XL 39 psi - <br />
14 84 XL 38 psi 42 psi <br />
15 85 XL 37 psi 40 psi <br />
16 86 XL 36 psi 39 psi <br />
17 87 XL 34 psi 37 psi

There are adjustments for high-speed driving. For example, an S tire is rated for 112 mph, but only with the minimum inflation increased by 3 psi for speeds above 99 mph. (TRA yearbook p. 1-06).

The factory tires on a Gen 1 Prius are P175/65/R14 84S. This is a tire with a 583 mm overall diameter. Or roughly 23 inches. Different tire sizes will give different diameters.

Tire Size
<br />
1 165/65R14 -2.6%22.4" 6.5" 14 x 4.5-6" <br />
2 185/60R14 -1.3%22.7" 7.3" 14 x 5-6.5" <br />
3 205/55R14 -0.4%22.9" 8.1" 14 x 5.5-7.5" <br />
4 225/50R14 -0.4%22.9" 8.9" 14" <br />
5 175/65R14 Equal23" 6.9" 14 x 5-6" <br />
6 195/60R14 +0.9%23.2" 7.7" 14 x 5.5-7" <br />
7 185/65R14 +2.2%23.5" 7.3" 14 x 5-6.5" <br />
8 175/70R14 +2.6%23.6" 6.9" 14 x 4.5-6" <br />
9 205/60R14 +3.0%23.7" 8.1" 14 x 5.5-7.5"

Special thanks to ChapmanF for doing the lion's share of the research. G1 tire requirements | PriusChat[/CENTER]
Mar 15, 2019