Do these tire size changes have any effect on the speedometer or gas mileage
Yes, different sized tires will effect your speedometer. There are charts I've seen that will tell you how much it will change between those sizes. I would think no significant fuel milage changes...
Re: speed - My observation with my Nav unit in the SSR, and Nav in several other vehicles, is the trailing edge of the speedo needle is the more accurate reflection of the actual vehicle speed. I believe the manufacturers do this to give you the driver a little room for error. I could totally be wrong.
Re: gas mileage - Likely negligible unless big changes are made. That said, wider tires will increase the rotational drag and actually increase the wind drag (even though it is under the vehicle). Both will cut into gas mileage, all things being equal. Narrower tires cut the wind and offer less rolling resistance (e.g. Prius), and are less likely to hydroplane, again all things being equal. My right foot has more to do with the mileage than the additional tire width. I've got an Excel spreadsheet charting mileage over the years, and if there were longer highway trips. When I do something to the Elsie, my mileage goes down for a tank.
What PSI are you running, front and rear? From your pics it looks like sidewall on front tire is low. Can you measure and post the dimensions of the sidewalls top and bottom? My tires also look lower in the front with 38PSI all around.
Re: PSI - They were low at 31PSI. That said, my son dropped the gauge so I'm skeptical of it. I typically run 35-36PSI. I'll get a better feel on my gauge after the new rears are put on tomorrow.
Re: dimensions - see below, I measured at current pressure.
Think my ride may be lower than yours in the front for sure. Take a look at these two shots I took today. Measurement from top center fender well opening to top of chrome wheel rim is approx 3.5". This is with stock tire setup now.
Yours does look lower. 1in? I couldn't tell the actual height in your picture, too fuzzy (24” monitors and computer glasses didn't help). I'd almost question if yours was lowered. Mine has stock springs and replacement Bilsteins via Mike in AZ (who is awesome).
You can see Elsie, the only
in relation to a few others in post #8 here: https://www.ssrfanatic.com/forum/f36/...akfast-230578/
The lowered ones stand out to me. I believe most in the pic were running RSAs.
Here are a bunch of measurements, which should help y'all sort things out. I made the measurements in the relatively level garage, with a minor slope toward the front wheels. The measurements are from the passenger side. I used 2' 1x4s to get the width and height of the tires, I didn't put a level on them, just eye balled it. Elsie had 3/4 a tank (of premium). She is an auto, which I think seem to ride higher in the rear.
The lower shock mount measurements will enable checking my tire height vs others as it contributes to ride height and the frame measurements will help workout spring height differences.
Fronts: 275/40ZR19 Michelin Pilot Super Sport, 31PSI (too low) < 1000 miles since new
Front wheel well height: 28 1/4"
Front tire height (at the crown in middle of tread): 26 5/8"
Front tire top sidewall height: 3 1/2"
Front tire bottom sidewall height: 3 1/16"
Front tire width, at hall height of the wheel: 10 1/16"
Front tire width, on ground (including sidewall bulge): 10 1/2" (width at 35PSI, 10 3/8”)
Ground to lowest point on lower shock mount (wheels straight): 6 1/2"h
Ground to "skid pad" in front of lower control arm mount: 5 3/4"
Rears: 315/35ZR20 Michelin Pilot Super Sport, 31 PSI (too low), > 10K miles, badly checked sidewalls (outdoor girl and the cover, only covers half the wheels).
Rear wheel well height: 30 1/2" (brand new tires at 35PSI = 30 5/8”)
Rear tire height (at the crown in middle of tread): 28 1/8" (brand new tires at 35 PSI = 28 1/4”)
Rear tire top sidewall height: 3 1/2"
Rear tire bottom sidewall height: 3 1/4"
Rear tire width, at half height of the wheel: 12 1/4"
Rear tire width, on ground (including sidewall bulge): 12 1/2" (brand new tires at 35 PSI = 12 1/4”)
Ground to lowest point on lower shock mount: 8"
Ground to lower control arm mount on frame: 7"