Smithengineered Posted November 4, 2023 Share Posted November 4, 2023 Anyone have good wheel offset/width advice for some 15” minilite wheels? Reading online gives me about 1000 different answers. I have a SV chassis with the de deion rear setup. Current wheels appear to be 8” wide with 205/45 16. I like the look of the deeper dish so ideally I’d like to go as deep dish as possible without fouling the front wings or sticking out in the rear. Anyone that can lead me in the right direction it would be much appreciated! Thanks! Link to comment Share on other sites More sharing options...
MV8 Posted November 5, 2023 Share Posted November 5, 2023 It doesn't look like you could go any deeper dished than you have now and still clear the outer fender lips. The size information should be embossed or etched into the existing wheels, so if the 15s are the same width, the offset should be the same for the same fender clearance. You could go with a 15x6 or 7 instead and have a different offset to keep the outer edge, dish, and fender clearance the same as you have now. The offset usually has an "ET" prefix. Link to comment Share on other sites More sharing options...
Taber10 Posted November 5, 2023 Share Posted November 5, 2023 (edited) Wow, 8 inch wide wheels seems impressive! I just replaced my original wheels (14 X 6) with VTO wheels (15 X 6) because I thought I'd have better tire choices at 15 inches. I was told by VTO that the 2007 Caterham 7 SV uses a 4 1/2 inch backspace. I had been told that "offset" was +15mm. I couldn't find either marked on the wheels. As you found, online you may read lots of numbers. Of course my car could be ordered with a choice of three wheel diameters, three different sets of front wing stays and at least two sizes of front wings, so that can lead to a variety of choices. My new tires are 195/50 R15 and JUST BARELY--less than 1/4 inch--clear the inboard wing stay. Good luck! Edited November 5, 2023 by Taber10 Link to comment Share on other sites More sharing options...
MV8 Posted November 5, 2023 Share Posted November 5, 2023 (edited) The rim size is typically under the center cap, in the voids between the stud holes on the hub side, or inboard on a spoke. You can also measure the size and offset with rulers. The rim flanges/lip thickness must be subtracted from the measurements. The first three digits are considered tread width to fit a standard rim width range for the number, then the next two digits are the sidewall height (aspect ratio) but they actually change the tire width to ensure the tire will still fit the rim width range. A 45 is wider than a 55 with the same tread width due to the reduced sidewall bulge. A tire mfg will list the rim width range for a given tire. Best to stay near the middle of the range for easier bead seating and prevent unseating if the pressure is run too low. The bigger the tire, the lower the pressure should be for a given curb weight. Edited November 5, 2023 by MV8 Link to comment Share on other sites More sharing options...
Smithengineered Posted November 6, 2023 Author Share Posted November 6, 2023 I was incorrect. They are 15x7 wheels et19. I’d like to go 15x8 on the rear. Is it safe to assume that a et19 will actually be a deeper dish and will stick out father on the outside since it’s a wider wheel? Link to comment Share on other sites More sharing options...
MV8 Posted November 6, 2023 Share Posted November 6, 2023 One inch wider with the same offset should put a 1/2 inch outboard and inboard, so it MIGHT fit. Assuming the actual tire size is 205-45-15, the tire with the closest outside diameter (0.4" larger/ 0.2" radius) that is available/common enough is 245-40-15. Eight inches is the minimum width for this tire. A 225/45-15 would be a better fit for the width but would be 0.7" larger (0.35" radius increase). These are the mfg specs and more accurate than calculating what it should be based just on the size number. I recommend a wheel with zero or slightly negative offset (this dishes the center by pushing the rim/hoop outboard) and a narrower rim/hoop as needed so the tire does not make contact with the outer fender. There are wheels that have a thinner center and spokes and appear to be a different offset but are the same size. They tend to be steel or forged without covered lugs. A high-end tire shop will have a tool for hanging a tire without a rim to check fit and determine what wheel offset is needed. Another alternative is narrowing the axle housing and shafts or widening the rear fenders. I could not find a 205/45-15 currently offered. Is that driving the change so you might as well have the dish look? Link to comment Share on other sites More sharing options...
Drakman Posted November 6, 2023 Share Posted November 6, 2023 Hi, I use this when comparing wheel and tyre sizes. https://www.wheel-size.com/calc/?wheel1=185-65-14X6ET23&wheel2=185-55-13X6ET23&fcl=50mm&scl=50mm&wcl=30mm&sr=0mm 2 Link to comment Share on other sites More sharing options...
Smithengineered Posted November 7, 2023 Author Share Posted November 7, 2023 1 hour ago, MV8 said: One inch wider with the same offset should put a 1/2 inch outboard and inboard, so it MIGHT fit. Assuming the actual tire size is 205-45-15, the tire with the closest outside diameter (0.4" larger/ 0.2" radius) that is available/common enough is 245-40-15. Eight inches is the minimum width for this tire. A 225/45-15 would be a better fit for the width but would be 0.7" larger (0.35" radius increase). These are the mfg specs and more accurate than calculating what it should be based just on the size number. I recommend a wheel with zero or slightly negative offset (this dishes the center by pushing the rim/hoop outboard) and a narrower rim/hoop as needed so the tire does not make contact with the outer fender. There are wheels that have a thinner center and spokes and appear to be a different offset but are the same size. They tend to be steel or forged without covered lugs. A high-end tire shop will have a tool for hanging a tire without a rim to check fit and determine what wheel offset is needed. Another alternative is narrowing the axle housing and shafts or widening the rear fenders. I could not find a 205/45-15 currently offered. Is that driving the change so you might as well have the dish look? yikes this wheel offset stuff is giving me a headache lol. Since I’m dropping down from a 16 205/45 to a 15” shouldn’t the tire go up to a 205/50 to make up for the loss of wheel diameter? The rears Ideally I’d like to go to a 225 if I could go to a 15x8, but still need to figure offset. Thanks Link to comment Share on other sites More sharing options...
Smithengineered Posted November 7, 2023 Author Share Posted November 7, 2023 I think I’ve got it figured out. If I went with 15x8 at a ET 0 and 225 width tire I’m adding roughly 1 5/8” to the outside width on the rear. Link to comment Share on other sites More sharing options...
MV8 Posted November 7, 2023 Share Posted November 7, 2023 I'm confused by your earlier post. You said that you were incorrect and that the wheels are 15x7, et19. Were you referring to what you have is not a 16" or what you want is a 15x7, et19? Nice link Drakman. That will help to keep the math straight if it is accurate. Link to comment Share on other sites More sharing options...
Smithengineered Posted November 7, 2023 Author Share Posted November 7, 2023 Sorry I meant the current wheels are 16x7 et19. I know if I drop to a 15” wheel that in the front they would need to stay 15x7 et19 with a tire size of 205/50/15. The rears I’d like to go with a 8” wide wheel with a 225/50/15 tire. Link to comment Share on other sites More sharing options...
MV8 Posted November 7, 2023 Share Posted November 7, 2023 Those will cause the speedo to read slower for a given speed, might bottom out in the fender at full bump, and will raise the ground clearance a bit, but it will be more dish and will probably clear the outer fender lip. Link to comment Share on other sites More sharing options...
Smithengineered Posted November 7, 2023 Author Share Posted November 7, 2023 Wouldn’t a 45 series tire on a 16” rim be equivalent to a 50 on a 15” rim? Link to comment Share on other sites More sharing options...
Vovchandr Posted November 7, 2023 Share Posted November 7, 2023 40 minutes ago, Smithengineered said: Wouldn’t a 45 series tire on a 16” rim be equivalent to a 50 on a 15” rim? https://tiresize.com/comparison/ If the width is the same, then yes its essentially identical Link to comment Share on other sites More sharing options...
MV8 Posted November 7, 2023 Share Posted November 7, 2023 (edited) 1 hour ago, Smithengineered said: Wouldn’t a 45 series tire on a 16” rim be equivalent to a 50 on a 15” rim? No. In this case, it is only a couple mph faster than indicated (varies with speed), but this assumes the speedo was corrected for the tires you have now. Edited November 7, 2023 by MV8 1 Link to comment Share on other sites More sharing options...
Smithengineered Posted November 7, 2023 Author Share Posted November 7, 2023 1 hour ago, Vovchandr said: https://tiresize.com/comparison/ If the width is the same, then yes its essentially identical Thanks for the link! Appears that it is .6” taller. Link to comment Share on other sites More sharing options...
ashyers Posted November 13, 2023 Share Posted November 13, 2023 Here's the wheel info for the 16", 5 spoke wheels. 7Jx16 ET19 Link to comment Share on other sites More sharing options...
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