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Wheel adapter and tire sizes for custom wheels?

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Ok, need your guys help. I am finally preparing to get some new wheels for my car this coming spring/summer (I know ive been saying this for years) but I need some help with the proper adapter and tire sizing... Have a seat, this is some long reading and lots of calculations.

The wheels I'm getting are not available in the 5x108 bolt pattern and I will be getting custom adapters to get them to fit. The adapters are going to be made through and are hubcentric and all that. There have been a couple other Esprit owners who have had this done with excellent results.

Anyways, the wheels I'm going with are only available in 18x9 for the rear and 18x8 for the front. I dont want to do 17inch fronts as this looks too small in my opinion. I want to get the offset correct so that the wheels would sit where they would be if they were V8 Esprit wheels. I also want to get the proper tire sizes so that they retain the same overall diameter of the V8 ones because they are the perfect diameter to fill the wheel arches.

1. As far as offsets go for the wheels, the 18x8 wheel I will be putting on the front has an offset of 40mm. The stock V8 wheel has an offset of 19... Considering I will be losing .5 of an inch by going with an 8 inch wide wheel versus the stock 8.5 inch wide, do I make the adapter an additional 12mm wider to accomodate for this? Am I correct in assuming that the adapter has to be about 33mm wide each then? (12mm to make up for the lost half inch and then 21mm to push them out to V8 distance)

2. For the back wheels, same as above, but this time I'm losing a whole inch by going with 18x9 instead of 18x10, does this mean I need to make the adapter a whole 25mm wider to make up for this right? The offsets of the new custom rear wheels are 45 versus the stock V8 size of 17. To get them to the right place am I correct in assuming that the adapters will have to be somwhere like 53mm wide each? (25mm to make up for lost inch and then 28mm to push them to V8 distance)

I should mention that the wheels im getting are avaialable in differnet bolt patterns like 5x114.3 that do come in smaller offsets if the adapters mentioned in the above calculations seem too wide. I just want to make sure I'm doing my math correctly and am not missing anything here... I also know that the adapters have to be at least 25mm thick so that is why I chose some of the higher offsets to make up for some of the room and amke sure the adapters would be above 25mm.

As far as tire sizing goes, I want the whole overall diameter of the tires to be the same as the stock V8 Esprit wheels.

3. For the front tires, since I'm going with 18s instead of 17s, I will definitely need thinner profile tires. The stock front tires for the V8 are 235/40/17. Would I have to go with a 235/35/18 to make up for the added inch of the wheel? This doesnt seem like a common tire size... Some other forum I found mentioned that 225/40/18 would be a good alternative for the 235/35/18 and probably have a ton more tires avaialbe in that size... The only difference would be an additional 17mm of overall diameter... 225/35/18 would be 5mm less in diamater versus the V8 tires...

4. For the rears, the only change versus the stock 285/35/18 is the loss of an inch of width of the wheel... How does this effect the tire? Being that they are skinnier wheels by an inch, doesnt that make the tire slightly taller? I want the tire faces to be flush with the wheel lip and not have any "overhang". What would be a good tire size for this? Is 275/35/18 a common size?

Thank you in advance for help in straightening all of this out!


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I did all the same calculations you're doing over the course of months and I couldn't have done it with out these two calculators:

I just skimmed your post but I think you're doing it right. I'm not in the mood to write a long rambling reply, but if you cant get answers to your staisfaction I'd be happy to discuss it with you on the phone. Ping me if interested.

PS... I'm thankful everyday that I was 17s on the front. Between the potholes and expansion joints here in the mid-Atlantic my car would be in pieces with less rubber. Sometimes you gotta compromise if you're building a driver.

Edited by karmavore

Luke Colorado, Super Spy.   -  Lotus Owner No Longer

1987 Zender Widebody 560SEC | 1994 Lotus Esprit S4 | 2013 Honda Fit EV (#269)

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Hmm, never thought my AWI's front 17" looked small...

Keep in mind that the V8 front wheels with 235/40-17 are actually about 1/2" taller than the SE tires. It is a noticeable difference. People often ask if my car is jacked up in the front...

I wouldn't run a tire on a rim that is 1" narrower than the normal wheel width... It'll make the sidewalls feel blobby and soft. The manufacturer has recommendations for wheel width for each tire.


Vulcan Grey 89SE


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