Wheel Sizes / Tyre ofset - Whats Appropiate 14 " 15 " 16" ?

Technical Area Wheels, Tyres & Brakes
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Hi All

 

I have a 1.8 mx5 MK1 VR LTD , the ride hight is slightly lower normal as standard due to running on Bilsteins -

The wheels ar 15" Enki’s - Tyre size 195 / 50 / R15

I need to replace the entire set of wheels / tyres with a secondhand set that i hope to locate .

The questions are : 

 

What size wheel can i fit on a like for like basis , can i fit a 16" wheel without any problems / does tyre size matter ?

Can i fit wheels from a Mk2 without trouble 15 and / or 16 " ?.

Do i need a specific ofset range that i must not exceed / need to adhere to ( sorry i don’t understand what this means )

 

I effect i keen to understand a range of sizes / ofsets / Mk1 & Mk2 wheels ? etc… that i can pick up second hand and fit without worry .

 

Any advice would be really appreciated …

 

Thankyou in advance

 

Regards

 

Andrew   

 

 

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 Standard wheel sizes and offset are very important to the very precise MX5 chassis. Mazda put a massive amount of R&D into it. They probably know best given their resources.

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You could put 16 's on if you reduce the tire profile to 45 as that will keep your rolling diameter the same although the ride will become harder

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You have a huge amount of variables in the questions you are asking. You can run out to 9" wide if you want. Offset and width will play a huge part in what will fit without body modifications. 

Offset is where the mounting face of the wheel (the face that contacts the brake disc) is relative to the centre of the wheel. Zero offset means this is in the centre of the wheel. Numbers, positive or negative mean it is moved off the centre line of the wheel. Most cars use negative offset these days, which is the oposite to the old Ford’s, Mini’s etc. where you would push the wheel outwards with lots of dish on the wheel. 

Standard Mazda offset is between about 45 and 35. It is not a desperately critical measurement. Race MK1’s run between 30 and 25 depending on the make of wheel. Many cars will go out to zero and there are lots of cars running round on 8" wide rims with 20 offset. 

Your first decision is to decide what you are looking for in your car, handling, looks, comfort tyre price etc. 16" tyres cost more than 15" Tyre side wall and weight of wheel will affect ride and to a less noticeable extent on the road, handling. 

All the TrakLike Gear and 6UL wheels will fit with no bodywork modifications up to 8" even with 225 45 tyres on. The 9" 6UL require a slight arch roll. 

 

 

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Have a look at the book by Norman H. Garrett. former Mazda project engineer.  Mazda Maita Performance Handbook,  published by MOTORBOOKS

A fantastic book not only covering the dos and donts of tuning our cars but a great insight into the development of the MX5 by the people who did the R&D.

Chapter 4,  wheels and Tyres [tires] is a must read for any one remotely interested in the MX5 set up.

[Page 21 quote]  The Maita wheel has three critical specifications: hubcentric collar diameter,weight and offset. IF you change any one of these three off from the original Mazda design,you can begin to degrade the Maita`s fine handling,rather than improve it.

It also goes onto state that the 45mm offset used by Mazda uses is unusual in the motor industry as most after market wheels run 35 to 37mm offset more in line with the common offset.

Mazda used 45mm after much R&D.

The book has great line drawings of all the critical measurements and angles as well as great photos too.

PS. I`m not on commission from the publishers or any book sellers 

1 Like
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Norman Garrett was a packaging engineer at Mazda (in case people think he designed the chassis); he has an impressive LinkedIn profile. A lot of what he said in that book was useful, worthwhile and correct. Some of it wasn’t. His book is very much his viewpoint, and not that of others from Mazda.

Wheel weight: How critical was it in the end when Mazda launched the Eunos Roadster M2-1001 in 1991 and M2-1002 in 1993. Both cars came fitted with Panasport Rallys; a 15x6.5" wheel weighing in at 14-15lbs. The M2-1001 was Mazda’s nippy clubman sport focussed car. So maybe wheel strength was judged to be more important than wheel weight. Panasports and other Minilite-style wheels are very strong. Lightweight wheels can be weak (cheap ones).

Hubcentric collar; bit irrelevant really. If you pick a wheel with a smaller hub opening, it won’t fit. If you buy a new wheel with a larger opening, suppliers seem to universally supply an adapter. If you fit used wheels from some other car, you are playing the safety lottery.

Offset: All Mk1s came from the factory with 45mm offset wheels, including those models with factory fitted 15" wheels (M2s, RS, R-Limited, VR-Limited, S-Special II). With the Mk2, its not quite the same story; those cars with factory fitted 14" wheels retained 45mm, but 15" alloy wheels went to 40mm. What changed?

Perhaps some of these specifications aren’t as critical as a former packaging engineer believed.

I have these wheels winging their way to me, £526 delivered:

http://www.ebay.co.uk/itm/4-Cerchi-Mazda-MX5-NA-NB-Minilite-7x15-4x100-ET35-Wheels-Felgen-Llantas-Jantes-/221878862683?hash=item33a902c35b

Correct centre bore, so no bits of plastic to mess around with/lose, 35mm offset, so nothing body-rubbing crazy, and a weight that I completely relaxed about. TUV certified to boot; not needed here, but gives some confidence in their quality.

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I read this stuff a lot about the criticality of the offset, weight etc and even the centre bore of the wheels. So I say this not bot criticise but to explain. 

Mazda may well have produced what the design engineers considered to be the best compromise of all factors at the time the original design was frozen, however things move on and standard Mazda wheels, the ones fitted as OEM have come in offsets from 45 down to 35. I have a Dakar and although I have not checked the offset looks close to 30. The width certainly is 7" wide. 

Weights vary amazingly across the designs, there is the well known BBS wheel, however I changed tyres on a Berkeley the other day and the OEM wheels were so heavy that I had to weight them. They were 9.4Kg That is nearly 21lb. 

The spigot diameter is far more of a function of the stub-shafts, bearing sizes, machining and cost of doing so than any maths in suspension design. The spigot diameter and inclusion of spigot ring or direct bore has no bearing on the wheels and unlike some internet truth, does not take the weight of the car and does not support the car or wheel while in motion. For it to bear the weight it would need to be an interference fit, and quite a heavy one and you would never remove the wheels by hand. Wheels are centred by the action of the conical or spherical seat of the nut (or bolt) or on the spigot bore in the case of washer face nuts, but in all instances the load and weight is taken by the friction generated at the mating face of the wheel and and hub. Knock Off / Spinner type hubs all have some form of taper to centre the wheel.