16" vs 17" wheels

what do people think are 17" wheels a real handling upgrade?
can people comment who have tried both, and what are peoples opinions on the positives and negatives?

I run 17s - have done for the last 5 or 6 years - I did it purely for aesthetic reasons (although I picked the lightest wheels I could find, so they are slightly ligter than the OE 16")

To be honest, I'm not sure I could tell the difference if I drove a car without knowing what was on it. When I used to compete at TOTB, I used standard wheels with trackday tyres and they felt pretty much the same as my 17"

I guess the only difference that I *might* be able to claim I could feel from inside the car would be how well they cope with poor road surfaces. The lower-sidewalled 17" is a bit less compliant, giving a slightly firmer ride.

As for pros and cons - the only negative to 17" is the cost of the tyres, but even so, it's pretty minimal (maybe £10 per corner - max)

I think if you used matching tyres on 16 and 17" wheels then you would notice a slight improvement, especially if you go for lighter alloys such as Nigel's Pro-Race.

Nigel may not have felt the difference going from a 17" with road tyre to 16" with track tyre which is always going to slightly stiffer in the side wall.

I've used the same Pro-Race as Nigel and I would agree that on a bumpy road you will feel the bumps a little more than with the standard size tyre.

I have heard other people say (jbt included) they prefer 16" wheels because the ride comfort is better and have even suggested there more "forgiving" at the limit.

i know what you mean jimbo, you have to compare the same tyre in 16" and 17" to get a true conclusion, but even then bigger tyres get stiffer side walls in the same make.
maybe 16" with a stiffer sidewall is all i need? but i suppose a 17" with a stiffer sidewall will be even better but will make the ride (and my wallet) suffer.

I have been thinking of getting some yokohama AD08 in a 225/45/16 as they have good reviews and suppose to have very stiff sidewalls, this is quite an interesting thread, nigel excuse the comments about the t1r

funny enough to add to the confusion they mention the falken 452 having fairly stiff sidewalls

If I change from 17" 215/45 profile to 16" 225/45 ill my ride comfort noticeably improve? Currently on Bilstein B6 (front) and Koni adjustable (rear) complimented with Eibach springs and I find the ride [cloud9] harsh unless I am on a motorway.

Yes I think so - my Black LE on 17's is quite crashy compared to my Red LE on 16's.

What tyres do you have on them Mike?

215/40 on the 17's and 225/45 on the 16's

if you have 215/45, you won't notice much difference if you move to 16"

The correct profile for 17" is 215/40, but you'll find that some tyres have a softer sidewall and ride OK

Apologies for the thread ressurection, but this is more specific to my query than the current 'wheels' threads...

I'm looking at moving from 16" to 17 wheels in the New Year with a mind to improving both handling and ride quality. I've been doing some reading on unsprung weight and the advantages of reducing it as well as the effects of a smaller sidewall and have a few questions and points - mainly for Nigel actually!



My reading has led me to believe that reducing unsprung weight can improve the ride quality by lessening the work the suspension has to do. The more unsprung weight, the higher the load when a sudden force goes through the suspension (such as a pothole etc). That said, it figures that by reducing the unsprung weight while moving to a bigger wheel with a lower profile, you can maintain the same level of ride quality by offsetting the lower level of compliance the sideway gives. I believe this is why you didn't notice a difference Nigel - heavier wheels would have been a LOT worse!



I have a spreadsheet for working out tyres sizes and I get the following results for a number of popular sizes of wheels and tyres for the coop and I have trouble understanding why 215/40/17 is the correct tyre size. If my calculations are right, then that size will cause the speedo to under-read. 225/40/17 would not only keep the speedo the same as it was with the standard wheels; it would improve the ride quality in the extar 4mm of sidewall. And itd look better with the extra 10mm of width!



A couple of other things. Nigel, I recall a post you made about your choice of wheel when moving to 17". You said you compiled a list of lightweight wheels and picked the one you liked the look of most. Do you still have this list by any chance?

Finally, when looking for a set of wheels, I'm currently going for:
17"
ET 35-40
PCD 98
4 stud
What is the required wheel width? 205 and 225 converted to inches give somewhere between 8-9 inches but I have no idea what I should be using.

Any help, comments or suggestions to any of this would be great

I've lost track how many times I've said this. You'll need to use the effective rolling radius to calculate the tyre you need. However, as it's quite a dynamic thing that'll vary with speed and temperature, best you'll manage is go off recommendations.

Hi Ryan

You're right - unsprung weight is the absolute enemy of good handling - there are two problems....

1) The springs and shocks need to be beefier to cope with heavier wheel (and tyres) - the extra damping and springing effort required to control an Azev over a Team Dynamics will be considerable

2) Rotational inertia - basically, the amount of additional effort required to turn a wheel as it gets heavier (note that for the same wheel weight, a larger wheel is harder to accelerate, as the weight is further from the centre)

The benefits of a smaller sidewall are pretty obvious - less cornering deflection giving a better feel of what's going on as rubber meets tarmac. It does give a slightly firmer ride, but I've always used T1-R, which as a fairly soft sidewall, so its not too bad. Finally, wheel tends to look better than tyre, so any reduction of the depth of sidewall is aesthetically pleasing.

When I was looking for bigger wheels for my Coupe, I had several criteria (in approximate order of importance)

1) Looks - no point in having a superb wheel if it looks rubbish
2) Weight - I did not want to suffer any performance or handling losses
3) Price
4) Availability in direct 20VT fitment (ie no spacers or wobble bolts)
5) Strength - this became a criteria after I cracked three of my original ProRace 1s on Coventry's awful roads

I didn't compile a hard-copy list - I just looked at the wheels that met my criteria and the ProRace 1 (and later, the 1.2) were what I chose

The wheel width you'll need is either 7" or 7.5"

Speedo inaccuracy isn't an issue with the 215/40 17, as it tends to partly correct the inherent over-reading of the stock wheel and tyre combo. My speedo is less than 3% out at three figure speeds (GPS confirmed) and almost spot-on at 30 - 60mph (depending of course on the state of the tyres)

Finally - I've just got off the phone from Team Dynamics, as I wanted to check the spec of the wheels I ordered - the offset on mine is 27, which leads to a VERY close spoke-to-caliper clearance. They normally go for 25. Anything less than 27 is going to require a spacer.

They currently have a set of 4x98 anthracite ProRace 1.2 on a VERY special offer (sub £400), but they have a 35 offset, so will require a 10mm+ spacer, which in turn will mean it needs to be hub-centric, as the hub isn't much more than 10mm proud of the disc face.

They also have a set in silver, at 38 offset

They also have some MonzaR (essentially a Pro Race 1.2 with a plastic centre cap) in e25 offset, but they only have three wheels in white and three in black - they would need to have some painted for the buyer.

Let me know if you want his details.

Hope this helps

Thanks for the concise reply Nigel!



Of course! I have been looking at the distribution of weight across the spokes of wheels too. My thinking is that if the spoke is 'fatter' at the hub, it'll reduce this effect. Probably to such a degree as to be negligable but hey... I wonder if the outside of the wheel is lighter on lightweight wheels or if it's just the spokes... or both...



Why were you keen to go for the direct fitment? I've seen people running weels with both spacers and wobbly bolts with no issues but then others with bolts that broke. I'm wondering if the ones that break are the cheap ones... Our options really are VERY slim if you go for direct as far as I can see.

Strength is an interesting one - how did you judge a wheel's strength? I'd imagine you have only reputation to go on... That said, you'd expect the lightest wheels to be used on cars that woill be driven harder and so break more often...



This is interesting as, in theory, the speedo should further under-read...



If I tried a 225 do you suppose a 7.5" would be required? I guess the smaller rim would mean better rim protection so best to go for that where possible. With the speedo over-reading so much as standard, I may look into 225/40/17 set-up for both the ride and the fatter looking tyres.

Thanks for the heads up regarding available wheels. Unfortunately, my first criteria 'Looks' prohibits the puchase of wheels with more than 5 spokes. I've looked at the Pro Race 3 (which is the only lightweight 5 spoke I have found yet) and even that isn't what I'm after...

the way that rotational inertia was described to me....

Think of a lightweight 26" bicycle wheel, with a spindle still fitted. Pretty easy to spin by hand, and being light, its pretty easy to change the direction once spinning (c'mon, we've all tried it haven't we? - great way of learning about gyroscopic forces)

OK - now tape four 1kg weight to the rim of the wheel and repeat the exercise - it will take far more effort to get the wheel turning, although once its spinning, it'll carry on for much longer than the un-weighted wheel. However, when you come to try the direction-change, it will be very hard - the wheel will want to carry on in the plane that's its already working in.

Next - remove the four 1kg weights and fasten them to the hub of the wheel - basically, as close to the centre as they'll go. The wheel still weighs the same as it did in the example above, but it will be much easier to spin up to speed and much easier to change direction while spinning. The only disdavantage is that it won't spin as long as the rim-mounted version.

Direct fitment was a priority for me because:-

1) I didn't want to be mucking around with spigot rings and wobble bolts, especially with the power I'm putting through them

2) Despite no concrete evidence to support me, I have an irrational fear of wobble bolts and spacers - they just don't seem right

3) Locking wheel bolts aren't cheap in wobble-bolt form

Strength wasn't a consideration when I bought my original Pro Race 1. I was going to have them refurbed and fit them to my Moonie, but when the tyres were removed, three wheels were found to be cracked. I spoke with team Dynamics, who said that the Pro race 1.2 had a much stiffer structure in order to combat inner-rim flex. The fact that it was also the official wheel for the BTCC was reassuring. If I'd wanted maximum strength, I would have followed Begbie and gone for Compomotive MO (a possible option for you - nice 5-spoke design)

The speedo under-over reading can be affected by tyre make and pressure - its not the rolling circumference that you need to work on, its the rolling radius, which is less than half of the static diameter of the tyre once its on the wheel - this increases the number of revolutions per mile, which increases the speedo reading

I certainly don't have any problem with rim protection on the 215/40 - only touched a curb once and that was on a heavily cambered road

IIRC, the Toyo website has a good table of fitments, including a list of possible and optimal rim widths for each tyre width

Pro Race 3 won't go over the Brembos, so not an option.

I have a feeling we will be running out of 225/16/45's in a couple of years, so I'm following with interest. Some requirements...

- 17" max - I don't want to go higher
- 225's
- beautiful, discrete and high quality (like 10-spokers or so)
- no special bolts or spacers (illegal here)

and then...

- exactly the same ET as standard (40)

Reading the above + other threads, I think the ET would be a problem to find, but it has (quite?) an effect on handling, forces on the joints and bolts and suspension,...

So I'm a bit lost. Converting to 5-hole hub would probably give more options.

Kayjey,I thought the standard ET was 35? I want to order some new wheels soon and the ET size is confusing me with all the searches i have done.

Can you or anyone confirm the size please?

That's not quite right. Rolling diameter would constitute the rolling circumference. They're part of the same thing. It's the effective radius that determines the rolling circumference and therefore the distance travelled by the wheel in one revolution.

For anyone else reading and wondering about this.To demonstrate the point consider the stock 20vt Wheel, with a flat tyre, fitted to a fully laden car. If you measure the distance from the ground to the wheel's centre you'll note a figure of maybe 8.5 inches. Now measure from the wheel centre straight up to the top of the tyre. The diameter measured will be more like 10 inches, or nearly 18% more.

The tricky bit now is working out this relationship on a fully inflated tyre at varying speed, pressure, and temperature.

szkom... So Nigel is correct... as you will calculate the circumference by taking the distance from the wheel center to the ground. If you just take the circumference you don't take into account the deformation of the tyre due to weight.

Joe... there is really a lot of confusion going on, as official sources say different things:

"Fiat Coupe 16v, 95 to 01" = 35 to 42
"Fiat Coupe" = 30 to 38
"fiat coupe" = 40

I've always taken the "40" as a good figure, but then there's NO markings on any rims and there are claims that the Plus wheels would have a different ET to other rims.

So... I've gone to the garage and measured it all up. The results...

20vt Plus wheel: measured ET 39,5
20vt normal wheel: measured ET 39

Taking into account some surface imperfections and fractions of mm checking my ruler, I will personally stick with my 40mm ET.

Kayjey, he is and he isn't. He suggested you neglect the rolling circumference in favour of the rolling radius. I stated that they form part of the same measurement needed for comparison of tyre size.

I've then expanded on the concept to provide onlookers the opportunity to understand why this measurement is important, and why a static unloaded comparison of tyre diameters/radius/circumference can be more than misleading.

I've seen this type of question on tyre size asked a number of times on here. It seems very poorly documented the impact tyre deformation has on compatibility with our cars. So therefore, although it's being picky (as I'm sure Nigel knows exactly what he's explaining), it's important that future readers aren't confused by the clashing terms.

That makes perfect sense, and it adds to the total view that future readers should get!

I'll add though...

Here in Belgium (MOT), the difference between official, calculated circumference and the circumference calculated when you have non-official parts should be within 10% of the official figure. That's actually quite a lot, but it shows that if you are talking about circumference you have to start from official measurements. Overinflation or underinflation should be separated from official measurements, although they have an impact on indeed eg. circumference. That said, this also means that tyre pressure as officially stated in the manuals, take into account tyre construction at that time and tyre sizes as homologated. Meaning that if you go to a different size or different construction, you will have to adapt. Tyre manufacturing has come quite a way since 1993. A general guideline would be to inflate the tyre to max. tyre pressure as stated on the tyre minus about 5 to 10%. At least... that is a good starting point if you want to experiment (and know what yuo're doing).

szkom is right - my explanation wasn't quite right

The point we're making is that the diameter of a tyre when the wheel is off the car (or when the car is off the ground) cannot be used to calculate a circumference - the tyre is compressed by the weight of the car (and to a degree, by cornering forces) which reduces the effective radius of the tyre surface from the centre point, which in turn lowers the gearing, screws with speedo accuracy and even (up to a point) alters the castor setting

Klaas - just a point worth mentioning - the wheel offset cannot be taken as applying across all wheel designs. The stock 20vt wheel has heavily curved spokes, so it will clear the Brembos with a greater offset figure than a wheel with straight spokes. The offset on my Pro Race 1.2 is just 27 - anything more than this and there would be contact. In short, different wheel designs may require different offsets to fit a Coupe 20vt

Nigel, I'm glad you picked up on the wheels. I acquired a set of 20vt rims a while back. They're machined heavily on the back to clear the brakes*. So it's very unlikely any aftermarket wheel will fit with the same offset as standard.

However as generally a wider tyre is used on aftermarket rims the design intent of the geometry doesn't suffer too badly.

*I actually believe this machining is the weak spot that leads to the cracking of spokes we've seen.

Thanks for the info Klaas.
Would having a 17inch after market wheel alter the ET?.

For instance i am thinking of going with the same wheels as Begbie and his are a 35ET
They obviously fit over his Brembo calipers ok.
But i was wondering if the wheel size alters the ET.

There's no direct link between offset and wheel diameter.

What you can find is that due to the shape of the spokes a different ET can be required to allow the caliper to fit behind the spokes.

For example when I replaced my wheels I tried identical 17 inch and 18 inch alloys with the same offset. The 17 wouldn't fit. The 18 would.

Ok. Thankyou Szkom

Okay, the reason why I'm so analy about ET is NOT the clearance of the calipers. In fact I was going to measure spoke distance from mating surface as well at a number of key points but I forgot.

But... ET... and why I want it to be the same.

ET is actually the position of the center of the wheel (center as in the visible side <> the invisible side) with regards to the mating surface of the wheel.



If you're changing the ET, you will be changing the point where the forces act on. It's like changing a lever so it causes forces to act differently. And... causing more wear in suspension and steering. Not just that, it may garble the steering feel, cause inconsistency in steering feedback and steering weight, introduce torque steer, cause the steering to slap around on bad surfaces or when cornering hard,...

All in all, ET is one of those delicate measurements that are part of the entire geometry of suspension and steering. If you change it, you're affecting other stuff.

So that why I want an ET value that is real close to the OEM and why I will never 'just take a wheel that clears the spokes'.

There's a lot of talk about how the Coupe behaves so badly as standard. And then you see an ET value of...? I've taken a spacered-up Coupe from Belgium to the UK to get it serviced (not mine) and the steering was a complete mess. One of the things the owner wanted to get done was change the wheels back to regular Plus ones (he didn't get them with the car). The car was transformed. And we didn't change any other suspension parts.

Just saying... ET is indeed MUCH MUCH more than caliper clearance!

Fantastic thread guys. This has certainly got me thinking. I really do not want to spoil the handling of the car when moving to 17" wheels so this is all good stuff!



Good luck with that. I looked into the Compomotive MO5 after reading Nigel's suggestion and quickly discovered that the company has gone under. I REALLY wanted to get the MO1777 but they don't appear to sell them anywhere now

Sorry if I'm being thick, but if you were to buy a wheel style with an offest to match the installation in your diagram, would the wheel have more material on the back for the positive offest and less for the negative offset?

OH! i have just been looking at thier website. Nuts! The search goes on.

Yes very good thread guys.

Compomotive haven't gone under, just the company that made the wheels for Compomotive have gone under. Compomotive are still trading / finding a new company to make wheels for them.

It would indeed.

I hope this explains it more - without having different style rims in the image.



Here, there is a larger positive offset but less spoke clearance than with the one on the right (which has smaller positive offset but larger spoke clearance).

And... here is the problem a bit with the Fiat Coupe... it has quite a large positive offset (40mm) but also needs large spoke clearance. The standard rims flow to the outside of the wheel (the spokes sit slightly proud if you lie the wheel on the ground with the backside on the surface), but many wheels have just straight spokes that don't go beyond the top surface of the barrel.

Kayjey is this why most people that buy the 17" team dynamic pro race 1.2's in a et 25 so there's room

Yups. Which is almost 50% out of spec.

On track cars I understand non-standard choices sometimes as going for lower offset will give you a wider track, which makes for changes in handling that may be positive. And parts are replaced on a regular basis so the extra wear and tear doesn't matter too much. But on a car used mainly on the road...

It's one of those thing I don't get about the lack of regulation with regards to MOT's. Sure, I don't get some of the regulations here neither, but at least it makes you think about 'why', rather that ''anything goed so I'll fit tires that are -80 offset and to make sure I comply with some weird rule about wheels sticking out I'll just pull out the wheel arches a good 6cm so all's well".

Klaas - despite my low offset figure, my track could not be any narrower - ultimately, we are looking at an increase in track of maybe 15mm each side - I doubt many people would notice the difference and I'm fairly confident that there have been no ill-effects on the handling on my car

Pretty sure many items contribute to the handling of your car Nigel! Anything written above should not be taking as extremely affecting the handling or causing instant failure. But it contributes to the general feel of the car. Indeed I doubt it would be instantly noticeable, but having had the joy of comparing a 17 inch (ET unknown) with extra spacers added and how it felt reluctant to turn in (admittedly also 245mm wide I believe and not the lightest wheels either) - and then the transformation and how much lighter and agile it felt on the way back...

Anyways... I always tend to be part of the gang that thinks a manufacturer has a lot of reasons to make a car as it is, and if you want to enhance the performance and handling, it'll be a case of meticulously investigating, measuring, trying and analysing (*). Trial and error WILL get you far, and the benefit of scale and many people trying different things here is a Big Plus. But I just want to say that there ARE drawback and you can't just lower the car 5cm, beef up the dampers and springs and get a 20mm wider track without affecting anything else.

Eg. as we've seen (and I believe you yourself were part of the thread) you can beef up the suspension to the point where you get rid of any compliance of certain parts (to the benefit of handling) but then concentrating the strain of the forces going through it all on other points which may then break or suffer wear. As said - a manufacturer will compromise on ALL parts, and if you want to get the best you will have to optimise ALL parts. People who run slick tires know which strains it can put on bearings, welds,... because of the added grip.

(*) Talking 'regular' cars here, not homologation specials where they deliberately turn down the power / disconnect extra injectors / ... I'm thinking Ford Cosworth RS500 for example, RX-7,... where a couple of magic tricks can do wonders because the manufacturers already prepared them for racing reasons.

I've been thinking about wheels again and got so fed up with the whole offset, track, caliper clearance thing, that I've drawn it p for my own clarity



Sick of seeing these types of images on the internet, I've tried to add some points of reference... i.e. car wheel arch bodywork, brake caliper, brake disc and, therefore, wheel mounting face.

I've done it for two wheels and (hopefully) it represents the difference between a standard 20vT wheel, and one of Nigel's wheels.

Standard wheel
7x16"
4x98
34ET
58.1CB

Team dynamics 1.2
7x17"
4x98
25ET
58.1CB

One of the things I found difficult to grasp was why a bigger offset brough the wheel into the car. I get it now!

I have also gained an appreciation of caliper clearance and now see that an important measurement for us, is the distance between the inside of the spokes and the wheel's inner mount surface. I measured it on my spare wheel set last night and it was 47mm. The caliper must stick out miles!

Another thing that was being touched on in this thread, was the increase in track due to an decrease in ET. Is it a fair statement that (for a wheel of equal width) the track increase by the same amount that the ET decreases?

I'm thinking a spreadsheet for wheel fitment will be created shortly...

Everyone knows that 15" are the future.

Going on with rolling circumference. It's easy to tell the difference on my lorry.

Our trucks are limited to 52mph.
My truck with worn tyres would do 51mph.
I had new rear tyres fitted and can now do 53mph.

I overtook another one of our lorries and when I got back to the depot, the other driver was complaining my truck was faster than his.
When I told him it was because I had new tyres fitted the whole place errupted in laughter.

They just couldn't understand the idea of a larger rolling circumference.
I had to draw a picture in the end.

The difference is significant on a lorry tyre.
My new tread depth is almost 25mm
plus they can have grooves cut into them as they wear down.
In effect reducing the circumference massively.
Thereby reducing the maximum speed irrespective of the speed limiter.
Which is why the tacho is calibrated fairly often.

Ok at last i have found a set of compomotive rims. They are 17 inch 98x4 with an ET 37.

Can anyone confirm that they will fit over the Brembo's please?

With that ET they should Joe. But I don't think anyone can say a resounding yes to your question! Is it possible to test fit?

Well the ET of a standard wheel is 34 so you'll be cutting it to close because you need a lower ET number to bring the wheel/spokes away from the caliper.

If my thinking is right they won't clear but I could be wrong

Remember that very important factor is what style are the spokes. Take a note that standard 16's have spokes curved to the outer side of the rim to clear the caliper.

This is with ET 35

But aren't the k sport calipers smaller in height but longer in length if you know what I mean. Standard calipers bulge out towards the spokes etc

True, forgot I had the Brembo's and these wheels, so here's a different picture

The wheel model number is MO1783 ET 37 17 x 8 inch.

I think i am going to take the coupe for a trial fit. Or are 8 inch to wide?

With a gap like that he should be fine then.

Seems like only a few months back that we had this conversation...

Anyway, here's a good website that allows you to tinker with the variables of a wheel to see how it all works and what it actually means. Helps my simple brain no end!!