17" Wheel Size

[Antti Salonen]

I'm getting my brand new C4 Coupé in July, a silver 1.6-litre with the glass roof. The first thing I intend to do with it is to replace the stock 16" wheels with some nice-looking 17" alloy wheels. The stock wheels appear to be size 6.5x16 ET26.

 

So the question is - If I get wheels of size 7x17 or 7.5x17, what's the acceptable range for rim inset (the ET number)? One wheel which I'm considering is 7x17 ET25, which I guess should be a near-perfect fit. One, however, is 7.5x17 ET18, so the centerline of the rim would be 8 mm outer than with the stock wheels. Would this cause problems with bodywork clearance or handling?

[wozza]

Putting wheels further out usually gives you better handling. Why some of the cars with suspension upgrades as standard move the wheels further out.

 

And clearance I dont see an issue with the wheels sit quite far in the arch to be fair they could be pulled out a bit.

[VTSowner]

Putting wheels further out usually gives you better handling. Why some of the cars with suspension upgrades as standard move the wheels further out.

 

And clearance I dont see an issue with the wheels sit quite far in the arch to be fair they could be pulled out a bit.

 

sometimes i hear about cars which handle better with 18s or 19s etc and sometimes certain sizes reduces handling. why is this and whats best for the c4

[Z3M Roadster]

I would have thought that the smaller the wheel the better the handling. That certainly goes for the VX220.

 

Obviously the larger the wheel you go for the lower the profile tyre and therefore a harsher ride and a greater chance of tramlining.

 

You may find that putting larger wheels will shorten the life of your wheel bearings

[wozza]

Depends on the car. Going above an 18" is rarely ever needed. And the only reason for going to a bigger rim is usually because wider tyres are available which might be needed on some of the very high end sports cars to get traction.

 

Thats about it. On cars like ours 16" - 17" is about perfect for handling. But they would look prettier with 18" as the arches are huge it would fill it out a bit more.

[billynibbles]

Thinking about the wider tyres for a moment - do I recall you can get the power steering reprogrammed to 'work harder' so you don't have to struggle with all the extra rubber on the road?

[Z3M Roadster]

I doubt the steering will get that much heavier with bigger wheels/tyres, not enough to need to modify the power steering anyhow unless you are Mr Muscle

[Antti Salonen]

Thanks for the input, everyone.

 

I don't intend to go any wider with the tyres. I think I'm getting 205/50R17, which should have almost exactly the same width and diameter as the stock 205/55R16 tyres. The law here (Finland) requires different tyres for winter use, so I need to get a second set of wheels anyway, and I'm looking at 17" for purely aesthetic reasons.

[wozza]

205/50/R17 is what we have as standard on the VTR+ and VTS 17" rim. So will be fine. Im sure KFK said there is a thing on the computer to tell the car your have 17" rims fitted though.

[Z3M Roadster]

205/50/R17 is what we have as standard on the VTR+ and VTS 17" rim. So will be fine. Im sure KFK said there is a thing on the computer to tell the car your have 17" rims fitted though.

 

Do you need to? Surely if you increase the diameter of the wheel you decrease the profile of the tyre and as such you have the same rolling radius?

[wozza]

I wouldnt bother i just remember when KFK listed it in all the options you could enable etc it stuck out. Its probably just to correct that slight variation of the speedo / mileage its only a tiny percentage but I suppose after a fair few thousands of miles could alter the reading somewhat. But to the majority of us...no it doesnt matter.

 

its reading 0.55mph difference at 70mph thats all.

[Antti Salonen]

its reading 0.55mph difference at 70mph thats all.

Yeah, I guess we're consulting the same calculator (link), because that's the number I've seen too. Considering that on most cars the speedometer shows higher than the real speed, I think increasing the tyre diameter a bit should actually get you closer to the truth.

[hertsnminds]

Considering that on most cars the speedometer shows higher than the real speed,

 

The C4 speedo is much more acurate than most. Always matches the display on my GPS unless I am doing under 10MPH, then it seems to be out by 1 or 2 MPH.

 

 

Ian

Black 55 VTR+

[Z3M Roadster]

I noticed how accurate the speedo was, matched the GPS perfectly.

 

I have a 2.0tdci Mondeo at the moment while I await my Jetta and the speedo is about 6-7mph slower than the speedo indicates at 75mph

[Goon]

Larger rims (18s and 19s+) have also got a tendency to buckle and distort more easily. Makes sense as the circumference of the rim is larger resulting in a flatter curve.

 

The Offset is the more important issue as it is critical to the handling set up and as has previously been said, can result in increased wear to the bearings. I remember a few years ago all Vauxhalls had to have a 49mm offset and most after market alloys had 36mm. Some people said they didn't notice a difference but I went in few and the handling was absolutely dire= tramling, tramping, it was a nightmare. Bear in mind your insurance company will also have something to say on the matter...

[wozza]

Most big rims Tramline anyway though. It cant really be helped. And vauxhalls have never been known for there handling prowess. It took them till they had lotus building cars for them to get any decent handling.

 

same to this day I mean look at the corsa / Atra VXR / Vectra...Not exactly cars that give you confidence in the cornering department.