Wheel/Tyre Size

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Jenno007

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I am currently at the stage where I'm about to buy a second set of wheels.

These will be lightweight reasonably expensive wheels so I want to get it right the first time!

Firstly, for the track how important is getting the correct center bore size? If the wheel has a larger center bore so it fits, will this be okay?

My main question however is what size wheels should I get.

I'll be getting either 17" (minimum required to clear brakes) or 18".

I'm leaning towards 17" because I believe they will be better on the track and I don't care about the extra 'bling' of the 18s.

Also I'm insure of 8" or 8.5" width. 8" and I will run 225's, 8.5" and I will run 245s. I'm wondering if 245s will be overkill or would I see a noticeable gain in grip? I'm getting thick antiroll bars so I think I should go with the 245's to make the most of them!

Just after peoples thoughts!

The plan is to run regular high performance tyres on the standard wheels and then a road legal semi slick on the new wheels for when I want to take the car to the track.
 
17's all day long , more progressive tyre feedback and less unsprung weight.

The 8" with the narrower tyres would be lightest .
 
Gazwould said:
17's all day long more progressive feedback and less unsprung weight.

The 8" with the narrower tyres would be lighter .
Click to expand...

I'm glad you agree on the 17s

In terms of wheel and tyre width it's a bit harder to decide.

Yes the 225s are slightly lighter. There is also less chance of any rubbing on the guards, tyres will be cheaper, no poke (which is illegal in Australia).

However, the 245's should give more grip and make the car handle better even though they weigh more (I am guessing here but that seems like a logical assumption). 245s will also look better, last longer (to offset part of the greater cost).

The ultimate issue here is grip/handling. This is the reason I'm buying new wheels and should be the deciding factor when I eventually do get the wheels. Therefore, I'm leaning towards 245s
 
Personal experience with wider road based tyres (Eagle F1 Assy 2's for example) is that they tend to have wider water channels than more actual rubber... probably due to the need to get the water out more easily in the wet etc...

Also be mindful of the aspect ratio... wider tyres on a 40/45 aspect ratio means the sidewalls get taller and more wobbly...

17's don't have a fantastic choice of wider rubber, Bill has been struggling to get decent rubber for the Ibiza and the 255/40/217 Porsche fitment tyres he ran this bank holiday were too wide and too wobbly

<tuffty/>
 
<tuffty/> said:
Personal experience with wider road based tyres (Eagle F1 Assy 2's for example) is that they tend to have wider water channels than more actual rubber... probably due to the need to get the water out more easily in the wet etc...
<tuffty/>
Click to expand...

Interesting point, however I will be getting semi slicks for these new wheels so I can't imagine they will have much in the way of water channels. I will put standard wheels back on should I ever need to drive this car in the rain (I really doubt this will ever occur).

<tuffty/> said:
Also be mindful of the aspect ratio... wider tyres on a 40/45 aspect ratio means the sidewalls get taller and more wobbly...

17's don't have a fantastic choice of wider rubber, Bill has been struggling to get decent rubber for the Ibiza and the 255/40/217 Porsche fitment tyres he ran this bank holiday were too wide and too wobbly

<tuffty/>
Click to expand...

Hmm interesting point... I was thinking of 245/45r17 to make the gears very marginally taller. Maybe I will have to go 18s after all?
 
In my opinion the 17" wheel looks too small on the s3. 18's fill the arches and compliment the arches much better in my opinion and i have had both sizes.
 
235/45/17's on 8J here for road use:





They sit nice and square, but are probably a fraction on the tall side for serious track use. I got them purely for road use.


I prefer 17's for track use. I think they ride better and handle better, but 18's will ultimately allow bigger brakes.
 
When I get home I'll check the rolling radius of each option and try find one that isn't a clown tyre, is 235 or 245 wide and has a slightly larger/same rolling radius.
 
the profile measurement is a percentage of the width, so a 245/45 will be a taller tyre than a 235/45, which is in turn taller than a 225/45.

Check it out on a RR calc and it'll all make sense :)
 
Sorry if this is considered a thread hijack, but I have been getting an error code (16885) that says 'vehicle speed sensor, implausible signal'. I recently calculated the RR of my 225/40R18 wheels, compared to the standard sizes, and there is a 0.4% difference. Would that be enough to cause the code? Can this be fixed somehow?
 
Prawn said:
the profile measurement is a percentage of the width, so a 245/45 will be a taller tyre than a 235/45, which is in turn taller than a 225/45.

Check it out on a RR calc and it'll all make sense :)
Click to expand...

Hey mate thanks for clarifying that.

I do understand that it's just finding the perfect combination of rolling radius and side wall size.

Would you say a 245/40 in either 17 or 18 is suitable for the track? I would have thought on an 18 it would be okay.
 
Erikn89nl said:
Sorry if this is considered a thread hijack, but I have been getting an error code (16885) that says 'vehicle speed sensor, implausible signal'. I recently calculated the RR of my 225/40R18 wheels, compared to the standard sizes, and there is a 0.4% difference. Would that be enough to cause the code? Can this be fixed somehow?
Click to expand...

Not a problem posting it here mate. The issue won't be down to your wheel size I'm going to say it's most likely a dodgy sensor. I've never had this issue but I'm sure if you search you will find a post explaining how to identify what sensor has gone. Replacing it should be easy enough.
 
Jenno007 said:
Hey mate thanks for clarifying that.

I do understand that it's just finding the perfect combination of rolling radius and side wall size.

Would you say a 245/40 in either 17 or 18 is suitable for the track? I would have thought on an 18 it would be okay.
Click to expand...
That's far too big a sidewall on an 18
 
I just found out that a 245/40r17 is smaller than a 245/40r18.

I always thought that the last number just indicated how big the hole was in the tyre, didn't realise it also increased/decreased the overall tyre size!

I will be researching a couple of options and post here shortly!


edit:

Just checked 245/35r18 out. Slightly smaller rolling radius which could only be avoided by going 255 (don't want to do this as I'm worried it will rub on the arch), or go to a 40 profile which seems like a bad idea.

Do people think the 245/35r18 is a good choice? I know that some would say that 17" wheels are better but this does allow me to upgrade my brakes in future should I want to.
 
superkarl said:
That's far too big a sidewall on an 18
Click to expand...

Just searching google for tyre sizes people use at a track day and it's actually quite a common size. I'm not saying I disagree with you but it seems like quite a few people do use this size tyre, and a lot of manufacturers are making semi slicks in this size (I can't find as many for 245/35r18).

Seems weird as everyone here has been saying the same thing you are...
 
Last edited:
Jenno007 said:
Just searching google for tyre sizes people use at a track day and it's actually quite a common size. I'm not saying I disagree with you but it seems like quite a few people do use this size tyre, and a lot of manufacturers are making semi slicks in this size (I can't find as many for 245/40r18).

Seems weird as everyone here has been saying the same thing you are...
Click to expand...
Which size, I'm saying 245/40R18 is too big, you've just said you can't find many in that size.
 
superkarl said:
Which size, I'm saying 245/40R18 is too big, you've just said you can't find many in that size.
Click to expand...

Sorry edited my post it didn't make sense.

I can find a lot of posts where people use 245/40r18, and a lot of semi slicks for sale that size

I can't find many posts where people use 245/35r18, and not as many semi slicks are for sale in that size
 
Just re-read your original post!!... centre bore has to be correct... this is the main support for the wheel on the hub and HAS to fit correctly and centrally... the bolts are there to secure the wheel clamping it to the hub and not there to support the weight of the car

<tuffty/>
 
<tuffty/> said:
Just re-read your original post!!... centre bore has to be correct... this is the main support for the wheel on the hub and HAS to fit correctly and centrally... the bolts are there to secure the wheel clamping it to the hub and not there to support the weight of the car

<tuffty/>
Click to expand...

Thanks for confirming that. I had read that before but wasn't sure how important it is. When you go to buy second hand wheels there is no mention of center bore size!! What a joke when you could argue it's the most important thing.

The wheels I want apparently have a much larger centre bore size, are hub centric rings okay? Like these:

http://www.ebay.com.au/itm/Hub-Cent...37?pt=LH_DefaultDomain_15&hash=item2ec7cc88b1


As it currently stands I have some hubcentric spacers from Bill. So with wheels it will go like this

Wheel Hub > Hub centric spacer > hub centric adaptor > wheel.

Seems a little dodgy to me unless you think that would be okay? Maybe lose the spacers?
 
Don't double up on spacers... ideally you would use the minimum sized spacer to do the job as this adds more load to the bearings (longer lever)...

Ideally buy the wheels closest to the offset you require... account for caliper clearance and jobs a good un...

I personally wouldn't use hub adaptors period... not a massive fan unless they are the steel insert type but I'd be looking at wheels with the right PCD and offset

Team Dynamics do a pretty big range

<tuffty/>
 
<tuffty/> said:
Don't double up on spacers... ideally you would use the minimum sized spacer to do the job as this adds more load to the bearings (longer lever)...

Ideally buy the wheels closest to the offset you require... account for caliper clearance and jobs a good un...

I personally wouldn't use hub adaptors period... not a massive fan unless they are the metal insert type but I'd be looking at wheels with the right PCD and offset

Team Dynamics do a pretty big range

<tuffty/>
Click to expand...

Thanks mate. I had the spacers just to fill the arch a little more, but with wider wheels I probably wont need them.

I will get wheels the correct offset to clear my brakes and the correct PCD. The only thing is they come with a much larger centre bore, do you think the metal inset hub adaptors like the ones I linked would be okay? I will be thrashing this car on a track so I don't want to lose a wheel!
 
Jenno007 said:
Thanks mate. I had the spacers just to fill the arch a little more, but with wider wheels I probably wont need them.

I will get wheels the correct offset to clear my brakes and the correct PCD. The only thing is they come with a much larger centre bore, do you think the metal inset hub adaptors like the ones I linked would be okay? I will be thrashing this car on a track so I don't want to lose a wheel!
Click to expand...

Prawn said:
Spigot rings are fine yes.
Click to expand...

What he said :)

<tuffty/>
 
Prawn said:
Spigot rings are fine yes.
Click to expand...

didn't see you sneak a comment in thanks for that.

Thanks for all the help guys! I will most likely be going with 245/35r18s at this stage, still have two months to think it over though :p
 
Jenno007 said:
Not a problem posting it here mate. The issue won't be down to your wheel size I'm going to say it's most likely a dodgy sensor. I've never had this issue but I'm sure if you search you will find a post explaining how to identify what sensor has gone. Replacing it should be easy enough.
Click to expand...
What's baffling me is how the speed displayed on the dash is consistent with GPS speed. I'd imagine a dodgy sensor would give dodgy readings on the dash, too. Oh well, the search continues...
 
Erikn89nl said:
What's baffling me is how the speed displayed on the dash is consistent with GPS speed. I'd imagine a dodgy sensor would give dodgy readings on the dash, too. Oh well, the search continues...
Click to expand...

Dash speed is usually an overestimate anyway, it might just be balancing that out.
 
Stock speedo over reads Erik, add larger wheels and it actually gets more accurate! The differences in rolling radius will make no real difference what so ever, and certainly not the cause of your code.
 
Implausible signal is a fault variation thrown when a control module doesn't trust the signal its receiving... this is normally due to a faulty sensor...

<tuffty/>
 
<tuffty/> said:
Just re-read your original post!!... centre bore has to be correct... this is the main support for the wheel on the hub and HAS to fit correctly and centrally... the bolts are there to secure the wheel clamping it to the hub and not there to support the weight of the car

<tuffty/>
Click to expand...

Very unusual for me to disagree with you but this isn't quite right. The cars weight isn't supported by the spigot at all, it's supported by the friction between the wheels mounting face and the mounting face of your disk. In fact the friction created by one wheel bolt being correctly torqued up is more than enough to support the entire cars weight without transferring any load into the spigot.

If the centre-bore really was load bearing then it would have to be an interference fit to avoid fretting enlarging it very quickly as the wheel would shift in use. On most cars it's not an interference fit with no adverse effect.

This is why a lot of spigot rings sold by reputable manufacturers are plastic, because their primary purpose is simply to make sure the wheel is properly centred when the wheel bolts are torqued up. A lot of older cars don't actually have a spigot and rely on the wheel studs to centre the wheel, but bolts aren't as good at centreing the wheel as studs plus there is some added safety from having the spigot there should the wheel come loose.

In other words, yes, it's worth making sure the centre-bore is correct, but a spigot ring will do the job fine. It's not actually dangerous to run with a miss-matched centre-bore, there's just some chance of wobbly wheels if you bolt them up off-centre. (I know of many track and rally cars that run without matching spigots with no issues.)

I can't help with tyre sizes I'm afraid, my cars wheels and tyres are tiny!
 
audi upgrades
Robin thanks for the post mate. Very interesting what you say.

For the $20 they cost there is no downside to go for the spigots because if nothing else they will centre the wheel.

The reason why I asked if bore sizes are important because I've seen the argument you've just put forward before.

So I will buy them to make sure the bore is correct, if all they do is centre the wheel I'll still be happy because I won't have to worry about something being 'not quite right'
 
2 sets of my track wheels run with plastic spigot rings. my 2 other sets of wheels have the correct 57.1mm centre bore. Neither seem any different in use.

I'm staying out of the spigot being load bearing or not argument :laugh: but either way, spigot rings are most definitely not an issue.
 
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I'm glad your plastic ones hold up on the track, I shouldn't have any problems with aluminum ones then!
 
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