Tyres, opinions please?

QuattroCalum

QuattroCalum

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Not what kind of tyre but what size of tyre? I'm currently running on 225/40/18 and find it under geared when travelling a fair distance. I'm thinking about going up to 245/45/18 to make it cruise a little better. The car in question is a B6 1.8t quattro 163 hp, I wonder if the 245/45/18 might be a step too far and if 245/40/18 might be a better compromise? Currently running on Eibach springs so it's 30mm lower if it needs to be taken into consideration, thanks in advance for any opinions.
Tire Size 225/40R18
mm inches
Tire
Width 225 8.86
Aspect
Ratio 40 -
Rim
Diameter 457 18.00
Sidewall
Height 90 3.54
Tire
Diameter 637 25.08
Circum-
ference 2000 78.74
Revolutions 500/km 806/mi

Tire Size 245/40R18
mm inches
Tire
Width 245 9.65
Aspect
Ratio 40 -
Rim
Diameter 457 18.00
Sidewall
Height 98 3.86
Tire
Diameter 653 25.71
Circum-
ference 2050 80.71
Revolutions 488/km 787/m

Tire Size 245/45R18
mm inches
Tire
Width 245 9.65
Aspect
Ratio 45 -
Rim
Diameter 457 18.00
Sidewall
Height 110 4.33
Tire
Diameter 678 26.69
Circum-
ference 2129 83.82
Revolutions 470/km 758/mi
 
I see the 245 45 alot on Vauxhall Insignia etc and they are bulbous , they'll lift up the chassis too much , a step too far .

225 40 is definitely on the slim side anyway both in width and profile .

This year on another car did 245 40 18 in place of 225 45 and it's just right .
 
Gazwould said:
I see the 245 45 alot on Vauxhall Insignia etc and they are bulbous , they'll lift up the chassis too much , a step too far .

225 40 is definitely on the slim side anyway both in width and profile .

This year on another car did 245 40 18 in place of 225 45 and it's just right .
Click to expand...

It did have 245/40 on it when I got it, I wish I’d stuck with that size.
That’s what I’ll fit next time, should improve the stance, the rear has settled nicely with the Eibach springs but as always B6 front end is just a little high maybe a half inch. B5 spring perches in my future I think.
Thanks Gaz.


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Front is higher 'cause it's a taller arch to allow for a turned wheel under compression to keep clear .
 
Gazwould said:
Front is higher 'cause it's a taller arch to allow for a turned wheel under compression to keep clear .
Click to expand...

Yeah but doesn’t help the look d’you think B5 perches would cause problems?


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Also, where can I find what rpm's it'll be pulling with the different sizes? I had considered a diesel gearbox and diff but that's a lot of work/money and a bit extreme. Crasher on VwAudi forum reckons the 1.8t would cope fine with the diesels gear ratios.
 
It's not what the Eibach engineers had in mind and they seriously fine tune .

Tyres aren't a precise science as tyre widths and profiles vary from make to make despite being the same size .
 
Yeah, probably look better with the 245/40's in there.
 
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225/45/18 for looks
245/40/18 for performance
245/45/18 for comfort

Edit: Well 225/40/18 for looks really but that wasn't an option, best to calculate the speedo difference either way.
 
Last edited:
225 / 40 for bone shaker elastic bands

245 / 40 the perfect compromise

245 / 45 big foot tyres
 
audi upgrades
The 225/40 really aren’t bad at all comfort wise.


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235/40 x 18 would seem the sensible compromise?
 
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quattrojames said:
235/40 x 18 would seem the sensible compromise?
Click to expand...

Well yeah but I’m going with 245/40/18 next time because the wheels are 9J and need all the rubber they can get. As it is I can’t sit the wheel down flat without the rim hitting the ground and the rim protection just doesn’t.


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Theres only about 2.5% difference in rolling diameter between those 2 tyres so very little difference really in cruising comfort.
If you currently cruise at 3000 RPM to maintain the same speed with the larger tyres you will be doing 2925 RPM, Just 75 rpm less.
But on 9J rims I would say 225/40 tyres are stretched. The 245/45 is a step too far all it serves to do is raise the car further off the ground , offers no extra width on the rim and is probably a more expensive tyre as it's not as common.
225/40/18 diameter 637mm
245/40/18 diameter 653mm 2.5% bigger 75 rpm less at 3K cruising car sits 8mm higher off the ground
245/45/18 diameter 678mm 6.4% bigger 180 rpm less at 3k cruising car sits 20mm higher off the ground
I take a reference tyre available in all sizes and just do a quick check on it's cost. You usually get a good idea of the relative costs. Michelin pilot sport 4
225/40/18 tyreleader £101.49
245/40/18 £130
245/45/18 £145
I would definitely go 245/40/18
I think rim protection with a 245/40/18 on a 9J rim is a bit of a moot point. It just won't work. On my 8J rims with 245/40/18 GY eagle assy 3 there is little in the way of protection.
 
desertstorm said:
Theres only about 2.5% difference in rolling diameter between those 2 tyres so very little difference really in cruising comfort.
If you currently cruise at 3000 RPM to maintain the same speed with the larger tyres you will be doing 2925 RPM, Just 75 rpm less.
But on 9J rims I would say 225/40 tyres are stretched. The 245/45 is a step too far all it serves to do is raise the car further off the ground , offers no extra width on the rim and is probably a more expensive tyre as it's not as common.
225/40/18 diameter 637mm
245/40/18 diameter 653mm 2.5% bigger 75 rpm less at 3K cruising car sits 8mm higher off the ground
245/45/18 diameter 678mm 6.4% bigger 180 rpm less at 3k cruising car sits 20mm higher off the ground
I take a reference tyre available in all sizes and just do a quick check on it's cost. You usually get a good idea of the relative costs. Michelin pilot sport 4
225/40/18 tyreleader £101.49
245/40/18 £130
245/45/18 £145
I would definitely go 245/40/18
I think rim protection with a 245/40/18 on a 9J rim is a bit of a moot point. It just won't work. On my 8J rims with 245/40/18 GY eagle assy 3 there is little in the way of protection.
Click to expand...

Thanks Karl for the comprehensive reply, I really thought there would be more difference than that.
I was a bit miffed at the amount of fuel used on my last foray up to the Isle of Skye but to be fair it was a lot colder than usual which has to be taken into consideration.
I guess I should just buy a diesel but I dislike them and don’t do mega mileage anyway.
Could always fit a diesel fifth gear but I’m not sure all that it entails.


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TBH the cost against the savings don't stack up if you don't do many miles. The best way of getting more mpg is leave an hour earlier and drive slower :) .
 
desertstorm said:
TBH the cost against the savings don't stack up if you don't do many miles. The best way of getting more mpg is leave an hour earlier and drive slower :) .
Click to expand...

To be honest 37mpg in a quattro over 500 miles isn’t terrible by any means, half the problem was I never filled it right up before I left.
Up north super unleaded just doesn’t exist and it doesn’t run as well on it.
What do you use in the TT, I find the only difference between momentum and Shell is the price.


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I have only ever filled it up with Tesco Momentum. When I went for a test drive in it the guy selling it put some normal Asda fuel in it. When I first filled it myself I used Tesco Momentum and noticed it ran better pretty much straight away so it's all I have ever out in it.
 
I can’t believe how many petrol threads I’ve read and some saying they can’t notice the difference between unleaded and super unleaded.


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Regarding tire size what about 235/40-18 which is considered the "stock" size on my 2006 A4 Cabriolet...so as to not make too radical a jump at once. Does going up one tire size/aspect ratio really make that much of a difference?...Probably not nearly as much as your driving habits and proper inflation pressures for the desired load/ride with regards to fuel mileage. JMHO
 
I don't know why you chose 9" either , adds to unsprung weight , lessens wheel rim protection etc.

Still could be worse , some pony head comes along and wants 225 on 10.5" .
 
You misunderstand Gaz, I have 8J rims but I thought they were 9J. Anyway, I hit a pothole on Tuesday morning and the front drivers side tyre is toast, I've bought a part worn tyre just to do for now until I need to replace the rest, I'd rather replace them all as a set.
 
As you've pointed out - this is the bit that people always forget: the tyre profile (e.g. the "40" in 245/40R18) is a ratio of the width - as as per the first post: the diameter will go down if you reduce the width, even if you keep the side profile the same.

Depending on each car, the speedo, odometer, etc is usually set so that they allow for the tyre diameter to be around 8-10% larger than the factor size - part of the reason why your car speedometer reads about 10% higher than the GPS on your Lynx/RoadAngel/phone. I always tell people to do their calculations and try to keep it to around 5% of whatever the stock ratios should have been.

If you keep the overall diameter of the tyres similar (approx 5%) and the tyres still fit on the alloys, you should be fine. As you change the ride height, wheel widths, etc you reduce that wriggle room... so you will need to judge this for yourself, but the 5% is probably still a safe bet.

I used this tool to work out my tyre sizes on my B6: https://tiresize.com/calculator/

The A4 V6 TDI quattro Sport that I had was on stock tyres originally (205/55R16), using the "comparison" tab on that site, when I put new winter tyres on the 16" wheels, I went for 225/55R16's - which is a 3.2% increase in diameter over stock and a bit fatter.

AND I got some 18" S4 Avus alloys and a set of new summer tyres - for those I went for the same diameter as the new winter tyres : 245/40R18's (also 3.2% larger than stock).... if I'd kept the car, I think I would have replaced the summer tyres with 225/45R18's as those are only a further 1.2% higher and I still had plenty of clearance, even on Sports suspension, S-Line body kit and 25mm spacers.... and it would have given me longer gearing and narrower tyres than the 245's - plus the tyre width was still wider than the original 205's....
 
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QuattroCalum said:
You misunderstand Gaz, I have 8J rims but I thought they were 9J. Anyway, I hit a pothole on Tuesday morning and the front drivers side tyre is toast, I've bought a part worn tyre just to do for now until I need to replace the rest, I'd rather replace them all as a set.
Click to expand...

Ah cool , I confused 'thought' with 'bought' and the late 8" correction..

****** pot holes , I didn't blow the tyre
( probably because of a decent profile ) but buckled a 16" once .

Do you think you would of not suffered if it was a 245 40 , 245 45 , is the alloy OK and are you claiming ?

The advice still stands at 245 40 as done that in June last year on a 8J .

You need all the meat you can get on a tyre without going too far ( 245 45 ).
 
Gazwould said:
Ah cool , I confused 'thought' with 'bought' and the late 8" correction..

****** pot holes , I didn't blow the tyre
( probably because of a decent profile ) but buckled a 16" once .

Do you think you would of not suffered if it was a 245 40 , 245 45 , is the alloy OK and are you claiming ?

The advice still stands at 245 40 as done that in June last year on a 8J .

You need all the meat you can get on a tyre without going too far ( 245 45 ).
Click to expand...

Ah the wheel is fine, sidewall was holed on the tyre.
I knew fine that the pothole was there and usually keep tight to the left. It with all the snow at the edge of the road I was slightly too far right, just enough to hit it bang on.
I don’t think it would have mattered what the tyre profile was, a 16 inch wheel with 205/55/16 would probably have survived it.
Not going to bother claiming as it will only wind me up, they’ll just give me the runaround till I get pee’d off, which to be honest, wouldn’t be long.


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8e65c26fb7424e413a9b20b6473c40e9.jpg


I appreciate this is not a good photo but this is the offending pothole. It’s around 8 inches long and four inches deep, the tyre never had a chance.

I must have covered two miles when it happened, the tyres are XL and allowed me to continue a further two miles to the nearest village with no damage to the alloy wheel. Tyre was Nexen N8000.


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