245/45/17 vs 235/40/17

[fredT]

Hi

Putting winter tyres on my w203 320 cdi. Rear tyres in standard size 245/40/17 seems to be relatively rare (expensive). What alternative sizes would work? 235/45/17 for example is a fair bit more common/cheaper.

Thanks,
Fred

 

[fredT]

Messed the title up, it should read 245/40/17 vs 235/45/17 doh..

or do Igo 225/45/17 all around?

 

[V12]

225/45/17 would be preferable over 235/45/17
They will be very slightly stretched onto the wheel but should be ok.

 

[neilrr]

Do you need winter tyres in London?

 

[fredT]

Do you need winter tyres in London?

Snow and ice is just as slippery in London as anywhere else in my experience.

 

[Lord-WYBMAnE220]

225/45/17 would be preferable over 235/45/17
They will be very slightly stretched onto the wheel but should be ok.

He needs to take the effect that the change of gearing will have, into account.
45 is not a dimension but a percentage of 225 - so obviously varies with change in width ... thereby altering wheel diameter and so gearing.
A little too high and you'll render top gear an overdrive (ie - too high for the engine output to overcome going uphill at motorway speeds).
There are many tyre size calculators on the interwebz.

 

[fredT]

I think the gearing is almost identical between 225/45 and 245/40. With 235/40 the gearing would be 8-9% taller..? Not sure if this matters at all?

More worried if the slightly stretched 225/45 would perform properly, as it will be slightly deformed compared to a tyre designed for the 8.5" rim? I am guessing this is negligible..?

 

[Lord-WYBMAnE220]

I think the gearing is almost identical between 225/45 and 245/40. With 235/40 the gearing would be 8-9% taller..? Not sure if this matters at all?

More worried if the slightly stretched 225/45 would perform properly, as it will be slightly deformed compared to a tyre designed for the 8.5" rim? I am guessing this is negligible..?

Just 2% can make top gear unusable.
You have been warned.

 

[V12]

He needs to take the effect that the change of gearing will have, into account.
45 is not a dimension but a percentage of 225 - so obviously varies with change in width ... thereby altering wheel diameter and so gearing.
A little too high and you'll render top gear an overdrive (ie - too high for the engine output to overcome going uphill at motorway speeds).
There are many tyre size calculators on the interwebz.

Hence why I recommended the correct size over the one that would have a much larger diameter.

Just 2% can make top gear unusable.
You have been warned.

Source?

Maybe some of the newer cars with more advanced electronic trickery are more sensitive to tyre sizes.
A 203 will be fine with the 1% larger diameter tyres, I know as I have experimented with this on my 209 clk which has the same drivetrain as a 203.
Even MB themselves fit different wheels to the same car which can be up to 1% different.

And just to wrap this up, he has a 320cdi so really doesn't need to worry about being down on power.

 

[Lord-WYBMAnE220]

Hence why I recommended the correct size over the one that would have a much larger diameter.



Source?

Maybe some of the newer cars with more advanced electronic trickery are more sensitive to tyre sizes.
A 203 will be fine with the 1% larger diameter tyres, I know as I have experimented with this on my 209 clk which has the same drivetrain as a 203.
Even MB themselves fit different wheels to the same car which can be up to 1% different.

And just to wrap this up, he has a 320cdi so really doesn't need to worry about being down on power.

Engine size is irrelevant.
If your top gear is too high, it's too high - no matter if it's a Ford Fiesta or a Lamborghini.
But it's on a spectrum - and the higher the overgear, the worse the symptoms.
Manufacturers take a lot of trouble to gear correctly.

 

[V12]

OK, take one example of standard MB fitments from the factory.

W209 CLK with standard 16" avantgarde wheels -
225/50/16 on the front - diameter 631.4mm

Upgrade to the 18" AMG wheels from the factory -
225/40/18 on the front - diameter 637.2mm

That's a 0.92% change and that's just the first example I remember from my 209 research.

If it was so critical then MB would never deviate from the one wheel size that they determine to be ideal.

If you're on the track and using your car to 100% of it's potential then I can see the necessity to have the gearing absolutely spot on.

In the real world, on real roads, the effect is little to nothing.

Engine size is not irrelevant, a big turbo diesel engine has lots of torque and if it has to pull along at 20rpm lower to maintain the same speed, it's likely to have little problem.
As you say, a spectrum.

Ideally MB would set up our gearing for the UK market, but we know that just isn't going to happen. Most of our cars don't perform optimally at 70mph.

Add to that the fact that MB recycle drivetrains across a large range of vehicles, that includes engines, gearboxes and differentials.

Basically, what i'm pointing to, is the fact that the top gear will likely already be compromised in some way and if the OP wants to save himself a few pennies by fitting some tyres that are 1% larger and are the same size as his front tyres anyway...it's no big deal.

 

[fredT]

Thanks.

SO actually the gearing difference between 245/40 and 235/45 is actually only about 2.5%. I really can't see it making a difference.

Wouldn't the 235/45 suit the rim (8.5" i think) then the 225/45? Looks like the 235 is 7mm higher then standard though, would that matter on a car running standard (sport) ride height?

Thanks

 

[V12]

225 will be fine.
Audi run 225 tyres on an 8J wheel.
Your wheels are only just over 10mm wider, the stretch will be negligible.

The polo boys run 185/195 section tyres on 8J wheels all the time, not that I recommend it!

 

[kit17]

I have run 225x45 R17 winter tyres on a 8.5 rim with no problems for the last three years.

These are the places I check for winter tyres:

tyres online @ mytyres.co.uk: tyre dealer for cheap passenger, summer, winter tyres

Tyres Online ? tyres, tyre, cheap tyres, new tyres online, car tyres UK

Tyres, Tyre Accessories and Vehicle Accessories | lovetyres.com

Cheap Car Tyres Online » FREE DELIVERY » Oponeo.co.uk

Might be worth a look if you haven't already done so.

 

[gIzzE]

Can't rate these highly enough, a stunning tyre.

I have done the lot pretty much and these are so impressive...

http://www.camskill.co.uk/m97b0s637...Eff_:_E_Wet_Grip:_C_NoiseClass:_1_Noise:_68dB


Or...

Dunlop Tyres / Winter Snow Car / Dunlop WinterSport 3D SP Dunlop Winter Sport 3D - 225/45 R17 91H (MO) MFS TL Fuel Eff.: F Wet Grip: E NoiseClass: 1 Noise: 68dB Winter - Snow - Cold Weather - Car/MPV Tyres - 17" R17" - 225/45/17, 225/45R17 <span clas

Mercedes stamped as well.
But I do think the 4D is far better.

 

[fredT]

Thanks everyone. Ordered Dunlop 4D 225/45/17 all around.

Ready for 'winter'!

 

[gIzzE]

Please post back your thoughts on them, especially the difference in noise levels, I have never had such a quiet tyre.

 

[fredT]

Actually changed the order to 3D MO fitment as camskill only had 3 of the 4D in stock and i need the tyres for this weekend.

I will report back with first impressions after the weekend.