Different width wheels
- Thread starter tomo
- Start date
OP
OP
tomo
Petrolheads
Yesas the rolling radius is the same
Thats a great news
It is so hard to find a really nice set of wheels with same width all around.
OP
OP
tomo
Petrolheads
I have heard the same but just looking for info on the internet now and people say if the rolling radius is same with around 3-5% tolerance it is fine. A half of inch is not much so it should be fine I suppose.
they also say change tyres in pairs iirc
Thought the same.. the guys local to me in the tire shop also said this before. One has an M3, the other has a Boxy civic. They well into their motors too and gave some wheel related explanation to me that I can't remember lol
Keadeen
Well-known member
Joe is 100% correct.
As long as you have the same size tires on all 4 wheels... or tires that are roughly within 1% the same rolling circumference, then there will be no adverse effect on diffs or ABS etc.
The width of the alloy has no bearing on any differences in rotational circumference, only the "size" of the wheel changes that (17" vs 18")... and it is even possible to run different sized alloys as long as you match them with tyre sizes that are different such that the end rotational circumference is the same between all wheels (or within 1%). There are plenty of calculators online that you can google that will show the percentage difference between alloy/wheel size combos to give you a better idea.
It is only if the rotational circumference is different that you run into issues with diffs and ABS as it would mean the revs/min would be different between wheels and that is what causes the issues. If different the diff breaks as it is designed to see same revs either side of diff, and affects ABS as it will think wheels are losing traction as not rotating same speed.
What IS a concern on a WRX (or all "narrow" track cars) is the extra loading the wider wheels put on wheel bearings.
They are not designed to take that additional loading... so whether you fit wider wheels, or track oriented "sticky" rubber... those bearings will fail much quicker (and to some extend this applies to oem bushings not designed for increased side loading). The "wide" track cars got beefier bearings to better deal with wider/higher grip tyres as the older smaller bearings were recognised as a weak point.
Also... the size tyre you mentioned there is fairly small for a 9 or 9.5" width wheel and more suited to an 8 or 8.5" wheel.
"Stretching" tyres like that will adversely affect handling and safety... not what you want on a daily driver... and also something that can land you into trouble with law enforcement and your insurance.
Another thing to consider is the different off sets that are needed to keep wheels within the bodywork and clear of body and other parts.
As long as you have the same size tires on all 4 wheels... or tires that are roughly within 1% the same rolling circumference, then there will be no adverse effect on diffs or ABS etc.
The width of the alloy has no bearing on any differences in rotational circumference, only the "size" of the wheel changes that (17" vs 18")... and it is even possible to run different sized alloys as long as you match them with tyre sizes that are different such that the end rotational circumference is the same between all wheels (or within 1%). There are plenty of calculators online that you can google that will show the percentage difference between alloy/wheel size combos to give you a better idea.
It is only if the rotational circumference is different that you run into issues with diffs and ABS as it would mean the revs/min would be different between wheels and that is what causes the issues. If different the diff breaks as it is designed to see same revs either side of diff, and affects ABS as it will think wheels are losing traction as not rotating same speed.
What IS a concern on a WRX (or all "narrow" track cars) is the extra loading the wider wheels put on wheel bearings.
They are not designed to take that additional loading... so whether you fit wider wheels, or track oriented "sticky" rubber... those bearings will fail much quicker (and to some extend this applies to oem bushings not designed for increased side loading). The "wide" track cars got beefier bearings to better deal with wider/higher grip tyres as the older smaller bearings were recognised as a weak point.
Also... the size tyre you mentioned there is fairly small for a 9 or 9.5" width wheel and more suited to an 8 or 8.5" wheel.
"Stretching" tyres like that will adversely affect handling and safety... not what you want on a daily driver... and also something that can land you into trouble with law enforcement and your insurance.
Another thing to consider is the different off sets that are needed to keep wheels within the bodywork and clear of body and other parts.
I know the rotational size has to be the same etc but, with a wider wheel, it has to be heavier too, even if only .5 in the difference the weight difference would be minimal but still present, would that not have any side effects?
Like, I've no idea either way, I'm only curious lol
Extra load on the rear or something. The guys in the tire shop were adament that they had to be the exact same...
I suppose if it's in the 5% tho as said above...
Cool info lads, handy to know ????
There is loads of knowledge floating around this forum
Like, I've no idea either way, I'm only curious lol
Extra load on the rear or something. The guys in the tire shop were adament that they had to be the exact same...
I suppose if it's in the 5% tho as said above...
Cool info lads, handy to know ????
There is loads of knowledge floating around this forum
dont tow a awd car with front wheels in the air
mr nct cant 2wd test a awd car
and keep alloys same size front and rear
these are some rules iv learned from my imaginery subaru handbook .
again charles has blown us out of the water with his detailed response which is probably far more accurate than my handbook , but i still wouldnt do it on a awd car . i hear what joe is saying about rotational being the same but width wise , in a turning circle surley cant be the same . so thats my reasoning .
This is my logic: In pure geometry terms if you fit the same size tire to a different width wheels the tire on 9.5" wheel will be more stretched than on 9" so if you choose the right size tire on 9" wheel the shape fitted will be close to rectangular but if you fit same size tire to wider wheel where the side walls are stretched the shape will be more tr@pezoid and the distance between the wheel barrel and the top wall of the tire should be smaller. Now how significant that difference would be and would that affect the diff l don't know.
The only difference l would consider is in offset which is often used with wheels that dont clear BBK.
The only difference l would consider is in offset which is often used with wheels that dont clear BBK.
Keadeen
Well-known member
@DonTommy: you have a valid point there... and not one that came immediately to mind when I answered yesterday. There could well be a significant difference in circumference (over 1%). Of course there is no calculator on line to tell you the percentage difference in circumference as it would differ between different tyre makes/modes. The reason for this is because tyre shape deformation is hugely dependent on tyre construction and inflation pressure (side-wall stiffness/support, running surface shape, compound).
Personally I would never put the size tyres mentioned on rims that wide. 9" is the max width for the tyre size indicated by the OP and already not recommended... and 9.5" is just too wide for that tyre size to be safe. It will adversely affect handling and if anything happens you will not be insured, it will cause issues at NCT time, plus it only takes one Gard who half knows his/her stuff to stop you.
CLICK HERE for a link that has a handy table in it giving min-max tyre width to wheel width index (half way on page).
In general though... if say changing from a 17" rim which is 7-8" wide running 225/45/17 tyres, to an 18" rim which is 8.5" wide running 18/40/225 - and you put the same on all 4 corners is fine as all 4 will rotate at similar speeds.
Here's a link to another calculator to see the difference in circumference between tyre sizes to help choose correct size when saying going up a rim size.
It will give you an idea of rotational circumference changes with different wheel/tyre combos; however, it doesn't allow for circumference distortion due to different wheel width front/back as per DonTommy's point (which will easily be 1cm). Now on new tyres that difference you'd get away with that as <1%, but as the tyres wear you could end up with 1.5-2% difference... and that could be too much for diffs and abs.
Personally I would never put the size tyres mentioned on rims that wide. 9" is the max width for the tyre size indicated by the OP and already not recommended... and 9.5" is just too wide for that tyre size to be safe. It will adversely affect handling and if anything happens you will not be insured, it will cause issues at NCT time, plus it only takes one Gard who half knows his/her stuff to stop you.
CLICK HERE for a link that has a handy table in it giving min-max tyre width to wheel width index (half way on page).
In general though... if say changing from a 17" rim which is 7-8" wide running 225/45/17 tyres, to an 18" rim which is 8.5" wide running 18/40/225 - and you put the same on all 4 corners is fine as all 4 will rotate at similar speeds.
Here's a link to another calculator to see the difference in circumference between tyre sizes to help choose correct size when saying going up a rim size.
It will give you an idea of rotational circumference changes with different wheel/tyre combos; however, it doesn't allow for circumference distortion due to different wheel width front/back as per DonTommy's point (which will easily be 1cm). Now on new tyres that difference you'd get away with that as <1%, but as the tyres wear you could end up with 1.5-2% difference... and that could be too much for diffs and abs.
