If you are thinking of changing your car tyre size or are planning on buying a new wheel/tyre combination then you can use the flash tool below for a visual tyre size comparison of your stock wheel and tyre size versus your new wheel and tyre combination.
Got a comment or question regarding the current version of the tyre size calculator? Click here to leave a comment or ask a question.
Vesion 2 of the tyre size calculator is in development, if there’s anything you’d like to see in version 2 then please feel free to leave a comment here: Tyre Size Calculator V2: Wishlist.
Why is this important?
Matching the combined wheel and tyre diameter is important as it will ensure your ride height and speedometer readings don’t change drastically. An example of this would be fitting 17″ wheels to a car that has 14″ wheels as standard, there are three main consequences:
- the ride height will change, the car body will be further from the ground.
- the top speed will increase slightly and the speedometer will under read.
- the car will accelerate slower.
Read on to see the reason for this in detail.
Tyre Size Guide
Ride Height
Take the default example in the flash tyre size calculator above, here we have a stock tyre size of 165/55R14 and a new tyre size of 215/45R17. There is a total difference of 8.82cm in the two wheel and tyre diameters, if we divide this by two we get a difference in radius of 4.41cm. If we ignore tyre pressures and the effects of adding larger, wider wheels to suspension geometry; then this is roughly how much higher the car will be from the ground.
Speedometer
Then there’s the speedometer, a cars speed reading is usually taken from the transmission and is set based on a number of predefined constants. When you change your wheel and tyre combination you are taking one of these constants and making it variable. The speedometer does not know the new value and so continues to read based on the original wheel & tyre size. If you look at the above default example again you will see that with a 215/45R17 wheel and tyre combination there is a difference of 16.4% in the speedometer reading over the stock setup. As you can see, at 60mph your speedometer should actually be reading 69.9mph!
Acceleration
If we fall back to the default example again, the 215/45R17 wheel and tyre combination has a larger overall diameter by 8.82cm. A larger diameter has a greater rotational inertia which requires more energy to accelerate. Or in other words: the bigger the wheel, the slower the acceleration.
It should be noted that putting a bigger wheel and tyre combination on your car does not reduce your cars power. Your cars power remains the same; however it takes more force to turn your car’s wheels resulting in slower acceleration.
Tyre Width Equivalency Table
You may also find the following table of recommended tyre widths for given rim widths useful when changing your tyre width.
Rim width | Min tyre width | Ideal tyre width | Max tyre width |
|---|---|---|---|
5 .0 inches | 155 mm | 165 ou 175 mm | 185 mm |
5.5 inches | 165 mm | 175 ou 185 mm | 195 mm |
6.0 inches | 175 mm | 185 ou 195 mm | 205 mm |
6.5 inches | 185 mm | 195 ou 205 mm | 215 mm |
7.0 inches | 195 mm | 205 ou 215 mm | 225 mm |
7.5 inches | 205 mm | 215 ou 225 mm | 235 mm |
8.0 inches | 215 mm | 225 ou 235 mm | 245 mm |
8.5 inches | 225 mm | 235 ou 245 mm | 255 mm |
9,0 inches | 235 mm | 245 ou 255 mm | 265 mm |
9.5 inches | 245 mm | 255 ou 265 mm | 275 mm |
10.0 inches | 255 mm | 265 or 275 mm | 285 mm |
10.5 inches | 265 mm | 275 or 285 mm | 295 mm |
11.0 inches | 275 mm | 285 or 295 mm | 305 mm |
11.5 inches | 285 mm | 295 or 305 mm | 315 mm |
12.0 inches | 295 mm | 305 or 315 mm | 325 mm |
12.5 inches | 305 mm | 315 or 325 mm | 335 mm |
Absolutely Brilliant!!! Best on the web.
Hi there what would the off set be on a lotus esprit 1988 car,the front tyres are 205/55R15 and the rear are 245/45ZR16
Cheeky HROD, but the 3rd result down gives an offset of 35mm for the Lotus Esprit V8 front and back. I’ve no idea if thats right or not tho.
Try here http://tinyurl.com/y96dvgk
If am upgrading my tyres from 205/65/R15 to 215/65/R15 or 215/70/R15, do I have to change to a new rim ?
You should be fine at that, although it does depend on the width of your wheels. If you know the width of your wheel then you can scroll down this page a bit to find a Wheel Width/Tyre Size table to help you make a descision.
Unless your certain I would advise consulting your local tyre fitter before buying new tyres.
I have changed cars and where I currently live we must by law to put on winter tyres on the our car between end of October to End of April, my old winter car tyres are 205 55 R16 (from a Jag x-type) my new car tyres are 225 55 R16 (Audi A4 Avant), my question is can I use my old cars winter tyres on the new car if they are still in good condition?
Your old tyres might be stretched a fair bit depending on the Avant’s wheel width. Its a difficult one to answer with out knowing the widths of the wheels.
I wonder what the BEST diameter to soup up the MOnStar Starex to look mean but yet practical…
Hi, how is this tyre size calculator help if i want to change just the rim size? I want to change the alloy rim of my corolla seg from 14 to 15 or 16. Will it affect the speedometer and accelaration too?
Not necessarily Eric, as you increase the size of the rim you would usually decrease the profile of the tyre that you fit. For example a 14 inch wheel with 165/55R14 tryres fitted would have the exact same rolling radius as a 15 inch wheel with 195/40R15 tyres.
Of course, the tyre size 195/40R15 may not exist, go to an online tyre company like blackcircles.com and you can search to see if that size exists, if that size isn’t available you can fiddle with the calculator till you find a size that is and doesn’t affect the speedo too much.
Hope that helps.
what is the maximum size of alloy wheels and size of tyres for the same can be best for ford fusion plus 1.6
Hi, I expect your plus will have 15 inch wheels, I know that the Ford Fusion can have up to 17 inch wheels as standard (or factory fit options) on the higher specced models. If the car is still in warranty then I wouldn’t advise going any larger than that and to try and keep the wheel width and offset the same as the standard 17″ ford options. This should stop you voiding your warranty as some dealerships can be very picky about non standard parts.
My Corsa had a bad wobble between 20-30mph and I noticed one wheel never ran true (had a slight flat spot on rotation).
I got a new tyre and during rebalancing found the wheel was 20g out. Also during the re-fit I noticed a 4″ flat spot on the alloy rim itself which the tyre shop said wouldn’t cause the wobble because it wasn’t bad enough. Re-fitted the new tyre and balanced perfectly the wobble has reduced a lot but is still there, only now it is between 35-40mph.
Anyway….I’m convinced the flat spot on the alloy is the problem, so have found a new one with a 195/50/R15 tyre fitted.
My originals are 185/55/R15 and the difference would be 8mm lower.
Assuming the new alloy is perfectly round, will this cure the wobble regardless of the new or old tyre fitted?
Currently got 185/55/R15 on a Corsa but got a flat spot on the alloy which I think is causing a wobble around 40-45mph. (wheel balanced perfectly)
I have found a new alloy with a 195/50/R15 tyre and worked out it is only 8mm lower. If the alloy is perfectly round will that cure the wobble, even if I keep / change the tyre?
Hi Eddie,
Whatever caused the flat spot may have affected your tracking so you should probably have that checked too. The new alloy should have the odd size tyre removed and a 185/55R15 fitted before you put it on the car, especially if its a drive wheel.
Of course it may not be limited to just that, have a look at this good Popular Mechanics article which might help:
Diagnosing And Repairing Wheel Vibration
I am planning to change my stock tyres 275/45R19 to 255/55R19. some people recommend not to change sizes more than 3%. I am safe to change to 255/55R19
Hi Garry, 3% usually relates to one width up or down e.g. 285 or 265 for your 275 width tyre. However I have heard a few tyre fitters say that if the new tyre width is 0 to 1 inch wider or narrower than your rim width then you should be safe, 1 inch to 2 inches and your pushing it, and if the difference is over 2 inches you’re unsafe.
Assuming your rim is 10 inches wide I would expect a width of 255 would be fine but I would say a 255/50R19 would be better as it minimises any speedo error. If your rim is any wider then I would say 255 tyres aren’t worth the risk and always check with your tyre fitter before purchasing… don’t rely on my work as I’m far from perfect 😉
very usefull but just cant get why cahnging the tyre width alters the diameter of the tyre/wheel combo,eg 265/70/17 is a bigger diameter than 235/70/17? any help on this would be greatly recieved.
Hi Dave, the reason the overall diameter increases is because the tyre profile (the second number, 70 in this instance) is a percentage of the tyre width. So 70% of 235mm is 164.5mm and 70% of 265mm is 185.5mm.
To get the overall diameter we convert 17 inches to millimeters: 431.8mm, and add 2x the sidewall height.
235/70/17 is 431.8+164.5+164.5 = 760.8mm
265/70/17 is 431.8+185.5+185.5 = 802.8mm
I hope that helps
can someone pl advise me on following:
my honda civic currently has stock tyres of 205/55-R16. i want to change the tyres to 205/60-R16 to increase ground clearance. the overall dia increases by 18mm. pl advise if it can be done without comprising on cars performance and handling.
Hi Maz. The sidewall height will increase by 9mm, you may find the ride is a touch more wobbly as there will be a little more flex in the sidewall but I doubt it would be noticable. If you’re on standard suspension then you shouldn’t have to worry about fouling on the arch liner either.
can u explain how effected on changed those things to the our lovely car if speedometer is more or lesser than original spec? your explaining
will help me dude..tq
NHC, You speedometer isn’t technically being affected, what is happening is that your cars speed is often read from the gearbox and the speedometer is calibrated to be fairly accurate across a small range of stock wheel sizes for that model. If the overall circumference of the wheel & tyre package increases (or decreases) then you risk moving out of this calibrated range and you can no longer be sure your speedometer reading is accurate… or at least as accurate as the manufacturer intended. My calculator gives you an idea of the changes you can expect.
In my car for example, a 2008 Mazda 3 with nothing modified yet the speedometer over-reads by 5mph. I have confirmed this with three different makes of GPS. When my speedometer reads 50mph my road speed is actually 45, 60mph is 55, 70mph 65 etc.
On my girlfriends old micra the stock tyres were an awkward size and quite expensive, by using the calculator I was able to find a more common size that was cheaper and the circumference change brought the road speed closer to the speedometer reading, although it still over-read by a couple of mph.
hi i drive a 2008 saga blm which comes wif 175/70R13.. I wanna change to 205/40R16.. what would differ in terms of handling and stability and hw would that affect performance?would I have the risk of the tyres hittin on the walls of the tire well?
Hi Ravind. I’d guess you’re moving from a 5.5/6″ wheel to a 6.5/7″ wide wheel, in that case you’ll have a greater tyre contact patch which will increase grip. The lower tyre profile will reduce sidewall flex which again improves handling but at the expense of comfort as the reduced flex means less shock absorption. Larger wheels also mean the engine needs to work harder to accelerate but you will travel further for each rotation of the wheel. Simply this means slower acceleration but increased top speed.
Whether your tyres rub or foul on the tyre well depends on how tight things are to begin with and the offset you choose. It is pretty simple to work out what the ideal offset would be for your 205/40/16 wheels and tyres, so long as you know the stock offset, I will assume the offset of original wheel is +35:
1) Get two bits of paper, or card which would be better.
2) Cut one to 30mm by 175mm (strip A) and the other to the new width 30mm x 205mm (strip B)
3) Centre of original tyre is 175/2 = 87.5mm, draw this line on strip A
4) Centre of original tyre is 205/2 = 102.5mm, draw this line on strip B
5) Offset is +35 so the offset line is 35mm closer to the face of the wheel from the centre line, mark this line on strip A
6) Now, if you sit strip A on top of your original wheel (while it is still on the car) you can line up the center line of strip B and start sliding it back and forth to work out the ideal position of the new wheel. When your done, mark the position of the offset line on strip A onto strip B.
7) measure the distance from the centre line on strip B to the offset line you just marked and this is your new ideal offset.
Things to consider are the height of your new wheel, use my calculator to see how much taller the new radius will be (wheel & tyre) and bear this in mind as this may foul the arch liner or lip. Don’t use the rolling radius value on the calculator tho as it is showing the circumference.
Hi Nadeem,
In your example 145/80 and 155/80 the number 80 is the aspect ratio, the sidewall height as a percentage of the tyre width. If the aspect ratio remains the same (80), but the tyre width increases (145 to 155) then the sidewall height will increase as 80% of 155 is greater than 80% of 144. Hope that helps
@Spike: I’ll add a section for special tyres in V2, do you happen to know of anywhere that I can get a comprehensive list of sizes, like a good mud tyre sales site?.
@Michael: Without knowing the exact details of your cars setup… I would suggest camber adjustment. By adjusting the camber you could increase the contact patch of the wider tyres and thus increase the grip. But you couldn’t do this with your standard suspension. Is it overall poor handling or when your turning for example?
Why In case of 145/80/12 and 155/80/12 the height is getting changed, where as 145 and 155 are for width?
Hey, your tire sizes don’t include mud type tires such as 31×10.5
Great tool for the right decision on rims & tyres
I have recently upgraded the tyre size on my Kia Sorrento from 245/70R17 to 265/65R17 and this has effected the handling of the car are they compensation setting’s that i can do to the wheel alignment to make the car more steady on the road.
one more thing about changing ur tyres diameter from the OEM standard, It will not just affect the speedometer reading but odometer too.Taking example, if ur change ur tyre diameter size smaller than standard,ur odometer will show higher travel distance than the actual and vice versa.So it is important to note this matter as it will affect the oil changing period and timing belt/chain replacement or other necessary services.
Hi Ian, yes rolling radius is actually circumference. I vaguely remember there being a reason for refering to it as “rolling radius” but its lost to me now.
Its not a great label but most people seem to get the gist. I’ll change it in the next version.
Just used your calculator and it’s giving me a rolling radius of 196cm! Is that supposed to be the circumference? The overall diameter comes out at 62.5cm – which sounds a bit more credible.
@John: I’ve not got one specifically for bikes, but I will be adding more tyre sizes to the next revision which should be useful to bike owners
@Kyle: You’re calculations are almost there but you need to double the value for sidewall height. The diameter for any given wheel and tyre combination is measured tread to tread, e.g. sidewall height + rim diameter + sidewall height.
Hope that helps
If I understand correctly, The Total Diameter of 185/65/14
will be the following
185 * 65% = 120.25mm = sidewall height, and if you add that with the rim size of 14 inch(or 355.6 mm) the total diameter will be:
120.25 + 355.6 = 475.85 mm or 47.6 cm to round it off. Why does the calculator for this size display 59.61cm??
Tyre Size Calculator is really helpful….thanks
this is a great tool. do you have one for motorcycle tires?
@Ammar: I assume your in America so I couldn’t be specific about brands of tyres. What tyres do you want to widen, are you just buying tyres or new alloys as well?
@Brian: Yes, you can put a slightly wider (or narrow) tyre on the rim, to determine the max width of tyre you can fit then convert the metric width of the tyre into inches and subtract the width of your rim. If the result is 0 to 1″ then your pretty much spot on, 1″ to 2″ and your pushing it, and if the difference is over 2″ you’re unsafe.
On Euro cars the fashion is (or was) to run narrow tyres on a wheel to give a stretched look, although I’m not sure if my rule-of-thumb calculation above works in reverse for running narrow tyres.
Can i put a slightly wider tyre on the rim that came from factory.
yes – just look at the gray table up there ^^, look at the *wheel* for the width measurement, don’t use the tyres fitted as someone may have already done the same and you’re not looking at standard factory fit sizes
i have a dodge charger with 255/60R18 tyres. i want to change these tyres into wider ones with higher performance, which one should i go for?? please advice
Hi Andy,
I’ve never had runflats but had heard they could be pretty harsh. I know the sidewalls on the runflat tyres are very stiff compared to regular tyres but I also found this which may be of interest:
I’d consult some other BMW owners before changing to non runflats first, this applies to changing the entire wheel and tyre package as well.
Try the follwoing forums and clubs for owners views:
http://www.bmwcarclubforum.co.uk/forum/forum_topics.asp?FID=29
http://www.pistonheads.com/gassing/forumGroup.asp?c=77&catname=BMW
I have a BMW 2008 320d M Sport with 225/45R17 & 255/40R17 run flats and the ride is very jittery. I like the stiff suspension, but I do not like the high frequency vibrations coming through which I think is through the tyres being really stiff.
In peoples opinion, what effect will have replacing the tyres (and wheels?) to
A) the same size non run flats
B 205/55R16 wheels and tyres non runflat.
Thanks in advance Andy
Thnak
Peter, it might be worth hitting CTRL+F5 or clearing your browser cache. The address for the calculator has changed and you browser is likely still looking for it in the old location.
Not bored, I like learning new stuff
Hi Insomniac. No calculator yet I’m afraid just a big white space
Still banging on about this tyre size against speed thing, most modern sport-ish bikes have electronic speedos even if they are analogue rather than digital. They assume a standard rear tyre and use the engine revs and gear position to compute the speed. However…. on a lot of trail bikes like my old Suzuki DR600 the speedo is mechanical driven by a cable from a small gearbox on one end of the front hub. So it will be the front tyre size which will affect the reading. Getting boring now ? Peter.
@Peter:
No there’s nothing wrong with your flash player, I lost all my site files when the latest version of my blog deleted every file on my hosting account. I got distracted trying to setup my site again with a new theme and better backup routine, I’ve restored the tyre size calculator and you should see it again now.
Thanks for the additional info too, I notice the front wheels can go as low as 90 in width so I may tweak the options a little to include some values from that site.
To Insomniac. Hi, with regard to motorcycles the size range was perfect for me.The standard rear for my bike is only 150.70×17 I am running a 160.70×17 at present which puts me on the wrong side of the speedo error thing. I will be changing my tyres soon and if it will go in I will have a 170.60×17 rear. This will mean the speedo will be slightly under reading. To see typical bike sizes go to….. http://www.motorcycletyresuk.com/
Which is a local supplier.
Incidentaly the calculator has recently gone somewhat less visual. In fact it is not apearing at all. Everything else on the page is present. Do I have a problem with flash player?
just fitted 215/60/17`s to back of my previa to try to eeck a bit more mpg. found your website and tyre calculator most helpful, thanks, Danny
@Peter:
I’d not thought of the tyre size calculator in terms of motorbikes, although the basics should all remain the same. Are the range of widths, sidewall heights and tyre sizes sufficient for bikes or would it be useful if I added more?
Glad the tool was of use
@Danny:
I’m glad my little utility helped, always good to get feedback and to know that people appreciate it
I have just used the visual tyre size calculator to look at the effect of possible alternative sizes for motorcycles. It was exactly what I needed as I particularly wanted to check the indicated/actual speed situation. I will be posting a message on the Suzuki Owners Club site as I’m sure others will find it usefull. Many thanks,
Peter.
I have a 2005 BMW 7 Series and the Tyre Size is 275 34 R20. I also have a set of Tyres from my old 1997 BMS 7 Series which I have now sold. Would I be able to use my old wheels and tyres on my new car. They are 235 60 R16
@Malcolm: There actually isn’t a whole lot of difference between the two sets of wheels & tyres in terms of overall rolling radius; your old 16″ wheels being a little under 4cm shorter with those tyres. What you would need to watch is the PCD, Center bore and offsets of the two sets of wheels. I believe that BMW are pretty consistent with their PCD/Center bores which are usually 5×120 and around 72mm for the C/Bore I think, although you should check because I’ve been wrong before. The offset will almost certainly be different as there is a 40mm difference in width between the two sets of tyres.
I’ve a visual offset calculator that would help if I ever got round to finishing it, but off the top of my head (and without checking offsets) I expect your old wheels and tyres would fit but sit fairly deep inside the arches.
I hope thats of some help.
How much effect on riding quality does tyre size have (particularly wall thickness)? Say 245/45 R17 against 255/50 R127 tyres, which would give the softer ride on the same suspension?
@Barry: As a rule of thumb a bigger sidewall will often have a softer ride. In your example, if you were comparing a 245/45R17 Toyo Proxes to 255/50R17 Toyo Proxes the 50 profile tyre sidewall will be 17mm deeper, and assuming all tyres were made equal they would offer the more comfortable ride while sacrificing a tiny amount of handling due to the increased sidewall flex. However all tyres aren’t equal and there are variances in rubber compound and construction that could make a difference.
Hope that helps
hi, can you tell me what the difference in mm’s would be from a trye with a profile of 50 to one with a 60 profile please, assuming that they are 15″ rims and 195 in width.
Easy, 195mm width, 50% of the width gives the wall, 15” rim diameter. In a wheel total diameter you have walls and 1rim:
195mm 2×50% 15inches
195mm 100% 15”
195mm 195mm 15”
New tire:
195mm 2×60% 15inches
195mm 120% 15”
195mm 235mm 15”
235-195=40, so your new tire is 40mm bigger than the stock one.
But, the rule for bigger tires is max 3% bigger in total diameter, and your new tire is almost 7% bigger so I really don’t recommend it.
Hope it helps