Hold your mouse over each field for additional instructions on how to use the calculator. See the bottom for tire sizing tips, real world vs. calculated tire sizes, and VW TDI gear ratios.
- look for this mark on the outer sidewall
In this example 205/60/16:
-205 is the tire width (section width) in mm. This is the overall tire width, not the tread width.
-60 is the aspect ratio. It gives you the sidewall height as a percentage of the section width. 60% of 205mm is 123mm sidewall height.
-R means radial (almost every car tire)
-16 is the wheel diameter in inches.
-92H is the service description. 92 is the load rating (the tire can support 1389 lbs or 640 kg). H is the speed rating (130 mph rated).
Reading wheel size - look for a stamp behind the spokes. In the
-width is 8.5"
-diameter is 18"
-offset (ET) is 45 mm
-J is the tire bead profile shape code and H2 is the bead hump profile (double hump): (99.99% of the time, ignore these two).
|Sidewall height (inches):|
|Wheel/tire overall height (inches):|
|Ride height change (inches):|
|Tire width change (inches):|
|Tire outer circumference (inches):|
|Wheel diameter change (inches):|
|Wheel width change (inches):|
|Wheel offset change (mm):|
|Wheel/tire inboard clearance (positive is less clearance, negative is more clearance. inches):|
|Wheel/tire outboard movement (positive is sticking out, negative is tucked in. inches):|
|Wheel/tire stance ( inches):|
|At an indicated mph on the speedometer, the actual speed is:|
|% speedometer error with new tire/wheel:|
Engine - gearing output
|Engine RPM at indicated speed:
|Effective final drive ratio with new tire/wheel combination:|
|Theoretical top speed with redline ( indicated mph):|
In general, it's suggested to keep the overall wheel/tire height and width the same to make sure the new tire fits correctly. VW TDI are somewhat low to the ground and the the odometer/speedometer tend to read fast so my personal preference is to upsize the tire aspect ratio by 1 size larger. This will also slightly increase gearing, increasing fuel economy and fixing the common "my speedometer reads too high" problem on VWs. This is a common problem on German cars because they are not allowed to read slow but are allowed to read slightly fast. If you have a mk4 VW you can remove the instrument cluster and manually move the needle to adjust it. See 1000q: mk4 instrument cluster removal for tips. If you have a mk5 VW you can adjust the speedometer through the distance impulse setting. See 1000q: mk5 speedometer correction for details and 1000q: mk5/6 instrument cluster removal.
Many German cars tend to have a decent amount of wheel gap between the wheel and fender which allows for slightly upsizing tires. Some space isn't a bad thing because tire rubbing on the autobahn at 140 mph could lead to catastrophic tire failure. Unless the new tire/wheel tires rub on the fenders during hard cornering or big bumps it shouldn't be a problem. Always check for adequate clearance on the inside and outside faces of the wheel/tire against the brake rotor/caliper, brake lines, suspension arms, fender lip, fuel filler neck, or wheel well liners! Since the fuel filler neck is only on one side, make sure to check that side for inside wheel clearance.
Note - tire width is not the same as tread contact patch width! Tire section width is measured at the widest point when mounted on a specific design (test sizing) wheel. Contact patch width varies by tire model and even size because they have different sidewall shapes and tread patterns for different sizes. Tire contact patch size also varies according to loading (weight on that corner) and tire pressure. Two different models or aspect ratios of the same tire with the same section width may have different "actual widths". This will result in actual clearance being slightly off what is calculated here. For example, one tire could be constructed to have a square sidewall profile where the entire width is tread and the other could have a rounder sidewall profile where only 75% of the width is tread. Look at the tire in person or find the specs online before buying a tire.
Offset is the distance in millimeters from the mounting surface of the wheel hub to the centerline of the wheel width. It's usually marked as ET or Einpresstiefe (German for insertion depth or press in depth). To the right is a cutaway diagram that should help explain it. If you play with the calculator it will show you how inside clearance changes according to positive/negative offset, wheel width, and spacers. Wheel hub spacers will increase offset and make the wheels poke out. Always make sure the lug bolts/studs are long enough when using spacers.
If the offset is wrong the wheel could interfere with the brake calipers, rotors, brake or fuel lines, the suspension, or the fenders. Inner wheel clearance depends on spoke and wheel design as well. Tire choice also effects if the wheel/tire combo will fit on the car. If it sticks out too far then handling characteristics will change and the tires will fling road debris all over the sides and behind the car. Wider wheels may require a change in offset due to clearance.
On many cars, assuming the same wheel/tire width, a +/- 5 change in offset usually won't do anything but +/- 10 is a difference of 10mm and it will be more noticeable. In addition to using the calculator above, look at your current wheels to see if there's a difference in front vs. rear wheel hubs and inside clearance.
A new wheel of the same width
should have about the same offset as your old wheel. Everything else being
-Cars with positive offset (all modern VW and Audi that I can think of) - the lower the offset the more the wheels stick out.
-Cars with negative offset - the lower the offset (the higher the absolute value, if you don't remember your math -50 has a lower value but higher absolute value than -30) the less the wheels will stick out.
Below is a picture of stock mk5 Jetta wheels with positive offset 50 and new wheels with offset 37 showing the difference between front and rear offsets. Rear before: the stock wheel is tucked in slightly in the fender. Rear after: the new wheel is flush with the fender because it has a lower positive offset. Front after: the front wheel sticks out beyond the fender because the front wheel hub sticks out farther than the rear wheel hub.
Final drive and top gear ratios for Volkswagen TDI
|Manual transmission final drive||Manual transmission top gear||Automatic transmission final drive||Automatic transmission top gear|
|Jetta/Passat 1.9L 90hp engine w/ 02a transmission, model CTN||3.157||.755||-||-|
|Jetta/Golf 1.9L 90hp engine w/02j transmission, model DQY, EBJ, and EGR||3.389||.756||-||-|
|New Beetle 1.9L engine w/4 speed auto||3.2||.742|
|Jetta/Golf 1.9L 90hp engine w/01m transmission, model DMP, ECN, ELT, EPB, EPP, and FDB||-||-||3.7||.742|
|Jetta/Golf 1.9L 100hp engine w/01m transmission, model EUH||3.389||.744||-||-|
|Passat 2.0L 138hp engine w/ 01v transmission, model GMR||-||-||?||?|
|2005.5-2006 Jetta 1.9L 100hp w/ 0a4 transmission, model GQQ||3.389||.769 (might be .74)||-||-|
|2005.5-2006 Jetta 1.9L 100hp w/ DSG transmission||-||-||3.33||.91 (might be .76)|
|2009 Jetta/Golf 2.0L140hp engine w/ 6 speed manual transmission||2.76||.81||-||-|
|2009 Jetta/Golf 2.0L140hp engine w/ DSG transmission||-||-||3.04||.756|
|2010-12 Jetta/Golf 2.0L140hp engine w/ 6 speed manual transmission||2.76||.717||-||-|
|2010-12 Jetta /Golf 2.0L140hp engine w/ DSG transmission||-||-||3.04||.756|
|2012 Passat TDI w/6 speed manual 140hp engine||2.92||.72||?||?|
*NOTE: VW USA's website shows the 2009 manual transmission gear ratios for the 2012 Sportwagen but this is most likely a mistake. The gear ratios should be the 2010+ ratios.
Have more questions on what wheels or tires will fit on your TDI? Please ask in the TDI forums.