Bigger tyres vs gear ratios

[Druk]

I'm currently running 205-55-16s (632mm dia) and am considering changing to 225-55-16s (654mm dia).
Tyre calculator says this will give a 3.5% increase in diameter. http://www.tyresave.co.uk/tyresize.html

My math is crap but I reckon the wheel will travel an extra 70mm per revolution.

Since I feel the car is vastly undergeared anyway (4000rpm @ 80mph approx) and has plenty power to spare....

does the forum think this is acceptable?



I don't care about the speedo reading.

 

[allias]

If its for 4wd - need to remeber to change all of them at once. If its diffrent case it wont make a difference. Its 18mm dirrence which in many cases is a difffrence between brand new and completly bold tyre. As long it wont have fitment isses - other I wouldnt worry.

I would recommend 215/55-16 then going straight to 225/55 but ideal would be 225/50-16 (-1% difference).

Need to play around your choices: use this web Tire size calculator

 

[coupe deville]

Since I feel the car is vastly undergeared anyway (4000rpm @ 80mph approx) and has plenty power to spare....

snap ! so is mine, running 205 60 15, if i changed to 225 60 15 it would up the gearing by nearly 4%
question would 225's fit my car and the original 8 hole alloys

 

[allias]

Turn your wheels to max lock both ways and check for gap. Remeber that your tires will be 20mm wider so it makes it avg 10mm on each side so if you have a gap each way as well as decent gap on top so it wont rub ob fenders while on bumps then you ill be OK.

 

[Druk]

Bump. Anyone have any thoughts on what the extra circ will do?

 

[Bobby Dazzler]

It is indeed a increase in circumference of 3.5%, and I don't think this will cause any problems providing that the circumference of all four tyres are increased by a similar proportion (can cause problems with Cruise Control).

Performance shouldn't be blunted given the torque available with a 320, but the flip side to that is that I don't think it's enough to make a night and day difference to engine speed when cruising either.

 

[Druk]

Thanks for the answer BobbyD. It's the 107 they're going on so...no cruise, but not quite so much torque either. Vastly undergeared all the same.
These tyres are coming pre-fitted to rims I've bought so just have to try and see. I was hoping for some informed foresight just the same.

 

[allias]

Use link I gave you and make you own calculation to what you see on your car. That way you will now best. Tyres can be effected on each individual cars. I saw once two Volvo`s with same rims and same tyres (diffrent brands tyres) and one was rubbing on inside arches other one was just fine... Better check yourself how much gap you have with which each aspect of turn of your wheels. You want better answer then that. Rest of it (look and handling) it will be your own prefernce.

 

[Bobby Dazzler]

Sorry I hadn't realised. I don't think it will have a dramatic difference on the 107 either. Keep us posted now though - interested to hear!!

 

[jefrs]

Examples
Radius of tyre = height of sidewall + radius of wheel = (55% x 205) + (25.4 x 16/2) = 316mm, therefore diameter = 632mm

Circumference of tyre = pi D = 3.14159 x 632 = 1985mm (205/55R16)
Therefore (225/55R16) diameter = 2054mm
This is an increase of just 69mm rolling distance, or a decrease of 3.4% in rpm

Which car is doing 4000rpm at 80mph cruise? - that seems very high revs for a 320.
I would expect under 3000rpm, my rears are 265/35ZR18 = 2019mm circumference.
Are you sure it is in top gear?

 

[jefrs]

Since I feel the car is vastly undergeared anyway (4000rpm @ 80mph approx) and has plenty power to spare....

snap ! so is mine, running 205 60 15, if i changed to 225 60 15 it would up the gearing by nearly 4%
question would 225's fit my car and the original 8 hole alloys

Are you sure it's 4000rpm at ~80mph

Given the top speed and the red-line that's like 2/3 of max speed - somewhere around 110mph.

So are you sure it's actually got up into top gear? I'm assuming auto.

I did not know you could put a 15-in wheel on a 320
the W210/S210 E320 gets
215/55R16 7½Jx16
235/45R17 8Jx17
235/40RZR18 8Jx18 (plus 265/35ZR18 9Jx18 rear if staggered set)

Only the W210/S210 E200 and E240 get OEM 15-in wheels
195/65R15 6½Jx15
205/65R15 7Jx15

So 205/60 may be too small a diameter, do check the technical manual.


I've had mine stick in low ratio once (switch off and restart) and do scary things like drop into 2nd on the motorway when I jabbed the throttle to overtake up a hill. It also got stuck in winter-mode, which does funny things to the gearbox, fixing that probably also cured the stay in low problem.