Will increasing the size of my Wheels effect my gear ratios?

Question

I have an MGBGT, 1974 chrome bumper.

I currently have 14inch wheels on it (club sport if it matters), but have been offered some rostyles which are 15inches.

Will the extra inch:
A) Fit in the arch
B) Mess up my gear ratios/differential?

Answers on a postcard (underneath here is also fine)

Thanks
Dan

Answer 1

You will be fitting lower profile tyres on so it will be exactly the same rolling circumference which means you will have no problems at all.

Answer 2

If you fit low profile tyres as well, then it'll make no difference at all.

If you fit standard tyres, then its a different ball game altogether, 1, your speedo will give wrong info - it'll say 30mph, but you'll be doing slightly more (should be ok around town - but on motorway, probably about 75, when reading 70). 2, your turning circle will be wider, as the wheels will start rubbing on your inner arches. 3, the gap between tyres and wings will be less, so watch out for potholes. 4, here's a good one for you, if you fit "non standard" wheels, you "should" inform your insurance provider ! ! ! ! why?? say you..... well, you have technically modified the vehicle, and if you have a claim, they will say you haven't declared modifications and have every right to nullify your insurance policy, and the miserable sods wont pay out.

As for the mechanical side of things, it wont do anything different than standard wheels and tyres.



If you do go for the new wheels, just fit low profiles, and all your doubts will disappear

Answer 3

The new wheels should be fitted with lower profile tyres.

You original tyres on this car should be 165.14, but if changing to 15" wheels you need 185.65.15 tyres or 195.65.15 to keep the overall diameter the same, so they will fit in the wheel arch and so measurable change to gear ratios or ride height

Answer 4

Hello



It depends on the tyres you fit as size of tyres are worked out as



175/65/14

For example means

175 = Width of tyre in mm

65 = Depth of tyre as % of Width so 175 X 65% = 113.75 mm

14= 14 inch rims



So it will depend what tyres you fit, If the same 175/65 then yes as they would be bigger

You could try 175/60 as they would be slightly lower profile.



Andy C

Answer 5

Wheel size is not necessarily the "mess-up" factor. *The circumference of the tires can lower or raise the final drive ratio.



You are the type of person who would enjoy going to the tirerack.com website and find the stock tire size for your car. Open the word: SPECS under any stock tire size. At the far right you will see the words: Revs per mile.



If any other tire size rolls less revolutions per mile (larger circimference) your speedometer will read lower. A smaller circumference tire will always roll more revolutions per mile and the speedometer will read faster than stock.



Now you are really ready for fun. It's possible to find a *larger tire size with a lower aspect ratio (sidewall) and it will roll more revolutions per mile.



The people @ tire rack will know which tires will fit your car without fender-well modifications.

Answer 6

Not if the overall circumference of the tire is the same. When you get tires, make sure you tell the clerk you don't want to exceed the circumference of your old tire. The inner circumference will be 1" bigger, but that doesn't matter.

Otherwise, yes, it will effect each gear. You will lose acceleration, but get higher top speeds. From my experience with this, if you are used to a certain tire size, going bigger tends to wear out your clutch faster. Make sure you keep the outer dimensions the same.

Answer 7

Normally the extra inch will be balanced by a shallower tyre, so the overall rolling diameter will be much the same. you will of course get a harsher ride, and bigger risk of tyre/wheel damage on potholed roads

Answer 8

they wont be a problem if you drop the tyre profile ..say from 60 to 50 .. it works out at 10 to the inch