tommytwotanks

How much difference will it make for me to increase my front tyre profile from '70' to '80'?
Will the engine speed at 70mph be significantly different....? or so similar as to not be worth the extra few quid for the larger profile tyres?

Rod-Tarry

Not enough info given to calculate. 70 or 80 profile of what size/width tyres. I take it an accurate speedo is not required.

Martin-Hadland

iTrader: (2)

Mph per 1000 rpm might not be your only consideration! Tyre height may well be a limiting factor for clearance and even if they fit they may look very odd.

andy escos

iTrader: (1)

as Rod said need more information but for example if you had

215/70/17 tyres & you then put 215/80/17 tyres on it your speedo will be out by5.9%

ie 60mph indicated would be 63.5 mph actual speed.

Chaz888

remember its an aspect ratio so is a pecentage of width .

tommytwotanks

a girl friend of a mate at work is trying to reduce her petrol/travel costs, so he came up with the idea of fitting bigger tyres on the front, he's thinking about going from 175/70/14's to 175/80/14's, no idea what car it is though

andy escos

iTrader: (1)

that would be 5.8% which will make it 3.5mph faster than indicated



or buy a prius

Derby_Gav

I did similar on a car to help with gearing for motorway speeds but it was low geared so it worked for me.

Doing it to save fuel won't work unless it spends all its time on a flat road as the engine will have to work harder because of the increased gearing due to the tyres.

Two options...

Buy a more economical car or
Teach her how to drive more economically.

Gavin.

Derby_Gav

There is also the insurance to tell due to running larger than standard tyres.

tommytwotanks

thanks guy's i will pass the info on