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what the difference in the 120/60/17 and 120/70/17 apart from the size?

Both are for a 120mm wide rim (so I assume we're talking about a front here)
Both are for a 17" diameter rim.

On one, the profile height is 60% of the width (72mm), on the other it's 70% (84mm)

So your rolling radius of the wheel will be 12mm bigger - or about 4%.

In terms of what this actually does to the handling, etc. I'd guess it might turn in better because it will be more inclined to 'tip' onto the side of the tyre, but this assumes a lot of other things being equal. We'll have to wait for one of the racers to answer properly!

If nothing else, your speedo will read 4% lower.

any help please guys?

I thought that number was the height of the tyre from the rim?

it is the height. The tyre profile would be the height from the rim.

so is there any difference in performance would they still be good for the road?

Well i expect they would affect your handling somehow but i dont know in what way, but in general either would be good for the road i guess. Whats wrong with the standard size? Or do you just want to try something different?

nah i have just bought some pirelli diablos for 65 quid they have done 35 miles but didn't realise that the front tyre was a 120/60/17 so i was just wopndering what the differece was before i put them on