I'm the new owner of a 1990 R5 campus. It has a clean MOT, except for an advisory for rear brake balance which is only just within tolerances. I am replacing the front tyres on Thursday - one has gone out of shape and they are both old - and this prompted me to check more carefully the rear tyres. One of them is a 155/70 and the other is correct being a 145/70. So the height and width are different. I'm going to put new tyres on the back, but would the different sizes add to or cause differing measurements when the brakes were tested? I have jacked up the rear and both wheels respond equally to the handbrake.
- Thread starter Seabadger
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André4Renaults
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ABSOLUTELY! That's a fail, even if your garage's sympathetic to classic cars. Your cornering would feel different left to right and the car may slew under violent braking. The brake imbalance may have been caused by the odd tyres, as more tread would be on the ground on one side than the other. Buy some decent new tyres (a MATCHED pair!) and ask the garage to re-check the rear brake balance. The in-balance allowance at the rear is more than at the front, but the closer it is the better.
Homegrown
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I agree fully about that tyres should be matched.
But have nothing to do with breaking imbalances in the brake test. 145/70 vs 155/70 makes no difference. Better to look for the real problem.
Probably badly adjusted brake shoes/worn out.
The car had a fresh MOT when I bought it, so I guess the tester was in a hurry perhaps. Or may be the tyres were dirty. It doesn't look odd; you have to read the numbers to notice. But It does seem a curious thing to do. There's only one tyre worth saving of the 5, so I'm going to keep that as a spare. It seems I can refurbish the rear brakes, including new drums and flexible hose for under £100, so I shall do that when I've finished the front ones.
I was just curious about the possible effects on the MOT man's machine; the tyres being a (slightly) different width, height and circumference, but the drum obviously the same. If one side had a much bigger wheel acting on the same brake would the machine still measure the same effort, the length of the lever -or gearing if you like- being different?
Apologies in advance as this is all academic as no one, not even me, knowingly drives round with different sized tyres. Nor am I suggesting it as a method of balancing dodgy brakes!
I was just curious about the possible effects on the MOT man's machine; the tyres being a (slightly) different width, height and circumference, but the drum obviously the same. If one side had a much bigger wheel acting on the same brake would the machine still measure the same effort, the length of the lever -or gearing if you like- being different?
Apologies in advance as this is all academic as no one, not even me, knowingly drives round with different sized tyres. Nor am I suggesting it as a method of balancing dodgy brakes!