Having failed my IVA on brake bias, if I take it to an MOT centre will they be able to tell me if my brake bias is correct??
Cheers
Neil
No you really need to road test from slow speed on a clean dry good tarmac surface.
If you have a tandem master cylinder just put a pressure limiting or pressure proportioning valve in the rear circuit or if you have drum brakes fit
smaller bore rear wheel cylinders.
[Edited on 11/8/14 by britishtrident]
quote:
Originally posted by neilp1
Having failed my IVA on brake bias, if I take it to an MOT centre will they be able to tell me if my brake bias is correct??
Cheers
Neil
Don't take it to the MoT station to ask if it passes, ask them for the results. Use them to make adjustments.
The results from a normal MOT roller test are pretty well useless for setting up bias, even the method use at IVA is pretty hit or miss.
Question on the Bias settings, as I now have a duel setup with bias bar
My 7 is due an MOT next week, and I was going to take the readings of fronts together and backs off the screen and work out roughly what the 60/40
front to back split was, and adjust my set up accordingly
Will this not be of any use
Steve
The brake tests I've seen on MOT's only have one set of rollers, so I don't understand how they could work out brake bias anyway? They
can calculate brake efficiency (and left to right brake balance), but not necessarily compare effort between front and back wheels?
Is there something I'm missing?
On MOT rollers you get no weight transfer from the front to the rear wheels so the readings aren't reprentative of real stop also you can't
know if the pedal pressure is the same. Another problem with MOT rollers is the gripping surface of the rollers varies a lot, some older machines
have polished steel rollers that don't give much grip while others are very abrasive, this isn't much of problem for MOT testing because
the requirement for service brake efficiency was set in the days when Vauxhall Wyverns and Ford Anglias were on our roads.
The IVA test also can only replicate one particular set of conditions.
As long as the front brakes lock first on good clean dry tarmac all should be well, so aim for this plus a margin for error.
For race cars in the wet provided the relative sizes the front and rear calliper and master cylinders are in the correct ballpark then about 1 turn
extra towards the rear on the bias bar is the initial setting. With a correctly assembled balance bar bar if much more than a couple of turns are
required between wet and dry it is time to reconsider the master cylinder bore sizes.
Out of interest - could people link to specific brake 'reducing' valves they've used? I've seen several different ones mentioned in threads over the last few months (Ka, Sierra, Mini, Corsa) but they are all along the lines of 'get one from a scrappy' whereas i'd probably prefer to buy a new one...