It might be rather naïve but it comes as a real shock when you discover that there exist people who apparently believe that cars should be left exactly as the manufacturer made them and that any modification is likely to be a retrograde step.

Having been immersed in car modification and other technical circles for a very long time, I’d literally forgotten that there are people like this around.

The eye-opening discovery was made when I contributed a post to a discussion group. I read lots of discussion groups – normally by backtracking from the AutoSpeed daily referrers’ list – but I very seldom post to any of them. But after I bought a Japanese import Toyota Prius, I joined a Yahoo discussion group devoted to the technical aspects of the car. The Prius is one of the most technically sophisticated cars on the road and I figured I could learn a lot from those who had been playing with them for years.

However, after reading the group for a few weeks, I started realising that while these people were enthusiastic about the car, and while they discussed lots of technical aspects of the hybrid, they did little or nothing with the knowledge. For them, working out how the car functioned was an end in itself. Did the ICE (internal combustion motor) stay on or go off when certain driving conditions were met? How much current flowed from the high voltage battery to the electric motor? Stuff like that.

To me that’s all well and good, but the importance of knowledge is what you then do with it.

So when I swapped the drum brakes on the back of the Prius for Corolla discs, I posted about it. Initially I was having a problem with brakes dragging and asked if anyone knew of the presence of a residual pressure valve in the system. There was a loud silence, although one person said that if it existed, it was probably at the master cylinder. I sorted the brake dragging problem (it wasn’t in fact a pressure build up) and then questions started to come in about the swap.

The US-delivered first model Prius (they call it the ‘Classic’!) all had drum brake rears while the Australian and European cars got rear discs. It doesn’t take much nous to work out why – drums are cheaper than discs and Toyota thought they could get away with drums in the US market in a way they simply couldn’t in the Euro and Aust markets. So I figured that lots of the Americans in the discussion group would be keen on doing such a brake conversion.

At around the same time another poster asked how hard it would be to fit side airbags to his Prius – in the US, side airbags were available on the Classic. (They weren’t available on the car here in Australia – and just the same marketing logic can be applied as to brakes. Toyota knew they could get away optionally fitting side airbags in this market but couldn’t in the US.) The poster intended to use all factory parts, including replacing the whole seats (if required) and installing the new wiring harness, side impact sensors and so on.

So it was all starting to get interesting – sophisticated mods using parts from the Toyota parts bin that could dramatically improve the primary and secondary safety of the car.

And then in come the wet blankets.

First it was the airbags.

If you really want side airbags then sell your current car and buy one that has them. What you are proposing looks like a great way to blow a few thousand dollars with no particular guarantee of success.

I’ll even put my safety engineer’s hat on. Suppose you have an accident, and the side airbag goes off, and injures your passenger?

What will your insurance company do? I’ll tell you, they’ll say unauthorised mods to safety systems of car, fitting pyrotechnics is stupid, you are on your own.

Please don’t do it.

Then it was the rear discs.

In my opinion, retrofitting airbags and/or rear disk brakes is strongly not recommended. The safety and liability issues have already been stated by others.

A manufacturer at the design stage has access to lots of specialised testing and measuring equipments for proving everything is working to the correct parameters.

Further, regarding the adding of rear disk brakes, I really doubt if there is any significant benefit in stopping power. The front wheels do the majority of the work anyway. The ABS system is a finely balanced one. Any changes in the relative braking force applied to any of the wheels, could result in an unbalanced and non optimal braking system. I am sure that if the drum brakes were not up to the job, then Toyota would have made the drums bigger or fitted disks as standard. They would certainly not have released the vehicle for sale in the US with inadequate or inferior brakes.

My guess is that the rear disks we in the UK get *probably* do not work significantly any better than the US rear drums do. I reckon we get the rear disks just for marketing reasons. Why else would Prius *need* different brakes in the UK/EU versus the US?

There are some major problems with these views.

Firstly, they are completely non-specific and non-technical. What does “the ABS system is finely balanced” actually mean? As far as I can tell, nothing. In specific, technical terms, why does fitting factory side airbags to a car optionally sold with them have “no particular guarantee of success”?

Secondly, the statements contain hypotheses which on the available evidence, are very unlikely to be true. “Suppose you have an accident, and the side airbag goes off, and injures your passenger?” Hmmmm, what conditions would need to exist for this to occur? Suppose you have the tyres changed and then a wheel falls off? Well, it’s very unlikely to do that if the wheel-nuts are correctly tightened…. So why would a correctly installed inflating side airbag injure a passenger?

Regarding disc brakes, “any changes in the relative braking force applied to any of the wheels, could result in an unbalanced and non optimal braking system”. Of course that’s possible, I suppose, but is it likely on this car? If so, what specific mechanism could result in this outcome? If you do not know of a specific mechanism, you’re just pissing in the wind. Maybe going to better quality pads could cause the ABS system to fail. But there’s simply no evidence that this is the case…

The ‘classic’ Prius has small brakes for its mass – at the front they’re much the same as the lighter current model Corolla, while as indicated earlier, on some models they’re small drums at the rear, versus the rear discs used on the Corolla. So in the Prius we have a heavier car with brakes inferior to a car not regarded as having anything particularly good in brakes. (Cross-reference that with the bigger brakes fitted to the local Corolla Sportivo.) And while the Prius in standard form ABS’s to a halt very well, as you’d expect with that hardware, in prolonged, strong braking, the brakes feel lousy. (But I guess if you’ve never driven anything with good brakes, you wouldn’t know. Perhaps that’s part of the problem.)

The handling of the first model is also quite poor – mushy understeer with an unresponsive, dull chassis.

However, both the handling and the brakes are easily upgraded to a competent standard. In my case not only have I fitted rear discs but I have also gone to high performance slotted RDA discs all-round, EBC Kevlar pads and Castrol Response brake fluid. And, just as you’d expect, the braking is now light-years ahead of standard. That doesn’t make it an Evo Lancer, but at least it’s now pretty good.

The handling has been tackled with a front camber kit and a custom-made rear sway bar. Again, now it’s at least competent.

It seems to me that those who suggest mods shouldn’t be carried out do so for two reasons. The first is one that I come across all the time, especially after writing new car tests. It can best be summarised by: how dare you suggest that the car I have bought is anything less than perfect? The second reason is simple ignorance: if you don’t understand how something works, changes to it are feared.

And this sort of perspective is not confined to Prius circles: watch out for those who would denigrate the mods you’d like to make. I’d forgotten people like that exist… but they are out there, waiting to scoff and scorn…