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IanP66

Joined:

Oct 09

Posts: 7

IanP66 says:

What does restricted to 25kW really mean?

 

Most motorcycle manufacturers quote their power figures at the engine and not what the bike actually produces on the road.

 

Question: Which power measurement does the law refer to?

 

I have heard so many people casually say they've had their bike "dyno'd" and have got a print-out to confirm '33bhp', so they think they're legal. But 33 hp at the wheel is a good bit more at the crank... For what it's worth, I contacted FI International - the 'sole UK distributor for approved restrictor kits' - and I was told that their kits are certified to restrict power to 25kW/33bhp at the crankshaft.

 

I've heard most of the 'informed opinion' and 'my mate said' sort of answers - and I've had conflicting verbal advice from DVLA, insurance companies, local traffic police and bike shops. There's an awful lot of disinformation and obfuscation - and downright old cobblers -  on this subject and I think people - particularly new riders and the 'average Joe' who has no intention of flouting the law - should not be misled into being found at fault - and uninsured - if things go wrong. 

 

 

 

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  • Posted 5 years ago (29 May 2010 11:00)

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BBCTom

Joined:

Apr 09

Posts: 73

BBCTom says:

33bhp

I have always understood that the 33bhp (25kw) restriction was measured at the rear wheel and not at the crank.

If the power is restricted at the crank, then the rwhp will be lower than 33bhp anyway, so it wouldn't be anything to worry about.

I am certain that the bike must be less than 33bhp at the rear wheel though :)

However, the bike must NOT weigh any less than 156.25kg in order to achieve a power to weight ratio of no more than 0.16 kW/kg.

Hope this helps matey
:smile

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IanP66

Joined:

Oct 09

Posts: 7

IanP66 says:

What does restricted to 25kW really mean?

It makes sense to specify a power limit that can be easily checked - ie on a rolling road. It's not the folk who have 33bhp at the crank I'm worried about - it's the ones with 33bhp at the rear wheel. 

Thanks mate, but yours is still a 'my mate said' answer!

I still can't find anything in writing that clearly states what the law means.

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Andyvfr1

Joined:

Apr 10

Posts: 245

Andyvfr1 says:

Such a stupid law.

Worst bit of vague arse legislation ever, the best bit is im yet to meet a copper who knows anything about this law either. Id imagine they test it at the wheel, since it would be awkward to get a crank measurement.

 

Fi international would restrict it at the crank as then they are guaranteed to produce less than 33bhp at the wheel, they could not make a restrictor set for 33bhp at the wheel as each bike would get more or less more to the road depending on the state of it, if the engine can not produce more than 33bhp, there is no way 33bhp is getting to the wheel.

The thing is no policeman ive spoke to know anything about it, ive heard all sorts of tripe from the certificate is legally required to having to have markings on the bike to having "anti tamper" screws to show the bike hasnt been opened up and had the restrictors taken out, tbh mate, the only way they can check is to take your bike off you and dyno it, that will give a rwhp measurement, and to seize your bike they need a bloody good reason, e.g you did 150 bazillion mph or the insurance company wants to look it over before paying out because you crashed. If they seize it just because they dont like the look of you, you have a big tantrum, rant and rave and make a tonne of complaints because the policeman who took it off you genuinely had no reason to take the bike off you, infact hes not even allowed to pull you over unless your doing something illegal.

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BBCTom

Joined:

Apr 09

Posts: 73

BBCTom says:

Just measure it at the rear wheel...?

Power of the engine and power at the crank are irrelevant - the power at the rear wheel is what matters.

Of all the people I've known with restrictions on their bikes have all had 33rwbhp, not a 33bhp engine with 15rwbhp :winkie:

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IanP66

Joined:

Oct 09

Posts: 7

IanP66 says:

25kW

I agree - all very sensible, and the law is ambiguous. But 33bhp at the back wheel means FI International's kits aren't doing what they're certified to do. I'm just trying to get to the bottom of all this

I think I'll go for a ride... Is it a Sprint or a Street Triple sort of day?

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AdieR

Joined:

Apr 08

Posts: 3042

AdieR says:

FI international

as I recall a few months back got a public dredging through the media for providing (and charging £80 for) "worthless" 33bhp restriction certificates which had no legal bearing.

Any "certification" only proves that it has been submitted for restriction - if you remove the restriction 2 weeks later the paperwork is worthless.

If a traffic patrol believed it was de-restricted, it'd be dyno'd / rolling road-tested. If the insurance had doubts it'd be examined by an assessor (insurance assessors tend to be pretty clued up; there's not much you'd get past them).

Hope that helps.


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IanP66

Joined:

Oct 09

Posts: 7

IanP66 says:

Be thankful for the confusion

I’ve been doing some more digging, and the bottom line here is if you have a bike which was homologised to European Whole Vehicle Type Approval then virtually any modification from production standard requires a Certificate of Technical Change which attests that the change has not compromised the Type Approval standards on noise and emissions, or performance and handling.

The regulation which specifies the method of measuring the power restriction is EU Directive 95/1/EC.

“ANNEX II SECTION 3. 3.1.1. Accessories to be fitted.

During the test the accessories needed for operation of the engine [...] must be located on the test bench as far as possible in the position they would occupy for the application under consideration.”

This means that the restricted power output is to be measured at the crankshaft.

A simple ‘Dyno’ run printout will only give you power between the rear tyre and the rollers – it can’t tell you what’s available at the crankshaft - and if it comes up as ‘33bhp’ then you’re in the sh1t. And besides, a ‘Dyno’ run can’t provide EC recognised proof that noise, emissions, or riding characteristics have not been adversely affected and therefore that Type Approval will remain in effect. But don’t worry, because this is such a mess of disconnected legislation that nobody who is in a position to make life difficult for you seems to have a f-ckin’ clue. Just be thankful for all the confusion out there.

[This Reply has been modified by the Author]

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djpert1

Joined:

Feb 10

Posts: 469

djpert1 says:

Ok.

So if it is manufactured to restrict the power to 33bhp at the crank, then it will show less than 33 on a rolling road. Does that mean then, as they test on a rolling road dyno, that if I fit an aftermarket can that adds something little like 1hp to the power making it more than 33 at the crank but still less than 33 at the wheel, I should be able to get away with it and stay legal?

Fuck! This is so confusing!!:blink::wacko:

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AdieR

Joined:

Apr 08

Posts: 3042

AdieR says:

logic says

that if it requires 33bhp crank bhp, the manufacturer will have accounted for that when they submit the machine for type approval, and restriction systems will generally be bike/engine specific (I stand corrected if anyone knows better). (How the hell do you test the crank bhp with an engine that is fitted, short of stripping the machine down?)

A dyno run can't prove that noise/emissions/handling haven't been adversely affected: that should be self evident - the manufacturer can only type approve the machine as they've designed and built it (they have no control what happens once the machines are sold).

 Quite apart from anything else, not all insurers are enthusiastic about "restricted" bikes due to people removing the restriction before its due (thus voiding any insurance). Not only that, but 33bhp restriction doesn't necessarily reduce the machines performance to any significant extent.

Your quote "During the test the accessories needed for operation of the engine(...) must be located on the test bench as far as possible in the position they would occupy for the application under consideration..." - that sounds to me the rules that manufacturers have to work round when they submit an application for type approval. What is defined as "accessories needed for operation of the engine"? Exhaust systems? engine management units? cooling systems? Charging systems?

Just a few thoughts.

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