rolling road rejection, twice!!

[Andy70]

I had my 335i N54 booked to go on a rolling road for a custom remap a while ago and the tuner didn't proceed as there were several error codes that he wouldn't recommend I continue as the ECU could have been damaged. So he contacted a mate that worked for BMW in Germany and provided him with software upgrades hat should sort it... So second go I went back, this time he got the car on the rolling road ready to go and I noticed he was feathering the throttle and to my disappointment he told me he couldn't continue as the car was loosing traction at around 298bhp. firstly he said the tyres my not be any good ( but they are almost new pilot sports I bought as was recommended on here for best grip) so he said the suspension could be at fault, a dodgy bush or something. So I booked it into Mill Lane, a reputable garage near me to diagnose any issues and all they could come up with was a leaky shock so they replaced the pair at a cost of nearly 400 quid, a bit of a st as I do shocks myself normally, but never mind!!

Any way, would a leaky shock be enough to cause a car to loose traction on a rolling road?? I appreciate that suspension is massively important on the road, but when the car is stationary???? Any way he said there was another 100bhp to go as I have decent mods and a tuning chip which I wanted him to remove. The point is I got decats to put on the car now and suspect that the car car handle the power it has got, without shelling money for now on an LSD am I screwed? So gutted for now. would going up a tyre size help on the back, 265's for example?

[anonymous-user]

ECU fault codes? Leaky shock absorbers? I’d spend the money getting the car to pass an MOT. Understandably he doesn’t want to try and tune a sick car, spilling oil all over his rollers.

[Andy70]

He said the car was probably going to reach 400bhp looking at the curve on the graph butvthatbwas where it was slipping. The car has just had the shocks done yesterday. I just found it hard to believe a shock would cause that. Can't remember the faults now. However like I said he had an upgrade for it so that should be sorted too. So far shouldn't be poorly now

[mickyh7]

Clutch?

[Andy70]

mickyh7 said:

Clutch?

Brand new

[Andy70]

anonymous said:

[redacted]

I shouldn't have to. He wasn't mapping it to 298. If you read the post that's when it was breaking traction I know the car has over 300 standard. In fact with the tuning box it's closer to 400. All the more confusing. The car wasn't coping with less than standard and I was curious if a dodgy shock would be enough

[Das speck]

Yes. If a shock is faulty it will upset the car on the rollers as the power is increased.

It’s because the geometry changes as the suspension compresses on 1 side more than the other and that “could” pull it off the rollers as the thrust angle of the axle changes.

[Andy70]

Das speck said:

Yes. If a shock is faulty it will upset the car on the rollers as the power is increased.

It’s because the geometry changes as the suspension compresses on 1 side more than the other and that “could” pull it off the rollers as the thrust angle of the axle changes.

Brilliant that's good news at least thanks

[Andy70]

anonymous said:

[redacted]

It's a JB4 and they are supposed to be quite good aren't they? I inherited that when I bought the car. I'll sell it as soon as it comes out

[mat205125]

anonymous said:

[redacted]

Maybe the 298 is a wheels number, rather than a crank calculation

As they say, measuring crank bhp is like measuring your cock from behind the balls

[Andy70]

mat205125 said:

Maybe the 298 is a wheels number, rather than a crank calculation

As they say, measuring crank bhp is like measuring your cock from behind the balls

Whatever, there was more power there, that's just where it started slipping, it would be interesting to know the torque at that point

[mickyh7]

mat205125 said:

Maybe the 298 is a wheels number, rather than a crank calculation

As they say, measuring crank bhp is like measuring your cock from behind the balls

Bugger!

[Andy70]

mickyh7 said:

mat205125 said:

Maybe the 298 is a wheels number, rather than a crank calculation

As they say, measuring crank bhp is like measuring your cock from behind the balls

Bugger!

Yeah !!!

[mmm-five]

mat205125 said:

Maybe the 298 is a wheels number, rather than a crank calculation

As they say, measuring crank bhp is like measuring your cock from behind the balls

I measure my cock by cranks per hour, or if I'm bored stroke x bore

[Andy70]

Ok, so hopefully my new shocks should solve the rolling road issue, but if i did need a tad more grip, what size tyres would give me the same rolling rotation on the back to keep the outside diameter the same? I have 255-30-19, so would 265-35-19 be an equivalent? tyre sizes confuse me, I know the side wall is a percentage of the width, but believe it or not a tyre fitter couldn't tell me, to me that's like a footballer not knowing what a football was????... Yes I know the best option would be an LSD but as I live miles away from Birds and struggling for free time, for now that is not an option

[Huskyman]

Simple google brought up this https://www.tyresizecalculator.com/tyre-wheel-calc...

Put in your sizes and go from there, you want to keep the rolling radius similar, a new set of dampers on the rear will improve traction no end.

[320d is all you need]

mat205125 said:

anonymous said:

[redacted]

Maybe the 298 is a wheels number, rather than a crank calculation

As they say, measuring crank bhp is like measuring your cock from behind the balls

My view on WHP/Flywheel is that in either case it's an estimation.

I generally find WHP to be a way of making a car sound like it has more power than it actually does.
You can still go to multiple dynamometers which measure WHP and still get very different results.

"Well it does 300WHP" - Okay, great??

Usually WHP is used by Americans. America has very wildly optimistic dynos and performance times show this when a European car with 700 HP measured at the Flywheel posts faster times than a 700 "WHP" car (the same car) from the USA

[Andy70]

Huskyman said:

Simple google brought up this https://www.tyresizecalculator.com/tyre-wheel-calc...

Put in your sizes and go from there, you want to keep the rolling radius similar, a new set of dampers on the rear will improve traction no end.

Fantastic thanks

[mmm-five]

320d is all you need said:

Usually WHP is used by Americans. America has very wildly optimistic dynos and performance times show this when a European car with 700 HP measured at the Flywheel posts faster times than a 700 "WHP" car (the same car) from the USA

But I bet none of those were actually 'measured at the flywheel' - they were all calculated from WHP with 'assumed' drivetrain losses.

Any flywheel is only good for measuring the same car, on the same rollers, in the same conditions, to see how specific modifications have changed the power curve.

Using them to compare your car, to your mates car, with results from different dynos, at different temperatures, strapped down differently, with a dodgy operator, is a fool's errand.

[anonymous-user]

320d is all you need said:

My view on WHP/Flywheel is that in either case it's an estimation.

I generally find WHP to be a way of making a car sound like it has more power than it actually does.
You can still go to multiple dynamometers which measure WHP and still get very different results.

"Well it does 300WHP" - Okay, great??

Usually WHP is used by Americans. America has very wildly optimistic dynos and performance times show this when a European car with 700 HP measured at the Flywheel posts faster times than a 700 "WHP" car (the same car) from the USA

All dynos measure whp then estimate fwhp. So whp is more accurate. Only way to measure fwhp is to remove the engine from the car and put it on an engine dyno.