Seems to be quite a few people asking the same Qs about Rolling Roads (RR) and Power Runs (PR) so I thought I'd put together a quick guide. This guide should also be followed if you are planning on getting your car mapped (Unichip, livemap or aftermarket ECU) Feel free to add as long as its on topicINTRODUCTION
We all like to know how much power our car has, how it is running and how 'quick' it is. One of the best ways to do this is by taking it to a Rolling Road. This is basically just a huge treadmill for cars. It normally works by putting the drive wheels (ie front wheels for a coupe) on two pairs of metal rollers (imagine 4 beer kegs on their side and the front wheels sitting on them) and then the car is strapped down so it can't move. There are I believe two main types of RR. The 1st uses inertia ie how fast the rollers spin and the second uses Braking forces on the rollers to measure the power. Both then use lots of trick hardware and calculations to produce torque and bhp figures. You can also get RRs that physically bolt onto the hubs. These aren't as common, but supposedly can be more accurate.
Talking of accurancy, how accurate are RRs? Good question as the simple answer is 'how long is a piece of string?' The most accurate way to measure power is at the engine itself. ie take it out the car and put it on a very fancy dyno that can measure cranking force etc. That way it bypasses transmission loss, wheel tolerances and various other variables. Only problem is that option isn't exactly practical for most of us.
So we are left with standard RRs which can be affected by heat / cooling (esp on a turbo car), how well the rollers are calibrated, the type of rollers, software used, air pressure, size of alloys, tyre pressure and the list goes on and on... I have seen RRs over/under read by between 1% and 30%. 'Misreadings' can be caused by bad calibration, the way the car is being run on the RR and even just the operator wanting to massage egos CHOOSING A RR
This is really down to personal choice. Some people will go to the closest while others will choose the cheapest. Others will go on personal recommendation. I would speak to your mates, read the forums and then pick up the phone. Speak to the guys and ask questions that are important to you.
I would start by saying I've got a Fiat Coupe and see how they react. You can tell straight away if they know the cars and have run them before. This has the advantage of knowing what to look for and they can often compare your graphs to other coupes run on the same RR.
The next Q I would ask is what BHP can it handle? Maybe not an issue for a standard 20vt, but some RRs only go up to say 300bhp.
Then cost. Prices can range from £30 to £200 an hour. Ask what you get for your money. Is it just a power run or is it a full hour? What sensors do they use? Do they check fueling? Do they read boost? Do they give you a nice print out and what does it show? (Some RRs only give an at the wheels figure, some only fly and some both) How do they run the car? ie is it staged, is it ragged to death etc? Oh, and ask if its plastic or cash
Theres loads more detail I could go into but thats the basics.PREPARING THE CAR
So you have made your choice and booked it in. 1st thing is to check your oil and water (a sensible RR will double check, but no point looking like an idiot) is topped up. If you haven't done your oil / plugs for a while - think about a change before hand. Also check your tyre pressures and think if the wheel alignment is ok. I've seen a number of cars told they can't run because the tracking is way out. Also fill up your fuel tank with the fuel you use day to day. If you use supermarket 95ron stick to it. No point puting in Ultimate for one day (giving false readings) if you aren't going to keep to it. Same goes with octane boosters. Also dig out your towing eye if you can. It helps strapping the car down. Your clutch should also be in good condition, there is little or no point in RR'ing a car with the clutch slipping - it will only get worse. The more information you can tell the operator about your car spec the better, similarly ask questions - this may trigger some information which will help the RR guys.
If your car is very uprated then it might be an idea to take along an uprated Fuel pressure regulator. If your injectors are maxxed out then a bit more fuel pressure will add just that little extra fuel.
Keep copies of your RR graphs. They will come in handy when comparing runs. Tell the operator what has changed since the last RR and it might help in the mapping.
Make sure your car is in good general health. Before any modifications its worth carrying out a compression test and inspection of the engines condition. Loud knocking, screeching belts, overheating or lots of smoke are not advisable.
Above all if you are not mechanically minded then get someone else to check it over.
WHAT TO EXPECT
When you get there, introduce yourself and answer any Qs they ask honestly. No point going 'yeah its got this, its got that when its bog standard'. If you think there is something up with the car tell them about it. That way they can use their knowledge and data from the rollers to pin point the problem. The operator will strap the car down and calibrate everything. Some will let you get stuck in with them while others prefer you to watch from a safe distance.
Be prepared to be cold around the fans etc and remember it will be LOUD. When the operator is happy they will warm your car up and begin to run it. Depending how the RR works they may increase the revs in stages or just floor it. Most will lift off as soon as they see power drop. If you have a boost controller etc they will offer to adjust it for you to improve the performance. Up to you if you want them to or not. Usually they will manage 3 or 4 proper runs in an hour which is more than enough.WHY RR?
The RR is a great way of checking fueling, power, seeing how the boost comes in and getting advice about how to make your car 'better'. The RR guys will have a lot of experience of different cars and will tell you the pros + cons of exhausts, turbos, FMICs etc. Take it with a pinch of salt, but normally they aren't too far from the money.WHAT NEXT?
Post up your graph so we can see! Remember its not all about peak power. A car with a larger area under the line (ie a larger power band) could be just as quick if not quicker than a car with huge peak power. If the graph shows it, look how the boost builds. Could you improve on the lag etc?
If you do some more mods to your car or get a fault fixed, go back to the SAME RR for another PR. That way you have back to back graphs that will be good to compare. If your car is in the same tune, you could also try a different RR and see how the figures compare. Remember different boost will give different results so ideally you want to keep all the variables the same.RR DAYS
This is the cheapest and probably the most fun way to get a simple power reading. Usually costing between £10 and £40 depending on the number of cars and the deal agreed. Make sure you do the oil etc checks 1st as the operators run it like a production line, doing each car as quick as possible (within reason). You will normally get a graph for your money and some 'operators comments' ie 'good power', 'its [cloud9]', 'get a bigger exhaust', 'its lean at the top end' etc. The real beauty of RR days is you get to see other cars and compare graphs. For example if somebody says they have a 400bhp monster, have a look and see what it makes on the day. Then compare to your standard 20vt and laugh as you make 230@fly and they only make 300... If theres a skyline or supra, stand back in awe when it makes 700bhp. You get the drift
Remember it doesn't have to be a Fiat or Coupe day. Have a look on the local car forums and PM the organisors and tell them what you have. Most folk love to see different types and specs of car, esp if they have 200bhp+! Just make you turn up if you say you will. Having too many cars can be as bad as not having the numbers expected.