Rolling Roads

Article by: Tim Lamont

The Rolling road plays a very important part in the tuning business, they provide a safe reliable method of tuning, more commonly used for hi-performance cars such as TVR’s. I would happily recommend there use to anybody, but be prepared for disappointment as most people believe that there cars are more powerful than they really are.

TVR Griffith ready to be tuned		Rolling road assembly

The problem arises from manufacturers providing power figures from bench dyno’s on which engines run with no ancillaries, this does not only apply to TVR, I’m talking of many different manufacturers. Remember that it is the torque curve that is important not the peak figure.

Safety strap		Tuning / diagnostic setup

I have listed below a few common questions and have also included one or two useful tips:-

Q. Why are Rolling roads better than a normal diagnostic machine ?
A. Because the car is effectively being driven under load, it gives a more thorough assessment of fuelling requirements of the car.

Q. Will it damage my car ?
A. Cars are very rarely damaged and its safe to assume that if anything did break, a weakness was there in the first place.

Q. Will my engine be over-revved ?
A. No, the procedure is to take the engine to peak power plus 200-500 rpm, this will give a full picture of the power curve. for example a TVR Rover engine normally makes peak power at around 5500 rpm and its normally safe to rev to 6200.

Q. How accurate are rolling roads ?
A. In theory they should be fairly accurate as they will calculate for atmospheric conditions as well as transmission losses, but there will be variation from one rolling road to the next, but you will get a consistent torque curve/ shape, wheel figures tend to be more reliable.

Q. How much will it cost me ?
A. Most will charge about £50-80 per hour+ about £40 per hour for any second / specialist technicians, the average is 1-2 hours per vehicle.

Useful tips

• Make sure the car has plenty of fuel in the tank.

• Increase tyre pressure by 10-15% as for motorway use (most TVR’s have 24psi in which case increase to around 27psi.

• Fit new spark plugs and make sure that all other electrical components are in good condition and preferably eliminate any misfire or any other electrical problem - dyno time is more expensive than normal garage rates.

• Check that oil and coolant levels are correct.

• Allow plenty of time as each car may take 1-2 hrs its not unusual to spend a full day at a rolling road.

There are limitations however, for cars producing over 250bhp at the wheels it will be very difficult to maintain traction and get a "true figure, this does not apply to Rover powered TVR’s unless heavily modified.

As a guide, a well prepared stage 3, 4.6L Rover engine will produce something like 280bhp on a bench Dyno about 260bhp at the flywheel on a rolling road and about 210 at the wheels.

These are only a guide however.

Thanks to Tim Lamont from Act Performance Products for submitting this article.