Rolling road

[MR WEBER]

Hello! I am planing to build a rolling road, I am going to use it for car with 200-230 hp. I already got rolls that is 70 cm long and 19 cm in diameters. Is that going to work with the car or is the tire going to spin? I dont know the usually size of the rolls... I have a eddy current that i am going to brake it with...

[86rocco]

If you double up the rollers and space them 15-20 cm apart, so that the tire sits on both rollers. Around here the dyno's they use for emissions testing if designed that way with rollers not much more than 19cm

[84-1074663779]

I have wondered about this too.

It seems that some of the big differences between power figures measured on different chassis dynos might have a lot to do with how efficiently the power is coupled between the tyres and the rollers. If all you want to do is place some different controlled loads on the engine for tuning purposes, then it does not really matter where the power actually goes.

On the other hand, if you need to very accurately measure tractive horsepower, that is a very different requirement. The rollers need to be as large as possible and have a non slip surface. Some nice wide sticky slicks might help too.

Wedging the tyres between two small rollers, or adding massive extra weight, is only going to eat up power deforming the tyres so they will not slip. For most accurate power measurement a hub dyno is going to be more consistently reliable, but that might not be so convenient to use.

I suppose it comes down to what you really expect from your chassis dyno.

[MR WEBER]

I have four rolls, two too each tire. I am going to search for as much hp as possible, is this gonig to work? What is the usual size of the rolls?

[MikeyFIN]

My Sun RoadamaticXI has twin rollers that are eaxtly 1 meter in circumference (you can count out the diameter) and they happen to be on the larger side of those used in Eddy current types. (you definitely want them I think at least as big as mine)
The brake is a Telma CC/CA series 135 (1350nM rating) so it should brake a bit.
For my engine dyno I got a Telma that was used in a truck for an emergency brake and it has to provide 85% of the braking power (the rest is with the exhaust brake) in an emergency situation when you operate in the Alps.It has a rating of 3300nM and therefore is sufficient for a 48ton Trailer combination so I think it will suffice ..specially when it only runs about 2600 tops in a truck.
So the braking would be better and more consistent in say 8000rpm... only thing I need is some software done for both of them to get them working with a PC.

Any ideas?