Rolling Radius and SPA dash
Discussion
Hi guys,
Well after 705 hours and 2 and a half years of spare time (with 3 months off recovering from being knocked down on a zebra crossing!!!!), I'm finally getting the dash done. Does anyone know the rolling radius or rolling circumference of the standard factory Kumho Ecsta 335/30/18 rear tyres so I can get the right figure into my SPA dash?
By the way, I have had to extend the ECU loom for the LS engine,if anyone has a similar issue I have an offer that might help posted later!!
Many thanks
Trev
Well after 705 hours and 2 and a half years of spare time (with 3 months off recovering from being knocked down on a zebra crossing!!!!), I'm finally getting the dash done. Does anyone know the rolling radius or rolling circumference of the standard factory Kumho Ecsta 335/30/18 rear tyres so I can get the right figure into my SPA dash?
By the way, I have had to extend the ECU loom for the LS engine,if anyone has a similar issue I have an offer that might help posted later!!
Many thanks
Trev
Hi Trev..... good to hear you're on the mend and back working on the car, that sounds like a nasty accident 
Impressive that you've kept track of your hrs, I decided early on that I'd not try to keep track of time spent on my build incase it upset me, LOL!!
Anyway, I have an XL spreadsheet for my Dash2 config and that tells me that the rollingradius circumference of the rear Ecstas is 2067mm. I'm not sure where I got that from, so hopefully someone will confirm it before I set you off on the wrong path!!
ETA
Impressive that you've kept track of your hrs, I decided early on that I'd not try to keep track of time spent on my build incase it upset me, LOL!!
Anyway, I have an XL spreadsheet for my Dash2 config and that tells me that the rolling
ETA
Edited by 356Speedster on Wednesday 20th March 09:50
Inflate the tyres to the correct pressure. Use chalk to mark the sidewall of the tyre, near the ground and continue the mark down to the ground too. Get someone to drive across a flat surface for ten revolutions. Count them. Measure the distance with one of those big measuring tapes. Divide the number by ten for a reasonable estimation of rolling circumference, get from rolling circumference to rolling radius by diving by 6.283, which is two Pi.
Do for front and rear.
Check your calibration with GPS, if it's wrong, then adjust to suit. Tyre rolling radius barely changes with tyre wear, but does vary between tyre makes.
Do for front and rear.
Check your calibration with GPS, if it's wrong, then adjust to suit. Tyre rolling radius barely changes with tyre wear, but does vary between tyre makes.
356Speedster said:
Hi Trev..... good to hear you're on the mend and back working on the car, that sounds like a nasty accident
Impressive that you've kept track of your hrs, I decided early on that I'd not try to keep track of time spent on my build incase it upset me, LOL!!
Anyway, I have an XL spreadsheet for my Dash2 config and that tells me that the rolling radius of the rear Ecstas is 2067mm. I'm not sure where I got that from, so hopefully someone will confirm it before I set you off on the wrong path!!
2067 mm is probably the rolling circumference.Impressive that you've kept track of your hrs, I decided early on that I'd not try to keep track of time spent on my build incase it upset me, LOL!!
Anyway, I have an XL spreadsheet for my Dash2 config and that tells me that the rolling radius of the rear Ecstas is 2067mm. I'm not sure where I got that from, so hopefully someone will confirm it before I set you off on the wrong path!!
Hi both,
I agree that 2067mm is probably the rolling circumference!!!! Otherwise I'll have 12 foot high wheels, but it sounds about right so thanks for that 356, much appreciated, let's see if others have the same figure. Thanks also for the thoughts, brain injury took 13 months to go away!! @ Kawa, I know exactly how to do it BUT that car's not registered and I don't want to fail the SVA because I've guessed a figure. The SVA manual says that The speedo can read 35mph and the minimum speed that the car is actaully doing can be no lower than 26mph, so I'll probably add 5% onto 2067 to be on the safe side, and yes that is the right way around
Thanks again
Trev
I agree that 2067mm is probably the rolling circumference!!!! Otherwise I'll have 12 foot high wheels, but it sounds about right so thanks for that 356, much appreciated, let's see if others have the same figure. Thanks also for the thoughts, brain injury took 13 months to go away!! @ Kawa, I know exactly how to do it BUT that car's not registered and I don't want to fail the SVA because I've guessed a figure. The SVA manual says that The speedo can read 35mph and the minimum speed that the car is actaully doing can be no lower than 26mph, so I'll probably add 5% onto 2067 to be on the safe side, and yes that is the right way around
Thanks again
Trev
TrevC said:
Hi both,
I agree that 2067mm is probably the rolling circumference!!!! Otherwise I'll have 12 foot high wheels, but it sounds about right so thanks for that 356, much appreciated, let's see if others have the same figure. Thanks also for the thoughts, brain injury took 13 months to go away!! @ Kawa, I know exactly how to do it BUT that car's not registered and I don't want to fail the SVA because I've guessed a figure. The SVA manual says that The speedo can read 35mph and the minimum speed that the car is actaully doing can be no lower than 26mph, so I'll probably add 5% onto 2067 to be on the safe side, and yes that is the right way around
Thanks again
Trev
OK, but you wouldn't have guessed the figure, you would have measured it!I agree that 2067mm is probably the rolling circumference!!!! Otherwise I'll have 12 foot high wheels, but it sounds about right so thanks for that 356, much appreciated, let's see if others have the same figure. Thanks also for the thoughts, brain injury took 13 months to go away!! @ Kawa, I know exactly how to do it BUT that car's not registered and I don't want to fail the SVA because I've guessed a figure. The SVA manual says that The speedo can read 35mph and the minimum speed that the car is actaully doing can be no lower than 26mph, so I'll probably add 5% onto 2067 to be on the safe side, and yes that is the right way around
Thanks again
Trev
Good luck with your SVA, you lucky baaastard!
Hi again,
I would have measured it I guess, but a figure from a dash that works is cool. I'll need good luck with the SVA, I've got a hot cam LS376 and it's the proverbial b*****d to get through emissions Im told. As a back up in case I fail, even with a soft remap, I've got a Honda bike air injection pump that I can plumb into the second cat take off, just to be sure
Rgds and thanks again
Trev
I would have measured it I guess, but a figure from a dash that works is cool. I'll need good luck with the SVA, I've got a hot cam LS376 and it's the proverbial b*****d to get through emissions Im told. As a back up in case I fail, even with a soft remap, I've got a Honda bike air injection pump that I can plumb into the second cat take off, just to be sure
Rgds and thanks again
Trev
TrevC said:
.....I'll need good luck with the SVA, I've got a hot cam LS376 and it's the proverbial b*****d to get through emissions Im told. As a back up in case I fail, even with a soft remap, I've got a Honda bike air injection pump that I can plumb into the second cat take off, just to be sure ...
What do you believe will change with the extra air?...I have another car which has been mapped spot on lambda 1 but the co and HC are off the scale and I can't find any guidance on what I can do to fix it.
Steve
Steve_D said:
What do you believe will change with the extra air?
I have another car which has been mapped spot on lambda 1 but the co and HC are off the scale and I can't find any guidance on what I can do to fix it.
Steve
It's a long shot, and some of my long shots work and some don't but all of them get shot down in flames so I just soldier on regardless and see if it works. The HC and CO figures are ppm (parts per million) figures, and all the residual exhaust air comes from the engine, so if you inject the same volume of fresh air that the engine chucks out it halves the ppm figures. It makes logical and mathematical sense,if it works in practice we'll seeI have another car which has been mapped spot on lambda 1 but the co and HC are off the scale and I can't find any guidance on what I can do to fix it.
Steve
Trev
Sorry,
Half a story again, and I'm bound to get the questions so here's the answers, well mine anyway, if they're wrong please put me right. A 6.2L V8 produces 130litres/sec of exhaust at 2500 rpm, so the pump would need to make a difference to that. The pumps (a mate can lend me) have 8 chambers that are roughly (very) say 10cc each, and the motor goes at 3500rpm, so that's almost 5litres/sec, so two of those should reduce the HC and CO by around 10% ish.
Not much but I'm told the engine's borderline, so I might not need any.
Hope this helps
Trev
Half a story again, and I'm bound to get the questions so here's the answers, well mine anyway, if they're wrong please put me right. A 6.2L V8 produces 130litres/sec of exhaust at 2500 rpm, so the pump would need to make a difference to that. The pumps (a mate can lend me) have 8 chambers that are roughly (very) say 10cc each, and the motor goes at 3500rpm, so that's almost 5litres/sec, so two of those should reduce the HC and CO by around 10% ish.
Not much but I'm told the engine's borderline, so I might not need any.
Hope this helps
Trev
Edited by TrevC on Wednesday 20th March 15:44
TrevC said:
Steve_D said:
What do you believe will change with the extra air?
I have another car which has been mapped spot on lambda 1 but the co and HC are off the scale and I can't find any guidance on what I can do to fix it.
Steve
It's a long shot, and some of my long shots work and some don't but all of them get shot down in flames so I just soldier on regardless and see if it works. The HC and CO figures are ppm (parts per million) figures, and all the residual exhaust air comes from the engine, so if you inject the same volume of fresh air that the engine chucks out it halves the ppm figures. It makes logical and mathematical sense,if it works in practice we'll seeI have another car which has been mapped spot on lambda 1 but the co and HC are off the scale and I can't find any guidance on what I can do to fix it.
Steve
Trev
TrevC said:
As a back up in case I fail, even with a soft remap, I've got a Honda bike air injection pump that I can plumb into the second cat take off, just to be sure
Which is what Porsche did with the 911sc, to get through US emissions testing, if I recall (use an air pump, that is, not a Honda bike one!).Best of luck with the test!
Pedders said:
Which is what Porsche did with the 911sc, to get through US emissions testing, if I recall (use an air pump, that is, not a Honda bike one!).
Best of luck with the test!
Hey Pedders,they did, but I got the idea from a 1995 RS2000 that I had and that injected high pressure air from a belt driven pump directly into the exhaust manifold. Let's wait and see Best of luck with the test!
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