Is SRM affected by changing rolling radius?

gumpy · 05-19-2010, 08:35 AM

Question to all those who changed the rolling radius of their z's tyres, did it affect your SRM operation? I'm pretty sure it'd be ok but would like to make sure.

thanks

Jeffblue · 05-19-2010, 08:42 AM

i dont think it should, it bases its calculations on drivetrain speed and engine speed. if your wheels are slightly smaller or larger rolling diameter, then that will affect the speed of your drivetrain, and srm would still rev match to that speed. as far as i know, the only thing changing your rolling radius would change is the readout on your speedometer. since SRM doesn't care what the number on your speedometer reads, i don't think it will make a difference.

ChrisSlicks · 05-19-2010, 09:37 AM

SRM is unaffected by any gearing change past the output shaft of the gearbox. You can change rear-end gears or tire diameters and it will still work.

VDC is affected by tire diameter change if the front and rear diameters (and hence revolution speed) are dissimilar by more than a certain margin.

bullitt5897 · 05-19-2010, 10:40 AM

Like others have said... NO, your all good.

gumpy · 05-19-2010, 06:50 PM

Quote:

Originally Posted by ChrisSlicks

SRM is unaffected by any gearing change past the output shaft of the gearbox. You can change rear-end gears or tire diameters and it will still work.

VDC is affected by tire diameter change if the front and rear diameters (and hence revolution speed) are dissimilar by more than a certain margin.

Damn good point about the vdc... i didn't consider that...

ChrisSlicks · 05-19-2010, 08:19 PM

Quote:

Originally Posted by gumpy

Damn good point about the vdc... i didn't consider that...

As long as you are even front to rear I don't think it matters what size they are overall other than for speedometer error.

gumpy · 05-19-2010, 10:43 PM

Quote:

Originally Posted by ChrisSlicks

As long as you are even front to rear I don't think it matters what size they are overall other than for speedometer error.

My speedo is off anyway, when i do 100kph the actual speed is 93. Increasing the RR will actually make it more accurate.

Nikon FM · 05-20-2010, 12:58 AM

Quote:

Originally Posted by ChrisSlicks

SRM is unaffected by any gearing change past the output shaft of the gearbox. You can change rear-end gears or tire diameters and it will still work.

VDC is affected by tire diameter change if the front and rear diameters (and hence revolution speed) are dissimilar by more than a certain margin.

Comparing front to rear diameter ratios OEM=1.01 (Bridgestone 245/40 275/35)

I changed to 1.00 for daily driving. (Hankook V12 255/35 295/30)

My track set is .98 but still good. (Toyo R888 265/30 295/30)

No SRM or VDC issues.

05-19-2010, 08:35 AM	#1 (permalink)
gumpy Enthusiast Member Join Date: Oct 2009 Location: Sydney Posts: 449 Drives: 09 370z white manual Rep Power: 16	Is SRM affected by changing rolling radius? Question to all those who changed the rolling radius of their z's tyres, did it affect your SRM operation? I'm pretty sure it'd be ok but would like to make sure. thanks

05-19-2010, 09:37 AM	#3 (permalink)
ChrisSlicks A True Z Fanatic Join Date: Mar 2009 Location: North East Posts: 6,203 Drives: 09 370Z Sport M6 Rep Power: 653	SRM is unaffected by any gearing change past the output shaft of the gearbox. You can change rear-end gears or tire diameters and it will still work. VDC is affected by tire diameter change if the front and rear diameters (and hence revolution speed) are dissimilar by more than a certain margin. __________________ Hotchkis ARB \| Stillen CAI \| Art Pipes \| Berk CBE \| Stillen AP Racing Brakes \| AE Performance Oil Cooler \| BC Racing ER Coilovers \| Doran Control Arms

05-19-2010, 10:40 AM	#4 (permalink)
bullitt5897 Premium Member Join Date: Jan 2009 Location: North GA Posts: 6,831 Drives: Twin Turbo Z34 Rep Power: 3682	Like others have said... NO, your all good. __________________ *Shop Cars: 2013 318whp Nismo VspecII 370z SOLD, 2009 1000hp+ 93oct 4.0L TT 370z Fast Intentions STAGE 4 #054*

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05-19-2010, 08:42 AM	#2 (permalink)
Jeffblue A True Z Fanatic Join Date: Dec 2009 Location: NY Age: 36 Posts: 9,192 Drives: Z32TT & 335xi Coupe Rep Power: 38	i dont think it should, it bases its calculations on drivetrain speed and engine speed. if your wheels are slightly smaller or larger rolling diameter, then that will affect the speed of your drivetrain, and srm would still rev match to that speed. as far as i know, the only thing changing your rolling radius would change is the readout on your speedometer. since SRM doesn't care what the number on your speedometer reads, i don't think it will make a difference.