RUF Wheels
09-13-2006, 06:23 AM
#3
Instructor
Thread Starter
RUF WHEELS and TYRE pressures
Steve
I should have said I have I'm running Pilot Sports 235/35 and 295/35 and had a typo moment on pressures and they are set at 36/40.
Have you rolled your wheel arches at the rear or are you using smaller spacers as mine touch at the rear over a 'sharp' speed bumps!?
I should have said I have I'm running Pilot Sports 235/35 and 295/35 and had a typo moment on pressures and they are set at 36/40.
Have you rolled your wheel arches at the rear or are you using smaller spacers as mine touch at the rear over a 'sharp' speed bumps!?
09-13-2006, 12:06 PM
#4
Nordschleife Master
Gordon,
I hope you mistyped again... 235/35 and 295/35 would NOT have anywhere near the same rolling diameter, and would kill your viscous coupler.
While each brand of tire has their own idea of size, my 305x25 pirellis are not even close to touching. I have the standard Ruf spacer of ~26mm. Next time I will need tires, I will use a 315x25... the wheels are plenty wide enuff to support them.
When I got the car, it had the same type of pirellis on it, but in a 295x30 size. This tire is about an inch taller than the 305x25 I am now using. I did find that this tire could actually touch the very front part of the rear bumper... on the inside edge of the bumper... if that makes sense.
Take another look at your tire sizes!
I hope you mistyped again... 235/35 and 295/35 would NOT have anywhere near the same rolling diameter, and would kill your viscous coupler.
While each brand of tire has their own idea of size, my 305x25 pirellis are not even close to touching. I have the standard Ruf spacer of ~26mm. Next time I will need tires, I will use a 315x25... the wheels are plenty wide enuff to support them.
When I got the car, it had the same type of pirellis on it, but in a 295x30 size. This tire is about an inch taller than the 305x25 I am now using. I did find that this tire could actually touch the very front part of the rear bumper... on the inside edge of the bumper... if that makes sense.
Take another look at your tire sizes!
09-27-2006, 07:23 PM
#5
Instructor
Thread Starter
Steve
Checked the tyre sizes and thats what they are, can you explain the problems this will create withe the viscous coupler please.
Many thanks
Gordon
Checked the tyre sizes and thats what they are, can you explain the problems this will create withe the viscous coupler please.
Many thanks
Gordon
09-27-2006, 07:44 PM
#7
Nordschleife Master
Gordon,
I just looked your tires up on www.Tirerack.com , and didn't see a michlein in the size 295x35x19. But they do have a 285x35x19 listed, so using that as an example, here's the problem:
235x35x19 has a diameter of 25.5" this works out to 817 revs per mile
285x35x19 has a diameter of 26.9", which is 774 revs per mile... a 295x35x19 will be even taller than this, and will by turning even fewer revs per mile.
Your viscous coupler (and your ABS, btw) wants to have the tires turning at about the same rate... some say that 5% is allowable... you are right on that edge. I think that 5% difference is huge, and may cause your viscous coupler to either not work fast enough when you need it, or quickly wear it out. In addition, the ABS certainly doesn't like big differences like this. Exact specs and tolerances are not known by me, but I would check this out pronto. Viscous couplers are expensive.
On my car, my rears are turning a tiny bit faster than the fronts... within a couple of revs per mile. This should keep the fluid warm (for instant use in wheel spin), but not overheat it. I will say that I've never successfully gotten any real data on what the optimum size ratios are, but intuitively, I think my sizes are perfect. In addition, my sizes are almost the exact same size (diameter and thus the revs/mile) as the original, stock 18" tires.
If you get any different data, please post back... I'm all ears.
I just looked your tires up on www.Tirerack.com , and didn't see a michlein in the size 295x35x19. But they do have a 285x35x19 listed, so using that as an example, here's the problem:
235x35x19 has a diameter of 25.5" this works out to 817 revs per mile
285x35x19 has a diameter of 26.9", which is 774 revs per mile... a 295x35x19 will be even taller than this, and will by turning even fewer revs per mile.
Your viscous coupler (and your ABS, btw) wants to have the tires turning at about the same rate... some say that 5% is allowable... you are right on that edge. I think that 5% difference is huge, and may cause your viscous coupler to either not work fast enough when you need it, or quickly wear it out. In addition, the ABS certainly doesn't like big differences like this. Exact specs and tolerances are not known by me, but I would check this out pronto. Viscous couplers are expensive.
On my car, my rears are turning a tiny bit faster than the fronts... within a couple of revs per mile. This should keep the fluid warm (for instant use in wheel spin), but not overheat it. I will say that I've never successfully gotten any real data on what the optimum size ratios are, but intuitively, I think my sizes are perfect. In addition, my sizes are almost the exact same size (diameter and thus the revs/mile) as the original, stock 18" tires.
If you get any different data, please post back... I'm all ears.
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09-27-2006, 08:06 PM
#8
Three Wheelin'
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steve,
regarding proper rolling diameters, what do you recommend for upgrading to use Mich PS2 - they do not make a 285 size for 18" wheel. Instead they have a 225 and 235 for front and only 295 for rear.
regarding proper rolling diameters, what do you recommend for upgrading to use Mich PS2 - they do not make a 285 size for 18" wheel. Instead they have a 225 and 235 for front and only 295 for rear.
09-27-2006, 08:55 PM
#9
Nordschleife Master
Rob,
Gadzooks... I feel like I'm coming off as an expert here, which I'm not. But I'm looking up tire specs on www/tirerack.com. For your 18" wheels, the Mich PS 2 come in these sizes that you might consider:
295x35x18 : 26.1" 797/revs/mile
235x40x18: 25.4 " 819 revs/mile
245x40x18: 25.7" 809 revs/mile
So, with these choices, the rear will be turning a bit more slowly bthan the fronts... which I "think" is less than ideal. The 245x40x18 is closer to the rears than the 235x40x18. Sometimes, one must choose from a different brand to get the desired tire sizes. Its a tricky game.
Gadzooks... I feel like I'm coming off as an expert here, which I'm not. But I'm looking up tire specs on www/tirerack.com. For your 18" wheels, the Mich PS 2 come in these sizes that you might consider:
295x35x18 : 26.1" 797/revs/mile
235x40x18: 25.4 " 819 revs/mile
245x40x18: 25.7" 809 revs/mile
So, with these choices, the rear will be turning a bit more slowly bthan the fronts... which I "think" is less than ideal. The 245x40x18 is closer to the rears than the 235x40x18. Sometimes, one must choose from a different brand to get the desired tire sizes. Its a tricky game.
09-28-2006, 09:30 AM
#12
Just because tire rack does not have a tire listed does NOT mean that the tire does not exist. For a while they did not have sport cups in 315's listed, but they have them. Second, on 4wd cars I was informed that the threshold should be 4% or less. The simple idea is that you want the front wheel turning the same revolutions as the rears i.e. within that 4% threshold, or you are adding stress to your viscous coupler or your 4WD linkage on your 993tt. Tire rack is quick resource on letting you know what your froont vs rear rolling diameter are.
09-28-2006, 05:55 PM
#13
Rennlist Member
the tire specs with ym new 19 inch rims are specs 19x8 235/35/19 ps2 and 19x11 305/30/19 michelin ps2 tires would this combo stress viscous coupler and your ABS copuld the rear suspension clicking i hear be the tires rubbing on the inside? i noticed new noises when i put these wheels on
09-28-2006, 07:01 PM
#14
Pro
Here's how you do it.
Tire size 295/30/18
295 is the width in mm
30 is the aspect ratio
18 is the wheel diameter in inches
Take the tire width in mm and divide it by 25.4 to get inches
Multiply that times the aspect ratio (30 would be .30). This gives you the height of the sidewall in inches
Multiply that number times two (sidewall is above and below)
Add the wheel diameter
So 295 divided by 25.4 = 11.61
Multiply by .3 = 3.48
Multiply by 2 = 6.97
Add 18 = 24.97 this is the overall tire diameter
Multiply by 3.1416 (pi) = 78.44 this is the tire circumference in inches
One mile is 5280 feet times 12 inches = 63360 inches divided by 78.44 (tire circumference) means the tire will make 807.75 revolutions per mile
Your front and rear wheels should be within 4 or 5 %
Tire size 295/30/18
295 is the width in mm
30 is the aspect ratio
18 is the wheel diameter in inches
Take the tire width in mm and divide it by 25.4 to get inches
Multiply that times the aspect ratio (30 would be .30). This gives you the height of the sidewall in inches
Multiply that number times two (sidewall is above and below)
Add the wheel diameter
So 295 divided by 25.4 = 11.61
Multiply by .3 = 3.48
Multiply by 2 = 6.97
Add 18 = 24.97 this is the overall tire diameter
Multiply by 3.1416 (pi) = 78.44 this is the tire circumference in inches
One mile is 5280 feet times 12 inches = 63360 inches divided by 78.44 (tire circumference) means the tire will make 807.75 revolutions per mile
Your front and rear wheels should be within 4 or 5 %
09-28-2006, 07:55 PM
#15
Nordschleife Master
Here is why it is better to look up the specs for each different manufacturer:
mich ps2 295x30x19 26.0" 799 revs/mile
Pirelli asy 295x30x19 26.1" 801 revs/mile
In this case, they are pretty close, but not always. But its still a bit off from the calculated value as shown by md11plt. His calculations are handy if you haven't got the manufacturers specs.
In any event, the two sizes in sf's question were:
mich ps2 295x30x19 26.0" 799 revs/mile
mich ps2 235x35x19 25.5" 817 revs/mile
This is about a 2% difference, and should be OK. I wonder about the fact that the fronts are turning faster than the rears, but I've never gotten a solid answer on that.
On the rubbing noises... I found that when I was using that size rear tire, I would get a slight "touch" on the very front part of the rear bumper where it is part of the "wheel arch"... if that makes any sense. Look at that piece for any missing paint.
My current tire sizes are:
Pirelli asy: 255x30x19
Pirelli asy: 305x25x19
No rubbing and these tire are quite close to the stock 18" tires in overall diameter.
mich ps2 295x30x19 26.0" 799 revs/mile
Pirelli asy 295x30x19 26.1" 801 revs/mile
In this case, they are pretty close, but not always. But its still a bit off from the calculated value as shown by md11plt. His calculations are handy if you haven't got the manufacturers specs.
In any event, the two sizes in sf's question were:
mich ps2 295x30x19 26.0" 799 revs/mile
mich ps2 235x35x19 25.5" 817 revs/mile
This is about a 2% difference, and should be OK. I wonder about the fact that the fronts are turning faster than the rears, but I've never gotten a solid answer on that.
On the rubbing noises... I found that when I was using that size rear tire, I would get a slight "touch" on the very front part of the rear bumper where it is part of the "wheel arch"... if that makes any sense. Look at that piece for any missing paint.
My current tire sizes are:
Pirelli asy: 255x30x19
Pirelli asy: 305x25x19
No rubbing and these tire are quite close to the stock 18" tires in overall diameter.