Has anyone played with dif Ring and Pinions?
07-29-2003, 09:15 AM
#2
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Kevin-
I've asked the same question. Mostly the response by those who work these cars is "DON'T DO IT". The reason seems to be the strength of the replacement R&P. I hear Andial has the best, but nothing comes close to the original 930 transmission set up.
Also, there is the notion of street .vs. track. Gearing for the track is TOTALLY different, and usually 'track specific'. If your on the street, it's doubtful your going 150-175mph. You, like me perhaps, want to get to 125 faster and want to stay on boost while your getting there. To accomplish that 1st-3rd gear should be all you need, leaving 4th for your reasonable, engine saving, cruising-highway-overdrive gear.
To stay on boost the ratios between the 1-4 gears need to be closer so the rpm drop between gears become less. Stock 1st gear (if I remember) is 2.29:1, 2nd at 1.39:1 and 3rd is 0.86:1. When my synchro's go and I need to open the trannie, I was going to change 2nd to near 1.70:1 and 3rd to near 1.15:1 and put the original 3rd gear into 4th.
I guess one can change 1st gear too (of course that will force 2 and 3 to change) to jump out of the hole or stop light even quicker but you run out of gear real fast when you have to shift at 30mph!! That's especially true if you've modified your engine.
I've not driven a R&P changed over vehicle yet, but intend to sometime this summer so I can not speak with experience about it.
I've asked the same question. Mostly the response by those who work these cars is "DON'T DO IT". The reason seems to be the strength of the replacement R&P. I hear Andial has the best, but nothing comes close to the original 930 transmission set up.
Also, there is the notion of street .vs. track. Gearing for the track is TOTALLY different, and usually 'track specific'. If your on the street, it's doubtful your going 150-175mph. You, like me perhaps, want to get to 125 faster and want to stay on boost while your getting there. To accomplish that 1st-3rd gear should be all you need, leaving 4th for your reasonable, engine saving, cruising-highway-overdrive gear.
To stay on boost the ratios between the 1-4 gears need to be closer so the rpm drop between gears become less. Stock 1st gear (if I remember) is 2.29:1, 2nd at 1.39:1 and 3rd is 0.86:1. When my synchro's go and I need to open the trannie, I was going to change 2nd to near 1.70:1 and 3rd to near 1.15:1 and put the original 3rd gear into 4th.
I guess one can change 1st gear too (of course that will force 2 and 3 to change) to jump out of the hole or stop light even quicker but you run out of gear real fast when you have to shift at 30mph!! That's especially true if you've modified your engine.
I've not driven a R&P changed over vehicle yet, but intend to sometime this summer so I can not speak with experience about it.
07-29-2003, 01:59 PM
#3
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I have the Andial R&P. It is a quality unit made in Germany. Much of the reliability issues with these comes from improper installation. If you don't get the backlash right they will wear our very quickly, whether you install a stock unit or an aftermarket one.
I wish my first was just a bit taller, but otherwise I like the change for street driving.
John
'79 930
I wish my first was just a bit taller, but otherwise I like the change for street driving.
John
'79 930
07-30-2003, 01:31 AM
#4
I raised my ratios by changing tires. With 275/40-17 rear tires I can now cruise a residential neiborhood comfortably in 1st. 1st is now a useful gear instead of a throw away.
On the track, I was getting close to the red line in a few places but didn't want to upshift. Now I have room to spare and am actually going faster. I can now hold 3rd longer down the back straight and take advantage of the power longer.
Finally, I get an extra inch of rubber on the back end which makes the car easier to drive fast in corners. I'm more confident that if the tail steps out, I have more to catch it with.
All for a few extra bucks per tire -- a fraction of the price of a transmission rebuild.
Sure, it's not as fast off the line in 1st... But it's not a drag car. I get a much more useful 2nd and 3rd. And can cruise the highway at 2000 rpm while still risking a speeding ticket.
Of course the speedo doesn't reflect any of this. Interestingly, I had my wife pacing me in her Boxster S with 18" stock wheels and tires. Even though I am running one size oversized, her speedo reading was identical to mine at 100km/h.
On the track, I was getting close to the red line in a few places but didn't want to upshift. Now I have room to spare and am actually going faster. I can now hold 3rd longer down the back straight and take advantage of the power longer.
Finally, I get an extra inch of rubber on the back end which makes the car easier to drive fast in corners. I'm more confident that if the tail steps out, I have more to catch it with.
All for a few extra bucks per tire -- a fraction of the price of a transmission rebuild.
Sure, it's not as fast off the line in 1st... But it's not a drag car. I get a much more useful 2nd and 3rd. And can cruise the highway at 2000 rpm while still risking a speeding ticket.
Of course the speedo doesn't reflect any of this. Interestingly, I had my wife pacing me in her Boxster S with 18" stock wheels and tires. Even though I am running one size oversized, her speedo reading was identical to mine at 100km/h.
07-30-2003, 12:11 PM
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umm... you brought up a very interesting point about speedo is off.
I run the same rear tire size as Peter, but based on comments from other drivers on the track, my speedo seems to be way off at the high end (>180km), but when I measured it against our family car 100-120km, it seems that its accurate there.
I would have thought the speedo is either off by a fixed % or not? So the % of error should be consistent regardless of speed?
I run the same rear tire size as Peter, but based on comments from other drivers on the track, my speedo seems to be way off at the high end (>180km), but when I measured it against our family car 100-120km, it seems that its accurate there.
I would have thought the speedo is either off by a fixed % or not? So the % of error should be consistent regardless of speed?
07-30-2003, 02:21 PM
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It's funny you guys should mention the tire/speedo connection. I'm running the standard set-up... 16" Fuchs w/245-45-16s in the rear. When my speedo says 80mph, my wife tells me her Caravan is doing 75mph; this is at 2900rpm. I've checked with the former owner and he did NOT change the R&P, nor did any gearset changes.
Is there a big difference in tire diameter from one mfg to another to create a discrepancy in speedo readings? I'm running Bridgestone Potenzas. Also, who's speedo is right? What are your rpm/mph readings?
Is there a big difference in tire diameter from one mfg to another to create a discrepancy in speedo readings? I'm running Bridgestone Potenzas. Also, who's speedo is right? What are your rpm/mph readings?
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07-30-2003, 05:39 PM
#8
245s are actually under sized...
Here is a spreadsheet I made to do the comparison. Some numbers are taken from spec sheets while others are calculated using the published size. They do vary from manufacturer to manufacterer. I think I took the numbers mostly from Pirelli P Zero Cs.
With all the different tire combinations Porsche has offered over the years, I don't think they changed anything in the speedo to compensate for the changes. They probably make the speedo read a little under on purpose to avoid liability for speeding tickets.
The T/R ratio is a calculation of the width of the tire versus the width of the rim. I read somewhere (reputable) that you should stay between .88 and 1. Less than .88 (i.e. wide tire on a narrow rim) and the car will wander all over. I had 275-17s on 9" rims for a while and on the track the car wandered all over as if you were driving in a hurricane. One instructer refused to get in it.
Here is a spreadsheet I made to do the comparison. Some numbers are taken from spec sheets while others are calculated using the published size. They do vary from manufacturer to manufacterer. I think I took the numbers mostly from Pirelli P Zero Cs.
With all the different tire combinations Porsche has offered over the years, I don't think they changed anything in the speedo to compensate for the changes. They probably make the speedo read a little under on purpose to avoid liability for speeding tickets.
The T/R ratio is a calculation of the width of the tire versus the width of the rim. I read somewhere (reputable) that you should stay between .88 and 1. Less than .88 (i.e. wide tire on a narrow rim) and the car will wander all over. I had 275-17s on 9" rims for a while and on the track the car wandered all over as if you were driving in a hurricane. One instructer refused to get in it.
08-03-2003, 09:30 PM
#9
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Short R&P
I have a "short" r&p in mt 86. I thought it was installed incorrectly because there is a distinct whine to the r. I have since learned that various manufactures of the gears may produce "noise". I am not sure of the set in my car other than they are Italian....nothing like a little Italian whine to keep you into it!..Ed
08-04-2003, 11:43 PM
#11
I had a couple of sets of RE-71s 245/40-17 and 275/35-17 that were the spec tire for an old Valvoline race series. They lwere RE-71s but had no DOT label so I was told they were done specially for the series. Maybe with some special rubber? There was apparently an RE-71R but they were not labeled that way. When those ran out, I had to go to the 275/40-17 and I lost a LOT of gearing. The car was noticibly not-as-fast (the car was never slow). Although, the taller gearing works pretty well at Mosport except for 4th which is way to tall now.
You can also feel the gearing change as 1st was a complete waste of time. 2nd was the low speed cruising gear. With the 275/40s, you cruise a residential neibourhood comfortable in 1st. Obviously, the speedo readings are off a bit too.
You can also feel the gearing change as 1st was a complete waste of time. 2nd was the low speed cruising gear. With the 275/40s, you cruise a residential neibourhood comfortable in 1st. Obviously, the speedo readings are off a bit too.
