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Syncronoid Samba Member
Joined: January 21, 2012 Posts: 1110 Location: Stanford, CA and Bend, OR
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Posted: Wed Aug 15, 2018 12:07 pm Post subject: Bigger tires, changing gearing. |
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I'm sure this has been discussed at nauseam, but hoping to keep this simple.
1990 Syncro Westy, GW2.5L, 3-knobs. I'm considering larger tires.
Currently, I'm using 215/70R16 (27.9" tall/8.5" wide) tires with 2" GW springs, Fox Shocks, stock 4:86 R&P and gearing, 930 axles and 16" rear trailing arms from Burley.
I'm fairly happy with the way the van drives with the existing gearing/tire size combination, but if I were to go with larger tires, which would you choose?.
225/70R16 (28.4" tall/8.9" wide) with 5.43 (11.7% taller) R&P
or
235/70R16 (29" tall/9.3" wide) with 5.43 (11.7% taller) R&P
or
235/70R16 (29" tall/9.3" wide) with 5.83 (20% taller) R&P _________________ '90 Syncro Westy w/GW2.5L |
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E1 Samba Member
Joined: January 21, 2013 Posts: 6379 Location: Westfalia, Earth
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Posted: Wed Aug 15, 2018 1:05 pm Post subject: Re: Bigger tires, changing gearing. |
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We have a 5.43 with a stock 1.9 and absolutely love it.
16s with KO2s, 27.01" tall. With the power of a Subie I am not sure you need/want the extra revs, but think I would if my van to make it a climbing beast. The option of more revving is far easier on a climbing engine than not.
We swapped the .85 4th for a new .78 from Paul at Guard Transmission, a fine guy worth our circle's business. That setup mathed out to about 50-100 less revs on the highway in 4th, and a little bigger gap from 3rd to 4th now — but it's yet to show any distinct disadvantage beyond not having a 3rd to pass with as easily at the wrong speeds the once a year we actually need a quick pass.
Old gearing and stock tires, 3rd redline @ 65 mph, now @ 59 with the 27" tires, though we rarely push that hard.
Have you considered a 5-speed conversion? I'd have done that if I'd been thinking and spending just a little harder…
Arizona Transaxle HUGELY recommended also. _________________ ‘84 Westy, 2.1L with Digijet, 5.43 R+P, GT Gears
"Adding power makes you faster on the straights.
Subtracting weight makes you faster everywhere."
— Colin Chapman |
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gears Samba Member
Joined: October 28, 2002 Posts: 4391 Location: Tamarack, Bend, Kailua
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Posted: Wed Aug 15, 2018 3:41 pm Post subject: Re: Bigger tires, changing gearing. |
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With your present tire, you should be doing about 80mph @4,000rpm
With 29" and 5.43, you would be doing about 75 @4,000, which is pretty optimal for a 2.5
Strength-wise, I like the 5.43 7-tooth pinion more than the 5.83 6-tooth. _________________ aka Pablo, Geary
9.36 @ 146 in '86 Hot & Sticky
'90 Syncro Westy SVX
'87 Syncro GL 2.5
https://guardtransaxle.com |
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crazyvwvanman Samba Member
Joined: January 28, 2008 Posts: 9895 Location: Orbiting San Diego
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Posted: Wed Aug 15, 2018 6:43 pm Post subject: Re: Bigger tires, changing gearing. |
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According to BFG specs,
215/70R16 _ does 746 revs per mile
225/70R16 _ does 732 revs per mile, only 2% taller
235/70R16 _ does 718 revs per mile, only 4% taller
From 4.86 down to 5.43 is about 10% shorter
So switching to 5.43 would give more perceived power in all gears and higher revs at all speeds, no matter which of those tires you choose.
Mark
Syncronoid wrote: |
I'm sure this has been discussed at nauseam, but hoping to keep this simple.
1990 Syncro Westy, GW2.5L, 3-knobs. I'm considering larger tires.
Currently, I'm using 215/70R16 (27.9" tall/8.5" wide) tires with 2" GW springs, Fox Shocks, stock 4:86 R&P and gearing, 930 axles and 16" rear trailing arms from Burley.
I'm fairly happy with the way the van drives with the existing gearing/tire size combination, but if I were to go with larger tires, which would you choose?.
225/70R16 (28.4" tall/8.9" wide) with 5.43 (11.7% taller) R&P
or
235/70R16 (29" tall/9.3" wide) with 5.43 (11.7% taller) R&P
or
235/70R16 (29" tall/9.3" wide) with 5.83 (20% taller) R&P |
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Syncronoid Samba Member
Joined: January 21, 2012 Posts: 1110 Location: Stanford, CA and Bend, OR
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Posted: Wed Aug 15, 2018 7:02 pm Post subject: Re: Bigger tires, changing gearing. |
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Currently, it seems closer to 75 @4,000. I usually cruise @3600-3800 on the Hwy. I'm in no hurry and like to keep the revs a little lower for longevity. Perhaps a different 4th gear??
gears wrote: |
With your present tire, you should be doing about 80mph @4,000rpm
With 29" and 5.43, you would be doing about 75 @4,000, which is pretty optimal for a 2.5
Strength-wise, I like the 5.43 7-tooth pinion more than the 5.83 6-tooth. |
_________________ '90 Syncro Westy w/GW2.5L
Last edited by Syncronoid on Wed Aug 15, 2018 7:17 pm; edited 2 times in total |
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Syncronoid Samba Member
Joined: January 21, 2012 Posts: 1110 Location: Stanford, CA and Bend, OR
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Posted: Wed Aug 15, 2018 7:06 pm Post subject: Re: Bigger tires, changing gearing. |
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Which is good for climbing, acceleration and offroad, but not as much for hwy, I presume.
crazyvwvanman wrote: |
According to BFG specs,
215/70R16 _ does 746 revs per mile
225/70R16 _ does 732 revs per mile, only 2% taller
235/70R16 _ does 718 revs per mile, only 4% taller
From 4.86 down to 5.43 is about 10% shorter
So switching to 5.43 would give more perceived power in all gears and higher revs at all speeds, no matter which of those tires you choose.
Mark
Syncronoid wrote: |
I'm sure this has been discussed at nauseam, but hoping to keep this simple.
1990 Syncro Westy, GW2.5L, 3-knobs. I'm considering larger tires.
Currently, I'm using 215/70R16 (27.9" tall/8.5" wide) tires with 2" GW springs, Fox Shocks, stock 4:86 R&P and gearing, 930 axles and 16" rear trailing arms from Burley.
I'm fairly happy with the way the van drives with the existing gearing/tire size combination, but if I were to go with larger tires, which would you choose?.
225/70R16 (28.4" tall/8.9" wide) with 5.43 (11.7% taller) R&P
or
235/70R16 (29" tall/9.3" wide) with 5.43 (11.7% taller) R&P
or
235/70R16 (29" tall/9.3" wide) with 5.83 (20% taller) R&P |
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_________________ '90 Syncro Westy w/GW2.5L |
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E1 Samba Member
Joined: January 21, 2013 Posts: 6379 Location: Westfalia, Earth
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Posted: Wed Aug 15, 2018 7:31 pm Post subject: Re: Bigger tires, changing gearing. |
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What highway speed do you like? _________________ ‘84 Westy, 2.1L with Digijet, 5.43 R+P, GT Gears
"Adding power makes you faster on the straights.
Subtracting weight makes you faster everywhere."
— Colin Chapman |
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Syncronoid Samba Member
Joined: January 21, 2012 Posts: 1110 Location: Stanford, CA and Bend, OR
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Posted: Wed Aug 15, 2018 7:45 pm Post subject: Re: Bigger tires, changing gearing. |
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3750 RPM.
70-75 is fine. Would settle for 70 if it meant getting the tire size I want.
E1 wrote: |
What highway speed do you like? |
_________________ '90 Syncro Westy w/GW2.5L |
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E1 Samba Member
Joined: January 21, 2013 Posts: 6379 Location: Westfalia, Earth
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Posted: Wed Aug 15, 2018 7:49 pm Post subject: Re: Bigger tires, changing gearing. |
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Do you like your current first gear on rough dirt climbs? _________________ ‘84 Westy, 2.1L with Digijet, 5.43 R+P, GT Gears
"Adding power makes you faster on the straights.
Subtracting weight makes you faster everywhere."
— Colin Chapman |
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Syncronoid Samba Member
Joined: January 21, 2012 Posts: 1110 Location: Stanford, CA and Bend, OR
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Posted: Wed Aug 15, 2018 7:56 pm Post subject: Re: Bigger tires, changing gearing. |
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Yes, though I have the Syncro low gear as well.
E1 wrote: |
Do you like your current first gear on rough dirt climbs? |
_________________ '90 Syncro Westy w/GW2.5L |
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crazyvwvanman Samba Member
Joined: January 28, 2008 Posts: 9895 Location: Orbiting San Diego
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Posted: Wed Aug 15, 2018 8:25 pm Post subject: Re: Bigger tires, changing gearing. |
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With your current 746 rev per mile tires and stock tranny gearing......
75 mph = 1.25 miles per minute
746 x 1.25 = 933 tire revs per minute
933 x 4.86 = 4534 pinion shaft revs per minute
4534 x .85 (4th gear) = 3854 mainshaft revs per minute
mainshaft turns at engine speed, so....
----75 mph = 3850 with your current setup, approx------
----73 mph = 3750 with your current setup, approx------
----70 mph = 3600 with your current setup, approx------
now change to 235/70R16 and 5.43
75 mph would be 4150 rpm, approx
70 mph would be 3865 rpm, approx
68 mph would be 3750 rpm, approx
So the fairly big change to 5.43 can't be compensated for even with the larger of your tire options.
Jumping past that to 5.83 would seem out of the question for you.
Mark |
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Syncronoid Samba Member
Joined: January 21, 2012 Posts: 1110 Location: Stanford, CA and Bend, OR
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Posted: Wed Aug 15, 2018 8:43 pm Post subject: Re: Bigger tires, changing gearing. |
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So, essentially, if I want the bigger tires and all around comparable driveability, I will need to slow down on the hwy. The rest should be ok, no?
crazyvwvanman wrote: |
With your current 746 rev per mile tires and stock tranny gearing......
75 mph = 1.25 miles per minute
746 x 1.25 = 933 tire revs per minute
933 x 4.86 = 4534 pinion shaft revs per minute
4534 x .85 (4th gear) = 3854 mainshaft revs per minute
mainshaft turns at engine speed, so....
----75 mph = 3850 with your current setup, approx------
----73 mph = 3750 with your current setup, approx------
----70 mph = 3600 with your current setup, approx------
now change to 235/70R16 and 5.43
75 mph would be 4150 rpm, approx
70 mph would be 3865 rpm, approx
68 mph would be 3750 rpm, approx
So the fairly big change to 5.43 can't be compensated for even with the larger of your tire options.
Jumping past that to 5.83 would seem out of the question for you.
Mark |
_________________ '90 Syncro Westy w/GW2.5L |
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gears Samba Member
Joined: October 28, 2002 Posts: 4391 Location: Tamarack, Bend, Kailua
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Posted: Wed Aug 15, 2018 9:23 pm Post subject: Re: Bigger tires, changing gearing. |
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Syncronoid wrote: |
Perhaps a different 4th gear?? |
The choices are almost unlimited:
_________________ aka Pablo, Geary
9.36 @ 146 in '86 Hot & Sticky
'90 Syncro Westy SVX
'87 Syncro GL 2.5
https://guardtransaxle.com |
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Syncronoid Samba Member
Joined: January 21, 2012 Posts: 1110 Location: Stanford, CA and Bend, OR
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Posted: Wed Aug 15, 2018 9:35 pm Post subject: Re: Bigger tires, changing gearing. |
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Oh dear, so many choices. Something that keeps RPM's down a bit at Hwy speeds, but isn't too much of a jump from 3rd to where I have to shift down from 4th on modest hills.
I'm at my house in Bend the last week of August, perhaps a sit down and a couple of crowlers to discuss!
gears wrote: |
Syncronoid wrote: |
Perhaps a different 4th gear?? |
The choices are almost unlimited:
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_________________ '90 Syncro Westy w/GW2.5L |
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gears Samba Member
Joined: October 28, 2002 Posts: 4391 Location: Tamarack, Bend, Kailua
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Posted: Wed Aug 15, 2018 10:01 pm Post subject: Re: Bigger tires, changing gearing. |
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This is a pretty good graph website:
http://gearwars.net/ _________________ aka Pablo, Geary
9.36 @ 146 in '86 Hot & Sticky
'90 Syncro Westy SVX
'87 Syncro GL 2.5
https://guardtransaxle.com |
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Pcforno Samba Member
Joined: October 14, 2014 Posts: 575 Location: Santa Fe, nm
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Posted: Thu Aug 16, 2018 6:11 am Post subject: Re: Bigger tires, changing gearing. |
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I have a Syncro westy, 1.8t with about 265ft lbs torque.
I have a 4.86 R and P, normal 4th heat (IIRC .77).
I have run stock tires, 215/70 R 16, and most currently 235/70 R16
I’m loving the 236/70 R16
Highway RPM (70-75 mph) is about 3500. My MPG increased by 1-2 and I don’t notice any effect on crawling speed.
Plenty of power, no real change in when I shift.
Your Subaru engine should be fine as your torque curve is much flatter than mine due to turbo lag |
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davevickery Samba Member
Joined: July 16, 2005 Posts: 2887 Location: Fort Collins, CO
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Posted: Thu Aug 16, 2018 7:22 am Post subject: Re: Bigger tires, changing gearing. |
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Huge difference between GW 2.5 and chipped 1.8T. I like the idea of 225/70-16 and 5.43. I would compare stock tires and gearing to your change and it that puts you back close to stock. But it's a lot of money considering you can just keep it like it is. |
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Pcforno Samba Member
Joined: October 14, 2014 Posts: 575 Location: Santa Fe, nm
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Posted: Thu Aug 16, 2018 8:11 am Post subject: Re: Bigger tires, changing gearing. |
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True Dave - although might be interesting to compare torque curves. If the 2.5 GW Is like the EJ25 then He may have more torque low down. Still if I agree I’d i had to change R and P I’d just keep it where it’s at... |
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gears Samba Member
Joined: October 28, 2002 Posts: 4391 Location: Tamarack, Bend, Kailua
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Posted: Thu Aug 16, 2018 9:09 am Post subject: Re: Bigger tires, changing gearing. |
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.
This is a graph I did for someone going from stock tire size to 29", retaining a waterboxer engine (2.2). It shows a potential 3rd & 4th gear change.
This is a graph showing 5.43 R&P installed with 29" tires, stock gearing:
I've contemplated changing from 4.86 to 5.43 in my own SVX Syncro with 27" tires, more to get a lower G gear than for any other reason. (I now have a selection of mainshafts suitable for any combo.) The only thing holding me back is that I like the 4.86 more than any other R&P, strength-wise. 5.43 is certainly OK, though .. _________________ aka Pablo, Geary
9.36 @ 146 in '86 Hot & Sticky
'90 Syncro Westy SVX
'87 Syncro GL 2.5
https://guardtransaxle.com |
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Waldi Samba Member
Joined: February 28, 2014 Posts: 1752 Location: Germany
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Posted: Thu Aug 16, 2018 10:38 am Post subject: Re: Bigger tires, changing gearing. |
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Orinal Syncro 16 with 112hp DJ has a 5,83x0,85 box.
You should stay close to that.
5,43x0,85 is good.
But i would take 205/80-16 or 6,50x16 if you realy want to go for taler tires and not for the look. |
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