I'm confused with my swamper calculations

darrenmhaine

darrenmhaine

Member
I'm wanting to go swamper and I'm struggling with the age-old problem of trying to calculate tire size o_O

Please could someone confirm if my calculations are right? I am currently running a 275/35 ZR20 setup on my T6 T32 and I want to try and get as close to the current overall diameter with the BF Goodrich AT's.

So current is 35% of 275mm is 96.25mm = 3.79" X2 = 7.58" + 20" rim = 24.58" O/D.
BF Goodrich: 235/45 17 is 105.75mm = 4.16" X2 = 8.32" + 17" rim = 25.32" O/D

That's a difference of + 0.74". the speedo has been recalibrated from the standard for the current setup; how much would the 0.74" increase put the speedo out and would it mean at speedo 30, 40, 50, 60, and 70mph would my actual speed be faster or slower than the speedo reads? :sleep:

like I said, are my calculations right even? I'm confused!!

All help and advice gratefully received!
 
darrenmhaine said:
I just noticed that as well :eek:
Click to expand...
I’ve bought 245/65/17 on the strength of others saying it will be fine. My neighbour has 225/65/17 on his with standard suspension and looking at them there’s plenty of clearance so I’m happy the 245s will be fine
 
Hey Ray, thanks for that; are you saying that you have already fitted th BFG's and you're having no problems with rub even on full lock? If so, please can I ask what rims you have and what width and offset they are?
Sorry for the Spanish Inquesition :grin bounce:
 
darrenmhaine said:
Hey Ray, thanks for that; are you saying that you have already fitted th BFG's and you're having no problems with rub even on full lock? If so, please can I ask what rims you have and what width and offset they are?
Sorry for the Spanish Inquesition :grin bounce:
Click to expand...
I don’t have my van yet but I bought the wheels in advance. I’ve heard of others that have fitted 245 with no trouble. 245 have a slightly larger diameter to 225 and looking at my neighbours van with 225, there’s plenty of room. These are the rims I bought. They are 17x8 ET35 5x120 from Rogue Alloys
D7D43A76-C57A-43E3-B0E8-1F3166284A44.png
 
I’ve run 225 65 R17 KO2 and currently running 245 65 R17 KO2.

They both fit without modification on standard suspension on the 4Motion California without the table in the sliding door rubbing. There is very little mud clearance between the outer diameter of the tyre and the rear of the rear wheel arch though. I really need a lift. 89F8C622-A2AB-4A3F-8D54-730476CEF312.jpeg99F2115B-4C9B-471C-ACA8-046B9FCF8170.jpeg78376F9D-CA69-4AB2-95E6-9497A0C265FC.jpeg
 
RayF said:
I don’t have my van yet but I bought the wheels in advance. I’ve heard of others that have fitted 245 with no trouble. 245 have a slightly larger diameter to 225 and looking at my neighbours van with 225, there’s plenty of room. These are the rims I bought. They are 17x8 ET35 5x120 from Rogue Alloys
View attachment 94595
Click to expand...
mmm, they look nice :cool:
 
7.58" + 20" rim = 24.58"
Nope. Stay behind and see teacher after class!
 
California 4x4 said:
I’ve run 225 65 R17 KO2 and currently running 245 65 R17 KO2.

They both fit without modification on standard suspension on the 4Motion California without the table in the sliding door rubbing. There is very little mud clearance between the outer diameter of the tyre and the rear of the rear wheel arch though. I really need a lift. View attachment 94604View attachment 94605View attachment 94606
Click to expand...
They look fantastic IMO, but that's an 8% increase in gearing over OE, does it still drive OK?
 
DaveD said:
They look fantastic IMO, but that's an 8% increase in gearing over OE, does it still drive OK?
Click to expand...
I think I worked it out as 7% (maybe optimistically) when I was considering the upgrade. I have found my speedo now matches GPS speed, so I have to be careful at pushing any speed limits, however I don’t drive it terribly hot otherwise my cutlery tray and tries to overtake me on roundabouts. My fuel consumption at the computer reads higher but I didn’t do any manual calls before or after to confirm. I have found on long steep inclines, I might have to drop a gear. I don’t remember this occurring frequently on standard tyres. I planned to only use them in the winter, but have found the ride comfortable and the peace of mind while off road to be reassuring so they’ve stayed on.
 
RayF said:
I don’t have my van yet but I bought the wheels in advance. I’ve heard of others that have fitted 245 with no trouble. 245 have a slightly larger diameter to 225 and looking at my neighbours van with 225, there’s plenty of room. These are the rims I bought. They are 17x8 ET35 5x120 from Rogue Alloys
View attachment 94595
Click to expand...
Hey Ray
Don’t suppose there’s any chance you could take a couple of sneaky pictures of your neighbours van with 225 please?
 
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