Smaller Tyres - pros (?) and cons - Defender Source
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  #1  
Old January 24th, 2016, 08:00 PM
agentmulder
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Smaller Tyres - pros (?) and cons

The diameter for 225/75-16 tyres works out at:

225*0.75*2 + 16*25.4 = 744mm

Compared to ~805mm for both 265/75-16 and 235/85-16

That's a 744/805 = 92.4% reduction in diameter and circumference.

Why might someone choose tyres this small?

What advantages and disadvantages would they afford a user?

At the least I see potential cons:
  • revving high just to get it moving out of the lights in first
  • overestimates in speedo/odometer readings
  • lower clearance
And (some questionable) potential plusses:
  • revving high to get it moving in first - i.e. lower gearing for towing
  • steering end stops could be extended for tighter turning circle (?)
  • Assuming material surface area cost is major determining factor then they might have a cheaper unit cost (?) (but then with less circumference they might wear faster...)

I've driven both, the only difference in actual driving I could immediately feel is the getting away at the lights thing.
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  #2  
Old January 24th, 2016, 08:54 PM
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I would not go smaller than 265/75 on a Defender. 225/75 would look silly
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  #3  
Old January 24th, 2016, 09:14 PM
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Silly because of implied technical reasons? Or just aesthetically?
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  #4  
Old January 24th, 2016, 09:16 PM
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Purchased my 110 (2.5 petrol) with 205/85r26s on it. I know that those are definitely not as small as yours, but I am definitely feeling the effects of smaller tires. 3500rpm+ to travel highway speeds, only 10kph in first gear, 12-15mpg, etc
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  #5  
Old January 24th, 2016, 09:34 PM
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This is not a 94% reduction. It's a 7.6% reduction.

I've run 29 inch street tires on my defender years ago, mostly to keep it low and quiet. It was great. Helluva lot better on the road than running my swampers. Some folks on here have posted pictures of it and it does look pretty goofy, IMHO. Even 31's look small on a Defender, and 33's look just right.

From experience, your concerns about "revving high to get away from the lights" (what?) are totally exaggerated. There's virtually no discernable difference between 29's and 32's at low speeds.

Lower ground clearance, sure.

They are a lot cheaper.

But if you don't wheel on rocks, who cares. This line of thinking is totally hypothetical. Are you rock crawling?
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Old January 24th, 2016, 09:35 PM
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Quote:
Originally Posted by DocB View Post
Purchased my 110 (2.5 petrol) with 205/85r26s on it. I know that those are definitely not as small as yours, but I am definitely feeling the effects of smaller tires. 3500rpm+ to travel highway speeds, only 10kph in first gear, 12-15mpg, etc
755mm ... 94%

The Defenders I refer to are both Puma 6 speed, so highway and mpg aren't a major consideration. As far as my experience tell me the 6th gives you more than the 5th as driving in 5th on a TD5 with 265/75 I was revving more to get the speeds I was used to with a 235/75 equipped 6 speed.

But yeah, first gear certainly is time-consuming! I often opt for pulling out in 2nd if I can get a forward roll after releasing the brakes...

------ Follow up post added January 25th, 2016 03:45 PM ------

Quote:
Originally Posted by sonoronos View Post
From experience, your concerns about "revving high to get away from the lights" (what?) are totally exaggerated. There's virtually no discernable difference between 29's and 32's at low speeds.
But if you don't wheel on rocks, who cares. This line of thinking is totally hypothetical. Are you rock crawling?
Assuming same clutch action, I have to give it 6.4% more (1/0.94) revs to achieve the same velocity/distance travelled as 805mm dia tyres. That 6% is audibly different (to me at least) suggesting a non-linear relationship between revs and perceived 'engine pitch/loudness'

This logic applies to all speeds, but seems more apparent (as a human observer) the lower you go.

I don't wheel on rocks, but I guess you could say that as a matter of enjoyment occasionally take the road less travelled, and certainly blat about the hills/dirt tracks on the farm in a way that makes diff-lock necessary. (no issues with clearance yet)
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  #7  
Old January 24th, 2016, 09:59 PM
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Quote:
Originally Posted by sonoronos View Post
From experience, your concerns about "revving high to get away from the lights" (what?) are totally exaggerated. There's virtually no discernable difference between 29's and 32's at low speeds.
I mistyped one number (205/75r16) but still, 28" tires and 32" tires act drastically different at all speeds! Off the line (stoplight), on the highway, gas mileage, RPMS, etc

For the OP, the changes are constant over all size changes, so with smaller changes come with smaller differences. Any reduction in tire circumference causes changes. Smaller tire=more revolutions per mile=higher RPMS,etc.
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  #8  
Old January 24th, 2016, 10:19 PM
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Quote:
Originally Posted by DocB View Post
For the OP, the changes are constant over all size changes, so with smaller changes come with smaller differences. Any reduction in tire circumference causes changes. Smaller tire=more revolutions per mile=higher RPMS,etc.
Yip, and it will be different by the linear ratio of the two diameters (or circumferences)

So 32/28 = 14.2% more revs required for the smaller tyre for any given velocity (or RPM, all other things kept equal).

Seems like that would be a deal breaker with the 5-speed transmissions trying to keep up on the motorway.

Cheaper tyres eventually costing you in the long run ... Unless of course you were selling - I'm beginning to think it was a dodgy dealer applying some typical tactics. But in saying that 6-speed makes it usable.
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  #9  
Old January 25th, 2016, 01:11 AM
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Quote:
Originally Posted by agentmulder View Post
Yip, and it will be different by the linear ratio of the two diameters (or circumferences) So 32/28 = 14.2% more revs required for the smaller tyre for any given velocity (or RPM, all other things kept equal). Seems like that would be a deal breaker with the 5-speed transmissions trying to keep up on the motorway. Cheaper tyres eventually costing you in the long run ... Unless of course you were selling - I'm beginning to think it was a dodgy dealer applying some typical tactics. But in saying that 6-speed makes it usable.
A "deal breaker" with the 5 speed? I ran for a year on my 29's on mostly highway, and wheeled at Rausch Creek until those little things tore a sidewall. You don't need a 6 speed to run 29 inch tires on a Defender. And this is with a 200tdi coupled to an lt77.

The tone of these posts goes counter to my experience, therefore I am highly skeptical
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  #10  
Old January 25th, 2016, 01:19 AM
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My lt77 has the 1.6:1 gears, that coupled with the 205/75r16s, highway driving is horrendous. Both for everyone in the car and for the wallet. 35-3800rpm for 65mph ends up with a consistent <10mpg

The stock tire size is around 30" right? I'd say stick with whatever is stock. That would be the size that was used to develop the gear sets for the transmission, speedo gears, etc
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  #11  
Old January 25th, 2016, 01:20 AM
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Quote:
Originally Posted by sonoronos View Post
A "deal breaker" with the 5 speed? I ran for a year on my 29's on mostly highway, and wheeled at Rausch Creek until those little things tore a sidewall. You don't need a 6 speed to run 29 inch tires on a Defender. And this is with a 200tdi coupled to an lt77.
I've only driven the 5-speed once, but IMHO it was noticeably asking for more revs than the puma transmissions in trying to maintain the speed limit here in NZ ... (keep in mind that was with standard tyres, compared to the puma with the smalls)

But what do I know

I'm not sure where, but I imagine the gear ratios for would be easy enough to find. Would be interesting to see if the relative difference in ratios in 5th for yours and 6th in the pumas is similar in magnitude to the circumferential ratio difference in tyres we've been discussing.
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  #12  
Old January 25th, 2016, 01:25 AM
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Quote:
Originally Posted by DocB View Post
My lt77 has the 1.6:1 gears, that coupled with the 205/75r16s, highway driving is horrendous. Both for everyone in the car and for the wallet. 35-3800rpm for 65mph ends up with a consistent <10mpg The stock tire size is around 30" right? I'd say stick with whatever is stock. That would be the size that was used to develop the gear sets for the transmission, speedo gears, etc
That I can definitely see. Running a 1.6 LT230 (assuming you meant tcase) would present a big problem at highway speeds with a smaller tire.

As I understand it, you're in 35" territory there, gearing-wise.
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  #13  
Old January 25th, 2016, 08:38 AM
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Quote:
Originally Posted by sonoronos View Post
That I can definitely see. Running a 1.6 LT230 (assuming you meant tcase) would present a big problem at highway speeds with a smaller tire.

As I understand it, you're in 35" territory there, gearing-wise.
Correct, LT77/LT230. 35"s would probably be right at home with the current set up, but they wouldn't fit on the car lol. I'm going with the common 235/85r16s because from what I hear they SHOULD fit without any problems and also for all the reasons already stated ;-). Hopefully those will reduce some of the stress of highway driving until I can save up for new t-case gears
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Old January 25th, 2016, 08:39 AM
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Let's try and simplify this:
29 inch tires-205/16, 225/7516, 235/70-16 650r16
30.5 inch 245/75-16 215/85-16 700R16
32 inch 235/86-16, 750r16
33 inch 255/85-16 285/75-16

Taken mostly from notes written up in my d1 days when wheel arch size limited tire size. D1 drivers really sweated size especially at the rear.
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  #15  
Old January 25th, 2016, 09:28 AM
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One huge difference is ride. The larger the diameter of a wheel tire combo the smoother bumps in the road are to the occupants. Lower sidewall profile means the tires ability to absorb an impact is reduced. Short tires = harsh choppy ride, where every highway expansion join or piece of road debris can be felt.
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Old January 25th, 2016, 10:31 AM
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Quote:
Originally Posted by sonoronos View Post

I've run 29 inch street tires on my defender years ago, mostly to keep it low and quiet. It was great. Helluva lot better on the road than running my swampers. Some folks on here have posted pictures of it and it does look pretty goofy, IMHO. Even 31's look small on a Defender, and 33's look just right.
Hope this is not too much of a thread drift.

Am on 35" SSRs, now...

Does anyone have a photo of how a 3" OME spring lift looks with 255/85R16s (33s), please ?

too goofy ?



(just cannot find suitable replacement alternatives and the swampers have gone up tremendously in price since getting them new )
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Old May 23rd, 2016, 02:56 PM
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Quote:
Originally Posted by ersatzknarf View Post
Hope this is not too much of a thread drift.

Am on 35" SSRs, now...

Does anyone have a photo of how a 3" OME spring lift looks with 255/85R16s (33s), please ?

too goofy ?



(just cannot find suitable replacement alternatives and the swampers have gone up tremendously in price since getting them new )

bump, please ?
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Old May 23rd, 2016, 03:27 PM
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Originally Posted by ersatzknarf View Post
bump, please ?
Frank

This is a little higher lift than 3" (nearer to 4"), with SAM-78 swampers. These are 32's so I don't think you have anything to worry about with 33's.

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  #19  
Old May 23rd, 2016, 04:15 PM
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This is 3" RTE with some slightly worn out 255/85's. It doesn't look ideal in my opinion, but it isn't bad by any means.

-Ash
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  #20  
Old May 23rd, 2016, 04:29 PM
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Holey crap that looks goofy! No offense.



Quote:
Originally Posted by Ash View Post
This is 3" RTE with some slightly worn out 255/85's. It doesn't look ideal in my opinion, but it isn't bad by any means.

-Ash
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