how much power loss can i expect with larger wheels

Submitted: Sunday, Dec 02, 2007 at 12:01
ThreadID: 52172 Views:3033 Replies:8 FollowUps:18
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I am planning on putting larger tyres 265\7516 and lifting the suspension on my NJ 3ltr pajero - how much power can i expect to lose and will it seriously effect sand driving.
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Reply By: Bonz (Vic) - Sunday, Dec 02, 2007 at 12:06

Sunday, Dec 02, 2007 at 12:06
Whatre u running at the moment?

Take a look at this tyre calculator for some handy information.

I went to 265/75's on the Patrol from 265/70's (std) and didnt notice any change. Now going to 285's and wondering the same thing.
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Follow Up By: Mike Harding - Sunday, Dec 02, 2007 at 12:12

Sunday, Dec 02, 2007 at 12:12
A note below that tyre calculator says:

"# When changing tire sizes, we recommend staying within 3% of the diameter/height of the original tire. Any more than this and you face the risk of brake failure."

I am perplexed; why would different size tyres be likely to cause brake failure?

Mike Harding
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Follow Up By: Bonz (Vic) - Sunday, Dec 02, 2007 at 12:17

Sunday, Dec 02, 2007 at 12:17
Read the same thing myself Mr Harding and wondered same also.

If I think thru the physics then the brakes would be trying to wash off speed with less revolutions of the wheel to create the brake pad to disc union. That would do what?

It would mean that to stop in the same distance there would be more heat in the disc, but hey..I have seen them race cars run red hot discs and they run on ok still.

It would also mean that is you were to stop with the same revolutions then slighly more distance would be required, = no impact on brakes.....

Yep its got me tossed
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Follow Up By: Member - Matt (Perth-WA) - Sunday, Dec 02, 2007 at 15:33

Sunday, Dec 02, 2007 at 15:33
Gents without reading the article....a suggestion is that if you increase the tyre size(dia) then you are increasing the torque at the wheel.

The distance from the fulcrum...ie turning point has increased giving the turning force at the wheels more leverage over the brakes trying to stop.

Its the opposite of losing pick-up when you increase the tyre size...harder to take off due to now having a higher velocity ratio as apposed to the mechanical advantage of a smaller wheel. Lower cruising RPM at same given road speed though.

I think they are being a tad melodramatic at stating it as 'brake failure'.... the brakes would need more time to stop at the same speed as the vehicle with smaller dia wheels.

All the best.

Matt.
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FollowupID: 538293

Follow Up By: lost in the dust - Sunday, Dec 02, 2007 at 15:40

Sunday, Dec 02, 2007 at 15:40
Not at home at the moment(desert dwelling) but from memory I have 235/75R15 - I had some trouble in the sand a while back as the car is quite low and even lower when you let the tyres down. So I am planning on raising it a little to help me out but i dont want to loose to much power.
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FollowupID: 538294

Follow Up By: Member - Oldplodder (QLD) - Monday, Dec 03, 2007 at 09:30

Monday, Dec 03, 2007 at 09:30
I have gone up 10% in tyre size (see later post) and therefore I have 10% less effective brakes, i.e. , 10% less retardation being applied to the road contact point with the same brake pedal force as previously. I can still lock up the tyres (no ABS) with extra brake pedal pressure, so brakes OK, but I make sure I change brake fluid on a regular basis and have good quality pads to keep the system in top condition.
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FollowupID: 538373

Reply By: burnsy - Sunday, Dec 02, 2007 at 13:18

Sunday, Dec 02, 2007 at 13:18
In a nut shell it is tractive force that you put on the ground. The further away from your axle center the ground the less force you can put on the ground which leads to less" push" The same goes for your brakes which will give you less braking force at the road the further the disk is away from the road. If you can imagine turning the wheel with a short wheelbrace with the brakes on you may not move it Change to a long wheel brace & you may be able to over ride the brake. This is the main reason the the law restricts tyre sizes from standard as it reduces braking effort.If the tyre is too large the brakes may not supply enough braking effort to stop you quick enough in a emergency
You can get very complicated with this but if you can get your head around what I am saying you can understand the theory
AnswerID: 274668

Reply By: Member - Davoe (Yalgoo) - Sunday, Dec 02, 2007 at 15:57

Sunday, Dec 02, 2007 at 15:57
265x75 are a common fitment to Pajs and i dont think you will notice any great difference or encounter problems
AnswerID: 274678

Reply By: marq - Sunday, Dec 02, 2007 at 16:03

Sunday, Dec 02, 2007 at 16:03
Like towing a 1ton trailer
AnswerID: 274679

Reply By: Froilan - Sunday, Dec 02, 2007 at 19:56

Sunday, Dec 02, 2007 at 19:56
did the same size upgrade on my previous nm paj. did not notice any power loss, however the nm was a 3.5 litre. fuel consumption went up though I would say due the heavier tires. they were LT construction.
AnswerID: 274694

Follow Up By: Andrew from Vivid Adventures - Sunday, Dec 02, 2007 at 20:16

Sunday, Dec 02, 2007 at 20:16
was this actual fuel consumption when you calibrate your speedo for the error introduced?
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FollowupID: 538322

Follow Up By: Froilan - Sunday, Dec 02, 2007 at 20:31

Sunday, Dec 02, 2007 at 20:31
did not calibrate the speedo at that time. just kept the speed about 5km/h below what the speed limit. i drove the paj as a truck and not as a car, meaning no high revving during take offs and no sudden braking. used to get just over 600km with a full tank with oem tires. but after the upgrade, i was lucky if i got 550km.
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FollowupID: 538324

Follow Up By: Andrew from Vivid Adventures - Sunday, Dec 02, 2007 at 21:12

Sunday, Dec 02, 2007 at 21:12
Well most of the difference is because the odometer is under-reading now. It is travelling more km than you are giving it credit for.

The rest is probably from the extra weight of the tyres and the need to drive it a little harder on the hills.
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FollowupID: 538331

Follow Up By: 96 GXL 80 series - Monday, Dec 03, 2007 at 00:43

Monday, Dec 03, 2007 at 00:43
You will expect slower take off's from standing starts due to more load on the drive line.
This will use more fuel to get the vehicle rolling and up to speed, due to more strain.

You will be lower in rev's say at 100k's and will need more gear changes for hills / over taking and in towns and cities you will be changing gears more often.

4WD'ing you will be putting more strain on the drive line, axles / gearbox / transfer box.

Towing it will be very noticeable, in some cases like towing in 5th gear compared to 4th.
Engines of today don't like to be laboured or under reved in other words.

Take notice of what rev's your vehicle is sitting on at 100klms an hour.
Say for example you are doing 2500rpm at 100k's and change everything so you are getting exact readings and now it shows 2000rpm at 100k's then the engine is starting to show signs of labouring and you will feel like changing down a gear to help it keep up the speed so more fuel both ways.

If you want it to sit on the 2500rpm then your speed will increase to say 115klm's per hour, so you will be over the speed limit.
This is where you will notice brake ware also in trying to slow down a big vehicle, and it will be harder slowing from 100k's to 60k's and will take longer than a normal vehicle of the same type.

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FollowupID: 538351

Follow Up By: Andrew from Vivid Adventures - Monday, Dec 03, 2007 at 07:58

Monday, Dec 03, 2007 at 07:58
crikey GXL - it's not that bad is it?

Andrew who has 285/75s on his 1HZ and thinks life is rosey, esp for the extra clearance.
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FollowupID: 538358

Follow Up By: madfisher - Monday, Dec 03, 2007 at 16:36

Monday, Dec 03, 2007 at 16:36
we just went to 10r 31 15 and the power loss was noticable on a 3lt paj. Also the turning circle appears to be bigger or am I* going mad?
Cheers Pete
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FollowupID: 538443

Follow Up By: 96 GXL 80 series - Monday, Dec 03, 2007 at 19:08

Monday, Dec 03, 2007 at 19:08
Andrew,
it might be partly okay around town re the strain on the drive train, but try and put it through what it was built for and you will have upset the whole Geometry of the vehicle from what the manufacturer built it for.

More strain on the whole set up unless you modify diff ratio's / heavy duty clutch / brakes just to name a couple.

Then you can also get into the engineering side of it, and if allowed to do it without an engineers certificate?

Also who is at fault if in an accident? even if you were in the right.
The vehicle should not have been on the road, so the tide will turn and you could be at fault.

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FollowupID: 538484

Follow Up By: Andrew from Vivid Adventures - Monday, Dec 03, 2007 at 19:40

Monday, Dec 03, 2007 at 19:40
You are particularly melodramatic today GXL.

"Who is at fault if in an accident?"

What sort of accident? That is a pretty ridiculous question surely. As if totally legal tyres should have any impact on who is at fault.

Why should the vehicle not have been on the road? It is totally legal to have larger tyres - there are limits, but most 285/75s on a 1HZ are legal.

"Try and put it through what it was built for"... now, what do you have in mind? Do you forget that it travels from one end of the country to the other including some of the most challenging tracks, the desert, the high country, the Kimberley, to name a few, fully loaded to manufacturer's limits including with a trailer.

"Upset the whole geometry of the vehicle" - more melodrama and hyperbole. In many ways, my vehicle with modified suspension rides and handles better than the stock vehicle when fully loaded. Very little of the geometry of the vehicle is affected by putting on bigger tyres - think through exactly what you are saying. That an inch or so extra height from slightly bigger wheels changes everything? Sure it has some effects, but not so much as you imply.

Even my insurers are happy to cover the vehicle explicitly with 285/75s and given the number of vehicles with this setup, you'd think they'd know if it was a higher risk.

The vehicle has done 150,000 ks in its current setup with no particular strains on the drive train noticeable... it is checked over meticulously very regularly and is doing very well. Perhaps with a Paj things might be different, but with my truck I think it can be recommended if you're happy with the clear implications - less power and speedo error, in particular.

When you don't know what you're talking about don't talk about it.
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FollowupID: 538491

Follow Up By: 96 GXL 80 series - Tuesday, Dec 04, 2007 at 16:51

Tuesday, Dec 04, 2007 at 16:51
Andrew,
have a look on ThreadID: 52203
The link that DougT has added and read the comments about tyre size.

I have been through all that and never again.
Not on the LC but in a sedan.

If in an accident, on the day it is up to the Insurance assessor and not the insurance company.

Have a look on the front door of the vehicle and it will tell you what tyres etc you have to use.

This is what the assessor goes by, not what you tell him.

I am not arguing about it, just trying to help.
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FollowupID: 538620

Follow Up By: Andrew from Vivid Adventures - Tuesday, Dec 04, 2007 at 17:26

Tuesday, Dec 04, 2007 at 17:26
Well if you were not aware enough to put it on your insurance policy explicitly, I guess you left yourself open to it, but it is L E G A L legal to put larger tyres on.

The assessor goes by the legality.

Now, if you put mammoth tyres on, the situation may be different if the are ILlegal.

Yes, you are not arguing - just melodramatic.
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FollowupID: 538626

Reply By: Ozboc - Monday, Dec 03, 2007 at 07:02

Monday, Dec 03, 2007 at 07:02
Trying to pretend to be a standard nissan ??? :)

Boc

AnswerID: 274731

Reply By: Member - Oldplodder (QLD) - Monday, Dec 03, 2007 at 09:19

Monday, Dec 03, 2007 at 09:19
Put some 32" od 235/85/16 on my 1996 NH GLX, same OD as the 265/75/16.
Original tyres were 235/75/15 (29"), so 10% change.

If yours is a GLS, they had 30" OD tyres, so not as much difference as my GLX.

There is a noticeable difference (10% less power to be exact), but then i have the 2.8 diesel as well.

Petrols have more torque down low , while the diesel has some turbo lag until it gets to 1500rpm, then the torque cuts in. So off the line, there is noticeably less power for me, would not be so obvious with a petrol, but you will feel it.
About the same as being empty and having 5 people aboard.

Still tackle most sand in high range 1st or second, and no noticeable difference once you get going, since it is only 1 to 2 km/hr per 1000 revs.
1st was 6.3km/hr @ 1000 revs, now 7.0.
2nd was 10.8km.hr @ 1000 revs, now 12.
Big advantage for me in sand is greater clearance under the front bash plate on rutted sand tracks. It doesn't play bull dozer as much since the front is now 1.5" (38mm) higher due to increase in tyre radius. You could jack it up another 1" (25mm) on the torsion bars. I have 2" lift in the rear coils.

Getting better economy once you adjust for the speedo, especially on the highway. Improved about 5 to 10%. But you may not see that with the wider tyres.


I find my speedo now reads 3km/hr under at 100 (100 is really 103), and the odometer under reads by 5% (95 km travelled is 100km).

4th is now better for overtaking on the highway and hills, since it is higher, and you can easily rev it out to 120. Pajero always felt under geared before, and I was looking for 6th on the highway.
Pajeros have a low first gear, so not so much difference (but there is some) pulling away from the lights, as stated above.

Not quite so good in low range 1st on knarly tracks, but if I was serious, could drop in some 2.85 gears in the transfer case instead of stock 1.9 for low range.

Hope that helps :o)
AnswerID: 274742

Follow Up By: Member - Oldplodder (QLD) - Monday, Dec 03, 2007 at 09:41

Monday, Dec 03, 2007 at 09:41
PS - wife, with shorter legs can still get in the car, but any higher and I would have major complaints about the step :o)
And tight skirts are definitely out of the question. :o))))

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FollowupID: 538377

Follow Up By: lost in the dust - Monday, Dec 03, 2007 at 10:22

Monday, Dec 03, 2007 at 10:22
thanks for that - thats exactly what i am finding, it feels like I am pushing half the beach along with the bash plate and having to work pretty hard.

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FollowupID: 538387

Follow Up By: Member - Oldplodder (QLD) - Monday, Dec 03, 2007 at 13:20

Monday, Dec 03, 2007 at 13:20
No problems.

Before you do go the tyres, just check your ride height at the front.
Friends pajero had the same problem on sand.
Found the front torsion bars needed winding up an inch.
The top and lower A arms should have about equal clearance to the top and bottom bump stops.
Or you could go a little higher than stock.
Don't wind up too far, otherwise you end up with no drop in the suspension and the car rides terribly, besides putting more load inot the CV joints.
Simple job to adjust by the bolts on the ends of the bars under the front seats. You might need another wheel alignment afterwards though.
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FollowupID: 538410

Reply By: Mike Harding - Monday, Dec 03, 2007 at 19:25

Monday, Dec 03, 2007 at 19:25
Thanks for the explanations about larger wheels and brakes everyone - I now understand what the issue is.

Mike Harding
AnswerID: 274824

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