i am wanting to upgrade my Navara wheels from 16 inch to 17 inch and go from a 255/70/16 tyre to a 265/70/17.
Somebody told me that if i increase too much i will not be able to move off the mark when towingdue to the fact that it will alter the gear ratio.
can anybody explain this to me or offer some advice.
yes, the increased rolling diameter will alter your final drive ratio. ie. revolutions of the motor compared to revolutions of the wheel. i doubt it will affect you to the stage of not being able to move, but it will place extra strain on your clutch and drivetrain when taking off loaded. you will have lower rev's for the same km/h speed effectively.
Yes it will alter the ratio, your speedo will be out a little also, I fully suspect that you will be able to tow Ok it's not a huge amount your contemplating.
Try a google on "tyre size calculator" for more details, don't forget the yanks write tyre as tire I think.
cheers fnq
thanks Guy's. i have noticed that the speedo is out by about 6klm, according to my GPS ( it says that i am going faster than i really am) hopefully this will bring it closer to the actual speed. i think the final difference is about 40 mm.
not good news about the extra strain on the clutch, its very light as it is.Originally Posted by PADDLES
Hello Orrsum,
It is all to do with the outside diameter of the tyres.
Try the tyre websites for specifications, eg. Toyo.
225/70/16 OD of 0.726m.
265/70/17 OD of 0.804.
That is about a 10 percent increase in diameter, which equates to a 10 percent increase in distance travelled per revolution of the wheel.
Would it make the car harder to get rolling?.
Yes it would, by 10 percent.
Remember that this is 10 percent in all gears, you may have trouble holding fifth on hills.
Acceleration will be reduced in all gears.
Will 10 percent be noticable?
Unless you get a scientific reply from someone who has made the same change, you don't know.
You may be able to do a quick swap with someone who has taller tyres to try it out.
You speedo will under-read by 10 percent, 100 indicated will 110 actual, watch out for radars.
Be aware that there will be issues of legality to do with non-standard tyre diameter, your insurance company can decline a payout if ther is a claim.
the navara 'Outlaw' came out with 17inch wheels and the ST-X came out with 16inch, thats why i didnt think it would make too much difference.
I had 10% bigger tyres on my last hilux.
The effect was noticeable in that it was more sluggish, harder to hold top gear, and most importantly - the brakes hated it and did not work anywhere near as well as they should have. They were also illegal in my case (33").
There are upsides for a higher volume tyre offroad which is why I did it.
A tyre shop will be able to tell you the diameter of the outlaw tyres.
the original is 765OD and the new ones will be 804OD so its not even 10% my calc is 4.85% increase or am i working it out incorrectly?
Note that technically, legally in qld you can only increase the overall diameter of your tyres by a maxiimum of 15mm.
bigger tires threw my speedo out by 11K's, clutch hated it big time
If they arent the same brand tyre you had before. Best thing to do is measure the difference physically. Tyres arent tyres anymore in the 16 range and I HATE THEM. eg.. A maxxis 275 70 16 isnt the same size as a bfg 275 70 16. It can vary from manufacturer by upto 45mm. The jargen is 16's are a better fitment and handle better on the road. All true. But they cost alot more aswell!!!
You will lose power and eco in height and width. But your getter much more millage then the odo shows unless you get it recalibrated. Change your diff gears to suite.
Had a similar problem with my car , its a nissan gu , put a set of 315 - 70's on it and had to change the diff ratio's to 4:6's , goes like the clappers now but speedo is about 10% out .
Sam.
isnt that all going to change in July? i heard to a max of 50mm.
had to change the diff ratio's to 4:6'show do you alter the gear ratio?Change your diff gears to suite.
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